Aims. Treatment of end-stage anteromedial osteoarthritis (AMOA) of the knee is commonly approached using one of two surgical strategies: medial unicompartmental knee arthroplasty (UKA) or total knee arthroplasty (TKA). In this study we aim to investigate if there is any difference in outcome for patients undergoing UKA or TKA, when treated by high-volume surgeons, in high-volume centres, using two different clinical guidelines. The two strategies are ‘UKA whenever possible’ vs TKA for all patients with AMOA. Methods. A total of 501 consecutive AMOA patients (301 UKA) operated on between 2013 to 2016 in two high-volume centres were included. Centre One employed clinical guidelines for the treatment of AMOA allowing either UKA or TKA, but encouraged UKA wherever possible. Centre Two used clinical guidelines that treated all patients with a TKA, regardless of wear pattern. TKA patients were included if they had isolated AMOA on preoperative radiographs. Data were collected from both centres’ local databases. The primary outcome measure was change in Oxford Knee Score (OKS), and the proportion of patients achieving the patient-acceptable symptom state (PASS) at one-year follow-up. The data were 1:1 propensity score matched before regression models were used to investigate potential differences. Results. The matched cohort included 400 patients (mean age 67 years (SD 9.55), 213 (53%) female, mean BMI 30.2 kg/m. 2. , 337 (84%) American Society of Anesthesiologists grade ≤ 2). We found a mean adjusted difference in change score of 3.02 points (95% confidence interval (CI) 1.41 to 4.63; p < 0.001) and a significantly larger likeliness of achieving PASS (odds ratio 3.67 (95% CI 1.73 to 8.45); p = 0.001) both in favour of the UKA strategy. Conclusion. UKA and TKA are both good strategies for treating end-stage AMOA. However, when compared as a strategy, UKA achieved larger improvements in OKS, and were more likely to reach the PASS value at one-year follow-up. Cite this article: Bone Jt Open 2022;3(5):441–447

We report a study of 112 patients with primary anteromedial osteoarthritis of the knee and their families. Sibling risk was determined using randomly selected single siblings. Spouses were used as controls. The presence of symptomatic osteoarthritis was determined using an Oxford knee score of ≥ 29 supported by a Kellgren and Lawrence radiological score of II or greater. Using Fisher’s exact test we found that there was a significant increased risk of anteromedial osteoarthritis (OA) relative to the control group (p = 0.031). The recurrence risk of anteromedial OA to siblings was 3.21 (95% confidence interval 1.12 to 9.27). These findings imply that genetic factors may play a major role in the development of anteromedial OA of the knee

Medial tibial plateaux excised during 46 unicompartmental arthroplasties for osteoarthritis were collected and photographed. The anterior cruciate ligament was intact in all joints. In every case the cartilage and bone erosion was centred anteriorly on the plateau and the posterior cartilage was intact. The site of the lesion and the intact state of the cruciate ligaments taken together explain why varus deformity was observed only in the extended knee, and why the deformity was correctable and had not become fixed. Failure of the anterior cruciate ligament may allow the erosion to extend posteriorly, producing fixed varus deformity and leading to degeneration of the lateral compartment. Anteromedial osteoarthritis is a distinct clinicopathological entity; its radiographic features enable it to be diagnosed from lateral radiographs; its anatomical features render it suitable for treatment by unicompartmental arthroplasty

From a search of MRI reports on knees, 20 patients were identified with evidence of early anteromedial osteoarthritis without any erosion of bone and a control group of patients had an acute rupture of the anterior cruciate ligament. The angle formed between the extension and flexion facets of the tibia, which is known as the extension facet angle, was measured on a sagittal image at the middle of the medial femoral condyle. The mean extension facet angle in the control group was 14° (3° to 25°) and was unrelated to age (Spearman’s rank coefficient, p = 0.30, r = 0.13). The mean extension facet angle in individuals with MRI evidence of early anteromedial osteoarthritis was 19° (13° to 26°, SD 4°). This difference was significant (Mann-Whitney U test, p < 0.001). A wide variation in the extension facet angle was found in the normal control knees and an association between an increased extension facet angle and MRI evidence of early anteromedial osteoarthritis. Although a causal link has not been demonstrated, we postulate that a steeper extension facet angle might increase the duration of loading on the extension facet during the stance phase of gait, and that this might initiate failure of the articular cartilage

We determined the outcome of 56 ‘Oxford’ unicompartmental replacements performed for anteromedial osteoarthritis of the knee between 1982 and 1987. Of these, 24 were in patients who had died without revision, one was lost to follow-up and two had been revised. Of the remaining 29 knees, 26 were examined clinically and radiologically, two were only examined clinically and one patient was contacted by telephone. The mean age of the patients was 80.3 years. At a mean follow-up of 11.4 years (10 to 14) the measurements of the knee score, range of movement and degree of deformity were not significantly different from those made one to two years after operation, except that the range of flexion had improved. Comparison of fluoroscopically-controlled radiographs at a similar interval of time showed no change in the appearance of the lateral compartments. The retained articular cartilage continued to function for ten or more years which suggests that anteromedial osteoarthritis may be considered as a focal disorder of the knee. This justifies continued efforts to develop methods of treatment which preserve intact joint structures

The Cementless Oxford Unicompartmental Knee Replacement (OUKR) was developed to address problems related to cementation, and has been demonstrated in a randomised study to have similar clinical outcomes with fewer radiolucencies than observed with the cemented device. However, before its widespread use it is necessary to clarify contraindications and assess the complications. This requires a larger study than any previously published. We present a prospective multicentre series of 1000 cementless OUKRs in 881 patients at a minimum follow-up of one year. All patients had radiological assessment aligned to the bone–implant interfaces and clinical scores. Analysis was performed at a mean of 38.2 months (19 to 88) following surgery. A total of 17 patients died (comprising 19 knees (1.9%)), none as a result of surgery; there were no tibial or femoral loosenings. A total of 19 knees (1.9%) had significant implant-related complications or required revision. Implant survival at six years was 97.2%, and there was a partial radiolucency at the bone–implant interface in 72 knees (8.9%), with no complete radiolucencies. There was no significant increase in complication rate compared with cemented fixation (p = 0.87), and no specific contraindications to cementless fixation were identified. Cementless OUKR appears to be safe and reproducible in patients with end-stage anteromedial osteoarthritis of the knee, with radiological evidence of improved fixation compared with previous reports using cemented fixation. Cite this article: Bone Joint J 2013;95-B:181–7

Anterior knee pain and/or radiological evidence of degeneration of the patellofemoral joint are considered to be contraindications to unicompartmental knee replacement. The aim of this study was to determine whether this is the case. Between January 2000 and September 2003, in 100 knees (91 patients) in which Oxford unicompartmental knee replacements were undertaken for anteromedial osteoarthritis, pre-operative anterior knee pain and the radiological status of the patellofemoral joint were defined using the Altman and Ahlback systems. Outcome was evaluated at two years with the Oxford knee score and the American Knee Society score. Pre-operatively 54 knees (54%) had anterior knee pain. The clinical outcome was independent of the presence or absence of pre-operative anterior knee pain. Degenerative changes of the patellofemoral joint were seen in 54 patients (54%) on the skyline radiographs, including ten knees (10%) with joint space obliteration. Patients with medial patellofemoral degeneration had a similar outcome to those without. For some outcome measures patients with lateral patellofemoral degeneration had a worse score than those without, but these patients still had a good outcome, with a mean Oxford knee score of 37.6 (SD 9.5). These results show that neither anterior knee pain nor radiologically-demonstrated medial patellofemoral joint degeneration should be considered a contraindication to Oxford unicompartmental knee replacement. With lateral patellofemoral degeneration the situation is less well defined and caution should be observed

Patellofemoral joint degeneration is often considered a contraindication to medial unicompartmental knee replacement. We examined the validity of this preconception using information gathered prospectively on the intra-operative status of the patellofemoral joint in 824 knees in 793 consecutive patients who underwent Oxford unicondylar knee replacement for anteromedial osteoarthritis. All operations were performed between January 1998 and September 2005. A five-point grading system classified degeneration of the patellofemoral joint from none to full-thickness cartilage loss. A subclassification of the presence or absence of any full-thickness cartilage loss was subsequently performed to test selected hypotheses. Outcome was evaluated independently by physiotherapists using the Oxford and the American Knee Society Scores with a minimum follow-up of one year. Full-thickness cartilage loss on the trochlear surface was observed in 100 of 785 knees (13%), on the medial facet of the patella in 69 of 782 knees (9%) and on the lateral facet in 29 of 784 knees (4%). Full-thickness cartilage loss at any location was seen in 128 knees (16%) and did not produce a significantly worse outcome than those with a normal or near-normal joint surface. The severity of the degeneration at any of the intra-articular locations also had no influence on outcome. We concluded that, provided there is not bone loss and grooving of the lateral facet, damage to the articular cartilage of the patellofemoral joint to the extent of full-thickness cartilage loss is not a contraindication to the Oxford mobile-bearing unicompartmental knee replacement

We describe the outcome of a series of 124 Oxford meniscal-bearing unicompartmental arthroplasties carried out for osteoarthritis of the medial compartment. They had been undertaken more than ten years ago in a non-teaching hospital in Sweden by three surgeons. All the knees had an intact anterior cruciate ligament, a correctable varus deformity and full-thickness cartilage in the lateral compartment. Thirty-seven patients had died; the mean time since operation for the remainder was 12.5 years (10.1 to 15.6). Using the endpoint of revision for any cause, the outcome for every knee was established. Six had been revised (4.8%). At ten years there were 94 knees still at risk and the cumulative survival rate was 95.0% (95% confidence interval 90.8 to 99.3). This figure is similar to that reported by the designers of the prosthesis and to the best published results for independent series of total knee replacement. If patients are selected appropriately, this implant is a reliable treatment for anteromedial osteoarthritis of the knee

We report the outcome of 135 knees with anteromedial osteoarthritis in which the Oxford meniscal-bearing unicompartmental arthroplasty was inserted in a district general hospital by a single surgeon. All the knees had an intact anterior cruciate ligament, a correctable varus deformity and the lateral compartment was uninvolved or had only minor osteoarthritis. The mean follow-up was 5.82 years (2 to 12). Using revision as the end-point, the outcome for every knee was established. Five knees have been revised giving a cumulative rate of survival of the prosthesis at ten years of 94.04% (95% confidence interval 84.0 to 97.8). Knee rating and patient function were assessed using the modified Knee Society scoring system. The mean knee score was 92.2 (51 to 100) and the mean functional score 76.2 (51 to 100). The survival of the implant is comparable to that reported by the designers of the prosthesis and not significantly different from that for total knee replacement. Unicompartmental knee replacement offers a viable alternative in patients with medial osteoarthritis. Appropriate selection of patients and good surgical technique are the key factors

Satisfactory selection criteria are essential for the successful outcome of unicompartmental knee arthroplasty (UCA). We report the frequency of revision of the Oxford medial unicompartmental arthroplasty in knees previously treated for anteromedial osteoarthritis by high tibial osteotomy (HTO). The combined results from three sources were used to allow statistical analysis of this uncommon subgroup. In the combined series of 631 knees (507 patients) which had medial unicompartmental replacement, 613 were primary procedures and 18 were for a failed HTO. The mean follow-up times of the two groups were similar (5.8 years and 5.4 years, respectively). At review, 19 (3.1%) of the primary procedures and five (27.8%) of those undertaken for a failed HTO had been revised to total knee replacement. Survival analysis revealed the ten-year cumulative survivals to be 96% and 66%, respectively. The log-rank comparison of these survivals revealed a highly significant difference (p < 0.0001). We recommend that the Oxford UCA should not be used in knees which have previously undergone an HTO

Retrieval studies have shown that the use of fully congruent meniscal bearings reduces wear in knee replacements. We report the outcome of 143 knees with anteromedial osteoarthritis and normal anterior cruciate ligaments treated by unicompartmental arthroplasty using fully congruous mobile polyethylene bearings. At review, 34 knees were in patients who had died and 109 were in those who were still living. The mean elapsed time since operation was 7.6 years (maximum 13.8). We established the status of all but one knee. There had been five revision operations giving a cumulative prosthetic survival rate at ten years (33 knees at risk) of 98% (95% CI 93% to 100%). Considering the knee lost to follow-up as a failure, the ‘worst-case’ survival rate was 97%. No failures were due to polyethylene wear or aseptic loosening of the tibial component. One bearing which dislocated at four years was reduced by closed manipulation. The ten-year survival rate is the best of those reported for unicompartmental arthroplasty and not significantly different from the best rates for total knee replacement

The Oxford Unicompartmental Knee replacement (UKR) was introduced as a design to reduce polyethylene wear. There has been one previous retrieval study involving this implant, which reported very low rates of wear in some specimens but abnormal patterns of wear in others. There has been no further investigation of these abnormal patterns. The bearings were retrieved from 47 patients who had received a medial Oxford UKR for anteromedial osteoarthritis of the knee. None had been studied previously. The mean time to revision was 8.4 years (. sd. 4.1), with 20 having been implanted for over ten years. The macroscopic pattern of polyethylene wear and the linear penetration were recorded for each bearing. The mean rate of linear penetration was 0.07 mm/year. The patterns of wear fell into three categories, each with a different rate of linear penetration; 1) no abnormal macroscopic wear and a normal articular surface, n = 16 (linear penetration rate = 0.01 mm/year); 2) abnormal macroscopic wear and normal articular surfaces with extra-articular impingement, n = 16 (linear penetration rate = 0.05 mm/year); 3) abnormal macroscopic wear and abnormal articular surfaces with intra-articular impingement +/− signs of non-congruous articulation, n = 15 (linear penetration rate = 0.12 mm/year). The differences in linear penetration rate were statistically significant (p < 0.001). These results show that very low rates of polyethylene wear are possible if the device functions normally. However, if the bearing displays suboptimal function (extra-articular, intra-articular impingement or incongruous articulation) the rates of wear increase significantly

Cite this article: Bone Jt Open 2024;5(12):1120–1122.

The June 2023 Knee Roundup³⁶⁰ looks at: Cementless total knee arthroplasty is associated with early aseptic loosening in a large national database; Is cementless total knee arthroplasty safe in females aged over 75 years?; Could novel radiological findings help identify aseptic tibial loosening?; The Attune cementless versus LCS arthroplasty at introduction; Return to work following total knee arthroplasty and unicompartmental knee arthroplasty; Complications and downsides of the robotic total knee arthroplasty; Mid-flexion instability in kinematic alignment better with posterior-stabilized and medial-stabilized implants?; Patellar resurfacing does not improve outcomes in modern knees.

The June 2024 Knee Roundup³⁶⁰ looks at: The estimated lifetime risk of revision after primary knee arthroplasty influenced by age, sex, and indication; Should high-risk patients seek out care from high-volume surgeons?; Stability and fracture rates in medial unicondylar knee arthroplasties; Rethinking antibiotic prophylaxis for dental procedures post-arthroplasty; Evaluating DAIR: a viable alternative for acute periprosthetic joint infection; The characteristics and predictors of mortality in periprosthetic fractures around the knee; Patient health-related quality of life deteriorates significantly while waiting six to 12 months for total hip or knee arthroplasty; The importance of looking for diversity in knee implants.

Aims

A fracture of the medial tibial plateau is a serious complication of Oxford mobile-bearing unicompartmental knee arthroplasty (OUKA). The risk of these fractures is reportedly lower when using components with a longer keel-cortex distance (KCDs). The aim of this study was to examine how slight varus placement of the tibial component might affect the KCDs, and the rate of tibial plateau fracture, in a clinical setting.

Aims

The aim of this prospective multicentre study was to describe trends in length of stay and early complications and readmissions following unicompartmental knee arthroplasty (UKA) performed at eight different centres in Denmark using a fast-track protocol and to compare the length of stay between centres with high and low utilization of UKA.

Aims

Cementless unicompartmental knee arthroplasty (UKA) has advantages over cemented UKA, including improved fixation, but has a higher risk of tibial plateau fracture, particularly in Japanese patients. The aim of this multicentre study was to determine when cementless tibial components could safely be used in Japanese patients based on the size and shape of the tibia.

Aims

The mobile bearing Oxford unicompartmental knee arthroplasty (OUKA) is recommended to be performed with the leg in the hanging leg (HL) position, and the thigh placed in a stirrup. This comparative cadaveric study assesses implant positioning and intraoperative kinematics of OUKA implanted either in the HL position or in the supine leg (SL) position.