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

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

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

Introduction:. Isolated lateral compartment osteoarthritis (OA) occurs in 5–10% of knees with unicompartmental OA. Lateral unicompartmental knee arthroplasty has been limited in its prevalence due to challenging surgical technique issues. A robotic-arm assisted surgical technique has emerged as a way to achieve precise implant positioning which can potentially improve surgical outcomes. Methods:. 63 consecutive lateral unicompartmental knee arthroplasties were performed by a single surgeon with the use of a metal backed, cemented prosthesis installed with the three-dimensional intra-operative kinematics and haptic robotic guidance. The average age of the patient was 72.7 years (range: 59–87) and the average BMI was 27.2 (range: 19.0–38.6). The follow-up ranged from 2 months to 30 months. Results:. All patients recovered flexion to an average of 130° at 6 weeks post-operatively, compared to an average of 127° pre-operatively. There was one revision to a total knee at 26 months post-operatively for progression of OA to the patellofemoral compartment. Conclusion:. Early results of robotically guided lateral UKA are encouraging and provide evidence to show that lateral UKA is a viable option for patients with lateral OA disease. Three dimensional planning, intra-operative kinematic analysis and haptic robotic guidance provide a significant advantage over manual installation for lateral compartment arthroplasty of the knee. The significant anterior to posterior translation of the lateral femoral condyle along with the “screw-home” mechanism associated with the lateral compartment makes the tracking of the lateral compartment highly complex when retaining the cruciate ligaments. Intraoperative planning and adjustment of the preoperative plan provided only with this robotic system results in optimized lateral compartment kinematics. Further mid to long term studies are needed to determine survivorship as it compares to medial unicompartmental knee arthroplasty

Purpose. The aim of this study was to compare the short-term and mid-term outcome of lateral UKRs using a single prosthesis, the AMC Uniglide knee implant. Methods. Between 2003 and 2010, seventy lateral unicompartmental knee replacements (mean patient age 63.6±12.7 years) were performed at our unit for isolated lateral compartmental disease. Range of knee motion and functional outcome measures including the American Knee Society (AKSS), Oxford (OKS) and WOMAC scores were recorded from 19 knees at five years' post-operatively and compared to 35 knees at two-years and 53 knees at one-year post-op. Results. Mean range of motion at five-years post-op was 116° compared to 117° at two-years and 115° at one-year. Median AKSS was 177, 185 and 180 at 1, 2, and 5 years post-op with respective OKS of 39, 43, and 37. Total WOMAC scores were 19, 15 and 22 at 1, 2 and 5 years respectively. One-way ANOVA showed no significant decline in range of motion or functional outcome scores with increasing time since surgery (p>0.05). No lateral UKR required revision up to 5 years post-op. Conclusion. This study demonstrates that at five years' post-op, patients who have undergone a lateral compartmental knee replacement for lateral compartment osteoarthritis using this prosthesis maintain an acceptable range of knee motion and knee function. Revision rates for the lateral UKR were excellent at 5 years following surgery. The lateral fixed bearing UKR demonstrates good short and medium term results for treating isolated lateral compartmental osteoarthritis and should be a consideration when managing patients with a pattern of lateral compartment disease

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

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

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: Unicompartmental knee Arthroplasty (UKA) is a commonly used and accepted treatment for Osteoarthritis (OA) in the medial compartment. How-ever, despite some good results. 1. there is still a reluctance to use this procedure in the lateral compartment for the same indications, as the procedure is considered technically difficult, and not as successful. 2. This study reports the clinical outcome of lateral UKAs in comparison with medial UKAs, TKAs and a normal population group using a knee score designed to highlight the shortcomings of TKA. 3. . Methods: 20 consecutive patients over 2 years following lateral UKA were functionally assessed. They were compared with 3 groups of 20 age and sex matched patients: those who had undergone medial UKA or TKA in the same time period, or normal controls from an upper limb clinic. Clinical function was assessed at least 2 years postoperatively, using the ‘total knee questionaire’. 3. This consists of 55 scaled multiple choice questions. The score is derived from the product of three scales: the importance of a specific activity, the frequency with which it is undertaken, and the ease with a patient can perform it. Results: 90% of the patients reported that they were either satisfied or very satisfied with their lateral UKA, with 95% of the patients in the medial UKA group and 75% in the TKA group reaching this level of satisfaction. The average Composite Score for the lateral UKA group was significantly better compared with the TKA group (p < 0, 05). (Kneeling – (5,72/4,45), Gardening – (7,32/5,18), Pivoting – (7,83/6,78) and Walking with heavy bags (8,2/5,97)). The Total Composite Score was significantly better (p< 0, 05) in Patients after lateral UKA (7,14) compared to patients who underwent TKA (5,99). No statistically significant differences in the Total Composite Score was found between both the lateral & medial UKA patients taken as a single group compared with the control group. Conclusion: Lateral Unicompartmental Knee Arthroplasty achieves superior knee function in comparison to Total Knee Arthroplasty, so is worth considering as an option in for early OA of the lateral compartment

Introduction. It is documented in the literature the very good results of lateral unicompartmental knee arthroplasty (UKA) when the standard accepted indications are followed. In our experience these indications can be extended to include post-traumatic osteoarthritis (OA) with malunion secondary to tibial plateau fracture. We report our results concerning 15 UKAs in these particular situations. Material and methods. From 1985 to 2009, we performed 15 lateral UKAs in 15 patients for post traumatic OA secondary to malunion following a tibial plateau fracture. 7 were female and 8 male. The mean age of the patients at the time of the index procedure was 45±17 years and the mean delay from initial trauma was 5.4 years. The average follow-up was 108 months (range 12–265 months). Results. Twelve patients (12 over 15) were satisfied or very satisfied (80%). At follow up 2 had undergone a second operation: 1 osteosynthesis for patellar fracture and 1 conversion to TKA for progression of OA (at 13.7 years after UKA) and one remained unsatisfied. No revision surgery was necessary for wear or infection. The average femoral-tibial alignment was 4° valgus (range −6° to 8°). The mean IKS knee score was 95.3 points and mean IKS function score was 92 points. Discussion. Our results in the medium term are excellent. They support that the selection criteria for UKA can be extended to include these indications. A longer follow up is required before they can be routinely included in the conventional selection criteria for UKA

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

We describe 88 knees (79 patients) with lateral unicompartmental osteoarthritis which had been treated by the St Georg Sled prosthesis.

At a mean follow-up of nine years (2 to 21) 15 knees had revision surgery, nine for progression of arthritis, six for loosening, four for breakage of a component and four for more than one reason. Six patients complained of moderate or severe pain at the final follow-up. Only five knees were lost to follow-up in the 21-year period.

We performed survivorship analysis on the group using revision for any cause as the endpoint. At ten years the cumulative survival rate was 83%, and at 15 years, when ten knees were still at risk, it was 74%.

Based on our clinical results and survival rate the St Georg Sled may be considered to be a suitable unicompartmental replacement for isolated lateral compartment osteoarthritis.

Introduction

The results of the mobile bearing Oxford unicompartmental knee replacement (UKR) in the lateral compartment have been disappointing with a five year survival of 82%. Therefore, it is recommended that mobile bearings should not be used for lateral UKR. This low survivorship is primarily due to high dislocation rate, all occurring in the first year. A detailed analysis of the causes of bearing dislocation confirmed the elevated lateral tibial joint line to be a contributory factor. A new surgical technique was therefore introduced in which care was taken neither to remove too much bone from distal femur nor to over tighten the knee and thus ensure that the tibial joint line was not elevated. Other modifications to the technique were also introduced including use of a domed tibial component.

The results of mobile bearing Oxford unicompartmental knee replacement (UKR) in the lateral compartment have been disappointing (five-year survival: 82%). Therefore, it is recommended that mobile bearings should not be used for lateral UKR. This low survivorship is primarily due to a high dislocation rate. A detailed analysis confirmed the elevated lateral tibial joint line to be a contributory factor to bearing dislocation. A new surgical technique was therefore introduced in which care was taken neither to remove too much bone from the distal femur nor to over tighten the knee and therefore ensure that the tibial joint line was not elevated. Other modifications included use of a domed tibial component.

The aim of this study is to compare the outcome of these iterations: the original series (series I), those with improved surgical technique (series II) and the domed tibial component (series III). The primary outcome measure was bearing dislocation at one year. One year was chosen as all the dislocations in the first series occurred within a year. In the original series (n=53), implanted using a standard open approach, there were six dislocations in the first year, the average flexion 110°, and 95% had no/mild pain on activity. In the second series (n=65), there were 3 dislocations, the average flexion was 117°, and 80% had no/mild pain on activity.

In the third series with the modified technique and a convex domed tibial plateau, there was one dislocation, average flexion was 125° and 94% had no/mild pain on activity. At four years the cumulative primary dislocation rates were 10%, 5% and 0% respectively, and were significantly different (p=0.04).

The improved surgical technique and implant design has reduced dislocation rate to an acceptable level so a mobile bearing can now be recommended for lateral UKR.

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.

Introduction: The results of the mobile bearing Oxford unicompartmental knee replacement (UKR) in the lateral compartment have been disappointing with a five year survival of 82%. Therefore, it is recommended that mobile bearings should not be used for lateral UKR. This low survivorship is primarily due to high dislocation rate, all occurring in the first year. A detailed analysis of the causes of bearing dislocation confirmed the elevated lateral tibial joint line to be a contributory factor. A new surgical technique was therefore introduced in which care was taken neither to remove too much bone from the distal femur nor to over tighten the knee and therefore ensure that the tibial joint line was not elevated. Other modifications to the technique were also introduced including use of a domed tibial component.

Aim: The aim of this study is to compare the outcome of these iterations: the original series [series I], Series II with improved surgical technique and the domed tibial component [Series III].

Method: The primary assessment of outcome was bearing dislocation at one year. One year was chosen as all the dislocations in the first series occurred within a year. In series I, there were 53 knees, in series II 65 knees and in series III 60 knees, all with a minimum of one year follow up.

Results: In series I, there were 6 bearing dislocations (11%) and the average range of movement (ROM) was 110°. In the second series, there were 2 dislocations (3%) and the average ROM was 118°. In the third series, there were no primary dislocations and the average ROM was 125°.

Conclusions: The improved surgical technique and implant design has reduced the dislocation rate to an acceptable level so a mobile bearing can now be recommended for lateral UKR.

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.

Between 29th May 2001 and 15th May 2003, 233 consecutive Preservation unicompartmental knee replacements (UKR) were performed. Of these, 30 were lateral UKRs (13%) performed in 12 men and 16 women (2 bilateral cases) with a mean age of 67 years (range 36 to 93 years). A metal-backed mobile bearing tibial component was used in 13 knees and an all-polyethylene fixed bearing tibial component in 17 knees. The patients were reviewed prospectively at 1 and 2 years. The 2 year results show no difference in range of motion or function between the mobile and fixed bearing versions of the Preservation knee when used on the lateral side. This is similar to the reported results on the medial side. There were 3 early revisions, all in the mobile bearing group. The incidence of revision has been reduced by the introduction of an improved cementing technique.

Introduction

Unicompartmental knee arthroplasty (UKA) has seen renewed interest in recent years due to improved surgical techniques and prosthetic design, and the desire for minimally invasive surgery. For patients with limited degenerative disease, UKA offers a viable alternative to total knee arthroplasty. Historically, the outcomes of lateral compartment UKA have been inferior to medial compartment UKA, with suboptimal patient satisfaction and 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. The hypothesis of the study was that robotic-assisted lateral UKA results in superior outcomes compared to conventional UKA.