The migration patterns of two versions of the Furlong cementless femoral stem: a randomised, controlled trial using radiostereometric analysis

We have evaluated the difference in the migration patterns over two years of two cementless stems in a randomised, controlled trial using radiostereophotogrammetric analysis (RSA). The implants studied were the Furlong HAC stem, which has good long-term results and the Furlong Active stem, which is a modified version of the former designed to minimise stress concentrations between the implant and bone, and thus to improve fixation. A total of 23 Furlong HAC and 20 Furlong Active stems were implanted in 43 patients. RSA examinations were carried out immediately post-operatively and at six, 12 and 24 months post-operatively. The subsidence during the first year in the Furlong HAC stem, was approximately one-third that of the Furlong Active stem, the measured mean subsidence of the femoral head at six months being 0.27 mm (95% confidence interval (CI) 0.03 to 0.51) and 0.99 mm (95% CI 0.38 to 1.60), respectively (p = 0.03). One Active stem continued to subside during the second year. All hips, regardless of the type of stem were clinically successful as judged by the Oxford hip score and a derived pain score without any distinction between the two types of stem. The initial stability of the Furlong Active stem was not as good as the established stem which might compromise osseo-integration to the detriment of long-term success. The changes in the geometry of the stem, to minimise stress have affected the attainment of initial stability.     

Design modifications of the uncemented Furlong hip stem result in minor early subsidence but do not affect further stability: A randomized controlled RSA study with 5-year follow-up

Background and purpose —

Even small design modifications of uncemented hip stems may alter the postoperative 3-D migration pattern. The Furlong Active is an uncemented femoral stem which, in terms of design, is based on its precursor—the well-proven Furlong HAC—but has undergone several design changes. The collar has been removed on the Active stem along with the lateral fin; it is shorter and has more rounded edges in the proximal part. We compared the migration patterns of the uncemented Furlong HAC stem and the modified Furlong Active stem in a randomized, controlled trial over 5 years using radiostereometry (RSA).

Patients and methods —

50 patients with primary osteoarthritis were randomized to receive either the HAC stem or the Active stem. The patients underwent repeated RSA examinations (postoperatively, at 3 months, and after 1, 2, and 5 years) and conventional radiography, and they also filled out hip-specific questionnaires.

Results —

During the first 3 months, the collarless Active stem subsided to a greater extent than the collar-fitted HAC stem (0.99 mm vs. 0.31 mm, p = 0.05). There were, however, no other differences in movement measured by RSA or in clinical outcome between the 2 stems. After 3 months, both stem types had stabilized and almost no further migration was seen.

Interpretation —

The Active stem showed no signs of unfavorable migration. Our results suggest that the osseointegration is not compromised by the new design features.Since the introduction of the Charnley cemented hip stem, it has been emphasized that immediate stability is of great importance for achievement of long-term stem survival (Loudon and Charnley 1980). Nowadays, it is well documented that different design features influence the migration pattern of the stem. Highly polished, collarless cemented stems like the Exeter continuously subside within the cement mantle without compromising the long-term survival of the stem (Stefansdottir et al. 2004, Nieuwenhuijse et al. 2012). Uncemented stems depend on osseointegration to stabilize, and the common perception is that postoperative migration should not be tolerated (Kirk et al. 2007, Demey et al. 2011, Gortchacow et al. 2012). According to several RSA investigations, however, many modern uncemented stems show a small degree of initial migration before osseointegration occurs (Strom et al. 2006a,b, 2007, Campbell et al. 2011).Over the last decade, long-term follow-up has shown good results for the contemporary uncemented stems (McNally et al. 2000, Skinner et al. 2003, Eskelinen et al. 2006, Sharma and Brooks 2006, Gabbar et al. 2008, Rajaratnam et al. 2008, Hailer et al. 2010, Vidalain 2011), including a 99% survival rate for the Furlong HAC stem (JRI Ltd., London, UK) at 13–15 years (Shetty et al. 2005). The design of the Furlong HAC stem has not changed since its introduction in the mid-eighties, but demands for a more modern, shorter and less bulky femoral stem have led to the introduction of a modified version of the Furlong HAC stem with the aim of making it easier to implant: the Furlong Active stem (JRI Ltd, London, UK). From here on, the stems will be referred to as the HAC and the Active. The lateral fin, which was originally designed to improve rotational stability, has been removed. The rationale for this change is the risk of fracturing the trochanter major when using the lateral fin cutter (“breadknife”) in order to make room for the fin. The Active stem has more rounded edges both medially and laterally in the proximal part (Figure 1). Proximally, the Active stem is slightly double-tapered whereas the HAC stem is parallel-sided in the coronal plane. In the AP view, the central section of the stem has more or less remained the same in the form of a cone to provide transfer of body weight under hoop stress. The transition zone from the cone-shaped proximal section to the distal cylindrical section is less distinct in the Active stem, and the distal cylindrical section is shorter. Similarly to the HAC stem, it is made from forged titanium alloy and is vacuum plasma-sprayed with a 200-µm-thick layer of Supravit (150-µm hydroxyapatite ceramic on 50-µm titanium substrate), which provides a high-density coating without metal-to-bone contact.Open in a separate windowFigure 1.A. Furlong HAC. B. Furlong Active, both with tantalum markers. C. Superimposition of outlines (right image).It is important that the postoperative 3-D migratory pattern is well established before a prosthesis of new or modified design is implanted on a larger scale, thereby reducing the risk of potential future complications for patients (Karrholm et al. 1997). The most accurate radiographic method used to identify early warning signs of prosthesis migration and to predict long-term results with a specific prosthesis is radiostereometry (RSA) (Valstar et al. 2005).The main goal of our study was to compare the 3-D migration patterns of the Active stem and the well-proven HAC stem using RSA. We wanted to determine if the design changes would have any impact on the migration behavior, influence the osseointegration, and thereby affect the long-term result.     

Small and similar amounts of micromotion in an anatomical stem and a customized cementless femoral stem in regular-shaped femurs

Background and purpose — High primary stability is important for long-term survival of uncemented femoral stems. Different stem designs are currently in use. The ABG-I is a well-documented anatomical stem with a press-fit design. The Unique stem is designed for a tight customized fit to the cortical bone of the upper femur. This implant was initially developed for patients with abnormal anatomy, but the concept can also be used in patients with normal femoral anatomy. We present 5-year radiostereometric analysis (RSA) results from a randomized study comparing the ABG-I anatomical stem with the Unique femoral stem.

Patients and methods — 100 hips with regular upper femur anatomy were randomized to either the ABG-I stem or the Unique femoral stem. RSA measurements were performed postoperatively and after 3, 6, 12, 24, and 60 months.

Results — RSA measurements from 80 hips were available for analysis at the 5-year follow-up. Small amounts of movement were observed for both stems, with no statistically significant differences between the 2 types.

Interpretation — No improvement in long-term stability was found from using a customized stem design. However, no patients with abnormal geometry of the upper femur were included in this study.     

Good stability of a cementless,anatomically designed femoral stem in aging women: a 9-year RSA study of 32 patients

Background and purpose — We previously reported a transient, bone mineral density (BMD)-dependent early migration of anatomically designed hydroxyapatite-coated femoral stems with ceramic–ceramic bearing surfaces (ABG-II) in aging osteoarthritic women undergoing cementless total hip arthroplasty. To evaluate the clinical significance of the finding, we performed a follow-up study for repeated radiostereometric analysis (RSA) 9 years after surgery.

Patients and methods — Of the 53 female patients examined at 2 years post-surgery in the original study, 32 were able to undergo repeated RSA of femoral stem migration at a median of 9 years (7.8–9.3) after surgery. Standard hip radiographs were obtained, and the subjects completed the Harris Hip Score and Western Ontario and McMaster Universities Osteoarthritis Index outcome questionnaires.

Results — Paired comparisons revealed no statistically significant migration of the femoral stems between 2 and 9 years post-surgery. 1 patient exhibited minor but progressive RSA stem migration. All radiographs exhibited uniform stem osseointegration. No stem was revised for mechanical loosening. The clinical outcome scores were similar between 2 and 9 years post-surgery.

Interpretation — Despite the BMD-related early migration observed during the first 3 postoperative months, the anatomically designed femoral stems in aging women are osseointegrated, as evaluated by RSA and radiographs, and exhibit good clinical function at 9 years.     

Good stability but high periprosthetic bone mineral loss and late-occurring periprosthetic fractures with use of uncemented tapered femoral stems in patients with a femoral neck fracture

Background and purpose— We previously evaluated a new uncemented femoral stem designed for elderly patients with a femoral neck fracture and found stable implant fixation and good clinical results up to 2 years postoperatively, despite substantial periprosthetic bone mineral loss. We now present the medium-term follow-up results from this study.

Patients and methods— In this observational prospective cohort study, we included 50 patients (mean age 81 (70–92) years) with a femoral neck fracture. All patients underwent surgery with a cemented cup and an uncemented stem specifically designed for fracture treatment. Outcome variables were migration of the stem measured with radiostereometry (RSA) and periprosthetic change in bone mineral density (BMD), measured with dual-energy X-ray absorptiometry (DXA). Hip function and health-related quality of life were assessed using the Harris hip score (HHS) and the EuroQol-5D (EQ-5D). DXA and RSA data were collected at regular intervals up to 4 years, and data concerning reoperations and hip-related complications were collected during a mean follow-up time of 5 (0.2–7.5) years.

Results— At 5 years, 19 patients had either passed away or were unavailable for further participation and 31 could be followed up. Of the original 50 patients, 6 patients had suffered a periprosthetic fracture, all of them sustained after the 2-year follow-up. In 19 patients, we obtained complete RSA and DXA data and no component had migrated after the 2-year follow-up. We also found a continuous total periprosthetic bone loss amounting to a median of –19% (–39 to 2). No changes in HHS or EQ-5D were observed during the follow-up period.

Interpretation— In this medium-term follow-up, the stem remained firmly fixed in bone despite considerable periprosthetic bone mineral loss. However, this bone loss might explain the high number of late-occurring periprosthetic fractures. Based on these results, we would not recommend uncemented femoral stems for the treatment of femoral neck fractures in the elderly.     

Peri-apatite coating decreases uncemented tibial component migration: long-term RSA results of a randomized controlled trial and limitations of short-term results

Background and purpose — Biological fixation of uncemented knee prostheses can be improved by applying hydroxyapatite coating around the porous surface via a solution deposition technique called Peri-Apatite (PA). The 2-year results of a randomized controlled trial, evaluating the effect of PA, revealed several components with continuous migration in the second postoperative year, particularly in the uncoated group. To evaluate whether absence of early stabilization is diagnostic of loosening, we now present long-term follow-up results.

Patients and methods — 60 patients were randomized to PA-coated or uncoated (porous only) total knee arthroplasty of which 58 were evaluated with radiostereometric analysis (RSA) performed at baseline, at 3 months postoperatively and at 1, 2, 5, 7, and 10 years. A linear mixed-effects model was used to analyze the repeated measurements.

Results — PA-coated components had a statistically significantly lower mean migration at 10 years of 0.94?mm (95% CI 0.72–1.2) compared with the uncoated group showing a mean migration of 1.72?mm (95% CI 1.4–2.1). Continuous migration in the second postoperative year was seen in 7 uncoated components and in 1?PA-coated component. All of these implants stabilized after 2 years except for 2 uncoated components.

Interpretation — Peri-apatite enhances stabilization of uncemented components. The number of components that stabilized after 2 years emphasizes the importance of longer follow-up to determine full stabilization and risk of loosening in uncemented components with biphasic migration profiles.     

Denosumab reduces early migration in total knee replacement

Background and purpose — Aseptic loosening is a main cause of late revision in total knee replacement (TKR). Migration of implants as measured by radiostereometric analysis (RSA) can predict future loosening. This migration is associated with bone resorption. Denosumab is a human monoclonal antibody that binds to receptors on osteoclast precursors and osteoclasts. This prevents osteoclast formation, resulting in less bone resorption in cortical and trabecular bone. We investigated whether denosumab can reduce migration of TKR, as measured with RSA.

Patients and methods — In this 2-center, randomized, double-blind placebo-controlled trial, 50 patients with osteoarthritis of the knee were treated with an injection of either denosumab (60?mg) or placebo 1?day after knee replacement surgery and again after 6 months. RSA was performed postoperatively and after 6, 12, and 24 months. The primary effect variable was RSA maximal total point motion (MTPM) after 12 months. We also measured other RSA variables and the knee osteoarthritis outcome score (KOOS).

Results — The primary effect variable, MTPM after 12 months, showed that migration in the denosumab group was statistically significantly less than in the controls. Denosumab MTPM 12 months was reduced by one-third (denosumab: median 0.24?mm, 10% and 90% percentiles: 0.15 and 0.41; placebo: median 0.36?mm, 10% and 90% percentiles: 0.20 and 0.62). The secondary MTPM variables (6 and 24 months) also showed a statistically significant reduction in migration. There was no significant difference in MTPM for the period 12–24 months. KOOS sub-variables were similiar between denosumab and placebo after 12 and 24 months.

Interpretation — Denosumab reduces early migration in total knee replacement, as in previous trials using bisphosphonates. As migration is related to the risk of late loosening, denosumab may be beneficial for long-term results.     

Accuracy of migration analysis in hip arthroplasty Digitized and conventional radiography,compared to radiostereometry in 51 patients

We assessed the accuracy of migration measurements on conventional and digitized radiographs of total hip arthroplasties by comparing the results with radiostereometry (RSA). 4 stem and 3 acetabular designs were studied. 2 of the stem designs and 1 cup design were uncemented. 180 manual and 202 digitized measurements were done on 120 conventional radiographic examinations.

The readings on digitized radiographs did not differ from the manual measurements on the same radiographs. A comparison of the measurements from plain radiographs and with RSA of the femoral stems revealed an accuracy (absolute mean + 2 SD) of between 3.9 and 12.3 mm, depending on the choice of landmarks. The greatest accuracy was obtained by using tantalum markers inserted into the greater or the lesser trochanter and the shoulder of the stem. The most medial point of the lesser trochanter proved to be the best bony landmark. Measurements, including both the center of the femoral head and the greater trochanter, were associated with poor accuracy. The accuracy as regards horizontal cup migration varied from 4.4 to 6.5 mm and the accuracy as regards vertical migration varied between 4.4 and 6.3 mm.

The intraobserver error (2 SD) ranged from 1.6 mm to 5.6 mm, The corresponding figures for the inter-observer error were 2.6 mm and 6.6 mm, respectively. One of the cemented cup designs was associated with inferior accuracy. Stem design did not affect the accuracy.     

Stable fixation of an osseointegated implant system for above-the-knee amputees

Background and purpose Rehabilitation of patients with transfemoral amputations is particularly difficult due to problems in using standard socket prostheses. We wanted to assess long-term fixation of the osseointegrated implant system (OPRA) using radiostereometric analysis (RSA) and periprosthetic bone remodeling.

Methods 51 patients with transfemoral amputations (55 implants) were enrolled in an RSA study. RSA and plain radiographs were scheduled at 6 months and at 1, 2, 5, 7, and 10 years after surgery. RSA films were analyzed using UmRSA software. Plain radiographs were graded for bone resorption, cancellization, cortical thinning, and trabecular streaming or buttressing in specifically defined zones around the implant.

Results At 5 years, the median (SE) migration of the implant was –0.02 (0.06) mm distally. The rotational movement was 0.42 (0.32) degrees around the longitudinal axis. There was no statistically significant difference in median rotation or migration at any follow-up time. Cancellization of the cortex (plain radiographic grading) appeared in at least 1 zone in over half of the patients at 2 years. However, the prevalence of cancellization had decreased by the 5-year follow-up.

Interpretation The RSA analysis for the OPRA system indicated stable fixation of the implant. The periprosthetic bone remodeling showed similarities with changes seen around uncemented hip stems. The OPRA system is a new and promising approach for addressing the challenges faced by patients with transfemoral amputations.     

Small and similar amounts of micromotion in an anatomical stem and a customized cementless femoral stem in regular-shaped femurs: A 5-year follow-up randomized RSA study

Background and purpose

High primary stability is important for long-term survival of uncemented femoral stems. Different stem designs are currently in use. The ABG-I is a well-documented anatomical stem with a press-fit design. The Unique stem is designed for a tight customized fit to the cortical bone of the upper femur. This implant was initially developed for patients with abnormal anatomy, but the concept can also be used in patients with normal femoral anatomy. We present 5-year radiostereometric analysis (RSA) results from a randomized study comparing the ABG-I anatomical stem with the Unique femoral stem.

Patients and methods

100 hips with regular upper femur anatomy were randomized to either the ABG-I stem or the Unique femoral stem. RSA measurements were performed postoperatively and after 3, 6, 12, 24, and 60 months.

Results

RSA measurements from 80 hips were available for analysis at the 5-year follow-up. Small amounts of movement were observed for both stems, with no statistically significant differences between the 2 types.

Interpretation

No improvement in long-term stability was found from using a customized stem design. However, no patients with abnormal geometry of the upper femur were included in this study.High mechanical stability is a crucial factor for correct performance of uncemented femoral stems. Micromovements along the implant-bone interface may prevent ingrowth of bone to the surface of the prosthesis, and it may lead to the formation of a fibrous membrane and eventually to loosening of the implant. The critical thresholds of micromovements that can be tolerated are not exactly known, but they are probably dependent on both patient- and implant-specific factors (Viceconti et al. 2006). It has been shown, however, that interfacial motion of around 40 μm leads to partial bone ingrowth whereas motions exceeding 150 μm completely prevent ingrowth of bone (Pilliar et al. 1986, Jasty et al. 1997).Uncemented, customized femoral stems are mainly designed and manufactured for patients with abnormal size and shape of the proximal femur, but this does not preclude their use in patients with regular-shaped proximal femurs. The requirement for maximum primary stability with uncemented off-the-shelf stems also applies to customized stems. The optimized fit and fill of a customized stem should theoretically promote even better mechanical fixation than with standard implants.Radiostereometric analysis (RSA) enables measurement of migration and rotation in the range of 0.1 mm and 0.05º, respectively (Selvik 1989, Kadar et al. 2011). There is a correlation between postoperative migration of femoral stems and early loosening (Freeman and Plante-Bordeneuve 1994, Linder 1994, Karrholm et al. 2006, Karrholm 2012). On the other hand, a new implant showing large degrees of micromovement should not necessarily be regarded as having a performance equivalent to long-term failure (Karrholm et al. 2006). Recently published studies reporting medium- to long-term RSA results will probably contribute to a better understanding of the topic (Nieuwenhuijse et al. 2012, Rohrl et al. 2012).This randomized study was performed as part of the clinical documentation of the Unique customized stem (Scandinavian Customized Prosthesis (SCP), Trondheim, Norway), to compare the migration pattern of the Unique stem with that of a standard anatomical uncemented stem with a clinically well-proven stem design (the ABG-I).Our aim was to measure migration of the Unique customized stem and the ABG-I stem using RSA. Our hypothesis was that there would be no difference in migration between the 2 types of uncemented femoral stems in patients with regular anatomy in the upper femur.     

A 2-year RSA study of the Vanguard CR total knee system: A randomized controlled trial comparing patient-specific positioning guides with conventional technique

Background and purpose — There is some concern regarding the revision rate of the Vanguard CR TKA in 1 registry, and the literature is ambiguous about the efficacy of patient-specific positioning guides (PSPGs). The objective of this study was to investigate the stability of the cemented Vanguard CR Total Knee using 2 different surgical techniques. Our hypothesis was that there is no difference in migration when implanting the Vanguard CR with either PSPGs or conventional technique. We hereby present a randomized controlled trial of 2-year follow-up with radiostereometric analysis (RSA).

Patients and methods — 40 TKAs were performed between 2011 and 2013 with either PSPGs or the conventional technique and 22 of these were investigated with RSA.

Results — The PSPG (8 knees) and the conventional (14 knees) groups had a mean maximum total point motion (MTPM) (95% CI) of 0.83 (0.48–1.18) vs. 0.70 (0.43–0.97) mm, 1.03 (0.60–1.43) vs. 0.86 (0.53–1.19), and 1.46 (1.07–1.85) vs. 0.80 (0.52–1.43) at 3, 12, and 24 months respectively (p = 0.1). 5 implants had either an MTPM >1.6?mm at 12 months and/or a migration of more than 0.2?mm between 1- and 2-year follow-ups. 2 of these also had a peripheral subsidence of more than 0.6?mm at 2 years.

Interpretation — 5 implants (3 in the PSPG group) were found to be at risk of later aseptic loosening. The PSPG group continuously migrated between 12 and 24 months. The conventional group had an initial high migration between postoperative and 3 months, but seemed more stable after 1 year. Although the difference was not statistically significant, we think the migration in the PSPG group is of some concern.     

Comparison of the uncemented Cone and the cemented Bimetric hip prosthesis in young patients with osteoarthritis: an RSA, clinical and radiographic study

BACKGROUND: There is no consensus as to whether uncemented or cemented femoral stems should be used in younger patients. We compared the uncemented Cone stem to the cemented Bimetric stem in young patients with osteoarthritis. PATIENTS AND METHODS: We randomized 45 relatively young patients (< 65 years old, mean age 54 years) with osteoarthritis to either an uncemented Cone stem or a cemented Bimetric stem. All patients were followed for 2 years. Outcome was assessed by the Merle d'Aubigné score, conventional radiography and repeated radio-stereometric analysis (RSA). We also followed 81 Cone stems for 8 (7-12) years with revision as endpoint. RESULTS: The clinical outcome was excellent. No patient had postoperative thigh pain. The migration was small. The Bimetric stem was stable during the whole observation period, while the Cone stem subsided and rotated to retroversion during the first 3 months post-operatively, and then remained stable. In the follow-up study of 81 Cone stems, 1 stem was revised. INTERPRETATION: We conclude that both the cemented Bimetric stem and the uncemented Cone stem are stable and give excellent clinical results after 2 years in relatively young patients with osteoarthritis. Although designed for CDH hips, the Cone stem appears to be suitable also for patients with osteoarthitis.     

Migration of the uncemented Echo Bi-Metric and Bi-Metric THA stems: a randomized controlled RSA study involving 62 patients with 24-month follow-up

Background and purpose — Despite the good results after total hip arthroplasty (THA), new implants are continuously being developed to improve durability. The Echo Bi-Metric (EBM) THA stem is the successor to the Bi-Metric (BM) THA stem. The EBM stem includes many of the features of the BM stem, but minor changes in the design might improve the clinical performance. We compared the migration behavior with radiostereometric analysis (RSA) of the EBM stem and the BM stem at 24 months and evaluated the clinical outcome.Patients and methods — We randomized 62 patients with osteoarthritis (mean age 64 years, female/male 28/34) scheduled for an uncemented THA to receive either an EBM or a BM THA stem. We performed RSA within 1 week after surgery and at 3, 6, 12, and 24 months. The clinical outcome was evaluated using Harris Hip Score (HHS) and Oxford Hip Score (OHS).Results — At 24 months, we found no statistically significant differences in migration between the two implants. During the first 3 months both the EBM and the BM stems showed visible subsidence (2.5 mm and 2.2 mm respectively), and retroversion (2.5° and 2.2° respectively), but after 3 months this stabilized. The expected increase in HHS and OHS was similar between the groups.Interpretation — The EBM stem showed a migration at 24 months not different from the BM stem, and both stems display satisfying clinical results.

To improve the longevity of total hip arthroplasty (THA) new designs are continuously being developed. The introduction of new implants should optimally be done by phased stepwise introduction (Malchau 1995, Nelissen et al. 2011) including radiostereometric analysis (RSA) of implant migration.Some subsidence of hip stems is generally accepted within the first 3 months, but after that osseointegration and stability should have occurred. Mean subsidence of up to 1 mm of the stem at 24 months has been reported (Nysted et al. 2014, Weber et al. 2014, Hoornenborg et al. 2018, Sesselmann et al. 2018, Kruijntjens et al. 2020).This study investigates by RSA potential differences in migration at 24 months, between 2 different designs of porous-coated uncemented hip prosthesis; the Bi-Metric Full Proximal Profile THA stem (BM) and the Echo Bi-Metric (EBM) stem (Zimmer Biomet, Warsaw, IN, USA) (Figure 1). Both stems are press-fit titanium alloy stems with a proximal plasma spray porous titanium coating and a distal part with a roughened titanium surface. The BM has shown good clinical results and excellent stem survival in register studies since its introduction in 1984 (Jacobsen et al. 2003, Davies et al. 2010, Mäkelä et al. 2010, Lazarinis et al. 2011). The EBM is the successor to the BM and has 3 theoretical design improvements: a slimmer design of the neck to increase range of motion; a polished bullet-shaped distal tip to reduce distal stress; and an extended porous coating to support biological ingrowth proximally. Evaluation of adaptive bone remodeling and stress shielding will be addressed in another publication.Open in a separate windowFigure 1.The stems: on the left the Bi-Metric stem and on the right the Echo Bi-Metric stem.We hypothesized that the migration of the EBM was less at 24 months, compared with the BM stem.     

Monoblock versus modular polyethylene insert in uncemented total knee arthroplasty

Background and purpose — Backside wear of the polyethylene insert in total knee arthroplasty (TKA) can produce clinically significant levels of polyethylene debris, which can lead to loosening of the tibial component. Loosening due to polyethylene debris could theoretically be reduced in tibial components of monoblock polyethylene design, as there is no backside wear. We investigated the effect of 2 different tibial component designs, monoblock and modular polyethylene, on migration of the tibial component in uncemented TKA.

Patients and methods — In this randomized study, 53 patients (mean age 61 years), 32 in the monoblock group and 33 in the modular group, were followed for 2 years. Radiostereometric analysis (RSA) was done postoperatively after weight bearing and after 3, 6, 12, and 24 months. The primary endpoint of the study was comparison of the tibial component migration (expressed as maximum total point motion (MTPM)) of the 2 different implant designs.

Results — We did not find any statistically significant difference in MTPM between the groups at 3 months (p = 0.2) or at 6 months (p = 0.1), but at 12 and 24 months of follow-up there was a significant difference in MTPM of 0.36?mm (p = 0.02) and 0.42?mm (p = 0.02) between groups, with the highest amount of migration (1.0?mm) in the modular group. The difference in continuous migration (MTPM from 12 and 24 months) between the groups was 0.096?mm (p = 0.5), and when comparing MTPM from 3–24 months, the difference between the groups was 0.23?mm (p = 0.07).

Interpretation — In both study groups, we found the early migration pattern expected, with a relatively high initial amount of migration from operation to 3 months of follow-up, followed by stabilization of the implant with little migration thereafter. However, the modular implants had a statistically significantly higher degree of migration compared to the monoblock. We believe that the greater stiffness of the modular implants was the main reason for the difference in migration, but an initial creep in the polyethylene metal-back locking mechanism of the modular group could also be a possible explanation for the observed difference in migration between the 2 study groups.     

Trabecular metal tibial knee component still stable at 10 years

Background and purpose — Total knee replacement (TKR) in younger patients using cemented components has shown inferior results, mainly due to aseptic loosening. Excellent clinical results have been reported with components made of trabecular metal (TM). In a previous report, we have shown stabilization of the TM tibial implants for up to 5 years. In this study, we compared the clinical and RSA results of these uncemented implants with those of cemented implants.

Patients and methods — 41 patients (47 knees) aged ≤ 60 years underwent TKR. 22 patients (26 knees) received an uncemented monoblock cruciate-retaining (CR) tibial component (TM) and 19 patients (21 knees) received a cemented NexGen Option CR tibial component. Follow-up examination was done at 10 years, and 16 patients (19 knees) with TM tibial components and 17 patients (18 knees) with cemented tibial components remained for analysis.

Results — 1 of 19?TM implants was revised for infection, 2 of 18 cemented components were revised for knee instability, and no revisions were done for loosening. Both types of tibial components migrated in the first 3 months, the TM group to a greater extent than the cemented group. After 3 months, both groups were stable during the next 10 years.

Interpretation — The patterns of migration for uncemented TM implants and cemented tibial implants over the first 10 years indicate that they have a good long-term prognosis regarding fixation     

No effect of additional screw fixation of a cementless,all-polyethylene press-fit socket on migration,wear, and clinical outcome

Background and purpose — Additional screw fixation of the all-polyethylene press-fit RM cup (Mathys) has no additional value for migration, in the first 2 years after surgery. However, the medium-term and long-term effects of screw fixation remain unclear. We therefore evaluated the influence of screw fixation on migration, wear, and clinical outcome at 6.5 years using radiostereometric analysis (RSA).

Patients and methods — This study involved prolonged follow-up from a previous randomized controlled trial (RCT). We analyzed RSA radiographs taken at baseline and at 1-, 2-, and 6.5-year follow-up. Cup migration and wear were assessed using model-based RSA software. Wear was calculated as translation of the femoral head model in relation to the cup model. Total translation, rotation, and wear were calculated mathematically from results of the orthogonal components.

Results — 27 patients (15 with screw fixation and 12 without) were available for follow-up at 6.5 (5.6–7.2) years. Total translation (0.50?mm vs. 0.56?mm) and rotation (1.01 degrees vs. 1.33 degrees) of the cup was low, and was not significantly different between the 2 groups. Wear increased over time, and was similar between the 2 groups (0.58?mm vs. 0.53?mm). Wear rate (0.08?mm/year vs. 0.09?mm/year) and clinical outcomes were also similar.

Interpretation — Our results indicate that additional screw fixation of all-polyethylene press-fit RM cups has no additional value regarding medium-term migration and clinical outcome. The wear rate was low in both groups.     

Radiographic Subsidence in Asymptomatic Patients After THR Using the Furlong Active HAP Stem

Background

The short, tapered, collarless Furlong Active stem has been recently associated in the published literature with significant subsidence using Roentgen stereophotogrammetric analysis.

Questions/Purposes

The purpose of this study was to analyze the short-term radiographic subsidence in Furlong Active HAP stems and correlate the results with the age, gender, bone morphology, and bone quality of the proximal femur, stem diameter, and medullary canal filling.

Methods

Sixty-five consecutive patients (70 hips) receiving the Furlong Active HAP stems were enrolled in this prospective series. The average follow-up was 2.99 ± 1.38 years. All patients were evaluated clinically using the Harris Hip Score (HHS) and radiographically for femoral stem subsidence. In addition, proximal femoral osteopenia, proximal femur morphology, and medullary canal filling were also evaluated.

Results

The average subsidence was 2.4 mm (from 0 to 13 mm) at the end of the follow-up period. The average HHS score at the end of follow-up was 90 (range, 81–98). There was one intraoperative fracture.

Conclusions

Of the Furlong Active stems 61% subsided with initial weight bearing. Subsidence is higher in males, but no correlation has been found with age, stem diameter, morphology, osteopenia, or canal filling.

Electronic supplementary material

The online version of this article (doi:10.1007/s11420-013-9342-z) contains supplementary material, which is available to authorized users.     

Migration and clinical outcome of mobile-bearing versus fixed-bearing single-radius total knee arthroplasty

Background and purpose — Mobile-bearing total knee prostheses (TKPs) were developed in the 1970s in an attempt to increase function and improve implant longevity. However, modern fixed-bearing designs like the single-radius TKP may provide similar advantages. We compared tibial component migration measured with radiostereometric analysis (RSA) and clinical outcome of otherwise similarly designed cemented fixed-bearing and mobile-bearing single-radius TKPs.

Patients and methods — RSA measurements and clinical scores were assessed in 46 randomized patients at baseline, 6 months, 1 year, and annually thereafter up to 6 years postoperatively. A linear mixed-effects model was used to analyze the repeated measurements.

Results — Both groups showed comparable migration (p = 0.3), with a mean migration at 6-year follow-up of 0.90?mm (95% CI 0.49–1.41) for the fixed-bearing group compared with 1.22?mm (95% CI 0.75–1.80) for the mobile-bearing group. Clinical outcomes were similar between groups. 1 fixed-bearing knee was revised for aseptic loosening after 6 years and 2 knees (1 in each group) were revised for late infection. 2 knees (1 in each group) were suspected for loosening due to excessive migration. Another mobile-bearing knee was revised after an insert dislocation due to failure of the locking mechanism 6 weeks postoperatively, after which study inclusion was preliminary terminated.

Interpretation — Fixed-bearing and mobile-bearing single-radius TKPs showed similar migration. The latter may, however, expose patients to more complex surgical techniques and risks such as insert dislocations inherent to this rotating-platform design.     

No increased stem subsidence after arthroplasty in young patients with femoral head osteonecrosis:41 patients followed for 1–9 years

Background?Poor bone stock in patients with osteonecrosis of the femoral head may be a reason for poor outcome after hip replacement. One way of studying bone quality is to measure implant migration. We thus investigated the clinical and radiographic results of cementless THR in younger patients with femoral head osteonecrosis.

Patients and methods?We studied hips in 41 patients (mean age 48 (25–63) years) with a cementless hip arthroplasty after late stage osteonecrosis. Clinical evaluation was by the Harris hip score, the WOMAC score and the SF-36 score. Stem subsidence was measured with the Ein Bild Roentgen Analyse femoral component analysis (EBRA-FCA) at 3, 12, 24, 60, and 72 months after operation. The average duration of follow-up was 7(1–9) years, with less than 2 years for 2 patients.

Results?There was no revision of any hip. No radiographic or clinical stem loosening was seen. After 60 months, the cementless stems showed a median subsidence of –0.7?mm (95% CI: –0.9 to –0.2). No femoral osteolysis occurred. Femoral radiolucent lines, all < 1?mm, were seen in 10 hips. At the latest follow-up the Harris hip score was 83 (23–100) points.

Interpretation?Our findings for porous-coated stems in patients with femoral osteonecrosis indicate no greater risk of stem subsidence and rate of osteolysis after an average of 7 years follow-up. Thus, we continue to use uncemented stems in younger patients with femoral osteonecrosis. However, continued follow-up will be necessary to evaluate the long-term outcome.     

Is a hollow centralizer necessary when using a polished,tapered, cemented femoral stem?

Background and purpose — A tapered, polished and collarless stem is normally equipped with a hollow centralizer to prevent the stem from becoming end-bearing in the cement as the stem subsides. In a randomized clinical trial, we evaluated such a stem (MS-30), which was initially introduced with a solid centralizer but was later recommended to be fitted with a hollow centralizer. We hypothesized that while the stem would sink more, it would become rotationally stable and have less retroversion with a hollow centralizer than with a solid centralizer.

Patients and methods — We randomized 60 patients with primary hip arthritis to receive either a hollow centralizer or a solid centralizer with the stem. The effect was evaluated over a 10-year follow-up period with repeated RSA examinations, conventional radiographs, and clinical follow-ups using the WOMAC and SF-12 questionnaires.

Results — At 10-year follow-up, the group with hollow centralizers had subsided more than the group with solid centralizers (1.99?mm (hollow) as opposed to 0.57?mm (solid); p < 0.001). However, rotation was similar at 10-year follow-up (mean retroversion 1.34° (hollow) and 1.30° (solid)). Both groups showed excellent 10-year results, with similar clinical outcome, and none of the stems were radiographically loose or had been revised.

Interpretation — As expected, there was more subsidence in the group with hollow centralizers, and with similar magnitude to that reported in earlier RSA studies on conceptually similar prostheses. Interestingly, there was no difference in the rotational behavior of the prostheses. This stem type appears to have a design that, regardless of the type of centralizer and the possibility of subsidence, withstands the rotational forces it is subjected to very well. This study does not support the need for a hollow centralizer for these types of stems.