A review of current literature describes varying 10-year survival rates for the Oxford Unicompartmental Knee Replacement (Biomet Orthopedics Inc, Warsaw, Ind). Application of rigorous indications and meticulous surgical technique are two factors considered to reduce revision rates. A retrospective case-note review was conducted for 96 patients (128 knees) aged 42–89 (mean 57) who had an Oxford unicompartmental knee replacement for medial compartment osteoarthritis between January 2000 and January 2011. All procedures were performed, or directly supervised, by one 5 surgeons. The aim of the study was to ascertain the rate of revision to bicompartmental knee replacement and any associated contributory factors. Of the 128 unicompartmental knees, 10.9% were revised to either mobile- or fixed-bearing total knee replacements due to septic (0.5%) and aseptic (1.5%) loosening, patello-femoral pain (3.9%), periprosthetic fracture (0.8%) and bearing dislocation (3.1%). Of those knees requiring revision, mean patient age was 73 years, 50% had wound complications and 42% were performed by senior trainees. All patients had intact ACL and medial osteoarthritis. Mean time to revision was 2.7 years. In conclusion, revision of the unicompartmental knee was related to patient age > 65 years and early post-operative complications; grade of operating surgeon had little apparent effect

Introduction. Minimally invasive implanted unicompartmental knee arthroplasty (UKA) leads to excellent functional results. Due to the reduced intraoperative visibility it is difficult to remove extruded bone cement particles, as well as bone particles generated through the sawing. These loose third body particles are frequently found in minimally invasive implanted UKA. The aim of this study was to analyse the influence of bone and cement particles on the wear rate of unicompartmental knee prostheses in vitro. Material & Methods. Fixed- bearing unicompartmental knee prostheses (n = 3; Univation F®, Aesculap, Tuttlingen) were tested with a customized four-station servo-hydraulic knee wear simulator (EndoLab GmbH, Thansau, Germany) reproducing exactly the walking cycle as specified in ISO 14243-1:2002. After 5.0 million cycles crushed cortical bone chips were added to the test fluid for 1.5 million cycles to simulate bone particles, followed by 1.5 million cycles blended with PMMA- particles (concentration of the third-body particles: 5g/l; particle diameter: 0.5- 0.7 mm). Every 500 000 cycles the volumetric wear rate was measured (ISO 14243-2) and the knee kinematics were recorded. For the interpretation of the test results we considered four different phases: breaking in- (during the first 2.0 million cycles), the steady state- (from 2.0 million to 5 million cycles), bone particle- and cement particle phase. Finally, a statistical analysis was carried out to verify the normal distribution (Kolmogorov-Smirnov test), followed by direct comparisons to differentiate the volumetric wear amount between the gliding surfaces (paired Student's t-test, p<0.05). Results. The wear rate was 12.5±0.99 mm. 3. /mio. cycles in the breaking-in phase and decreased during the steady state phase to 4.4±0.91 mm. 3. /mio cycles (not significant, p = 0,3). The bone particles did not have any influence on the wear rate (3.0±1.27 mm. 3. /mio cycles; p = 0,83) compared to the steady state phase. The cement particles, however, lead to a significantly higher wear rate compared to the steady state phase (25.0±16.93 mm. 3. /mio cycles; p<0.05). Discussion. To our knowledge this is the first study demonstrating that free cement debris which can be found after minimally invasive implanted UKA increases significantly the wear- rate. Bone particles generated for instance through sawing during implantation, however, had no influence on the prostheses wear rate. Our Data suggests, that it is extremely important to remove all the extruded cement debris accurately during implantation in order to avoid a higher wear rate which could result in an early loosening of the prostheses

INTRODUCTION. Computer-aided systems have been developed recently in order to improve the precision of implantation of unicompartmental knee replacement (UKR). Minimal invasive techniques may decrease the surgical trauma related to the prosthesis implantation, but there might be a concern about the potential for a loss of accuracy. Mobile bearing prostheses have been developed to decrease the risk of polyethylene wear, but are technically more demanding. Navigation might help to compensate for these difficulties. We wanted to combine the theoretical advantages of the three different techniques by developing a navigated, minimal invasive, mobile bearing unicompartmental knee prosthesis. MATERIAL AND METHODS. 160 patients have been operated on at our institution with this system. The 81 patients with more than 2 year follow-up have been re-examined. Complications have been recorded. The clinical results have been analyzed according to the Knee Society Scoring System. The subjective results have been analyzed with the Oxford Knee Questionnaire. The accuracy of implantation has been analyzed on post-operative antero-posterior and lateral long leg X-rays. The 2-year survival rate has been calculated. RESULTS. We observed 8 complications related to the implant or the operative technique: 2 cases of meniscus instability (1 revision to TKR, 1 bearing exchange); 2 cases of tibia loosening (revised to TKR), 2 cases of femoral loosening (revised to TKR), 1 case of lateral disease progression (revised to TKR), 1 case of unexplained pain syndrome (revised to TKR). The mean Knee Score was 93 points, 44% had the maximum of 100 points, and only 10% have less than 85 points. The mean pain score was 48 points/50. The mean flexion angle was 128°, and 60% had at least 130° of knee flexion. The mean Function Score was 97 points, 84% have the maximum of 100 points, and only 5% had less than 85 points. The mean Oxford Knee Questionnaire score was 19 points (best result: 12 points, worst result: 60 points). Expected limb axis correction was obtained in 77% of the cases. 62% of the cases had an optimally implanted prosthesis for all studied criteria. The 2-year survival rate was 97%. DISCUSSION. Most of the revision cases were related to technical difficulties during the development phase. Fixation of the implant has been improved, and some imprecise steps of the software have been corrected. Since these changes occurred, no severe early complication related to implant or software has been observed. The current implant is considered reliable, and the current minimal invasive navigated technique is considered reliable as well

To our knowledge in medial unicompartmental knee arthroplasty (UKA) no study has specifically assessed the difference in outcome between matched gender groups. Previous unmatched gender studies have indicated more favourable results for women.

Joint registries report that 25–40% of UKR revisions are performed for pain. Proximal tibial strain and microdamage are possible causes of this “unexplained” pain. The aim of this study was to examine the effect of UKR implant design and material on proximal tibial cortical strain and cancellous microdamage.

Composite Sawbone tibias were implanted with cemented UKR components: 5 fixed bearing all-polyethylene (FB-AP), 5 fixed bearing metal backed (FB-MB), and 5 mobile bearing metal backed implants (MB-MB). Five intact tibias were used as controls. Tibias were loaded in 500N increments to 2500N. Cortical surface strain was measured using digital image correlation (DIC). Cancellous microdamage was measured using acoustic emission (AE), a technique which detects elastic waves produced by the rapid release of energy during microdamage events.

DIC showed significant differences in anteromedial cortical strain between implants at 1500N and 2500N in the proximal 10mm only (p<0.001) with strain shielding in metal backed implants. AE showed significant differences in cancellous microdamage (AE hits), between implants at all loads (p=0.001). FB-AP implants displayed significantly more hits at all loads than both controls and metal backed implants (p<0.001). FB-AP implants also differed significantly by displaying AE hits on unloading (p=0.01), reflecting a lack of implant stiffness. Compared to controls, the FB-AP implant displayed 15x the total AE hits, the FB-MB 6x and the MB-MB 2.7x. All-polyethylene medial UKR implants are associated with greater cancellous bone microdamage than metal backed implants even at low loads.

Unicompartmental knee osteoarthritis can be treated with either Total Knee Arthroplasty (TKA) or Unicompartmental Knee Arthroplasty (UKA) and controversy remains as to which treatment is best. UKA has been reported to offer a variety of advantages, however many still see it as a temporary procedure with higher revision rates. We aimed to clarify the role of UKA and evaluate the long-term and revision outcomes. We retrospectively reviewed the pain, function and total Knee Society Score (KSS) for 602 UKA and 602 TKA in age and gender matched patients over ten years. The total pre-operative KSS scores were not significantly different between UKA and TKA (42.67 vs 40.54 P=0.021). KSS (pain) was significantly better in the TKA group (44.39 vs 41.38 P= 0.007) at one year and at five years post-operatively (45.33 vs 43.12 P=0.004). There was no statistically significant difference for KSS (total) in TKA and UKA during the study period. 16.3% of UKA and 20.1% of TKA had a documented complication. 79 UKA (13%) and 36 TKA (6%) required revision surgery. Despite the higher revision rate, pre-operative KSS (total) before revision was not significantly different between UKA and TKA (42.94 vs 42.43 P=0.84). Performance for UKAs was inferior to TKAs in Kaplan-Meier cumulative survival analysis at 10 years (P<0.001). Both UKA and TKA are viable treatment options for unicompartmental knee osteoarthritis, each with their own merits. UKA is associated with fewer complications whereas TKA provides better initial pain relief and is more durable and less likely to require revision

Introduction. Unicompartmental knee arthroplasty (UKA) in patients with isolated medial osteoarthritis of the knee is nowadays a standard procedure with good results, especially with the minimally-invasive approach. However, the survival rate of the unicompartmental knee prostheses is inferior to that of total knee prostheses. Therefore, further studying of UKA is still necessary. In most mobile bearing designs the femoral component has a spherical surface and therefore its positioning is not crucial. The role of the tibial slope in UKA has not been investigated so far. The manufacturers recommend tibial slopes with values between 10° positive slope and 5° negative slope. Most surgeons try to reconstruct the anatomical slope with a high failure by measuring the slope on x-rays. The aim of this study was to investigate the influence of the tibial slope on the wear rate of a medial UKA. Materials and methods. In vitro wear simulation of medial mobile bearing unicompartmental knee prosthesis with a spherical femoral surface (Univation ®) was performed with a customized four-station servo-hydraulic knee wear simulator (EndoLab GmbH, Thansau, Germany) reproducing exactly the walking cycle as specified in ISO 14243–1:2002(E). The tibial tray was inserted with 2 different medial tibial slopes: 0°, 8° (n=3 for each group). The lateral tibial slope of the space-holder was not changed (0° for every group). We performed a total of 5 million cycles for every different slope, the gravimetric wear rate was determined gravimetrically using an analytical balance every 500 000 cycles according to the ISO 14243–2. Results. The wear rate in the 0° slope group was 3.46±0.59 mg/million cycles, and in the 8° slope group it was 0.99±0.42 mg/million cycles. The difference between the 0° tibial slope group and the 8° tibial slope group was highly significant (p<0.01, alternate t-test). Discussion. An increase of the tibial slope leads to a reduced wear rate in a mobile bearing UKA. Therefore, a higher tibial slope should be recommended for mobile bearing UKA. However, the influence on the ligaments has to be considered as a higher tibial slope leads to an increased strain on the anterior cruciate ligament. This influences needs to be investigated in further studies before a definite optimal range for the tibial slope can be recommended

There is a lack of information about the association between patellofemoral osteoarthritis (PFOA) and both adolescent Anterior Knee Pain (AKP) and previous patellar dislocations. This case-control study involved 222 participants from our knee arthroplasty database answering a questionnaire. 111 patients suffering PFOA were 1:1 matched with a unicompartmental tibiofemoral arthritis control group. Multivariate correlation and binary logistic regression analysis was performed, with odds ratios (ORs) and 95% confidence intervals (CIs) calculated. This analysis helps us assess the effect of both variables whilst adjusting for major confounders, such as previous surgery and patient-reported instability. An individual is 7.5 times more likely to develop PFOA if they have suffered adolescent AKP (OR 7.5, 95% CIs 1.51–36.94). Additionally, experiencing a patellar dislocation increases the likelihood of development of PFOA, with an adjusted odds ratio of 3.2 (95% CIs 1.25–8.18). A 44-year difference in median age of first dislocation was also observed between the groups. This should bring into question the traditional belief that adolescent anterior knee pain is a benign pathology. Patellar dislocation is also a significant risk factor. These patients merit investigation, we encourage clinical acknowledgement of the potential consequences when encountering patients suffering from anterior knee pain or patellar dislocation

The Oxford medial unicompartmental knee replacement has been shown to provide good long-tern results in numerous studies with survivorship at 10 years ranging from 82% to 100%. This prospective study describes the survival of 265 Oxford unicompartmental knee replacements implanted in one centre from 1995-2009. 8 were lost to follow up. 40 of the 265 knees were revised. For operation performed from1995-1999 the risk of revision at 5 years was 10%, operations from 2000-2004 the risk of revision was 15% and from 2005-2009 the risk of revision at 5 years was 36%. This study demonstrates that since 2005 there has been a significant increase in early failure of the Oxford unicompartmental knee at this institution and discusses the possible reasons for this

The surgical treatment of unicompartmental knee osteoarthritis remains controversial. This study aims to compare the medium-term outcomes of age and gender matched patients treated with unicompartmental knee replacement (UKR) and total knee replacement (TKR). We retrospectively reviewed pain, function and total knee society scores (KSS) for every UKR and age and gender matched TKR in NHS Tayside, with up to 10 years prospective data from Tayside Arthroplasty Audit Group. KSS was compared at 1, 3 and 5 years. Medical complications and joint revision were identified. Kaplan-Meier with revision as end-point was used for implants survival analysis. 602 UKRs were implanted between 2001 and 2013. Preoperative KSS for pain and total scores were not significantly different between UKRs and TKRs whereas preoperative function score was significantly better for UKRs. Function scores remained significantly better in UKRs from preoperative until 3 years follow up. Further analysis revealed no statistically significant difference in the change of function scores in both groups over time. There was a trend for TKRs to perform better than UKRs in pain scores. Total KSS for both groups were not significantly different at any point of the 5-year study. Fewer medical complications were reported in the UKR group. Kaplan-Meier analysis showed a survival rate of 93.7% in UKRs and of 97% in TKRs (Log rank p-value = 0.012). The revision rate for UKR was twice as much as TKR. The theoretical advantages of UKR are not borne out by the findings in this study other than immediate postoperative complications

Expectations of patients requiring knee arthroplasty surgery have become higher than in the past, with more strain being put on modern prostheses by fitter and younger patients. The objective of this study was to analyse the survivorship of primary knee arthroplasties at a minimum of ten years, with end points of revision and death. Patients who had a total (TKA) or unicompartmental (UKA) knee arthroplasty performed at a university teaching hospital were identified from the local arthroplasty database. Electronic and operative records were analysed to determine parameters including operative indication, subsequent revision surgery, and patient mortality. Results were collated and analysed using PASW software. A total of 1023 patients were recruited, with 566 (55%) female and 457 (45%) male. Minimum follow up was 10.1 years, with an average of 12.1 years (S.D 0.87). 64.9% of patients were alive at follow up, with an average age of 79.7 years (S.D 8.7). 92.8% were operated on for osteoarthritis (OA), 6.6% for rheumatoid arthritis (RA) and 0.6% for other indications. Kaplan–Meier analysis estimated survival of 94% (S.D 0.008) at eleven years, with no statistical difference found in survivorship of knees operated on for OA or RA. Similarly no statistical difference was found between survivorship of UKA or TKA implants. Of those that died by follow up, 95.2% did so with their original implant. We conclude that both TKA and UKA offer a lasting solution for patients, with excellent outcomes achieved in both rheumatoid and osteoarthritic patients

Background. A number of studies have reported on the early failure of the Oxford unicompartmental knee arthroplasty. However, less evidence is available regarding the outcome following revision of failed unicompartmental knee prostheses to total knee arthroplasty. The aims of this study were to determine the time to failure for the Oxford unicompartmental knee arthroplasty and to assess the short-term outcome following revision surgery. Methods. Details of consecutive patients undergoing revision of an Oxford unicompartmental knee arthroplasty to a total knee arthroplasty at our centre between January 2000 and December 2009 were collected prospectively. Data was collected on patient demographics, indication for revision surgery, and time to revision from the index procedure. Clinical and radiological outcome following revision arthroplasty was also assessed. Results. During the study period 22 (4.5%) of 494 Oxford unicompartmental knee arthroplasties were revised to a total knee arthroplasty. Mean age at the time of revision surgery was 61.8 yr and 13 (59%) patients were male. Mean time to revision surgery from the primary procedure was 3.0 yr (range 0.6–6.2 yr). The commonest reasons for revision were aseptic loosening of the femoral (n=9) or tibial component (n=2), and undiagnosed (n=5) or patellofemoral pain (n=2). All patients were revised to a cemented total knee arthroplasty with most not requiring bone grafts. During follow-up (range 0.5–4.5 yr) no further surgery was performed in the 22 patients. In addition, there were no major postoperative complications and no evidence of radiological failure. Discussion. The present study demonstrates most failures of the Oxford unicompartmental knee arthroplasty occur within three to four years following the index procedure and are due to aseptic component loosening. These findings are consistent with other published reports regarding the early failure of this particular prosthesis. The short-term outcome following revision surgery appears to be good, however longer follow-up periods are required to determine if these good results continue

Introduction. The options for the treatment of the young active patient with unicompartmental symptomatic osteoarthritis and pre-existing Anterior Cruciate Ligament (ACL) deficiency are limited. Patients with ACL deficiency and end-stage medial compartment osteoarthritis are usually young and active. The Oxford Unicompartmental Knee Replacement (UKA) is a well established treatment option in the management of symptomatic end-stage medial compartmental osteoarthritis, but a functionally intact ACL is a pre-requisite for its satisfactory outcome. If absent, high failure rates have been reported, primarily due to tibial loosening. Previously, we have reported results on a consecutive series of 15 such patients in whom the ACL was reconstructed and patients underwent a staged or simultaneous UKA. The aim of the current study is to provide an update on the clinical and radiological outcomes of a large, consecutive cohort of patients with ACL reconstruction and UKA for the treatment of end-stage medial compartment osteoarthritis and to evaluate, particularly, the outcome of those patients under 50. Methods. This study presents a consecutive series of 52 patients with ACL reconstruction and Oxford UKA performed over the past 10 years (mean follow-up 3.4 years). The mean age was 51 years (range: 36–67). Procedures were either carried out as Simultaneous (n=34) or Staged (n=18). Changes in clinical outcomes were measured using the Oxford Knee Score (OKS), the change in OKS (OKS=Post-op − Pre-op) and the American Knee Society Score (AKSS). Fluoroscopy assisted radiographs were taken at each review to assess for evidence of loosening, radiolucency progression, (if present), and component subsidence. Results. Five year survival was 90%. At last follow-up, the mean outcome scores for the group were: OKS 40 (SD: 8.3), objective AKSS 77 (SD: 16.1), functional AKSS 93 (SD: 13.7) and OKS of 11. Complications were recorded in three patients, (one early infection requiring a two-stage revision, a bearing dislocation and progression of OA in the lateral compartment). 25 patients, whose procedure occurred under the age of 50, had mean outcome scores of: OKS 38 (SD: 7.7), objective AKSS 73 (SD: 20.2), functional AKSS 93 (SD: 11.9) and OKS 12. No patients had radiological evidence of component loosening. Discussion and Conclusion. This study has demonstrated that combined ACL reconstruction and Oxford UKA provide good medium-term clinical and radiological results. The mobile bearing used in the Oxford knee minimises wear and our radiographic study has seen no suggestions of loosening

Introduction. Unicompartmental arthroplasty is still a controversial issue in knee replacement, mainly due to a marked variation in published survival rates of the implants. The aim of this study was to analyse possible risk factors for revision following Oxford unicompartmental knee arthroplasties (OUKA). Material and methods. Since 1997 data for all patients with primary and revision knee arthroplasties performed in our department have been stored in a database. Selected for the present study was all primary OUKA performed in the period 1997–2006 as well as any revision following these operations until the end of 2008. We got information from The National Health Register and the CPR register about any revision performed at other institutions and date in case of death. Primary OUKA were grouped in three categories according to the experience of the surgeon: 1 for operation done by a surgeon who had performed less than 20 OUKA, 2 for operation by a surgeon who had performed 20–40, and 3 for operation by a surgeon who had performed more than 40. Risk of revision was analysed by Cox regression. Revisions due to pain as the only reason were excluded from the analyses. Age and gender of the patients, previous surgical intervention, operation time, and the experience of the surgeon were included as possible risk factors in the analysis. Results. 445 primary Oxford knee arthroplasties were included. These were followed by 46 revisions. The indications for the revisions were: aseptic loosening 16 knees, progression of the osteoarthritis to the lateral compartment 7 knees, dislocation of the polyethylene meniscus 5 knees, varus-valgus instability 3 knees, fracture of the medial tibia condyle 3 knees, collision of the polyethylene meniscus and the femur condyle 1 knee, and pain as the only reason 11 knees. Age and gender of the patients as well as previous surgical intervention in the knee in question were not correlated to the risk of revision. Operation time was correlated to risk of revision with decreasing risk with increasing operation time (p=0,001). The experience of the surgeon was also correlated to risk of revision with decreasing risk with increasing experience (p=0,02). The 6 years survival rate for an experienced surgeon using an operation time at 90 min. or more was 97,5 % compared to a survival rate at 78,7 % for an inexperienced surgeon with an operation time less than 90 min. Conclusion. OUKA performed by an inexperienced surgeon and OUKA performed with short operation time had marked reduced survival rates. This seems to be an essential information to institutions performing OUKA