Survivorship of the St Georg Sled medial unicompartmental knee replacement beyond ten years

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

BACKGROUND

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 2 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 end point as revision of components.

RESULTS

There were 8 patients (5.0%) who underwent conversion to total knee arthroplasty for lateral UKA implant failure or progression of arthritis. There were 3 patients (1.9%) who underwent ipsilateral medial UKA due to medial compartment arthritis progression with preserved mechanical alignment and patellofemoral joint. There were 8 additional procedures that did not require implant changes, including 5 irrigation and debridements for acute periprosthetic joint infection (3.1%), 2 wound closures for dehiscence (1.3%), and one loose body removal (0.6%).

CONCLUSIONS

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.

Long-Term Outcomes in Unicompartmental Knee Arthroplasty: Survivorship of Medial versus Lateral Unicompartmental Knee Arthroplasty

Unicompartmental knee arthroplasties (UKAs) currently represent an important portion of knee arthroplasty procedures and their usage is on an upward trend. Despite offering better functional outcomes and a quicker recovery compared to total knee arthroplasties (TKAs), UKAs are often scrutinized for their longevity. This article provides an in-depth examination of the technical nuances and survival rates of medial versus lateral UKAs, drawing on recent advances and findings in the field. This manuscript thoroughly evaluates the comparability of patient populations undergoing medial and lateral UKAs, considering their anatomical, biomechanical, and demographic differences. It delves into the specific technical challenges associated with each type and systematically assesses the factors that influence failure, including the intricacies of implant design and patient-specific variables. Despite relevant anatomical and biomechanical contrasts between medial and lateral UKAs, recent literature points to comparable survival rates. The prevalence of early failures within the initial five years post-operation underscores the criticality of precise patient selection and refined surgical techniques. The paper succinctly summarizes pivotal literature and provides essential guidance for optimizing UKA survivorship. It underscores the importance of meticulous patient selection and precise surgical techniques, alongside the identification and mitigation of potential pitfalls that impact outcomes. Finally, robotic technology in UKA has considerably enhanced the precision and reproducibility, representing a viable solution to effectively meet and achieve the recommended technical objectives.

Associated patellofemoral osteoarthritis is not a contraindication for unicompartmental knee replacement. Report of one hundred ten prostheses with an average 6-year follow-up

INTRODUCTION

Associated patellofemoral joint osteoarthritis (APFJ-OA) has typically been considered a contraindication for unicompartmental knee arthroplasty (UKA) in the treatment of femorotibial joint osteoarthritis. However, this contraindication is being challenged. The aim of this study was to assess clinical and functional outcomes, complications, and implant survival in medial or lateral UKA, regardless of clinical symptoms or radiographic signs of APFJ-OA.

METHODS

This retrospective, comparative study included patients treated with medial or lateral UKA regardless of preoperative symptoms or signs of APFJ-OA, with a minimum 2-year follow-up. Intraoperatively, knees were subdivided based on APFJ-OA grade, according to the Outerbridge classification. Clinical and functional outcomes were analyzed using the 2011 Knee Society Score (KSS) at the last follow-up control. APFJ-OA was treated systematically, in a tailored, stepwise fashion according to its severity. Complications and implant survival rates were evaluated. Two-sided paired T-test, ANOVA, and Kruskal-Wallis tests were used with a significance level of 5%.

RESULTS

Finally, 110 UKAs were assessed 81 (73.6%) medial and 29 (26.4%) laterals. The average follow-up was 6 years (2-19.5). According to Outerbridge, 22 knees (20%) were in grade 2, 59 (53.6%) were in grade 3, and 29 (26.4%) were in grade 4. All three groups showed a statistically significant increase in KSS scores and range of motion. There were no significant differences in clinical KSS improvement and flexion contracture between Outerbridge groups (average 35.7 and -4.9, respectively). Group 3 showed statistically significant improvement in functional KSS when compared to group 2 (68.8 vs 61.2). In maximum flexion, groups 3 and 4 did significantly better than group 2 (20° vs 15°). Three prostheses (2.7%) needed revision after 7, 8.6, and 12 years due to aseptic tibial loosening. Implant survival was 100% at 5 (64 of 64), 97% at 7 (30 of 31), 93% at 9 (14 of 15), and 89% at 12 years, respectively (8 of 9).

CONCLUSION

Clinical and functional results, complications, and survival of medial or lateral UKA were not negatively affected by APFJ-OA assessed intraoperatively using the Outerbridge classification after an average follow-up of 6 years. We consider that APFJ-OA is not a contraindication for UKA when treated systematically according to its severity.

LEVEL OF EVIDENCE

IV.

A rare case of oxidized zirconium - All polyethylene tibia unicompartmental arthroplasty failure: A case report

Oxidized zirconium (Oxinium) implants has been claimed as the best material in terms of wear reduction. However, longevity of an all polyethylene uni knee arthroplasty (UKA) has been a long debate. We reported a rare case of 74 year old female who was performed all polyethylene UKA 6 years prior and fell 3 months prior. After the incident, patient was wheel-chair ridden afterwards. There was no evidence of fracture upon conventional radiography examination. Conversion of UKA to total knee replacement (TKA) was performed and patient was able to walk with aid after the surgery. The failed Oxinium all polyethylene UKA failure in this case is suspected due osteoarthritis progression.

St Georg Sled medial unicompartmental arthroplasty: survivorship analysis and function at 20 years follow up

PURPOSE

The peri-operative and short-term benefits of unicompartmental knee arthroplasty (UKA) are well supported in the literature. However, there remains concern regarding the higher revision rate when compared with total knee replacement. This manuscript reports the functional outcome and survivorship of a large series of fixed bearing, medial unicompartmental replacements (St Georg Sled), with a minimum of 20 years follow-up.

METHODS

Between 1974 and 1994, 399 patients (496 knees) underwent a medial fixed-bearing UKA. Prospective data were collected pre-operatively and at regular intervals post-operatively using the Bristol Knee Score (BKS), Oxford Knee (OKS) and Western Ontario MacMaster (WOMAC) scores. Kaplan-Meier survival analysis was used to determine survivorship, with revision or need for revision as end point, and differences assessed using Mantel-Cox log rank test.

RESULTS

Functional knee scores improved post-operatively, but demonstrated a slight decline from 10 years of follow-up onwards. Survivorship is estimated as 86% at 10 years, 80% at 15 years, and 78% at 20 years. Sixty knees were revised, with progression of disease in another compartment the commonest reason. Eighty eight percent were revised using a primary prosthesis. For patients over the age of 65 years at the time of index procedure, 93% died with a functioning prosthesis in situ.

CONCLUSION

Medial UKA demonstrates good long-term function and survivorship, and represents an excellent surgical option for patients aged over 65 years of age, where few patients will require a revision procedure.

LEVEL OF EVIDENCE

IV.

A Retrospective Study of Unicompartmental Knee Arthroplasty Functional Outcome and the Incidence of Medial Meniscus Posterior Root Tear in Spontaneous Osteonecrosis of the Knee

Background

Spontaneous osteonecrosis of the knee (SONK) can lead to severe knee osteoarthritis predominantly localized to the medial compartment. We aimed to determine whether unicompartmental knee arthroplasty was an effective treatment for primary SONK.

Methods

We analyzed the functional outcomes in 23 patients with SONK (with a magnetic resonance imaging- (MRI-) confirmed diagnosis) who underwent UKA at a single center. The mean follow-up time was 67 months post-UKA.

Results

Significant improvements in function were indicated by reduced Oxford Knee and Visual Analogue Scale scores after UKA, and there were no specific complications after the procedures. The incidence of MRI-identified medial meniscus posterior root tear (MMPRT) was 69.6% (16/23).

Conclusion

Unicompartmental arthroplasty for SONK is less destructive to the native knee structure than total knee arthroplasty but can achieve comparable prognosis with strict patient selection. While the precise etiology of SONK is unknown, one theory posits that a MMPRT may change the biomechanical circumstances of the knee joint, leading to osteonecrosis. Although not confirmatory, the high prevalence rate suggests that MMPRT may have a key role in the development of SONK. UKA is an effective treatment option for SONK, resulting in significant functional improvement. Long-term (>10 years) outcomes should be investigated.

Staged vs simultaneous bilateral unicompartmental knee arthroplasty for clinical outcomes: A protocol of systematic review and meta-analysis

BACKGROUND

Bilateral unicompartmental knee arthroplasty (UKA) can be divided into one or two stages clinically. Compared with staged bilateral UKA, whether simultaneous bilateral UKA has better clinical efficacy remains to be verified.

METHODS

PubMed, EBSCO, and Web of Science were searched by us for meta-analysis. Studies were considered eligible for inclusion if they included simultaneous and staged UKA. We excluded studies unrelated to the research question, studies in non-selected languages, and studies where the full-text was not available. The data were extracted by two independent investigators, and disagreements were resolved through discussions with a third party. If important data or information about the content of the paper were not available, authors were contacted. Publication bias in studies has been assessed. Meta-analysis was done using Review Manager 5.3.

RESULTS

The systematic review and meta-analysis identified 3370 trials, of which 8 studies (963 patients) compared simultaneous with staged bilateral UKA. The meta-analysis showed that the clinical outcomes of simultaneous bilateral UKA goes down in operating time (weighted mean difference [WMD] = -19.34, 95% confidence interval [CI] -22.44 to -16.25, P < .00001), postoperative hemoglobin (Std. mean difference [SMD] = -0.46, 95% CI -0.71 to -0.20, P = .0004), length of stay (LOS) (WMD = -4.73, 95% CI -6.39 to -3.06, P < .00001), hospital cost (SMD = -5.42, 95% CI -6.54 to -4.30, P < .00001). There were no significant difference in blood transfusion, venous thrombosis, infection, cardiac complications, pulmonary complications, Oxford Knee Score (OKS) between simultaneous and staged bilateral UKA.

CONCLUSION

Simultaneous bilateral UKA can effectively reduce the operating time, LOS, and hospital cost without increasing postoperative complications compared to stage bilateral UKA.

REGISTRATION NUMBER

CRD42020160056 (www.crd.york.ac.uk/prospero/).

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.

Bilateral Femoral Component Fractures After Primary Total Knee Arthroplasty With Cruciate-Retaining Femoral Component

A 69-year-old male presented with atraumatic bilateral femoral component fractures at different time intervals after simultaneous bilateral total knee arthroplasty using the cemented Biomet Ascent Knee System. The right and left knee implant fractures occurred 12 and 17 years after primary arthroplasty, respectively. This patient was notably tall (190.5 cm, 98th percentile) and maintained an active lifestyle before implant fractures. Sequential, bilateral knee implant fractures in a system with a previously acceptable track record suggest that biomechanics, patient characteristics, and surgical factors can significantly influence the risks for fracture of an implant.

Minimum 10-year outcomes of a fixed bearing all-polyethylene unicompartmental knee arthroplasty used to treat medial osteoarthritis

BACKGROUND

Unicompartmental knee arthroplasty (UKA) accounts for 8.9% of knee arthroplasty procedures in England, Wales and Northern Ireland. Fixed bearing UKA designs have shown favourable survivorship in registries when compared with mobile bearings but some studies suggest poor survival of all-polyethylene fixed tibial bearings. This study analyses long-term follow-up of patients with a medial fixed all-polyethylene tibial bearing UKA and reports survivorship and 10-year clinical outcomes.

METHODS

Data was collected prospectively for 214 medial unicompartmental all-polyethylene tibial bearing UKAs implanted in 184 patients at our tertiary referral centre between November 2002 and December 2007. The indication was osteoarthritis in all but one patient. Patient reported outcome scores were documented pre-operatively and at five, eight, 10 and 12 years of follow-up. The mean patient age was 70 years (range 41-87).

RESULTS

Outcome and survivorship data were collected for 214 medial all-polyethylene tibial bearing UKAs. There were outcomes recorded for 83 UKAs with at least 10-year follow-up. Twenty-four patients underwent revision of their UKA at an average of 5.84 years after the primary procedure. Kaplan-Meier analysis demonstrated survivorship of 89.1% at 10 years and the OKS, AKSS and WOMAC patient reported outcomes remained significantly improved in comparison to preoperatively. For those 70 years or older, 10-year survivorship was 92.4%, compared to 85.0% for those under 70 years old.

CONCLUSION

Medial fixed all-polyethylene tibial bearing UKA demonstrates acceptable long-term survivorship and patient outcomes. It appears to be a suitable option for the treatment of medial compartment OA, particularly in older patients.

Influence of tibiofemoral congruency design on the wear of patient-specific unicompartmental knee arthroplasty using finite element analysis

Objectives

Unicompartmental knee arthroplasty (UKA) is an alternative to total knee arthroplasty for patients who require treatment of single-compartment osteoarthritis, especially for young patients. To satisfy this requirement, new patient-specific prosthetic designs have been introduced. The patient-specific UKA is designed on the basis of data from preoperative medical images. In general, knee implant design with increased conformity has been developed to provide lower contact stress and reduced wear on the tibial insert compared with flat knee designs. The different tibiofemoral conformity may provide designers the opportunity to address both wear and kinematic design goals simultaneously. The aim of this study was to evaluate wear prediction with respect to tibiofemoral conformity design in patient-specific UKA under gait loading conditions by using a previously validated computational wear method.

Methods

Three designs with different conformities were developed with the same femoral component: a flat design normally used in fixed-bearing UKA, a tibia plateau anatomy mimetic (AM) design, and an increased conforming design. We investigated the kinematics, contact stress, contact area, wear rate, and volumetric wear of the three different tibial insert designs.

Results

Conforming increased design showed a lower contact stress and increased contact area. In addition, increased conformity resulted in a reduction of the wear rate and volumetric wear. However, the increased conformity design showed limited kinematics.

Conclusion

Our results indicated that increased conformity provided improvements in wear but resulted in limited kinematics. Therefore, increased conformity should be avoided in fixed-bearing patient-specific UKA design. We recommend a flat or plateau AM tibial insert design in patient-specific UKA.

Cite this article: Y-G. Koh, K-M. Park, H-Y. Lee, K-T. Kang. Influence of tibiofemoral congruency design on the wear of patient-specific unicompartmental knee arthroplasty using finite element analysis. Bone Joint Res 2019;8:156–164. DOI: 10.1302/2046-3758.83.BJR-2018-0193.R1.

High Rate of Early Revision After Custom-Made Unicondylar Knee Arthroplasty

BACKGROUND

There has been a recent interest in custom-made partial knee arthroplasties to provide patient-specific instrumentation and better fit of the prosthesis. While unicondylar knee arthroplasties (UKAs) have demonstrated good outcomes and durable results in many studies, there is little evidence on outcomes of these custom-made implants.

METHODS

We performed a retrospective review of all custom-made UKAs performed at our institution by one surgeon from 2008 to 2015. We analyzed preoperative demographics, clinical follow-up evaluations, and radiographs and performed an analysis of risk factors including age, gender, height, weight, body mass index, and tibial insert thickness. The incidence of revision surgery, radiographic failures indicating component loosening, and symptomatic clinically failed implants was calculated at an average of 54.0 months of follow-up.

RESULTS

We analyzed 115 consecutive custom-made medial UKAs from a single surgeon at our institution and found 29 (25.2%) UKAs had failed at an average of 33.1 months after surgery. Reasons for failure included aseptic femoral loosening (10), aseptic tibial loosening (8), loosening of both components (4), infection (3), progression of osteoarthritis (2), pain (1), and dislodged polyethylene insert (1). We found a significant relationship between implant failure and body mass index; no other study variables were statistically significant.

CONCLUSION

We found a relatively high rate of aseptic loosening and particularly femoral component loosening in the short- to intermediate-term follow-up period. While further study of larger numbers of custom-made UKA from multiple institutions may help verify these findings, we recommend careful consideration of the use of this implant.

Ten-year survival and patient-reported outcomes of a medial unicompartmental knee arthroplasty incorporating an all-polyethylene tibial component

INTRODUCTION

Biomechanical studies have suggested that proximal tibial strain is elevated in UKAs incorporating all-polyethylene tibial components with concern that this leads to premature failure. This study reports minimum 10-year outcomes for a UKA incorporating an all-polyethylene tibial component to determine whether these concerns were realised.

MATERIALS AND METHODS

109 fixed bearing UKAs (97 patients, mean age 68 (range 48-87), 54/97 (56%) female) with all-polyethylene tibial components were followed up for ≥ 10 years with Oxford Knee Scores, Forgotten Joint Scores and Kaplan-Meier analysis. 106/109 implants were 7 mm, 3 were 9.5 mm.

RESULTS

Ten-year survival was 85.5% (78.6-92.4 95% CI) with the end-point failure for any reason. Unexplained pain was the commonest mode of failure (6/17) followed by lateral compartment osteoarthritis (5/17) and tibial subsidence/loosening (4/17). Revision rate was highest at 2-5 years due to revisions for unexplained pain. Ten-year survival was worse in patients < 65 years old (p = 0.035), in those with BMI > 30 (p = 0.017) and in those with postoperative increases in medial tibial sclerosis (p < 0.001 log-rank). Implant malalignment was not significantly associated with failure. Radioisotope bone scans in 16 patients all remained "hot" at mean 6.1 years (range 2.1-11.5). Relative risk of failure in patients < 65 years was 2.9 (1.2-7.0 95% CI) and when BMI > 30 was 2.9 (1.2-6.9 95% CI). In those with intact UKAs at 10 years, mean Oxford Knee Score was 34.8 ± 10.7, Forgotten Joint Score was 37.9 ± 26.7 and 96% were satisfied with their knee.

CONCLUSION

The high rate of early failure between 2 and 5 years in this all-polyethylene tibial component UKA did not persist in the long term. Though medial proximal tibial metabolic changes appear to persist they are not necessarily symptomatic. BMI > 30 and age < 65 years were significant risk factors for revision.

Effect of lavage and brush preparation on cement penetration and primary stability in tibial unicompartmental total knee arthroplasty: An experimental cadaver study

BACKGROUND

Unicompartmental total knee arthroplasty (UKA) is a well-established treatment option for unicondylar osteoarthritis, and generally leads to better functional results than tricompartimental total knee arthroplasty (TKA). However, revision rates of UKAs are reported as being higher; a major reason for this is aseptic loosening of the tibial component due to implant-cement-bone interface fatigue. The objective of this study was to determine the effects of trabecular bone preparation, prior to implantation of tibial UKAs, on morphological and biomechanical outcomes in a cadaver study.

METHODS

Cemented UKAs were performed in 18 human cadaver knees after the bone bed was cleaned using pulsed lavage (Group A), conventional brush (Group B) or no cleaning at all (Group C, control). Morphologic cement penetration and primary stability were measured.

RESULTS

The area proportion under the tibial component without visible cement penetration was significantly higher in Group C (21.9%, SD 11.9) than in both Group A (7.1%, SD 5.8), and Group B (6.5%, SD 4.2) (P=0.007). The overall cement penetration depth did not differ between groups. However, in the posterior part, cement penetration depth was significantly higher in Group B (1.9mm, SD 0.3) than in both Group A (1.3mm, SD 0.3) and Group C (1.4mm, SD 0.3) (P=0.015). The mode of preparation did not show a substantial effect on primary stability tested under dynamic compression-shear test conditions (P=0.910).

CONCLUSION

Bone preparation significantly enhances cement interdigitation. The application of a brush shows similar results compared with the application of pulsed lavage.

Annual revision rates of partial versus total knee arthroplasty: A comparative meta-analysis

BACKGROUND

Utilization of unicompartmental knee arthroplasty (UKA) and patellofemoral arthroplasty (PFA) as alternatives to total knee arthroplasty (TKA) for unicompartmental knee osteoarthritis (OA) has increased. However, no single resource consolidates survivorship data between TKA and partial resurfacing options for each variant of unicompartmental OA. This meta-analysis compared survivorship between TKA and medial UKA (MUKA), lateral UKA (LUKA) and PFA using annual revision rate as a standardized metric.

METHODS

A systematic literature search was performed for studies quantifying TKA, MUKA, LUKA and/or PFA implant survivorship. Studies were classified by evidence level and assessed for bias using the MINORS and PEDro instruments. Annual revision rates were calculated for each arthroplasty procedure as percentages/observed component-year, based on a Poisson-normal model with random effects using the R-statistical software package.

RESULTS

One hundred and twenty-four studies (113 cohort and 11 registry-based studies) met inclusion/exclusion criteria, providing data for 374,934 arthroplasties and 14,991 revisions. The overall evidence level was low, with 96.7% of studies classified as level III-IV. Annual revision rates were lowest for TKA (0.49%, CI 0.41 to 0.58), followed by MUKA (1.07%, CI 0.87 to 1.31), LUKA (1.13%, CI 0.69 to 1.83) and PFA (1.75%, CI 1.19 to 2.57). No difference was detected between revision rates for MUKA and LUKA (p=0.222).

CONCLUSIONS

Revisions of MUKA, LUKA and PFA occur at an annual rate of 2.18, 2.31 and 3.57-fold that of TKA, respectively. These estimates may be used to inform clinical decision-making, guide patient expectations and evaluate the cost-effectiveness of total versus partial knee replacement in the setting of unicompartmental OA.

Primary stability of unicompartmental knee arthroplasty under dynamic flexion movement in human femora

BACKGROUND

The objective of our study was to evaluate the impact of a trabecular stem fixation versus a cortical teeth fixation technique on the primary stability of cemented unicompartmental femoral components under dynamic flexion movement loading conditions in human femora.

METHODS

Ten fresh-frozen human knees of a mean donor age of 73.9years were used to perform medial unicompartmental knee arthroplasty under a less invasive parapatellar surgical approach. The femora were divided into two groups of matched pairs based on comparable trabecular bone mineral density. To assess the primary stability, a new method based on a combination of dynamic flexion movement, double-peak loading simulating stair climbing, kinematic analysis of the femoral component migration relative to the bone and an evaluation of the cement layer by fragments cut through the implant-cement-bone interface in the sagittal plane of the medial condyle was introduced.

FINDINGS

For the "trabecular stem fixation" technique the mean load to failure was 2340 (SD 650) N and for "cortical teeth fixation" it was 1080 (SD 455) N, with a substantially enhanced dynamic fixation strength for the "trabecular stem fixation" (p=0.008). In the distal area the cement layer of the "trabecular stem fixation" showed a significant decreased thickness compared to the "cortical teeth fixation" (p=0.029), while a substantially deeper cement penetration (p=0.044) has been achieved for the "trabecular stem fixation".

INTERPRETATION

From our observations, we conclude that there is a significantly enhanced primary stability with a "trabecular stem fixation" compared to a "cortical teeth fixation" technique of cemented unicompartmental femoral components, in terms of dynamic failure load and migration characteristics.

Survivorship and clinical outcome of the minimally invasive Uniglide medial fixed bearing, all-polyethylene tibia, unicompartmental knee arthroplasty at a mean follow-up of 7.3years

BACKGROUND

Medial UKA performed in England and Wales represents seven to 11% of all knee arthroplasty procedures, and is most commonly performed using mobile-bearing designs. Fixed bearing eliminates the risk of bearing dislocation, however some studies have shown higher revision rates for all-polyethylene tibial components compared to those that utilize metal-backed implants. The aim of the study is to analyse survivorship and maximum eight-year clinical outcome of medial fixed bearing, Uniglide unicompartmental knee arthroplasty performed using an all-polyethylene tibial component with a minimal invasive approach.

METHODS

Between 2002 and 2009, 270 medial fixed UKAs were performed in our unit. Patients were reviewed pre-operatively, five and eight years post-operatively. Clinical and radiographic reviews were carried out. Patients' outcome scores (Oxford, WOMAC and American Knee Score) were documented in our database and analysed.

RESULTS

Survival and clinical outcome data of 236 knees with a mean of 7.3years follow-up are reported. Every patient with less than 4.93years of follow-up underwent a revision. The patients' average age at the time of surgery was 69.5years. The American Knee Society Pain and Function scores, the Oxford Knee Score and the WOMAC score all improved significantly. The five-year survival rate was 94.1% with implant revision surgery as an end point. The estimated 10years of survival rate is 91.3%. Fourteen patients were revised before the five-year follow-up.

CONCLUSION

Fixed bearing Uniglide UKA with an all-polyethylene tibial component is a valuable tool in the management of a medial compartment osteoarthritis, affording good short-term survivorship. Level of evidence IV.

The incidence of implant fractures after knee arthroplasty

PURPOSE

This study aimed to evaluate the incidence of "implant" fractures after knee arthroplasty using clinical literature and worldwide arthroplasty registers. The hypothesis was that register datasets report higher rates of these rare complications than clinical studies.

METHODS

Calculations were based on the pooled incidence of revision operations after fractures of knee arthroplasties, comparing clinical studies published in MEDLINE-listed journals and annual reports from worldwide arthroplasty registers in a structured literature analysis based on a standardized methodology.

RESULTS

Twelve clinical studies and datasets from six worldwide registers were included. Rates of fractures of knee arthroplasties were reported from 0.2 to 2.5 % in clinical studies versus 0.02-0.17 % in worldwide arthroplasty registers.

CONCLUSIONS

Fractures of knee arthroplasty systems are rare complications, with clinical studies showing higher incidence rates than worldwide arthroplasty registries. Unicompartmental knee arthroplasty (UKA) implanted before 2000, constrained primary or revision constrained total knee arthroplasties, and patellar replacements showed the highest incidence of implant fracture. The results of this analysis can help clinicians to counsel patients on potential complications following knee arthroplasty.

LEVEL OF EVIDENCE

III.

Mid-term results of Oxford phase-3 medial unicompartmental knee arthroplasty for medial arthritis in Chinese patients

BACKGROUND

The purpose of this study was to evaluate the mid-term results of an Oxford phase-3 unicompartmental knee arthroplasty (UKA) for medial arthritis in Chinese patients.

METHODS

The study included 64 patients who underwent a minimally invasive Oxford phase-3 UKA for medial knee arthritis. The patients were clinically evaluated preoperatively and at the final follow-up according to the clinical and functional components of the Knee Society Score (KSS), the Hospital for Special Surgery knee score and range of motion. A Kaplan-Meier survivorship analysis was performed with revision surgery as the end point.

RESULTS

The mean preoperative clinical KSSs increased from 63.2 to 91.4 post-operatively, and the mean functional KSSs increased from 54.9 to 86.5 post-operatively. In addition, the mean Hospital for Special Surgery scores increased from 59.5 to 86.4. The mean active knee flexion increased from 109.1° preoperatively to 123.6° post-operatively. A total of six patients (six knees) required revision surgery at the time of the maximum 10-year follow-up. Four conversions to total knee arthroplasty were performed because of arthritis progression in the lateral compartment. One revision to total knee arthroplasty was performed for aseptic loosening, and one liner exchange was performed for wear. The cumulative survival rates at the 6- and 8-year follow-ups were 97% and 93%, respectively.

CONCLUSION

Oxford phase-3 UKA was largely applicable for medial arthritis in Chinese patients. However, the Oxford phase-3 medial UKA selection criteria for young Chinese males need further exploration to obtain the best treatment effect.

Development and clinical application of meniscal unicompartmental arthroplasty

About one-third of osteoarthritic patients requiring knee replacement have focal lesions limited mainly to the medial compartment and can achieve excellent postoperative function after medial unicompartmental replacement. However, late failures of many unicompartmental prostheses require revision at a rate about twice that of total knee replacement. The use of a fully conforming mobile-bearing meniscal unicompartmental prosthesis in the hands of experienced surgeons can reduce revision rates to levels equivalent to the best results achieved with total knee replacement. The paper argues the case for such a prosthesis and demonstrates that the usual modes of failure of unicompartmental arthroplasty, most of them biomechanical, can thereby be avoided.

Hydrogels as a Replacement Material for Damaged Articular Hyaline Cartilage

Hyaline cartilage is a strong durable material that lubricates joint movement. Due to its avascular structure, cartilage has a poor self-healing ability, thus, a challenge in joint recovery. When severely damaged, cartilage may need to be replaced. However, currently we are unable to replicate the hyaline cartilage, and as such, alternative materials with considerably different properties are used. This results in undesirable side effects, including inadequate lubrication, wear debris, wear of the opposing articular cartilage, and weakening of the surrounding tissue. With the number of surgeries for cartilage repair increasing, a need for materials that can better mimic cartilage, and support the surrounding material in its typical function, is becoming evident. Here, we present a brief overview of the structure and properties of the hyaline cartilage and the current methods for cartilage repair. We then highlight some of the alternative materials under development as potential methods of repair; this is followed by an overview of the development of tough hydrogels. In particular, double network (DN) hydrogels are a promising replacement material, with continually improving physical properties. These hydrogels are coming closer to replicating the strength and toughness of the hyaline cartilage, while offering excellent lubrication. We conclude by highlighting several different methods of integrating replacement materials with the native joint to ensure stability and optimal behaviour.

Why Do Medial Unicompartmental Knee Arthroplasties Fail Today?

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Systematic review of medial versus lateral survivorship in unicompartmental knee arthroplasty

BACKGROUND

Unicompartmental knee arthroplasty (UKA) has gained popularity in patients with isolated unicompartmental osteoarthritis. To our knowledge no systematic review has assessed and compared survivorship of medial and lateral UKA. We performed a systematic review assessing medial and lateral UKA survivorship and comparing survivorship in cohort studies and registry-based studies.

METHODS

A search was performed using PubMed, Embase and Cochrane systems. Ninety-six eligible studies reported survivorship, of which fifty-eight reported medial and sixteen reported lateral UKA survivorship. Nineteen cohort studies and seven registry-based studies reported combined medial and lateral survivorship.

RESULTS

The five-year, ten-year and fifteen-year medial UKA survivorship was 93.9%, 91.7% and 88.9%, respectively. Lateral UKA survivorship was 93.2%, 91.4% and 89.4% at five-year, ten-year and fifteen-year, respectively. No statistical difference between both compartments was found. At twenty years and twenty-five years survivorship of medial UKA was 84.7% and 80%, respectively, but no studies reported lateral UKA survivorship at these follow-up intervals. Survivorship of cohort studies was not significantly higher compared to registry-based studies at five years (94.3 vs. 91.7, respectively, p=0.133) but was significantly higher at ten years (90.5 vs. 84.1, p=0.015).

CONCLUSION

This is the first systematic review that shows no difference in the five-, ten- and fifteen-year survivorship of medial and lateral UKA. We found a lower survivorship in the registry-based studies compared to cohort studies.

Tibial baseplate positioning in robotic-assisted and conventional unicompartmental knee arthroplasty

This study compared tibial baseplate alignment (TBA) between robotic-arm-assisted (RAA) and conventional (CONV) unicompartmental knee arthroplasties (UKAs). We hypothesized that RAA would increase the percentage of implants within a predetermined safe zone (SZ). We identified 177 CONV and 87 RAA UKAs through our center's patient registry. Two individuals reviewed postoperative knee radiographs and determined TBA. Coronal baseplate positioning was more accurate (i.e., within the SZ) for RAA (2.6° ± 1.5° vs. 3.9° ± 2.4°, p < 0. 0001). Conversely, sagittal alignment was more accurate for CONV (4.9° ± 2.8° vs. 2.4° ± 1.6°, p < 0.0001). RAA was more precise in both planes (p < 0.0001). There was no difference in the percentage of implants within the SZ between the two groups (p = 1.0).

[Modern unicondylar knee arthroplasty. Tips and tricks]

BACKGROUND

Unicondylar knee arthroplasty (UKA) is an established therapeutic option for advanced medial or lateral gonarthrosis.

OBJECTIVES

The cornerstones of a successful UKA, careful patient selection, preoperative planning and precise operation technique, are discussed in this overview article.

IMPORTANCE

In contrast to total knee arthroplasty, UKA allows preservation of the contralateral and patellofemoral compartments as well as the cruciate ligaments and is often associated with rapid postoperative recovery, improved knee kinematics and knee function. However, UKA is technically very demanding. High revision rates have been reported in particular with widespread application, according to national joint replacement registries.

CONCLUSION

Successful UKA relies on meticulous patient selection, preoperative planning and surgical technique. It is justified to broaden classic UKA indications. In medial and lateral UKA three types of mechanical varus-valgus deformity can be encountered: type 1 (isolated intraarticular deformity), type 2 (pronounced deformity due to extraarticular varus deformity in medial UKA or valgus deformity in lateral UKA), type 3 (reduced deformity due to extraarticular valgus deformity in medial UKA or varus deformity in lateral UKA). We believe these deformities should be addressed accordingly with surgical technique.

Causes of revision following Oxford phase 3 unicompartmental knee arthroplasty

PURPOSE

Revision of unicompartmental knee arthroplasty (UKA) is relatively rare, but there is concern that the minimally invasive approach might result in more complications and a higher rate of revision. Current data regarding the revision of UKA using the Oxford phase 3 prosthesis are confined to a few reviews of single-institution experience. The purpose of this study was to provide an evidence-based summarisation of the revision of UKA with a pooled analysis of the reported cases.

METHODS

A systematic review of published studies that evaluated the causes that required further surgical intervention after UKA using the Oxford phase 3 prosthesis was performed. A structured literature review of multiple databases referenced articles from 1998 to 2012. The revision rates between Asian population and western population were compared.

RESULTS

A total of 2,683 patients (3,138 knees) from 17 published studies were assessed. The median age of the patients was 62.5 (range 32-93) years. The median follow-up period was 5.6 (range 0.1-11) years. Postoperative revision was necessary in 146 knees with a pooled percentage of 4.6 %. Bearing dislocation was found to be the single most important predisposing cause of revision, with a pooled percentage of 1.5 % (47/3,138 knees). The rate of bearing dislocation was significantly higher in Asian population than that in western population (p < 0.001).

CONCLUSIONS

Mobile bearing UKA seems to be less appropriate for the Asian population as extreme knee flexion is required for cultural purposes.

Patient-specific instrumentation and return to activities after unicondylar knee arthroplasty

In the past decade, there has been a major increase in the use of unicompartmental knee arthroplasty (UKA) as surgical techniques have been refined and patient selection has improved. UKAs now account for 8% to 10% of knee arthoplasty procedures. Recent studies have suggested excellent medium- and long-term results of UKA. Overall, results have shown 85% to 90% survivorship at 10 years, with 90% of patients reporting good to excellent subjective and objective outcomes. Recent studies suggest that unicompartmental arthroplasty allows a high percentage of patients to return to presurgical sport and activity participation.

Primary stability of unicompartmental knee arthroplasty under dynamic compression-shear loading in human tibiae

BACKGROUND

The objective of our study was to evaluate the impact of a single- ("implant only") versus a double-layer ("implant & bone") cementing technique on the primary stability of unicompartmental tibial plateaus under dynamic compression-shear loading conditions in human tibiae.

METHODS

Twelve fresh-frozen human knees of a mean donor age of 72.3 years were used to perform medial UKA under a less invasive parapatellar surgical approach. The tibiae were divided into two groups of matched pairs based on comparable trabecular bone mineral density. To assess the primary stability, a new method based on a combination of dynamic compression-shear testing, kinematic analysis of the tibial plateau migration relative to the bone and evaluation of the cement layer by CT-scans and fragments cut through the implant-cement-bone interface in the frontal plane was introduced.

FINDINGS

For the "implant only" cementation technique the mean load to failure was 2600 (SD 675) N and for "implant & bone" it was 2820 (SD 915) N. Between the final load level at failure and the bone mineral density a significant correlation was found for the groups "implant only" (r(s) = 0.875) and "implant & bone" (r(s) = 0.907).

INTERPRETATION

From our observations, we conclude that there is no significant difference between a single- ("implant only") and double-layer ("implant & bone") cementing technique in the effect on the primary stability of unicompartmental tibia plateaus, in terms of failure load, correlation between final load at failure and bone mineral density, migration characteristics, cement layer thickness and penetration depth.

Common causes of failed unicompartmental knee arthroplasty: a single-centre analysis of four hundred and seventy one cases

PURPOSE

We performed this retrospective study to determine the main causes for early and late failures of unicompartmental knee arthroplasty (UKA).

METHODS

Between January 2000 and March 2012, all patients treated for a failed medial UKA in the authors' institution were retrospectively reviewed. A total of 471 patients were identified, and causes of failure were analysed based on the medical records and radiographs at the time of revision.

RESULTS

The cohort included 161 males and 310 females, with a mean age of 67.7 years (range, 42-91 years; SD = 10.1) at the time of revision. The mean time from index arthroplasty to revision surgery was 6.1 years (range, 0.1-27.9 years; SD = 5.6). A total of 254 cases (53.9 %) failed within five years after primary implantation, and 108 cases (22.9 %) failed after ten years. The major reason for failure was the development of other compartment arthritis (39.5 %), followed by aseptic loosening (25.4 %).

CONCLUSIONS

Of importance, the mean time to failure after UKA was 6.1 years, with more than 50 % of failures occurring within the first five years postoperatively.

Revision of unicompartmental knee arthroplasty: implants used and causes of failure

Objective

to determine the causes of unicondylar knee arthroplasty failures, as well as identify the implants used and the need of bone grafting in patients undergoing revision UKA in Center of Knee Surgery at the Instituto Nacional de Traumatologia e Ortopedia (INTO) in the period between January 1990 and January 2013.

Methods

a retrospective analysis of the medical documentation and imaging, determining the cause of failure of UKA and the time of its occurrence, as well as prosthetic components implanted during the review and the need for bone grafting.

Results

in this study, 27 UKA failures in 26 patients were included. Collapse of one or more components was the main cause of failure, occurring in 33% of patients. Aseptic failure was identified in 30% of cases, progression of osteoarthrosis in 15%, infection and pain 7% each, and osteolysis and polyethylene failure in 4% each. Early failure occurred in 41% of all revisions of UKA and late failure in 59%. 23 patients have undergone revision of UK.

Conclusion

in 35% of revisions the use of bone grafting was needed in tibial area; in 3 cases we needed allograft from Tissue Bank. We did not use metal increase in any of the revision. In one patient we used implant constraint for instability.

A flat all-polyethylene tibial component in medial unicompartmental knee arthroplasty: a long-term study

PURPOSE

The aim of this study is to present the clinical and radiological results of a cemented unicompartmental knee arthroplasty (UKA) using a flat all-polyethylene tibial component at long-term follow-up, in a homogeneous group of patients with medial femoro-tibial knee arthritis.

METHODS

The study group included 53 knees in 51 patients who were treated between January 1998 and November 1999 using a flat all-polyethylene tibial component. The same surgical technique was used for all patients. Inclusion criteria included a diagnosis of atraumatic arthritis, pre-operative flexion greater than 100° with no flexion deformity, a varus deformity of less than 10°, and a body mass index (BMI) less than 35. A neutral mechanical axis was considered the end-point in all interventions. The patients were assessed clinically using the International Knee Society (IKS) and the functional scores at follow-up. Plain radiographs were used to determine the alignment of the mechanical axis at 5, 10 and 14.7-year follow-up. A radiographic analysis of loosening, based on the method described by the IKS, was performed and the degree of arthritic progression in the non-resurfaced compartment was also assessed.

RESULTS

At latest follow-up five patients had died and the data for three patients had not been collected. At final review four knees had undergone revision surgery and a further patient had declined a recommended revision TKA. The main indication for revision surgery was progressive aseptic loosening of the tibial component in female patients. No revisions were required because of arthritic progression in the lateral compartment. Over time the clinical outcomes did not show statistically significant differences. There was a significant worsening of the mechanical axis at the last follow-up compared with the results at five and ten year review.

CONCLUSIONS

This study demonstrated that, in primary arthritis involving the medial femoro-tibial compartment, UKA using a flat all-polyethylene component could be considered an effective surgical option. Attention should be paid to progressive worsening of the mechanical axis over time associated with progressive radiolucency especially in female patients.

LEVEL OF EVIDENCE

IV.

Medium to long-term results of the UNIX uncemented unicompartmental knee replacement

INTRODUCTION

We report the first non-designer study of the Unix uncemented unicompartmental knee prosthesis.

MATERIALS AND METHODS

Eighty-five consecutive UKRs were carried out with sixty-five available for follow-up. Oxford Knee Scores, WOMAC questionnaire and radiological assessment were completed.

RESULTS

The mean Oxford Knee Score was thirty-eight and WOMAC Score was twenty. Overall Kaplan Meier survival estimate is 76% (95% confidence interval 60%-97%) at 12years and 88% (95% confidence interval 76-100%) with aseptic loosening as the endpoint. Radiographic assessment showed lysis in the tibia in 6% of patients with no lysis evident around the central fin.

DISCUSSION

Survivorship is comparable to other published series of UKRs. We suggest the central fin design is key to dissipating large forces throughout the proximal tibia, resulting in low levels of tibial loosening. Level of evidence IV.

Results and outcomes of unicompartmental knee arthroplasty

Precise outcome evaluation is mandatory to improve analysis of the results of knee replacement procedures. Patients' expectations toward surgery and activity levels have increased with changes in patient populations and improvement of surgical results. It is difficult, however, to accurately assess outcomes because objective evaluation of patient function performed only by a surgeon remains highly inaccurate. New methods of objective evaluation after unicompartmental knee arthroplasty have been developed. These devices provide information about range of motion and patient function during daily activities. This article provides up-to-date information concerning the different tools of function evaluation after unicompartmental knee arthroplasty.

Cementless unicondylar knee arthroplasty

Cementless fixation is an increasingly popular option in unicondylar knee arthroplasty (UKA). Early cementless UKAs suffered from unreliable fixation and uptake of cementless UKA was limited. However, modern designs of cementless UKA have demonstrated excellent results with improved radiographic appearances when compared with cemented implants. This is supported by early joint registry data, which demonstrate a survival advantage with cementless fixation in one design of UKA. This review explains the rationale for cementless UKA, summarizes the results from published trials, and highlights technical aspects points to be aware of when implanting cementless UKA.

Simultaneous versus staged bilateral unicompartmental knee replacement

We prospectively followed 171 patients who underwent bilateral unicompartmental knee replacement (UKR) over a period of two years. Of these, 124 (72.5%) underwent a simultaneous bilateral procedure and 47 (27.5%) underwent a staged procedure. The mean cumulative operating time and length of hospital stay were both shorter in the simultaneous group, by 22.5 minutes (p < 0.001) and three days (p < 0.001), respectively. The mean reduction in haemoglobin level post-operatively was greater by 0.15 g/dl in the simultaneous group (p = 0.023), but this did not translate into a significant increase in the number of patients requiring blood transfusion (p = 1.000). The mean hospital cost was lower by $8892 in the simultaneous group (p < 0.001). There was no significant difference in the rate of complications between the groups, and at two-year follow-up there was no difference in the outcomes between the two groups.

We conclude that simultaneous bilateral UKR can be recommended as an appropriate treatment for patients with bilateral medial compartment osteoarthritis of the knee.

Cite this article: Bone Joint J 2013;95-B:788–92.

Clinical and technical factors influencing outcomes of unicompartmental knee arthroplasty: Retrospective multicentre study of 944 knees

INTRODUCTION

Unicompartmental knee arthroplasty (UKA) is reserved for osteoarthritis confined to a single femoro-tibial compartment with an intact anterior cruciate ligament. UKA remains controversial. The objective of this retrospective multicentre study in a large sample was to assess the influence of age, sex, body mass index (BMI), patellofemoral involvement, and implant design on functional outcomes and prosthesis survival rates.

MATERIAL AND METHODS

Nine hundred and forty-four patients who underwent UKA at centres located in western France between 1988 and 2008 were re-evaluated. The IKS scores and KOOS were determined. Prosthesis survival according to various factors was assessed using the Kaplan-Meier method.

RESULTS

A clinical evaluation was performed in 720 cases after a mean follow-up of 62 months. The IKS function score improved by 23.6 points in men and 17.3 points in women (P=0.007). Ten-year prosthesis survival was 83.7% overall; 79% in women versus 87% in men (P<0.01); and 76.7% in patients younger than 70 years versus 88.3% in those 70 years or over (P<0.01). BMI had no significant influence on prosthesis survival. No significant differences between clinical outcomes or prosthesis survival were found across implant design categories.

DISCUSSION

The retrospective design and large number of centres and surgeons mandate caution when interpreting our results. Subgroup sizes were too small for an analysis of factors such as anterior cruciate ligament deficiency, BMI>40 kg/m(2), or cementless implant.

LEVEL OF EVIDENCE

Level IV, retrospective study.

The impact of a high tibial valgus osteotomy and unicondylar medial arthroplasty on the treatment for knee osteoarthritis: a meta-analysis

PURPOSE

Both high tibial valgus osteotomy (HTO) and unicompartmental medial knee arthroplasty (UKA) are established methods for the treatment for moderate stages of OA. This is the first global meta-analysis to compare the long-term effects of both methods regarding survival, outcomes and complications of total arthroplasty.

METHODS

Literature research was performed using established medical databases: MEDLINE (via PubMed), EMBASE (via OVID) and the Cochrane register. Criteria for inclusion were as follows: English or German papers, a clinical trial with a clear description of survival, an outcome evaluation using a well-described knee score and a follow-up >5 years. Statistical analysis was performed using the special meta-analysis software called "Comprehensive Meta Analysis" (version 2.0; Biostat, Englewood, NJ, USA).

RESULTS

Final meta-analysis after the full-text review included 46 studies about valgus HTO and 43 studies about medial UKA. There were no significant differences between valgus HTO and medial UKA in terms of the number of total required replacements. After a 5- to 8-year follow-up, 91.0% of the valgus HTO patients and 91.5% of medial UKA patients did not need a total replacement. This value was 84.4% for valgus HTOs and 86.9% for medial UKAs after a 9- to 12-year follow-up. Mean survival time to TKA was 9.7 years after valgus HTO and 9.2 years after medial UKA. Clinical outcome was significantly better after medial UKA in a 5- to 12-year follow-up. After more than 12 years, results were comparable in both groups. No significant differences were seen in the complication rates.

CONCLUSIONS

This meta-analysis aimed to find the advantages and disadvantages of two established methods for the treatment for medial compartment knee osteoarthritis. Valgus HTO is more appropriate for younger patients who accept a slight decrease in their physical activity. Medial UKA is appropriate for older patients obtaining sufficient pain relief but with reduced physical activity.

LEVEL OF EVIDENCE

II.

Long-term survivorship and failure modes of unicompartmental knee arthroplasty

BACKGROUND

In a previously reported series of 51 patients with 62 cemented, fixed-bearing unicompartmental knee arthroplasties, we reported a 10-year, 98% survival rate with an average knee score of 92 points. The survivorship and modes of failure past 10 years are incompletely understood.

QUESTIONS/PURPOSES

At 15-year followup we sought to determine (1) the overall durability and survivorship of this design; (2) modes of failure; and (3) the progression of arthritis in the nonresurfaced compartments.

METHODS

Nineteen knees in 16 patients were available for study with 34 patients lost to death and one lost to followup. At 15 years, we analyzed the Kaplan-Meier survivorship as well as durability with regard to radiographic loosening and knee scores, determined modes of failure, and assessed radiographs for degeneration in the nonresurfaced compartments.

RESULTS

Fifteen-year survivorship was 93% and 20-year survivorship was 90%. Four of 62 knees were revised to total knee arthroplasty at a mean of 144 months. One knee was revised for patellofemoral and lateral compartment degeneration, one for lateral compartment degeneration, one for polyethylene disengagement and metallosis, and one for pain of unclear etiology. No patients had aseptic loosening or osteolysis. The mean knee score was 78 at latest followup. Arthritic progression in the nonresurfaced compartments was common although symptomatic in only two patients.

CONCLUSIONS

With this cemented, fixed-bearing design, the failure rates were low, there were no cases of failure secondary to wear or loosening, and the survivorship was similar to that reported for total knee arthroplasty.

Unicompartmental versus total knee arthroplasty database analysis: is there a winner?

BACKGROUND

TKA and unicompartmental knee arthroplasty (UKA) are both utilized to treat unicompartmental knee arthrosis. While some surgeons assume UKA provides better function than TKA, this assumption is based on greater final outcome scores rather than on change in scores and many patients with UKA have higher preoperative scores.

QUESTIONS/PURPOSES

We therefore asked whether TKA would demonstrate (1) better change in clinical outcome scores from preoperative to postoperative states and (2) better survivorship than UKA.

METHODS

We evaluated 4087 patients with 5606 TKAs and 179 patients with 279 UKAs performed between 1978 and 2009. Patients with TKA were older and heavier than patients with UKA (mean age, 68 versus 66 years; mean BMI, 32 versus 29). We compared preoperative, latest postoperative, and change in Knee Society Clinical Rating System (KSCRS), SF-12, and WOMAC scores. Minimum followup was 2 years (UKA: mean, 7 years; range, 2.0-23 years; TKA: mean, 6.5 years; range, 2.0-33 years). Preoperative outcome measure scores (WOMAC, SF-12, KSCRS) were higher in the UKA group.

RESULTS

Patients with UKA had higher postoperative KSCRS and SF-12 mental scores. Changes in score for all WOMAC domains were similar between groups. Total KSCRS changes in score were similar between groups, although patients with TKA had higher knee scores (49 versus 43) but lower function scores than UKA (21 versus 26). Cumulative revision rate was higher for UKA than for TKA (13% versus 7%). Kaplan-Meier survivorship at 5 and 10 years was 95% and 90%, respectively, for UKA and 98% and 95%, respectively, for TKA.

CONCLUSIONS

While patients with UKA had higher pre- and postoperative scores than patients with TKA, the changes in scores were similar in both groups and survival appeared higher in patients with TKA.

Outcomes of unicompartmental knee arthroplasty stratified by body mass index

Patients who have high body mass indices can have disabling medial compartment knee osteoarthritis, which might benefit from unicompartmental knee arthroplasty (UKA). The purpose of this study was to compare clinical and radiographic outcomes of UKAs in patients with body mass indices (BMIs) greater and less than 35 kg/m(2). Thirty-four patients (40 knees) had BMIs of 35 kg/m(2) or greater, whereas the remaining 33 patients (40 knees) had BMIs below 35 kg/m(2), with 2-year minimum follow-up. In the high-BMI group, 5 knees were revised to total knee arthroplasty, compared with none in the lower BMI group. Knee Society scores were lower in the surviving high-BMI knees. All surviving components were radiographically stable. The results suggest that UKA should be approached with caution in patients who have high BMIs.

Mobile or fixed unicompartmental knee prostheses? In-vitro wear assessments to solve this dilemma

The unicompartmental knee prosthesis is an attractive alternative to total knee arthroplasty. Current UKP devices can be subdivided into two groups based on different design principles: fixed bearing knees, where the ultra-high molecular weight polyethylene meniscal component snap or press fits into the tibial tray, and mobile bearing designs which facilitate movement of the insert relative to the tray. The present study was aimed at comparing the in-vitro wear behaviour of fixed and mobile unicompartmental knee menisci under two configurations: the femoral components were cemented into a custom-made metallic block or, as a novelty of the present study, into a synthetic femur (i.e. under conditions which should better reproduce the in-vivo behaviour). Analyses were performed using a displacement-control knee wear simulator with "three-plus-one" stations. All the kinematics tests were set in accordance with the ISO 14243-1,2,3. Fixed and mobile polyethylene menisci showed a different wear behaviour: the fixation-frame influenced directional load transfer through each component in a qualitative and quantitative way. In fact, gravimetric results showed that under the metal block holder fixation, mobile components worn more than fixed components (weight losses of 8.7±2.0 mg and 2.6±1.09 mg, respectively); on the other hand, under the synthetic femur configuration, differences in wear behaviour were less pronounced and mobile menisci underwent a slightly lower weight loss than fixed components (4.5±2.2 mg vs. 6.7±1.4 mg). This different trend was explained in relation to the kinematic schemes of the two fixation methods. Raman spectroscopy, used to evaluate the UHMWPE crystallinity changes induced by mechanical stress, showed that mobile menisci specimens were more affected than the fixed components in both their superior and inferior surfaces, independent of the fixation-frame. In conclusion, if tested under conditions which should better reproduce the in-vivo behaviour, mobile UKPs did not show a worse wear behaviour than fixed components in terms of weight losses, although UHMWPE changes at the molecular scale could be detrimental.

The practice of unicompartmental knee arthroplasty in the United Kingdom

PURPOSE

To survey the current practice of unicompartmental knee arthroplasty (UKA) in the United Kingdom.

METHODS

Questionnaires were sent to all 341 local members of the British Association for Surgery of the Knee to inquire into their practice of UKA, including clinical indications, preoperative investigations, surgical approach, preferences in implant design, and the role of UKA in relation to high tibial osteotomy.

RESULTS

56% of respondents performed less than 16 UKAs per year, whereas 16.5% performed over 30 per year. 89.5% of the respondents used anteroposterior radiographs as their main investigation tool. Only 30% and 16.5% used posteroanterior 30 degrees flexion and varus/valgus stress radiographs, respectively, despite being better investigation tools. 57% considered arthroscopy, despite its invasive nature. The main contra-indications to UKA were anterior cruciate ligament deficiency with instability (95%), focal grade-III osteoarthritis in the contralateral compartment (87%), and osteoporosis with rheumatoid arthritis (80.5%), but only 59% of respondents considered an inability to passively correct a pre-existing varus or valgus deformity as a contra-indication. 51.5% of respondents preferred minimally invasive approach, 96% preferred cemented fixation, and over two thirds used the mobile bearing design. 72% of respondents expressed preference for total knee arthroplasty over UKA in localised lateral compartment osteoarthritis.

CONCLUSION

Modern UKA has gained popularity in properly selected patients with localised medial compartment osteoarthritis, provided the knee is not anterior cruciate ligament deficient and any deformity is passively correctable.

Polyethylene insert damage in unicondylar knee replacement: a comparison of in vivo function and in vitro simulation

Modification of knee joint wear simulation methods has included 'anatomic attachment' of unicondylar knee replacements (UKR) onto synthetic femurs with material properties and morphology similar to human femurs. The present study assesses the effect of such modification by comparing the damage patterns on UKR polyethylene inserts after in vitro simulation using standard and modified simulation methods with those on inserts retrieved after in vivo function. Three groups of UKR inserts were evaluated after retrieval (Explant Group, n = 17) or after knee joint wear simulation with the components attached to standard metal blocks (Standard Group, n = 6) or synthetic femurs (Anatomic Group, n = 6). All UKR had similar non-conforming articular surfaces. Articular damage patterns (mode, frequency, and area) were quantified using digital image photogrammetry. Although some common damage modes were noted, knee joint wear simulation with standard or 'anatomic' attachment did not generate damage pattern sizes similar to the explanted UKR. A focal damage pattern consistent with contact between the metal femoral articular surface and the polyethylene inserts was evident on all inserts, but only the Explant Group had evidence of dispersed damage dominated by abrasive modes. Synthetic femurs added complexity to the wear simulation without generating wear patterns substantially more similar to those observed on retrieved inserts.