Abstract. Background. The Oxford Domed Lateral (ODL) Unicompartmental Knee Replacement (UKR) has some advantages over other lateral UKRs, but the mobile bearing dislocation rate is high (1–6%). Medial dislocations, with the bearing lodged on the tibial component wall, are most common. Anterior/posterior dislocations are rare. For a dislocation to occur distraction of the joint is required. We have developed and validated a dislocation analysis tool based on a computer model of the ODL with a robotics path-planning algorithm to determine the Vertical Distraction required for a Dislocation (VDD), which is inversely related to the risk of dislocation. Objectives. To modify the ODL design so the risk of medial dislocation decreases to that of an anterior/posterior dislocation. Methods. The components were modified using Solidworks. For each modification the dislocation analysis tool was used to determine the VDD for medial dislocation (with bearing 0–6mm from the tibial wall). This was compared with the original implant to identify the modifications that were most effective at reducing the dislocation risk. These modifications were combined into a final design, which was assessed. Results. Modifying the tibial component plateau, changing the femoral component width and making the bearing wider medially had little effect on VDD. Shifting the femoral sphere centre medially decreased VDD. Shifting the femoral sphere laterally, increasing tibial wall height and increasing bearing width laterally increased VDD. A modified implant with a femoral sphere centre 3mm lateral, wall 2.8mm higher, and bearing 2mm wider laterally, implanted so the bearing is ≤4mm from the tibial wall with a bearing thickness ≥4mm had a minimum VDD for medial dislocation of 5.75mm, which is larger than the minimum VDD for anterior/posterior dislocation of 5.5mm. Conclusions. A modified ODL design should decrease the dislocation rate to an acceptable level, however, further testing in cadavers is required. Declaration of Interest. (a) fully declare any financial or other potential conflict of interest

Aims. The optimal bearing surface design for medial unicompartmental knee arthroplasty (UKA) remains controversial. The aim of this study was to compare outcomes of fixed-bearing (FB) and mobile-bearing (MB) UKAs from a single high-volume institution. Methods. Prospectively collected data were reviewed for all primary cemented medial UKAs performed by seven surgeons from January 2006 to December 2022. A total of 2,999 UKAs were identified, including 2,315 FB and 684 MB cases. The primary outcome measure was implant survival. Secondary outcomes included 90-day and cumulative complications, reoperations, component revisions, conversion arthroplasties, range of motion, and patient-reported outcome measures. Overall mean age at surgery was 65.7 years (32.9 to 94.3), 53.1% (1,593/2,999) of UKAs were implanted in female patients, and demographics between groups were similar (p > 0.05). The mean follow-up for all UKAs was 3.7 years (0.0 to 15.6). Results. Using revision for any reason as an endpoint, five-year survival for FB UKAs was 97.2% (95% CI 96.4 to 98.1) compared to 96.0% for MB (95% CI 94.1 to 97.9; p = 0.008). The FB group experienced fewer component revisions (14/2,315, 0.6% vs 12/684, 1.8%; p < 0.001) and conversion arthroplasties (38/2315, 1.6% vs 24/684, 3.5%; p < 0.001). A greater number of MB UKAs underwent revision due to osteoarthritis progression (FB = 21/2,315, 0.9% vs MB = 16/684, 2.3%; p = 0.003). In the MB group, 12 (1.8%) subjects experienced bearing dislocations which required revision surgery. There were 15 early periprosthetic tibia fractures (0.6%) in the FB group compared to 0 for MB (p = 0.035). Conclusion. In similar patient populations, FB UKAs demonstrated slightly higher survival than a commonly used MB design. Adverse event profiles differed by bearing type, with an increased risk of bearing dislocation and OA progression with MB designs, and early periprosthetic tibia fractures for FB designs. Cite this article: Bone Joint J 2024;106-B(9):916–923

Aims. Unicompartmental knee arthroplasty (UKA) has higher revision rates than total knee arthroplasty (TKA). As revision of UKA may be less technically demanding than revision TKA, UKA patients with poor functional outcomes may be more likely to be offered revision than TKA patients with similar outcomes. The aim of this study was to compare clinical thresholds for revisions between TKA and UKA using revision incidence and patient-reported outcomes, in a large, matched cohort at early, mid-, and late-term follow-up. Methods. Analyses were performed on propensity score-matched patient cohorts of TKAs and UKAs (2:1) registered in the New Zealand Joint Registry between 1 January 1999 and 31 December 2019 with an Oxford Knee Score (OKS) response at six months (n, TKA: 16,774; UKA: 8,387), five years (TKA: 6,718; UKA: 3,359), or ten years (TKA: 3,486; UKA: 1,743). Associations between OKS and revision within two years following the score were examined. Thresholds were compared using receiver operating characteristic analysis. Reasons for aseptic revision were compared using cumulative incidence with competing risk. Results. Fewer TKA patients with ‘poor’ outcomes (≤ 25) subsequently underwent revision compared with UKA at six months (5.1% vs 19.6%; p < 0.001), five years (4.3% vs 12.5%; p < 0.001), and ten years (6.4% vs 15.0%; p = 0.024). Compared with TKA, the relative risk for UKA was 2.5-times higher for ‘unknown’ reasons, bearing dislocations, and disease progression. Conclusion. Compared with TKA, more UKA patients with poor outcomes underwent revision from early to long-term follow-up, and were more likely to undergo revision for ‘unknown’ reasons, which suggest a lower clinical threshold for UKA. For UKA, revision risk was higher for bearing dislocations and disease progression. There is supporting evidence that the higher revision UKA rates are associated with lower clinical thresholds for revision and additional modes of failure. Cite this article: Bone Joint J 2023;105-B(3):269–276

Aims. Medial unicompartmental knee arthroplasty (mUKA) is an advised treatment for anteromedial knee osteoarthritis. While long-term survival after mUKA is well described, reported incidences of short-term surgical complications vary and the effect of surgical usage on complications is less established. We aimed to describe the overall occurrence and treatment of surgical complications within 90 days of mUKA, as well as occurrence in high-usage centres compared to low-usage centres. Methods. mUKAs performed in eight fast-track centres from February 2010 to June 2018 were included from the Lundbeck Foundation Centre for Fast-track Hip and Knee Replacement Database. All readmissions within 90 days of surgery underwent chart review and readmissions related to the surgical wound or the prosthesis were recorded. Centres were categorized as high-usage centres when using mUKA in ≥ 20% of annual knee arthroplasties. The occurrence of complications between high- and low-usage centres were compared using Fisher’s exact test. Results. We included 3,757 mUKAs: 2,377 mUKAs from high-usage centres and 1,380 mUKAs from low-usage centres. Surgical complications within 90 days occurred in 69 cases (1.8%), 45 (1.9%) in high-usage centres and 24 (1.7%) in low-usage centres (odds ratio (OR) 1.1 (95% confidence interval (CI) 0.65 to 1.8)). The most frequent complications were periprosthetic joint infections (PJIs) (n = 18; 0.48%), wound-related issues (n = 14; 0.37%), and periprosthetic fractures (n = 13; 0.35%). Bearing dislocations (n = 7; 0.19%) occurred primarily in procedures from high-usage centres. In high-usage centres, seven periprosthetic fractures (0.29%) occurred compared to six (0.43%) in low-usage centres (OR 0.68 (95% CI 0.20 to 2.0)). In high-usage centres, nine PJIs (0.38%) occurred compared to nine (0.65%) in low-usage centres (OR 0.58 (95% CI 0.22 to 1.6)). Conclusion. Surgical complications are rare after fast-track mUKA surgery and with no difference in overall occurrence of surgical complications between high- and low-usage centres, although the risk of some specific surgical complications may favour high-usage centres. Cite this article: Bone Jt Open 2023;4(6):457–462

Background: Metal-on-metal (MOM) bearing surfaces with low diametric clearance possess a surface tension that prevents easy separation of the surfaces when lubricated. Potentially this ‘suction-fit’ may increase the torque required for dislocation. This study assessed the protective role of a MOM bearing surface as a single risk factor for dislocation.

Method: Prospective data was recorded on a series of 229 patients undergoing 249 primary THR for osteoarthritis. From 1993–8, patients under 70 years old were routinely given a 28mm ceramic-on-polyethylene (COP) bearing surface. Due to a high dislocation rate (see results below), an alternative was sought (1998–2001) and a 28mm metal-on-metal (MOM) bearing system chosen. For all cases in both groups, the acetabulum was uncemented with a modular 10° posterior lip insert allowing the same primary arc range (Duraloc/PFC/ Ultima, Johnson & Johnson). The cemented femoral component was the same in all cases (Ultima). All operations were performed by the same surgeon using the posterior approach. Variables in patient and prosthesis factors were compared. Statistical analysis was performed by the Chi-square and student’s t-test where appropriate.

Results: We identified 140 THR in 129 patients who received a COP bearing and 109 THR in 100 patients who received a MOM bearing. Nine of 140 (6.4%) COP bearings dislocated within 3 months of surgery compared to 1 of 109 (0.9%) in the MOM group (p=0.028). No significant differences were identified between groups when comparing factors relating to the patient or prosthesis.

Discussion: This study has shown a high dislocation rate for a COP bearing that was reduced to a low dislocation rate by changing the bearing surface to a MOM design. A potential mechanism for this may be the ‘suction fit’ from the surface tension of the low clearance, high tolerance that the metal-on-metal bearing possesses, requiring increased torque to dislocate during impingement.

Source of the study: University of Auckland, Auckland, New Zealand. Unicompartmental knee arthroplasty (UKA) is effective for patients with isolated compartment osteoarthritis, however the procedure has higher revision rates. Long-term survivorship and accurate characterisation of revision reasons are limited by a lack of long-term data and standardised revision definitions. We aimed to identify survivorship, risk factors and revision reasons in a large UKA cohort with up to 20 years follow-up. Patient, implant and revision details were recorded through clinical and radiological review for 2,137 consecutive patients undergoing primary medial UKA across Auckland, Canterbury, Counties Manukau and Waitematā DHB between 2000 and 2017. Revision reasons were determined from review of clinical, laboratory, and radiological records for each patient using a standardised protocol. To ensure complete follow-up data was cross-referenced with the New Zealand Joint Registry to identify patients undergoing subsequent revision outside the hospitals. Implant survival, revision risk and revision reasons were analysed using Cox proportional-hazards and competing risk analyses. Implant survivorship at 15 years was comparable for cemented fixed-bearing (cemFB; 91%) and uncemented mobile-bearing (uncemMB; 91%), but lower for cemented mobile-bearing (cemMB; 80%) implants. There was higher incidence of aseptic loosening with cemented implants (3–4% vs. 0.4% uncemented, p<0.01), osteoarthritis (OA) progression with cemMB implants (9% vs. 3% cemFB/uncemMB; p<0.05) and bearing dislocations with uncemMB implants (3% vs. 2% cemMB, p=0.02). Compared with the oldest patients (≥75 years), there was a nearly two-fold increase in risk for those aged 55–64 (hazard ratio 1.9; confidence interval 1.1-3.3, p=0.03). No association was found with gender, BMI or ASA. Cemented mobile-bearing implants and younger age were linked to lower implant survivorship. These were associated with disease progression and bearing dislocations. The use of cemented fixed-bearing and uncemented mobile-bearing designs have superior comparable long-term survivorship

Cementless fixation is an alternative to cemented unicompartmental knee replacement (UKR), with several advantages over cementation. This study reports on the 15-year survival and 10-year clinical outcomes of the cementless Oxford unicompartmental knee replacement (OUKR). This prospective study describes the clinical outcomes and survival of first 693 consecutive cementless medial OUKRs implanted in New Zealand. The sixteen-year survival was 89.2%, with forty-six knees being revised. The commonest reason for revision was progression of arthritis, which occurred in twenty-three knees, followed by primary dislocation of the bearing, which occurred in nine knees. There were two bearing dislocations secondary to trauma and a ruptured ACL, and two tibial plateau fractures. There were four revisions for polyethylene wear. There were four revisions for aseptic tibial loosening, and one revision for impingement secondary to overhang of the tibial component. There was only one revision for deep infection and one revision where the indication was not stated. The mean OKS improved from 23.3 (7.4 SD) to 40.59 (SD 6.8) at a mean follow-up of sixteen years. In conclusion, the cementless OUKR is a safe and reproducible procedure with excellent sixteen-year survival and clinical outcomes

Source of the study: University of Auckland, Auckland, New Zealand and University of Otago, Christchurch, New Zealand. Patient reported outcome measures (PROMs) are predictors of knee arthroplasty revision. Unicompartmental knee arthroplasty (UKA) is effective for patients with the correct indications, however has higher revision rates than total knee arthroplasty (TKA). Different revision thresholds for the procedures have been postulated. Our aims were to investigate: 1) if PROMs could predict knee arthroplasty revision within two years of the score at six months, five years and ten years follow-up, and 2) if revision ‘thresholds’ differed between TKA and UKA. All TKAs and UKAs captured by the New Zealand Joint Registry between 1999 and 2019 with at least one OKS response at six months (TKA n=27,708, UKA n=8,415), five years (TKA n=11,519, UKA n=3,365) or ten years (TKA n=6,311, UKA n=1,744) were included. were propensity-score matched 2:1 with UKAs for comparison of revision thresholds. Logistic regression indicated that for every one-unit decrease in OKS, the odds of TKA and UKA revision decreased by 10% and 11% at six months, 10% and 12% at five years and 9% and 5% at ten years. Fewer TKA patients with ‘poor’ outcomes (≤25) subsequently underwent revision compared with UKA at six months (5.1% vs. 19.6%, p<0.001), five years (4.3% vs. 12.5%, p<0.001) and ten years (6.4%vs. 15.0%, p=0.02). Compared with TKA, UKA patients were 2.5 times more likely to undergo revision for ‘unknown’ reasons, bearing dislocations and disease progression. The OKS is a strong predictor of subsequent knee arthroplasty revision within two years of the score from early to late term. A lower revision threshold was found with UKA when compared with a matched TKA cohort. Higher revision rates of UKA are associated with both lower clinical thresholds for revision and additional modes of UKA failure

Introduction: The results of the mobile bearing Oxford partial knee replacement (PKR) in the lateral compartment have been disappointing with a five year survival of 82%. Bearing dislocation is a particular concern, and to address this issue a new domed implant was introduced with a modified surgical technique. The aim of this study was to compare the risk of dislocation between a domed and flat lateral PKR. Methods: Separate kinematic models were generated for the domed and flat bearings. The femoral component, tibial tray and bearing were aligned in a neutral position; the flat bearing was positioned centrally on the tibial tray and 2 mm from the side wall; the domed bearing was placed concentrically on the domed tibial tray. Dislocation in the Posterior (A-P), Lateral (M-L) and Medial against the tray wall (L-M-wall) were investigated. For each dislocation the tibial tray was restrained in all degrees of freedom (DOF) and the femoral component was restrained in five DOF; A-P and M-L displacements; A-P, M-L and Superior-Inferior (S-I) rotations. The bearing was restrained from rotating about the S-I axis for each dislocation. For the L-M-wall dislocation the underside of the bearing was held in contact with the tibial tray wall such that the lowest S-I displacement of the femoral component was achieved. The least amount of distraction required for bearing dislocation to occur was calculated for the seven bearing sizes available. The effect of medial-lateral positioning of the femur on dislocation was investigated. Results: The minimum femur distraction to cause A-P flat and domed bearing dislocation ranged from 4.68mm to 3.91mm and 6.29mm to 5.59mm respectively as the bearing thickness increased from 3.5mm to 9.5mm. The minimum femur distraction to cause L-M-wall flat and domed bearing dislocation ranged from 3.42mm to 4.16mm and 4.55mm to 5.44mm respectively as the bearing thickness increased from 3.5 mm to 9.5 mm. The femur distraction required for L-M-wall bearing dislocation increased from 4.55mm to 6.3mm with a 2 mm medial movement of the femoral component. A 4 mm lateral movement of the femoral component decreased the distraction from 4.55mm to 2.35mm. Discussion: A domed bearing can lead to an increased femoral distraction of between 25% and 37%, significantly reducing the likelihood of dislocation. This may be significant during everyday activities and demonstrates that the new domed design should reduce the incidence of bearing dislocation by increasing the amount of entrapment; our current series of 200 patients has no dislocations. Increasing the thickness of the bearing has a small effect on the distraction required to allow bearing dislocation. The medial-lateral placement of the femoral component has a pronounced effect on the femoral distraction required for bearing dislocation over the tray wall; medial placement of the femoral component is advisable

Oxford Medial Unicompartmental Knee Replacement (OMUKR) is a well-established treatment option for isolated medial compartment arthritis, with good patient reported outcome measures (PROMs). We present our results of the Oxford Domed Lateral Unicompartmental Knee Replacement (ODLUKR) to establish if patients benefit as much as with OMUKR. Retrospective review of prospectively collected data of a single surgeon series of consecutive UKR from 2007 to 2014 were collated with a minimum 2 years follow-up. PROMs data were collected using pre- and post-operative Oxford Knee Scores (OKS) (best score of 48). One hundred and twenty-eight OMUKR and 27 ODLUKR were performed in the study period. There was no significant difference in the age at time of surgery, but there were significantly more women in the ODLUKR group (74% vs 53%). There was no significant difference in pre-op OKS between the groups (OMUKR = 16/48; ODLUKR = 20/48), or the improvement in OKS post-op (OMUKR = 19 points; ODLUKR = 17 points). One ODLUKR was revised to Total Knee Replacement (TKR) for pain. There were three (11.1%) bearing dislocations, which were treated with thicker bearing exchange, with no subsequent problems. There were no bearing dislocations in the OMUKR. Four OMUKR were revised to TKR due to pain. The overall implant survivorship was 96.3% for ODLUKR and 96.9% for OMUKR. ODLUKR is a good treatment option for isolated lateral compartment arthritis and gives results equivalent to OMUKR. There is, however, an increased risk of bearing dislocation so should be performed by a high volume UKR surgeon

Introduction. The results of the original mobile bearing Oxford unicompartmental knee replacement (UKR) in the lateral compartment have been disappointing because of high dislocation rates (11%). This original implant used a flat bearing articulation on the tibial tray. To address the issue of dislocation a new implant (domed tibia with biconcave bearing to increase entrapment) was introduced with a modified surgical technique. The aim of this study was to compare the risk of dislocation between a domed and flat lateral UKR. Methods. Separate geometric computer models of an Oxford mobile bearing lateral UKR were generated for the two types of articulation between the tibial component and the meniscal bearing: Flat-on-flat (flat) and Concave-on-convex (domed). Each type of mobile bearing was used to investigate three distinct dislocation modes observed clinically: lateral to medial dislocation, with the bearing resting on the tray wall (L-M-Wall); medial to lateral dislocation, out of the joint space (M-L); anterior to posterior dislocation, out of the joint space (A-P). A size C tray and a medium femoral component and bearing were used in all models. The femoral component, tibial tray and bearing were first aligned in a neutral position. For each dislocation the tibial tray was restrained in all degrees of freedom. The femoral component was restrained from moving in the anterior-posterior directions and in the medial-lateral directions. The femoral component was also restrained from rotating about the anterior-posterior, medial-lateral and superior-inferior directions. This meant that the femoral component was only able to move in the superior-inferior direction. Different bearing sizes were inserted into the model and the effect that moving the femoral component medially and laterally had on the amount of distraction required to cause bearing dislocation was investigated. Results. The average femur distraction to allow bearing dislocation in the A-P, M-L and L-M-wall directions was 1.62 mm (27%), 0.51 mm (26%) and 1.2 mm (24%) greater respectively for the domed bearing. There was a 3% increase in femoral distraction required to cause L-M-Wall dislocation, per increment of bearing thickness for both the domed and lateral bearings. There was on average a 7% increase in femoral distraction required to cause L-M-Wall dislocation per mm increment of medial femoral component movement. Discussion. Dislocation over the tray wall is a particular clinical problem and using a domed bearing can lead to an increased required femoral distraction of between 25% and 37%. This may be significant during everyday activities and demonstrates that the new domed design should reduce the incidence of bearing dislocation by increasing the amount of entrapment. Increasing the thickness of the bearing has a small effect on the distraction required to allow bearing dislocation. Lateral placement of the femoral component markedly reduced the femoral distraction required for bearing dislocation over the tray wall. Medial placement of the femoral component is advisable so long as impingement with the tray wall is avoided

Background. To evaluate the causes and modes of complications after unicompartmental knee arthroplasty (UKA), and to identify its prevention and treatment method by analyzing the complications after UKA. Materials and Methods. A total of 1,576 UKAs were performed between January 2002 and December 2014 at a single-institution. Postoperative complications occurred in 89 knees (83 patients, 5.6%), and 86 of them were found in females and 3 in males. Their mean age was 61 years (range, 46 to 81 years) at the time of initial UKA and 66 years (range, 46 to 82 years) at the time of revision surgery. We analyzed the complications after UKA retrospectively andinvestigated the proper methods of treatment (Table 1). Results. A total of 89 complications (5.6%) occurred afterUKA. Regarding the type of complications after UKA, there were bearing dislocation (n=42), component loosening (n=23), 11 cases of femoral component loosening, 8 cases of tibial component loosening, and 4 cases of both femoral and tibial component loosening, periprosthetic fracture (n=6), polyethylene wear/ destruction (n=3), progression of arthritis to the other compartment (n=3), medial collateral ligament (MCL) injury (n=2), impingement (n=2), infection (n=5), ankylosis (n=1), and unexplained pain (n=2) (Table 2). The most common complication after UKA was mobile bearing dislocation in mobile-bearing type and loosening of prosthesis in fixed-bearing type, but polyethylene wear and progression of arthritis were relatively rare. The mean interval from UKA to the occurrence of complications was 4 years and 6 months (range, 0 [during operation] to 12 years). Of those complications following UKA, 58 knees were treated with conversion TKA, 1 with revision UKA, and 21 with simple bearing change. Complications in the remaining knees were treated with arthroscopic management (n=2), open reduction and internal fixation (n=3), closed reduction and internal fixation (n=1), manipulation (n=1), and MCL repair (n=2) (Table 3). Discussion. In this single-center study, we reviewed the causes and types of complications (n=89) that occurred following UKA (n=1,576) and investigated optimal treatment methods. The incidence and type of complications were also compared among patients classified according to gender, medial/lateral UKA, and implant design and type. The strengths of this study include that all the patients were enrolled from the same institution and the sample size (UKA cases and complication cases) was relatively large compared to that in previous publications. The most common complication following UKA was bearing dislocation in the mobile-bearing knees and component loosening in the fixed-bearing knees. The incidence of polyethylene wear and progression of arthritis to the other compartment was relatively low. The results of our study are in some discrepancy with those of studies involving Western patients. This can be attributed to the differences in patient characteristics such as lifestyle and in the type and design of implant used. Conclusion. Thorough understanding of UKA, proper patient selection, appropriate implant choice are essential to reduce complications following UKA and obtain satisfactory outcomes. We suggest that complications following UKA should be treated differently according to the type and cause of complication and conversion TKA can be the most effective treatment when revision operation is determined necessary

Purpose. Unicompartmental Knee Arthroplasty (UKA) has been indicated for inactive elderly patients over 60, but for young and active patients less than 60 years old, it has been regarded as a contraindication. The purpose of this study is to evaluate the usefulness of UKA performed on young Asian patients under 60 years of age by analyzing clinical outcomes, complications and survival rate. Materials and Methods. The subjects were 82 cases, which were followed up for at least 5 years (from 5 to 12 years). Only Oxford phase III® (Biomet Orthopedics, Inc, Warsaw, USA) prosthesis was used for all cases. The clinical evaluation was done by the range of motion, Knee society score (KSS), WOMAC score. The radiographic evaluation was performed on weight bearing long-leg radiographs, AP and lateral view of the knee and skyline view of the patella. The survival rate was estimated by Kaplan-Meier survival analysis. Results. Three bearing dislocations, one medial tibial collapse and one lateral osteoarthritis occurred, so the complication rate was 6.1% (5/82). Among the 3 cases of bearing dislocation, 2 cases were resolved by replacing with a thicker bearing and 1 case was converted to TKA due to repeated dislocation. One case of medial tibia collapse and one lateral osteoarthritis were converted to total knee arthroplasty (TKA). All clinical outcomes measured by KSS scores and WOMAC score showed a statistically significant difference (p<0.001). The 10 year cumulative survival rate using Kaplan-Meier survival method was 94.7% (95% CI: 88.7%–100%). Conclusion. The clinical outcomes and the survival rate of young asian patients less than 60 years of age who underwent Oxford medial UKA showed good clinical results and a good survival rate in the mid-term results. However, long-term follow-up is needed for more reliable clinical results

The Oxford unicompartmental knee replacement (UKR) was introduced in 1976 with good results. Mobile bearings in the lateral compartment have been associated with unacceptably high bearing dislocation rates, due to greater movement between the lateral femoral condyle and tibia, and the lateral collateral ligament's laxity in flexion. The new domed implant is designed to counter this with a convex tibial prosthesis and a fully-congruent, bi-concave mobile bearing allowing a full range-of-movement (ROM), minimising dislocation risk and bearing wear. We present complication rates and clinical outcomes for a consecutive series of our first 20 patients undergoing Oxford domed lateral UKR, between June 2006 and August 2009, with minimum 6-month follow-up. There was one unrelated death (31 months post-UKR) and one postop MI. We had no bearing dislocations, infections or loosening nor other complications. All patients had post-op Oxford Knee Scores; eleven had pre-op scores and demonstrated a significant improvement – mean pre-op 22.75 to post-op 35.45 (p=0.01). All achieved full extension with average ROM 116°, mean change in ROM was –2.6°(p=0.6). This study adds to previous work in confirming a low level of complications with this new procedure (including the early learning curve), particularly bearing dislocation and demonstrates excellent functional outcomes

Introduction. The results of the mobile bearing Oxford unicompartmental knee replacement (UKR) in the lateral compartment have been disappointing with a five year survival of 82%. Therefore, it is recommended that mobile bearings should not be used for lateral UKR. This low survivorship is primarily due to high dislocation rate, all occurring in the first year. A detailed analysis of the causes of bearing dislocation confirmed the elevated lateral tibial joint line to be a contributory factor. A new surgical technique was therefore introduced in which care was taken neither to remove too much bone from distal femur nor to over tighten the knee and thus ensure that the tibial joint line was not elevated. Other modifications to the technique were also introduced including use of a domed tibial component. Aim. The aim of this study is to compare the outcome of these iterations: the original series [series I], Series II with improved surgical technique and the domed tibial component [Series III]. Method. The primary assessment of outcome was bearing dislocation at one year. One year was chosen as all the dislocations in the first series occurred within a year. In series I, there were 53 knees, in series II 65 knees and in series III 100 knees, all with a minimum of one year follow up. Results. In series I, there were 6 bearing dislocations (11%) and the average range of movement (ROM) was 110°. In the second series, there were 2 dislocations (3%) and the average ROM was 118°. In the third series, there were no primary dislocations and the average ROM was 125°, the difference between range of movement as well as dislocation rate being significant. Conclusions. The improved surgical technique and implant design have reduced the dislocation rate to an acceptable level and therefore a mobile bearing can now be recommended for lateral UKR

Introduction: The results of the mobile bearing Oxford unicompartmental knee replacement (UKR) in the lateral compartment have been disappointing with a five year survival of 82%. Therefore, it is recommended that mobile bearings should not be used for lateral UKR. This low survivorship is primarily due to high dislocation rate, all occurring in the first year. A detailed analysis of the causes of bearing dislocation confirmed the elevated lateral tibial joint line to be a contributory factor. A new surgical technique was therefore introduced in which care was taken neither to remove too much bone from the distal femur nor to over tighten the knee and therefore ensure that the tibial joint line was not elevated. Other modifications to the technique were also introduced including use of a domed tibial component. Aim: The aim of this study is to compare the outcome of these iterations: the original series [series I], Series II with improved surgical technique and the domed tibial component [Series III]. Method: The primary assessment of outcome was bearing dislocation at one year. One year was chosen as all the dislocations in the first series occurred within a year. In series I, there were 53 knees, in series II 65 knees and in series III 60 knees, all with a minimum of one year follow up. Results: In series I, there were 6 bearing dislocations (11%) and the average range of movement (ROM) was 110°. In the second series, there were 2 dislocations (3%) and the average ROM was 118°. In the third series, there were no primary dislocations and the average ROM was 125°. Conclusions: The improved surgical technique and implant design has reduced the dislocation rate to an acceptable level so a mobile bearing can now be recommended for lateral UKR

The aim of this study was to evaluate the risk factors for dislocation of the bearing after a mobile-bearing Oxford medial unicompartmental knee replacement (UKR) and to test the hypothesis that surgical factors, as measured from post-operative radiographs, are associated with its dislocation. From a total of 480 UKRs performed between 2001 and 2012, in 391 patients with a mean age of 66.5 years (45 to 82) (316 female, 75 male), we identified 17 UKRs where bearing dislocation occurred. The post-operative radiological measurements of the 17 UKRs and 51 matched controls were analysed using conditional logistic regression analysis. The post-operative radiological measurements included post-operative change in limb alignment, the position of the femoral and tibial components, the resection depth of the proximal tibia, and the femoral component-posterior condyle classification. We concluded that a post-operative decrease in the posterior tibial slope relative to the pre-operative value was the only significant determinant of dislocation of the bearing after medial Oxford UKR (odds ratio 1.881; 95% confidence interval 1.272 to 2.779). A post-operative posterior tibial slope < 8.45° and a difference between the pre-operative and post-operative posterior tibial slope of > 2.19° may increase the risk of dislocation. Cite this article: Bone Joint J 2014; 96-B:914–22

Aims. The aim of this to study was to compare the previously unreported long-term survival outcome of the Oxford medial unicompartmental knee arthroplasty (UKA) performed by trainee surgeons and consultants. . Patients and Methods. We therefore identified a previously unreported cohort of 1084 knees in 947 patients who had a UKA inserted for anteromedial knee arthritis by consultants and surgeons in training, at a tertiary arthroplasty centre and performed survival analysis on the group with revision as the endpoint. Results. The ten-year cumulative survival rate for revision or exchange of any part of the prosthetic components was 93.2% (95% confidence interval (CI) 86.1 to 100, number at risk 45). Consultant surgeons had a nine-year cumulative survival rate of 93.9% (95% CI 90.2 to 97.6, number at risk 16). Trainee surgeons had a cumulative nine-year survival rate of 93.0% (95% CI 90.3 to 95.7, number at risk 35). Although there was no differences in implant survival between consultants and trainees (p = 0.30), there was a difference in failure pattern whereby all re-operations performed for bearing dislocation (n = 7), occurred in the trainee group. This accounted for 0.6% of the entire cohort and 15% of the re-operations. . Conclusion. This is the largest single series of the Oxford UKA ever reported and demonstrates that good results can be achieved by a heterogeneous group of surgeons, including trainees, if performed within a high-volume centre with considerable experience with the procedure. Cite this article: Bone Joint J 2016;(10 Suppl B):22–7

Aims

The aim of this study was to describe the pattern of revision indications for unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) and any change to this pattern for UKA patients over the last 20 years, and to investigate potential associations to changes in surgical practice over time.

When the Oxford unicompartmental meniscal bearing arthroplasty (UCA) is used in the lateral compartment of the knee 10% of the bearings dislocate. An in-vitro cadaveric study was performed to investigate if the anatomy and joint geometry of the lateral compartment was a contributory factor in bearing dislocation. More specifically, the study investigated if the soft tissue tension of the lateral compartment, as determined by the length of the lateral collateral ligament (LCL), was related to bearing dislocation. A change in length of greater than 2 mm is sufficient to allow the bearing to dislocate. The Vicon Motion Analysis System (Oxford Metrics, Oxford, UK) was used to assess length changes in the LCL of seven cadaveric knees. Measurements were made of the LCL length through knee flexion and of the change in LCL length when a varus force was applied at a fixed flexion angle. Measurements were made in the normal knee and with the knee implanted with the Oxford prosthesis. In the intact knee the mean LCL change was 5.5mm (8%) over the flexion range. After implantation with the Oxford UCA the mean change in length was only 1 mm (1%). There was a significant difference in the LCL length at 90° (p=0.03) and 135° (p=0.01) of knee flexion compared to the intact knee. When a varus force was applied the LCL length change of the intact knee (5.4 mm) was significantly different (p=0.02) to that of the knee with the prosthesis implanted (2.7 mm). This study used a new method to dynamically measure LCL length. It found that after implantation of the Oxford lateral UCA the LCL remains isometric over the flexion range and does not slacken in flexion as it in the normal knee. This would suggest that the soft tissue tension was adequate to contain the bearing within the joint. However, when a varus force was applied the LCL did not sufficiently resist a displacing force producing an LCL length change greater than 2 mm. The evidence provided by this study is contradictory. The “lack of change in LCL length through flexion” suggests that the ligament remains tight through range and is unlikely to allow dislocation. However, the amount of distraction possible when an adducting moment is applied is sufficient to allow bearing dislocation. The length tension properties of the lateral structures are therefore implicated in the mechanism of dislocation

Background. A commonly held belief amongst surgeons and patients is that progression of disease (arthritis) to other compartments is a major cause of early failure of UKRs. Methods. We analysed the NJR database records of 17,643 primary UKRs performed between April 2003 and April 2009. Where these had been revised the reason for revision was noted. Results. Of the 17,643 primary UKRs, 308 had died and were excluded from the analysis. Of the living, 505 had been revised (3%) at a mean 3.45 years (range 2-6 years) following the primary procedure. Reason for revision was recorded in 472 cases (93%). Aseptic loosening was the commonest cause for revision in 154 cases (33%), followed by non specific pain in 129 cases (27%), bearing dislocation in 58 cases (12%), Instability in 33 cases (7%), Infection 28 cases (6%), progression of disease 23 cases (5%), periprosthetic fracture 19 cases (4%) and malalignment 15 cases (3%). 35% failed within 1 year, 38% within 2 years and 16% within 3 years of the index operation. Conclusion. Similar findings has been reported on the New Zealand Registry 10 year report where the overall revision rate was 284/4,826 (5.9%), and revision due to disease progression 7.7%. Progression of disease is not a major cause of early failure of UKRs. 73% of the failures occurred within two years of surgery. Other causes such as aseptic loosening, bearing dislocation and instability are more common and could be possibly ameliorated by improved surgical technique, better patient selection and component choice

The August 2023 Knee Roundup³⁶⁰ looks at: Curettage and cementation of giant cell tumour of bone: is arthritis a given?; Anterior knee pain following total knee arthroplasty: does the patellar cement-bone interface affect postoperative anterior knee pain?; Nickel allergy and total knee arthroplasty; The use of artificial intelligence for the prediction of periprosthetic joint infection following aseptic revision total knee arthroplasty; Ambulatory unicompartmental knee arthroplasty: development of a patient selection tool using machine learning; Femoral asymmetry: a missing piece in knee alignment; Needle arthroscopy – a benefit to patients in the outpatient setting; Can lateral unicompartmental knees be done in a day-case setting?

The results of mobile bearing Oxford unicompartmental knee replacement (UKR) in the lateral compartment have been disappointing (five-year survival: 82%). Therefore, it is recommended that mobile bearings should not be used for lateral UKR. This low survivorship is primarily due to a high dislocation rate. A detailed analysis confirmed the elevated lateral tibial joint line to be a contributory factor to bearing dislocation. A new surgical technique was therefore introduced in which care was taken neither to remove too much bone from the distal femur nor to over tighten the knee and therefore ensure that the tibial joint line was not elevated. Other modifications included use of a domed tibial component. The aim of this study is to compare the outcome of these iterations: the original series (series I), those with improved surgical technique (series II) and the domed tibial component (series III). The primary outcome measure was bearing dislocation at one year. One year was chosen as all the dislocations in the first series occurred within a year. In the original series (n=53), implanted using a standard open approach, there were six dislocations in the first year, the average flexion 110°, and 95% had no/mild pain on activity. In the second series (n=65), there were 3 dislocations, the average flexion was 117°, and 80% had no/mild pain on activity. In the third series with the modified technique and a convex domed tibial plateau, there was one dislocation, average flexion was 125° and 94% had no/mild pain on activity. At four years the cumulative primary dislocation rates were 10%, 5% and 0% respectively, and were significantly different (p=0.04). The improved surgical technique and implant design has reduced dislocation rate to an acceptable level so a mobile bearing can now be recommended for lateral UKR

The aim was to identify frequency and pattern of early UKR failure in New Zealand. We analysed data from the New Zealand National Joint Register in a 44 month period of 2000–2003. Thirty-five percent of the 1790 registered UKRs were performed in the last 8 months [ie. in 18% of the total time period]. The ratio of UKRs to TKRs performed was 1:6.25. Fifty two revisions meant a failure rate of 2.9% for UKR (n=1790) compared with 1.6% for TKR (n=11243). The most commonly used implants were the Oxford P3 (68% of total with 2.2% revision rate), MG uni (14.6% with 4.6% revision rate) and Preservation (7% with 5.6 revision rate). The most common reasons for revision (n=52) were aseptic loosening (28%), bearing dislocation or impingement (19%), and unexplained pain (13%). The deep sepsis rate for UKR was 0.33% compared to 0.43% for TKR. UKR usage is rapidly increasing in NZ. The revision rate for UKR was 1.8 x that for TKR. The revision rate for deep sepsis was 77% that for TKR. Unexplained pain in apparently technically normal UKR was the 3rd most common reason for revision. Bearing impingement was as common as bearing dislocation as a cause for failure in the Oxford P3 UKR. Early polythene wear was the reason for revision only in the 8mm MG prosthesis

Purpose: To analyze the clinical and radiographic results of patients treated by Oxford minimally invasive unicompartmental knee arthroplasty. Materials and Methods: We have operated 166 patients 188 knees of minimally invasive unicompartmental knee arthroplasty(Oxford Uni. ®. ) from January 2002 to December 2005. The mean ages was 65.3 (44–82) years and 16 cases of male and 150 cases of female. The mean follow-up period was 57 (36–77) months. Preoperative diagnosis were osteoarthritis in 166 cases, avascular necrosis of medial femoral condyle in 20 cases and chondrocalcinosis in 2 cases. The clinical results were evaluated using the HSS knee score and the range of motion of knee preoperatively and at the final follow up. At the final follow up, the ability of the patient to assume the squatting and cross-leg position were checked. The tibiofemoral angle was measured preoperatively and postoperatively. Component loosening, radiolucent lines were checked. Result: The HSS knee score was 67.5 (52–86) preoperatively and 89.9 (59–100) at the final follow up. The mean preoperative flexion contracture was 6.5° (0–20) and 0.81 (0–5) at the final follow up. Active full flexion was possible within postoperative 2 months. The squatting position was possible in 133 patients (80.1%) and the cross-leg position was possible in 152 patients (91.6%). The tibiofemoral angle was improved varus 1.5° to valgus 4.8°. Complication occurred in 14 cases (7.4%). Meniscal bearing dislocation in 8 cases (4.3%). Tibial components loosenig in 3 cases (1.6%). Femoral components loosening in 2 cases (1.1%). The average time of meniscal bearing dislocation was 11.3 (3–24)months postoperatively. Six cases returned to the predislocation level of activity with the insertion of thicker bearings and 2cases required TKR conversion. Conclusion: Minimally invasive unicompartmental knee arthroplasty(Oxford Uni. ®. ) provides rapid recovery, good pain relief and excellent function quite suitable to Korean life-style. But given the high complicate rate in mid-term results. Oxford Uni. ®. gives less reliability compared with TKR

Introduction: Increasing experiences in determining the indication for UKA and improvements in design and materials of the prosthesis led to better results. The AMC-Uniglide has an unconstrained mobile bearing with congruent area contact. This ensures complete freedom to rotate and slide upon one other with physiologic kinematic and low intrinsic stability. Material and Methods:. Minimal-invasive technique 30 patients with minimal-invasive AMC-Uniglide implantation technique were compared with 30 conventional implanted AMC’s and 30 total knee replacements in regard to rehabilitation and accuracy of implantation. 361AMC-Uniglides 361 consecutive patients were investigated after AMC-Uniglide implantation. The mean duration of follow-up was 5.5 (2.3-12.5) years. Patients were reviewed using the American Knee Society Rating System. The roentgenographic analyses were performed with the American Knee Society Evaluation System. Results:. Minimal-invasive technique The comparison of 30 minimal-invasive UKA with 30 conventional UKA and 30 total knee replacements show an advantage of minimal invasive technique with regard to a reduced time of rehabilitation. The accuracy of implantation was comparable between the conventional and the minimal-invasive technique. 361 AMC-Uniglides Ninety-five percent of patients had no pain or slight pain at the latest follow-up, ninety-two percent had good or excellent clinical outcome. Three knees were revised for mobile bearing dislocation after medial UCA and three for lateral mobile bearing dislocation after lateral UCA. Five revisions because of component loosening were performed and there was one case of deep infection. Conclusion: The clinical results of the investigated patients demonstrate that the AMC-Uniglide is a successful concept with a safe anchorage of the prosthesis and a good durability of the mobile bearings. An advantage of minimal invasive technique with regard to a reduced time of rehabilitation was found. The accuracy of implantation was comparable between the conventional and the minimal-invasive technique

Aims

Unicompartmental knee arthroplasty (UKA) has a higher risk of revision than total knee arthroplasty (TKA), particularly for younger patients. The outcome of knee arthroplasty is typically defined as implant survival or revision incidence after a defined number of years. This can be difficult for patients to conceptualize. We aimed to calculate the ‘lifetime risk’ of revision for UKA as a more meaningful estimate of risk projection over a patient’s remaining lifetime, and to compare this to TKA.

INTRODUCTION. Wear and polyethylene damage have been implicated in up to 22% of revision surgeries after unicompartmental knee replacement. Two major design rationales to reduce this rate involve either geometry and/or material strategies. Geometric options involve highly congruent mobile bearings with large contact areas; or moderately conforming fixed bearings to prevent bearing dislocation and reduce back-side wear, while material changes involve use of highly crosslinked polyethylene. This study was designed to determine if a highly crosslinked fixed-bearing design would increase wear resistance. METHODS. Gravimetric wear rates were measured for two unicompartmental implant designs: Oxford unicompartmental (Biomet) and Triathlon X3 PKR (Stryker) on a knee wear simulator (AMTI) using the ISO-recommended standard. The Oxford design had a highly conforming mobile bearing of compression molded Polyethylene (Arcom). The Triathlon PKR had a moderately conforming fixed bearing of sequentially crosslinked Polyethylene (X3). A finite element model of the AMTI wear simulation was constructed to replicate experimental conditions and to compute wear. This approach was validated using experimental results from previous studies. The wear coefficient obtained previously for radiation-sterilized low crosslinked polyethylene was used to predict wear in Oxford components. The wear coefficient obtained for highly crosslinked polyethylene was used to predict wear in Triathlon X3 PKR components. To study the effect design and polyethylene crosslinking, wear rates were computed for each design using both wear coefficients. RESULTS. Wear rates were significantly lower (69%) for the Triathlon fixed-bearing design compared to the Oxford mobile-bearing design (Fig 1, p<0.01). The FEA model predicted 46% of wear occurring at the back side of the mobile bearing (Fig 2). When wear was computed for the Triathlon PKR design using the wear coefficients used for the low crosslinked polyethylene, wear rates increased to 13.9 mg/million cycles. DISCUSSION. We used a combined experimental and computational approach to quantify factors contributing to polyethylene wear after unicompartmental knee arthroplasty. To isolate the effect of crosslinking level and mobile-bearing design, we computed wear rates for both designs using the same wear coefficient obtained for low crosslinked polyethylene. Wear rates in the low crosslinked Triathlon PKR insert increased by more than 160% relative to those in the highly crosslinked Triathlon X3 PKR. The finite element method facilitates computation of relative back-side to front-side wear, which is challenging to obtain experimentally. The back-side wear Oxford mobile bearing was 46% of total wear. Major factors contributing to the difference in wear were back-side wear (46%) and increased crosslinking (63%) with the combined effect having an additive effect. Our FEA-predicted wear penetration rates (0.024 mm/million cycles) also compare well to in vivo studies, which reported penetration rates of 0.022 mm/year for Oxford bearings. A validated computer model is extremely valuable for efficient evaluation of wear performance and design development. In summary, increasing conformity to increase contact area and reduce contact stress may not be the sole predictor of wear performance. A highly crosslinked polyethylene insert in a fixed-bearing design may provide the high wear performance of a mobile-bearing design without the increased risk for bearing dislocation

Background. The purpose of this study is to report the outcome of navigation-assisted cruciate-retaining total knee arthroplasty (TKA) using one type of cemented, second-generation, floating-platform (FP), mobile-bearing system. Methods. We retrospectively reviewed 42 patients (51 knees) who underwent cruciate retaining TKAs using e.motion-FP prostheses under navigational guidance. The preoperative diagnosis was osteoarthritis in all knees except one rheumatoid arthritis. There were 2 men (2 knees) and 40 women (49 knees) with a mean age of 64.0 ± 4.7 years (range, 51 – 76 years) at the time of index surgery. The mean follow-up was 120.0 months (range, 106 – 126 months). Clinical and radiographic results as well as mechanical survival rate of this type prosthesis were investigated at a mean follow-up of 10 years. Results. The mean mechanical femorotibial angle was improved from 11.7° ± 3.3° (range, 5.0° to 19.7°) preoperatively to 1.4° ± 1.7° (range, −2.9° to 6.4°) at the latest follow-up. No prosthesis-related complications such as bearing dislocation or breakage occurred and no knees showed aseptic loosening or progressive osteolysis. Kaplan-Meier survivorship at 10.5 years was 100% with an endpoint of revision for any prosthesis-associated reason. Conclusions. The emotion-floating platform mobile-bearing design yielded satisfactory mid-term durability and implant performance under navigational guidance

The dual mobility (DM) bearing concept was introduced to reduce the risk of dislocation in total hip arthroplasty (THA). Our aim was to evaluate the early outcomes following the utilisation of DM in primary and revision THA in our unit. Prospectively collected data on all patients undergoing a DM bearing at was reviewed between July 2012and December 2015. The primary outcome assessed was dislocation, with a secondary outcome revision for any reasons. All data was gathered from patient clinical records and the digital picture archiving and communication system (PACS). 30 primary THA were undertaken and 54 revision THAin the time period described. 11 of the procedures involved a proximal femoral endoprosthesis. The mean age in the primary setting was 65 and 73 in the revision population. The main indications for using DM bearing in the primary setting were; trauma (40%), residual dysplasia (40%) and malignancy (17%). There were no dislocations in the primary THA category. Indications in the revision THA cohort included 33% for aseptic loosening, 11% for instability, 18% for ALVAL reactions, 20% for infection, 18% for fracture. 1 out of the 54 revision THA had one large bearing dislocation requiring closed reduction. Subsequent analysis confirmed that implant alignment was satisfactory and this was a patient compliance issue due to mental health concerns. To date no patient in either cohort required revision surgery. Overall dislocation rate was 1.2%. Our early experience with DM bearings has been positive with no evidence of early failure or loosening. The dislocation rate overall has been low and matches the current large series in the literature

It is very important for implanting tibial component to prevent bearing dislocation in Oxford UKA. One of the keys is accurate rotational position of tibia. But the problem remains what is accurate rotation of tibia in UKA. Oxford Signature decided the rotation of tibia component from MRI images. We measured the component rotation of tibia using CT after operation. Patients and Methods. 14 patients were operated by Oxford Signature and 11 patients were operated by Microplasty method. Patients were examined by CT 2 or 3 weeks later after operation. We compared component axis of tibia and A-P axis by best fit circle, Akagi's line. Results. In Oxford Signature group, component angle were 7.1 degree external rotation compared with A-P axis by best fit circle and were 3.6 degree external rotation compared with Akagi's line. In Microplasty group, component angle were 8.1 degree external rotation compared with A-P axis by best fit circle and were 3.8 degree external rotation compared with Akagi's line. Discussion. It is difficult to decide accurate position of tibial component for UKA. The A-P axis by best fit circle and Akagi's line are reliable methods for tibial axis in TKA. We examined component axis of Signature Oxford and Microplasty, these were same tendency toward external rotation

Aims

Uncemented mobile bearing designs in medial unicompartmental knee arthroplasty (UKA) have seen an increase over the last decade. However, there are a lack of large-scale studies comparing survivorship of these specific designs to commonly used cemented mobile and fixed bearing designs. The aim of this study was to evaluate the survivorship of these designs.

Background. Wear and fatigue damage to polyethylene components remain major factors leading to complications after total knee and unicompartmental arthroplasty. A number of wear simulations have been reported using mechanical test equipment as well as computer models. Computational models of knee wear have generally not replicated experimental wear under diverse conditions. This is partly because of the complexity of quantifying the effect of cross-shear at the articular interface and partly because the results of pin-on-disk experiments cannot be extrapolated to total knee arthroplasty wear. Our premise is that diverse experimental knee wear simulation studies are needed to generate validated computational models. We combined five experimental wear simulation studies to develop and validate a finite-element model that accurately predicted polyethylene wear in high and low crosslinked polyethylene, mobile and fixed bearing, and unicompartmental (UKA) and tricompartmental knee arthroplasty (TKA). Methods. Low crosslinked polyethylene (PE). A finite element analysis (FEA) of two different experimental wear simulations involving TKA components of low crosslinked polyethylene inserts, with two different loading patterns and knee kinematics conducted in an AMTI knee wear simulator: a low intensity and a high intensity. Wear coefficients incorporating contact pressure, sliding distance, and cross-shear were generated by inverse FEA using the experimentally measured volume of wear loss as the target outcome measure. The FE models and wear coefficients were validated by predicting wear in a mobile bearing UKA design. Highly crosslinked polyethylene (XLPE). Two FEA models were constructed involving TKA and UKA XLPE inserts with different loading patterns and knee kinematics conducted in an AMTI knee wear simulator. Wear coefficients were generated by inverse FEA. Results. Predicted wear rates were within 5% of experimental wear rates during validation tests. Unicompartmental mobile bearing back-side wear accounted for 46% of the total wear in the mobile bearing. Wear during the swing phase was 38% to 44% of total wear. Discussion & Conclusions. Crosslinking polyethylene primarily decreased (by nearly 10-fold) the wear generated by cross-shear. This result can be explained by the reduced propensity of crosslinked polyethylene molecules to orient in the dominant direction of sliding. A highly crosslinked fixed-bearing polyethylene insert can provide high wear performance without the increased risk for mobile bearing dislocation. Finite element analysis can be a robust and efficient method for predicting experimental wear. The value of this model is in rapidly conducting screening studies for design development, assessing the effect of varying patient activity, and assessing newer biomaterials. This FEA model was experimentally validated but requires clinical validation

Background and Purpose of Study. The Valgus knee in total knee Arthroplasty, is considered a more demanding procedure, often with ligament balance a greater challenge than seen with neutral or Varus knees. It has also frequently been suggested that prostheses with higher levels of constraint be used to avoid late-onset instability. Various lateral release techniques have also been suggested in the literature. This study is aimed at assessing the outcomes of an unconstrained, rotating platform designed prosthesis, the LCS, using our technique, in the management of severe valgus deformity. Methods. 44 knees in 42 patients with a pre-operative valgus deformity of more than 10 degrees were included in our retrospective series. We analyzed the radiographs for the degree of correction, the angle of tibial tray implantation, and femoral implantation angle, tibial slope, as well as the presence (or degree) of lift off and any complications were noted. In this group, 7 had a Valgus deformity of greater than 25 degrees, with a mean Valgus deformity of 17,36 degrees. The mean age at operation was 65. Clinical and radiological analysis was done Pre-hospital discharge and again post-operatively 6 weeks. Results. The mean coronal alignment was corrected from 17,36 degrees to 5 degrees of Valgus post operatively. 2 knees were corrected past neutral to varus alignment. There was 1 case of bearing spin out experienced early on in the series. The mean tibial implant angle was 1,7 degrees from neutral. Lift off in the early post-operative X-rays was seen in 6 patients, however at 3 month follow up the knees appeared to be well balanced. There were no infections or revisions for wear, one re-operation for bearing dislocation, and no cases of loosening in our series. There were no cases of delayed instability. Patient satisfaction was 86 %. Conclusions. The rotating platform, mobile bearing prosthesis, using our technique, provided a reproducible correction of deformity in Valgus knees, a well-balanced knee, a low complication rate, and an excellent degree of patient satisfaction. NO DISCLOSURES

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

Aims

Bi-unicondylar arthroplasty (Bi-UKA) is a bone and anterior cruciate ligament (ACL)-preserving alternative to total knee arthroplasty (TKA) when the patellofemoral joint is preserved. The aim of this study is to investigate the clinical outcomes and biomechanics of Bi-UKA.

Ultra-high molecular weight polyethylene (UHMWPE) is a commonly used as bearing material in joint replacement devices. UHMWPE implants can be hard to see on a standard X-ray because UHMWPE does not readily attenuate X-rays. Radiopaque UHMWPE would enable direct imaging of the bearing both during and after surgery, providing in vivo assessment of bearing position, dislocation or fracture, and potentially a direct measure of wear. The X-ray attenuation of UHMWPE was increased by diffusing an FDA approved contrast agent (Lipiodol) into UHMWPE parts (Zaribaf et al, 2018). The aim of this study was to evaluate the optimal level of radiopacity for a UHMWPE bearing. Samples of un-irradiated medical grade UHMWPE (GUR 1050) were machined into 4mm standard medium Oxford Unicompartmental bearings. Samples were immersed in Lipiodol Ultra Fluid (Guerbert, France) at elevated temperatures (85 °C, 95 °C and 105 °C) for 24 h to achieve three different levels of radiopacity. A phantom set-up was used for X-ray imaging; the phantom contained two perspex rods to represent bone, with the metallic tibial tray and polyethylene bearing fixed to the end of one rod and the metallic femoral component fixed to the other rod. Radiographs of the samples were taken (n=5) with the components positioned in full extension. To ensure consistency, the images of all the samples were taken simultaneously alongside an untreated part. The results of our ongoing study demonstrate that the radiopacity of UHMWPE can be enhanced using Lipiodol and the parts are visible in a clinical radiographs. The identification of the optimal treatment from a clinical perspective is ongoing; we are currently running a survey with clinicians to find the consensus on the optimal radiopacity taking into account the metallic components and alignment. Future work will involve a RSA study to assess the feasibility of measuring wear directly from the bearing

Purpose. We analyzed the frequency, causes and treatment of dislocation of polyethylene insertion among various causes of failure of unicompartmental knee arthroplasty. Materials and Methods. We studied 69 knee joints of 65 patients who underwent medial unicompartmental knee arthroplasty using from June 2005 to December 2010. Average age was 61.8 and average follow-up period was 20 months. Radiologic results evaluated preoperative and postopertative mechanical axis deviation, tibio-fibular angle and postoperative implant position in total 69 knees(A group), failed 15 cases(B group) and 10 cases(C group) of bearing dislocation. We demonstrated treatment on failure group and analyzed preoperative and postoperative HSS and Lysolm score. Results. Failures were observed in 15 cases(21.7%) on follow-up. dislocation of polyethylene insertion was observed in 10 cases at average 26.7 months (3–60). There were 2 cases of dislocation of insert without loosening of implant and 8 cases of dislocation of insert with loosening of implant. Tibio-femoral angle in A, B and C group were corrected form preoperative varus 8.1°, 7.3° and 6.3° to postoperative valgus 3.6°, 4.0° and 3.5°. Thickness of inserted polyethylene in A, B and C were 4.7 mm, 5.2 mm and 4.8 mm, but each groups didn't show statistical significance. HSS and Lysolm score improvement had statistical significance. Conclusion. Dislocation of polyethylene insert (66.1%) in cases of the failure was most common. Coronal correction angle and thickness of inserted polyethylene showed no difference between dislocation gourp and non-dislocation group, so we consider that polyethylene dislocation after unicompartmental knee arthroplasty seems to be due to structural problem of the implant

Background: Durable long-term independent results with the Low Contact Stress rotating-platform (mobile-bearing) and the Insall Burstein-II (fixed-bearing) total knee prostheses have been reported, but no studies describing either the mid-term or long-term results and comparing the two prostheses are available, to our knowledge. Methods: Thirty-two patients who had bilateral arthritis of the knee with similar deformity and preoperative range of motion on both sides and who agreed to have one knee replaced with a mobile-bearing total knee design and the other with a fixed-bearing design were prospectively evaluated. Comparative analysis of both designs was done at a mean follow-up period of six years, minimizing patient, surgeon, and observer-related bias. Clinical and radiographic outcome, survival, and complication rates were compared. Results: Patients with osteoarthritis had better function scores and range of motion compared with patients with rheumatoid arthritis. However, with the numbers available, no benefit of mobile-bearing over fixed-bearing designs could be demonstrated with respect to Knee Society scores, range of flexion, subject preference, or patellofemoral complication rates. Radiographs showed no difference in prosthetic alignment. Two knees with a mobile-bearing prosthesis required a reoperation: one had an early revision because of bearing dislocation and another required conversion to an arthrodesis to treat a deep infection. Conclusions: We found no advantage of the mobile-bearing arthroplasty over the fixed-bearing arthroplasty with regard to the clinical results at mid-term follow-up. The risk of bearing subluxation and dislocation in knees with the mobile-bearing prosthesis is a cause for concern and may necessitate early revision

Aims

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

Purpose. To identify the causes of failure after unicompartmental knee arthroplasty (UKA), and to evaluate considerations for surgical procedures and the results of revision total knee arthroplasty (TKA) performed after failure of UKA. Materials and Methods. Eight hundreds and fifty-two cases of UKA were performed from January 2002 to June 2011. Forty-seven cases of failures after UKA were analyzed for the cause of the failures, and thirty-five cases of revision TKA after failure were analyzed for the operative findings and surgical technique. The clinical results were measured for thirty cases which were followed-up on at least two years after TKA. The mean duration of follow-up was four years and one month after revision TKA and the mean patient age at the time of surgery was sixty-five years. Results. For the cause of failures after UKA, there were twenty-two cases of early loosening of prosthesis, seventeen cases of simple mobile bearing dislocation, five cases of infection, one case of fracture of medial tibial condyle and two cases of unknown origin pain. In operative findings of thirty-five cases of TKA after failed UKA, there were twenty-five cases of bone defect requiring treatment and the mean thickness of the defect was 10.6 mm. For the treatment of bone defect, there were five cases of autogenous bone graft, twenty-one cases of metal blocks, and one case of autogenous bone graft with metal block. The stem was used in tibial implants for nineteen cases, and one case of use in tibial and femoral implants. For thirty cases where follow ups were possible at least two years after operation, the mean knee score was improved from 68.2 to 85.2 and the mean knee function score was improved from 67.7 to 78.0 at the last follow-up, respectively. The mean range of knee motion was 107.2° pre-operatively, which was recovered to 120.7° after the operation. The mean tibiofemoral angle was changed from 1.7° of valgus to 5.2° of valgus. Conclusion. As shown in this study, the tibial bone defect was the most important problem in revision TKA after failure of UKA. Therefore, proper indication and accurate surgical technique using autogenous bone graft, metal block and stemmed implants would be able to achieve satisfactory results in revision TKA after failure of UKA

Mobile bearings in knee arthroplasty carry the theoretical advantage of lower wearing prostheses. However, dislocating mobile bearings can be a significant issue in mobile bearing knee replacement arthroplasty. Our aim is to report our design alterations to the insert to address bearing spinout. A total of 598 RBK mobile bearing total knee arthroplasties were performed by the senior author over a 10–year period. The standard bearing was subjected to three design changes to address spinout and increase flexion range. The first alteration involved a deeper dish with a higher anterior lip. Subsequently, a reduced footprint insert (RFI) was created. The final modification was a shaved off posterior rim to allow for greater flexion (high flex). An overall bearing dislocation rate of 1.0% (6 out of 595) was obtained. Of these 595 knees, 132 were of the initial insert design, 194 were deep-dished inserts, 71 inserts were RFI, and 198 were high flex. There were four (3%) dislocations with the initial insert design and two (1%) dislocations in the final implant version. In our series the dislocated bearings have in all but one required revision to higher constrained prostheses. The mechanism of dislocation is speculated to be instability in flexion, leading to posterior loading of the insert and spinning out of the bearing. Most of the bearing subluxations have been medial but one was observed intra operatively to be a lateral extrusion. With respect to the two dislocations in the final implant design, one dislocation was attributed to a technical error of under sizing the insert. At revision surgery he was also found to have a disrupted MCL, which was repaired. He has had no further issues after the insert was upsized. The cause of spin out in the second patient was speculated to be obesity and a diminished pre- operative range of movement. She required a revision to a higher constrained prosthesis. Insert spinout has a multifactorial aetiology. The occurrence of spinout can be minimised by a combination of good surgical technique, such as balanced flexion and extension gaps and design modifications to the insert as we have instituted

About ten years ago we introduced sophisticated instrumentation and an increased range of component sizes for the Oxford unicompartmental knee replacement (UKR) to facilitate a minimally invasive surgical (MIS) approach. The device is now routinely implanted through an incision from the medial pole of the patella to the tibial tuberosity. This has resulted in a more rapid recovery and an improved functional result. As the access to the knee is limited there is a concern that the long term results may be compromised. The aim of this study was to determine the 10 year survival. A prospective follow up of all Phase 3 minimally invasive Oxford UKR implanted by two senior authors (DWM & CAFD) has been undertaken. So far 1015 UKRs have been implanted for anteromedial osteoarthritis. All patients received a cemented implant through a MIS approach and were followed up prospectively by an independent observer. The data was collected prospectively regarding pre-operative status, complications and clinical as well as functional outcome at predetermined intervals. The average age of patients was 66.4 years (range: 33 – 88) with mean Oxford Knee Score 41 (SD: 7.9) at the time of last follow up, Knee Society Score (objective) of 84 (SD: 13) and Knee Society Score (functional) of 83 (SD: 21). At ten years the survival of this cohort is 96%. There were 22 revisions including 7 for progression of arthritis, 5 for infection, 5 for bearing dislocation, 4 for unexplained pain and one for rupture of ACL secondary to trauma. We conclude that the Oxford Knee can be implanted reliably through a minimally invasive approach, giving excellent long term results

Purpose. To identify the incidence and reasons for revision of the Oxford prosthesis (OXF) in New Zealand. Methods. Review and compare UKA and TKA data including patient-generated Oxford scores after operation. Results. 105 surgeons performed 3,624 OXF (66.5% of all UKA). UKA made up 12.8% of all knee arthroplasties. There were 216 OXF revisions and revision rate (RR) of 1.39 per 100 component-years (p100cy); for UKA this was 1.42 p100cy, and for TKA 0.54 p100cy (OXF vs TKA p< 0.0001). The indications for OXF revisions were unexplained pain (38.0%); aseptic loosening (38.0%); bearing dislocation (9.3%) and deep sepsis (4.2%). For TKA, unexplained pain (28%) was significantly lower than from OXF (p=0.005). Revision for deep sepsis was significantly lower for OXF compared with TKA (4.2% vs 13.1%, p < 0.001). The Oxford scores 6 months post-op were excellent or good in 79% of OXF vs 72% TKA patients (p< 0.0001); at 5 years after operation these were 88% for OXF and 81% for TKA (p=0.001). Twenty high-use OXF surgeons (10 or more operations/year) performed 44% of the operations (RR of 1.3 p100cy), 62 medium-use surgeons (2-9/year) performed 54% (RR of 1.3 p100cy). 23 low-use surgeons (2 or less/year) performed 2% (RR of 3.9p100cy). The differences in RR high vs low users (p< 0.001) and medium vs low groups (p< 0.001) were significant. RR for OXF high or medium users was significantly higher than the overall rate for TKA (p< 0.001). Conclusion. RR for the OXF was 2.5 times greater than that for TKA. Deep infection rate was lower, and 6-month and 5-year function scores were significantly higher OXF vs TKA

Introduction: Unicompartmental knee replacement (UKR) is a popular alternative to total knee replacement (TKR) in medial compartment disease. Early problems include bearing dislocation, persistent pain, stiffness and infection. Revision to TKR is well described as a late endpoint. Objective: Investigate the early surgical management of persistent pain and debility following UKR, identify common themes and rate effectiveness of any re-intervention. Methods: 381 UKRs implanted over 5 years included, and patients requiring re-operation reviewed retrospectively. Findings: 27 re-operations performed on 17 patients at a mean 16.8 months (95% CI 9.5 to 24.1), with symptom onset post-operatively at 9 months (95% CI 4–14). There were 10 arthroscopies, 10 total knee replacements (revision), 4 manipulations under anaesthesia, 2 bearing exchanges, and 1 tibial-plateau fracture fixation. Manipulation under anaesthesia improved stiffness in 2 of 3 patients. Arthroscopy was successful in 2 patients with loose cement-bodies but did not provide a diagnosis in 8 patients, of whom 7 were revised subsequently after 17.1 months (95% CI 10.1 to 24.1) with 6 reporting symptom resolution. Overall there were 10 revisions: 9 were performed for persistent pain and 9 reported symptom improvement. Intra-operative findings included aseptic loosening (n=4), synovitis (n=2), increased posterior slope of the tibial cut (n=1), dislocated bearing (n=1), and no cause of failure in 2. Only two cases required revision implants with medial augments for bone loss. There were no deep infections. Conclusions: The early re-intervention rate at our unit is 4.5% (95% CI 2.4 to 6.5), with a revision rate of 2.6% (95% CI 1.0 to 4.2) after a mean (±SD) follow-up of 40.1 (±16) months. Arthroscopy is a poor diagnostic and therapeutic option against persistent pain following UKR. In contrast, the decision to revise, although initially disappointing for both patient and surgeon, gave symptom improvement in 90%

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

Aim: This paper presents the 20-year survival and 10-year clinical follow-up results from the entire series of all medial Oxford meniscal bearing unicompartmental knee arthroplasties performed in a single centre in Sweden, between 1985 and 2004. Method: Patients were contacted and information about the state of the knee collected. Revision surgery was used in the life-table survival analysis performed. For the entire cohort clinical follow up at 10-years is routinely performed, using the HSS knee score. Results: The entire group comprised of 683 knees in 572 patients. The mean age at implantation was 69.7 (range 48–94). There had been 30 revision procedures: 8 for lateral arthrosis, 7 for component loosening, 3 for infection, 6 for bearing dislocation, 1 for bearing fracture and 5 for unexplained pain. The 10-year, 15-year and 20-year survival (all cause revision) were 94.1 % (CI 2.9, 237 at risk), 93.5% (CI 4.6, 101 at risk) and 92.3% (CI 15.1, 11 at risk) respectively. From the patients reviewed clinically the mean pre-operative HSS knee score was 57 (95% CI 1), compared to 87 (95% CI 1) at 10-years. Using HSS criteria the results were: 68% excellent, 23% good, 6% moderate and 2% poor. Conclusion: The results show that this mobile bearing unicompartmental prosthesis offers patients excellent clinical results during the first decade and is durable during the second decade after implantation

Introduction. Radiolucencies beneath the tibial component are well recognized in knee arthroplasty; the aetiology and significance are poorly understood. Non-progressive narrow radiolucencies with a sclerotic margin are thought not to be indicative of loosening. Factors which decrease the incidence of radiolucencies include cementless fixation and the use of pulse lavage. Leg/component alignment or BMI do not influence radiolucency. We are not aware of any studies that have looked at the effect of load type on radiolucency. The Oxford domed lateral tibial component was introduced to decrease the bearing dislocation rate that was unacceptably high with the flat tibial tray. However, the introduction of the domed tibial component alters the forces transmitted through the implant-cement-bone interface. As the Oxford UKR uses a fully congruent mobile bearing, the forces transmitted through the interface with a flat tray are compressive, except for the effect of friction. However, with the domed tibial component shear forces are introduced. The aim of this study was to assess the prevalence of radiolucency beneath the previous flat design and the new domed tibial tray. Patients and methods. A consecutive series of 248 cemented lateral UKRs (1999–2009) at a single institution were assessed. The first 55 were with a flat tibia and the subsequent 193 with a domed component. One year post-op radiographs were assessed, by two observers, for the presence (full or partial) and distribution of radiolucency. The distribution and thickness of each radiolucency. Cases were excluded for missing or poorly aligned radiographs. Results. In the flat group there were 42 patients (17 male, 25 female) with 42 joints. In the domed group there were 139 patients (44 male, 95 female) with 146 joints. There was a statistical significant difference between groups for the presence and extent of radiolucency (p<0.001). In the flat group, 6 (14%) had a full radiolucency and 18 (43%) had a partial radiolucency. 14 of the 18 partial radiolucencies involved the far lateral zones (1&2) and 3 partial radiolucencies involved the keel. In the domed group 6, (4.1%) had a full radiolucency and 13 (8.9%) had a partial radiolucency. All radiolucencies observed were less than 1 mm thick. Intra-class correlation for inter-observer agreement for assessment of radiolucency was 0.679. Discussion. The introduction the domed lateral tibial component results in a reduction in prevalence of radiolucency compared to a flat component. This suggests, as the mode of fixation is identical, that the forces across the tibial-cement-bone interface have a significant effect on the development of the tissue at that interface. In particular it suggests that compressive forces alone tend to cause soft tissue to be formed at the interface, whereas shear force causes bone

Introduction: Oxford Unicompartmental knee arthroplasty (UKA) is now performed using a minimally invasive surgical (MIS) technique. Although early results are encouraging, the studies assessing outcome could be criticised for the restricted number of patients and centres involved. A multi-centre follow-up of patients is required to confirm the preliminary findings. Aim: To examine early clinical outcome in patients with minimally invasive Oxford medial UKA using a multi-centre, multi-surgeon design. Materials and Methods: This prospective study was carried out in three centres with involvement of six surgeons. All patients undergoing cemented Oxford UKA for medial OA using MIS were included. 231 consecutive UKAs with a minimum follow up of 2 years (mean: 2.84) were assessed using objective and functional Knee Society Score (KSS). Results: There were 108 females and 102 males (21-bilateral) with average age of 66.8 years (42 – 86). No significant difference was noted between various age groups or between different surgeons. Three knees were revised: one for infection, one for unexplained pain and one for bearing dislocation. Cumulative survival rate at 2 years was 98.6% with 93% patients having good or excellent KSS rating. Conclusions: This multi-centre study has confirmed preliminary findings that Oxford UKA using a minimally invasive approach is safe and effective

To identify frequency and patterns of Oxford Phase 3 UKA failure in New Zealand through analysis of national primary and revision data. Retrospective audit examining all revision Oxford Phase 3 UKAs recorded in the New Zealand National Joint Register from January 2000 to October 2003 were analysed along with surgeons’ clinical notes and patient x-rays. Seventy-three Orthopædic Surgeons performed 1216 Oxford UKAs. The average age was 66.4 years (range 35–94). Osteoarthritis was the primary diagnosis for 1163 (96%) patients. Mean time to revision was 437 days (14.4 months). The early revision rate was 2.2% (n=27). The most common reasons for revision were aseptic loosening (n=7, 26%), bearing dislocation (n=5, 19%) and pain (n=4, 15%). The deep infection rate was 0.16% (2/1216). Eighteen surgeons (high use > 8 UKAs/year) performed 787 (64%) operations, with a revision rate of 1.5%. Twenty-two surgeons (low use ≤ 1 UKA/year) performed 38 (3%) operations, with a revision rate of 8%. This was statistically significant, p= 0.03 (odds ratio 5.7). The early revision rate for the Oxford UKA is 1.4 times greater than TKA. High use surgeons revision rate is lower than TKA. An inverse relationship between failure and surgeon experience exists. This confirms Swedish Knee Arthroplasty Register findings