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

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

Aims. In the last decade, interest in partial knee arthroplasties and bicruciate retaining total knee arthroplasties has increased. In addition, patient-related outcomes and functional results such as range of movement and ambulation may be more promising with less invasive procedures such as bicompartmental arthroplasty (BCA). The purpose of this study is to evaluate clinical and radiological outcomes after a third-generation patellofemoral arthroplasty (PFA) combined with a medial or lateral unicompartmental knee arthroplasty (UKA) at mid- to long-term follow-up. Methods. A total of 57 procedures were performed. In 45 cases, a PFA was associated with a medial UKA and, in 12, with a lateral UKA. Patients were followed with validated patient-reported outcome measures (Oxford Knee Score (OKS), EuroQol five-dimension questionnaire (EQ-5D), EuroQoL Visual Analogue Scale (EQ-VAS)), the Knee Society Score (KSS), the Forgotten Joint Score (FJS), and radiological analysis. Results. The mean follow-up was nine years (6 to 13). All scores significantly improved from preoperatively to final follow-up (mean and SD): OKS from 23.2 (8.1) to 42.5 (3.5), EQ-5D from 0.44 (0.25) to 0.815 (0.1), EQ-VAS from 46.7 (24.9) to 89.1 (9.8), KSS (Knee) from 51.4 (8.5) to 94.4 (4.2), and KSS (Function) from 48.7 (5.5) to 88.8 (5.2). The mean FJS at final follow-up was 79.2 (4.2). All failures involved the medial UKA + PFA group. Overall, survival rate was 91.5% for all the combined implants at ten years with 95% confidence intervals and 22 knees at risk. Conclusion. Excellent clinical and radiological outcomes were achieved after a third-generation PFA combined with a medial or lateral UKA. BCA with unlinked partial knee prostheses showed a good survival rate at mid- to long-term follow-up. Cite this article: Bone Joint J 2021;103-B(5):840–845

Aims

Unicompartmental knee arthroplasty (UKA) and bicompartmental knee arthroplasty (BCA) have been associated with improved functional outcomes compared to total knee arthroplasty (TKA) in suitable patients, although the reason is poorly understood. The aim of this study was to measure how the different arthroplasties affect knee extensor function.

Background. Lateral Unicompartmental Knee Arthroplasty (UKA) is a recognised treatment option in the management of lateral Osteoarthritis (OA) of the knee. Whilst there is extensive evidence on the indications and contraindcations in Medial UKA there is limited evidence on this topic in Lateral UKA. The aim of this study was to assess our experience of mobile lateral UKR and to look specifically at the effect of Contraindications on the outcome. Method. 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 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%). In total, 14 (4%) were for dislocation, of which 12 had no recurrence following insertion of a new bearing. In all, 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. Mobile (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. Younger age, heavier weight, high activity, and patellofemoral erosions did not detrimentally affect outcome, so should not be considered contraindications

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

Aims. It remains controversial whether patellofemoral joint pathology is a contraindication to lateral unicompartmental knee arthroplasty (UKA). This study aimed to evaluate the effect of preoperative radiological degenerative changes and alignment on patient-reported outcome scores (PROMs) after lateral UKA. Secondarily, the influence of lateral UKA on the alignment of the patellofemoral joint was studied. Methods. A consecutive series of patients who underwent robotic arm-assisted fixed-bearing lateral UKA with at least two-year follow-up were retrospectively reviewed. Radiological evaluation was conducted to obtain a Kellgren Lawrence (KL) grade, an Altman score, and alignment measurements for each knee. Postoperative PROMs were assessed using the Kujala (Anterior Knee Pain Scale) score, Knee Injury and Osteoarthritis Outcome Score Joint Replacement (KOOS JR), and satisfaction levels. Results. A total of 140 knees (130 patients) were identified for analysis. At mean 4.1 years (2.0 to 8.5) follow-up, good to excellent Kujala scores were reported. The presence of mild to moderate preoperative patellofemoral joint osteoarthritis had no impact on these scores (KL grade 0 vs 1 to 3, p = 0.203; grade 0 to 1 vs 2 to 3, p = 0.674). Comparable scores were reported by patients with osteoarthritis (Altman score of ≥ 2) evident on either the medial or lateral patellofemoral joint facet (medial, p = 0.600 and lateral, p = 0.950). Patients with abnormal patellar congruence and tilt angles (≥ 17° and ≥ 14°, respectively) reported good to excellent Kujala scores. Furthermore, lateral UKA resulted in improvements to patellofemoral alignment. Conclusion. This is the first study demonstrating that mild to moderate preoperative radiological degenerative changes and malalignment of the patellofemoral joint are not associated with poor patient-reported outcomes at mid-term follow-up after lateral fixed-bearing UKA. Our data suggest that this may be explained by realignment of the patella and thereby redistribution of loads across the patellofemoral joint. Cite this article: Bone Joint J 2020;102-B(6):727–735

Aims. Limited evidence is available on mid-term outcomes of robotic-arm assisted (RA) partial knee arthroplasty (PKA). Therefore, the purpose of this study was to evaluate mid-term survivorship, modes of failure, and patient-reported outcomes of RA PKA. Methods. A retrospective review of patients who underwent RA PKA between June 2007 and August 2016 was performed. Patients received a fixed-bearing medial or lateral unicompartmental knee arthroplasty (UKA), patellofemoral arthroplasty (PFA), or bicompartmental knee arthroplasty (BiKA; PFA plus medial UKA). All patients completed a questionnaire regarding revision surgery, reoperations, and level of satisfaction. Knee Injury and Osteoarthritis Outcome Scores (KOOS) were assessed using the KOOS for Joint Replacement Junior survey. Results. Mean follow-up was 4.7 years (2.0 to 10.8). Five-year survivorship of medial UKA (n = 802), lateral UKA (n = 171), and PFA/BiKA (n = 35/10) was 97.8%, 97.7%, and 93.3%, respectively. Component loosening and progression of osteoarthritis (OA) were the most common reasons for revision. Mean KOOS scores after medial UKA, lateral UKA, and PFA/BiKA were 84.3 (SD 15.9), 85.6 (SD 14.3), and 78.2 (SD 14.2), respectively. The vast majority of the patients reported high satisfaction levels after RA PKA. Subgroup analyses suggested tibial component design, body mass index (BMI), and age affects RA PKA outcomes. Five-year survivorship was 98.4% (95% confidence interval (CI) 97.2 to 99.5) for onlay medial UKA (n = 742) and 99.1% (95% CI 97.9 to 100) for onlay medial UKA in patients with a BMI < 30 kg/m. 2. (n = 479). Conclusion. This large single-surgeon study showed high mid-term survivorship, satisfaction levels, and functional outcomes in RA UKA using metal-backed tibial onlay components. In addition, favourable results were reported in RA PFA and BiKA. Cite this article: Bone Joint J 2020;102-B(1):108–116

Aims

Commonly performed unicompartmental knee arthroplasty (UKA) is not designed for the lateral compartment. Additionally, the anatomical medial and lateral tibial plateaus have asymmetrical geometries, with a slightly dished medial plateau and a convex lateral plateau. Therefore, this study aims to investigate the native knee kinematics with respect to the tibial insert design corresponding to the lateral femoral component.

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

Objectives. Unicompartmental knee arthroplasty (UKA) is a demanding procedure, with tibial component subsidence or pain from high tibial strain being potential causes of revision. The optimal position in terms of load transfer has not been documented for lateral UKA. Our aim was to determine the effect of tibial component position on proximal tibial strain. Methods. A total of 16 composite tibias were implanted with an Oxford Domed Lateral Partial Knee implant using cutting guides to define tibial slope and resection depth. Four implant positions were assessed: standard (5° posterior slope); 10° posterior slope; 5° reverse tibial slope; and 4 mm increased tibial resection. Using an electrodynamic axial-torsional materials testing machine (Instron 5565), a compressive load of 1.5 kN was applied at 60 N/s on a meniscal bearing via a matching femoral component. Tibial strain beneath the implant was measured using a calibrated Digital Image Correlation system. Results. A 5° increase in tibial component posterior slope resulted in a 53% increase in mean major principal strain in the posterior tibial zone adjacent to the implant (p = 0.003). The highest strains for all implant positions were recorded in the anterior cortex 2 cm to 3 cm distal to the implant. Posteriorly, strain tended to decrease with increasing distance from the implant. Lateral cortical strain showed no significant relationship with implant position. Conclusion. Relatively small changes in implant position and orientation may significantly affect tibial cortical strain. Avoidance of excessive posterior tibial slope may be advisable during lateral UKA. Cite this article: A. M. Ali, S. D. S. Newman, P. A. Hooper, C. M. Davies, J. P. Cobb. The effect of implant position on bone strain following lateral unicompartmental knee arthroplasty: A Biomechanical Model Using Digital Image Correlation. Bone Joint Res 2017;6:522–529. DOI: 10.1302/2046-3758.68.BJR-2017-0067.R1

INTRODUCTION. Medial and lateral unicompartmental knee arthroplasty (UKA) are both reliable treatment options for isolated osteoarthritis. Postoperative lower leg alignment is known to play an important role on short-term functional outcomes, which is an important argument for the use of robotic-assisted surgery. Since several anatomical and kinematic differences exist between both compartments, it seems inaccurate to aim for similar postoperative lower leg alignment in medial and lateral UKA. Purpose of this study was (I) to compare outcomes between both procedures and (II) to assess the role of preoperative and postoperative alignment on short-term outcomes in both procedures. METHODS. Patients who underwent robotic-assisted medial or lateral UKA were included if they completed functional outcomes questionnaires preoperatively and postoperatively (Western Ontario and McMaster Universities Arthritis score) and completed an artificial joint awareness questionnaire (Forgotten Joint Score) postoperatively (not used preoperatively). A total of 143 medial UKA and 36 lateral UKA patients were included and mean follow-up was 2.4-years (range: 2.0 – 5.0 year). Postoperative alignment was measured using hip-knee-ankle radiographs with a standardized method. Alignment was categorized in medial and lateral UKA as undercorrection (3° to 7° varus or valgus, respectively), neutral (−1° to 3° varus or valgus, respectively), or overcorrection (3° to 7° valgus or varus, respectively). Outcomes were compared using independent t-tests and Pearson correlation analysis was performed to assess a correlation between alignment and outcomes. RESULTS. No preoperative differences in functional outcomes were seen between medial UKA (54.9 ±14.9) and lateral UKA (50.3 ±13.4, p=0.304). Postoperatively, equivalent outcomes were noted between medial and lateral UKA in overall function (89.8 ±11.7 vs. 90.2 ±12.4, respectively, p=0.855) and joint awareness (71.2 ±24.5 vs. 70.9 ±28.2, respectively, p=0.956). Correlation analysis did not show a correlation between preoperative alignment and both functional outcomes and joint awareness for both procedures (all p > 0.4, Figure 1). More undercorrection was correlated with better functional outcomes (−0.355, p = 0.039) and less joint awareness (−0.540, p=0.005) in lateral UKA (Figure 2). In medial UKA, no correlation was noted between postoperative alignment and both functional outcomes (p=0.104) and joint awareness (p=0.069, Figure 2). With neutral postoperative alignment, less joint awareness was noted following medial UKA than lateral UKA (72.6 ±22.6 vs. 55.3 ±28.5, p=0.024). With undercorrection, however, significantly less joint awareness (85.3 ±19.5 vs. 68.2 ±26.8, p=0.024) and better functional outcomes (96.0 ±5.4 vs. 88.5 ±11.6,p=0.001) were noted following lateral UKA than medial UKA (Figure 3). CONCLUSION. At short-term follow-up, equivalent outcomes were noted between medial and lateral UKA but the optimal postoperative alignment differed between both procedures. Undercorrection (3° to 7° valgus) resulted in most optimal outcomes in lateral UKA, while this was with neutral alignment (−1° to 3° varus) in medial UKA. This study showed that postoperative alignment plays a role on short-term outcomes of UKA and suggests that precise control of postoperative alignment should be pursued, which is possible with computer navigation or robotic-assisted surgery in UKA. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Introduction. Patient Specific Instrumentation (PSI) has the potential to allow surgeons to perform procedures more accurately, at lower cost and faster than conventional instrumentation. However, studies using PSI have failed to convincingly demonstrate any of these benefits clinically. The influence of guide design on the accuracy of placement of PSI has received no attention within the literature. Our experience has suggested that surgeons gain greater benefit from PSI when undertaking procedures they are less familiar with. Lateral unicompartmental knee replacement (UKR) is relatively infrequently performed and may be an example of an operation for which PSI would be of benefit. We aimed to investigate the impact on accuracy of PSI with respect to the area of contact, the nature of the contact (smooth or studded guide surfaces) and the effect of increasing the number of contact points in different planes. Method. A standard anatomy tibial Sawbone was selected for use in the study and a computed tomography scan obtained to facilitate the production of PSI. Nylon PSI guides were printed on the basis of a lateral UKR plan devised by an orthopaedic surgeon. A control PSI guide with similar dimensions to the cutting block of the Oxford Phase 3 UKR tibial guide was produced, contoured to the anterior tibial surface with multiple studs on the tibial contact surface. Variants of this guide were designed to assess the impact of design features on accuracy. These were: a studded guide with a 40% reduction in tibial contact area, a non-studded version of the control guide, the control guide with a shim to provide articular contact, a guide with an extension to allow distal referencing at the ankle and a guide with a distal extension and an articular shim. All guides were designed with an appendage that facilitated direct attachment to a navigation machine (figure 1). 36 volunteers were asked to place each guide on the tibia with reference to a 3D model of the operative plan. The order of placement was varied using a counterbalanced latin square design to limit the impact of the learning effect. The navigation machine recorded deviations from the plan in respect of proximal-distal and medial-lateral translations as well as rotation around all three axes. Statistical analysis was performed on the compound translational and rotational errors for each guide using ANOVA with Bonferroni correction with statistical significance at p<0.05. Results. Contact points in greater than one plane led to a trend for increasing accuracy and precision of PSI guide placement with respect to rotational alignment, this achieved statistical significance relative to the control guide only with the guide that included articular and distal contact points (figure 2). No significant differences were found with respect to translation. Changes in contact area within the same plane and the use of smooth or studded contact points made no significant difference to accuracy. Conclusion. PSI guide design significantly impacts on accuracy of placement. PSI guides for UKR should endeavour to include widely separated reference points in different planes to maximise rotational accuracy

Introduction. Isolated lateral compartment osteoarthritis (OA) occurs in 5–10% of knees with OA [1, 2]. Lateral unicompartmental knee arthroplasty (LUKA) emerged as a treatment to this disease in the early 80s but challenging surgical technique has limited the prevalence of this treatment option [1–3]. A robotic-arm assisted surgical technique (MAKO Surgical Corp.) has emerged as a way to achieve precise implant positioning which can potentially improve surgical outcomes. Objectives. The purpose of this study was to evaluate short term outcomes for patients that received LUKA using a novel robotic-arm assisted surgical technique. Methods. Thirty-seven (37) patients (12 male, 25 female - mean age 63.7 years) with lateral OA received a robotic-arm assisted LUKA between July 2011 and September 2013 from 3 surgeons. All patients were evaluated by an independent surgeon not involved in the treatment of these patients at an average follow-up of 15.9 months (8–27). Range of motion and limb alignment was compared pre- and post-operatively. Results. Lateral UKA using robotic-arm assistance improved the post-operative range of motion an average of 4.8 ± 7.1º (p<0.0001) from a starting value of 136.5 ± 8.6º to a post-operative value of 141.6 ± 8.0º. In addition, patients began with a pre-operative deformity of 3.1 ± 3.2º of valgus and resulted in a post-operative alignment of 0.8 ± 1.9º of valgus corresponding to an average correction of 2.4 ± 2.3º less valgus (p<0.000001). The average operative time was 44.0 ± 10.8 minutes with 97% of the cases completed within 60 minutes. Conclusion. These results suggest that LUKA with robotic-arm assistance provides excellent post-operative alignment and demonstrate a reliable option for management of isolated lateral knee OA

Introduction. Chronic uneven distribution of forces over the articular cartilage, which are present in OA, has been shown to be a risk factor for the development of OA. Certain regions of the articular cartilage will be exposed to increased chronic peak loads, whereas other regions encounter a corresponding relative reduction of transmitted forces. This has a well known influence on cartilage viability and is a precursor of degenerative progression. Congruence of joints has an important impact on force distribution across articular surfaces. Therefore, tibiofemoral incongruence could lead to alterations of load distribution and ultimately to progressive degenerative changes. In clinical practice the routine method for evaluation of progressive OA is analysis of joint space width (JSW) using weight bearing radiographs. Recent studies have suggested that JSW has a strong positive correlation with cartilage compression, volume and meniscal extrusion. Lateral unicondylar knee arthroplasty (UKA) has gained increasing popularity over the last decade in the treatment of isolated unicompartmental osteoarthritis (OA). However, progressive degenerative alterations of the medial compartment following lateral unicompartmental knee arthroplasty remains a leading cause of revision surgery. Therefore, the purpose of this study is to evaluate the medial compartment congruence (MCC) and joint space width (JSW) alterations following lateral UKA. Methods. The MCC of 53 knees following lateral UKA was evaluated on pre- and postoperative radiographs and compared to 41 healthy knees, using an Interative Closest Point (ICP) algorithm. The ICP algorithm calculated the Congruence Index (CI) by performing a rigid transformation that best aligns the digitized tibial and femoral surfaces (figure 1A). Inner, middle and outer JSW was measured by subdividing the medial compartment into four quarters on weight bearing tunnel view radiographs pre- and postoperatively (figure 1B). Results. The measured CI of the healthy control group was 0.99. The pre-operative CI of knees undergoing lateral UKA was 0.92, which significantly improved to 0.96 (p<0.0001) post-operatively (figure 2). Post-operatively the inner JSW increased (p=0.006) and the outer decreased (p=0.002). JSW was restored post-operatively since no significant differences were noted in all three measured post-operative JSW locations compared to the control group (figure 3). Conclusion. Our data suggests that lateral UKA improves MCC and normalizes JSW of the medial compartment, potentially preventing osteoarthritic progression in the uninvolved medial compartment

Partial knee arthroplasty (PKA), either medial or lateral unicompartmental knee artroplasty (UKA) or patellofemoral arthroplasty (PFA) are a good option in suitable patients and have the advantages of reduced operative trauma, preservation of both cruciate ligaments and bone stock, and restoration of normal kinematics within the knee joint. However, questions remain concerning long-term survival. The goal of this review article was to present the long-term results of medial and lateral UKA, PFA and combined compartmental arthroplasty for multicompartmental disease. Medium- and long-term studies suggest reasonable outcomes at ten years with survival greater than 95% in UKA performed for medial osteoarthritis or osteonecrosis, and similarly for lateral UKA, particularly when fixed-bearing implants are used. Disappointing long-term outcomes have been observed with the first generation of patellofemoral implants, as well as early Bi-Uni (ie, combined medial and lateral UKA) or Bicompartmental (combined UKA and PFA) implants due to design and fixation issues. Promising short- and med-term results with the newer generations of PFAs and bicompartmental arthroplasties will require long-term confirmation.

Cite this article: Bone Joint J 2015;97-B(10 Suppl A):9–15.

Progressive degenerative changes in the medial compartment of the knee following lateral unicompartmental arthroplasty (UKA) remains a leading indication for revision surgery. The purpose of this study is to evaluate changes in the congruence and joint space width (JSW) of the medial compartment following lateral UKA. The congruence of the medial compartment of 53 knees (24 men, 23 women, mean age 13.1 years; sd 62.1) following lateral UKA was evaluated pre-operatively and six weeks post-operatively, and compared with 41 normal knees (26 men, 15 women, mean age 33.7 years; sd 6.4), using an Interactive closest point algorithm which calculated the congruence index (CI) by performing a rigid transformation that best aligns the digitised tibial and femoral surfaces. Inner, middle and outer JSWs were measured by sub-dividing the medial compartment into four quarters on pre- and post-operative, weight bearing tunnel view radiographs. The mean CI of knees following lateral UKA significantly improved from 0.92 (sd 0.06) pre-operatively to 0.96 (sd 0.02) (p < 0.001) six weeks post-operatively. The mean CI of the healthy control group was 0.99 sd 0.01. Post-operatively, the mean inner JSW increased (p = 0.006) and the outer decreased (p = 0.002). The JSW was restored post-operatively as no significant differences were noted in all three locations compared with the control group (inner JSW p = 0.43; middle JSW p = 0.019, outer JSW p = 0.51).

Our data suggest that a well conducted lateral UKA may improve the congruence and normalise the JSW of the medial compartment, potentially preventing progression of degenerative change.

Cite this article: Bone Joint J 2015;97-B:50–5.

Mobile-bearing unicompartmental knee replacements (UKRs) with a flat tibial plateau have not performed well in the lateral compartment, owing to a high dislocation rate. This led to the development of the Domed Lateral Oxford UKR (Domed OUKR) with a biconcave bearing. The aim of this study was to assess the survival and clinical outcomes of the Domed OUKR in a large patient cohort in the medium term.

We prospectively evaluated 265 consecutive knees with isolated disease of the lateral compartment and a mean age at surgery of 64 years (32 to 90). At a mean follow-up of four years (sd 2.2, (0.5 to 8.3)) the mean Oxford knee score was 40 out of 48 (sd 7.4). A total of 12 knees (4.5%) had re-operations, of which four (1.5%) were for dislocation. All dislocations occurred in the first two years. Two (0.8%) were secondary to significant trauma that resulted in ruptured ligaments, and two (0.8%) were spontaneous. In four patients (1.5%) the UKR was converted to a primary TKR. Survival at eight years, with failure defined as any revision, was 92.1% (95% confidence interval 81.3 to 100).

The Domed Lateral OUKR gives good clinical outcomes, low re-operation and revision rates and a low dislocation rate in patients with isolated lateral compartmental disease, in the hands of the designer surgeons.

Cite this article: Bone Joint J 2014;96-B:59–64.

Introduction

There has been renewed interest in the use of unicompartmental knee arthroplasty (UKA) for patients with limited degenerative disease of the knee due to improved surgical techniques and prosthetic design, and the desire for minimally invasive surgery. However, patient satisfaction following UKA for lateral compartment disease have been suboptimal with increased revision rates. Robotic-assisted UKA has been shown to improve precision and accuracy of component placement, which may improve outcomes of lateral UKA. The purpose of this study was to compare the outcome of robotic-assisted UKA to conventional UKA for degenerative disease of the lateral compartment with the hypothesis that robotic-assisted lateral UKA results in superior outcomes compared to conventional UKA.