Aims. Higher osteoblastic bone activity is expected in aseptic loosening and painful unicompartmental knee arthroplasty (UKA). However, insights into normal bone activity patterns after medial UKAs are lacking. The aim of this study was to identify the evolution in bone activity pattern in well-functioning medial mobile-bearing UKAs. Methods. In total, 34 patients (13 female, 21 male; mean age 62 years (41 to 79); BMI 29.7 kg/m. 2. (23.6 to 42.1)) with 38 medial Oxford partial UKAs (20 left, 18 right; 19 cementless, 14 cemented, and five hybrid) were prospectively followed with sequential 99mTc-hydroxymethane diphosphonate single photon emission CT (SPECT)/CT preoperatively, and at one and two years postoperatively. Changes in mean osteoblastic activity were investigated using a tracer localization scheme with volumes of interest (VOIs), reported by normalized mean tracer values. A SPECT/CT registration platform additionally explored cortical tracer evolution in zones of interest identified by previous experimental research. Results. Significant reduction of tracer activity from the preoperative situation was found in femoral and anteromedial tibial VOIs adjacent to the UKA components. Temporarily increased osteoblastic bone activity was observed in VOIs comprising the UKA keel structure at one year postoperatively compared to the preoperative activity. Persistent higher tracer uptake was found in the posterior tibial cortex at final follow-up. Multivariate analysis showed no statistical difference in osteoblastic bone activity underneath cemented or cementless components. Conclusion. Well-functioning medial mobile-bearing UKAs showed distinct changes in patterns of normalized bone tracer activity in the different VOIs adjacent to the prosthetic components, regardless of their type of fixation. Compared to the preoperative situation, persistent high bone activity was found underneath the keel and the posterior tibial cortex at final follow-up, with significant reduced activity only being identified in femoral and anteromedial tibial VOIs. Cite this article: Bone Joint J 2022;104-B(1):34–44

This study compared the outcome of total knee replacement (TKR) in adult patients with fixed- and mobile-bearing prostheses during the first post-operative year and at five years’ follow-up, using gait parameters as a new objective measure. This double-blind randomised controlled clinical trial included 55 patients with mobile-bearing (n = 26) and fixed-bearing (n = 29) prostheses of the same design, evaluated pre-operatively and post-operatively at six weeks, three months, six months, one year and five years. Each participant undertook two walking trials of 30 m and completed the EuroQol questionnaire, Western Ontario and McMaster Universities osteoarthritis index, Knee Society score, and visual analogue scales for pain and stiffness. Gait analysis was performed using five miniature angular rate sensors mounted on the trunk (sacrum), each thigh and calf. The study population was divided into two groups according to age (≤ 70 years versus > 70 years). Improvements in most gait parameters at five years’ follow-up were greater for fixed-bearing TKRs in older patients (> 70 years), and greater for mobile-bearing TKRs in younger patients (≤ 70 years). These findings should be confirmed by an extended age controlled study, as the ideal choice of prosthesis might depend on the age of the patient at the time of surgery

Mobile-bearing (MB) total knee replacement (TKR) was introduced to reduce the risk of aseptic loosening and wear of polyethylene inserts. However, no consistent clinical advantages of mobile- over fixed-bearing (FB) TKR have been found. In this study we evaluated whether mobile bearings have an advantage over fixed bearings with regard to revision rates and clinical outcome scores. Furthermore, we determined which modifying variables affected the outcome. A systematic search of the literature was conducted to collect clinical trials comparing MB and FB in primary TKR. The primary outcomes were revision rates for any reason, aseptic loosening and wear. Secondary outcomes included range of movement, Knee Society score (KSS), Oxford knee score (OKS), Short-Form 12 (SF-12) score and radiological parameters. Meta-regression techniques were used to explore factors modifying the observed effect. . Our search yielded 1827 publications, of which 41 studies met our inclusion criteria, comprising over 6000 TKRs. Meta-analyses showed no clinically relevant differences in terms of revision rates, clinical outcome scores or patient-reported outcome measures between MB and FB TKRs. It appears that theoretical assumptions of superiority of MB over FB TKR are not borne out in clinical practice. Cite this article: Bone Joint J 2013;95-B:1209–16

The purpose of this study was to undertake a meta-analysis to determine whether there is lower polyethylene wear and longer survival when using mobile-bearing implants in total knee replacement when compared with fixed-bearing implants. Of 975 papers identified, 34 trials were eligible for data extraction and meta-analysis comprising 4754 patients (6861 knees). We found no statistically significant differences between the two designs in terms of the incidence of radiolucent lines, osteolysis, aseptic loosening or survival. There is thus currently no evidence to suggest that the use of mobile-bearing designs reduce polyethylene wear and prolong survival after total knee replacement. Cite this article: Bone Joint J 2013;95-B:1057–63

This prospective randomised controlled double-blind trial compared two types of PFC Sigma total knee replacement (TKR), differing in three design features aimed at improving flexion. The outcome of a standard fixed-bearing posterior cruciate ligament-preserving design (FB-S) was compared with that of a high-flexion rotating-platform posterior-stabilised design (RP-F) at one year after TKR.

The study group of 77 patients with osteoarthritis of the knee comprised 37 men and 40 women, with a mean age of 69 years (44.9 to 84.9). The patients were randomly allocated either to the FB-S or the RP-F group and assessed pre-operatively and at one year post-operatively. The mean post-operative non-weight-bearing flexion was 107° (95% confidence interval (CI) 104° to 110°)) for the FB-S group and 113° (95% CI 109° to 117°) for the RP-F group, and this difference was statistically significant (p = 0.032). However, weight-bearing range of movement during both level walking and ascending a slope as measured during flexible electrogoniometry was a mean of 4° lower in the RP-F group than in the FB-S group, with 58° (95% CI 56° to 60°) versus 54° (95% CI 51° to 57°) for level walking (p = 0.019) and 56° (95% CI 54° to 58°) versus 52° (95% CI 48° to 56°) for ascending a slope (p = 0.044). Further, the mean post-operative pain score of the Western Ontario and McMaster Universities Osteoarthritis Index was significantly higher in the RP-F group (2.5 (95% CI 1.5 to 3.5) versus 4.2 (95% CI 2.9 to 5.5), p = 0.043).

Although the RP-F group achieved higher non-weight-bearing knee flexion, patients in this group did not use this during activities of daily living and reported more pain one year after surgery.

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

Mobile-bearing posterior-stabilised knee replacements have been developed as an alternative to the standard fixed- and mobile-bearing designs. However, little is known about the in vivo kinematics of this new group of implants. We investigated 31 patients who had undergone a total knee replacement with a similar prosthetic design but with three different options: fixed-bearing posterior cruciate ligament-retaining, fixed-bearing posterior-stabilised and mobile-bearing posterior-stabilised. To do this we used a three-dimensional to two-dimensional model registration technique. Both the fixed- and mobile-bearing posterior-stabilised configurations used the same femoral component. We found that fixed-bearing posterior stabilised and mobile-bearing posterior-stabilised knee replacements demonstrated similar kinematic patterns, with consistent femoral roll-back during flexion. Mobile-bearing posterior-stabilised knee replacements demonstrated greater and more natural internal rotation of the tibia during flexion than fixed-bearing posterior-stabilised designs. Such rotation occurred at the interface between the insert and tibial tray for mobile-bearing posterior-stabilised designs. However, for fixed-bearing posterior-stabilised designs, rotation occurred at the proximal surface of the bearing. Posterior cruciate ligament-retaining knee replacements demonstrated paradoxical sliding forward of the femur. We conclude that mobile-bearing posterior-stabilised knee replacements reproduce internal rotation of the tibia more closely during flexion than fixed-bearing posterior-stabilised designs. Furthermore, mobile-bearing posterior-stabilised knee replacements demonstrate a unidirectional movement which occurs at the upper and lower sides of the mobile insert. The femur moves in an anteroposterior direction on the upper surface of the insert, whereas the movement at the lower surface is pure rotation. Such unidirectional movement may lead to less wear when compared with the multidirectional movement seen in fixed-bearing posterior-stabilised knee replacements, and should be associated with more evenly applied cam-post stresses

Objectives. Unicompartmental knee arthroplasty (UKA) is an alternative to total knee arthroplasty with isolated medial or lateral compartment osteoarthritis. However, polyethylene wear can significantly reduce the lifespan of UKA. Different bearing designs and materials for UKA have been developed to change the rate of polyethylene wear. Therefore, the objective of this study is to investigate the effect of insert conformity and material on the predicted wear in mobile-bearing UKA using a previously developed computational wear method. Methods. Two different designs were tested with the same femoral component under identical kinematic input: anatomy mimetic design (AMD) and conforming design inserts with different conformity levels. The insert materials were standard or crosslinked ultra-high-molecular-weight polyethylene (UHMWPE). We evaluated the contact pressure, contact area, wear rate, wear depth, and volumetric wear under gait cycle loading conditions. Results. Conforming design inserts had the lower contact pressure and larger contact area. However, they also had the higher wear rate and volumetric wear. The improved wear performance was found with AMD inserts. In addition, the computationally predicted volumetric wear of crosslinked UHMWPE inserts was less than half that of standard UHMWPE inserts. Conclusion. Our results showed that increasing conformity may not be the sole predictor of wear performance; highly crosslinked mobile-bearing polyethylene inserts can also provide improvement in wear performance. These results provide improvements in design and materials to reduce wear in mobile-bearing UKA. Cite this article: Bone Joint Res 2019;8:563–569

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

Background. Currently there are various knee prosthesis designs available each with its plus and minus points; there is no general consensus on whether mobile-bearing knees are functionally better than fixed-bearing ones. This study is designed to compare outcomes after total knee arthroplasty with both of the above prostheses. Materials & Methods. 50 patients (68 knees) who'd had a total knee arthroplasty between April 1999 and April 2008 at both Akhtar and Kian Hospitals for primary osteoarthritis were selected. In 30 cases a fixed-bearing knee (Scorpio(r), Stryker) and in the remaining 38 a mobile-bearing prosthesis (Rotaglide(r), Corin Group) was used. Patients' knees were scored before and after the operation according to the Knee Society Scoring System. The mobile-bearing group had an average age of 65 and 34 months' follow-up; in the fixed-bearing group the average age was 69 and the average follow-up 30 months. Results. The average knee score in the mobile-bearing group rose from 29 to 64 while in the fixed-bearing group the score changed from 31 to 68. The average functional score moved from 45 to 67 in the mobile-bearing group and from 34 to 57 in the fixed-bearing group. The average overall score, for the fixed-bearing group, moved from 65 to 125 and in the mobile-bearing group from 75 to 128. Conclusion. In both groups the average knee/functional knee scores increased after the operation and all patients were happy with the results, however statistically there was no meaningful relationship between pre-and post-operation scores. So regarding to our findings, there is no preference between these two types of prosthesis

Aims. Since redesign of the Oxford phase III mobile-bearing unicompartmental knee arthroplasty (UKA) femoral component to a twin-peg design, there has not been a direct comparison to total knee arthroplasty (TKA). Thus, we explored differences between the two cohorts. Patients and Methods . A total of 168 patients (201 knees) underwent medial UKA with the Oxford Partial Knee Twin-Peg. These patients were compared with a randomly selected group of 177 patients (189 knees) with primary Vanguard TKA. Patient demographics, Knee Society (KS) scores and range of movement (ROM) were compared between the two cohorts. Additionally, revision, re-operation and manipulation under anaesthesia rates were analysed. Results. The mean follow-up for UKA and TKA groups was 5.4 and 5.5 years, respectively. Six TKA (3.2%) versus three UKAs (1.5%) were revised which was not significant (p = 0.269). Manipulation was more frequent after TKA (16; 8.5%) versus none in the UKA group (p <  0.001). UKA patients had higher post-operative KS function scores versus TKA patients (78 versus 66, p < 0.001) with a trend toward greater improvement, but there was no difference in ROM and KS clinical improvement (p = 0.382 and 0.420, respectively). Conclusion. We found fewer manipulations, and higher functional outcomes for patients treated with medial mobile-bearing UKA compared with TKA. TKA had twice the revision rate as UKA although this did not reach statistical significance with the numbers available. . Cite this article: Bone Joint J 2016;98-B(10 Suppl B):28–33

Bone mineral density (BMD) around the femoral component has been reported to decrease after total knee replacement (TKR) because of stress shielding. Our aim was to determine whether a cemented mobile-bearing component reduced the post-operative loss of BMD. In our study 28 knees receiving a cemented fixed-bearing TKR were matched with 28 receiving a cemented mobile-bearing TKR. They underwent dual-energy x-ray absorptiometry, pre-operatively and at three weeks and at three, six, 12, 18 and 24 months post-operatively. The patients were not taking medication to improve the BMD. The pre-operative differences in the BMD of the femoral neck, wrist, lumbar spine and knee in the two groups were not significant. The BMD of the femur decreased postoperatively in the fixed-bearing group, but not the mobile-bearing group. The difference in the post-operative change in the BMD in the two groups was statistically significant (p < 0.05) at 18 and 24 months. Our findings show that a cemented mobile-bearing TKR has a favourable effect on the BMD of the distal femur after TKR in the short term. Further study is required to determine the long-term effects

We have examined the outcome of 400 consecutive patients who underwent total knee replacement with the Low Contact Stress mobile-bearing system between 1993 and 1994 and were followed up for a minimum of ten years. All operations were performed by surgeons in Christchurch, New Zealand, who used no other knee prosthesis during the study time. At ten years after operation 238 patients (244 knees) remained for independent clinical and radiological assessment. There was a significant improvement (p < 0.001) in the postoperative knee scores at one, three, seven and ten years, although a slight deterioration in the score occurred between seven and ten years which did not reach statistical significance. The survival for polyethylene wear or loosening was 97% (95% CI 96 to 98) and survival using reoperation for any cause was 92% (95% CI 90 to 94) at 12 years. Polyethylene wear was more common in the meniscal-bearing component, with five knees requiring revision and a further eight demonstrating early wear. Osteolysis was not seen in the rotating platform component, but was present in three of the meniscal-bearing knees. There was no association between the radiological alignment at one year and those knees that subsequently required revision. However, there was an association between the overall limb alignment and the Western Ontario McMasters University score (p < 0.001). The Low Contact Stress mobile-bearing total knee replacement has proved to be a reliable implant at ten years when used in primary knee replacement irrespective of the deformity and diagnosis

Mobile-bearing total knee arthroplasty was developed to provide low contact stress and reasonably unrestricted joint motion. We studied the results of a cementless, posterior cruciate ligament (PCL)-retaining total knee arthroplasty (TKA), with a mobile-bearing insert in rotation and anterior-posterior (AP) translation (Innex. ®. Anterior-Posterior Glide, Zimmer). Kinematic analyses were performed on a series of 51 primary TKA. The patients’ mean age was 71±8 years at operation. Patients were studied at 23 months average follow-up with weight-bearing radiographs at full-extension, 30° flexion and maximum flexion (“lunge” position). Three dimensional position and orientation of the mobile-bearing relative to the femoral and the tibial component during flexion were determined using model-based shapematching techniques. The average weight-bearing range of implant motion was 110°±14°. In flexion, the mobile-bearing was internally rotated 3°±3° with respect to the femoral component (p< 0.0001) and the tibial tray was internally rotated 5°±7° with respect to the mobile-bearing (p< 0.0001). On average, the mobile-bearing did not translate relative to the tibial base plate from full extension to 45° flexion [0±2 mm (range −5 mm to 6 mm)]. However, the mobilebearing did translate anteriorly 1±2 mm (range −2 mm to 9 mm, p< 0.0001) between 45° flexion and maximal flexion. We conclude that the mobile-bearing insert showed a progressive increase in internal rotation during flexion. Most of this rotational mobility occurred between the mobile insert and the tibial base plate. With flexion, AP translation did occur between the femoral component and mobile-bearing, and between the mobile-bearing and tibial base plate, but mobile-bearing translation was unpredictable with this unconstrained design

We compared patient-reported outcomes of the Kinemax fixed- and mobile-bearing total knee replacement in a multi-centre randomised controlled trial. Patients were randomised to the fixed- or the mobile-bearing prosthesis via a sealed envelope method after the bone cuts had been made in the operating theatre. Randomisation was stratified by centre and diagnosis. Patients were assessed pre-operatively and at eight to 12 weeks, one year and two years post-operatively. Validated questionnaires were used which included the Western Ontario MacMasters University, Short-Form 12, Mental Health Index-5, Knee Injury and Osteoarthritis Outcome Score for Knee-Related Quality of Life and Function in Sport and Recreation scales and a validated scale of satisfaction post-operatively. In total, 242 patients (250 knees) with a mean age of 68 years (40 to 80) were recruited from four NHS orthopaedic centres. Of these, 132 patients (54.5%) were women. No statistically significant differences could be identified in any of the patient-reported outcome scores between patients who received the fixed-bearing or the mobile-bearing knee up to two-years post-operatively

Aims. This study compares the PFC total knee arthroplasty (TKA) system in a prospective randomized control trial (RCT) of the mobile-bearing rotating-platform (RP) TKA against the fixed-bearing (FB) TKA. This is the largest RCT with the longest follow-up where cruciate-retaining PFC total knee arthroplasties are compared in a non-bilateral TKA study. Patients and Methods. A total of 167 patients (190 knees with 23 bilateral cases), were recruited prospectively and randomly assigned, with 91 knees receiving the RP and 99 knees receiving FB. The mean age was 65.5 years (48 to 82), the mean body mass index (BMI) was 29.7 kg/m. 2. (20 to 52) and 73 patients were female. The Knee Society Score (KSS), Knee Society Functional Score (KSFS), Oxford Knee Score (OKS), Western Ontario and McMaster Universities Arthritis Index (WOMAC), and 12-Item Short-Form Health Survey Physical and Mental Component Scores (SF-12 PCS, SF-12 MCS) were gathered and recorded preoperatively, at five-years’ follow-up, and at ten years’ follow-up. Additionally, Knee Injury and Osteoarthritis Outcome Scores (KOOS) were collected at five- and ten-year follow-ups. The prevalence of radiolucent lines (RL) on radiographs and implant survival were recorded at five- and ten-year follow-ups. Results. At the ten-year follow-up, the RP group (n = 39) had a statistically significant superior score in the OKS (p = 0.001), WOMAC (p = 0.023), SF-12 PCS (p = 0.019), KOOS Activities of Daily Living (ADL) (p = 0.010), and KOOS Sport and Recreation (Sport/Rec) (p = 0.006) compared with the FB group (n = 46). The OKS, SF-12 PCS, and KOOS Sport/Rec at ten years had mean scores above the minimal clinically important difference (MCID) threshold. There was no significant difference in prevalence of radiolucency between groups at five-years’ follow-up (p = 0.449), nor at ten-years’ follow-up (p = 0.08). Implant survival rate at 14 years postoperative was 95.2 (95% CI 90.7 to 99.8) and 94.7 (95% CI 86.8 to 100.0) for the RP and FB TKAs, respectively. Conclusion. At ten-year follow-up, the mobile-bearing knee joint arthroplasty had statistically and clinically relevant superior OKS, SF-12 PCS, and KOOS (Sport/Rec) than the fixed-bearing platform. No difference was seen in prevalence of radiolucent lines. There was a greater than 94% implant survival rate for both cohorts at 14 years. Cite this article: Bone Joint J 2018;100-B:1336–44

We prospectively reviewed patients who had undergone a Revision Total Knee Replacement (TKR) to a mobile-bearing arthroplasty. We wanted to assess functional outcome and survival, and to determine whether the perceived advantages of a mobile-bearing arthroplasty could be expanded to the revision situation. We divided the patients into two groups. Group 1 consisted of 40 patients who were revised to a rotating platform, with or without stems and augments, and group 2 consisted of 41 patients revised to a varus-valgus constrained mobile-bearing device that still allowed rotation of the bearing. All were assessed with Knee Society Knee Scores, WOMAC, and New Jersey Knee Scores and standard radiographs by an independent examiner. Group 1 had an average age of 71 years at revision and a follow-up of 5–9 years. Seventy-six percent had excellent or good results with 89% survival at 9 years. Group 2 had an average age of 71 years at revision and a follow-up of 2–5 years. The patient satisfaction score was 8/10 and the normality score was 6.8/10. There was only one case of instability in both groups in a patient with a patellar fracture. A mobile-bearing TKR can be used in the revision situation with acceptable clinical results and patient outcome without compromising the stability or survivorship in the short-term. It has proved to be a “patellar-friendly” procedure with reduced re-operation for patellar complications; however longer-term studies are required to determine whether the rates of polyethylene wear are reduced by the use of a more congruent articulation

Aims. The aims of this retrospective study were to determine the incidence of extra-articular deformities (EADs), and determine their effect on postoperative alignment in knees undergoing mobile-bearing, medial unicompartmental knee arthroplasty (UKA). Patients and Methods. Limb mechanical alignment (hip-knee-ankle angle), coronal bowing of the femoral shaft and proximal tibia vara or medial proximal tibial angle (MPTA) were measured on standing, full-length hip-to-ankle radiographs of 162 patients who underwent 200 mobile-bearing, medial UKAs. Results. Incidence of EAD was 7.5% for coronal femoral bowing of >5°, 67% for proximal tibia vara of >3° (MPTA<87°) and 24.5% for proximal tibia vara of >6° (MPTA<84°). Mean postoperative HKA angle achieved in knees with femoral bowing ≤5° was significantly greater when compared to knees with femoral bowing >5° (p=0.04); in knees with proximal tibia vara ≤3° was significantly greater when compared to knees with proximal tibia vara >3° (p=0.0001) and when compared to knees with proximal tibia vara >6° (p=0.0001). Conclusion. Extra-articular deformities are frequently seen in patients undergoing mobile-bearing medial UKAs, especially in knees with varus deformity>10°. Presence of an EAD significantly affects postoperative mechanical limb alignment achieved when compared to limbs without EAD and may increase the risk of limbs being placed in varus>3° postoperatively. Clinical Relevance. Since the presence of an EAD, especially in knees with varus deformity>10°, may increase the risk of limbs being placed in varus>3° postoperatively and may affect long-term clinical and implant survival outcomes, UKR in such knees should be performed with caution

The Oxford mobile-bearing unicompartmental knee replacement (UKR) is an effective and safe treatment for osteoarthritis of the medial compartment. The results in the lateral compartment have been disappointing due to a high early rate of dislocation of the bearing. A series using a newly designed domed tibial component is reported. The first 50 consecutive domed lateral Oxford UKRs in 50 patients with a mean follow-up of three years (2.0 to 4.3) were included. Clinical scores were obtained prospectively and Kaplan-Meier survival analysis was performed for different endpoints. Radiological variables related to the position and alignment of the components were measured. One patient died and none was lost to follow-up. The cumulative incidence of dislocation was 6.2% (95% confidence interval (CI) 2.0 to 17.9) at three years. Survival using revision for any reason and aseptic revision was 94% (95% CI 82 to 98) and 96% (95% CI 85 to 99) at three years, respectively. Outcome scores, visual analogue scale for pain and maximum knee flexion showed a significant improvement (p < 0.001). The mean Oxford knee score was 43 (. sd. 5.3), the mean Objective American Knee Society score was 91 (. sd. 13.9) and the mean Functional American Knee Society score was 90 (. sd. 17.5). The mean maximum flexion was 127° (90° to 145°). Significant elevation of the lateral joint line as measured by the proximal tibial varus angle (p = 0.04) was evident in the dislocation group when compared with the non-dislocation group. Clinical results are excellent and short-term survival has improved when compared with earlier series. The risk of dislocation remains higher using a mobile-bearing UKR in the lateral compartment when compared with the medial compartment. Patients should be informed about this complication. To avoid dislocations, care must be taken not to elevate the lateral joint line.

Aims. Spontaneous osteonecrosis of the knee (SONK) mainly affects the medial femoral condyle, would be a good indication for UKA. The primary aim of this study was to assess the clinical, functional and radiographic outcomes at middle to long-term follow-up, of a consecutive series of fifty UKA used for the treatment of SONK. The secondary aim was to assess the volume of necrotic bone and determine if this influenced the outcome. Patients and Methods. We reviewed 50 knees who were treated for SONK. Patients included ten males and 38 females. The mean age was 73 years (range, 57 to 83 years). The mean height and body weight were, respectively 153 cm (141 ∼171 cm) and 57 kg (35 ∼75kg). All had been operated on using the Oxford mobile-bearing UKA (Zimmer-Biomet, Swindon, United Kingdom) with cement fixation. The mean follow-up period was 8.4 years (range, 4 to 15years). We measured the size (width, length and depth) and the volume to be estimated (width x length x depth) of the necrotic bone mass using MRI in T1-weighted images. The clinical results were evaluated using the Knee Society Scoring System (KSS) and Oxford Knee Score (OKS). The flexion angle of the knee was evaluated using lateral X-ray images in maximum flexion. Results. There were no implant failures, but there were 4 deaths (from causes unrelated to UKA) mean 6.6 years after surgery(5∼8), 3 cases were lost mean 3.3 years after surgery(2∼5). The mean size of the necrotic lesion were 17.2mm (14.7∼25.3) in width, 28.2mm (6.2∼38.3) in length and 11.3mm (3.2∼14.3) in depth. The mean volume of it was calculated to be approximate 5.4 cm. 3. (0.7∼11.1). The mean flexion of the knee, KSS Knee Score, Function Score and OKS increased from a preoperative 128.7 degrees (110 ∼ 140 degrees) to 137.5 degrees (110 ∼ 153 degrees), 52.3 (30 ∼ 64) to 91.3 (87 ∼ 100), 39.7 (15∼ 55) to 90.2 (65 ∼ 100) and 21.6 (12∼ 28) to 40.2 (34∼ 48), respectively at the latest follow-up. At last follow-up all patients had good or excellent OKS. Conclusions. There was a 100% survival rate of the Oxford Phase 3 UKA for SONK in the middle to long-term (up to 15 years after surgery) in this independent study. All patients had good/excellent results at last follow-up and there were no reoperations or major complications. This suggests that Oxford mobile-bearing UKA is a good and definitive treatment for medial femoral SONK, whatever the size of the lesion