Mid-term results of lateral unicondylar mobile bearing knee arthroplasty: a multicentre study of 363 cases

Long-term functional success and robust implant survival in lateral unicompartmental knee arthroplasty: A case series with a mean follow-up of twenty two and a half years

PURPOSE

Lateral unicompartmental knee arthroplasty (UKA) is an accepted treatment option in cases of end-stage lateral osteoarthritis. While lateral UKA has many proposed advantages compared to total knee arthroplasty, its technical challenges and relatively small number of cases make this an uncommon procedure. The aim of this study was to report the survivorship and functional outcomes beyond 20 years of follow-up of isolated UKA.

METHODS

Between January 1988 and October 2003, 54 lateral UKAs were performed in a single center. The fitted prosthesis was a fixed plate and cemented polyethylene (PE). All patients had isolated lateral tibiofemoral osteoarthritis, including five open meniscectomies, three arthroscopies, and three open reductions of lateral tibial plateau fractures. Patients with a minimum of 20 years of follow-up were included in the final analysis.

RESULTS

Of the 54 UKA, 22 died before reaching the minimum follow-up period and four were lost to follow-up. Twenty-eight were included in the final analysis. Among them, 21 patients remained alive and an additional seven were deceased after 20 years. The mean age at the last follow-up was 84.8 ± 11.9 years with a mean follow-up duration of 22.5 ± 2.1 years. Of the 28 knees, eight underwent revision surgery (5 for the progression of osteoarthritis; 2 for aseptic loosening; 1 for PE wear). Kaplan-Meier survival analysis revealed a survival rate at 20 and 25 years of 72.3% (CI 59.1; 88.6). The average time to revision was 14.9 ± 4.9 years. At the last follow-up, the mean function Knee Society Score (KSS) was 41.5 ± 32.9 and the mean objective KSS score was 79.4 ± 9.7. In the unrevised population, 94.7% of patients (n = 18) reported being satisfied or very satisfied with the surgery.

CONCLUSION

Lateral UKA remains a viable treatment option for patients with isolated lateral tibiofemoral osteoarthritis, providing satisfactory 20-year implant survivorship and high patient satisfaction.

Advantages and limitations of mobile-bearing unicompartmental knee arthroplasty: an overview of the literature

INTRODUCTION

Interest in unicompartmental knee arthroplasty (UKA) has recently grown. Mobile bearing UKA, in which the bearing is not fixed but rather perfectly conforms with femoral and tibial components and moves completely passively between the femoral and tibial implant, has now been used for approximately half a century.

AREAS COVERED

Alongside the recognized advantages of UKA, the mobile-bearing variant benefits from an extremely low rate of polyethylene wear and tolerable minor malalignment. Revision rates for UKA have been reported to exceed those of total knee arthroplasty, but long-term survival rates and outcomes from mobile-bearing UKA have been found to be satisfactory. In addition to the lateral osteoarthritis and loosening, which are main complications of UKA, bearing dislocation is a specific complication of mobile bearing UKA. Fractures and valgus subsidence are more prevalent than in the cementless UKA. While these continue to be features to be addressed, they have been partially solved.

EXPERT OPINION

Given the manifold benefits of UKA, its application could be extended to a larger patient population. Successful outcomes rely on careful patient selection and the surgeon's extensive familiarity with the procedure. Looking ahead, the incorporation of robotic surgery, already a feature of some fixed-bearing UKAs, might shape the future trajectory of mobile-bearing UKA.

Clinical Outcomes and Survivorship of Lateral Unicompartmental Knee Arthroplasty: A Large Single Surgeon Cohort

INTRODUCTION

Lateral unicompartmental knee arthroplasty (UKA) is an effective treatment for isolated lateral compartment osteoarthritis. However, due to the rarity of the procedure, long-term outcomes and survivorship are poorly understood. We report the clinical and radiographic outcomes after lateral UKA.

METHODS

We retrospectively reviewed a consecutive series of patients who underwent lateral UKA by a single fellowship-trained arthroplasty surgeon from 2001 to 2021 with a minimum two year follow up. There were 161 knees in 153 patients (average age 69 years) that met inclusion criteria, with a mean follow up of 10.0 years (range 0.05 to 22.2). All patients underwent the procedure via a minimally invasive lateral parapatellar approach with a fixed-bearing implant. Patient demographics, complications, radiographic findings, patient-reported outcomes, and the need for revision surgery were evaluated. Survivorship was defined with the endpoint as revision of components.

RESULTS

There were eight patients (5.0%) who underwent conversion to TKA for lateral UKA implant failure or progression of arthritis. There were three patients (1.9%) who underwent ipsilateral medial UKA due to medial compartment arthritis progression with preserved mechanical alignment and patello-femoral joint. There were eight additional procedures that did not require implant changes, including five irrigation and debridements for acute periprosthetic joint infection (PJI) (3.1%), two wound closures for dehiscence (1.3%), and one loose body removal (0.6%).

CONCLUSION

Lateral UKA showed a survivorship rate of 98.0% at 5 years, 96.0% at 10 years, and 94.5% at 15 years. When including patients who underwent additional surgery for the progression of arthritis, survivorship was 97.4% at 5 years, 95.4% at 10 years, and 91.3% at 15 years. Lateral UKA should be seen as a durable treatment option for isolated lateral compartment osteoarthritis.

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.

Robotic-assisted unicompartmental knee arthroplasty improves functional outcomes, complications, and revisions

Aims

Robotic-assisted unicompartmental knee arthroplasty (R-UKA) has been proposed as an approach to improve the results of the conventional manual UKA (C-UKA). The aim of this meta-analysis was to analyze the studies comparing R-UKA and C-UKA in terms of clinical outcomes, radiological results, operating time, complications, and revisions.

Methods

The literature search was conducted on three databases (PubMed, Cochrane, and Web of Science) on 20 February 2024 according to the guidelines for Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA). Inclusion criteria were comparative studies, written in the English language, with no time limitations, on the comparison of R-UKA and C-UKA. The quality of each article was assessed using the Downs and Black Checklist for Measuring Quality.

Results

Among the 3,669 articles retrieved, 21 studies on 19 series of patients were included. A total of 3,074 patients (59.5% female and 40.5% male; mean age 65.2 years (SD 3.9); mean BMI 27.4 kg/m2 (SD 2.2)) were analyzed. R-UKA obtained a superior Knee Society Score improvement compared to C-UKA (mean difference (MD) 4.9; p < 0.001) and better Forgotten Joint Score postoperative values (MD 5.5; p = 0.032). The analysis of radiological outcomes did not find a statistically significant difference between the two approaches. R-UKA showed longer operating time (MD 15.6; p < 0.001), but reduced complication and revision rates compared to C-UKA (5.2% vs 10.1% and 4.1% vs 7.2%, respectively).

Conclusion

This meta-analysis showed that the robotic approach for UKA provided a significant improvement in functional outcomes compared to the conventional manual technique. R-UKA showed similar radiological results and longer operating time, but reduced complication and revision rates compared to C-UKA. Overall, R-UKA seems to provide relevant benefits over C-UKA in the management of patients undergoing UKA.

[Dealing with early complications in unicondylar knee arthroplasty-what works, what does not?]

Complications in the early postoperative period following the implantation of a unicondylar knee arthroplasty (UKA) are both rare and rarely described in the literature. Often, only small case series or individual case reports are available. In this article, the most common complications of periprosthetic infection, periprosthetic tibial fracture, inlay dislocation and intra-articular cement residue in (loose bone cement body) are described and recommendations for conservative and surgical treatment are presented, including case examples. Ideally, surgical errors or an infection should be recognized at an early stage and revised as soon as possible.

Short- to mid-term results of minimally invasive lateral unicompartmental knee replacement: 133 cases in a non-designer series

INTRODUCTION

The aim of the current study was to demonstrate short- to mid-term survivorship as well as clinical outcome of lateral unicompartmental knee replacement (UKR) with a fixed-bearing (FB) design from a non-designer center using the Oxford Fixed Lateral prosthesis.

MATERIALS AND METHODS

This single-center retrospective cohort study reports the results of 133 consecutive lateral FB-UKR. Survivorship analysis was performed with different endpoints and clinical outcome was measured using the Oxford-Knee-Score (OKS), American-Knee-Society-Score (AKSS-O), range-of-motion (ROM) and visual-analog-scale for pain (VAS).

RESULTS

There were two revision surgeries with conversion to total knee replacements (TKR) due to persistent pain resulting in a survival rate of 98.5% (95% CI 93.5-99.6) with a mean follow-up (FU) of 3.3 ± 1.8 years (range 1-8.5). All outcome scores, VAS and ROM showed a significant improvement at final FU (p < 0.001). The OKS improved from 26 ± 7.8 (range 11-45) preoperatively to 39 ± 8.3 (range 13-48), the AKSS-O from 49.2 ± 14.6 (range 18-90) to 81.8 ± 15.1 (range 40-100), the AKSS-F from 53 ± 23.7 (range 0-100) to 80.4 ± 21.4 (range 5-100) and the ROM from 118 ± 17 (range 90-160) to 134 ± 9.5 (range 100-155).

CONCLUSIONS

The short- to mid-term results following lateral FB-UKR demonstrate a high survivorship and good clinical outcome from an independent series. We, therefore, suggest that FB-UKR is a safe treatment option for isolated lateral OA if sufficient surgical experience is provided.

LEVEL OF EVIDENCE

Retrospective cohort study, level IV.

Fixed-bearing is superior to mobile-bearing in lateral unicompartmental knee replacement: a retrospective matched-pairs analysis

PURPOSE

Due to low incidence of isolated lateral osteoarthritis (OA), there are limited data on whether a fixed-bearing (FB) or a mobile-bearing (MB) design is superior for lateral unicompartmental knee replacement (UKR). The aim of this matched-pairs analysis was to compare both designs in terms of implant survival and clinical outcome.

METHODS

Patients who received MB-UKR (Group A) and FB-UKR (Group B) at a single centre were matched according to gender, age at time of surgery and body mass index (BMI). Survivorship analysis was performed with the endpoint set as "revision for any reason". Clinical outcome was assessed using the Oxford knee score (OKS), visual analogue scale for pain (VAS), patients' satisfaction, University of California Los Angeles activity scale (UCLA) and the Tegner activity score (TAS).

RESULTS

A total of 60 matched pairs were included with a mean follow-up (FU) of 3.4 ± 1.3 (range 1.2-5.0) years in Group A and 2.7 ± 1.2 (range 1.0-5.0) years in Group B. Survivorship between both groups differed significantly (Group A: 78.7%; Group B: 98.3%, p = 0.003) with bearing dislocation being the most common reason for revision in Group A (46.2%). The relative and absolute risk reduction were 92.2% and 20%, respectively, with 5 being the number needed to treat. There were no differences in OKS (Group A: 41.6 ± 6.5; Group B: 40.4 ± 7.7), VAS (Group A: 2.9 ± 3.2; Group B: 1.6 ± 2.2), UCLA (Group A: 5.7 ± 1.3; Group B: 5.9 ± 1.8) and TAS (Group A: 3.0 ± 1.0; Group B: 3.1 ± 1.2) between both groups on follow-up.

CONCLUSION

Despite modern prosthesis design and surgical technique, implant survival of lateral MB-UKR is lower than that of FB-UKR on the short- to mid-term due to bearing dislocation as the most common cause of failure. Since clinical results are equivalent in both groups, FB-UKR should be preferred in treatment of isolated lateral OA.

LEVEL OF EVIDENCE

Retrospective case-control study, Level III.

Complications after lateral unicompartmental knee arthroplasty in a fast-track setting: a prospective cohort study of 170 procedures

BACKGROUND AND PURPOSE

In existing studies on fasttrack unicompartmental knee arthroplasty (UKA), the majority of surgeries are medial. There are substantial differences between lateral and medial UKA, which is why outcomes cannot automatically be compared. To gain information on the feasibility and safety of fast-track protocols in lateral UKAs, we investigated length of stay (LOS) and early complications after lateral UKA, performed using a fast-track protocol in well-established fast-track centers.

PATIENTS AND METHODS

We retrospectively evaluated prospectively collected data on patients undergoing lateral UKA in a fast-track setup from 2010 to 2018 at 7 Danish fast-track centers. Data on patient characteristics, LOS, complications, reoperations, and revisions was analyzed using descriptive statistics. Safety and feasibility were defined as complication and reoperation rates within 90 days comparable to non-fast track lateral UKA or fast-track medial UKA.

RESULTS

We included 170 of patients with a mean age of 66 (SD 12) years. Median LOS was 1 day (interquartile range 1-1), which was unchanged from 2012-2018. 18% were discharged on the day of surgery. Within 90 days, 7 patients experienced medical complications and 5 patients experienced surgical complications. 3 patients underwent reoperation, 2 were soft tissue revisions and the third was removal of an exostosis due to catching of the patella. 1 patient was revised due to a bearing dislocation.

CONCLUSION

Our findings suggest that lateral UKA in a fast-track setting is feasible and safe.

[Treatment of unicompartmental osteoarthritis of the knee]

Osteoarthritis of the knee is one of the most important degenerative joint diseases in the clinical routine. The treatment of knee osteoarthritis is not only based on the stage, symptoms and duration of the joint disease, but also depends on the existing arthrosis pattern. In the case of unicompartmental arthrosis, damage typical for osteoarthritis is limited to just one joint compartment. Both the conservative and the surgical treatment of unicompartmental osteoarthritis of the knee have to respect the individual characteristics of the respective forms of osteoarthritis. In the context of this manuscript, the genesis, the diagnostics and the guideline-based stage-adapted conservative and operative treatment of unicompartmental osteoarthritis of the knee are addressed.

Survival of lateral unicompartmental knee arthroplasty at short-, mid-, and long-term follow-up: a systematic review and meta-analysis

BACKGROUND

The infrequency of lateral unicompartmental knee arthroplasty (UKA) has led to a lack of understanding of its survival. This study aimed to systematically evaluate the survivorship results of lateral UKA at different follow-ups based on available literature.

METHODS

Five databases were searched for eligible studies. Pooled survivorships with 95% confidence intervals (CIs) at 3, 5, 10, 15, and 20 years after lateral UKA were estimated using a random-effect model. Subgroup and sensitivity analyses were performed.

RESULTS

A total of 26 studies involving 5470 lateral UKAs were included. Survivorships of lateral UKA at 3-, 5-, 10-, 15-, and 20-year follow-ups were 96% (95% CI: 95-98%, I2 : 77.5%), 94% (95% CI: 93-96%, I2 : 70.8%), 88% (95% CI: 84-91%, I2 : 70.8%), 85% (95% CI: 79-91%, I2 : 70.8%), and 78% (95% CI: 71-85%, I2 : 54.2%), respectively. Subgroup analyses found that bearing type, the number of surgeons, and year of publication might be associated with implant survival outcomes.

CONCLUSION

Lateral UKA is an effective procedure with excellent survivorships at short-, mid-, and long-term follow-ups. Results suggest a single-surgeon lateral UKA using fixed-bearing. Additional well-designed studies are needed to elucidate the current findings.

Disease progression, aseptic loosening and bearing dislocations are the main revision indications after lateral unicompartmental knee arthroplasty: a systematic review

IMPORTANCE

Lateral unicompartmental knee arthroplasty (UKA) is a surgical option for patients with isolated lateral osteoarthritis however, the procedure has higher revision rates than medial UKA. The reason for this remains unclear; therefore, a better understanding of the indications for lateral UKA revision is needed.

AIM

The primary aim of this systematic review was to identify revision indications for lateral UKA. Secondary aims were to further investigate if revision indications were influenced by implant design and time from surgery.

EVIDENCE REVIEW

A systematic literature review was performed according to the PRISMA 2020 guidelines. Search was performed in January 2022 in MedLine, EMBASE, CINAHL and the Cochrane Library using the keywords "knee arthroplasty", "unicompartmental", "reoperation", synonyms and abbreviations. Articles published in 2000-2021 that were at least level III retrospective cohort studies with at least 10 lateral UKAs and reported all failure modes were included. Risk of bias was assessed using the ROBINS-I tool. Revision indications, patient characteristics, study design, implant types and time to failure were extracted from the selected studies. Collated data were tabulated and differences were tested using Chi-square or Fisher's exact test.

FINDINGS

A total of 29 cohort and 4 registry studies that included 7,668 UKAs met the inclusion criteria. Studies were judged as having moderate or severe risk of bias; this was associated with the retrospective nature of studies required to investigate long-term outcomes of knee arthroplasty. The main indications for lateral UKA revision were OA progression (35%), aseptic loosening (17%) and bearing dislocation (14%). The incidence of revision was similar for mobile-bearing implants (7.6%) and fixed-bearing (6.4%). For mobile-bearing implants, there was introduction of bearing dislocations as an additional mode of failure (24% cf. 0%, p < 0.001). For fixed-bearing implants, the incidence of revision was higher for all-poly-ethylene (13.9%) than metal-backed (1.8%) tibial components. Early lateral UKA failures were associated with bearing dislocations (sequential decrease from 69% under 6 months to 0% 10+ years, p < 0.001), whereas late failures were associated with OA progression (sequential increase from 0% under 6 months to 100% > 10+ years, p < 0.01). Compared with medial UKA, OA progression (41% cf. 30%, p = 0.004), malalignment (2.7% cf. 0.8%, p = 0.02), instability (4% cf. 1%, p = 0.02) and bearing dislocations (20% cf. 10%, p < 0.001) were more common for lateral UKA.

CONCLUSIONS AND RELEVANCE

OA progression, aseptic loosening and bearing dislocation were the three main revision indications for lateral UKA. Compared to medial UKA, OA progression, malalignment, instability and bearing dislocations were more common revision indications for lateral UKA. Higher survivorship of metal-backed fixed-bearing implants was found. The findings suggest that the outcomes of lateral UKA may be improved with more optimal alignment, gap balancing and patient selection.

LEVEL OF EVIDENCE

Level III systematic review.

Does Implant Design Influence Failure Rate of Lateral Unicompartmental Knee Arthroplasty? A Meta-Analysis

BACKGROUND

Lateral unicompartmental knee arthroplasty (UKA) is a viable solution for isolated lateral compartment arthritis. Several prosthetic designs are available such as fixed-bearing metal-backed (FB M-B), fixed-bearing all-polyethylene (FB A-P), and mobile-bearing metal-backed (MB M-B) implants. The purpose of this meta-analysis is to compare failure rates of different prosthetic designs.

METHODS

Preferred Reporting Items for Systematic Reviews and Meta-Analyses systematic review was conducted using 4 databases (MEDLINE, EMBASE, Cochrane, and PubMed) to identify all studies that investigate outcomes of lateral UKA. Twenty-one studies met the inclusion criteria, and failure rates were compared by implant type and follow-up time separately in order to assess potential confounding factors. Two separate analyses have been performed among different implant designs (FB M-B vs FB A-P vs MB M-B) and different follow-ups (<5 years, between 5 and 10 years, >10 years).

RESULTS

The failure rate of FB M-B lateral UKA was significantly lower compared to other lateral UKA designs present in the market (0.8% vs 8.6% and 7.1% for FB M-B, FB A-P, and MB M-B, respectively). No significative difference among groups has been detected when comparing all implants with regard to follow-up time.

CONCLUSION

Considering actual evidence, for a surgeon approaching lateral UKA, the FB M-B design is preferable, given the lower failure rates and subsequently a longer implant survivorship.

Early results of fixed-bearing unicompartmental knee replacement designed for the lateral compartment

Background

Isolated lateral compartment knee arthritis is less prevalent than medial. While the reported results of medial unicompartmental knee replacement (UKR) have been good and comparable to total knee replacement, the results of lateral UKR have been mixed. We present the short-term results and survivorship of a fixed-bearing UKR designed specifically for the lateral compartment.

Methods

We report the result of 130 primary fixed-bearing lateral Oxford (FLO) UKRs (123 patients) performed between 2015 and 2019 with a minimum follow-up of 1 year. The indications for lateral UKR were: isolated lateral osteoarthritis (n = 122), post-trauma (n = 5) and osteonecrosis (n = 3). The mean age was 69.1 (± 11.6), mean BMI 28.4 (± 4.9), 66.9% female, 60% right-sided, and mean follow-up 3 (range 1–4.8 years, standard deviation ± 1) years. The primary outcome measure was the Oxford knee score (OKS). Survival analysis was performed with “revision for any reason”, “reoperation”, and “implant failure” as the endpoints.

Results

Six patients died from unrelated reasons. None of the implants failed. One required the addition of a medial UKR for medial arthritis. There were no other reoperations. At 4 years, the survival for implant failure was 100% and for both revision and all reoperations was 99.5% (95% CI 96.7–99.9%). At the last review, at a mean of 3 years, the mean Oxford knee score was 41.

Conclusion

The good survivorship and outcome scores suggest that UKR designed for the lateral compartment is an excellent alternative to total knee replacement in selected patients with isolated lateral tibiofemoral arthritis at short-term follow-up.

Cemented Lateral Unicompartmental Knee Replacement: A retrospective single centre independent series

Background

Unicompartmental knee replacement (UKR) has functional and economic benefits when compared with total knee replacement, however it is technically demanding and may be associated with higher failure rates. The primary aim of this independent series study was to evaluate the survival of lateral UKRs implanted in our institution and their clinical outcomes. The secondary outcome was to compare the results of mobile and fixed-bearing prostheses.

Methods

This is a retrospective series study of 183 cemented lateral UKRs implanted in 170 patients, for advanced isolated lateral compartment arthritis, under the care of two senior surgeons. Fixed or mobile-bearing prostheses were used according to the surgeon's preference. Kaplan Meier analysis was used to evaluate prosthesis survival with the endpoint being revision for any reason. A subgroup analysis of survival was also done for each bearing type. Functional outcomes were evaluated using the Oxford knee score (OKS) at final follow-up.

Results

This series included 103 Fixed-bearing and 80 mobile-bearing prostheses. Median follow-up was 6.9 years. 9 knees required revision. The commonest reason for revision was progression of arthritis to the medial compartment. Dislocation was the commonest cause of revision in the mobile-bearing group. Survival at 10 years was 91.9% with no significant difference ( p = 0.083) between bearing types (fixed-bearing 93.8% and mobile-bearing 90.6%). The OKS were comparable in both groups, the mean OKS was 44/48.

Conclusion

Good survival and functional outcomes can be achieved using cemented lateral UKRs with both bearing types. There was a trend towards superior outcomes in the fixed-bearing group.

A 180° Spin of the Femoral Component in Unicompartmental Knee Arthroplasty: A Report of 2 Cases

CASE

We report 2 cases of undescribed lateral unicompartmental knee arthroplasty failure: a 180° rotation of the femoral component. The patients experienced a locking event several years after arthroplasty, and radiographs revealed a perfect 180° rotation of the implant. Each patient underwent revision surgery to a total knee arthroplasty. At the 13-year follow-up, the first patient had no pain and a range of motion of 140°. The second patient, at 3 months, could walk without crutches with a flexion at 145°.

CONCLUSION

Excessive laxity, coronal or sagittal, might be associated with this complication.

The Oxford Domed Lateral Unicompartmental Knee Replacement implant: Increasing wall height reduces the risk of bearing dislocation

Due to lateral ligament laxity, bearing dislocation occurs in 1%–6% of Oxford Domed Lateral replacements. Most dislocations are medial but they do rarely occur anteriorly or posteriorly. The aim was to decrease the risk of dislocation. For a bearing to dislocate the femoral component has to be distracted from the tibial component. A robotic-path-planning-algorithm was used with a computer model of the implant in different configurations to determine the Vertical Distraction needed for Dislocation (VDD). With current components, VDD anteriorly/posteriorly was 5.5 to 6.5 mm and medially was 3.5 to 5.75 mm. A thicker bearing increased VDD medially and decreased VDD anteriorly/posteriorly (0.1 mm/1 mm thickness increase). VDD medially increased with the bearing closer to the tibial wall (0.5 mm/1 mm closer), or by increasing the tibial wall height (1 mm/1 mm height increase). VDD anteriorly/posteriorly was not influenced by bearing position or wall height. To prevent collision between the femoral and tibial components an increase in wall height must be accompanied by a similar increase in minimum bearing thickness. Increasing the wall height and minimum bearing thickness by 2 mm and ensuring the bearing is 4 mm or less from the wall increased the minimum VDD medially to 5.5 mm. The lower VDD medially than anteriorly/posteriorly explains why medial dislocation is more common. If the wall height is increased by 2 mm, the minimum bearing thickness is 5 mm and the surgeon ensured the bearing is 4 mm or less from the wall, the medial dislocation rate should be similar to the anterior/posterior dislocation rate, which should be acceptable.

High survivorship rate and good clinical outcomes at mid-term follow-up for lateral UKA: a systematic literature review

PURPOSE

The purpose of this paper is to systematically review the available literature to understand the effectiveness, the survivorship, the clinical outcomes and the complications of lateral UKA.

METHODS

A review of the current literature available about lateral UKA was performed in March 2020, according to the PRISMA guidelines. Selection was based on the following inclusion criteria: (1) clinical reports of any level of evidence, (2) written in English language, (3) published from 1996 to 2020, (4) dealing with clinical data on lateral UKA. A total of 47 articles, published between 1996 and 2020, were included in the review. Quality of every article was assessed using the Modified Coleman Methodology Score.

RESULTS

A total of 47 studies were included. Mean mCMS was 45.27 (range 30-62). Mean age at surgery was 64.5 years (range 34.1-88.0 years). In 1741 patients (65.5%) a metal back implant was used and in 421 patients (15.8%) an all poly design was used. Several scores were used to evaluate clinical results (OKS, AKSS, IKS, KOOS, WOMAC, VAS). Range of motion improved with an overall mean value of 120.3° (range: 105.9°-143.3°). The mean follow-up was 60.7 months (range, 7-204 months), mean survivorship (absence of a revision) with a minimum 60 months of follow-up was 88.6% (range 74.5-100) and mean satisfaction of patients was 78.5% (range 41.0-97.9).

CONCLUSIONS

Lateral UKA seems to be an effective solution to manage lateral osteoarthritis (OA), based on preliminary results, with survivorship and satisfaction rate comparable to medial UKA and total knee arthroplasty (TKA). Nonetheless, this review highlights that the quality of studies available in current literature is low.

LEVEL OF EVIDENCE

Systematic review of level IV studies.

Lateral Unicompartmental Knee Arthroplasty

Lateral unicompartmental knee arthroplasty affords excellent functional results and implant survivorship for properly selected patients. More high-quality studies are necessary to determine whether expanded indications for medial unicompartmental knee arthroplasty also apply to lateral unicompartmental knee arthroplasty. Operative adjuncts such as robotics, custom implants, and navigation technology hold promise in minimizing the technical burden and unfamiliarity of lateral unicompartmental knee arthroplasty. Improvements in lateral-specific implants may translate to operational efficiency and improved outcomes, but few lateral-specific implants currently exist. Mobile-bearing devices have increased rates of failure due to bearing dislocation, and further studies are warranted to evaluate this complication with newer designs. Future registry and cohort studies should show medial unicompartmental knee arthroplasty and lateral unicompartmental knee arthroplasty separately to allow for better understanding of the nuances and technical differences between these uniquely different procedures.

Fixed bearing, all-polyethylene tibia, lateral unicompartmental arthroplasty - A final outcome study with up to 28 year follow-up of a single implant

BACKGROUND

Lateral unicompartmental arthroplasty (UKA) constitutes only 5-10% of all unicompartmental replacements performed. Whilst the short and medium term benefits are well documented, there remains concern regarding the higher revision rate when compared with total knee replacement. We report the long term clinical outcome and survivorship of a large series of lateral UKA.

PATIENTS AND METHODS

Between 1974 and 1994, 71 patients (82 knees) underwent a lateral fixed-bearing St Georg Sled UKA. Prospective data was collected pre-operatively and at regular intervals post-operatively using the Bristol Knee Score (BKS), with later introduction of the Oxford Knee (OKS) and Western Ontario MacMaster (WOMAC) scores. Kaplan Meier survival analysis was used, with revision, or need for revision, as end point. 85% of the patients were female. No patients were lost to follow-up.

RESULTS

Functional knee scores improved post-operatively up to 10 years, at which point they demonstrated a steady decline. Survivorship was 72% at 15 years, and 68% at 20 and 25 years. Nineteen knees were revised, with progression of disease in another compartment the commonest reason. There were two revisions due to implant fracture. In patients aged over 70 years at time of index procedure, 81% died with a functioning prosthesis in situ.

CONCLUSION

This represents the longest follow-up of a large series of lateral UKA. Results of this early design of fixed bearing UKA demonstrate satisfactory long term survivorship. In elderly patients, further intervention is rarely required. More contemporary designs or techniques may show improved long term survivorship in time.

Systematic review and meta-analysis of bearing dislocation in lateral meniscal bearing unicompartmental knee replacement: Domed versus flat tibial surface

BACKGROUND

Bearing dislocation is a problem following mobile bearing Oxford lateral Unicompartmental Knee Replacement (UKR). Therefore, the design of the tibial component was changed from a flat tibial surface to a domed tibial surface with a biconcave bearing to increase bearing entrapment. This systematic review compared the dislocation and revision rates of the two designs.

METHODS

Two authors independently searched MEDLINE, EMBASE and ISI Web of Science, reference lists of retrieved articles, and the internet. Randomised, cohort, case-control and case studies of adult patients with lateral knee osteoarthritis treated with flat or domed Oxford lateral UKR and their outcomes were included. The overall dislocation rate and the annual revision rate (per 100 component years) were determined.

RESULTS

Nine studies (937 knees) met the inclusion criteria (3 flat, 6 domed). Four studies (all domed) had a low risk of bias and five had a high risk (3 flat, 2 domed), so data should be interpreted with caution. The bearing dislocation rate decreased from 17% (flat) to 3.7% (domed). Dislocations occurred on average at 16 months and medial dislocations were most common. The revision rate excluding dislocation decreased from 1.1%pa to 0.7%pa. PROSPERO registration: CRD42019139250.

CONCLUSION

Modifying the tibial component from a flat to a domed shape decreased the bearing dislocation rate to 3.7% and increased the 10 year survival rate excluding dislocation to 93%. The dislocation rate is still relatively high so bearing stability should be assessed intra-operatively and if unacceptable, a fixed bearing version of the Oxford lateral tibial component can be inserted.

The Mid- to Long-Term Outcomes of the Lateral Domed Oxford Unicompartmental Knee Replacement: An Analysis From the National Joint Registry for England, Wales, Northern Ireland, and the Isle of Man

BACKGROUND

Lateral unicompartmental knee replacement (UKR) is an alternative to total knee replacement for isolated lateral unicompartmental knee arthritis. The geometry and mechanics of the lateral compartment differ to the medial compartment with the Lateral Domed Oxford UKR designed to address this. We used the National Joint Registry (NJR) data to report the mid- to long-term outcomes of this device.

METHODS

We performed a retrospective observational study using NJR data on 992 Lateral Domed Oxford UKRs implanted between 1st January 2005 and 31st December 2017. Outcomes of interest were implant survival and revision indications.

RESULTS

The 10 year cumulative implant survival rates were 88.6% (CI 85.3-91.2). When compared with <55 year age group, the 55-64, 65-74 and ≥75 groups had significantly lower revision rates (hazard ratio (HR) = 0.56 (CI 0.32-0.98, P = .04), HR 0.40 (CI 0.22-0.72, P = .003), and HR 0.27 (CI 0.12-0.58, P = .001), respectively). The obese group had significantly (P = .04) increased revision risk compared with normal BMI (HR 2.33, CI 1.06-5.12). The commonest reasons for revision surgery were dislocation (n = 23, 2.3%), pain (n = 15, 1.5%), and aseptic loosening (n = 14, 1.4%).

CONCLUSION

The Lateral Domed Oxford UKR provides a good option for isolated lateral compartment osteoarthritis. However, dislocation of the mobile bearing remains a problem, occurring in 2.3% of the patients and accounting for 30% of the revisions. To help prevent dislocation, it is now possible to assess bearing stability intraoperatively and if very unstable to implant a compatible fixed bearing tibial component, without the need for further bone preparation.

Bilateral unicompartmental knee arthroplasty for windswept knee osteoarthritis: A report of 13 cases

BACKGROUND

Windswept deformity is a condition of the lower limbs with a valgus knee on one side and a varus knee on the other. We present a case series of bilateral unicompartmental knee arthroplasty (UKA) for windswept knee osteoarthritis (WSKO).

METHODS

We analysed the outcomes of 26 knees of 13 consecutive patients with WSKO treated with bilateral UKA. The mean age was 73.0 years and the mean follow up period was 2.6 years. Pre- and postoperative Oxford Knee Score (OKS) and Japanese Orthopaedic Association (JOA) score, radiological measurements and postoperative complications were evaluated. No knees required revision for either infection or loosening.

RESULTS

The mean preoperative OKS was 25.3 ± 9.7, which increased to 34.9 ± 5.8 at the latest follow up. The mean preoperative JOA scores for the varus and the valgus sides were 64.6 ± 12.5 and 66.9 ± 14.1, which increased to 85.0 ± 11.3 and 84.6 ± 11.2, respectively, after operation.

CONCLUSIONS

Our results show that good short-term clinical results can be achieved by bilateral UKA in cases of WSKO. Bilateral UKA may be an effective treatment for WSKO if indications are met.

Oxford domed lateral unicompartmental knee arthroplasty

AIMS

To report mid- to long-term results of Oxford mobile bearing domed lateral unicompartmental knee arthroplasty (UKA), and determine the effect of potential contraindications on outcome.

METHODS

A total of 325 consecutive domed lateral UKAs undertaken for the recommended indications were included, and their functional and survival outcomes were assessed. The effects of age, weight, activity, and the presence of full-thickness erosions of cartilage in the patellofemoral joint on outcome were evaluated.

RESULTS

Median follow-up was seven years (3 to 14), and mean age at surgery was 65 years (39 to 90). Median Oxford Knee Score (OKS) was 43 (interquartile range (IQR) 37 to 47), with 260 (80%) achieving a good or excellent score (OKS > 34). Revisions occurred in 34 (10%); 14 (4%) were for dislocation, of which 12 had no recurrence following insertion of a new bearing, and 12 (4%) were revised for medial osteoarthritis (OA). Ten-year survival was 85% (95% confidence interval (CI) 79 to 90, at risk 72). Age, weight, activity, and patellofemoral erosions did not have a significant effect on the clinical outcome or survival.

CONCLUSION

Domed lateral UKA provides a good alternative to total knee arthroplasty (TKA) in the management of lateral compartment OA. Although dislocation is relatively easy to treat successfully, the dislocation rate of 4% is high. It is recommended that the stability of the bearing is assessed intraoperatively. If the bearing can easily be displaced, the fixed rather than the mobile bearing version of the Oxford lateral tibial component should be inserted instead. Younger age, heavier weight, high activity, and patellofemoral erosions did not detrimentally affect outcome, so should not be considered contraindications. Cite this article: Bone Joint J 2020;102-B(8):1033-1040.

Unicompartmental knee arthroplasty, an enigma, and the ten enigmas of medial UKA

Unicompartmental knee arthroplasty (UKA) is a bone- and ligament-sparing alternative to total knee arthroplasty in the patients with end-stage single-compartment degeneration of the knee. Despite being a successful procedure, the multiple advantages of UKA do not correlate with its usage, most likely due to the concerns regarding prosthesis survivability, patient selection, ideal bearing design, and judicious use of advanced technology among many others. Therefore, the purpose of this study is to review and summarize the debated literature and discuss the controversies as “Ten Enigmas of UKA.”

Excellent outcomes for lateral unicompartmental knee arthroplasty: Multicenter 268-case series at 5 to 23 years' follow-up

INTRODUCTION

Isolated lateral compartment osteoarthritis of the knee (LCOA) is 10 times less frequent than medial compartment involvement. Long-term assessments of unicompartmental knee arthroplasty (UKA) in this indication are rare, with small series.

HYPOTHESIS

Survival and functional outcome of lateral UKA in a large series are quite acceptable; the strategy is suited for isolated LCOA.

MATERIAL AND METHOD

A multicenter retrospective study in 6 French health establishments included all lateral UKAs performed between January 1988 and September 2014. Clinical data (range of motion, International Knee Society (IKS) knee and function scores, satisfaction), paraclinical data (radiologic angles) and complications were prospectively entered in medical files during follow-up and analyzed retrospectively at end of follow-up.

RESULTS

During the study period, 311 lateral UKAs were performed in 295 patients, using 5 fixed-bearing implant models. Twenty-eight patients died within 5 years, and 15 (4.8%) were lost to follow-up. The series thus comprised 268 lateral UKAs in 63 male and 205 female patients, with a mean age of 68.8±10.5 years, including 7 cases of post-traumatic osteoarthritis and 4 of aseptic osteonecrosis. Mean follow-up was 9.1 years (range, 5-23 years), implant survivorship with failure defined as all-cause revision surgery was 85.4% at 10 years and 79.4% at 20 years. At last follow-up, IKS knee score was 87.0 and IKS function score 80.2. Maximal flexion was 125°. 94.3% of patients were satisfied or very satisfied. The main cause of revision surgery was osteoarthritis in another knee compartment (66,7%, n=26).

CONCLUSION

Lateral UKA showed good survivorship, comparable to medial UKA, with good functional results and excellent long-term satisfaction.

LEVEL OF EVIDENCE

IV, retrospective cohort study.

Robotic-arm assisted medial unicondylar knee arthroplasty versus jig-based unicompartmental knee arthroplasty with navigation control: study protocol for a prospective randomised controlled trial

Background

There remains a paucity of clinical studies assessing how any differences in accuracy of implant positioning between robotic-arm assisted unicompartmental knee arthroplasty (RO UKA) and conventional jig-based unicompartmental knee arthroplasty (CO UKA) translate to patient satisfaction, functional outcomes, and implant survivorship. The objectives of this study are to compare accuracy of implant positioning, limb alignment, patient satisfaction, functional outcomes, implant survivorship, cost-effectiveness, and complications in CO UKA versus RO UKA. Computer navigation will be used to assess intraoperative knee kinematics in all patients undergoing CO UKA.

Methods and analysis

This prospective randomised controlled trial will include 140 patients with symptomatic medial compartment knee arthritis undergoing primary UKA. Following informed consent, patients will be randomised to CO UKA (control group) or RO UKA (investigation group) at a ratio of 1:1 using an online random number generator. The primary objective of this study is to compare accuracy of implant positioning in CO UKA versus RO UKA. The secondary objectives are to compare the following outcomes between the two treatment groups: limb alignment, surgical efficiency, postoperative functional rehabilitation, functional outcomes, quality of life, range of motion, resource use, cost effectivness, and complications. Observers will review patients at regular intervals for 2 years after surgery to record predefined study outcomes pertaining to these objectives. Ethical approval was obtained from the London-Bloomsbury Research Ethics Committee, UK. The study is sponsored by University College London, UK.

Discussion

This study compares a comprehensive and robust range of clinical, functional, and radiological outcomes in CO UKA versus RO UKA. The findings of this study will provide an improved understanding of the differences in CO UKA versus RO UKA with respect to accuracy of implant positioning, patient satisfaction, functional outcomes, implant survivorship, cost-effectiveness, and complications.

Trial registration

ClinicalTrials.gov NCT04095637. Registered on 19 September 2019.

A Comprehensive Evaluation of Lateral Unicompartmental Knee Arthroplasty Short to Mid-Term Survivorship, and the Effect of Patient and Implant Characteristics: An Analysis of Data From the Dutch Arthroplasty Register

BACKGROUND

The rarity of lateral unicompartmental knee arthroplasty (UKA) results in a lack of large cohort studies and understanding. The aim of this study is to comprehensively evaluate survivorship of lateral UKA with registry data and compare this to medial UKA.

METHODS

Lateral (n = 537) and medial UKAs (n = 19,295) in 2007-2017 were selected from the Dutch Arthroplasty Register. Survival analyses were performed with revision for any reason as primary endpoint. Adjustments were made for patient and implant characteristics. Stratified analyses according to patient and implant characteristics were performed. Reasons and type of revision were grouped according to laterality and bearing design.

RESULTS

The 5-year revision rate was 12.9% for lateral UKA and 9.3% for medial UKA. Multivariable regression analyses showed no significant increased risk for revision for lateral UKA (hazard ratio 0.87, 95% confidence interval 0.66-1.15). Stratified analyses showed that the effect of patient characteristics on revision was comparable between lateral and medial UKA; however, the use of mobile-bearing design for lateral UKA was associated with increased revision rate. Progression of osteoarthritis was the main reason for revision on both sides accompanied by tibia component loosening for medial UKA. Reasons and type of revision varied depending on bearing design.

CONCLUSION

Similar survivorship of lateral and medial UKA was reported. Specifically, there is a notable risk for revision when using mobile-bearing designs for lateral UKA. Failure modes and type of revision depends on laterality and bearing design. These findings emphasize that surgical challenges related to anatomy and kinematics of the lateral and medial knee compartment need to be considered.

Wear Morphology on the Surfaces of CoCrMo Unicompartmental Knee Joint Endoprostheses as Elements of Metal-Metal Friction Nodes

The article assesses the strength and structural parameters of load-bearing layers of metal biobearings made of CoCrMo alloy. The research material consisted of unicompartmental knee joint endoprostheses used in the human body, removed due to excessive wear. No patient participated in the examinations. The endoprostheses used as research material underwent the liquidation procedures in the hospital, which has all necessary permissions and certifications to perform endoprosthetic procedures. Endoprostheses selected for the examinations had been used for 6 to 12 years at similar load conditions as declared by the patients, i.e., body weight of F = 835 N, declared activity expressed as the number of load cycles up to 100 thousand/year, and no artificial joint infections. To assess the homogeneity of the research material, the analysis of chemical composition using a Joel scanning electron microscope with EDS (Energy-dispersive X-ray spectroscopy) was made to exclude endoprostheses with various alloying additives. Microscopic examinations were performed using the Phenom XL microscope, while the wear surface was examined using a Keyence VHX-900F microscope. Several experimental tests were also carried out on load-bearing surfaces to assess changes in strength parameters of the base material after a known life cycle and load conditions. Material hardness using the Vickers method, yield point, critical value of stress intensity coefficient, and the coefficient of friction µ were evaluated. The examinations allowed for the systematization of wear in the knee and femoral components of unicompartmental hip endoprostheses. The statistical evaluation of the number and costs of hip joint replacement surgeries in Poland was also made.

Ten-Year Survivorship, Patient-Reported Outcomes, and Satisfaction of a Fixed-Bearing Unicompartmental Knee Arthroplasty

Background

We sought to determine the 10-year survivorship and reasons for revision for a fixed-bearing unicompartmental knee arthroplasty (UKA) design. In addition, we report on patient-reported outcomes and satisfaction and compare results of medial vs lateral compartment UKA and cemented vs cementless UKA with the same design.

Methods

We performed a retrospective cohort study on a single-surgeon case series using a single fixed-bearing UKA design in 158 consecutive patients who underwent 177 UKA procedures between July 2000 and December 2010. Cases missing follow-up within the last year, clinically or via telephone, were excluded (n = 17, 10%). A cumulative incidence competing risk model was used to evaluate the cumulative incidence of failure.

Results

Cumulative incidence of revision at a mean follow-up of 10 years was 13%. The majority of revisions (43%, 10/23) were for aseptic tibial component loosening, followed by progression of osteoarthritis (5/23, 22%). All Patient Reported Outcomes Measurement Information System measures demonstrated mean T-scores within one standard deviation from the US population norm. The mean Knee Injury and Osteoarthritis Outcome Score for Joint Replacement was 96.9 (range, 40-100). The mean pain score was 3.8 (range, 0-8). Eighty-six percent of patients were satisfied with the UKA.

Conclusions

At 10-year follow-up, the most common causes for revision were aseptic tibial loosening and adjacent compartment knee arthroplasty, and similar results were found for medial vs lateral compartment and for cemented vs cementless UKA. Surgeons should consider these findings for future UKA designs, and this represents the first study reporting on survivorship and outcomes of this specific UKA design.

Mid-term survivorship and patient-reported outcomes of robotic-arm assisted partial knee arthroplasty

Aims

Limited evidence is available on mid-term outcomes of robotic-arm assisted (RA) partial knee arthroplasty (PKA). Therefore, the purpose of this study was to evaluate mid-term survivorship, modes of failure, and patient-reported outcomes of RA PKA.

Methods

A retrospective review of patients who underwent RA PKA between June 2007 and August 2016 was performed. Patients received a fixed-bearing medial or lateral unicompartmental knee arthroplasty (UKA), patellofemoral arthroplasty (PFA), or bicompartmental knee arthroplasty (BiKA; PFA plus medial UKA). All patients completed a questionnaire regarding revision surgery, reoperations, and level of satisfaction. Knee Injury and Osteoarthritis Outcome Scores (KOOS) were assessed using the KOOS for Joint Replacement Junior survey.

Results

Mean follow-up was 4.7 years (2.0 to 10.8). Five-year survivorship of medial UKA (n = 802), lateral UKA (n = 171), and PFA/BiKA (n = 35/10) was 97.8%, 97.7%, and 93.3%, respectively. Component loosening and progression of osteoarthritis (OA) were the most common reasons for revision. Mean KOOS scores after medial UKA, lateral UKA, and PFA/BiKA were 84.3 (SD 15.9), 85.6 (SD 14.3), and 78.2 (SD 14.2), respectively. The vast majority of the patients reported high satisfaction levels after RA PKA. Subgroup analyses suggested tibial component design, body mass index (BMI), and age affects RA PKA outcomes. Five-year survivorship was 98.4% (95% confidence interval (CI) 97.2 to 99.5) for onlay medial UKA (n = 742) and 99.1% (95% CI 97.9 to 100) for onlay medial UKA in patients with a BMI < 30 kg/m2 (n = 479).

Conclusion

This large single-surgeon study showed high mid-term survivorship, satisfaction levels, and functional outcomes in RA UKA using metal-backed tibial onlay components. In addition, favourable results were reported in RA PFA and BiKA. Cite this article: Bone Joint J 2020;102-B(1):108–116

Minimally invasive lateral unicompartmental knee replacement: Early results from an independent center using the Oxford fixed lateral prosthesis

PURPOSE

The aim of the present study was to assess clinical outcome as well as short-term survivorship of fixed-bearing lateral unicompartmental knee replacement (UKR) from a non-designer centre using the Oxford Fixed Lateral prosthesis.

METHODS

This single-centre retrospective cohort study reports the short-term results of 51 consecutive patients (52 knees) after fixed-bearing lateral UKR with a minimum follow-up of one year. Survivorship analysis was performed with different endpoints and clinical outcome was measured using the Oxford Knee Score (OKS), objective American Knee Society Score (AKSS-O), range-of-motion (ROM), visual analog scale for pain (VAS), Tegner activity score and UCLA score.

RESULTS

There was no revision surgery, defined as exchange of at least one of the components resulting in a survival rate of 100% at two years. Three patients required further surgical treatment resulting in a survival rate of 94.2% (95% confidence interval (CI): 83.2-98.1%) with the endpoint 'any reoperation'. Outcome scores, VAS and ROM showed a statistically significant improvement at final follow-up (P < .001). The OKS improved from 26.4 ± 6.9 (12-41) preoperatively to 39.7 ± 8.4 (15-48), the AKSS-O from 54.3 ± 15.3 (18-90) to 82.2 ± 15.6 (40-100), the American Knee Society Functional Score from 56.4 ± 21.3 (10-100) to 83.1 ± 20.2 (five to 100) and the ROM from 123.5 ± 13.5 (90-140) to 134 ± 10.3 (95-150).

CONCLUSION

Early results of fixed-bearing lateral UKR using the Oxford-Fixed-Lateral prosthesis were encouraging with a significant improvement in pain and knee function as well as an excellent survivorship of 100% at a mean follow-up of two years. Further follow-up is necessary to evaluate the long-term effectiveness of this device and the surgical technique.

LEVEL OF EVIDENCE

Level IV, retrospective cohort study.

Bearing design influences short- to mid-term survivorship, but not functional outcomes following lateral unicompartmental knee arthroplasty: a systematic review

PURPOSE

To determine survivorship and functional outcomes of fixed and mobile-bearing designs in lateral unicompartmental knee arthroplasties (UKA).

METHODS

Medline, EMBASE and Cochrane databases were searched. Annual revision rate and functional outcomes were assessed for both fixed and mobile-bearing designs.

RESULTS

A total of 28 studies, of which 19 fixed-bearing and 9 mobile-bearing, representing 2265 lateral UKAs were included for survivorship and functional outcome analyses. The mean follow-up of fixed and mobile-bearing studies was 7.5 and 3.9 years, respectively. Annual revision rate of fixed-bearing designs was 0.94 (95% CI 0.66-1.33) compared to 2.16 (95% CI 1.54-3.04) for mobile-bearing. A subgroup analysis of the domed shaped mobile-bearing design noted an annual revision rate of 1.81 (95% CI 0.98-3.34). Good-to-excellent functional outcomes were observed following fixed and mobile-bearing lateral UKAs; no significant differences were found.

CONCLUSION

Mobile-bearing lateral UKAs have a higher rate of revision compared to fixed-bearing lateral UKAs with regard to short- to mid-term survivorship; however, the clinical outcomes are similar. Despite the introduction of the domed shaped mobile-bearing design, findings of this study suggest fixed-bearing implant design is preferable in the setting of isolated lateral osteoarthritis (OA). This systematic review was based on low to moderate evidence, therefore, future registry data are needed to confirm these findings. However, this study included a large number of patients, and could provide information regarding risk of revision and functional outcomes of mobile and fixed-bearing type lateral UKA.

LEVEL OF EVIDENCE

IV.

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.

High Survival Rate and Very Low Wear of Lateral Unicompartmental Arthroplasty at Long Term: A Case Series of 54 Cases at a Mean Follow-Up of 17 Years

BACKGROUND

Survivorship of lateral unicompartmental knee arthroplasty (UKA) has progressively improved. However, there are few studies describing long-term results, and no study reports on polyethylene (PE) wear in lateral unicompartmental arthroplasty. The aims of this study are to determine the survival rate of lateral UKA with a fixed, all-PE bearing, and the PE wear of the tibial implant at a minimum of 15 years follow-up.

METHODS

From January 1988 to October 2003, we performed 54 lateral UKAs in 52 patients. All patients had isolated lateral osteoarthritis (OA). The mean age at the index procedure was 65.4 ± 11 years. Thirty-nine UKAs were available for follow-up (30 alive and 9 dead after 15 years). Twelve patients had died before 15 years and 3 patients were lost to follow-up. The mean follow-up was 17.9 years (range, 15-23 years).

RESULTS

At the final follow-up, 8 knees of 39 (20.5%) had a surgical revision. The cumulative survival rate was 82.1% at 15 years and 79.4% at 20 years. The main reason of revision was progression of OA (87.5%), followed by aseptic loosening of the tibial component (12.5%). With a mean follow-up of 17.9 years, the mean PE wear was 0.061 mm/y. There was no radiographic loosening in the surviving implants and no revisions for wear. The mean functional International Knee Society score was 66.5 ± 26.8, with a mean objective score of 84.4 points ± 13.2. In the population without revision, 90.5% were satisfied or very satisfied at the latest follow-up.

CONCLUSION

Lateral UKA with a fixed, all-PE tibial bearing and a femoral resurfacing implant presents a high survivorship at long term, with very low PE wear.

A randomized controlled trial of fixed- versus mobile-bearing total knee arthroplasty: a follow-up at a mean of ten years

Aims

It has been suggested that mobile-bearing total knee arthroplasty (TKA) might lead to better outcomes by accommodating some femorotibial rotational mismatch, thereby reducing contact stresses and polyethylene wear. The aim of this study was to determine whether there is a difference between fixed- and mobile-bearing versions of a contemporary TKA with respect to durability, range of movement (ROM) and function, ten years postoperatively.

Patients and Methods

A total of 240 patients who were enrolled in this randomized controlled trial (RCT) underwent a primary cemented TKA with one of three tibial components (all-polyethylene fixed-bearing, modular metal-backed fixed-bearing and mobile-bearing). Patients were reviewed at a median follow-up of ten years (IQR 9.2 to 10.4).

Results

There was no difference in durability, as measured by survivorship free of revision for any reason, nor in mean maximal ROM at ten years (p = 0.8). There was also no difference in function, as measured by Knee Society (KS) function scores (p = 0.63) or the prevalence of patellar tilt (p = 0.12).

Conclusion

In this clinical RCT, the mobile-bearing design of TKA was found to be reliable and durable, but did not provide better maximum knee flexion, function or durability ten years postoperatively compared with a posterior-stabilized, fixed-bearing design incorporating either an all-polyethylene or a modular-metal-backed tibial component. Cite this article: Bone Joint J 2018;100-B:925-9.