Fixed- versus mobile-bearing unicondylar knee arthroplasty: are failure modes different?

Lateral unicompartmental knee arthroplasty: is really a good option?

INTRODUCTION

Lateral unicompartmental knee arthroplasties (LUKA) account for only < 1% of all knee arthroplasties and for only 5-10% of all unicompartmental knee replacements. This means that there is less published literature on these procedures and that the surgeon's experience with them is smaller than with medial UKA. The aim of this study was to analyze the survival and the clinical-functional outcomes of LUKA according to the type of bearing surface (all-polyethylene versus metal-backed) used.

MATERIALS AND METHODS

This was a retrospective study including 42 LUKAs operated between 2009 and 2021. Two fixed polyethylene-bearing models were used: the all-polyethylene ACCURIS knee (38%) and the metal-backed Triathlon PKR system (62%). Demographic parameters, knee range of motion (ROM), tibiofemoral alignment, implant survival (as estimated with the Kaplan-Meier curve), and clinical-functional outcomes (as measured with the Knee Society Score) were analyzed.

RESULTS

Average patient age was 65.5 (range, 36-87) years and mean follow-up was 8.2 (range, 2.1-12.8) years. Thirty LUKAs (71.4%) were implanted in women. The main reason for performing a LUKA was osteoarthritis (88.1%). No patient developed post-surgical complications or had to be re-operated. Overall LUKA survival was 100% at 1-year and 5-year's follow-up. Knee Society Score, knee ROM and tibiofemoral alignment all improved significantly post-surgery (p < 0.001). The clinical Knee Society Score increased from 46.5 ± 14.5 pre-surgery to 93.5 ± 10.3 post-surgery, the functional Knee Society Score increased from 48.1 ± 13.5 pre-surgery to 94.6 ± 9.3 post-surgery, maximum flexion increased from 108.5 ± 8.7 degrees pre-surgery to 121 ± 8.9 degrees post-surgery and tibiofemoral alignment was corrected from 13.1 ± 1.74 degrees pre-surgery to 5.7 ± 0.8 degrees post-surgery. There were no statistically significant clinical-functional improvement or knee ROM differences between groups (p < 0.05, respectively).

CONCLUSION

LUKA is a valid and definitive option for patients with lateral tibiofemoral osteoarthritis, with a survival rate of > 95% at 5-years follow-up. Clinical-functional outcomes are the same, irrespective of the tibial component used.

Unicompartmental knee replacement: controversies and technical considerations

BACKGROUND

Unicompartmental knee replacement (UKR) is one of the effective interventions for the treatment of symptomatic knee osteoarthritis. Moreover, it has multiple advantages over total knee arthroplasty (TKA), including reduced intraoperative blood loss, decreased risk of transfusion, and faster recovery. This study aimed to discuss critical technical considerations regarding UKR and some of the controversies and updates.

METHODS

We conducted a review to provide an overview of the controversies and technical considerations about UKR in several aspects. Only peer-reviewed articles were included, up to December 2023 using PubMed, Google Scholar, ERIC, and Cochrane database for systematic reviews databases.

RESULT

UKR is associated with superior patient-reported clinical and functional outcomes, as well as shorter hospital stays, fewer postoperative complications, and revealed favorable outcomes in patients' return to sport. The choice between mobile- and fixed-bearing prostheses depends, in part, on the surgeon's preference. The mobile-bearing UKR is a less constrained prosthesis and can potentially result in less wear, but it is more technically demanding. While no significant difference between mobile-bearing versus fixed-bearing prostheses, cementless is superior to cemented design. Furthermore, UKR can be a good alternative for high tibial osteotomy (HTO) and still can be considered after a failed HTO. Lastly, recent reviews have shown a revision rate comparable to that of TKA. This is probably influenced by Improved comprehension of the best indications, patient selection criteria, as well as of the design, materials, and technological advances.

CONCLUSION

UKR treatment for unicompartmental knee osteoarthritis is secure and effective. Based on clinical and functional outcomes, decreased morbidity and mortality, and cost-effectiveness, long-term studies suggest that UKR is superior to TKA. Further investigation in this area is warranted.

Unicompartmental knee arthroplasties: does the type of tibial component selected influence implant survival?

INTRODUCTION

Few information has been published on the survival of unicompartmental knee arthroplasty (UKA) and fixed-bearing tibial components. The aim of this study is to analyze if UKA survival varies according to UKA model used and to analyze the possible risk factors for UKA revision.

MATERIALS AND METHODS

A retrospective study analyzing 301 UKAs (ACCURIS, all-polyethylene tibial component, 152; Triathlon PKR, metal-backed tibial component, 149) was performed. Demographic parameters as well as implant survival and cause of prosthetic revision were analyzed. The Kaplan-Meier survival analysis, the log-rank test and the Cox multiple regression were used for the analysis.

RESULTS

Average follow-up was 8.1 ± 3.08-years. Average age was 68.1 ± 8.6-years; 70.4% of subjects were women. The ACCURIS UKA group had a UKA revision rate higher compared to the Triathlon PKR group (16/152, 10.6% vs 5/149, 3.4%, respectively; p < 0.001). The main cause of prosthetic revision was aseptic loosening (5/21, 23.8%). All aseptic loosening cases and tibial component collapse were reported with the ACCURIS UKA group. Overall UKA survival was 98.01% (95% CI 95.62-99.1) at 1-year, 94.27% (95% CI 90.95-96.4) at 5-years and 92.38% (95% CI 88.48-94.99) at 10-years' follow-up. There were no differences in the Kaplan-Meier survival curves regarding operated side or affected tibiofemoral compartment (log-rank test = 0.614 and 0.763, respectively). However, Kaplan-Meier survival curve according to UKA model used was different (log-rank test = 0.033). The metal-backed component appeared to be a protector factor for UKA revision when adjusted for age, sex, operated side, and affected tibiofemoral compartment (Hazard Ratio 0.32, p = 0.031).

CONCLUSION

Fixed-bearing UKAs showed excellent mid- and long-term survival rates. Aseptic loosening is the main cause of implant failure. PKR group (metal-backed component) seem to be a protector factor to UKA revision when it was compared with ACCURIS UKA group (all-polyethylene tibial component).

Fixed-bearing unicompartmental knee arthroplasty provides a lower failure rate than mobile-bearing unicompartimental knee arthroplasty when used after a failed high tibial osteotomy: a systematic review and meta-analysis

Despite the fact that the choice of bearing design has been thought to influence the functional outcomes and longevity of unicompartimental knee arthroplasty (UKA), there is a lack of clinical evidence supporting the decision-making process in patients who have undergone high tibial osteotomy (HTO). A systematic review of studies was carried out that reported the outcomes of fixed-bearing (FB) or mobile-bearing (MB) medial UKA in patients with a previous HTO. A random effect meta-analysis using a generalized linear mixed-effects model to calculate revision rates was done. Seven retrospective cohort studies were included for this study. Regarding the fixation method, 40 were the FB-UKA and 47 were MB-UKA. For both groups, the mean post-operative follow-up was 5.8 years. The survival rates were 92% for the FB-UKA with a mean follow-up of 10 years. For the MB-UKA, it ranged from 35.7 to 93%, with a mean follow-up of 4.2 years. For the FB, the time to revision was reported as 9.3 years, while 1.2, 2.5 and 2.91 years was reported for the MB. The results of the meta-analysis showed that the revision rate for the patients receiving a FB-UKA after failed HTO was 8%, compared to 17% in those who received an MB-UKA. The results of the review suggest that the use of the FB-UKA is associated with lower revision rates and a longer survival time than the MB-UKA and have similar functional ability scores.Level of evidence: III (systematic review of level-III studies).

Similar clinical and radiographic outcomes after two different hypoallergenic medial unicompartmental knee in patients with metal allergy

BACKGROUND

The purpose in the present study was to compare clinical and radiological outcomes of patients who had undergone a mobile-bearing unicompartmental knee arthroplasty (UKA) with either titanium niobium nitride (TiNbN) alloy implants or with fixed-bearing oxidized zirconium alloy implants.

METHODS

The records of two consecutive cohorts for a total of 86 hypoallergenic implants were prospectively analyzed. The first cohort consisted of 49 consecutive implantations of the hypoallergenic UKA Journey Uni Oxinium (Ox Group), while the second consisted of 37 consecutive series of UKA Oxford (TiNbN Group). All patients were evaluated by two independent surgeons who were not involved in the index surgery. The clinical evaluation consisted of evaluating each patient's Oxford Knee Score and Knee Society Score day before surgery (T₀), and with two consecutive follow-ups at T₁ (minimum follow-up 9 months) and T₂ (minimum follow-up 24 months).

RESULTS

The two groups were homogeneous in all preoperative values, except Body Mass Index (BMI) and duration of final follow-up [both statistically higher (p < 0.05) in the TiNbN group]. Both groups showed a clinically significant improvement for all scores at final follow-up (p < 0.05). The only differences between the two groups involved a higher pre-operative Oxford Score in TiNbN group (p = 0.031), and different tibial and femoral angles at the final follow-up.

CONCLUSIONS

Both TiNbN and Oxinium UKA procedures enabled patients from good to excellent clinical and radiographic outcomes after the final follow-up, regardless of the age, gender, BMI bearing type, and implant size.

LEVEL OF EVIDENCE

LEVEL II: Comparative study.

Mobile Bearing versus Fixed Bearing for Unicompartmental Arthroplasty in Monocompartmental Osteoarthritis of the Knee: A Meta-Analysis

Introduction: Whether mobile-bearing (MB) unicompartmental knee arthroplasty (UKA) performs better than fixed-bearing (FB) implants in patients with monocompartmental osteoarthritis (OA) still remains unclear. Therefore, a meta-analysis comparing MB versus FB for UKA was conducted to investigate the possible advantages of MB versus FB in patient-reported outcome measures (PROMs), range of motion (ROM), and complications. We hypothesised that the MB design performs better than FB. Methods: This systematic review was conducted according to the 2020 PRISMA guidelines. In December 2021, PubMed, Web of Science, Google Scholar, and Embase were accessed, with no time constraints. All the clinical investigations comparing MB versus FB bearing for UKA were accessed. Only studies published in peer-reviewed journals were considered. Studies reporting data on revision settings were excluded, as were those combining unicompartmental and total knee arthroplasty. Results: Data from 25 studies (4696 patients) were collected; 58% (2724 of 4696 patients) were women. The mean length of follow-up was 45.8 ± 43.2. The mean age of the patients was 65.0 ± 5.6 years. No difference was found in range of motion (p = 0.05), Knee Scoring System (p = 0.9), function subscale (p = 0.2), and Oxford Knee Score (p = 0.4). No difference was found in the rate of revision (p = 0.2), aseptic loosening (p = 0.9), deep infections (p = 0.99), fractures (p = 0.6), and further extension of OA to the contralateral joint compartment (p = 0.2). Conclusion: The present meta-analysis failed to identify the possible superiority of the MB implants over the FB for UKA in patients with monocompartmental knee osteoarthritis. Long observational investigations are required to evaluate possible long-term complications and implant survivorship. These results should be interpreted within the limitations of the present study.

Do Fixed or Mobile Bearing Implants Have Better Survivorship in Medial Unicompartmental Knee Arthroplasty? A Study From the Australian Orthopaedic Association National Joint Replacement Registry

BACKGROUND

During the last 5 years, there has been an increase in the use of unicompartmental knee arthroplasty (UKA) to treat knee osteoarthritis in Australia, and these account for almost 6% of annual knee replacement procedures. However, there is debate as to whether a fixed bearing or a mobile bearing design is best for decreasing revision for loosening and disease progression as well as improving survivorship. Small sample sizes and possible confounding in the studies on the topic may have masked differences between fixed and mobile bearing designs.

QUESTIONS/PURPOSES

Using data from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR), we selected the four contemporary designs of medial compartment UKA: mobile bearing, fixed modular, all-polyethylene, and fixed molded metal-backed used for the treatment of osteoarthritis to ask: (1) How do the different designs of unicompartmental knees compare with survivorship as measured by cumulative percentage revision (CPR)? (2) Is there a difference in the revision rate between designs as a function of patient sex or age? (3) Do the reasons for revision differ, and what types of revision procedures are performed when these UKA are revised?

METHODS

The AOANJRR longitudinally maintains data on all primary and revision joint arthroplasties, with nearly 100% capture. The study population included all UKA procedures undertaken for osteoarthritis between September 1999 and December 2018. Of 56,628 unicompartmental knees recorded during the study period, 50,380 medial UKA procedures undertaken for osteoarthritis were included in the analysis after exclusion of procedures with unknown bearing types (31 of 56,628), lateral or patellofemoral compartment UKA procedures (5657 of 56,628), and those performed for a primary diagnosis other than osteoarthritis (560 of 56,628). There were 50,380 UKA procedures available for analysis. The study group consisted of 40% (20,208 of 50,380) mobile bearing UKA, 35% (17,822 of 50,380) fixed modular UKA, 23% (11,461 of 50,380) all-polyethylene UKA, and 2% (889 of 50,380) fixed molded metal-backed UKA. There were similar sex proportions and age distributions for each bearing group. The overall mean age of patients was 65 ± 9.4 years, and 55% (27,496 of 50,380) of patients were males. The outcome measure was the CPR, which was defined using Kaplan-Meier estimates of survivorship to describe the time to the first revision. Hazard ratios from Cox proportional hazards models, adjusted for sex and age, were performed to compare the revision rates among groups. The cohort was stratified into age groups of younger than 65 years and 65 years and older to compare revision rates as a function of age. Differences among bearing groups for the major causes and modes of revision were assessed using hazard ratios.

RESULTS

At 15 years, fixed modular UKA had a CPR of 16% (95% CI 15% to 17%). In comparison, the CPR was 23% (95% CI 22% to 24%) for mobile bearing UKA, 26% (95% CI 24% to 27%) for all-polyethylene UKA, and 20% (95% CI 16% to 24%) for fixed molded metal-backed UKA. The lower revision rate for fixed modular UKA was seen through the entire period compared with mobile bearing UKA (hazard ratio 1.5 [95% CI 1.4 to 1.6]; p < 0.001) and fixed molded metal-backed UKA (HR 1.3 [95% CI 1.1 to 1.6]; p = 0.003), but it varied with time compared with all-polyethylene UKA. The findings were consistent when stratified by sex or age. Although all-polyethylene UKA had the highest revision rate overall and for patients younger than 65 years, for patients aged 65 years and older, there was no difference between all-polyethylene and mobile bearing UKA. When compared with fixed modular UKA, a higher revision risk for loosening was shown in both mobile bearing UKA (HR 1.7 [95% CI 1.5 to 1.9]; p < 0.001) and all-polyethylene UKA (HR 2.4 [95% CI 2.1 to 2.7]; p < 0.001). The revision risk for disease progression was higher for all-polyethylene UKA at all time points (HR 1.4 [95% CI 1.3 to 1.6]; p < 0.001) and for mobile bearing UKA after 8 years when each were compared with fixed modular UKA (8 to 12 years: HR 1.4 [95% CI 1.2 to 1.7]; p < 0.001; 12 or more years: HR 1.9 [95% CI 1.5 to 2.3]; p < 0.001). The risk of revision to TKA was higher for mobile bearing UKA compared with fixed modular UKA (HR 1.4 [95% CI 1.3 to 1.5]; p < 0.001).

CONCLUSION

If UKA is to be considered for the treatment of isolated medial compartment osteoarthritis, the fixed modular UKA bearing has the best survivorship of the current UKA designs.

LEVEL OF EVIDENCE

Level III, therapeutic study.

A Comparison of Mobile- and Fixed-Bearing Unicompartmental Knee Arthroplasties in the Treatment of Medial Knee Osteoarthritis: A Systematic Review and Meta-analysis of 1,861 Patients

Many studies have compared mobile-bearing (MB) and fixed-bearing (FB) unicompartmental knee arthroplasties (UKAs) in patients with unicompartmental knee osteoarthritis (OA). The present systematic review and meta-analysis examined the differences in the clinical and radiological outcomes of MB UKA and FB UKA. PubMed, EMBASE, and Cochrane databases, as well as Google Scholar were searched for relevant studies. Randomized controlled trials (RCTs) and cohort studies that compared MB UKA and FB UKA were included. The weighted mean difference in the knee scores and range of motion (ROM) as well as the summary odds ratio of postoperative mechanical axis alignment, radiolucency, revision rate, and complications were calculated in the MB UKA and FB UKA groups. Finally, 2 RCTs and 11 cohort studies that involved 1,861 patients (1,996 knees) were included. The FB UKA group showed better postoperative Knee Society score (KSS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and ROM than the MB UKA group. However, the MB UKA group had more knees with a neutral limb alignment and a lower incidence of polyethylene wear than the FB UKA group. No significant differences were observed between the groups with respect to radiolucency, revision rate, and complications, such as arthritis progression, aseptic loosening, and postoperative pain. This meta-analysis has demonstrated that both prostheses provided excellent clinical outcomes and survivorship in patients with unicompartmental knee OA. The MB UKA group achieved the expected postoperative neutral limb alignment as compared with the FB UKA group, while the FB UKA group showed higher knee scores and superior ROM than the MB UKA group. Limited evidence is currently available; therefore, the results of our meta-analysis should be interpreted with caution.

[Recommendations for unicondylar knee replacement in the course of time : A current inventory]

BACKGROUND

A higher patient satisfaction stands in contrast to higher revision rates of unicondylar knee joint endoprosthetics (UKE) compared to total knee joint endoprosthetics (TKE). Furthermore, old "dogmas" regarding indications and contraindications persist, which is still reflected in the significantly different case numbers.

AIM

The aim of this article is to provide an overview of the current literature regarding 1. indication and contraindication (BMI, age, sport, arthrosis of other compartments, ligament status) and 2. the "eternal rival" fixed or mobile bearing for UKE.

RESULTS

The choice of the right patient remains essential, even if all the old "dogmas" of contraindications have been relativized or even outdated. Arthroses of the contralateral (in medial UKE correspondingly lateral) compartment and advanced arthroses of the lateral patella facet remain the only persistent contraindications. In contrast, a high BMI, age, chondrocalcinosis, medial patella facet and a defective (but particularly functionally stable) ACL are not contraindications; however, severe obesity is responsible for a significantly higher complication rate and probably a higher rate of loosening. Rather, the experience and thus the number of UKEs of the individual surgeon is decisive for the outcome, to which the discussion about mobile or fixed inlays must also be completely subordinated.

CONCLUSION

The indications for UKE can, therefore, be extended with a clear conscience on the basis of literature, and the current 1:10 UKE:TKE ratio in Germany can be shifted significantly.

Unicompartmental knee arthroplasty has higher revisions than total knee arthroplasty at long term follow-up: a registry study on 6453 prostheses

PURPOSE

The purpose of this study is to analyse long-term unicompartmental knee arthroplasty (UKA) focusing on survivorship, causes of failure and revision strategy.

METHODS

This study is a retrospective analysis of data from a regional arthroplasty registry for cases performed between 2000 and 2017. A total of 6453 UKAs were identified and the following information was analysed: demographic data, diagnosis leading to primary implant, survivorship, complication rate, causes of failure, revision strategies. UKA registry data were compared with total knee arthroplasty (TKA) registry data of 54,012 prostheses, which were implanted in the same time period.

RESULTS

6453 UKAs were included in the study: the vast majority of them (84.4%) were implanted due to primary osteoarthritis followed by deformity (7.1%) and necrosis of the condyle (5.1%). When compared to TKA, UKA showed lower perioperative complication rate (0.3% compared to 0.6%) but higher revision rate (18.2% at 15 years, compared to 6.2% for TKA). No correlation was found between diagnosis leading to primary implant and prosthesis survival. The most frequent cause of failure was total aseptic loosening (37.4%), followed by pain without loosening (19.8%). Of the 620 UKAs requiring revision, 485 were revised with a TKA and 61 of them required a re-revision; on the other hand, of the 35 cases where another UKA was implanted, 16 required a re-revision.

CONCLUSION

UKA is associated with fewer perioperative complications but higher revision rates when compared to TKA. Its survivorship is not affected by the diagnosis leading to primary implant. Revision surgery of a failed UKA should be performed implanting a TKA, which is associated with a lower re-revision rate when compared to another UKA.

LEVEL OF EVIDENCE

Level 3, therapeutic study.

Effects of contact stress on patellarfemoral joint and quadriceps force in fixed and mobile-bearing medial unicompartmental knee arthroplasty

Background

Unicompartmental knee arthroplasty (UKA) is an effective treatment for end-stage, symptomatic unicompartmental osteoarthritis of the knee joint. However, patellofemoral joint degeneration is a contraindication to medial UKA. Therefore, the objective of this study was to evaluate the biomechanical effect of medial UKA using fixed-bearing (FB) and mobile-bearing (MB) design prostheses on the patellofemoral joint.

Methods

A three-dimensional finite-element model of a normal knee joint was developed using medical image data. We performed statistical analysis for each model. The differences in contact stress on the patellofemoral joint and the quadriceps force between the FB and MB designs were evaluated under a deep-knee-bend condition.

Results

At an early flexion angle, the results of contact stress showed no significant difference between the FB and MB medial UKA models compared with the intact model. However, at high flexion angles, we observed a significant increase in contact stress with the FB models compared with the intact model. On the contrary, in the case of the MB models, we found no statistically significant increment compared with the intact model. A larger quadriceps force was needed to produce an identical flexion angle for both the FB and MB UKA designs than for the intact model. At high flexion angles, a significant increase quadriceps force whit the FB model compared with the intact model.

Conclusions

Our results indicate that with medial UKA, the contact stress increased and greater quadriceps force was applied to the patellofemoral joint. However, performing UKA on a patellofemoral joint with osteoarthritis should not be difficult, unless anterior knee pain is present, because the increase in contact stress is negligible.

Comparison of Fixed-Bearing and Mobile-Bearing Unicompartmental Knee Arthroplasty: A Systematic Review and Meta-Analysis

BACKGROUND

Prior studies have compared fixed-bearing unicompartmental knee arthroplasty (FB-UKA) with mobile-bearing UKA (MB-UKA), suggesting that both procedures have good clinical outcomes. However, which treatment is more beneficial for patients is controversial. The purpose of our study is to evaluate the postoperative outcomes, including the revision rate, complications, functional results, range of motion, and femoral-tibial angle, between the 2 procedures.

METHODS

We searched the MEDLINE, EMBASE, Cochrane Library, and Web of Science databases starting from August 2017 to May 2018. The publication date of articles was not restricted. Before we submit our contribution, we have re-searched it again. Articles that directly compared the postoperative outcomes of the 2 prosthesis type were included.

RESULTS

A total of 15 comparative studies were included in our meta-analysis. The pooled data indicated no differences between the 2 operation modes in terms of revision rates, complications, and knee function, but earlier failure occurred more frequently with the MB design.

CONCLUSION

Both the arthroplasty types provided satisfactory clinical results for patients with classic indications. However, MB-UKA tended to fail in early postoperative years whereas fixed-bearing UKA in later postoperative years. Therefore treatment options should be carefully considered for each patient, and surgeons should still use their personal experience when deciding between these options.

Equal tibial component fixation of a mobile-bearing and fixed-bearing medial unicompartmental knee arthroplasty: a randomized controlled RSA study with 2-year follow-up

Background and purpose - Differences in stress distribution in a mobile-bearing and fixed-bearing unicompartmental knee arthroplasty (UKA) design might lead to a difference in fixation of the tibial component. We compared tibial component migration of a mobile-bearing (MB) UKA and a fixed-bearing (FB) UKA using radiostereometric analysis.Patients and methods - In a randomized, patient-blinded clinical trial 62 patients received either the MB Oxford UKA or the FB Sigma UKA. The patients were followed for 24 months with radiostereometric analysis. Clinical outcome was assessed with Oxford Knee Score (OKS), RAND-36 and leg extension power.Results - Migration of the tibial components was similar between groups throughout follow-up. At 12 months, MTPM of the tibial component was 0.44 mm (95% CI 0.34-0.55) for the MB group and 0.40 mm (CI 0.31-0.50) for the FB group. Between 12 and 24 months, the tibial components migrated with a median MTPM increase of 0.03 mm (CI -0.02 to 0.08) in the MB group and 0.03 mm (CI -0.02 to 0.07) in the FB group. Continuous migration of the tibial component was found for 1 MB UKA and 2 FB UKAs. Both groups showed similar and clinically relevant improvement in clinical outcome.Interpretation - MB and FB tibial components had similar good fixation and clinical improvement until 2 years. Based on this study, a low 5- to 10-year revision rate can be expected for both implants.

Long-term outcomes of unicompartmental knee arthroplasty in patients requiring high flexion: an average 10-year follow-up study

INTRODUCTION

To evaluate the long-term survival of unicompartmental knee arthroplasty (UKA) in the Asian population and assess differences in clinical outcomes between mobile- and fixed-bearing UKA.

MATERIALS AND METHODS

Among 111 cases of UKA that were performed by 1 surgeon from January 2002 to December 2009, we retrospectively reviewed 96 cases (36 mobile-bearing, 62 fixed-bearing) for this study. We examined cause of revision or failure, type of reoperation/revision, and duration from the surgery date to the revision upon reviewing the medical record. Survival analysis was conducted using the Kaplan-Meier method. Functional outcomes were evaluated based on range of motion and patient-reported outcome (PRO) measures (Knee Injury and Osteoarthritis Outcome Score) for cases with at least 8 years of follow-up (average, 10.2 years).

RESULTS

Overall, the 10-year survival was 88% [95% confidence interval (CI) 0.81-0.95], and the estimated mean survival time was 13.4 years (95% CI 12.5-14.2). In a comparison of survival between the mobile- and fixed-bearing groups, the former had a 10-year survival of 85% (95% CI, 0.72-0.97) and an estimated mean survival time of 13.5 years (95% CI 12.2-14.7) and the latter had a 10-year survival of 90% (95% CI 0.82-0.99) and an estimated mean survival time of 13.4 years (95% CI 12.3-14.4). Thus, there was no significant difference in survival between the two groups (log-rank test, p = 0.718). In addition, no significant difference in functional outcomes was observed between the two groups (p > 0.05 for all).

CONCLUSIONS

UKA performed in the Asian population showed a relatively good functional outcome and survival rate at an average 10-year follow-up. No difference in survival and PROs was observed according to the bearing type. Although the present study demonstrated a good survival rate, similar to that in other Western studies, further studies investigating the impact of the Asian lifestyle on the long-term survival of UKA is necessary.

Clinical results and 12-year survivorship of the Physica ZUK unicompartmental knee replacement

BACKGROUND

The Physica ZUK is a fixed bearing unicompartmental knee replacement. The purpose of this prospective cohort study was to determine the mid-term clinical outcomes and survivorship of the Physica ZUK.

METHODS

From 2005 to 2017 a total of 466 Physica ZUK prostheses were implanted in 398 patients by a single surgeon. The series consisted of 452 medial and 14 lateral unicompartmental knee arthroplasties (UKAs). Three hundred and sixty-seven medial UKAs with a minimum follow-up of two years (median 5.4 years) and 14 lateral UKAs with a minimum follow-up of 18 months (median 5.3 years) were analysed using the Knee Society Knee Score (KS-KS) and Function Score (KS-FS) at latest follow-up. Kaplan Meier survivorship analysis was performed with implant revision as the end point.

RESULTS

Mean age at the time of surgery was 67 (range 42-88) and 58 (47-69) years for patients undergoing medial and lateral UKA respectively. For medial UKAs the KS-KS and KS-FS improved significantly compared to the pre-operative values from 53.6 and 54.0 to 93.4 and 91.0 respectively (p = 0.0001). For lateral UKAs the KS-KS and KS-FS improved significantly from 46.4 and 48.7 to 91.3 and 93.1 respectively (p = 0.0001). Six cases of medial UKA were revised to total knee arthroplasty. Medial implant survivorship was 97.9% (95% confidence intervals, 95.6-99.0%) at both five and 10 years. No lateral implants were revised.

CONCLUSION

This prospective cohort study shows encouraging short to mid-term clinical results and survivorship for the Physica ZUK unicompartmental knee replacement.

Midterm Survivorship and Patient Satisfaction of Robotic-Arm-Assisted Medial Unicompartmental Knee Arthroplasty: A Multicenter Study

BACKGROUND

Studies have showed improved accuracy of lower leg alignment, precise component position, and soft-tissue balance with robotic-assisted unicompartmental knee arthroplasty (UKA). No studies, however, have assessed the effect on midterm survivorship. Therefore, the purpose of this prospective, multicenter study was to determine midtem survivorship, modes of failure, and satisfaction of robotic-assisted medial UKA.

METHODS

A total of 473 consecutive patients (528 knees) underwent robotic-arm-assisted medial UKA surgery at 4 separate institutions between March 2009 and December 2011. All patients received a fixed-bearing, metal-backed onlay tibial component. Each patient was contacted at minimum 5-year follow-up and asked a series of questions to determine survival and satisfaction. Kaplan-Meier method was used to determine survivorship.

RESULTS

Data were collected for 384 patients (432 knees) with a mean follow-up of 5.7 years (5.0-7.7). The follow-up rate was 81.2%. In total, 13 revisions were performed, of which 11 knees were converted to total knee arthroplasty and in 2 cases 1 UKA component was revised, resulting in 97% survivorship. The mean time to revision was 2.27 years. The most common failure mode was aseptic loosening (7/13). Fourteen reoperations were reported. Of all unrevised patients, 91% was either very satisfied or satisfied with their knee function.

CONCLUSION

Robotic-arm-assisted medial UKA showed high survivorship and satisfaction at midterm follow-up in this prospective, multicenter study. However, in spite of the robotic technique, early fixation failure remains the primary cause for revision with cemented implants. Comparative studies are necessary to confirm these findings and compare to conventional implanted UKA and total knee arthroplasty.

Low implant migration of the SIGMA® medial unicompartmental knee arthroplasty

PURPOSE

The purpose of this study was to evaluate implant migration of the fixed-bearing Sigma^® medial unicompartmental knee arthroplasty (UKA). UKA is a regularly used treatment for patients with medial osteoarthritis (OA) of the knee. UKA has a higher revision rate than total knee arthroplasty. Implant migration can be used as a predictor of implant loosening.

METHODS

A prospective radiostereometric cohort study was performed. Forty-five patients with medial OA of the knee were included and received a cemented Sigma^® UKA. The patients were followed for 24 months with radiostereometric analysis (RSA) and clinical outcome scores (Oxford knee score). Clinical precision was based on double determinations taken at 4 and 12 months. Tibial implants were classified as stable (difference in MTPM < 0.2 mm between 1 2 and 24 months) or as continuously migrating (difference in MTPM > 0.2 mm between 12 and 24 months).

RESULTS

No significant differences in migration were found for the femoral component. For the tibial component, a difference of 0.05 mm was shown for translation on the x-axis between 4 months and 12 (p < 0.01) and between 4 months and 24 months (p < 0.01). A difference of - 0.23 to - 0.50° was shown for rotation around the x-axis (p < 0.01) and a difference of - 0.11° was shown for rotation around the z-axis between 4 and 12 months (p = 0.02). These differences in migration over time were small and fall within the clinical precision of the measurements. Tibial components were divided into a stable group (N = 26) and a continuously migrating group (N = 11), which showed a significant difference in maximal total point motion (MTPM) (p < 0.01). The Oxford knee score improved significantly from poor before surgery (23.2) to good at follow-up (37.5-40.9).

CONCLUSIONS

The Sigma^® UKA showed low implant migration and good clinical outcomes, suggesting that the Sigma UKA can be used in clinical practice. However, continuous migration was found in 30% of our patients which could indicate a risk of later revision surgery in this group.

LEVEL OF EVIDENCE

II.

Unicompartmental knee replacement - Current perspectives

Unicompartmental knee replacement (UKR) is an effective treatment for end-stage, symptomatic unicompartmental osteoarthritis of the knee. However, certain aspects of the procedure are still debated. These areas of discussion include patient selection criteria, implant design and the discrepancy in survival rates between national registries and independent case series. These may contribute in limiting the more widespread acceptance of unicompartmental knee replacement. The aim of this paper is to review the up-to-date evidence on UKR and discuss the most relevant controversies regarding this procedure.

Early functional outcome after lateral UKA is sensitive to postoperative lower limb alignment

PURPOSE

The predictive role of patient-specific characteristics and radiographic parameters on medial unicompartmental knee arthroplasty (UKA) outcomes is well known, but knowledge of these predictors is lacking in lateral UKA. Therefore, purpose of this study was to assess the predictive role of these parameters on short-term functional outcomes of lateral UKA.

METHODS

In this retrospective cohort study, Western Ontario and McMaster Universities Arthritis Index scores were collected at 2-year follow-up (median 2.2 years, range 2.0-4.0 years) in 39 patients who underwent lateral UKA. Patient-specific characteristics included age, BMI and gender, while radiographic parameters included osteoarthritis severity of all three compartments and both preoperative and postoperative hip-knee-ankle alignment.

RESULTS

BMI, gender, age and preoperative valgus alignment were not correlated with functional outcomes, while postoperative valgus alignment was correlated with functional outcomes (0.561; p = 0.001). Postoperative valgus of 3°-7° was correlated with better outcomes than more neutral (-2° to 3° valgus) alignment (96.7 vs. 85.6; p = 0.011). Postoperative alignment was a predictor when corrected for patient-specific characteristics (regression coefficient 4.1; p < 0.001) and radiological parameters (regression coefficient 3.8; p = 0.002).

CONCLUSIONS

Postoperative valgus alignment of 3°-7° was correlated with the best short-term functional outcomes in lateral UKA surgery, while patient-specific parameters and preoperative alignment were not correlated with functional outcomes. Based on these findings, a surgeon should aim for valgus alignment of 3°-7° when performing lateral UKA surgery for optimal functional outcomes.

LEVEL OF EVIDENCE

Prognostic study, Level II.

Why do patellofemoral arthroplasties fail today? A systematic review

BACKGROUND

Historically poor results of patellofemoral arthroplasty (PFA) were reported in the setting of isolated patellofemoral osteoarthritis (OA). In order to lower PFA failure rates, it is important to identify failure modes using a standardized method. In this systematic review, PFA failure modes were assessed and compared in early vs. late failures and older vs. recent studies.

METHODS

Databases of PubMed, Embase and Cochrane and annual registries were searched for studies reporting PFA failures. Failure modes in studies with mean follow-up <5years were classified as early failures while >5years were classified late failures. Cohorts started before 2000 were classified as older studies and started after 2000 as recent studies.

RESULTS

Thirty-nine cohort studies (10 level II and 29 level III or IV studies) and three registries were included with overall low quality of studies (GRADE criteria). A total of 938 PFA failures were included and were caused by OA progression (38%), pain (16%), aseptic loosening (14%) and patellar maltracking (10%). Pain was responsible for most early failures (31%), while OA progression was most common in late failures (46%). In older studies, OA progression was more commonly reported as failure mode than in more recent studies (53% vs. 39%, p=0.005).

CONCLUSION

This level IV systematic review with low quality of studies identified OA progression and pain as major failure modes. Reviewing these studies, appropriate patient selection could prevent PFA failures in select cases. Future studies assessing the role of PFA in isolated patellofemoral OA are necessary.

Unicondylar knee arthroplasty: Key concepts

The concept of unicondylar knee arthroplasty (UKA) has been described as early as 1950s following the introduction of the MacIntosh and McKeever hemiarthroplasty. With improvements in implant design, patient selection, and surgical technique, there has been an increase in utilization of UKA as a less-invasive alternative to total joint arthroplasty for the treatment of localized symptomatic osteoarthritis. The purpose of this review article is to highlight five trending concepts in UKA based on current evidence: bearing design, fixation technique, medial vs. lateral UKA, implant survivorship, and revision surgery.

Why Do Medial Unicompartmental Knee Arthroplasties Fail Today?

BACKGROUND

Failure rates are higher in medial unicompartmental knee arthroplasty (UKA) than total knee arthroplasty. To improve these failure rates, it is important to understand why medial UKA fail. Because individual studies lack power to show failure modes, a systematic review was performed to assess medial UKA failure modes. Furthermore, we compared cohort studies with registry-based studies, early with midterm and late failures and fixed-bearing with mobile-bearing implants.

METHODS

Databases of PubMed, EMBASE, and Cochrane and annual registries were searched for medial UKA failures. Studies were included when they reported >25 failures or when they reported early (<5 years), midterm (5-10 years), or late failures (>10 years).

RESULTS

Thirty-seven cohort studies (4 level II studies and 33 level III studies) and 2 registry-based studies were included. A total of 3967 overall failures, 388 time-dependent failures, and 1305 implant design failures were identified. Aseptic loosening (36%) and osteoarthritis (OA) progression (20%) were the most common failure modes. Aseptic loosening (26%) was most common early failure mode, whereas OA progression was more commonly seen in midterm and late failures (38% and 40%, respectively). Polyethylene wear (12%) and instability (12%) were more common in fixed-bearing implants, whereas pain (14%) and bearing dislocation (11%) were more common in mobile-bearing implants.

CONCLUSION

This level III systematic review identified aseptic loosening and OA progression as the major failure modes. Aseptic loosening was the main failure mode in early years and mobile-bearing implants, whereas OA progression caused most failures in late years and fixed-bearing implants.

Fixed- versus mobile-bearing UKA: a systematic review and meta-analysis

PURPOSE

Two design concepts are currently used for unicondylar knee arthroplasty (UKA) prostheses: fixed bearing (FB) and mobile bearing (MB). While MB prostheses have theoretical advantages over their FB counterparts, it is not clear whether they are associated with better outcomes. A systematic review was conducted to examine survivorship differences and differences in failure modes of between FB and MB designs.

METHODS

PubMed, Scirus and Cochrane library databases were searched for medial UKA outcome studies. A total of 44 papers, involving 9,463 knees, were eligible. Outcomes examined included knee function, survivorship and the reasons for, and incidence of, revision for FB and MB prostheses. Random effects meta-analysis was employed to obtain pooled revision rate estimates. Where available, cause-specific time to revision was extracted.

RESULTS

Mean follow-up was 8.7 years for FB and 5.9 years for MB prostheses. There were no other relevant baseline differences. The overall crude revision rate for FB and for MB prostheses was 0.90 (95 % confidence interval (CI) 0.65-1.21) and 1.51 (95 % CI 1.11-1.93) per 100 component years, respectively. After stratification on follow-up time and age, the revision rates were not substantially different, aside for younger patients in short term from studies with short-term follow-up.

CONCLUSION

No essential differences between the two designs were observed. MB and FB UKA designs have comparable revision rates. As our study is based on predominantly observational data, with large variations in reporting standards, inferences should be drawn with caution.

LEVEL OF EVIDENCE

IV.

Outcome of Unicompartmental Knee Arthroplasty: A Systematic Review of Comparative Studies between Fixed and Mobile Bearings Focusing on Complications

The purpose of this systematic review is to collate results of studies comparing fixed and mobile bearing unicompartmental knee arthroplasty (UKA), focusing on complications and timing for reoperations. Out of 723 results derived from PubMed, EMBASE and Cochrane database search engines on bearings in arthroplasty, 10 studies comparing clinical results of fixed bearings to mobile bearings in UKA were found eligible for analysis. The reoperation rate was calculated using a novel method such as reoperations per hundred component years, and the causes of specific reoperations were investigated. The overall reoperation rate per hundred component years was similar between the mobile bearings (1.392) and fixed bearings (1.377); however, mobile bearings were more susceptible to reoperations in cases with aseptic loosening (0.393>0.255), progression of arthritis (0.428>0.357) and implant dislocation (0.286>0). The overall incidence of complications is similar for fixed and mobile bearing designs in UKA. The discussion on complications presented above may assist surgeons in their choice of bearing design.

Metal backed fixed-bearing unicondylar knee arthroplasties using minimal invasive surgery: a promising outcome analysis of 132 cases

BACKGROUND

Unicondylar knee arthroplasty (UKA) is a well-established treatment for isolated osteoarthritis (OA) of the medial knee compartment. Aim of this retrospective study was to evaluate the early clinical and radiological outcomes of a consecutive series of patients treated with medial metal backed fixed-bearing UKA. Furthermore, the influence of the component orientation on the outcome was analyzed.

METHODS

From 09/2006 to 11/2010 106 patients (132 knees; 69 ± 9 years) were treated using a metal backed fixed-bearing UKA with a MIS approach. All patients underwent a standardized clinical and radiological follow-up at 6 weeks, 1, 2 and 5 years. Mean follow-up was 3.4 ± 1.0 years. Two patients (three UKAs) deceased and two patients (two UKAs) were lost to follow-up. Three different survival analyses were performed using three different endpoints defining failure: (a) revision with exchange of any UKA component (b) aseptic loosening and (c), a worst case scenario, where it was assumed that all progressive radiolucencies would lead to aseptic loosening and thus these were additionally counted. Clinical outcome was assessed using the American knee society score (AKS) and the Oxford knee score (OKS). Radiographic analysis was done according to the American Knee Society Evaluation and Scoring System adapted for UKA and correlated with the AKS and OKS.

RESULTS

Five UKAs (3.8 %) were revised to total knee arthroplasties (TKAs) after a median of 25 (10-33) months. Five year survival was 95.2, 97.5 and 87.7% for the aforementioned endpoints. At final follow-up the median AKS knee score was 99 (50-100) points and the median AKS function score was 100 (60-100) points. The median OKS was 43 (8-48) points. Clinical outcome was independent of the component orientation.

CONCLUSION

Fixed-bearing UKA showed excellent clinical and radiological results at up to 5 years follow-up. Outcome was independent of component orientation.

RETRACTED: Efficacy of bisphosphonates against hip fracture in elderly patients with stroke and Parkinson diseases: meta-analysis of randomized controlled trials

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. This paper includes a meta-analysis based on papers by another author group that have since been retracted. Researchers can be misled by reading this paper, thus we have retracted it.