We describe injuries to the posterior root of the medial meniscus in patients with spontaneous osteonecrosis of the medial compartment of the knee. We identified 30 consecutive patients with spontaneous osteonecrosis of the medial femoral condyle. The radiographs and MR imaging were reviewed. We found tears of the posterior root of the medial meniscus in 24 patients (80%). Of these, 15 were complete and nine were partial. Complete tears were associated with > 3 mm of meniscal extrusion. Neither the presence of a root tear nor the volume of the osteonecrotic lesion were associated with age, body mass index (BMI), gender, side affected, or knee alignment. The grade of osteoarthritis was associated with BMI. Although tears of the posterior root of the medial meniscus were frequently present in patients with spontaneous osteonecrosis of the knee, this does not prove cause and effect. Further study is warranted

We prospectively examined the physical and imaging findings, including MRI, of 23 patients with spontaneous osteonecrosis of the knee after obtaining informed consent to acquire tissue specimens at surgery. There were four men and 19 women, with a mean age of 67.5 years (58 to 77). Plain radiographs were designated as stages 1, 2, 3 or 4 according to the classification of Koshino. Five knees were classified as stage 1, five as stage 2, seven as stage 3 and six as stage 4. The histological specimens were stained with haematoxylin and eosin and tetrachrome. In the early stages of the condition, a subchondral fracture was noted in the absence of any features of osteonecrosis, whereas in advanced stages, osteonecrotic lesions were confined to the area distal to the site of the fracture which showed impaired healing. In such cases, formation of cartilage and fibrous tissue, occurred indicating delayed or nonunion. These findings strongly suggest that the histopathology at each stage of spontaneous osteonecrosis is characterised by different types of repair reaction for subchondral fractures

The natural history of spontaneous osteonecrosis of the medial tibial plateau remains controversial and incomplete. We have studied 21 patients (aged between 53 and 77 years) with clinical and scintigraphic features of spontaneous osteonecrosis of the medial tibial plateau who were observed prospectively for at least three years (37 months to 8.5 years). The mean duration of follow-up was 5.6 years. The mean duration of symptoms at presentation was 4.7 weeks (3 days to 12 weeks). Radiographs of the affected knee at the first visit were normal in 15 patients and mildly arthritic in six. The characteristic radiographic lesion of osteonecrosis was noted at presentation in five of the mildly arthritic knees and during the evolution of the disease in eight of the radiographically normal knees. During the follow-up, subchondral sclerosis of the affected medial tibial plateau was noted in 16 knees. There are three distinct patterns of outcome: 1) acute extensive collapse of the medial tibial plateau in two knees within three months of onset; 2) rapid progression to varying degrees of osteoarthritis in 12 knees, in eight within a year, in all within two years and deterioration of the pre-existing osteoarthritis in three; and 3) complete resolution in four knees, two of which were normal at presentation and two mildly osteoarthritic. The two patients with acute extensive collapse and three who had rapid progression to severe osteoarthritis required total knee arthroplasty. We conclude that osteonecrosis of the medial tibial plateau progresses in most cases to significant degenerative disease of the knee

Aims

Primary (or spontaneous) and secondary osteonecrosis of the knee can lead to severe joint degeneration, for which either total or unicompartmental arthroplasty may be considered. However, there are limited studies analyzing outcomes of unicompartmental knee arthroplasties (UKAs) for osteonecrosis involving an isolated compartment of the knee. The aims of this study were to analyze outcomes of UKAs for osteonecrosis with specific focus on 1) survivorship free of any revision or reoperation, 2) risk factors for failure, 3) clinical outcomes, and 4) complications.

Purpose: Spontaneous osteonecrosis of the knee is a potentially greatly debilitating condition. While success has been reported with non-operative treatment of this disorder in its earliest stages, knee arthroplasty is the only viable modality if allowed to progress to condylar collapse. The purpose of this report is to review the etiologic and pathophysiologic principles of spontaneous osteonecrosis of the knee, to present our experience with joint-preserving surgical treatment of this condition, and finally to introduce a treatment algorithm developed based on this knowledge. Method: Seventeen patients with a clinical and/or radiographic a diagnosis of spontaneous osteonecrosis of the knee, and exclusion of secondary osteonecrosis, who failed non-operative modalities were treated with joint-preserving surgery at a single center between January 2000 and December 2006. Treatment modalities included arthroscopy, and either percutaneous core decompression and/or osteochondral autograft transfer. Three knees were lost to follow-up, leaving 14 knees with a mean follow-up of 37 months (range, 11 to 84 months). Results: Twelve of 14 knees (86%) had knee joint survival with a mean Knee Society Score of 80 points (range, 45 to 100 points) at final follow-up. One patient was treated with serial core decompression followed by osteochondral transfer, and was included in both groups. Six of 7 patients (86%) treated with core decompression alone had a successful clinical outcome, as did 7 of 8 patients (87%) treated with osteochondral autograft transfers. Two patients (14%) progressed to condylar collapse, and were treated with total knee arthroplasty with successful results. Conclusion: Based on these results, we propose a treatment algorithm that begins with non-operative treatment, followed by joint-preserving surgery consisting of arthroscopy, core decompression, and/or osteochondral autograft transfer. Although our sample size is small, the results suggest that this proposed treatment algorithm can successfully postpone the need for knee arthroplasty in selected patients with pre-collapse spontaneous osteonecrosis of the knee

Introduction: The data reporting clinical and radiological outcomes after modern unicompartmental knee arthroplasty (UKA) for spontaneous avascular osteonecrosis are limited. We hypothesized that UKA for spontaneous osteonecrosis may be as reliable and durable as it is for osteoarthritis. Materials and Methods: We retrospectively reviewed 40 cemented UKA operated for spontaneous osteonecrosis of the knee in two different centers between 1989 and 2004. Twenty-six patients were women and 14 men, mean patient age was 67 years (range, 45 to 84) and mean body mass index was 27.4 Kg/m2 (range, 18 to 44). Clinical and radiological evaluations were performed by an independent observer in each center according to the same protocol at a minimum follow-up of 3 years (mean 8 years; range, 3–17.5 years). Results: The mean Knee Society Knee score improved from 60 preoperatively to 95 post-operatively. The mean Knee Society Function score improved from 50 preoperatively to 89 post-operatively. Restoration of an appropriate lower-limb mechanical axis was achieved for 36 knees (90%). Two knees were revised for aseptic loosening. The Kaplan–Meier survivorship was 95% at 12 years. Discusssion and conclusion: Our data suggest UKA is a reasonable solution for restoring clinical function and radiological lower-limb alignment for spontaneous osteonecrosis of the knee, with a durable survivorship

Abstract. INTRODUCTION. A paucity of literature exists regarding efficacy of lateral unloader bracing in treatment for pathologies effecting the lateral compartment of the knee. We evaluate patient outcomes following customised lateral unloader bracing (cLUB) in treatment of lateral compartment osteoarthritis (LCOA), lateral tibial plateau fractures (LTPF) and spontaneous osteonecrosis of knee (SONK). METHODS. Institutional study approval was obtained. All patients undergoing cLUB between January 2013 and January 2021 were included, and prospectively followed-up. Visual Analogue Scales (VAS), Oxford Knee Scores (OKS) and Knee Injury and Osteoarthritis Outcome Scores (KOOS) were assessed at brace fitting and final follow-up. Brace compliance, complications and surgical interventions were also collected. Statistical analysis utilised paired t-test. RESULTS. 71 patients (LCOA n=47, LTPF n=21, SONK n=3) were analysed. VAS, OKS and KOOS scores show significant improvements after bracing (p<0.05). Brace compliance was 90.5%. One patient developed a deep-vein thrombosis, 12.7% suffered skin irritation (n=5 LTPF/n=4 LCOA) managed with bio-skin calf sleeves, and brace intolerance occurred in 8.5% (n=6). Brace survivorship was 64.8% (n=46). Twenty-five patients underwent post-bracing surgery; LTPF n=2, LCOA n=22, SONK n=1. The mean time interval between brace fitting and arthroplasty for LKOA patients was 2.1 (range 0.5-4) years. CONCLUSION. Our cohort demonstrates good compliance and significant improvements with cLUB across acute and chronic pathologies. Surgery and associated risks were avoided in certain cases. Further research is required alongside a cost-analysis. However, with increasing disease burden and surgical waiting times cLUB could be a crucial component of management in selected knee pathology cases

Spontaneous osteonecrosis of the knee (SONK) is a distinct clinical condition occurring in patients without any associated risk factors. There is controversy as to the best method of treatment, and the available literature would suggest that patients with SONK have a worse outcome. We evaluated the clinical and radiographic outcomes of unicompartmental knee arthroplasty using Oxford prosthesis in patients with spontaneous osteonecrosis. Between September 2002 and March 2008, 20 knees (18 patients) with SONK were treated with Oxford unicompartmental knee arthroplasty. There were fifteen women and three men with a mean age of 61.1 years old. The mean follow up was 37 months. The clinical assessment was performed using the American knee society score rating system. The preoperative radiography and MRI were analyzed according to size and stage of the osteonecrotic lesion and the osteoarthritic changes. Postoperatively, new osteonecrotic lesion, loosening of implant, subsidence, arthritic changes of other compartment were recorded. The mean preoperative knee score and the knee function score were 52.5 and 56.0 points, respectively. The knee score was improved to 89.2 points (p < 0.05) and the knee function score was also improved to 85.2 points (p < 0.05) at last follow up. There were no implant failures. There was no new necrotic lesion in the lateral compartment, loosening, subsidence and arthritic change. The Oxford Unicompartmental knee arthroplasty for spontaneous osteonecrosis of the knee provided satisfactory clinical and radiological results in a short to medium term. However, a longer term follow up will be needed

Introduction. Osteonecrosis of the knee encompasses three conditions; spontaneous osteonecrosis of the knee, secondary osteonecrosis (ON) and post-arthroscopic ON. Early stage lesions can be managed by non-operative measures that include protected weight-bearing and analgesia. The aim of this study was to report the experience of the authors in managing early stages of knee ON by analysing the functional outcome and need for surgical intervention. Methods. All patients treated for osteonecrosis of the knee between 1st August 2001 and 1st April 2014 were prospectively collected. Treatment consisted of touch-down weight bearing for four to six weeks. The cases were retrospectively reviewed. MR imaging was evaluated for the stage of disease according to Koshino's Classification system, the condyles involved and the time taken for resolution. Tegner Activity Scale, VAS pain, Lysholm, WOMAC and IKDC scores were recorded at presentation and final follow up. Results. 51 cases were treated for knee ON at our centre; 40 cases of SONK, seven secondary ON and four post-arthroscopic ON. Of the seven cases of secondary osteonecrosis; 5 were secondary to self-reported high ethanol intake and two secondary to corticosteroid treatment. The mean age of the group was 56.9 years and 68.7% were male. The medial femoral condyle was the most commonly affected (54.9%). 86% reported resolution of clinical symptoms and a statistically significant improvement was reported in all functional outcome measures. Four patients required total knee arthroplasty; three in the post-arthroscopic group within 15 months and one following ON secondary to corticosteroids performed at 5 months. Conclusion. Early stage spontaneous osteonecrosis of the knee can be managed successfully without surgery if diagnosed early. Although secondary and post-arthroscopic ON seem to be more resistant. Larger studies are required to confirm or refute this. Level of Evidence. IV – a case series. Conflict of Interests. The authors confirm that they have no relevant financial disclosures or conflicts of interest. Ethical approval was not sought as this was a systematic review

The December 2013 Knee Roundup. 360 . looks at: Conflict of interest and hyaluronic acid; Will time indeed tell in microfracture?; Contralateral knee pain and joint replacement outcomes; Patient satisfaction and knee replacement?; Hope in the cytokines for painful TKRs?; Pain severity, cytokines and osteoarthritis?; Quadriceps weakness and pain; and spontaneous osteonecrosis of the knee

Introduction:. Unicompartmental knee arthroplasty has been shown to have lower morbidity, quicker rehabilitation and more normal kinematics compared to conventional TKA, but subchondral defects, or severe osteoarthritic changes, of the medial compartment may complicate component positioning. Successful UKA in these patients requires proper planning and exact placement of the components to ensure adequate and stable fixation and proper postoperative kinematics. This study presents a series of three patients with spontaneous osteonecrosis of the knee receiving a UKA with CT-based haptic robotic guidance. Methods:. This series includes two females and one male with spontaneous osteonecrosis of the medial femoral condyle who underwent outpatient mini-incision medial UKA using the MAKO Surgical Rio Robotic Arm System. Pre-operatively all patients were found to have pain with weight bearing that would not improve despite non-arthroplasty treatment. Results:. The first patient was a 69 year old female (BMI of 22.85) with a left medial femur size 3, tibia size 4, bearing size 4×8 mm. The patient improved her ROM from 3–112° pre-operatively to 0–130° at 18 months post-operatively. The second patient was a 69 year old female (BMI of 25.68) with a right medial size 2 femur and 3 tibia and a 3×9 mm bearing. ROM increased from 0–120° pre-operatively to 0–145° at 2 year follow-up. The third patient was a 74 year old male (BMI of 26.5) who underwent previous knee arthroscopy with subsequent SPONK. Conclusion:. The difficulty in treatment of SPONK with UKA solutions includes planning for the full coverage of the ON lesions while also addressing alignment, tracking and balancing needs simultaneously. Using the advanced planning tools of the MAKO Rio software, full coverage of ON lesions can be safely planned and verified preoperatively. The intraoperative flexibility of the system allows surgeon to map out the lesions intraoperatively, where visible, and aid in the proper implant positioning and size adjustment as necessary

Osteonecrosis of the knee comprises two separate disorders, primary spontaneous osteonecrosis which is often a self-limiting condition and secondary osteonecrosis which is associated with risk factors and a poor prognosis. In a series of 61 knees (38 patients) we analysed secondary osteonecrosis of the knee treated by a new technique using multiple small percutaneous 3 mm drillings. Total knee replacement was avoided in 59 knees (97%) at a mean follow-up of 3 years (2 to 4). Of the 61 knees, 56 (92%) had a successful clinical outcome, defined as a Knee Society score greater than 80 points. The procedure was successful in all 24 knees with small lesions compared with 32 of 37 knees (86%) with large lesions. All the procedures were performed as day cases and there were no complications. This technique appears to have a low morbidity, relieves symptoms and delays more invasive surgery

Introduction This study assesses the outcome of medial unicompartmental knee arthroplasty (UKA) using the Oxford prosthesis for end-stage focal spontaneous osteonecrosis of the knee (SONK, Ahlback grades III & IV). Methods A total of 29 knees (27 patients) with SONK were assessed using the Oxford Knee Score. Twenty-six had osteonecrosis of the medial femoral condyle; 3 had osteonecrosis of the medial tibial plateau. This group was compared to a similar group who had undergone Oxford Medial UKA for primary osteoarthritis. Patients were matched for age, sex and time since operation. Results Mean length of follow-up was 5.2 years (range 1–13 years). There were no implant failures in either group, but there was one death 9 months post-arthroplasty from unrelated causes in the group with osteonecrosis. The mean Oxford Knee Score (SD) in the group with osteonecrosis was 37.8 (7.6) and 40.0 (6.6) in the group with osteoarthritis. There was no significant difference between the two groups using Student’s t-test (p=0.29). Interpretation Use of the Oxford Medial UKA for focal spontaneous osteonecrosis of the knee is reliable in the short to medium term, and gives similar results to when used for patients with primary osteoarthritis

Introduction: This study assesses the outcome of medial unicompartmental knee arthroplasty (UKA) using the Oxford prosthesis for end-stage focal spontaneous osteonecrosis of the knee (SONK, Ahlback grades III & IV). Methods: A total of 29 knees (27 patients) with SONK were assessed using the Oxford Knee Score. Twenty-six had osteonecrosis of the medial femoral condyle; 3 had osteonecrosis of the medial tibial plateau. This group was compared to a similar group who had undergone Oxford Medial UKA for primary osteoarthritis. Patients were matched for age, sex and time since operation. Results: Mean length of follow-up was 5.2 years (range 1–13 years). There were no implant failures in either group, but there was one death 9 months post-arthroplasty from unrelated causes in the group with osteonecrosis. The mean Oxford Knee Score in the group with osteonecrosis was 37.8 (± 7.6) and 40.0 (± 6.6) in the group with osteoarthritis. There was no significant difference between the two groups using Student’s t-test (p=0.31). Interpretation: Use of the Oxford Medial UKA for focal spontaneous osteonecrosis of the knee is reliable in the short to medium term, and gives similar results to when used for patients with primary osteoarthritis

Spontaneous osteonecrosis of the knee (SPONK) usually involves a single condyle or plateau. The medial femoral condyle is most often involved and spontaneous osteonecrosis of medial tibial plateau is a rare condition, representing only 2 % of all necrosis reported in the knee. Therefore, SPONK with both involvement of medial femoral condyle(MFC) and medial tibial plateau(MTP) might be extremely rare. SPONK in each MFC or MTP respectively might be extended into corresponding side of the knee at their advanced final stage, howevere, in that situations, significant degenerative change would accompany and it might be difficult to differentiate final staged SPONK form severe osteoarthritis. To the best of our knowledge, SPONK affecting both medial femoral condyle and medial tibial plateau without significant secondary osteoarthritis changes is not reported, even though it was difficult to know which occurred first. We experienced 3 patients with histologically proven osteonecrosis of the medial tibial condyle and medial tibial plateau, and report their radiologic features. All 3 patients showed similar ridiograhic patterns. Medial portion of medial tibial plateau and lateral portion of medial femoral condyle showed longitudinal fracture like-subchondral collapse. Standing anteroposterior radiograph at 30 degree knee flexion showed well fitted features such as “locked” medial condyle. Varus angulation was present. Significant degenerative changes was not shown except for subchondral sclerosis. T1-weighted coronal and Fat suppressed T2-weighted MR images showed subchondral collapse with ill-defined diffuse bone marrow edema changes on both tibial and femoral condyles. At surgical findings, longitudinal track-like groove was shown in both medial femoral condyle and medial tibial plateau. Articular cartilage was denuded and showed glistening surface with bone defect of lateral side of medial femoral condyle and medial side of tibial articular surface. Histological analysis shows necrotic bone, surrounded by an area of fibrovascular granulation tissue on both femoral and tibial sides. Total knee arthoplasty was performed in all 3 patients. As a result of very low prevalence of both involvement of MFC and MTP and limited number of our cases, we could not conclude that radiologic features in our cases are typical radiologic pattern of both involvement. However, based on our cases, we believe that this characteristic radiologic features may considered as one of the possible various radiologic findings of simultaneous involvement in MFC and MTP and allow diagnosis for SPONK with both involvement in MFC and MTP to be facilitated

This prospective study reports the 15-year survival and ten-year functional outcome of a consecutive series of 1000 minimally invasive Phase 3 Oxford medial UKAs (818 patients, 393 men, 48%, 425 women, 52%, mean age 66 years; 32 to 88). These were implanted by two surgeons involved with the design of the prosthesis to treat anteromedial osteoarthritis and spontaneous osteonecrosis of the knee, which are recommended indications. Patients were prospectively identified and followed up independently for a mean of 10.3 years (5.3 to 16.6). At ten years, the mean Oxford Knee Score was 40 (standard deviation (. sd. ) 9; 2 to 48): 79% of knees (349) had an excellent or good outcome. There were 52 implant-related re-operations at a mean of 5.5 years (0.2 to 14.7). The most common reasons for re-operation were arthritis in the lateral compartment (2.5%, 25 knees), bearing dislocation (0.7%, seven knees) and unexplained pain (0.7%, seven knees). When all implant-related re-operations were considered as failures, the ten-year rate of survival was 94% (95% confidence interval (CI) 92 to 96) and the 15-year survival rate 91% (CI 83 to 98). When failure of the implant was the endpoint the 15-year survival was 99% (CI 96 to 100). This is the only large series of minimally invasive UKAs with 15-year survival data. The results support the continued use of minimally invasive UKA for the recommended indications. Cite this article: Bone Joint J 2015;97-B:1493–99

The role of unicompartmental knee arthroplasty (UKA) in spontaneous osteonecrosis of the knee (SONK) remains controversial, even though SONK usually involves only medial compartment of the knee joint. We aimed to compare the survival rate and clinical outcomes of UKA in SONK and medial compartment osteoarthritis (MOA) via a meta-analysis of previous studies. MEDLINE database in PubMed, the Embase database, and the Cochrane Library were searched up to January 2018 with keywords related to SONK and UKA. Studies were selected with predetermined inclusion criteria: (1) medial UKA as the primary procedure, (2) reporting implant survival or clinical outcomes of osteonecrosis and osteoarthritis, and (3) follow-up period greater than 1 year. Quality assessment was performed using the risk of bias assessment tool for non-randomised studies (RoBANs). A random effects model was used to estimate the pooled relative risk (RR) and standardised mean difference. The incidence of UKA revision for any reason was significantly higher in SONK than in MOA group (pooled RR = 1.83, p = 0.009). However, the risk of revision due to aseptic loosening and all- cause re-operation was not significantly different between the groups. Moreover, when stratified by the study quality, high quality studies showed similar risk of overall revision in SONK and MOA (p = 0.71). Subgroup analysis revealed worse survival of SONK, mainly related to high failure after uncemented UKA. Clinical outcomes after UKA were similar between SONK and MOA (p = 0.66). Cemented UKA has similar survival and clinical outcomes in SONK and MOA. Prospective studies designed specifically to compare the UKA outcomes in SONK and MOA are necessary

Bone marrow lesions (BMLs), identified by MRI, are defined as a region of cancellous bone with high T2 and low T1 signal intensity. They are associated with various knee pathologies including spontaneous osteonecrosis of the knee (SPONK), AVN, trauma (fracture and bone contusion), following arthroscopy and secondary to overuse (i.e., after completing a marathon). They also are commonly recognised in patients with knee OA (referred to as OA-BMLs) and their substantial importance in knee OA pathogenesis has been recently identified. Depending upon the etiology (i.e., bone contusion, overuse, etc.) of the BML, these lesions can be “acute” in nature and spontaneously resolve over time. However, OA-BMLs generally are considered to be a “chronic” condition and overtime they have been shown to often persist and increase in size. Retrieval studies following THA and TKA, in patients with a preoperatively identified BML, have greatly expanded our understanding of OA – BMLs and these investigations consistently identify the critical role subchondral bone plays in OA disease progression. Histologic, histochemical and mechanical studies of OA-BMLs demonstrate significant alternations from healthy subchondral bone. The effected bone contains regions where fibrous tissue has replaced cancellous bone, microfractures are present and vascularity is increased. There is an increased concentration of inflammatory mediators and the bone structural integrity is compromised. Standard radiographs of the knee correlate only modestly with patient symptoms, but conversely, the presence of an OA-BML is an extremely strong predictor of pain and knee joint dysfunction. Felson et al. reported this relationship. In a large group of patients with painful knee OA, 77.5% of these patients had a BML. Both the presence and size of the BML, following multiregression analysis, were significant predictors of knee pain severity. Additionally, likely secondary to inadequate subchondral bone plate support, the presence of an OA-BML is associated with subchondral bone attrition (SBA). SBA leads to collapse of the subchondral bone plate and progressive joint deformity. Based on the association of an OA-BML with pain, joint dysfunction and deformity, it is not surprising that these lesions are prognostic for patients seeking knee arthroplasty. Several studies have demonstrated that the odds of knee arthroplasty performance are substantially higher in patents with an OA-BML. This enhanced understanding of knee OA pathogenesis and the critical role of subchondral bone in this process creates an opportunity for development of novel prevention and treatment strategies. Prevention of OA-BML formation has been considered and pharmacologic interventions proposed. Recent studies have reported positive results for treatment with bisphosphonates in patients with knee OA. One study reported significant pain and OA-BML size reduction in patients receiving a bisphosphonate for 4 months. A strategy aimed at repairing and/or enhancing subchondral bone compromised by an OA-BML has also been proposed. Early results reported with this intervention are encouraging, but preliminary

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

Since 2005, the author has performed nearly 1000 Oxford medial unicompartmental arthroplasties (UKA) using a mobile bearing. The indications are 1) Isolated medial compartment osteoarthritis with ‘bone-on-bone’ contact, which has failed prior conservative treatment, 2) Medial femoral condyle avascular necrosis or spontaneous osteonecrosis, which has failed prior conservative treatment. Patients are recommended for UKA only if the following anatomic requirements are met: 1) Intact ACL, 2) Full thickness articular cartilage wear limited to the anterior half of the medial tibial plateau, 3) Unaffected lateral compartment cartilage, 4) Unaffected patellar cartilage on the lateral facet, 5) Less than 10 degrees of flexion deformity, 6) Over 100 degrees of knee flexion, and 7) Varus deformity not exceeding 15 degrees. Exclusion criteria for surgery are BMI of more than 30, prior high tibial osteotomy, and inflammatory arthritis. All cases were performed with a tourniquet inflated using a minimally-invasive incision with a quadriceps-sparing approach. Both femoral and tibial components were cemented. Most patients were discharged home the next morning; bilaterals usually stayed a day longer. We have previously described our results and the factors determining alignment. In a more recent study, we have compared the coronal post-operative limb alignment and knee joint line obliquity after medial UKA with a clinically and radiologically (less than Grade 2 medial OA) normal contralateral lower limb. In our series, we have had 1 revision for aseptic loosening of both components, conversion to TKRs in a patient with bilateral UKAs who developed rheumatoid arthritis 3 years later, and 9 meniscal dislocations. There have been no cases of wound infections and thromboembolism. We have reviewed our patients with a minimum 10-year follow-up which will be presented. The vast majority of our patients have been generally very satisfied with the results. Our study shows that most patients (who have no disease in the contralateral knee) regain their ‘natural’ alignment and joint line obliquity comparable to their contralateral limb. Over the past few years our percentage of UKAs has been steadily rising to about a third of our knee cases. UKA serves as a definitive procedure in the elderly. We see it as a suitable procedure in middle-aged patients who want an operation that provides a quick recovery, full function and range of motion, and near-normal kinematics, with the understanding that they have a small chance of conversion to a total knee arthroplasty in the future