Mobile bearing medial unicompartmental knee arthroplasty in patients whose lifestyles involve high degrees of knee flexion: A 10-14year follow-up study

Impact of the sagittal spinopelvic and coronal lower extremity alignments on clinical outcomes after medial unicompartmental knee arthroplasty

Introduction

We evaluated whether the clinical outcomes, including postoperative knee range of motion (ROM), after unicompartmental knee arthroplasty (UKA) were associated with the sagittal spinopelvic parameters and coronal alignment of the full lower extremity.

Methods

Forty-two patients (50 knees: six men, seven knees; 36 women, 43 knees) who underwent medial UKA between April 2015 and December 2022 were included. Preoperative radiographic examinations of the index for sagittal spinopelvic alignment included the sagittal vertical axis (SVA), lumbar lordosis, sacral slope (SS), pelvic tilt (PT), and pelvic incidence. The anteroposterior hip-knee-ankle angle (HKAA) was calculated. The relationship of clinical outcomes and the risk of knee flexion angle ≤125° and knee flexion contracture ≥10° 1-year post-UKA with radiographic parameters were evaluated.

Results

Preoperative HKA angle affected postoperative knee flexion angle ≤125° (p = 0.017, 95% confidence interval [CI]: 0.473-0.930) in logistic regression analysis. Patients with a knee flexion angle ≤125° had a higher preoperative HKAA (9.8 ± 3.0°), higher SVA (83.8 ± 37.0 mm), and lower SS (23.7 ± 9.0°) than those with a flexion angle >125° (preoperative HKAA: 6.6 ± 4.0°, SVA: 40.3 ± 46.5 mm, SS: 32.0 ± 6.3°) (p = 0.029, 0.012, and 0.004, respectively). PT related to postoperative knee flexion contracture ≥10° (p = 0.010, 95% CI: 0.770-0.965) in the logistic regression analysis. Patients with flexion contracture ≥10° had higher PT (35.0 ± 6.6°) and SVA (82.2 ± 40.5 mm) than those with flexion contracture <10° (PT, 19.3 ± 9.0°; SVA, 42.4 ± 46.5 mm) (p = 0.001 and 0.028, respectively). The postoperative clinical outcome was correlated with the postoperative knee flexion angle and SVA (p = 0.036 and 0.020, respectively).

Conclusions

The preoperative HKAA affected postoperative knee flexion angle, and the knee flexion contracture and clinical outcomes post-UKA were associated with PT and SVA, respectively. To predict outcomes for knee ROM and clinical scores after UKA, radiographic examination, including the sagittal spinopelvic parameters and the coronal view of the full lower extremity, is essential.

Bearings can dislocate with smaller femoral components and thicker bearings in Oxford™ medial unicompartmental knee arthroplasty

BACKGROUND

A mobile bearing can dislocate when joint laxity is larger than jumping height, the height difference between the bottom and the peak of the bearing (the highest point of the upper bearing surface on each side). Significant laxity due to improper gap balancing should therefore be avoided. However, once the bearing rotates vertically on the tibial component, the bearing can dislocate with smaller laxity than the jumping height. We mathematically calculated the required laxity for dislocation (RLD) and the required rotation of the bearing for dislocation (RRD). The current study addressed the question: 1) could the femoral component size and the bearing thickness affect the RLD and RRD?

HYPOTHESIS

The femoral component size and the bearing thickness could affect the MLD and MRD.

METHODS

The RLD and RRD were calculated using the bearing dimensions provided by the manufacturer with femoral component size, bearing thickness, and directions (anterior, posterior, and medial/lateral) as the variables on a two-dimensional basis.

RESULTS

The RLD was 3.4 to 5.5mm in the anterior, 2.3 to 3.8mm in the posterior, and 1.4 to 2.4mm in the medial or lateral directions. The RLD decreased with a smaller femoral size or a thicker bearing. Similarly, the RRD decreased with a smaller femoral size or a thicker bearing thickness in all directions.

CONCLUSIONS

Increased bearing thickness and decreased femoral component size deceased the RLD and RRD, which would relate to an increased risk of dislocation. Selecting the femoral component as large as possible and the bearing as thin as possible would therefore be helpful in the prevention of dislocation.

LEVEL OF EVIDENCE

III; comparative computer simulation study.

Comparison of the scientific performance in hip and knee arthroplasty between the leading continents

Background

Scientific progress in the field of knee and hip arthroplasty has enabled the preservation of mobility and quality of life in the case of patients with many primary degenerative and (post-) traumatic joint diseases. This comparative study aims to investigate differences in scientific performance between the leading continents in the field of hip and knee arthroplasty.

Methods

Using specific search terms all studies published by the scientific leading continents Europe, North America, Asia and Oceania listed in the Web of Science databases were included. All identified publications were analysed and comparative conclusions were drawn regarding the qualitative and quantitative scientific merit of each continent.

Results

Europe, followed by North America, Asia, and Oceania, had the highest overall number of publications in the field of arthroplasty. Since 2000, there has been a strong increase in knee arthroplasty publication rate, particular pronounced in Asia. Studies performed and published in North America and those on knee arthroplasty received the highest number of fundings. Publications regarding hip arthroplasty achieved the highest average citation rate. In contradistinction to the others, in North America most funding was provided by private agencies.

Conclusion

Although Europe showed the highest total number of publications, authors and institutions, arthroplasty research from North America received greater scientific attention and financial support. Measured by citations, publications on hip arthroplasty attained higher scientific interest and studies on knee arthroplasty received higher economic affection.

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.

Mobile bearing versus fixed bearing medial unicompartmental knee replacement: an independent two center matched-pairs analysis

INTRODUCTION

The aim of the present study was to compare clinical outcome between patients following fixed-bearing (FB) or mobile-bearing (MB) unicompartmental knee replacement (UKR) for antero-medial knee osteoarthrosis (OA) at two independent orthopedic centers.

MATERIALS AND METHODS

Matched-pairs were built between 35 patients receiving FB-UKR and 52 patients following MB-UKR regarding age at time of surgery, body mass index (BMI) and range of motion (ROM) preoperatively. Clinical and functional outcome was measured postoperatively by the American Knee Society Score (AKSS-O/AKSS-F), ROM, Tegner Activity Scale (TAS) as well as the Short Form 36 Health Survey (SF-36).

RESULTS

The average treatment effect of the treated (ATT) after propensity score matching showed a significantly superior ROM in patients following MB-UKR (FB: 118°, MB: 124°). All remaining parameters had no statistically significant differences between both groups involving TAS, AKSS and SF-36.

CONCLUSIONS

The present study suggests that MB-UKR can provide a greater ROM compared to FB-UKR on comparable patients. The authors believe that both designs are suitable for adequate improvement of clinical outcome and ROM for patients suffering from antero-medial osteoarthrosis of the knee joint.

LEVEL OF EVIDENCE

Retrospective cohort study, Level IV.

The ability and factors related with floor sitting after total hip arthroplasty with a posterolateral approach

Background

Prosthesis dislocation following total hip arthroplasty (THA) is one complication that affects treatment outcome and increases the cost of treatment. Currently, many surgeons prohibit patients from performing floor-based activities; however, these prohibitions might affect the lifestyle of a number of patients.

Objective

This study aimed to evaluate the ability of floor sitting after THA, and factors associated with this ability.

Methods

This study was a retrospective cohort study, evaluating 240 patients who underwent THA with a posterolateral approach, in a single tertiary hospital. Patient demographic data, preoperative clinical data, prostheses type, and postoperative radiographic were extracted from the electronic medical records. Postoperative ability to perform floor sitting was evaluated at 6 months postoperatively.

Results

There were 52 patients (21.66%) who were able to sit on the floor postoperatively. Multivariate logistic regression analysis showed independent association between three factors with ability to sit on the floor after surgery: pre-operative external rotation range of motion (OR 1.03; 95% CI, 1.01-1.06; P = 0.01), pre-operative Harris Hip Scores (OR 1.05; 95% CI, 1.01-1.10; P = < 0.01), pre-operative ability to sit on the floor (OR 10.2; 95% CI, 3.65-28.5; P = < 0.01).

Conclusion

There were a number of patients who could sit on the floor after THA. However, there were factors which were associated with this ability. Hence, these results could be useful for adjusted patient preoperative expectations, and did not preclude all patients to perform floor activities.

Potential factors in postoperative dislocation of Oxford phase III mobile bearing UKA in Chinese patients: a single-center retrospective study

BACKGROUND

Bearing dislocation is the main complication after mobile bearing unicompartmental knee arthroplasty. The purpose of this study was to analyze the potential risk factors of bearing dislocation after Oxford phase III mobile bearing unicompartmental knee arthroplasty in Chinese patients.

METHODS

We retrospectively investigated 492 patients (578 knees) who underwent Oxford phase III mobile bearing unicompartmental knee arthroplasty in our institution between February 2009 and June 2019. The patients were divided into two groups based on surgeons' annual surgical volume. Those with/ without bearing dislocation were compared based on patient, surgeon and implant factors.

RESULTS

Among the 492 patients, 21 (4.3%, 4 men and 17 women) experienced bearing dislocation. Of these, 14 (4.0%) were in the high surgical volume group and 7 (5.1%) were in the low surgical volume group. Multivariate analysis revealed that trauma to the operated leg and daily life involving high knee flexion cumulatively predicted bearing dislocation (p < 0.05).

CONCLUSIONS

Trauma to the operated leg and daily life involving high knee flexion were risk factors for bearing dislocation after Oxford phase III mobile bearing unicompartmental knee arthroplasty.

Excellent outcomes with Oxford Uni-compartmental knee arthroplasty in anteromedial osteoarthritis patients (≤60 years) at mid-term follow-up

Background

The use of Oxford uni-compartmental knee arthroplasty (UKA) has rapidly increased worldwide,however,the relevance of younger patients for postoperative function after Oxford UKA remains unclear. The main purpose of our study is to clarify the effectivemess of Oxford UKA in the younger Chinese patients with anteromedial osteoarthritis (AMOA).

Methods

We retrospectively enrolled 252 consecutive patients who underwent Oxford UKA for AMOA with a minimum follow-up of 5 years between March 2013 and December 2016. The patients were divided into the younger (≤60 years) and elderly (> 60 years) age groups. The demographic data and surgery variables were recorded and compared. Patient satisfaction grade, range of motion (ROM), Oxford knee score (OKS), Hospital for Special Surgery (HSS) score, Western Ontario and McMaster (WOMAC) Universities Osteoarthritis Index score and postoperative complications were recorded. The 5-year survival of the implants were also compared with TKA revision as the endpoint.

Results

A total of 252 consecutive patients were recruited, including 96 aged 60 years or less and 156 aged over 60 years. The mean follow-up duration in the younger and elderly groups were 73.6 months (SD,standard deviation, 4.1) and 74.7 months (SD 6.2) respectively. Patient satisfaction rate was high in both groups (P = 0.805). Furthermore, no significant differences were observed in postoperative ROM(P = 0.299), OKS(P = 0.117), HSS(P = 0.357) and WOMAC scores(P = 0.151) between the younger and elderly groups (P>0.05). However, the incidence of joint stiffness (P = 0.033) and delayed wound dehiscence (P = 0.026) were significantly different between both groups. Five-year implant survival without revision were also similar in both groups (96.9% vs 97.4%, P = 0.871), and that for the entire cohort was 97.2% (95% CI 95.4–99.6).

Conclusion

Oxford UKA for AMOA demonstrated favorable results in younger patients aged ≤60 years at a minimum 5-year follow-up in terms of patient satisfaction, functional outcomes, implant survival and postoperative complications. Therefore, younger patients might not be considered as an absolute contraindication to Oxford UKA.

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.

Bearing dislocation of mobile bearing unicompartmental knee arthroplasty in East Asian countries: a systematic review with meta-analysis

Background

Bearing dislocation is a common postoperative complication of mobile-bearing unicompartmental knee arthroplasty, and East Asian patients tend to be at higher risk. However, whether this high dislocation rate is common in all East Asian populations remains unclear. This meta-analysis was performed to explore this issue and describe various features of dislocation in East Asians, including the onset time, dislocation direction, and re-dislocation rate.

Methods

The literature was searched in PubMed, Embase, Ovid, and Cochrane Library up to May 2020. Studies were scrutinized by two independent authors, and the bearing dislocation rate, onset time, direction, and re-dislocation rate were specifically analyzed. RevMan 5.3 was used for the statistical analysis.

Results

Seven case series from Korea, China, and Japan were included. The pooled analysis showed that the total dislocation rate was 2.37%, while the subgroup analysis showed that the dislocation rate in Korea and other countries was 4.50% and 0.74%, respectively (P < 0.01). Another subgroup analysis of the onset time showed a significant difference before and after the first 5 years postoperatively (P < 0.01). Anterior and posterior dislocations were more frequent than medial and lateral dislocations (P < 0.01). The average re-dislocation rate was 32.45%, which was approximately seven times higher than the primary dislocation rate (P < 0.01).

Conclusion

Our meta-analysis demonstrated that Korea had a higher bearing dislocation rate among East Asian countries, especially in the first 5 years after primary UKA. Anterior and posterior dislocations were common. The most important finding is that the re-dislocation rate can be much higher than the initial dislocation rate.

Efficacy and mid/long-term survivorship of mobile-bearing unicompartmental knee arthroplasty for medial compartment knee osteoarthritis combined patellofemoral joint arthritis: a prospective cohort study protocol

INTRODUCTION

Unicompartmental knee arthroplasty (UKA) is one of the most effective surgical procedures for treating isolated medial compartment knee osteoarthritis. However, previous studies have regarded patellofemoral osteoarthritis as a contraindication for UKA. In contrast, most current research shows that damage to the articular cartilage of the patellofemoral joint, even to the extent of full-thickness cartilage loss, has no influence on the outcome of UKA.

METHODS AND ANALYSIS

Study settings: This study is a prospective cohort study that will compare the Forgotten Joint Score and Lonner patellofemoral joint score of patients who have undergone UKA; the patients will be divided into two groups (with and without patellofemoral joint osteoarthritis (PFJOA)).

PRIMARY OBJECTIVE

Long-term follow-up will be used to evaluate the effect of the operation on the above-mentioned scores in both the groups.

SECONDARY OBJECTIVE

We will divide the patients from the with PFJOA group into three subgroups according to the localisation of patellofemoral cartilage lesions (medial zone, lateral zone and central zone). We aim to compare knee joint scores among these groups and clarify the impact of different wear sites on clinical efficacy. We will use CT to explore the potential mechanism through which UKA affects patellofemoral joint-related parameters (lateral patellar tilt, lateral patellar shift and tibia tuberosity-trochlear groove distance). We will also record mid-term/long-term post-surgery complications.

ETHICS AND DISSEMINATION

This study's protocol is in accordance with the Declaration of Helsinki. This study was approved by the Ethics Committee of Xuanwu Hospital. The results of this study will be disseminated in international peer-reviewed journals.

TRIAL REGISTRATION NUMBER

ChiCTR2000030310.

Survivorship of fixed vs mobile bearing unicompartmental knee replacement: A systematic review and meta-analysis of sixty-four studies and National Joint Registries

BACKGROUND

Unicompartmental knee replacement (UKR) prostheses can use fixed (FB) or mobile bearing (MB) constructs. We compared survivorship and failure modes of both designs.

METHODS

The inclusion criteria were studies published between 2005 and 2020 with minimum average follow-up of five years reporting the survival and/or number of revisions of specific designs in medial and lateral UKRs. Pooled rate of revision per 100 patient years (PTIR) was estimated using a random effects model.

RESULTS

Seventy cohorts of 17,405 UKRs with weighted mean follow-up of 7.3 years (0.1-29.4 years) were included. A total of 170,923 UKRs were identified in registry reports at a weighted mean implant survival time of 15.4 years. PTIR in MB UKR versus FB UKR was similar [1.45 vs 1.40, (p = 0.8)]. In cohort studies, the overall PTIR for MB was also similar to FB [1.03 vs 0.78, (p = 0.1)]. For medial UKR, the PTIR for MB was marginally greater but not significantly different to FB [0.96 vs 0.81, (p = 0.3)], whilst for lateral UKR, the PTIR for MB was significantly worse than for FB [2.20 vs 0.72, (p < 0.01)]. Polyethylene wear is more common in FB implants, whilst MB implants are revised more often for bearing dislocation.

CONCLUSIONS

Overall implant survival in mid- to long-term studies is similar for MB versus FB medial UKRs. MB have a four-fold higher risk of revision in comparison to FB when used for lateral UKR.

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.”

Dependence of knee range of motion on the alignment of femoral and tibial components after medial unicompartmental knee arthroplasty

INTRODUCTION

This study evaluated the relationship between postoperative knee flexion angles and the position of femoral and tibial components in unicompartmental knee arthroplasty (UKA).

MATERIALS AND METHODS

Eighteen patients (a total of 22 knees: three men, four knees; 15 females, 18 knees) who underwent navigation-assisted UKA were included. Pre- and postoperative computed tomography images were applied on 3D software, which were matched and used to calculate the position of femoral and tibial components. Correspondingly, we investigated the relationship between the knee range of motion (ROM) at 1-year postoperative follow-up and the position of femoral and tibial components.

RESULTS

At 1-year post-UKA, the knee flexion angle was associated with the posterior flexion angle of tibial components. This particular angle was significantly greater in the group with equal or greater postoperative knee ROM compared to preoperative ROM (5.2 ± 2.1°) than in the group with less postoperative knee ROM compared to preoperative ROM (2.6 ± 1.6°, p < 0.01). There was no significant difference between both groups in the femoral component position, preoperative posterior slope of the medial tibial plateau, change in the pre- to postoperative posterior tibial slope, and postoperative knee society score.

CONCLUSION

The posterior flexion angle of the tibial component affected the improvement/deterioration of the postsurgery knee flexion angle in navigation-assisted UKA. For improved outcomes after UKA using navigation systems, surgeons should aim to achieve a 5° to 8° posterior flexion angle of the tibial component.

Patient outcomes in Anteromedial osteoarthritis patients over 80 years old undergoing Oxford Unicompartmental knee Arthroplasty in China

Background

The use of Oxford Unicompartmental Knee Arthroplasty (UKA) has increased rapidly in both Western and Asian populations, with excellent functional outcomes and high patient satisfaction. While previous evidence regarding clinical outcomes and survival rates after Oxford UKA was based on studies in Western populations, the results may be different in Asian patients. The relevance of age for postoperative function after Oxford UKA also remains unclear. Hence, the aim of our study was to clarify the effectiveness and safety of Oxford UKA in Asian patients aged over 80 years.

Methods

A retrospective review was performed and included 195 patients (209 knees) who underwent an Oxford UKA between June 2015 and July 2018. We divided the patients into three groups by age: Group 1, 60–69 years; Group 2, 70–79 years; and Group 3, over 80 years. We used the Hospital for Special Surgery (HSS) score and Western Ontario and McMaster (WOMAC) Universities Osteoarthritis Index score to evaluate the general condition of the patients’ knees before surgery and at last follow-up. We also recorded perioperative and short-term complications.

Result

Group 1 consisted of 60 patients (60 knees); Group 2, 70 patients (79 knees); and Group 3, 65 patients (70 knees). The mean follow-up was 21.34 ± 12.04, 22.08 ± 11.38, and 21.76 ± 10.20 months in groups 1, 2, and 3, respectively. At last follow-up, the patients in Group 3 showed lower function scores compared to groups 1 and 2 (P < 0.05), but the HSS scores and the WOMAC scores were significantly improved in all three groups. In terms of perioperative and other complications, the three age groups did not differ significantly.

Conclusion

Oxford UKA is an effective and safe treatment for osteoarthritis, even in elderly patients in China. Elderly patients have lower knee function scores than younger patients. However, the knee joint pain of the elderly patients was relieved and function improved compared to the preoperative condition.

Epidemiology of Bearing Dislocations After Mobile-Bearing Unicompartmental Knee Arthroplasty: Multicenter Analysis of 67 Bearing Dislocations

BACKGROUND

This study investigated the epidemiology and causes of bearing dislocations following mobile-bearing unicompartmental knee arthroplasty (MUKA) and determined whether the incidence of primary bearing dislocations decreases as surgeon experience increases.

METHODS

We retrospectively reviewed the bearing dislocations following MUKAs performed by 14 surgeons with variable experience levels. Causes of bearing dislocations were determined based on the surgical records, radiographs, and operator's suggestion. Using a chi-squared test, the incidence of bearing dislocation was compared between the first 50, the second 50, and the next 100 unicompartmental knee arthroplasties (UKAs) of each surgeon's cohort.

RESULTS

There were 67 (3.6%) bearing dislocations from 1853 MUKAs. The mean time to bearing dislocations after index MUKAs was 33 months (range, 1-144 months); 55% of the bearing dislocations occurred within 2 years after the index MUKAs. Primary bearing dislocations (n = 58) were the most common, followed by secondary (n = 6) and traumatic dislocations (n = 3). There was no significant difference in the incidence of bearing dislocation between the first 50 and second 50 UKAs for each surgeon. Two surgeons showed a significant decrease in bearing dislocations in their second 100 UKAs, while the other surgeons did not show a difference between their first 100 and second 100 UKAs.

CONCLUSION

Most bearing dislocations after MUKAs were related to technical errors such as component malposition or gap imbalance. This study did not confirm that the incidence of bearing dislocations decreases as the number of cases increases.

LEVEL OF EVIDENCE

IV, Case series.

Update on unicompartmental knee arthroplasty: Current indications and failure modes

Despite the excellent success rates of modern implants, unicompartmental knee arthroplasty (UKA) continues to show relatively high failure and revision rates, especially when compared with total knee arthroplasty (TKA).

These higher rates of failure and revision are mainly observed during the early (< 5 years) post-operative period and are often due to incorrect indications and/or surgical errors.

The correct clinical and radiological indications for UKA have therefore been analysed and correlated as far as possible with the principal mechanisms and timing of failures of UKA.

Cite this article: EFORT Open Rev 2018;3:442-448. DOI: 10.1302/2058-5241.3.170060

Unicompartmental knee arthroplasty: Current indications, technical issues and results

An age younger than 60 years, a body weight of 180 lb (82 kg) or more, performing heavy work, having chondrocalcinosis and having exposed bone in the patellofemoral (PF) joint are not contraindications for unicompartmental knee arthroplasty (UKA).Severe wear of the lateral facet of the PF joint with bone loss and grooving is a contraindication for UKA.Medial UKA should only be performed in cases of severe osteoarthritis (OA) as shown in pre-operative X-rays, with medial bone-on-bone contact and a medial/lateral ratio of < 20%.The post-operative results of UKA are generally good. Medium-term and long-term studies have reported acceptable results at 10 years, with implant survival greater than 95% for UKAs performed for medial OA or osteonecrosis and for lateral UKA, especially when fixed-bearing implants are used.When all implant-related re-operations are considered, the 10-year survival rate is 94%, and the 15-year survival rate is 91%.Aseptic loosening is the principal failure mechanism in the first few years in mobile-bearing implants, whereas OA progression causes most failures in later years in fixed-bearing implants.The overall complication rate and the comprehensive re-operation rate are comparable in both mobile bearings and fixed bearings.The survival likelihood of the all-polyethylene UKA implant is similar to that of metal-backed modular designs for UKA.Notable cost savings of approximately 50% can be achieved with an outpatient UKA surgery protocol. Outpatient surgery for UKA is efficacious and safe, with satisfactory clinical results thus far. Cite this article: EFORT Open Rev 2018;3:363-373. DOI: 10.1302/2058-5241.3.170048.