Fixed lateral unicompartmental knee replacement is a reliable treatment for lateral compartment osteoarthritis after mobile-bearing medial unicompartmental replacement.

PURPOSE: Lateral osteoarthritis following medial unicompartmental knee replacement (UKR) is usually treated with total knee replacement, however, lateral UKR is a less invasive option that preserves a well-functioning medial UKR. This study aimed to determine the 5-year outcome of the cemented Fixed Lateral Oxford UKR (FLO) when used for the treatment of severe lateral disease after medial Oxford unicompartmental knee replacement. METHODS: Forty-four knees with lateral bone-on-bone osteoarthritis (n = 43) and avascular necrosis (n = 1) treated with the FLO following medial Oxford UKR were followed up prospectively. The Oxford Knee Score (OKS) and Tegner Activity Score (TAS) were collected pre- and post-operatively. Life-table analysis was used to determine survival rates. RESULTS: The mean patient age at the time of FLO surgery was 74.4 years with a mean time of 12.1 years between the primary medial UKR and the conversion to a bi-UKR with a FLO. Mean follow-up of the FLO was 3.5 years. After FLO no intra-operative or medical complications, re-admissions, or mortality occurred. There was one reoperation in which a bearing was exchanged for a medial bearing dislocation. There were no revisions of the FLO, so the FLO survival rate at 5 years was 100% (24 at risk). The mean pre-operative OKS was 22, which significantly (p < 0.0001) improved to a mean of 42, 42, and 40 at 1, 2, and 5 years, respectively. The median TAS had a non-significant improvement from 2.5 (Range 0-8) pre-operatively to 2 (Range 1-6) at 5 years postoperatively. CONCLUSION: The FLO is a reliable treatment for lateral osteoarthritis following medial UKR. At 5 years there was a 100% survival of the FLO with a mean OKS of 40. LEVEL OF EVIDENCE: IV, Prospective Case Series.

Oxford domed lateral unicompartmental knee arthroplasty.

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. METHODS: A total of 325 consecutive domed lateral UKAs undertaken for the recommended indications were included, and their functional and survival outcomes were assessed. The effects of age, weight, activity, and the presence of full-thickness erosions of cartilage in the patellofemoral joint on outcome were evaluated. RESULTS: Median follow-up was seven years (3 to 14), and mean age at surgery was 65 years (39 to 90). Median Oxford Knee Score (OKS) was 43 (interquartile range (IQR) 37 to 47), with 260 (80%) achieving a good or excellent score (OKS > 34). Revisions occurred in 34 (10%); 14 (4%) were for dislocation, of which 12 had no recurrence following insertion of a new bearing, and 12 (4%) were revised for medial osteoarthritis (OA). Ten-year survival was 85% (95% confidence interval (CI) 79 to 90, at risk 72). Age, weight, activity, and patellofemoral erosions did not have a significant effect on the clinical outcome or survival. CONCLUSION: Domed lateral UKA provides a good alternative to total knee arthroplasty (TKA) in the management of lateral compartment OA. Although dislocation is relatively easy to treat successfully, the dislocation rate of 4% is high. It is recommended that the stability of the bearing is assessed intraoperatively. If the bearing can easily be displaced, the fixed rather than the mobile bearing version of the Oxford lateral tibial component should be inserted instead. Younger age, heavier weight, high activity, and patellofemoral erosions did not detrimentally affect outcome, so should not be considered contraindications. Cite this article: Bone Joint J 2020;102-B(8):1033-1040.

The impact of patient-specific instrumentation on unicompartmental knee arthroplasty: a prospective randomised controlled study.

PURPOSE: Patient-specific instrumentation (PSI) has been proposed as a means of improving surgical accuracy and ease of implantation during technically challenging procedures such as unicompartmental knee arthroplasty (UKA). The purpose of this prospective randomised controlled trial was to compare the accuracy of implantation and functional outcome of mobile-bearing medial UKAs implanted with and without PSI by experienced UKA surgeons. METHODS: Mobile-bearing medial UKAs were implanted in 43 patients using either PSI guides or conventional instrumentation. Intra-operative measurements, meniscal bearing size implanted, and post-operative radiographic analyses were performed to assess component positioning. Functional outcome was determined using the Oxford Knee Score (OKS). RESULTS: PSI guides could not be used in three cases due to concerns regarding accuracy and registration onto native anatomy, particularly on the tibial side. In general, similar component alignment and positioning was achieved using the two systems (n.s. for coronal/sagittal alignment and tibial coverage). The PSI group had greater tibial slope (p = 0.029). The control group had a higher number of optimum size meniscal bearing inserted (95 vs 52%; p = 0.001). There were no differences in OKS improvements (n.s). CONCLUSION: Component positioning for the two groups was similar for the femur but less accurate on the tibial side using PSI, often with some unnecessarily deep resections of the tibial plateau. Although PSI was comparable to conventional instrumentation based on OKS improvements at 12 months, we continue to use conventional instrumentation for UKA at our institution until further improvements to the PSI guides can be demonstrated. LEVEL OF EVIDENCE: Therapeutic, Level I.

The Interaction of Caseload and Usage in Determining Outcomes of Unicompartmental Knee Arthroplasty: A Meta-Analysis.

BACKGROUND: Outcomes after unicompartmental knee arthroplasty (UKA) are variable and influenced by caseload (UKA/y) and usage (percentage of knee arthroplasty that are UKA), which relates to indications. This meta-analysis assesses the relative importance of these factors. METHODS: MEDLINE (Ovid), Embase (Ovid), and Web of Science (ISI) were searched for consecutive series of cemented Phase 3 Oxford medial UKA. The primary outcome was revision rate/100 observed component years (% pa) with subgroup analysis based on caseload and usage. RESULTS: Forty-six studies (12,520 knees) with an annual revision-rate ranging from 0% to 4.35% pa, mean 1.21% pa (95% confidence interval [CI], 0.97-1.47), were identified. In series with mean follow-up of 10-years, the revision-rate was 0.63% pa (95% CI, 0.46-0.83), equating to a 94% (95% CI, 92%-95%) 10-year survival. Aseptic loosening, lateral arthritis, bearing dislocation, and unexplained pain were the predominant failure mechanisms with revision for patellofemoral problems and polyethylene wear exceedingly rare. The lowest revision-rates were achieved with caseload >24 UKA/y (0.88% pa; 95% CI, 0.63-1.61) and usage >30% (0.69% pa; 95% CI, 0.50-0.90). Usage was more important than caseload; with high usage (≥20%), the revision-rate was low, whether the caseload was high (>12 UKA/y) or low (≤12 UKA/y; (0.94% pa; 95% CI, 0.69-1.23 and 0.85% pa; 95% CI, 0.65-1.08), respectively); with low usage (<20%), the revision-rate was high, whether the caseload was high or low (1.58% pa; 95% CI, 0.57-3.05 and 1.76% pa; 95% CI, 1.21-2.41, respectively). CONCLUSION: To achieve optimum results, surgeons, whether high or low caseload, should adhere to the recommended indications such that ≥20%, or ideally >30% of their knee arthroplasties are UKA. If they do this, then they can expect to achieve results similar to those of the long-term series, which all had high usage (>20%) and an average 10-year survival of 94%.

Evidence-Based Indications for Mobile-Bearing Unicompartmental Knee Arthroplasty in a Consecutive Cohort of Thousand Knees.

BACKGROUND: The indications for unicompartmental knee arthroplasty remain controversial. Previously recommended contraindications include the following: age under 60 years, weight 180 lb (82 kg) or over, patients undertaking heavy labor, chondrocalcinosis, and exposed bone in the patellofemoral joint. This study explores whether these contraindications are valid in mobile-bearing unicompartmental knee arthroplasty. METHODS: Using a prospective series of 1000 consecutive medial unicompartmental knee arthroplasties in which the reported contraindications were not applied, the functional outcome and survival in patients with or without contraindications were compared. RESULTS: Of the 1000 consecutive unicompartmental knee arthroplasties (818 patients), 68% (678 knees) would be considered contraindicated based on published contraindications. At a mean follow-up of 10 years (5-17), there was no difference in American Knee Society (AKS) Objective Scores (P = .05) or Oxford Knee Score (P = .08) between groups. However, knees with contraindications had significantly (P = .02) fewer poor outcomes and significantly better AKS Functional Scores (P < .001) and Tegner Activity Scores (P < .001). At 15 years, no difference in implant survival (P = .33) was observed. The 3% of unicompartmental knee arthroplasties performed in young men (age <60) weighing 180 lb or over with high activity levels, who have been reported to have poor outcomes after fixed-bearing unicompartmental knee arthroplasty, had significantly better AKS Functional Scores (P < .001), Oxford Knee Score (P = .01), and Tegner Activity Score (P < .001) at 10 years. No difference in AKS Objective Scores (P = .54) at 10 years or implant survival at 15 years (P = .75) was seen. CONCLUSION: This large case series provides evidence that patients with the previously reported contraindications do as well as, or even better than, those without contraindications. Therefore these contraindications should not apply to mobile-bearing unicompartmental knee arthroplasty.

Lateral osteophytes do not represent a contraindication to medial unicompartmental knee arthroplasty: a 15-year follow-up.

PURPOSE: Lateral osteophytes have been reported to be associated with lateral compartment disease and as such it is unclear whether medial unicompartmental knee arthroplasty should be performed if these are present. METHODS: Using the OARSI classification system, 0 (no osteophyte) to 3 (large osteophyte), radiographs from a series of cemented meniscal-bearing unicompartmental knee arthroplasty implanted in the setting of full-thickness lateral cartilage where lateral osteophytes were not considered a contraindication were identified and factors associated with the presence and size of lateral osteophytes, and their impact on clinical outcomes and implant survival were assessed. RESULTS: Pre-operative radiographs from 458 knees (392 patients), independently followed up for a mean 10.5 years (range 5.3-16.6), were assessed. Lateral osteophytes were present in 62 % of knees with 18 % scored as Grade 3. Inter-observer reliability was good (kappa = 0.70). The presence and size of lateral osteophytes was associated with younger age at joint replacement (p = 0.01) and increasing BMI (p = 0.01). No association was seen with gender, pre-operative status, assessed using the Oxford Knee Score (OKS), American Knee Society (AKSS) Objective or Functional Score, Tegner activity score, or size of medial tibial lesion. Subgroup analysis of Grade 3 Osteophytes revealed that these were associated with a greater degree of macroscopic ACL damage. At 10 years there was no difference in function (n.s.), and at 15 years no difference in implant survival or mechanism of failure between groups (n.s.). Subgroup analysis of Grade 3 osteophytes found no significant difference in functional outcome at 10 years or implant survival at 15 years. CONCLUSION: The presence of lateral osteophytes is not a contraindication to medial meniscal-bearing unicompartmental knee arthroplasty. The clinical relevance of this study is that it highlights the importance of an appropriate pre-operative assessment of the lateral compartment as in the setting of full-thickness cartilage at operation lateral osteophytes do not compromise long-term functional outcome or implant survival. LEVEL OF EVIDENCE: IV.

Does activity affect the outcome of the Oxford unicompartmental knee replacement?

BACKGROUND: High levels of activity are considered to be a contraindication to unicompartmental knee replacement (UKR) and are not recommended after UKR. To determine if these recommendations should apply to the mobile-bearing Oxford UKR, this study assessed the effect of post-operative activity level on the outcome of this device. METHODS: The outcome of the first 1000 Phase 3 cemented Oxford UKRs implanted between 1998 and 2010 was assessed using survival analysis, the Oxford Knee Score (OKS) and the American Knee Society Objective (KSS-O) and Functional (KSS-F) Scores. Patients were grouped according to the maximum post-operative Tegner Activity Score. RESULTS: The mean follow-up was 6.1 years (range 1 to 14). Overall, increasing activity was associated with superior survival (p=0.025). In the high activity group, with Tegner≥5 (n=115) 2.6% were revised and the 12-year survival was 97.3% (confidence interval (CI): 92.0% to 99.1%). In the low activity group, with Tegner≤4, (n=885) 4.3% were revised and the 12-year survival was 94.0% (CI: 91.4 to 95.8). The difference between the two groups was not significant (p=0.44). Although the final OKS and KSS-F were significantly better in the high activity group compared to the low activity group (OKS 45v40, KSS-F 95v78), there was no difference in the change in OKS or KSS-O. CONCLUSIONS: High activity does not compromise the outcome of the Oxford UKR and may improve it. Activity should not be restricted nor considered to be a contraindication.

Cementless unicondylar knee arthroplasty.

Cementless fixation is an increasingly popular option in unicondylar knee arthroplasty (UKA). Early cementless UKAs suffered from unreliable fixation and uptake of cementless UKA was limited. However, modern designs of cementless UKA have demonstrated excellent results with improved radiographic appearances when compared with cemented implants. This is supported by early joint registry data, which demonstrate a survival advantage with cementless fixation in one design of UKA. This review explains the rationale for cementless UKA, summarizes the results from published trials, and highlights technical aspects points to be aware of when implanting cementless UKA.

No difference in survivorship after unicompartmental knee arthroplasty with or without an intact anterior cruciate ligament.

PURPOSE: Anterior cruciate ligament deficiency (ACLD) has been considered a contraindication for Oxford unicompartmental knee arthroplasty (UKA) because of the reported higher incidence of failure when implanted in ACLD knees. However, given the potential advantages of UKA over total knee arthroplasty (TKA), we have performed UKA in a limited number of patients with ACL deficiency and end-stage medial compartment osteoarthritis (OA) over the past 11 years. The primary aim of this study was to establish the clinical outcome of this cohort; the secondary aim was to compare both clinical and radiographic data with a matched cohort of ACL-intact (ACLI) patients who have undergone UKA for anteromedial OA. METHODS: This retrospective observational study describes the clinical and radiological outcome in 46 medial Oxford UKAs implanted in 42 consecutive patients with ACL deficiency and concomitant symptomatic medial compartment OA at mean follow-up of 5 years. It also compares the outcomes with a matched cohort of UKA patients with an intact ACL (ACLI group). RESULTS: At the time of last follow-up, there was no significant difference in clinical results or survivorship between the two groups in this study. CONCLUSION: The successful short-term results of the ACLD group suggest ACL deficiency may not always be a contraindication to Oxford UKA as previously thought. Until long-term data is available, however, we maintain our recommendation that ACLD be considered a contraindication.

Does a mixed training course on the Oxford unicompartmental knee arthroplasty improve non-technical skills of orthopaedic surgeons?

PURPOSE: To determine whether a mixed course on the Oxford unicompartmental knee arthroplasty (UKA) could improve the non-technical (cognitive) skills of performing UKA. METHODS: 120 delegates consisting of consultant orthopaedic surgeons and advanced surgical trainees attended a 2-day course. 104 (87%) of the delegates had performed total knee arthroplasties, whereas 79 (66%) had performed UKAs. The course consisted of didactic lectures, interactive surgical demonstrations, and practical dry-bone skills workshops. Cognitive skills were assessed at the start (day 1) and end (day 2) of the course using 10 multiple-choice questions. The maximum test score was 10. Multilevel modelling was used to compare the pre- and post-course test scores. The pairings of pre- and post-course scores were not known because of a confidentiality clause. RESULTS: Of the 120 delegates, 71 (59%) took the pre-course test and 120 (100%) took the post-course test. The median score improved significantly from 2 (interquartile range [IQR], 0.5-3.5) to 6 (IQR, 4.5- 7.5) [bootstrap p<0.0001] for every single one of the randomly allocated pairings. Most delegates had poor cognitive skills for the UKA before the course and improved significantly after the course. Sub-analysis of each question topic showed significant improvement in scores for all topics after the course (bootstrap p<0.0001). Nonetheless, the extent to which individual topic scores improved varied widely. The odds ratio for the pre- versus post-course total test score was 4.36. CONCLUSION: A mixed continuing medical education course could enhance the non-technical (cognitive) skills for UKA.

Determination of femoral component size in unicompartmental knee replacement.

It is difficult to determine the ideal size of femoral component when a unicompartmental knee replacement (UKR) is implanted with a minimally invasive approach. The aim of the study was to identify the best method of determining femoral component size pre-operatively. This was done by assessing the accuracy with which it could be predicted by pre-operative templating, patient height, gender and tibial component size. One hundred patients who had had Oxford UKR were studied. Pre-operative radiographs were templated and patient height, gender and implanted tibial component size were recorded. From a review of post-operative radiographs and the known size of component used the ideal size of component that should have been used was established. By relating patient height, gender and tibial component size to the ideal femoral component size the range of these various parameters that best predicted each component size was identified. The reliability of these predictions was assessed assuming that a component one size off ideal was acceptable and two sizes off was unacceptable. Templating was correct in 67% of cases, acceptable in 33% and was never unacceptable. Height alone was correct in 56%, acceptable in 38% and unacceptable in 6%. Height based on gender was correct in 75%, acceptable in 25% and was never unacceptable. Tibial size was correct in 56%, acceptable in 41% and unacceptable in 3%. We conclude that both templating and height based on gender are reliable methods of assessing femoral component size. However because errors can occur surgeons are advised to use both.

After partial knee replacement, patients can kneel, but they need to be taught to do so: a single-blind randomized controlled trial.

BACKGROUND AND PURPOSE: Kneeling is an important functional activity frequently not performed after knee replacement, thus affecting a patient's ability to carry out basic daily tasks. Despite no clinical reason preventing kneeling, many patients fail to resume this activity. The purpose of this study was to determine whether a single physical therapy intervention would improve patient-reported kneeling ability following partial knee replacement (PKR). SUBJECTS: Sixty adults with medial compartment osteoarthritis, suitable for a PKR, participated. METHODS: This was a single-blind, prospective randomized controlled trial. Six weeks after PKR, participants randomly received either kneeling advice and education or routine care where no specific kneeling advice was given. Reassessment was at 1 year postoperatively. The primary outcome measure was patient-reported kneeling ability, as assessed by question 7 of the Oxford Knee Score. Other factors associated with kneeling ability were recorded. These factors were scar position, numbness, range of flexion, involvement of other joints, and pain. Statistical analysis included nonparametric tests and binary logistic regression. RESULTS: A significant improvement in patient-reported kneeling ability was found at 1 year postoperatively in those participants who received the kneeling intervention. Group allocation was the only factor determining an improvement in patient-reported kneeling ability at 1 year postoperatively. DISCUSSION AND CONCLUSION: The single factor that predicted patient-reported kneeling ability at 1 year postoperatively was the physical therapy kneeling intervention given at 6 weeks after PKR. The results of this study suggest that advice and instruction in kneeling should form part of a postoperative rehabilitation program after PKR. The results can be applied only to patients following PKR.

Medial tibial plateau fracture and the Oxford unicompartmental knee.

Tibial plateau fracture is a rare complication of unicompartmental knee arthroplasty. The fracture almost always occurs during surgery, and it is likely to be the result of a technical error, usually an unnecessarily deep vertical saw cut into the proximal tibia. However, anything that weakens or overloads the proximal tibia may contribute to fracture, such as damage to the posterior cortex, excess removal of bone particularly in small patients with osteopenic bones, inadequate preparation of the keel slot, or use of excessive force with a heavy hammer. This series of eight case reports presents our experience with this complication after medial Oxford unicompartmental knee arthroplasty and outlines a treatment protocol.

Oxford medial unicompartmental arthroplasty for focal spontaneous osteonecrosis of the knee.

BACKGROUND: 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 than those with primary osteoarthrosis when arthroplasty is performed. We assessed the outcome of medial unicompartmental knee arthroplasty (UKA) using the Oxford prosthesis for end-stage focal spontaneous osteonecrosis of the knee (SONK; Ahlbäck grades III and IV). PATIENTS AND METHODS: We assessed 29 knees (27 patients) with spontaneous osteonecrosis of the knee using the Oxford Knee Score. 26 knees had osteonecrosis of the medial femoral condyle and 3 had osteonecrosis of the medial tibial plateau. All had been operated on using the Oxford Medial Unicompartmental Knee Arthroplasty (UKA). This group was compared to a similar group (28 knees, 26 patients) who had undergone the same arthroplasty, but because of primary osteoarthrosis. Patients were matched for age, sex and time since operation. The mean length of follow-up was 5 (1-13) years. RESULTS: There were no implant failures in either group, but there was 1 death (from unrelated causes) 9 months after arthroplasty in the group with osteonecrosis. The mean Oxford Knee Score in the group with osteonecrosis was 38, and it was 40 in the group with osteoarthrosis. INTERPRETATION: Use of the Oxford Medial UKA for spontaneous focal osteonecrosis of the knee is reliable in the short to medium term, and gives results similar to those obtained when it is used for patients with primary osteoarthrosis.

Sagittal plane kinematics of a mobile-bearing unicompartmental knee arthroplasty at 10 years: a comparative in vivo fluoroscopic analysis.

This study compares in vivo sagittal plane kinematics of the Oxford mobile-bearing unicompartmental knee arthroplasty (UKA) at 1 and 10 years' postsurgery (10 knees) with a fixed-bearing total knee arthroplasty (TKA) (5 knees) and the normal knee (5 knees), using dynamic fluoroscopic measurement of the patellar tendon angle. The Oxford UKA preserved normal changes in patellar tendon angle with flexion, and this was maintained at 10 years. In contrast, an abnormal pattern was seen with the TKA. The results suggest that a normal pattern of sagittal plane knee kinematics exists following Oxford medial UKA and imply that anterior cruciate ligament function is maintained in the long term.