Dislocation of hemiarthroplasty after hip fracture is common and the risk is increased with posterior approach: result from a national cohort of 25,678 individuals in the Swedish Hip Arthroplasty Register

Background and purpose — Reported revision rates due to dislocation after hemiarthroplasty span a wide range. Dislocations treated with closed reduction are rarely reported despite the fact that they can be expected to constitute most of the dislocations that occur. We aimed to describe the total dislocation rate on the national level, and to identify risk factors for dislocation.Patients and methods — We co-processed a national cohort of 25,678 patients in the Swedish Hip Arthroplasty Register, with the National Patient Register (NPR) and Statistics Sweden. Dislocation was defined as the occurrence of any ICD-10 or procedural code related to hip dislocation recorded in the NPR, with a minimum of 1-year-follow-up. In theory, all early dislocations should thereby be traced, including those treated with closed reduction only.Results — 366/13,769 (2.7%) patients operated on with direct lateral approach dislocated, compared with 850/11,834 (7.2%) of those with posterior approach. Posterior approach was the strongest risk factor for dislocation (OR = 2.7; 95% CI 2.3–3.1), followed by dementia (OR = 1.3; CI 1.1–1.5). The older the patients, the lower the risk of dislocation (OR = 0.98 per year of age; CI 0.98–1.0). Neither bipolar design nor cementless stems influenced the risk.Interpretation — The choice of posterior approach and dementia was associated with an increased dislocation risk. When hips treated with closed reduction were identified, the frequency of dislocation with use of direct lateral and posterior approach more than doubled and tripled, respectively, compared with when only revisions due to dislocation are measured.

Displaced femoral neck fractures in elderly patients have traditionally been treated with hemiarthroplasty (HA). Dislocation of the prosthesis is a major complication, affecting 1.5–15% of patients (Enocson et al. 2008, Figved et al. 2009, Leonardsson et al. 2012, Bensen et al. 2014, Parker 2015, Svenoy et al. 2017). The varying rate may be explained by different surgical approach, follow-up time, age, and frailty of the patients. In addition, dislocation may be defined and reported in various ways, for example closed reduction, revision surgery, or both. A systematic review of 7 randomized trials, with a mix of approaches and 1–5 years’ follow-up time, reported a risk of revision due to dislocation of 3% (Burgers et al. 2012). Only open surgery due to dislocation (i.e., open reduction or revision) is reported in the Swedish Hip Arthroplasty (SHAR). By including closed reduction with a linkage to the National Patient Register (NPR) the under-reporting of dislocation can be highlighted.Risk factors for dislocation can be divided into surgically related, implant-related, and patient-related factors. Posterior approach is a known surgically related risk factor (Varley and Parker 2004, Enocson et al. 2008, Leonardsson et al. 2012, Abram and Murray 2015, Svenoy et al. 2017). The risk is even higher if complete posterior repair is not performed (Enocson et al. 2008, Kim et al. 2016, Svenoy et al. 2017). Others are discrepancy of offset (Madanat et al. 2012, Mukka et al. 2015, Li et al. 2016) and, for elective THA, faulty positioning of the stem (McCollum and Gray 1990). Gjertsen et al. (2012) showed increased risk of revision because of dislocation if an uncemented technique was used compared with cementation, while other studies concluded no such association (Varley and Parker 2004, Figved et al. 2009, Abram and Murray 2015). The influence of the prosthetic design, uni- or bipolar head, on the risk of reoperation or dislocation in hip fracture patients is unclear. Several studies found no difference (Varley and Parker 2004, Enocson et al. 2008, 2012), while Leonardsson et al. (2012) showed increased risk of reoperation caused by dislocation with bipolar HA. For fracture patients, 2 studies (Li et al. 2016, Kristoffersen et al. 2020) reported dementia to increase the risk of dislocation while others (Ninh et al. 2009, Madanat et al. 2012, Abram and Murray 2015, Svenoy et al. 2017) did not. Neurological disease (Li et al. 2016) and dysplasia (Madanat et al. 2012, Mukka et al. 2015) are reported patient-related risk factors, whereas age, sex, and comorbidity do not seem to be associated with risk of dislocation (Enocson et al. 2008, 2012, Madanat et al. 2012, Abram and Murray 2015, Kim et al. 2016, Mukka et al. 2015, Svenoy et al. 2017). The influence of other possible confounders such as socioeconomic factors on the risk of dislocation have not, to our knowledge, been studied earlier.We aimed to describe the total dislocation rate on a national level and to explore risk factors with possible influence on the dislocation rate.     

Prior hip arthroscopy does not affect 1-year patient-reported outcomes following total hip arthroplasty: a register-based matched case-control study of 675 patients

Background and purpose — Femoroacetabular impingement syndrome (FAIS) is a common cause of hip pain and may contribute to the development of osteoarthritis. We investigated whether a prior hip arthroscopy affects the patient-reported outcomes (PROMs) of a later total hip arthroplasty (THA).Patients and methods — Patients undergoing hip arthroscopy between 2011 and 2018 were identified from a hip arthroscopy register and linked to the Swedish Hip Arthroplasty Register (SHAR). A propensity-score matched control group without a prior hip arthroscopy, based on demographic data and preoperative score from the EuroQoL visual analogue scale (EQ VAS) and hip pain score, was identified from SHAR. The group with a hip arthroscopy (treated group) consisted of 135 patients and the matched control group comprised 540 patients. The included PROMs were EQ-5D and EQ VAS of the EuroQoL group, and a questionnaire regarding hip pain and another addressing satisfaction. Rate of reoperation was collected from the SHAR. The follow-up period was 1 year.Results — The mean interval from arthroscopy to THA was 27 months (SD 19). The EQ-5D was 0.81 and 0.82, and EQ VAS was 78 and 79 in the treated group and the matched control group respectively. There were no differences in hip pain, and reported satisfaction was similar with 87% in the treated group and 86% in the matched control group.Interpretation — These results offer reassurance that a prior hip arthroscopy for FAIS does not appear to affect the short-term patient-reported outcomes of a future THA and indicate that patients undergoing an intervention are not at risk of inferior results due to their prior hip arthroscopy.

Femoroacetabular impingement syndrome (FAIS) implies abnormal morphology on the femoral or acetabular side of the hip joint and is a common cause of hip pain and dysfunction in the young population (Matar et al. 2019, Zhou et al. 2020). It reportedly increases the risk of developing osteoarthritis (OA), presumably due to damage to the chondrolabral structures (Ganz et al. 2003, Beck et al. 2005).Arthroscopic treatment of FAIS has been proven successful with 1- and 5-years’ follow-up (Griffin et al. 2018, Ohlin et al. 2020). However, one of the most common reoperations is conversion to a total hip arthroplasty (THA) (Harris et al. 2013). Depending on the follow-up period and severity of chondrolabral damages, 3–50% of patients with a previous hip arthroscopy for FAIS are reported to undergo THA later in life (Harris et al. 2013).Whether a prior hip arthroscopy affects the result of a subsequent THA (Haughom et al. 2016, Charles et al. 2017, Perets et al. 2017, Hoeltzermann et al. 2019, Vovos et al. 2019) has previously been discussed. However, many of these studies have been underpowered and the results have been incongruent. Most studies suggested no differences in outcomes in THA for patients with a prior hip arthroscopy (Haughom et al. 2016, Charles et al. 2017, Hoeltzermann et al. 2019). Yet inferior patient satisfaction and higher complication rates were reported in some studies (Perets et al. 2017, Vovos et al. 2019).To optimize the results for patients undergoing THA surgery, it is important to understand factors that could affect the outcomes. The possible effect of hip arthroscopy on future THA should also be considered during patient selection.We investigated the influence of a prior hip arthroscopy on a subsequent THA with patient-reported outcome measures (PROMs) 1 year after THA.Open in a separate windowFlow chart of included patients. Excluded diagnoses: tumors, fractures, or trauma. Excluded missing data due to missing preoperatively patient-reported outcomes or demographic data. Abbreviations: SHAR: Swedish Hip Arthroplasty Register, THA: total hip arthroplasty.     

No increased mortality after total hip arthroplasty in patients with a history of pediatric hip disease: a matched,population-based cohort study on 4,043 patients

Background and purpose — Patients with pediatric hip diseases are more comorbid than the general population and at risk of premature, secondary osteoarthritis, often leading to total hip arthroplasty (THA). We investigated whether THA confers an increased mortality in this cohort.Patients and methods — We identified 4,043 patients with a history of Legg–Calvé–Perthes disease (LCPD), slipped capital femoral epiphysis (SCFE), or developmental dysplasia of the hip (DDH) in the Swedish Hip Arthroplasty Register (SHAR) between 1992 and 2012. For each patient, we matched 5 controls from the general population for age, sex, and place of residence, and acquired information on all participants’ socioeconomic background and comorbidities. Mortality after THA was estimated according to Kaplan–Meier, and Cox proportional hazard models were fitted to estimate adjusted hazard ratios (HRs) for the risk of death.Results — Compared with unexposed individuals, patients exposed to a THA due to pediatric hip disease had lower incomes, lower educational levels, and a higher degree of comorbidity but a statistically non-significant attenuation of 90-day mortality (HR 0.9; 95% CI 0.4–2.0) and a lower risk of overall mortality (HR 0.8; CI 0.7–0.9).Interpretation — Patients exposed to THA due to a history of pediatric hip disease have a slightly lower mortality than unexposed individuals. THA seems not to confer increased mortality risks, even in these specific patients with numerous risk factors.

Altered morphology of the hip joint due to pediatric hip diseases, e.g., Legg–Calvé–Perthes disease (LCPD), slipped capital femoral epiphysis (SCFE), or developmental dysplasia of the hip (DDH) is closely linked to early-onset, secondary osteoarthritis (OA) (Jacobsen and Sonne-Holm 2005, Pun 2016) which may lead to total hip arthroplasty (THA) at a young age (Froberg et al. 2011). Thus, the mean age at THA surgery in patients with a history of pediatric hip disease ranges from 38 to 55 years (Traina et al. 2011, Engesaeter et al. 2012), whereas it ranges from 65 to 70 years in patients with primary OA (Engesaeter et al. 2012, Fang et al. 2015, Cnudde et al. 2018). Studies from Nordic countries report that between 4% and 9% of all primary THAs are due to pediatric hip disease (Engesaeter et al. 2012).The long-term outcome and revision rates after THA in patients with previous pediatric hip disease have been studied (Thillemann et al. 2008, Traina et al. 2011), but 90-day mortality and overall mortality after THA in these patients have not yet been investigated. Comorbidities, such as attention deficit hyperactivity disorder (ADHD), depression, cardiovascular disease, hypothyroidism, obesity, and coagulation abnormalities are more common in patients with LCPD and SCFE (Hailer and Nilsson 2014, Perry et al. 2017, Hailer and Hailer 2018, Hailer 2020). In addition, patients with LCPD and SCFE have a higher overall mortality than the general population (Hailer and Nilsson 2014, Hailer 2020). Due to an increased comorbidity burden and possibly increased overall mortality one could therefore fear an increased mortality after THA surgery in these patients.We therefore investigated whether THA surgery in patients with a pediatric hip disease confers an increased 90-day and overall mortality when compared with the general population.     

Preoperative BMD does not influence femoral stem subsidence of uncemented THA when the femoral T-score is > –2.5

Background and purpose — It is believed that in uncemented primary total hip arthroplasty (THA) the anchorage of the stem is dependent on the level of bone mineral density (BMD) of the femoral bone. This is one of the reasons for the widely accepted agreement that a cemented solution should be selected for people with osteoporosis or age > 75 years. We evaluated whether preoperative BMD of the femur bone is related to femoral stem migration in uncemented THA.Patients and methods — We enrolled 62 patients (mean age 64 years (range 49–74), 34 males) scheduled for an uncemented THA. Before surgery we undertook DEXA scans of the proximal femur including calculation of the T- and Z-scores for the femoral neck. Evaluation of stem migration by radiostereometric analysis (RSA) was performed with 24 months of follow-up. In 56 patients both preoperative DEXA data and RSA data were available with 24 months of follow-up.Results — None of the patients had a T-score below –2.5. We found no statistically significant relationship between preoperative BMD and femoral stem subsidence after 3 or 24 months. When comparing the average femoral stem subsidence between 2 groups with T-score > –1 and T-score ≤ –1, respectively, we found no statistically significant difference after either 3 or 24 months when measured with RSA.Interpretation — In a cohort of people ≤ 75 years of age and with local femur T-score > –2.5 we found no relationship between preoperative BMD and postoperative femoral stem subsidence of a cementless THA.

Early migration of total hip arthroplasty (THA) femoral stems is expected to some extent (Alfaro-Adrian et al. 2001). Cemented stems migrate less than uncemented do, because the initial stabilization is secured with bone cement, but both migrate in a similar pattern (Nysted et al. 2014, Van Der Voort et al. 2015, Teeter et al. 2018). The fixation of the stem and the risk of fracture are believed to rely on the density of the surrounding bone, which is why it is considered rational to fixate THAs in elderly and/or people with osteoporosis (or other disorders affecting the bone) by using bone cement (Piarulli et al. 2013, Troelsen et al. 2013, Gulati and Manktelow 2017).The BMD of the hip is the most reliable estimate to predict hip fracture risk and is interpreted by using the World Health Organization’s definition of T- and Z-score (Johnell et al. 2005, Blake and Fogelman 2007).Radiostereometric analysis (RSA) is used to measure the rotations and translations. The migration of interest is primarily translation along the Y-axis (Y-translation), where a negative value is distal migration, i.e., subsidence (Li et al. 2014, Weber et al. 2014, Matejcic et al. 2015).There are few studies comparing the local BMD with the migration of an uncemented THA stem, but some show that lower femoral BMD leads to increased subsidence (Mears et al. 2009), while other studies cannot demonstrate such a relationship (Moritz et al. 2011). Women with low systemic BMD have been reported to have a tendency to higher migration (Aro et al. 2012, Nazari-Farsani et al. 2020).Our study is partly based on secondary endpoint data from a randomized controlled trial (RCT) (Dyreborg et al. 2020). The main aim of the present study was to evaluate whether preoperative BMD of 3 regions in the femoral bone is related to femoral stem subsidence in uncemented THA. Furthermore, we determined whether a standard hip dual-energy X-ray absorptiometry (DEXA) scan, normally used for diagnosis of osteoporosis, could be used for the above purpose.We hypothesized that low preoperative femoral BMD is related to higher stem subsidence.     

Deep neural networks with promising diagnostic accuracy for the classification of atypical femoral fractures

Background and purpose — A correct diagnosis is essential for the appropriate treatment of patients with atypical femoral fractures (AFFs). The diagnostic accuracy of radiographs with standard radiology reports is very poor. We derived a diagnostic algorithm that uses deep neural networks to enable clinicians to discriminate AFFs from normal femur fractures (NFFs) on conventional radiographs.Patients and methods — We entered 433 radiographs from 149 patients with complete AFF and 549 radiographs from 224 patients with NFF into a convolutional neural network (CNN) that acts as a core classifier in an automated pathway and a manual intervention pathway (manual improvement of image orientation). We tested several deep neural network structures (i.e., VGG19, InceptionV3, and ResNet) to identify the network with the highest diagnostic accuracy for distinguishing AFF from NFF. We applied a transfer learning technique and used 5-fold cross-validation and class activation mapping to evaluate the diagnostic accuracy.Results — In the automated pathway, ResNet50 had the highest diagnostic accuracy, with a mean of 91% (SD 1.3), as compared with 83% (SD 1.6) for VGG19, and 89% (SD 2.5) for InceptionV3. The corresponding accuracy levels for the intervention pathway were 94% (SD 2.0), 92% (2.7), and 93% (3.7), respectively. With regards to sensitivity and specificity, ResNet outperformed the other networks with a mean AUC (area under the curve) value of 0.94 (SD 0.01) and surpassed the accuracy of clinical diagnostics.Interpretation — Artificial intelligence systems show excellent diagnostic accuracies for the rare fracture type of AFF in an experimental setting.

Atypical fractures occur at atypical locations in the femoral bone and show a strong association with bisphosphonate treatment (Odvina et al. 2005, 2010, Shane 2010, Shane et al. 2010, Schilcher et al. 2011, 2015, Starr et al. 2018). In contrast to the metaphyseal area, which is the site for the majority of all fragility fractures, the diaphyseal region is where atypical fractures occur. As is the case for any other insufficiency-type fracture of the diaphysis, atypical fractures show specific radiographic features, such as a transverse or short oblique fracture line in the lateral femoral cortex and focal cortical thickening (Schilcher et al. 2013, Shane et al. 2014). These features differ from those of normal femur fractures (NFFs), which show oblique fracture lines and no signs of focal cortical thickening (Shin et al. 2016b).Early and correct diagnosis of AFF is essential for appropriate management (Bogl et al. 2020a), which minimizes the risk of healing complications (Bogl et al. 2020b). In clinical routine practice, conventional radiographs are used to diagnose complete AFF. However, routine diagnostic accuracy is poor, and < 7% of AFF cases are correctly identified in this way (Harborne et al. 2016).Artificial intelligence (AI), deep learning through convolutional networks, has proven effective in the classification (Russakovsky et al. 2015) and segmentation (Ronneberger et al. 2015) of medical images in general, and for bone fractures in particular (Brett et al. 2009, Olczak et al. 2017, Chung et al. 2018, Kim and MacKinnon 2018, Lindsey et al. 2018, Adams et al. 2019, Urakawa et al. 2019, Kalmet et al. 2020). Given the very specific radiographic pattern of these fractures, AI appears to be a useful tool for finding the needle (AFF) in the haystack (NFF).We evaluated the abilities of different deep neural networks to discriminate complete AFF from NFF on diagnostic plain radiographs in an experimental setting and we assessed the effect of limited user intervention on diagnostic accuracy.     

Rapid decline of yearly number of hip arthroscopies in Sweden: a retrospective time series of 6,105 hip arthroscopies based on a national patient data register

Background and purpose — Hip arthroscopies (HAs) have increased exponentially worldwide and are expected to continue rising. We describe time trends in HA procedures in Sweden (10 million inhabitants) between 2006 and 2018 with a focus on procedure rates, surgical procedures, and patient demographics such as age and sex distribution.Patients and methods — We retrospectively collected data from the Swedish National Patient Register (NPR) for all surgeries including surgical treatment codes considered relevant for HA from 2006 to 2018. Surgical codes were validated through a multiple-step procedure and classified into femoroacetabular impingement syndrome (FAIS) related or non-FAIS related procedure. Frequencies, sex differences, and time trends of surgical procedures and patient demographics are presented.Results — After validation of HA codes, 6,105 individual procedures, performed in 4,924 patients (mean age 34 years [SD 12]) were confirmed HAs and included in the analysis. Yearly HA procedure rates increased from 15 in 2006 to 884 in 2014, after which a steady decline was observed with 469 procedures in 2018. The majority (65%) of HAs was performed in males. Male patients were younger, and surgeries on males more frequently included an FAIS-related procedure.Interpretation — Similar to previous studies in other parts of the world, we found dramatic increases in HA procedures in Sweden between 2006 and 2014. Contrary to existing predictions, HA rates declined steadily after 2014, which may be explained by more restrictive patient selection based on refined surgical indications, increasing evidence, and clinical experience with the procedure.

Hip arthroscopy was long deemed impossible due to anatomic constraints. Easier arthroscopic access to knee and shoulder joints led to an increasing arthroscopy rate in these joints during the 1990s and 2000s (Kim et al. 2011, Colvin et al. 2012a). During the 1990s, improved surgical equipment and techniques enabled surgeons to gain easier access to the hip joint for diagnosis and treatment of a variety of pathologies (Griffiths and Khanduja 2012), including femoroacetabular impingement syndrome (FAIS), acetabular labrum tears, and chondral lesions (Bedi et al. 2013). Arthroscopic hip surgery has been one of the fastest emerging fields within orthopedics and might be at a tipping point for even wider use (Khan et al. 2016a).An exponential worldwide increase in performed HAs has been documented between 2000 and 2013, based on data from private insurance databases (Sing et al. 2015, Maradit Kremers et al. 2017, Bonazza et al. 2018), performance data from surgical trainees (Colvin et al. 2012b, Bozic et al. 2013) and data from national health services (Palmer et al. 2016). While exponentially more patients received HA, evidence for its effectiveness has been questioned (Reiman and Thorborg 2015). In recent years, RCTs have indicated that hip arthroscopy may be more effective than structured rehabilitation in the treatment of FAIS (Griffin et al. 2018, Palmer et al. 2019). The clinical relevance of the statistical superiority for HA found in these trials is debated (Ferreira et al. 2021); however, a continued rise in HA rates has been predicted worldwide (Khan et al. 2016a, Palmer et al. 2016). The only study assessing HA rates beyond 2013 reports declining rates in Finland after 2014 (Karelson et al. 2020). In Sweden, time trends regarding HA have not been investigated. It is therefore unknown whether the rise in HA has continued, or if surgical practice has changed over the years.Therefore, we describe frequency and time trends in performance of hip arthroscopies, with regards to performance rates, surgical procedures, and patient demographics (age and gender distribution) in Sweden.     

Below-elbow cast sufficient for treatment of minimally displaced metaphyseal both-bone fractures of the distal forearm in children: long-term results of a randomized controlled multicenter trial

Background and purpose — We have previously shown that children with minimally displaced metaphyseal both-bone forearm fractures, who were treated with a below-elbow cast (BEC) instead of an above-elbow cast (AEC), experienced more comfort, less interference in daily activities, and similar functional outcomes at 7 months’ follow-up (FU). This study evaluates outcomes at 7 years’ follow-up.Patients and methods — A secondary analysis was performed of the 7 years’ follow-up data from our RCT. Primary outcome was loss of forearm rotation compared with the contralateral forearm. Secondary outcomes were patient-reported outcome measures (PROMs) consisting of the ABILHAND-kids and the DASH questionnaire, grip strength, radiological assessment, and cosmetic appearance.Results — The mean length of FU was 7.3 years (5.9–8.7). Of the initial 66 children who were included in the RCT, 51 children were evaluated at long-term FU. Loss of forearm rotation and secondary outcomes were similar in the 2 treatment groups.Interpretation — We suggest that children with minimally displaced metaphyseal both-bone forearm fractures should be treated with a below-elbow cast.

Long-term follow-up of children with forearm fractures is scarce but essential, because the remodeling capacity by growth can behave as a friend or an enemy. Previous studies with short-term follow-up shown that metaphyseal both-bone fractures of the distal forearm could safely be treated with a below-elbow cast (BEC) (Bohm et al. 2006, Webb et al. 2006, Paneru et al. 2010, Hendrickx et al. 2011, Colaris et al. 2012, Van Den Bekerom et al. 2012). Our previous randomized multicenter controlled trial compared BEC with above-elbow cast (AEC) for the treatment of minimally displaced metaphyseal both-bone fractures of the distal forearm in children. This RCT concluded that children with minimally displaced metaphyseal both-bone fractures of the distal forearm should be treated with a below-elbow cast (Colaris et al. 2012). We now report the long-term 7-year follow-up of these 2 treatment groups regarding loss of forearm rotation, patient-reported outcomes measures (ABILHAND-kids questionnaire and DASH questionnaire (Hudak et al. 1996, Penta et al. 1998, Arnould et al. 2004), grip strength, radiological assessment, and cosmetic appearance (Bohm et al. 2006, Paneru et al. 2010, Hendrickx et al. 2011, Colaris et al. 2012, Van Den et al. 2012)     

Thromboprophylaxis in primary shoulder arthroplasty does not seem to prevent death: a report from the Norwegian Arthroplasty Register 2005–2018

Background and purpose — There is still no consensus on whether to use thromboprophylaxis as a standard treatment in shoulder replacement surgery. We investigated the use of thromboprophylaxis reported to the Norwegian Arthroplasty Register (NAR). The primary endpoint was early mortality after primary shoulder arthroplasty with and without thromboprophylaxis. Secondary endpoints included revisions within 1 year and intraoperative complications.Patients and methods — This observational study included 6,123 primary shoulder arthroplasties in 5,624 patients reported to the NAR from 2005 to 2018. Cox regression analyses including robust variance analysis were performed with adjustments for age, sex, ASA score, diagnosis, type of implant, fixation, duration of surgery, and year of primary surgery. An instrumental variable Cox regression was performed to estimate the causal effect of thromboprophylaxis.Results — Thromboprophylaxis was used in 4,089 out of 6,123 shoulder arthroplasties. 90-day mortality was similar between the thromboprophylaxis and no thromboprophylaxis groups (hazard ratio (HR) = 1.1, 95% CI 0.6–2.4). High age (> 75), high ASA class (≥ 3), and fracture diagnosis increased postoperative mortality. No statistically significant difference in the risk of revision within 1 year could be found (HR = 0.6, CI 0.3–1.2). The proportion of intraoperative bleeding was similar in the 2 groups (0.2%, 0.3%).Interpretation — We had no information on cause of death and relation to thromboembolic events. However, no association of reduced mortality with use of thromboprophylaxis was found. Based on our findings routine use of thromboprophylaxis in shoulder arthroplasty can be questioned.

Shoulder arthroplasty (SA) has gained wide acceptance as treatment for a variety of shoulder conditions, and the annual incidence rates are increasing (Lubbeke et al. 2017). Venous thromboembolism (VTE) is a recognized complication after hip and knee arthroplasties (Lie et al. 2002) but has been considered rare after SA. The number of reports of VTE after SA has increased with increasing number of SAs performed (Lyman et al. 2006, Jameson et al. 2011) and fatal outcome has also been reported (Saleem and Markel 2001, Madhusudhan et al. 2009). The true risk of VTE after SA has not been determined, and even though some studies suggest that the risk equals that of lower limb arthroplasty (Willis et al. 2009), most studies find a lower risk in the upper extremities (Isma et al. 2010, Saleh et al. 2013). Chemical thromboprophylaxis reduces the rates of symptomatic VTE following lower limb arthroplasty and is supposed to reduce mortality from thromboembolic complications (Dahl 1998, Senay et al. 2018). Thromboprophylaxis remains controversial among surgeons because it may carry a higher risk of bleeding, wound complication, and reoperation after orthopedic surgery (Kwong et al. 2012).Guidelines on thromboprophylaxis exist in Norway and in other countries (SIGN 2010, Falck-Ytter et al. 2012, Kristiansen et al. 2014, National Institute for Health and Clinical Excellence 2018, Samama et al. 2018). While thromboprophylaxis is recommended for all patients undergoing hip or knee arthroplasties, there are still no evidence-based guidelines specific for SA. Due to the low number of SAs performed and the low rate of deaths due to thromboembolic events, a randomized trial would not be feasible. Hence, the best option to study the effect of thromboprophylaxis is large cohort studies (Fender et al. 1997). Using an observational population-based design with data from the Norwegian Arthroplasty Register (NAR) we studied the use of thromboprophylaxis in patients undergoing SA. Our primary endpoint was the influence of thromboprophylaxis on 90-day mortality. Secondary endpoints were intraoperative bleeding complications and revision due to all causes and due to infection within 1 year.       

Knee flexion contracture impacts functional mobility in children with cerebral palsy with various degree of involvement: a cross-sectional register study of 2,838 individuals

Background and purpose — The impact of knee flexion contracture (KFC) on function in cerebral palsy (CP) is not clear. We studied KFC, functional mobility, and their association in children with CP.Subjects and methods — From the Swedish national CP register, 2,838 children were defined into 3 groups: no (≤ 4°), mild (5–14°), and severe (≥ 15°) KFC on physical examination. The Functional Mobility Scale (FMS) levels were categorized: using wheelchair (level 1), using assistive devices (level 2–4), walking independently (level 5–6). Standing and transfer ability and Gross Motor Function Classification (GMFCS) were assessed.Results — Of the 2,838 children, 73% had no, 14% mild, and 13% severe KFC. KFC increased from 7% at GMFCS level I to 71% at level V. FMS assessment (n = 2,838) revealed around 2/3 were walking independently and 1/3 used a wheelchair. With mild KFC (no KFC as reference), the odds ratio for FMS level 1 versus FMS level 5–6 at distances of 5, 50, and 500 meters, was 9, 9, and 8 respectively. Correspondingly, with severe KFC, the odds ratio was 170, 260, and 217. In no, mild, and severe KFC 14%, 47%, and 77% could stand with support and 11%, 25%, and 33% could transfer with support.Interpretation — Knee flexion contracture is common in children with CP and the severity of KFC impacts function. The proportion of children with KFC rose with increased GMFCS level, reduced functional mobility, and decreased standing and transfer ability. Therefore, early identification and adequate treatment of progressive KFC is important.

Knee flexion contracture is a common problem in children with cerebral palsy (CP) (Miller 2005, Cloodt et al. 2018). Due to muscle imbalance, short and spastic hamstring muscles, and prolonged sitting posture, knee flexion contracture may develop and often progresses in adolescence (Miller 2005, Rodda et al. 2006). Although the exact impact of knee flexion contracture and its contribution to the development of flexed knee gait is still not fully understood, it is associated with progressive deterioration of gait in the ambulating child (Bell et al. 2002, Rodda et al. 2006) and it results in difficulties maintaining functional standing, sitting, and transfer in non-ambulatory children (Miller 2005, Cloodt et al. 2018). In addition, knee flexion contracture generates increased forces on the knee joint, which may cause pain (Rodda et al. 2006, Steele et al. 2012, Schmidt et al. 2020).Prevention of knee flexion contracture has not been thoroughly studied, and physiotherapy treatment and focal spasticity reduction have been attempted without convincing effect (Hägglund et al. 2005, Galey et al. 2017). In ambulatory children, there are several reports of improvement of gait pattern and knee flexion contracture after orthopedic surgery (Ma et al. 2006, Rodda et al. 2006, Stout et al. 2008, Taylor et al. 2016). These studies are limited mainly to children in Gross Motor Function Classification System (GMFCS) level I–III, and occasionally level IV, and varies across age groups as well as according to the surgery performed (Ma et al. 2006, Rodda et al. 2006, Stout et al. 2008, Taylor et al. 2016).The Functional Mobility Scale (FMS), the Pediatric Outcomes Data Collection Instrument (PODCI), and the Gross Motor Function Measure dimension D (GMFM D) are often used to assess function after orthopedic surgery; all three instruments describe how the child actually moves in daily life, and not necessarily what his or her capacity is (Russell 1993, Daltroy et al. 1998, Graham et al. 2004).Knee flexion contracture is easy to assess by physical examination; however, there are limited reports on the prevalence of knee flexion contracture and distribution of functional mobility in larger cohorts of children with CP at all GMFCS levels (Rodby-Bousquet and Hägglund 2010, Cloodt et al. 2018). We studied knee flexion contracture, functional mobility, and their association in children with CP. We assumed that the presence and severity of knee flexion contracture contributes to decreased physical function in children with CP.     

Cat at home? Cat scratch disease with atypical presentations and aggressive radiological findings mimicking sarcoma,a potential diagnostic pitfall

Background and purpose — Cat scratch disease (CSD) is a self-limiting disease caused by Bartonella (B.) henselae. It is characterized by granulomatous infection, most frequently involving lymph nodes. However, it can present with atypical symptoms including musculoskeletal manifestations, posing a diagnostic challenge. We describe the prevalence and demographics of CSD cases referred to a sarcoma center, and describe the radiological, histological, and molecular findings.Patients and methods — Our cohort comprised 10 patients, median age 27 years (12–74) with clinical and radiological findings suspicious of sarcoma.Results — 7 cases involved the upper extremities, and 1 case each involved the axilla, groin, and knee. B. henselae was found in 6 cases tested using polymerase chain reaction and serology in 5 cases. 9 cases were soft tissue lesions and 1 lesion involved the bone. 1 patient had concomitant CSD with melanoma metastasis in enlarged axillary lymph nodes. On MRI, 5 soft tissue lesions were categorized as probably inflammatory. In 3 cases, with still detectable lymph node structure and absent or initial liquefaction, the differential diagnosis included lymph node metastasis. A sarcoma diagnosis was suggested in 4 cases. The MRI imaging features of the bone lesion were suspicious of a bone tumor or osteomyelitis.Interpretation — Atypical imaging findings cause a diagnostic challenge and the differential diagnosis includes malignant neoplasms (such as sarcoma or carcinoma metastasis) and other infections. The distinction between these possibilities is crucial for treatment and prognosis.

Bartonella (B.) henselae infection with regional lymphadenopathy may mimic neoplastic processes such as soft tissue or bone tumor, metastasis, or lymphoma, leading to a delayed diagnosis and unnecessary invasive procedures resulting in overtreatment (Huang et al. 1989, Gielen et al. 2003, Mazur-Melewska et al. 2015). The classical differentiation of CSD from soft tissue neoplasm are enlarged lymph node with preserved hilar architecture and reactive changes of the surrounding fat and fascia, suggesting inflammation (Wang et al. 2009, Mazur-Melewska et al. 2015, Bernard et al. 2016, Chen et al. 2018). In atypical CSD cases, soft tissue mass or a solitary bone lesion may mimic a sarcoma due to the overlapping clinical and radiological findings. Previous studies, analyzing B. henselae infections and their clinical and radiological presentation, are mainly focused on imaging features of lymphadenopathy/lymphadenitis at the epitrochlear region (Gielen et al. 2003, Bernard et al. 2016, Chen et al. 2018). However, the assessment regarding the potential differential diagnosis of sarcoma is scarce, as only single cases of atypical B.henselae infection mimicking sarcoma have been published so far (Frank et al. 1952, Nimityongskul et al. 1992, Fox and Gurtler 1993, Eichhorn-Sens et al. 2008, Colman et al. 2014, Dhal et al. 2020). To our knowledge, this retrospective study represents the first large case series of atypical CSD cases who were transferred to a sarcoma center with the primary diagnosis of sarcoma. The objectives of this study were (i) to describe the prevalence and demographics of atypical CSD cases in a musculoskeletal, orthopedic sarcoma center, (ii) to describe the radiological, histological, and molecular findings, (iii) to highlight the specific MRI criteria for differentiation, and (iv) to discuss differential diagnoses with the aim of raising awareness of this rare disease.     

30-day and 1-year mortality after skeletal fractures: a register study of 295,713 fractures at different locations

Background and purpose — Few studies have reported the mortality rate after skeletal fractures involving different locations, within the same population. We analyzed the 30-day and 1-year mortality rates following different fractures.Patients and methods — We included 295,713 fractures encountered in patients 16–108 years of age, registered in the Swedish Fracture Register (SFR) from 2012 to 2018. Mortality rates were obtained by linkage of the SFR to the Swedish Tax Agency population register. The standardized mortality ratios (SMR) at 30 days and 1 year were calculated for fractures in any location and for each of 27 fracture locations, using age- and sex-life tables from Statistics Sweden (www.scb.se).Results — The overall SMR at 30 days was 6.8 (95% CI 6.7–7.0) and at 1 year 2.2 (CI 2.2–2.2). The SMR was > 2 for 19/27 and 13/27 of the fracture locations at 30 days and 1 year, respectively. Humerus, femur, and tibial diaphysis fractures were all associated with high SMR, at both 30 days and 1 year.Interpretation — Patients sustaining a fracture had approximately a 7-fold increased mortality at 30 days and over 2-fold increased mortality at 1 year as compared with what would be expected in the general population. High mortality rates were seen for patients with axial skeletal and proximal extremity fractures, indicating frailty in these patient groups.

Compared with other medical conditions, the mortality rate after fractures has been considered to be low, and has not been frequently reported, with the exception of extensive literature on hip femur fractures; for review see Huette et al. (2020). For hip fractures, the importance of organizing care to decrease complications and mortality has been reported (von Friesendorff et al. 2016). Longer waiting time for surgery has reportedly been associated with increased mortality rates in some studies (Schnell et al. 2010, Pincus et al. 2017). A relationship between fractures in different locations and mortality rates can provide information on whether fractures in also other locations should be prioritized for treatment (Vestergaard et al. 2007a, Klop et al. 2017). Fracture types reported to be associated with increased mortality rates are vertebral fractures, distal radius fractures, diaphyseal, and distal femur fractures (Kado et al. 2003, Oyen et al. 2014, Larsen et al. 2020). There are, however, few reports comparing mortality rates for more than a few different fracture locations, within the same population. Hence, comparisons between mortality rates for different fracture locations are difficult.To describe the change in mortality rate associated with a specific condition, the standardized mortality ratio (SMR) is commonly used (Vandenbroucke 1982). We investigated the 30-day and 1-year SMR for patients with fractures in various locations by using data from the Swedish Fracture Register (SFR).     

No increase in postoperative contacts with the healthcare system following outpatient total hip and knee arthroplasty

Background and purpose — Discharge on the day of surgery (DDOS) after total hip arthroplasty (THA) and total knee arthroplasty (TKA) has been shown to be safe in selected patients. Concerns have been raised that discharging patients on the day of surgery (DOS) could lead to an increased burden on other parts of the healthcare system when compared with patients not discharged on the DOS (nDDOS). Therefore, we investigated whether discharging patients on the day of surgery (DOS) after THA and TKA leads to increased contacts with the primary care sector or other departments within the secondary care sector.Patients and methods — Prospective data on 261 consecutive patients scheduled for outpatient THA (n = 135) and TKA (n = 126) were collected as part of a previous cohort study. 33% of THA patients and 37% of TKA patients were discharged on the DOS. Readmissions within 3 months after surgery were recorded. Contacts with the discharging department, other departments, and primary care physicians within 3 weeks were registered.Results — No statistically significant differences were found when comparing DDOS patients and patients not discharged on the DOS (nDDOS) with regard to readmissions, physical contacts with the discharging department, and contacts with other departments as well as general practitioners. THA DDOS patients had significantly fewer contacts with the discharging department by telephone than THA nDDOS patients. TKA DDOS patients had significantly more contacts with the discharging department by telephone than TKA nDDOS patients.Interpretation — Patients discharged on the DOS following THA or TKA generally have similar postoperative contacts with the healthcare system when compared with patients not discharged on the DOS.

Total hip arthroplasty (THA) and total knee arthroplasty (TKA) are surgical procedures that have improved continuously perioperatively for many years as a result of implementation of fast-track principles (Husted 2012, Petersen et al. 2019). These changes have led to a reduced length of stay in hospital following THA and TKA while also limiting cost, morbidity, and mortality (Khan et al. 2014, Andreasen et al. 2017, Jørgensen et al. 2017, Burn et al. 2018, Petersen et al. 2020).The epitome of fast-track surgery is outpatient surgery, where patients are discharged from the hospital on the day of surgery (DOS) to their own homes. This has proven to be beneficial in several ways for selected patients, as these patients spend less time in the hospital while still having similar outcomes when compared with patients not discharged on the DOS with regard to both patient-reported outcome measurements (Husted et al. 2021) and safety (Goyal et al. 2017, Vehmeijer et al. 2018, Gromov et al. 2019). Finally, outpatient THA and TKA come with additional financial benefits (Lovald et al. 2014, Husted et al. 2018, Gibon et al. 2020).Although an early small study indicated that the reduction in number of hospital days from fast-track did not increase the number of patient contacts with the primary healthcare sector (Andersen et al. 2009), concerns exist that the reduced time patients discharged on the DOS spend in hospital has led to an increased potential burden on other parts of the healthcare system—specifically the primary healthcare system, an increase in readmissions, and/or more contacts with the discharging department as well as other departments (Shah et al. 2019). Therefore, we aimed to investigate whether discharging patients on the DOS after THA and TKA leads to an increased burden on other parts of the healthcare system when compared with patients not discharged on the DOS. This was achieved by comparing readmissions within 3 months, contacts with the discharging department, the surgeon, or other departments—both physical turnouts and by phone, as well as contacts with primary care physicians within 3 weeks.     

Proton-pump inhibitors are associated with increased risk of prosthetic joint infection in patients with total hip arthroplasty: a case-cohort study

Background and purpose — Proton-pump inhibitors (PPI) have previously been associated with an increased risk of infections such as community-acquired pneumonia, gastrointestinal infections and central nervous system infection. Therefore, we evaluated a possible association between proton-pump inhibitor use and prosthetic joint infection (PJI) in patients with total hip arthroplasty (THA), because they can be stopped perioperatively or switched to a less harmful alternative.Patients and methods — A cohort of 5,512 primary THAs provided the base for a case-cohort design; cases were identified as patients with early-onset PJI. A weighted Cox proportional hazard regression model was used for the study design and to adjust for potential confounders.Results — There were 75 patients diagnosed with PJI of whom 32 (43%) used PPIs perioperatively compared with 75 PPI users (25%) in the control group of 302 patients. The risk of PJI was 2.4 times higher (95% CI 1.4–4.0) for patients using PPI. This effect remained after correction for possible confounders.Interpretation — The use of PPIs was associated with an increased risk of developing PJI after THA. Hence, the use of a PPI appears to be a modifiable risk factor for PJI.

One important aspect of the prevention of prosthetic joint infection (PJI) is preoperative optimization of modifiable risk factors (Kunutsor et al. 2016). Medication may be an important category of modifiable risk factors, since they can be temporarily discontinued perioperatively or they can be switched to a less harmful alternative. Proton-pump inhibitors (PPI) are of special interest, because they have been associated with an increased risk of infections such as community-acquired pneumonia, gastrointestinal infections, and central nervous system infections (Lambert et al. 2015, Cunningham et al. 2018, Hung et al. 2018). The increased risk of these infections is probably due to the fact that PPIs decrease the effectiveness of neutrophils (Aybay et al. 1995, Agastya et al. 2000, Zedtwitz-Liebenstein et al. 2002). This increased risk of infection may also apply to total hip arthroplasty (THA), possibly leading to increased risk of PJI. However, the effect of PPIs on the risk of PJI is currently unknown. Therefore, we evaluated a possible association between perioperative PPI use and early-onset prosthetic joint infection in patients with total hip arthroplasty.     

Short-term functional outcome after fast-track primary total knee arthroplasty: analysis of 623 patients

Background and purpose — Early functional outcome after total knee arthroplasty (TKA) has been described before, but without focus on the presence of certain functional recovery patterns. We investigated patterns of functional recovery during the first 3 months after TKA and determined characteristics for non-responders in functional outcome.Patients and methods — All primary TKA in a fast-track setting with complete patient-reported outcome measures (PROMs) preoperatively, at 6 weeks, and 3 months postoperatively were included. Included PROMs were Oxford Knee Score (OKS), Knee disability and Osteoarthritis Outcome Score Physical Function Short-Form (KOOS-PS), and EuroQol 5 dimensions (EQ-5D) including the self-rated health Visual Analogue Scale (VAS). Patients with improvement on OKS less than the minimal clinically important difference (MCID) were determined as non-responders at that time point. Characteristics between groups of responders and non-responders in functional recovery were tested for differences: we defined 4 groups a priori, based on the responder status at each time point.Results — 623 patients were included. At 6 weeks OKS, KOOS-PS, and EQ-5D self-rated health VAS were statistically significant improved compared with preoperative scores. The mean improvement was clinically relevant at 6 weeks for KOOS-PS and at 3 months for OKS. Patient characteristics in non-responders were higher BMI and worse scores on EQ-5D items: mobility, self-care, usual activities, and anxiety/depression.Interpretation — Both statistically significant and clinically relevant functional improvement were found in most patients during the first 3 months after primary TKA. Presumed modifiable patient characteristics in non-responders on early functional outcome were BMI and anxiety/depression.

Most arthroplasty research has focused on long-term functional outcomes and survival of the prosthesis. These outcomes have frequently been used for quality assessments and performance outcomes of the prosthesis itself.Because around 20% of patients remain unsatisfied after total knee arthroplasty (TKA) (Baker et al. 2007, Bourne et al. 2010), studying early functional outcome patterns more closely might provide important information to further optimize rehabilitation and patient satisfaction.In a recent article by van Egmond et al. (2021) 3 distinct recovery trajectories were found after TKA, using preoperative, 6 months, and 12 months postoperative Oxford Knee Scores (OKS), of which 2 trajectories at 6 months had approximately the same trajectory and subsequently diverged. Relatively similar patterns have seen in total hip arthroplasty (THA) (Hesseling et al. 2019).Several studies on early function, pain, and quality of life outcomes after TKA have been published (Andersen et al. 2009, Larsen et al. 2012, Jakobsen et al. 2014, Castorina et al. 2017, Schotanus et al. 2017, Husted et al. 2021). Moreover, Canfield et al. (2020) concluded that most improvement in function and pain is gained during the first 6 months postoperatively.Although functional rehabilitation in TKA and THA patients before 6 months has been studied (Van Egmond et al. 2015, Klapwijk et al. 2017), the question remains whether differences in functional recovery patterns exist before the 6-month mark in TKA patients.We expect that rehabilitation might be further optimized with knowledge of early functional rehabilitation patterns. Therefore, the primary objective of this study was to determine patterns in functional outcome at 6 weeks and 3 months after primary TKA. Secondary objectives were a non-responder analysis and to determine characteristics for non-responders in early functional recovery.     

Stable glenoid component of reverse total shoulder arthroplasty at 2 years as measured with model-based radiostereometric analysis (RSA)

Background and purpose — Reverse total shoulder arthroplasty (TSA) is used for treating cuff arthropathy, displaced proximal humeral fractures (PHF), and in revision shoulder surgery, despite sparse evidence on long-term results. We assessed stability of the glenoid component in reverse TSA, using model-based RSA.Patients and methods — 20 patients (mean age 76 years, 17 female), operated on with reverse TSA at Oslo University Hospital, in 2015–2017 were included. Indications for surgeries were PHFs, malunion, cuff arthropathy, and chronic shoulder dislocation. RSA markers were placed in the scapular neck, the coracoid, and the acromion. RSA radiographs were conducted postoperatively, at 3 months, 1 year, and 2 years. RSA analysis was performed using RSAcore with Reversed Engineering (RE) modality, with clinical precision < 0.25 mm for all translations (x, y, z) and < 0.7° for rotations (x, z). Scapular “notching” was assessed in conventional radiographs.Results — 1 patient was excluded due to revision surgery. More than half of the patients displayed measurable migration at 2 years: 6 patients with linear translations below 1 mm and 8 patients who showed rotational migration. Except for one outlier, the measured rotations were below 2°. The migration pattern suggested implant stability at 2 years. 10 patients showed radiolographic signs of “notching”, and the mean Oxford Shoulder Score (OSS) at 2 years was 29 points (15–36 points).Interpretation — Stability analysis of the glenoid component of reversed total shoulder arthroplasty using reversed engineering (RE) model-based RSA indicated component stability at 2 years.

Reverse total shoulder arthroplasty (TSA) is a widely used procedure. It was originally intended for cuff arthropathy in elderly patients (Grammont and Baulot 1993), but is presently used for several indications, including acute proximal humeral fractures (PHFs) in the elderly, fracture malunions, chronic dislocations, and revision surgery (Clavert et al. 2019, Rugg et al. 2019, Malahias et al. 2020). For operative treatment of displaced 3- and 4-part PHFs in the elderly, reversed TSA has become the treatment of choice (Critchley et al. 2020), presently down to 60 years of age (Goldenberg et al. 2020).The increased use of reverse TSA has occurred despite sparse evidence concerning long-term clinical outcomes for the implant. However, short-term RSA may predict the longevity of implants (Valstar et al. 2005). For hips and knees, continuous micro-migration over 2 years has shown to be indicative of increased risk of implant loosening (Kärrholm et al. 1994, de Vries et al. 2014). To our knowledge, RSA stability analysis of the glenoid component of reverse TSA in patients has not previously been published.Much concern has been placed on the subject of “notching,” where the polyethylene liner of a reverse TSA over time erodes into the inferior scapular neck (Levigne et al. 2011). Several studies have related notching to poorer outcomes (Mollon et al. 2017, Simovitch et al. 2019), while others have voiced concerns about this causing instability and loosening of the glenoid component (Roche et al. 2013c, Huri et al. 2016).Model-based RSA has the advantage over traditional marker-based RSA of not having to alter implants by attaching markers, and the clinical precision of model-based RSA on the glenoid component is known (Fraser et al. 2018). With increased use, sparse long-term evidence, and with “notching” as the backdrop, we performed a stability analysis of the glenoid component of reversed TSA, using model-based RSA.     

Hip dysplasia is not uncommon but frequently overlooked: a cross-sectional study based on radiographic examination of 1,870 adults

Background and purpose — Hip dysplasia in adults is a deformity in which the acetabulum inadequately covers the femoral head. The prevalence is sparingly described in the literature. We investigated the prevalence in Malmö (Sweden) and assessed whether the condition was recognized in the radiology reports.Subjects and methods — All pelvic radiographs performed in Malmö during 2007–2008 on subjects aged 20–70 years with a Swedish personal identity number were assessed. 1,870 digital radiographs were eligible for analysis. The lateral center-edge angle (LCEA) and acetabular index angle (AIA) were measured. Hip dysplasia was defined as an LCEA ≤ 20°. Intraclass correlation coefficients (ICC) for intra-observer measurements ranged from 0.87 (AIA, 95% CI 0.78–0.93) to 0.98 (LCEA, CI 0.97–0.99).Results — The prevalence of hip dysplasia (LCEA ≤ 20°) was 5.2% (CI 4.3–6.3), (98/1,870). There was no statistically significant difference between the sexes for either prevalence of hip dysplasia or mean LCEA. The mean AIA was 0.9° (CI 0.3–1.3) higher in men (4.1 SD 5.5) compared with women (3.2 SD 5.4). The radiologists had reported hip dysplasia in 7 of the 98 cases.Interpretation — The prevalence of hip dysplasia in Malmö (Sweden) is similar to previously reported data from Copenhagen (Denmark) and Bergen (Norway). Our results indicate that hip dysplasia is often overlooked by radiologists, which may influence patient treatment.

Note: Please check the heading levelsHip dysplasia is an anatomical deformity defined by a reduced lateral center-edge angle (LCEA) expressing insufficient acetabular coverage of the femoral head. An angle ≤ 20° is considered pathologic, whereas an angle between 21° and 25° is said to be “borderline” (Wiberg 1939, Fredensborg 1976, Ogata et al. 1990, Jacobsen and Sonne-Holm 2005). The acetabular index angle (AIA) describes the slope of the acetabular roof (Tönnis 1976) and a normal range has been suggested as 3° to 13° (Tannast et al. 2015a). Adult hip dysplasia ranges from being an asymptomatic anatomic variation to a painful disease. Diagnosis requires referral for an anteroposterior (AP) radiograph of the pelvis. Although the radiographic measurements have been known for decades, a diagnostic delay is common as radiologists and clinicians often overlook the deformity (Nunley et al. 2011).The prevalence of hip dysplasia varies from 2% to 8% in the few previous studies and the definition of the diagnosis based on the LCEA is inconsistent (Croft et al. 1991, Smith et al. 1995, Inoue et al. 2000, Jacobsen and Sonne-Holm 2005, Engesaeter et al. 2013). The prevalence has not been studied in Sweden before. In an international comparison, we perceive adult hip dysplasia to be a seldom discussed diagnosis in Sweden. Therefore, we determined the prevalence of hip dysplasia in Malmö, an urban area in southern Sweden, and investigated whether hip dysplasia was recognized in radiologists’ reports.     

Impact of socioeconomic status on the 90- and 365-day rate of revision and mortality after primary total hip arthroplasty: a cohort study based on 103,901 patients with osteoarthritis from national databases in Denmark

Background and purpose — Socioeconomic inequality in health is recognized as an important public health issue. We examined whether socioeconomic status (SES) is associated with revision and mortality rates after total hip arthroplasty (THA) within 90 and 365 days.Patients and methods — We obtained SES markers (cohabitation, education, income, and liquid assets) on 103,901 THA patients from Danish health registers (year 1995–2017). The outcomes were any revision (all revisions), specified revision (due to infection, fracture, or dislocation), and mortality. We used Cox regression analysis to estimate adjusted hazard ratio (aHR) of each outcome with 95% confidence interval (CI) for each SES marker.Results — Within 90 days, the aHR for any revision was 1.3 (95% CI 1.1–1.4) for patients living alone vs. cohabiting. The aHR was 2.0 (CI 1.4–2.6) for low-income vs. high-income among patients < 65 years. The aHR was 1.2 (CI 0.9–1.7) for low liquid assets among patients > 65 years. Results were consistent for any revision within 365 days as well as for revisions due to infection, fracture, and dislocation. The aHR for mortality was 1.4 (CI 1.2–1.6) within 90 days and 1.3 (CI 1.2–1.5) within 365 days for patients living alone vs. cohabiting. Low education, low income, and low liquid assets were associated with increased mortality rate within both 90 and 365 days.Interpretation — Our results suggest that living alone, low income, and low liquid assets were associated with increased revision and mortality up to 365 days after THA surgery. Optimizing medical conditions prior to surgery and implementing different post-THA support strategies with a focus on vulnerable patients may reduce complications associated with inequality.

Socioeconomic inequality in health is increasingly recognized as an important public health issue (Agabiti et al. 2007). Socioeconomic status (SES) is associated with access to total hip arthroplasty (THA) and with greater vulnerability to complications after THA, all in favor of high status (Agabiti et al. 2007, Weiss et al. 2019, Edwards et al. 2021). However, few studies have investigated the impact of SES on the risk of revision and mortality and they all present contradicting results, from showing that low SES was associated with a higher risk of early mortality after a THA, to finding no association among SES, revision, and mortality (Mahomed et al. 2003, Agabiti et al. 2007, Jenkins et al. 2009, Peltola and Järvelin 2014, Maradit Kremers et al. 2015). Previous research is limited by assessing SES by only a single marker, by lack of adjustment for important confounders and hospital factors, and by a lack of clinically relevant differentiation between time periods regarding risk assessment. Disparities in the risk of revision and mortality are important as social inequality is a growing problem in Denmark despite universal tax-supported healthcare (Sundhedsstyrelsen and Folkesundhed 2020). Even though the inequality in Denmark and most Nordic countries is less than the inequality seen in the United States (OECD 2019), our hypothesis is that even within this smaller spectrum of inequality, we shall find SES disparities concerning the risk of revision and mortality. By examining and identifying these disparities, we may be able to improve patient outcome by more focused risk assessment with proper counselling and optimization of medical risk factors prior to surgery and by implementing different postoperative strategies.We examined the association between multiple SES markers and the rates of any revision as well as revisions due to infection, fracture, and dislocation, and mortality within 90 and 365 days after THA.     

Influence of body mass index and age on day-of-surgery discharge,prolonged admission,and 90-day readmission after fast-track unicompartmental knee arthroplasty

Background and purpose — The indications for unicompartmental knee arthroplasty (UKA) have become less restrictive and, today, high age and high BMI are not considered contraindications by many surgeons. While the influence of these patient characteristics on total knee arthroplasty is well documented, evidence on UKA is lacking. We investigated the effect of BMI and age on day of surgery (DOS) discharge, prolonged admission, and 90-day readmission following UKA surgery.Patients and methods — This retrospective cohort study included 3,897 UKA patients operated on between 2010 and 2018 in 8 fast-track arthroplasty centers. Patients were divided into 5 BMI groups and 5 age groups. Differences between groups in the occurrence of DOS discharge, prolonged admission > 2 days, and 90-day readmission was investigated using a chi-square test and mixed-effect models adjusted for patient characteristics using surgical center as a random effect.Results — Median LOS was 1 day. DOS discharge was achieved in 26% of patients with no statistically significant differences between BMI groups. DOS discharge was less likely in UKA patients aged > 70 years (age 71–80; odds ratio [OR] 0.7 [95% CI 0.6–0.9]). Prolonged admission was not affected by BMI or age in the adjusted analysis. 90-day readmission was more likely in patients with BMI > 35 (OR 1.9 [CI 1.1–3.1]) and patients aged 71–80 (OR 1.5 [CI 1.1–2.1]).Interpretation — Age > 70 years decreased the likelihood of DOS discharge after UKA. High BMI as well as advanced age increased the likelihood of 90-day readmission. This should be noted by surgeons operating on patients with high BMI and age.

The indications for unicompartmental knee arthroplasty (UKA) as treatment for osteoarthritis (OA) have become less restrictive in terms of age and weight. Early contraindications included age < 60 years and weight > 82 kg (Kozinn and Scott 1989). However, recent studies report that revision rates and patient-reported outcomes are not worse in such patients (Pandit et al. 2011, van der List et al. 2016, Hamilton et al. 2017). Current indications focus solely on the pathoanatomy of the knee OA (Goodfellow et al. 1988, Hamilton et al. 2017).Despite being informed of increased risk of certain postoperative complications in high BMI patients and young/old patients, these patients are increasingly undergoing UKA surgery as well as knee arthroplasty in general (Price et al. 2018, Henkel et al. 2019).While length of stay (LOS) and readmissions are not the primary factors when determining indications/contraindications of arthroplasty procedures, they do affect patient satisfaction, logistics and cost-effectiveness (Reilly et al. 2005, Molloy et al. 2017).The few studies investigating the effect of BMI and age on LOS and readmission after UKA have varying conclusions. Some studies have associated higher BMI with increased risk of prolonged admission as well as short-term complications, while others find no such association (Otero et al. 2016, Plate et al. 2017, Sephton et al. 2020). Likewise, day of surgery (DOS) discharge is reported to be less likely in older patients while some do not find this association (Haughom et al. 2015, Matsumoto et al. 2020). Due to the usage of UKA in patients with high BMI and advanced age, it is important to investigate the effect of BMI and age on the postoperative course after UKA.We therefore investigated the association between BMI and age and the proportion of UKA patients with DOS discharge, prolonged admission, and readmission within 90 days of surgery in a prospective unselected multicenter fast-track setup.     

Precision of CT-based micromotion analysis is comparable to radiostereometry for early migration measurements in cemented acetabular cups

Background and purpose — CT (computed tomography) based methods have lately been considered an alternative to radiostereometry (RSA) for assessing early implant migration. However, no study has directly compared the 2 methods in a clinical setting. We estimated the precision and effective radiation dose of a CT-based method and compared it with marker-based RSA in 10 patients with hip arthroplasty.Patients and methods — We included 10 patients who underwent total hip replacement with a cemented cup. CT and RSA double examinations were performed postoperatively, and precision and effective dose data were compared. The CT data was analyzed with CT micromotion analysis (CTMA) software both with and without the use of bone markers. The RSA images were analyzed with RSA software with the use of bone markers.Results — The precision of CTMA with bone markers was 0.10–0.16 mm in translation and 0.31°–0.37° in rotation. Without bone markers, the precision of CTMA was 0.10–0.16 mm in translation and 0.21°–0.31° in rotation. In comparison, the precision of RSA was 0.09–0.26 mm and 0.43°–1.69°. The mean CTMA and RSA effective dose was estimated at 0.2 mSv and 0.04 mSv, respectively.Interpretation — CTMA, with and without the use of bone markers, had a comparable precision to RSA. CT radiation doses were slightly higher than RSA doses but still at a considerably low effective dose.

Early migration of hip implants is associated with higher revision rates of prosthesis due to aseptic loosening (Kärrholm et al. 1994, Pijls et al. 2012). Radiostereometry (RSA) is the current gold-standard method to measure implant migration, given its accuracy and precision (Valstar et al. 2005). Lately there has been greater interest in using CT scans to measure implant migration to address some of the challenges with RSA, such as the need for specialized equipment and trained personnel to conduct and analyze examinations (Brodén et al. 2016, Otten et al. 2017). Previous experimental and clinical studies indicate that the accuracy and precision of CT techniques are comparable to those of RSA (Brodén et al. 2016, Scheerlinck et al. 2016, Brodén et al. 2019, 2020). However, to our knowledge there is no clinical study directly comparing CT and RSA in terms of precision for migration measurements on the same subjects. Recently a new commercial CT-based method, CT micromotion analysis (CTMA), was developed to analyze and measure implant migration between 2 CT images (Brodén et al. 2019, 2020). CTMA has features that make it possible to perform the migration analysis of CT data with tantalum beads and also with a technique relying solely on the surface anatomy of bone for the image registration, without the use of beads in the bone (Brodén et al. 2020). We compared the precision and effective dose of the 2 methods of CTMA with those of standard marker-based RSA in acetabular cups in patients with total hip arthroplasty (THA).     

Cancer incidence and cause-specific mortality in patients with metal-on-metal hip replacements in Finland: A population-based study with a mean follow-up of 4.6 (1–11) years

Background and purpose

Metal-on-metal hip implants have been widely used, especially in the USA, Australia, England and Wales, and Finland. We assessed risk of death and updated data on the risk of cancer related to metal-on-metal hip replacements.

Patients and methods

A cohort of 10,728 metal-on-metal hip replacement patients and a reference cohort of 18,235 conventional total hip replacement patients were extracted from the Finnish Arthroplasty Register for the years 2001–2010. Data on incident cancer cases and causes of death until 2011 were obtained from the Finnish Cancer Registry and Statistics Finland. The relative risk of cancer and death were expressed as standardized incidence ratio (SIR) and standardized mortality ratio (SMR). SIR/SIR ratios and SMR/SMR ratios, and Poisson regression were used to compare the cancer risk and the risk of death between cohorts.

Results

The overall risk of cancer in the metal-on-metal cohort was not higher than that in the non-metal-on-metal cohort (RR = 0.91, 95% CI: 0.82–1.02). The risk of soft-tissue sarcoma and basalioma in the metal-on-metal cohort was higher than in the non-metal-on-metal cohort (SIR/SIR ratio = 2.6, CI: 1.02–6.4 for soft-tissue sarcoma; SIR/SIR ratio = 1.3, CI: 1.1–1.5 for basalioma). The overall risk of death in the metal-on-metal cohort was less than that in the non-metal-on-metal cohort (RR = 0.78, CI: 0.69–0.88).

Interpretation

The overall risk of cancer or risk of death because of cancer is not increased after metal-on-metal hip replacement. The well-patient effect and selection bias contribute substantially to the findings concerning mortality. Arthrocobaltism does not increase mortality in patients with metal-on-metal hip implants in the short term. However, metal-on-metal hip implants should not be considered safe until data with longer follow-up time are available.Metal-on-metal hip implants have been widely used, especially in the USA, Australia, England and Wales, and Finland (AOANJRR 2010, NJR 2011, Cohen 2012, Seppänen et al. 2012). The theoretical health risks related to chronically elevated blood metal ion concentrations induced by abnormal wear and corrosion of the metal-on-metal implants—apart from local symptoms around the failing implant—include systemic symptoms of poisoning (Steens et al. 2006, Oldenburg et al. 2009, Rizzetti et al. 2009, Tower 2010, 2012, Mao et al. 2011, Sotos and Tower 2013, Zyviel et al. 2013) and carcinogenesis (Mäkelä et al. 2012, Smith et al. 2012, Brewster et al. 2013). Systemic metal ion toxicity cases due to a failed hip replacement are rare. However, there have been several recent reports of systemic cobalt toxicity following revision of fractured ceramic components, and also in patients with a failed metal-on-metal hip replacement (Steens et al. 2006, Oldenburg et al. 2009, Rizzetti et al. 2009, Tower 2010, 2012, Mao et al. 2011, Sotos and Tower 2013, Zyviel et al. 2013). Possible clinical findings include fatigue, weakness, hypothyroidism, cardiomyopathy, polycythemia, visual and hearing impairment, cognitive dysfunction, and neuropathy. Fatal cardiomyopathy due to systemic cobalt toxicity after hip replacement has been reported (Zyviel et al. 2013).Metal debris from hip replacement may be associated with chromosomal aberrations and DNA damage (Case et al. 1996, Bonassi et al. 2000, Daley et al. 2004). However, the risk of cancer is not increased after conventional metal-on-polyethylene total hip replacement or after first-generation metal-on-metal total hip arthroplasty (Visuri et al. 1996, 2010a). The short-term overall cancer risk after modern metal-on-metal hip arthroplasty is not increased either (Mäkelä et al. 2012, Smith et al. 2012, Brewster et al. 2013). However, recent linkage studies of overall cancer risk are based on hospital episode statistics, which may have less quality assurance than cancer registry data (Smith et al. 2012, Brewster et al. 2013). Annual updating of cancer registry data concerning the metal-on-metal issue is advisable.In this paper, we update our earlier published results on risk of cancer (Mäkelä et al. 2012) and give an assessment of the overall and cause-specific mortality in primary metal-on-metal and non-metal-on-metal hip replacement patients who were operated on from 2001 to 2010, by combining data from the Finnish Arthroplasty Register, the Population Register Centre, and the Finnish Cancer Registry. The reason for this early updating of the cancer data was to be able to detect a cancerogenic effect of metal-on-metal implants as early as possible.