INTRODUCTION. Computer-aided systems have been developed recently in order to improve the precision of implantation of unicompartmental knee replacement (UKR). Minimal invasive techniques may decrease the surgical trauma related to the prosthesis implantation, but there might be a concern about the potential for a loss of accuracy. Mobile bearing prostheses have been developed to decrease the risk of polyethylene wear, but are technically more demanding. Navigation might help to compensate for these difficulties. We wanted to combine the theoretical advantages of the three different techniques by developing a navigated, minimal invasive, mobile bearing unicompartmental knee prosthesis. MATERIAL AND METHODS. 160 patients have been operated on at our institution with this system. The 81 patients with more than 2 year follow-up have been re-examined. Complications have been recorded. The clinical results have been analyzed according to the Knee Society Scoring System. The subjective results have been analyzed with the Oxford Knee Questionnaire. The accuracy of implantation has been analyzed on post-operative antero-posterior and lateral long leg X-rays. The 2-year survival rate has been calculated. RESULTS. We observed 8 complications related to the implant or the operative technique: 2 cases of meniscus instability (1 revision to TKR, 1 bearing exchange); 2 cases of tibia loosening (revised to TKR), 2 cases of femoral loosening (revised to TKR), 1 case of lateral disease progression (revised to TKR), 1 case of unexplained pain syndrome (revised to TKR). The mean Knee Score was 93 points, 44% had the maximum of 100 points, and only 10% have less than 85 points. The mean pain score was 48 points/50. The mean flexion angle was 128°, and 60% had at least 130° of knee flexion. The mean Function Score was 97 points, 84% have the maximum of 100 points, and only 5% had less than 85 points. The mean Oxford Knee Questionnaire score was 19 points (best result: 12 points, worst result: 60 points). Expected limb axis correction was obtained in 77% of the cases. 62% of the cases had an optimally implanted prosthesis for all studied criteria. The 2-year survival rate was 97%. DISCUSSION. Most of the revision cases were related to technical difficulties during the development phase. Fixation of the implant has been improved, and some imprecise steps of the software have been corrected. Since these changes occurred, no severe early complication related to implant or software has been observed. The current implant is considered reliable, and the current minimal invasive navigated technique is considered reliable as well

Summary. UC TKA showed similar anteroposterior translation and more femoral external rotation of earlier onset when compared to PS TKA. Introduction. Recently highly conforming ultracongruent TKA has been reintroduced with improved wear characteristics and lower complications. The purpose of the study was to assess kinematics and clinical outcome of posterior stabilized and ultracongruent rotating-platform mobile bearing TKA. Methods. Ninety patients with primary osteoarthritis of the knee were randomized to undergo computer assisted TKA with PS(n = 45) or UC(n = 45) prostheses and were followed up for a minimum 2 years. The passive kinematic evaluation was performed before and after implantation with a navigation system. Three parameters of tibiofemoral relationship (anterior/posterior translation, varus/valgus alignment and rotation) were recorded from 0° to 120° of flexion. The patients were clinically and radiographically evaluated at final follow-up. Results. Paradoxical anterior translation of the femur was observed from 0° to 70° of flexion in PS(8.7mm) and 0° to 85° in UC knees(10.4mm, p = 0.064). The distance of femoral roll-back was 6.7mm and 5.5mm, but never reached the starting point. Paradoxical internal rotation of the femur was found from 0° to 62° of flexion in PS(9.9°) and 0° to 47° in UC knees(5.6°, p = 0.002). UC knees showed more external rotation of the femur during flexion from 0° to 120°(5.7:11.0, p = 0.048). There was no significant difference in the maximal flexion(123.3°:125.5°, p = 0.366), AKS knee scores(95.9:92.0, p = 0.101), AKS function scores(86.2:82.9, p = 0.435) and WOMAC index scores(13.4:15.9, p = 0.268). There was no progressive radiolucent line or loosening in all knees. Discussion and Conclusion. UC TKA showed similar anteroposterior translation and more femoral external rotation of earlier onset when compared to PS TKA. There was no difference in clinical outcome between two designs. UC TKA showed comparable kinematic and clinical results to PS TKA

Introduction. Unicompartmental knee arthroplasty (UKA) in patients with isolated medial osteoarthritis of the knee is nowadays a standard procedure with good results, especially with the minimally-invasive approach. However, the survival rate of the unicompartmental knee prostheses is inferior to that of total knee prostheses. Therefore, further studying of UKA is still necessary. In most mobile bearing designs the femoral component has a spherical surface and therefore its positioning is not crucial. The role of the tibial slope in UKA has not been investigated so far. The manufacturers recommend tibial slopes with values between 10° positive slope and 5° negative slope. Most surgeons try to reconstruct the anatomical slope with a high failure by measuring the slope on x-rays. The aim of this study was to investigate the influence of the tibial slope on the wear rate of a medial UKA. Materials and methods. In vitro wear simulation of medial mobile bearing unicompartmental knee prosthesis with a spherical femoral surface (Univation ®) was performed with a customized four-station servo-hydraulic knee wear simulator (EndoLab GmbH, Thansau, Germany) reproducing exactly the walking cycle as specified in ISO 14243–1:2002(E). The tibial tray was inserted with 2 different medial tibial slopes: 0°, 8° (n=3 for each group). The lateral tibial slope of the space-holder was not changed (0° for every group). We performed a total of 5 million cycles for every different slope, the gravimetric wear rate was determined gravimetrically using an analytical balance every 500 000 cycles according to the ISO 14243–2. Results. The wear rate in the 0° slope group was 3.46±0.59 mg/million cycles, and in the 8° slope group it was 0.99±0.42 mg/million cycles. The difference between the 0° tibial slope group and the 8° tibial slope group was highly significant (p<0.01, alternate t-test). Discussion. An increase of the tibial slope leads to a reduced wear rate in a mobile bearing UKA. Therefore, a higher tibial slope should be recommended for mobile bearing UKA. However, the influence on the ligaments has to be considered as a higher tibial slope leads to an increased strain on the anterior cruciate ligament. This influences needs to be investigated in further studies before a definite optimal range for the tibial slope can be recommended

Joint registries report that 25–40% of UKR revisions are performed for pain. Proximal tibial strain and microdamage are possible causes of this “unexplained” pain. The aim of this study was to examine the effect of UKR implant design and material on proximal tibial cortical strain and cancellous microdamage. Composite Sawbone tibias were implanted with cemented UKR components: 5 fixed bearing all-polyethylene (FB-AP), 5 fixed bearing metal backed (FB-MB), and 5 mobile bearing metal backed implants (MB-MB). Five intact tibias were used as controls. Tibias were loaded in 500N increments to 2500N. Cortical surface strain was measured using digital image correlation (DIC). Cancellous microdamage was measured using acoustic emission (AE), a technique which detects elastic waves produced by the rapid release of energy during microdamage events. DIC showed significant differences in anteromedial cortical strain between implants at 1500N and 2500N in the proximal 10mm only (p<0.001) with strain shielding in metal backed implants. AE showed significant differences in cancellous microdamage (AE hits), between implants at all loads (p=0.001). FB-AP implants displayed significantly more hits at all loads than both controls and metal backed implants (p<0.001). FB-AP implants also differed significantly by displaying AE hits on unloading (p=0.01), reflecting a lack of implant stiffness. Compared to controls, the FB-AP implant displayed 15x the total AE hits, the FB-MB 6x and the MB-MB 2.7x. All-polyethylene medial UKR implants are associated with greater cancellous bone microdamage than metal backed implants even at low loads

Introduction. Total knee replacement has been well-established form of treatment both for osteoarthritis and inflammatory arthritis. Both cemented and uncemented TKR have been used successfully. Since 1977 low contact stress (LCS) mobile bearing knee replacement has been in extensive use. Most of the intermediate and long term results reported are in osteoarthritis1–7. Though there are several studies reporting short term performance of TKR in rheumatoid arthritis8–19 there have been rare reports31 of intermediate to long-term performance of LCS uncemented TKR in rheumatoid arthritis. Methods. Retrospective, non-randomised and consecutive study. Case notes and radiological assessment done. Kaplan meyer survival analysis used. Radiological assessment between initial and final xrays done using T test statistics. Assessement done by two independent observer. Results. 108 knees in 67 patients are collected. 21 patients with 36 knees have died. Only 65 knees in 42 patients had both case notes and xrays which are included in this study. Of this 11 knees in 7 patients were dead. All 65 knees in 42 patients are sero-positive rheumatoid arthritis. Pre-operative bone loss was seen only in 4 knees. Bone loss was in the medial side in 3 knees (4,5 and 8mm respectively) and lateral in 1 knee (1 cm). None of these bone loss needed bone grafting or any special procedures. There was no subsidence in any of the 65 knees. Survival of uncemented LCS TKR in inflammatory arthritis patients is 100%. Aseptic failure is 0%. No infective failure. There is no significant change in the implant position. This is the longest follow for uncemented TKR in inflammatory arthritis ever reported in the literature. Conclusion and Discussion. In conclusion, our study has uniformity, as a single surgeon performed/supervised with senior trainees all the operations and all patients received the same level of post-operative care. Survival of LCS uncemented TKR in inflammatory arthritis patients is 100% up to 15years. This is the longest follow up in this patient population ever reported in the literature. Our study shows excellent survival and comparable to other cemented TKRs in this patient population reported in the literature. This study proves contrary to the general belief that uncemented TKR do poor in inflammatory arthritis due to osteoporotic bone

Introduction. The options for the treatment of the young active patient with unicompartmental symptomatic osteoarthritis and pre-existing Anterior Cruciate Ligament (ACL) deficiency are limited. Patients with ACL deficiency and end-stage medial compartment osteoarthritis are usually young and active. The Oxford Unicompartmental Knee Replacement (UKA) is a well established treatment option in the management of symptomatic end-stage medial compartmental osteoarthritis, but a functionally intact ACL is a pre-requisite for its satisfactory outcome. If absent, high failure rates have been reported, primarily due to tibial loosening. Previously, we have reported results on a consecutive series of 15 such patients in whom the ACL was reconstructed and patients underwent a staged or simultaneous UKA. The aim of the current study is to provide an update on the clinical and radiological outcomes of a large, consecutive cohort of patients with ACL reconstruction and UKA for the treatment of end-stage medial compartment osteoarthritis and to evaluate, particularly, the outcome of those patients under 50. Methods. This study presents a consecutive series of 52 patients with ACL reconstruction and Oxford UKA performed over the past 10 years (mean follow-up 3.4 years). The mean age was 51 years (range: 36–67). Procedures were either carried out as Simultaneous (n=34) or Staged (n=18). Changes in clinical outcomes were measured using the Oxford Knee Score (OKS), the change in OKS (OKS=Post-op − Pre-op) and the American Knee Society Score (AKSS). Fluoroscopy assisted radiographs were taken at each review to assess for evidence of loosening, radiolucency progression, (if present), and component subsidence. Results. Five year survival was 90%. At last follow-up, the mean outcome scores for the group were: OKS 40 (SD: 8.3), objective AKSS 77 (SD: 16.1), functional AKSS 93 (SD: 13.7) and OKS of 11. Complications were recorded in three patients, (one early infection requiring a two-stage revision, a bearing dislocation and progression of OA in the lateral compartment). 25 patients, whose procedure occurred under the age of 50, had mean outcome scores of: OKS 38 (SD: 7.7), objective AKSS 73 (SD: 20.2), functional AKSS 93 (SD: 11.9) and OKS 12. No patients had radiological evidence of component loosening. Discussion and Conclusion. This study has demonstrated that combined ACL reconstruction and Oxford UKA provide good medium-term clinical and radiological results. The mobile bearing used in the Oxford knee minimises wear and our radiographic study has seen no suggestions of loosening

Introduction. Radiolucencies beneath the tibial component are well recognized in knee arthroplasty; the aetiology and significance are poorly understood. Non-progressive narrow radiolucencies with a sclerotic margin are thought not to be indicative of loosening. Factors which decrease the incidence of radiolucencies include cementless fixation and the use of pulse lavage. Leg/component alignment or BMI do not influence radiolucency. We are not aware of any studies that have looked at the effect of load type on radiolucency. The Oxford domed lateral tibial component was introduced to decrease the bearing dislocation rate that was unacceptably high with the flat tibial tray. However, the introduction of the domed tibial component alters the forces transmitted through the implant-cement-bone interface. As the Oxford UKR uses a fully congruent mobile bearing, the forces transmitted through the interface with a flat tray are compressive, except for the effect of friction. However, with the domed tibial component shear forces are introduced. The aim of this study was to assess the prevalence of radiolucency beneath the previous flat design and the new domed tibial tray. Patients and methods. A consecutive series of 248 cemented lateral UKRs (1999–2009) at a single institution were assessed. The first 55 were with a flat tibia and the subsequent 193 with a domed component. One year post-op radiographs were assessed, by two observers, for the presence (full or partial) and distribution of radiolucency. The distribution and thickness of each radiolucency. Cases were excluded for missing or poorly aligned radiographs. Results. In the flat group there were 42 patients (17 male, 25 female) with 42 joints. In the domed group there were 139 patients (44 male, 95 female) with 146 joints. There was a statistical significant difference between groups for the presence and extent of radiolucency (p<0.001). In the flat group, 6 (14%) had a full radiolucency and 18 (43%) had a partial radiolucency. 14 of the 18 partial radiolucencies involved the far lateral zones (1&2) and 3 partial radiolucencies involved the keel. In the domed group 6, (4.1%) had a full radiolucency and 13 (8.9%) had a partial radiolucency. All radiolucencies observed were less than 1 mm thick. Intra-class correlation for inter-observer agreement for assessment of radiolucency was 0.679. Discussion. The introduction the domed lateral tibial component results in a reduction in prevalence of radiolucency compared to a flat component. This suggests, as the mode of fixation is identical, that the forces across the tibial-cement-bone interface have a significant effect on the development of the tissue at that interface. In particular it suggests that compressive forces alone tend to cause soft tissue to be formed at the interface, whereas shear force causes bone