Primary synovial epithelioid sarcoma of the knee: distinctly unusual location leading to its confusion with pigmented villonodular synovitis

Epithelioid sarcoma (ES) is a rare malignant soft tissue tumor occurring in the distal extremities of young adults and is characterized histologically by nodules of epithelioid cells showing central necrosis. Intra‐articular ES is extremely rare; only four cases have been reported, but their radiologic and histologic documentation of intra‐articular origin have been imprecise. We report the first radiologically and histologically well‐documented case of primary synovial ES. A 59‐year‐old woman presented with pain followed by swelling of her right knee for 6 months. MRI revealed an entirely intra‐articular nodular synovial mass in the lateral part of the right knee joint in a background of diffusely thickened synovium. Synovectomy was performed under the clinical impression of pigmented villonodular synovitis (PVNS), a diagnosis erroneously confirmed by the reporting pathologist. The tumor rapidly recurred 3 months afterward and the diagnosis of primary synovial ES was made. Despite above‐knee amputation, the tumor continued to spread proximally to the retroperitoneum. She developed multiple lung metastases and died 20 months after initial presentation. The nodular aggregates of tumor cells with central necrosis resulted in diffuse polypoid synovial thickening mimicking tuberculous synovitis and PVNS. The tumor cells showed positive staining for EMA, CK19, CD34, and complete loss of INI1 staining, establishing the diagnosis of primary synovial ES. The ES spread from the synovium to and along the joint capsule, and then extra‐articularly into the soft tissue surrounding the knee joint, with lymphovascular permeation. Such pattern of spread calls for radical surgical excision as the treatment of choice.     

Prospective sequential comparison of femoral roll-back between cruciate-retaining and posterior-stabilized total knee arthroplasty using an intra-operative sensor

BackgroundImplant design and surgical techniques affect postoperative knee kinematics in total knee arthroplasty (TKA). This study aimed to compare femoral roll-back between cruciate-retaining (CR) and posterior-stabilized (PS) TKA in the same knee by objectively quantifying the contact point kinematics of the tibiofemoral joint using a sensor.MethodsIn the present prospective study, we used an intraoperative sensor to compare medial and lateral roll-back during 0-120° knee flexion in 33 knees that underwent CR and PS TKA. We also examined the relationship between mediolateral balance and the lateral-to-medial roll-back ratio. We defined the contact percentage position as the vertical length to the contact point divided by the anteroposterior length of the tibial plate.ResultsThe roll-back percentage following PS TKA (19.8 ± 5.1%) was significantly higher than that after CR TKA in both the medial (19.8 ± 5.1% versus 7.1 ± 2.5%, P < 0.001) and lateral (26.8% ± 3.8% versus 18.7 ± 3.8%, P < 0.001) compartments. The medial contact pressure at 90° was significantly correlated with the increased lateral-to-medial roll-back ratio in both CR and PS TKA (both P < 0.001).ConclusionPS TKA resulted in a higher percentage of femoral roll-back in the medial and lateral compartments than CR TKA. CR TKA caused a higher lateral-to-medial roll-back ratio compared to PS TKA. To reproduce medial pivot knee motion similar to that of a normal knee, the medial soft tissue needed to be balanced more tightly than the lateral soft tissue during TKA. These findings provide some clinical evidence of TKA design selection and proper mediolateral balancing for successful TKA.     

Relationships between early postoperative gait biomechanical factors and patient-reported outcome measures 6 months after total knee arthroplasty

BackgroundThis study was focused on the gait parameters of the knee extensor and hip abductor muscle groups, which are believed to contribute to knee joint function improvement in early postoperative TKA. The associations between patient-reported outcome measures (PROMs) 6 months after total knee arthroplasty (TKA) and the early postoperative internal knee extension moment, knee extension negative joint power, and internal hip abduction moment while walking were investigated.MethodsTwenty-one patients who underwent primary TKA for knee osteoarthritis were included. Three weeks after TKA, gait at a comfortable speed was measured by three-dimensional motion analysis. The lower limb joint angle, internal joint moment, and joint power parameters on the operated side while standing were calculated. The PROMs 6 months after TKA were assessed using the Japanese Knee Osteoarthritis Measure (JKOM). The relationship between each gait biomechanical parameter and the JKOM was determined.ResultsThe maximum internal knee extension moment and maximum knee extension negative joint power during the early stance showed moderate negative correlations with the JKOM scores. The maximum internal hip abduction moment was not correlated with the JKOM scores. The maximum internal hip extension moment during the early stance and internal hip flexion moment during the late stance showed moderate negative correlations with the total JKOM scores.ConclusionThe early postoperative internal knee extension moment, maximum knee extension negative joint power, and internal hip extension and flexion moment are associated with patient PROMs 6 months after TKA.     

Comparison of intraoperative soft tissue balance measurement between two tensor systems in total knee arthroplasty

BackgroundDifferences in measurement outcomes using different tensors in total knee arthroplasty (TKA) remain unknown. This study aimed to compare intraoperative soft tissue balance between two measurement systems in TKA.MethodsThis study included 24 cruciate-retaining (CR) and 27 posterior-stabilized (PS) TKAs for varus-type osteoarthritis. All TKAs were performed with the measured resection technique. Intraoperative soft tissue balance was assessed with femoral component placement and patellofemoral joint reduction throughout the range of motion. Measurements were performed using the Offset Repo-Tensor (Zimmer) and Ligament Sensor Tensor (Depuy). Joint component gaps and varus/valgus ligament balance were compared statistically in CR and PS TKAs.ResultsJoint component gaps with the Offset Repo-Tensor were significantly larger at 0°, 10°, 30°, and 60° of knee flexion in CR TKA and at all knee flexion angles, except 0° and 135°, in PS TKA than those with the Ligament Sensor Tensor (P < .05). Varus balance with the Offset Repo-Tensor was significantly larger at 0°, 10°, and 30° of knee flexion in CR TKA and at 10°, 30°, 60°, 90°, and 120° of knee flexion in PS TKA than that with the Ligament Sensor Tensor (P < .05).ConclusionSurgeons should consider the discrepancy in assessing intraoperative soft tissue balance depending on the tensor used. The Ligament Sensor Tensor tended to underestimate soft tissue balance in CR and PS TKAs compared with the Offset Repo-Tensor, especially in PS TKA. Thus, surgeons should know the difference in values between the offset-type tensor with consistent distraction force and a spring-loaded tensor.     

Conversion total knee arthroplasty: A case complexity between primary and revision total knee arthroplasty

BackgroundConversion total knee arthroplasty (TKA) may represent a more complex procedure compared with primary TKA. The purpose of this study was to compare 30-day complications between conversion TKA and primary, non-conversion TKA as well as between conversion TKA and revision TKA on a national scale using a multi-center surgical registry.MethodsAdult patients undergoing conversion TKA from 2006 to 2018 were identified in the National Surgical Quality Improvement Program database and were compared with patients who underwent primary TKA and aseptic revision TKA. In this analysis, 30-day complications were assessed. Bivariate analyses, including chi-squared and analysis of variance, and multivariate logistic regressions were performed.ResultsOf 299,065 total patients undergoing knee arthroplasty, 1,310 (0.4%) underwent conversion TKA, 275,470 (92.1%) underwent primary TKA, and 22,285 (7.5%) underwent revision TKA. Following adjustment, patients who underwent conversion TKA were more likely to have increased risks of any complications (P < 0.001), mortality (P = 0.021), wound complications (P < 0.001), cardiac issues (P = 0.018), bleeding requiring transfusion (P < 0.001), and reoperation (P = 0.002) relative to primary TKA patients. Compared with patients who underwent revision TKA, conversion TKA patients were less likely to have septic complications (P = 0.009).ConclusionConversion TKA is associated with significantly higher rates of complications compared with primary, non-conversion TKA, but less risk of sepsis compared with revision TKA. Because current reimbursement classifications do not account for the case complexity of a conversion TKA, new classifications should be implemented with reimbursements for conversion TKA approximating reimbursements for revision TKA.     

Insufficient lateral joint laxity after bicruciate-retaining total knee arthroplasty potentially influences kinematics during flexion: A biomechanical cadaveric study

BackgroundSoft tissue balancing in bicruciate-retaining (BCR) total knee arthroplasty (TKA) is a challenge that must be overcome to achieve excellent clinical outcomes. However, the optimal degree of joint laxity has yet to be clarified. This cadaveric study sought to examine joint laxity after BCR TKA using a navigation system.MethodsKnee joint laxity was quantified using an image-free navigation system in 8 intact fresh frozen cadavers under three conditions: the native knee, BCR TKA knee, and BCR TKA knee after anterior cruciate ligament resection. Rotational kinematics in the BCR TKA knee during flexion were compared according to whether joint laxity was increased or decreased.ResultsKnee joint laxity after BCR TKA under varus-valgus movement, anterior translation, and internal-external rotation loadings was similar to that of the native knee. However, lateral joint laxity was decreased during flexion in some cases. BCR TKA-treated knees with decreased lateral joint laxity at 90° of flexion demonstrated more limited tibial internal rotation in deep flexion than the native knee (p < 0.05). The loss of internal rotation in deep flexion was partly recovered by using a lateral insert with a posterior slope of +3°.ConclusionsRestoring optimal joint laxity was not always straightforward in BCR TKA if the 4 ligaments were preserved. Lateral joint laxity was potentially decreased in BCR TKA and may result in kinematic conflict during flexion. Surgeons should be aware of the need to achieve sufficient lateral joint laxity in this type of BCR TKA.     

Assessment of isometricity before and after total knee arthroplasty: A cadaver study

Total knee arthroplasty (TKA) relies on soft tissue to regulate joint stability after surgery. In practice, the exact balance of the gaps can be difficult to measure, and various methods including intra-operative spreaders or distraction devices have been proposed. While individual ligament strain patterns have been measured, no data exist on the isometricity of the soft tissue envelope as a whole. In this study, a novel device was developed and validated to compare isometricity in the entire soft tissue envelope for both the intact and TKA knee.A spring-loaded rod was inserted in six cadaver knee joints between the tibial shaft and the tibial plateau or tibial tray after removing a 7 mm slice of bone. The displacement of the rod during passive flexion represented variation in tissue tension around the joint. The rod position in the intact knee remained within 1 mm of its initial position between 15° and 135° of flexion, and within 2 mm (± 1.2 mm) throughout the entire range of motion (0–150°). After insertion of a mobile-bearing TKA, the rod was displaced a mean of 6 mm at 150° (p < 0.001). The results were validated using a force transducer implanted in the tibial baseplate of the TKA, which showed increased tibiofemoral force in the parts of the flexion range where the rod was most displaced. The force measurements were highly correlated with the displacement pattern of the spring-loaded rod (r = − 0.338; p = 0.006).A simple device has been validated to measure isometricity in the soft tissue envelope around the knee joint. Isometricity measurements may be used in the future to improve implantation techniques during TKA surgery.     

Functional knee apparatus for the evaluation of ligamentous tensions on contact loads

BackgroundSoft tissue balancing is integral in providing stability following total knee arthroplasty (TKA). Although intraoperative contact load sensors are providing insights into the effects of soft tissue balancing, there is still a lack of understanding of the relationship between the knee’s ligamentous tensions and joint surface contact loads. This study reports on the development of a multifunctional testing apparatus that can quantify the effects of ligamentous tension on joint contact loads in a controlled repeatable environment.MethodsThe functional knee apparatus was constructed to act as an anatomical substitute for the benchtop assessment of intraoperative soft tissue balancing. The system was calibrated through reproduction of results from a cadaveric study that employed intraoperative load sensors. Experimentation was then conducted to quantify the effects of tensile pretension variation on measured contact loads throughout the full range of flexion.ResultsA linear relationship between the ligamentous tensions and contact loads was observed, with ligaments contributing to 74–80% of the measured contact loads. Ligamentous tensions could be approximated from measured contact loads to within ± 23 N.ConclusionThe proposed apparatus can prove to be a valuable tool in the continued exploration of currently undocumented effects (e.g. surgical alteration) in soft tissue balancing. In addition to quantifying the relationship between ligamentous tensions and joint contact loads, soft tissue loading conditions where bicondylar contact was lost (i.e. known sign of kinematic instability) were identified. As a corollary, this system may be able to provide insights on soft tissue balancing standards predictive of patient outcomes.     

Periprosthetic joint infection after primary TKA in the medicare population: How frequently are patients revised at a different hospital?

BackgroundPeriprosthetic infection (PJI) after total knee arthroplasty (TKA) places a significant burden on hospitals. We sought to describe the proportion of patients undergoing revision for PJI at a different hospital within one year of primary TKA and whether patient characteristics or hospital volume were associated with this change.MethodsMedicare data from 2005 to 2014 was retrospectively reviewed using PearlDiver. All patients over 64 years undergoing revision for PJI within one year of primary TKA were stratified by the revision occurring within 90 days. Hospitals were grouped by annual TKA volume as Low (<50), Medium (51–100), High (101–200), and Very High (>200). Associations of patient characteristics and hospital volume with revision at a different hospital were assessed using Chi-squared tests and Somers' D.ResultsOf 8,337 patients undergoing revision within 90 days of TKA, 1,370 (16%) were revised at a different hospital. Changing hospitals was associated with having primary TKA at a lower volume hospital (24% for low, 15% medium, 12% high, and 12% very high; P < 0.001). Of 7,608 patients undergoing revision between 91 and 365 days, 1,110 (15%) were revised at a different hospital. Changing hospitals was associated with having primary TKA at a lower volume hospital (26% for low, 14% medium, 10% high, and 9% very high; P < 0.001). Changing hospitals was not associated with sex or age.ConclusionPatients frequently undergo revision for PJI at a different hospital, even within 90 days of TKA. Further research is needed to understand these implications of this care pathway shift.     

Fast-track revision knee arthroplasty.

BackgroundLimited data exist on fast-track protocols in relation to revision knee arthroplasty. Hence, the aim of this study was to report length of stay (LOS), risk of LOS > 5 days and readmission ≤ 90 days after revision knee arthroplasty in centers with a well-established fast-track protocol in both primary and revision surgery.MethodsAn observational cohort study from the Centre for Fast-track Hip and Knee Replacement and the Danish Knee Arthroplasty Register. We included elective aseptic major component revision knee arthroplasties consecutively from 6 dedicated fast-track centers from 2010 to 2018.Results1439 revision knee arthroplasties were analyzed, including 900 total revisions, 171 large partial revisions (revision of either femoral or tibia component) and 368 revisions of unicompartmental knee arthroplasty (UKA) to total knee arthroplasty (TKA). Mean age was 65 years (SD 10.9) and 66% were females. Mean LOS was 3.7 days (SD 3.9) in the study period, but decreased to 2.4 days (SD 1.3) in 2018. Risk factors for LOS > 5 days was ≥ 1 previous revision, use of walking aid, BMI > 35, ages < 50, 70–79 and ≥ 80 years, whereas revision of UKA to TKA and large partial revision were negatively associated. The 90-day readmission and mortality risk was 9.1% and 0.5%. Cardiac disease and use of walking aid were associated with increased risk of readmission ≤ 90 days.ConclusionElective aseptic major component revision knee arthroplasty using similar fast-track protocols as in primary TKA is safe with short and decreasing LOS.     

Intraoperative changes in medial joint gap after posterior femoral condylar resection,posterior osteophyte removal,and femoral component placement during primary total knee arthroplasty

Background“Mid-flexion stability” is important for superior patient satisfaction following total knee arthroplasty (TKA). Thus, it is important to control medial joint gap intraoperatively as a countermeasure. However, reports on the precise intraoperative changes in medial joint gap during TKA are scarce. This study evaluated the intraoperative changes in medial joint gap during TKA.MethodsWe studied 167 knees with varus osteoarthritis that underwent 80 cruciate-retaining (CR) and 87 posterior-stabilized (PS) TKAs between January 2018 and December 2020. We measured the intraoperative changes in medial joint gap with a tensor device at 137.5 N.ResultsThe medial joint gap after posterior femoral condylar resection was significantly increased not only at 90° of flexion but also at 0° of extension in CR and PS TKAs (p < 0.01). The medial joint gap after posterior osteophyte removal was significantly increased not only at 0° of extension but also at 90° of flexion in CR and PS TKAs (p < 0.01). The medial joint gap at 0° of extension was reduced by 0.60 mm after femoral component placement in PS TKA.ConclusionSurgeons need to pay close attention to these intraoperative changes in medial joint gap by measuring the medial joint gap before and after each procedure or assuming the changes in those values before bone cutting to achieve superior patient satisfaction following TKA.     

The medial gap is a reliable indicator for intraoperative soft tissue balancing in posterior-stabilized total knee arthroplasty

BackgroundAppropriate soft tissue balance and accurate alignment are important for successful total knee arthroplasty (TKA). However, the optimal technique for establishing and measuring soft tissue balancing remains unclear. The aim of this study was to analyze the intraoperative medial and lateral gap pattern using digital knee balancer in posterior-stabilized (PS) TKA.MethodsThis study involved 55 patients with medial osteoarthritis who underwent a primary TKA using an image-free navigation system. The extension gap and the flexion gap at 90° knee flexion were assessed using an offset seesaw-type digital balancer. Continuous joint distraction force from 10 lb to 60 lb was applied. Medial gap, lateral gap, and varus angle were measured.ResultsThe medial bone gap difference between extension and flexion was constant regardless of the distraction force from 20 lb to 60 lb. The lateral bone gap was significantly greater than the medial bone gap in extension and flexion from 30 lb to 60 lb (P < 0.05). The varus angle changed depending on the distraction force, especially in flexion. The varus angle in flexion was significantly greater than that in extension from 40 lb to 60 lb (P < 0.05).ConclusionsThe medial bone gap is a reliable indicator unaffected by the distraction force during surgery and is useful for adjusting the medial gap in extension and flexion appropriately to ensure medial stability in PS-TKA. The digital knee balancer and navigation system support both precise gap assessment and surgery.     

Long-term results of revision total knee arthroplasty using a rotating hinge implant

BackgroundRotating hinge implants are commonly used in revision total knee arthroplasty (TKA) in the setting of significant ligamentous instability or bone deficiency. These highly constrained implants have been associated with variable clinical outcomes and uncertain long-term survivorship. The aim of this study is to establish long-term functional outcomes, radiographic results, and survivorship after revision TKA with a rotating hinge implant.MethodThis is a retrospective study of prospectively collected data of 41 consecutive patients undergoing revision TKA with rotating hinge components and minimum 10-years follow-up. The study included 22 females (53.7%) and 19 males (46.3%) with a mean age of 66.6 ± 8.5 years. Clinical outcomes recorded included the Oxford Knee Score (OKS) preoperatively and at latest follow-up. Range of motion, implant survivorship, and complications were also recorded. Predefined radiological outcomes were obtained using plain radiographs.ResultsThere was a significant improvement in OKS after revision TKA with a rotating hinge implant compared to preoperative scores (40.7 ± 4.2 vs. 21.4 ± 4.9 respectively, p < 0.001). At latest follow-up, mean range of motion was 111.5° ± 9.3° and mean overall limb alignment was 0.2° ± 2.0° varus. Implant survivorship at minimum 10-year follow-up was 90.2%. Radiographic lucent lines were observed in 14 patients (34.1%).ConclusionRevision TKA with a rotating hinge implant leads to satisfactory clinical outcomes and very good implant survivorship at long-term follow-up. Surgeons should have a low threshold to use these versatile implants in complex revision knee arthroplasty.     

Postoperative bleeding adversely affects total knee arthroplasty outcomes in hemophilia

BackgroundHemophilic arthropathy can result in severe degenerative arthritis and functional limitations in the knees of relatively young patients. Total knee arthroplasty (TKA) provides pain relief and gain of function in advanced-stage hemophilic arthropathy cases. However, little is known about the long-term effects of early major postoperative bleeding (MPOB) in people with hemophilia (PWH). The aim of this study was to evaluate the effects of early MPOB on the final functional outcome, complications, and implant survival of TKA in a single-center hemophilia cohort.MethodPWH who underwent TKA between 1998 and 2019 in a single center were reviewed. Demographic data, clinical data, and radiographic images were evaluated. Hospital for Special Surgery (HSS), Knee Society Score (KSS), and Knee Society Function Score (KSS-F) scores were used to determine function. Patients with early bleeding complications (wound dehiscence, ecchymosis, hemarthrosis, hematoma formation, prolonged or recurrent bleeding attacks) were defined as the bleeding group. Patients who did not experience these complications were assigned to the control group. The bleeding group was compared with controls. Survival of the primary arthroplasty was analyzed by Kaplan–Meier curves.ResultsForty-five TKAs in 29 patients were included in the study. TKA led to an increase in the mean range of motion from 46.08° to 84.59° (P < 0.01). HSS scores increased from 48.33 preoperatively to 82.67 postoperatively (P < 0.01). There were improvements in both KSS and KSS-F scores from 34.22 and 53.3 preoperatively to 82.00 and 84.63 (P < 0.01), respectively. Ten patients (10 TKAs) (34%) experienced major bleeding during the postoperative period. Six of these patients had moderate hemophilia, and four had severe hemophilia. Three of these patients had hemarthroses (10.2%), one patient had a hematoma (3.4%), one patient had hemorrhagic bullae formation (3.4%), and five had excessive/prolonged bleeding from the wound (17%). The bleeding group (34%) had significantly worse HSS (63.78 vs 92.75, P < 0.001), KSS (61.78 vs 93.25, P < 0.001), and KSS-F (60.71 vs 96.25, P = 0.005) scores compared with controls. Preoperative and postoperative flexion contractures were positively correlated (+0.33, P = 0.003). One of the patients with postoperative hemarthrosis also had an accompanying transient common peroneal nerve palsy, and one patient (3.4%) had a periprosthetic fracture. Three knees (6.6%), two of whom were in the bleeding group, developed periprosthetic infections. Four knees (8.8%) in three patients underwent revision surgery, and two knees (4.4%) ended up in arthrodeses. Kaplan–Meier analysis revealed a mean survival duration of 17.04 years for the bleeding group and 22.15 years for the control group (P = 0.83). Survival rates were 80.0% for the bleeding group and 96.4% for the control group (P = 0.83).ConclusionsIn this study, MPOB after TKA in PWH was common and led to significantly worse function. MPOB after TKA in PWH was associated with a higher rate of complications and lower survival rates, although the differences were not statistically significant. Efforts must be made to avoid MPOB after TKA in PWH.     

Highly cross-linked polyethylene (HXLPE) is equivalent to conventional polyethylene (CPE) in total knee arthroplasty: A systematic review and meta-analysis

BackgroundThe benefits of HXLPE in total knee arthroplasty (TKA) have not been as evident as total hip arthroplasty (THA). A systematic review and meta-analysis to assess the impact of highly-crosslinked polyethylene (HXLPE) on TKA outcomes compared to conventional polyethylene (CPE) is described.MethodsAll studies comparing HXLPE with CPE for primary TKA were included for analysis. The minimum dataset included revision rates, indication for revision, aseptic component loosening and follow-up time. The primary outcome variables were all-cause revision, aseptic revision, revision for loosening, radiographic component loosening, osteolysis and incidence of radiolucent lines. Secondary outcome measures included postoperative functional knee scores. A random-effects meta-analysis allowing for all missing data was performed for all primary outcome variables.ResultsSix studies met the inclusion criteria. In total, there were 2,234 knees (1,105 HXLPE and 1,129 CPE). The combined mean follow-up for all studies was 6 years. The aseptic revision rate in the HXLPE group was 1.02% compared to 1.97% in the CPE group. There was no difference in the rate of all-cause revision (p = 0.131), aseptic revision (p = 0.298) or revision for component loosening (p = 0.206) between the two groups. Radiographic loosening (p = 0.200), radiolucent lines (p = 0.123) and osteolysis (p = 0.604) was similar between both groups. Functional outcomes were similar between groups.ConclusionThe use of HXLPE in TKA yields similar results for clinical and radiographic outcomes when compared to CPE at midterm follow-up. HXLPE does not confer the same advantages to TKA as seen in THA.     

The oxford knee score minimal clinically important difference for revision total knee arthroplasty

BackgroundMinimal clinically important difference (MCID) is crucial for interpreting meaningful improvements in patient-reported outcome measures (PROMs). No previous study has evaluated the MCID for the Oxford Knee Score (OKS) in revision total knee arthroplasty (TKA). This study aimed to propose the OKS MCID for revision TKA.MethodsProspectively collected data from 191 patients who underwent revision TKA at a single institution was analysed. Clinical assessment was performed preoperatively and at 2 years using OKS and Short-Form 36 Physical Component Score (SF-36 PCS). MCID was evaluated with a three-pronged methodology, using (1) anchor-based method with linear regression, (2) anchor-based method with receiver operating characteristic (ROC) and area under curve (AUC), (3) distribution-based method with standard deviation (SD). The anchors used were improvement in SF-36 PCS ≥ 12, patient satisfaction, and implant survivorship following revision TKA.ResultsThe MCID determined by anchor-based linear regression method using improvements in SF-36 PCS was 4.9 points. The MCID determined by anchor-based ROC was 10.5 points for satisfaction (AUC = 74.8%) and 13.5 points for implant survivorship (AUC = 73.7%). The MCID determined by distribution-based method of 0.5 SD was 4.7.ConclusionThe proposed MCID for OKS following revision TKA is 4.9 points. Patients who achieve an improvement in OKS of at least 10.5–13.5 points by 2 years are likely to be satisfied with their surgery and not require a subsequent re-revision TKA. Patients undergoing revision TKA should aim for an improvement in OKS of at least 10.5–13.5 points as a target score.     

Predictors of functional outcome after revision total knee arthroplasty following aseptic failure

BackgroundThere are a limited number of studies related to quality of life and functional outcome after revision total knee arthroplasty (TKA). The present study aimed to identify predictors of functional outcome after revision TKA for aseptic failure.MethodsOne hundred seventy-five patients with mean age of 66.6 years (range, 35–88) who underwent revision TKA for aseptic failure at our institute from 2003 to 2007 were identified. Short-form 36 (SF-36), Western Ontario and McMaster Osteoarthritis Index (WOMAC) and Knee Society Scores (KSS) collected preoperatively and at 2 years follow up were evaluated. Univariate and multivariate analyses were performed to determine predictors of functional outcome in studied patients.ResultsBoth physical and mental dimensions of SF-36, pain, functional, and stiffness subscales of WOMAC and both functional and clinical scores of KSS improved significantly after revision TKA (p < 0.001). In the multivariate analysis, male gender, a lower Charlson comorbidity index, and higher preoperative functional KSS were predictors of higher functional KSS at 2 years after revision. Lower preoperative pain and higher clinical KSS were predictors of better outcome as measured by pain scale of WOMAC. Body mass index (BMI) and preoperative clinical KSS were significant predictors of function and stiffness as measured by WOMAC.ConclusionsBMI is a modifiable predictor of functional outcome after revision TKA. Moreover, patients with higher preoperative functional scores appear to have better postoperative function.Level of evidenceLevel II.     

Similar 20-year survivorship for single and bilateral total knee arthroplasty

BackgroundLong-term follow-up after total knee arthroplasty (TKA) is crucial to providing survivorship updates on available TKA implants to guide patient expectations when undergoing TKA. The purpose of this study was to compare implant survivorship between patients undergoing primary single, simultaneous bilateral, and staged bilateral TKA with 15-year minimum follow-up.MethodsThis retrospective study included 826 patients (n = 1089) who underwent primary single (n = 454), simultaneous bilateral (n = 266), or staged bilateral (n = 369) TKA using a single TKA system by a single surgeon from 1991-2005 with 15-year minimum follow-up. Demographics, clinical variables, and surgical outcomes were collected and compared using Student’s t-test, chi-squared tests, or Kaplan-Meier analyses. Reoperation was defined as all surgeries performed on the knee after the index procedure; revision TKA was defined as complete implant exchange. p < 0.05 significant.ResultsPatients in the staged TKA cohort were younger (65.4 years = staged, 67.8 = simultaneous, 67.1 = single, p < 0.019). Women were less likely to receive simultaneous TKAs (22 %vs.29%, p < 0.001). Postoperative range of motion was similar (116.8° = simultaneous, 114.9° = staged, 114.8° = single, p = 0.11). Overall 15-year implant survival based on revision TKA was similar (97.7% = simultaneous, 97.2% = staged, 96.7% = single, p = 0.45). The estimated 15-year reoperation rate was 7.0% (95% CI, 5.5–8.7%). Reoperations were secondary to infection (35.5%), implant wear (26.3%), arthrofibrosis (18.4%), traumatic injuries (10.5%), pain (6.6%), pathologic lesion (1.3%), and avascular necrosis (1.3%).ConclusionThis study demonstrated a high implant survival rate of 95–97% at 20-years after primary single, staged bilateral and simultaneous bilateral TKA. Furthermore, simultaneous bilateral TKAs exhibited similar range of motion, implant survival, and rates of reoperation to staged bilateral and single TKA.     

Can robot-assisted total knee arthroplasty be a cost-effective procedure? A Markov decision analysis

BackgroundTotal knee arthroplasty (TKA) is a frequently and increasingly performed surgery in the treatment of disabling knee osteoarthritis. The rising number of procedures and related revisions pose an increasing economic burden on health care systems. In an attempt to lower the revision rate due to component malalignment and soft tissue imbalance in TKA, robotic assistance (RA) has been introduced in the operating theatre.The primary objective of this study is to provide the results of a theoretical, preliminary cost-effectiveness analysis of RA TKA.MethodsA Markov state-transition model was designed to model the health status of sixty-seven-year-old patients in need of TKA due to primary osteoarthritis over a twenty-year period following their knee joint replacement. Transitional probabilities and independent variables were extracted from existing literature.ResultsThe value attributed to the utility both for primary and revision surgery has the biggest impact on the ICER, followed by the rate of successful primary surgery and the cost of RA-technology. Only 2.18% of the samples yielded from the probabilistic sensitivity analysis proved to be cost-effective (threshold set at $50000/QALY). A calculated surgical volume of at least 253 cases per robot per year is needed to prove cost-effective taking the predetermined parameter values into account.ConclusionBased upon transitional probabilities and independent variables derived from existing studies, RA TKA may be cost-effective at a surgical volume of 253 cases per robot per year when compared to conventional TKA.     

Relationship between leg extensor muscle strength and knee joint loading during gait before and after total knee arthroplasty

ObjectiveThe aim of the present study was to evaluate an isometric maximal voluntary contraction (MVC) force of the leg extensor muscles and its relationship with knee joint loading during gait prior and after total knee arthroplasty (TKA).MethodsCustom-made dynamometer was used to assess an isometric MVC force of the leg extensor muscles and 3-D motion analysis system was used to evaluate the knee joint loading during gait in 13 female patients (aged 49–68 years) with knee osteoarthritis. Patients were evaluated one day before, and three and six months following TKA in the operated and non-operated leg.ResultsSix months after TKA, MVC force of the leg extensor muscles for the operated leg did not differ significantly as compared to the preoperative level, whereas it remained significantly lower for the non-operated leg and controls. The knee flexion moment and the knee joint power during mid stance of gait was improved six months after TKA, remaining significantly lowered compared with controls. Negative moderate correlation between leg extensor muscles strength and knee joint loading for the operated leg during mid stance was noted three months after TKA.ConclusionsThe correlation analysis indicates that due to weak leg extensor muscles, an excessive load is applied to knee joint during mid stance of gait in patients, whereas in healthy subjects stronger knee-surrounding muscles provide stronger knee joint loading during gait.Level of Evidence: III (correlational study)