Source of the study: University of Auckland, Auckland, New Zealand. Unicompartmental knee arthroplasty (UKA) is effective for patients with isolated compartment osteoarthritis, however the procedure has higher revision rates. Long-term survivorship and accurate characterisation of revision reasons are limited by a lack of long-term data and standardised revision definitions. We aimed to identify survivorship, risk factors and revision reasons in a large UKA cohort with up to 20 years follow-up. Patient, implant and revision details were recorded through clinical and radiological review for 2,137 consecutive patients undergoing primary medial UKA across Auckland, Canterbury, Counties Manukau and Waitematā DHB between 2000 and 2017. Revision reasons were determined from review of clinical, laboratory, and radiological records for each patient using a standardised protocol. To ensure complete follow-up data was cross-referenced with the New Zealand Joint Registry to identify patients undergoing subsequent revision outside the hospitals. Implant survival, revision risk and revision reasons were analysed using Cox proportional-hazards and competing risk analyses. Implant survivorship at 15 years was comparable for cemented fixed-bearing (cemFB; 91%) and uncemented mobile-bearing (uncemMB; 91%), but lower for cemented mobile-bearing (cemMB; 80%) implants. There was higher incidence of aseptic loosening with cemented implants (3–4% vs. 0.4% uncemented, p<0.01), osteoarthritis (OA) progression with cemMB implants (9% vs. 3% cemFB/uncemMB; p<0.05) and bearing dislocations with uncemMB implants (3% vs. 2% cemMB, p=0.02). Compared with the oldest patients (≥75 years), there was a nearly two-fold increase in risk for those aged 55–64 (hazard ratio 1.9; confidence interval 1.1-3.3, p=0.03). No association was found with gender, BMI or ASA. Cemented mobile-bearing implants and younger age were linked to lower implant survivorship. These were associated with disease progression and bearing dislocations. The use of cemented fixed-bearing and uncemented mobile-bearing designs have superior comparable long-term survivorship

Background. Currently there are various knee prosthesis designs available each with its plus and minus points; there is no general consensus on whether mobile-bearing knees are functionally better than fixed-bearing ones. This study is designed to compare outcomes after total knee arthroplasty with both of the above prostheses. Materials & Methods. 50 patients (68 knees) who'd had a total knee arthroplasty between April 1999 and April 2008 at both Akhtar and Kian Hospitals for primary osteoarthritis were selected. In 30 cases a fixed-bearing knee (Scorpio(r), Stryker) and in the remaining 38 a mobile-bearing prosthesis (Rotaglide(r), Corin Group) was used. Patients' knees were scored before and after the operation according to the Knee Society Scoring System. The mobile-bearing group had an average age of 65 and 34 months' follow-up; in the fixed-bearing group the average age was 69 and the average follow-up 30 months. Results. The average knee score in the mobile-bearing group rose from 29 to 64 while in the fixed-bearing group the score changed from 31 to 68. The average functional score moved from 45 to 67 in the mobile-bearing group and from 34 to 57 in the fixed-bearing group. The average overall score, for the fixed-bearing group, moved from 65 to 125 and in the mobile-bearing group from 75 to 128. Conclusion. In both groups the average knee/functional knee scores increased after the operation and all patients were happy with the results, however statistically there was no meaningful relationship between pre-and post-operation scores. So regarding to our findings, there is no preference between these two types of prosthesis

Aims. The aims of this retrospective study were to determine the incidence of extra-articular deformities (EADs), and determine their effect on postoperative alignment in knees undergoing mobile-bearing, medial unicompartmental knee arthroplasty (UKA). Patients and Methods. Limb mechanical alignment (hip-knee-ankle angle), coronal bowing of the femoral shaft and proximal tibia vara or medial proximal tibial angle (MPTA) were measured on standing, full-length hip-to-ankle radiographs of 162 patients who underwent 200 mobile-bearing, medial UKAs. Results. Incidence of EAD was 7.5% for coronal femoral bowing of >5°, 67% for proximal tibia vara of >3° (MPTA<87°) and 24.5% for proximal tibia vara of >6° (MPTA<84°). Mean postoperative HKA angle achieved in knees with femoral bowing ≤5° was significantly greater when compared to knees with femoral bowing >5° (p=0.04); in knees with proximal tibia vara ≤3° was significantly greater when compared to knees with proximal tibia vara >3° (p=0.0001) and when compared to knees with proximal tibia vara >6° (p=0.0001). Conclusion. Extra-articular deformities are frequently seen in patients undergoing mobile-bearing medial UKAs, especially in knees with varus deformity>10°. Presence of an EAD significantly affects postoperative mechanical limb alignment achieved when compared to limbs without EAD and may increase the risk of limbs being placed in varus>3° postoperatively. Clinical Relevance. Since the presence of an EAD, especially in knees with varus deformity>10°, may increase the risk of limbs being placed in varus>3° postoperatively and may affect long-term clinical and implant survival outcomes, UKR in such knees should be performed with caution

Aims. Spontaneous osteonecrosis of the knee (SONK) mainly affects the medial femoral condyle, would be a good indication for UKA. The primary aim of this study was to assess the clinical, functional and radiographic outcomes at middle to long-term follow-up, of a consecutive series of fifty UKA used for the treatment of SONK. The secondary aim was to assess the volume of necrotic bone and determine if this influenced the outcome. Patients and Methods. We reviewed 50 knees who were treated for SONK. Patients included ten males and 38 females. The mean age was 73 years (range, 57 to 83 years). The mean height and body weight were, respectively 153 cm (141 ∼171 cm) and 57 kg (35 ∼75kg). All had been operated on using the Oxford mobile-bearing UKA (Zimmer-Biomet, Swindon, United Kingdom) with cement fixation. The mean follow-up period was 8.4 years (range, 4 to 15years). We measured the size (width, length and depth) and the volume to be estimated (width x length x depth) of the necrotic bone mass using MRI in T1-weighted images. The clinical results were evaluated using the Knee Society Scoring System (KSS) and Oxford Knee Score (OKS). The flexion angle of the knee was evaluated using lateral X-ray images in maximum flexion. Results. There were no implant failures, but there were 4 deaths (from causes unrelated to UKA) mean 6.6 years after surgery(5∼8), 3 cases were lost mean 3.3 years after surgery(2∼5). The mean size of the necrotic lesion were 17.2mm (14.7∼25.3) in width, 28.2mm (6.2∼38.3) in length and 11.3mm (3.2∼14.3) in depth. The mean volume of it was calculated to be approximate 5.4 cm. 3. (0.7∼11.1). The mean flexion of the knee, KSS Knee Score, Function Score and OKS increased from a preoperative 128.7 degrees (110 ∼ 140 degrees) to 137.5 degrees (110 ∼ 153 degrees), 52.3 (30 ∼ 64) to 91.3 (87 ∼ 100), 39.7 (15∼ 55) to 90.2 (65 ∼ 100) and 21.6 (12∼ 28) to 40.2 (34∼ 48), respectively at the latest follow-up. At last follow-up all patients had good or excellent OKS. Conclusions. There was a 100% survival rate of the Oxford Phase 3 UKA for SONK in the middle to long-term (up to 15 years after surgery) in this independent study. All patients had good/excellent results at last follow-up and there were no reoperations or major complications. This suggests that Oxford mobile-bearing UKA is a good and definitive treatment for medial femoral SONK, whatever the size of the lesion

Purpose. The mobile-bearing total knee arthroplasty was designed to increase the contact area with the polyethylene bearing, through the functional range of motion, and subsequently decrease the wear rate previously seen in fixed-bearing implants. In the literature there is no clear clinical advantage between the different designs in the short to mid-term follow-up. The purpose of this study was to compare the results between a cruciate retaining mobile-bearing design (SAL II, Sulzer) and two cruciate retaining fixed-bearing designs (AMK, Depuy, and the Genesis II, Smith and Nephew). Method. Ninety patients were randomised to receive either the mobile-bearing or one of the two fixed-bearing designs between 2000 and 2002. Patients were evaluated preoperatively and postoperatively using the WOMAC and the SF-12, both of which are validated scores. One patient was withdrawn due to dementia before three months and eleven patients died. Two patients were revised due to infection (both had received the SAL II). One patient was revised for aseptic loosening and one patient was revised for pain (both had received the Genesis II). Of the 74 patients (77 knees) that remain, they were last seen on average 6.4 years (2–10) after their surgery. Their average age at the surgery was 69.2 years (52–81). Results. There was no statistically significant difference between the change scores (postoperative score minus preoperative score) for each of the outcome measures between the mobile-bearing and the two fixed-bearing designs. Conclusion. In conclusion, after mid-term follow-up there is no clinical difference between a cruciate retaining mobile-bearing design and two cruciate retaining fixed-bearing designs

Introduction. Accurate soft tissue balancing in knee arthroplasty is essential in order to attain good postoperative clinical results. In mobile-bearing UKA (Oxford Partial Knee unicompartmental knee arthroplasty, Biomet), since determination of the thickness of the spacer block depends on the individual surgeon, it will vary and it will be difficult to attain appropriate knee balancing. The first objective of the present study was to investigate flexion and extension medial unicompartmental knee gap kinematics in conjunction with various joint distraction forces. The second objective of the study was to investigate the accuracy of gap measurement using a spacer block and a tensor device. Methods. A total of 40 knees in 31 subjects (5 men and 26 women) with a mean age of 71.5 years underwent Oxford UKA for knee osteoarthritis and idiopathic osteonecrosis of the medial compartment. According to instructions of Phase 3 Oxford UKA, spacer block technique was used to make the extension gap equal to the flexion gap. Adequate thickness of the spacer block was determined so that the surgeon could easily insert and remove it with no stress. Following osteotomy, the tensor devise was used to measure the medial compartmental gap between the femoral trial prosthesis and the tibial osteotomy surface (joint component gap) (Fig. 1 and 2). The medial gap was measured at 20° of knee flexion (extension gap) and 90° of knee flexion (flexion gap) with 25N, 50N, 75N, 100N, 125N, 150N of joint distraction force. Corresponding size of bearing was determined for the prosthesis. The interplay gap was calculated by subtracting the thickness of the tibial prosthesis and the thickness of the selected size of bearing from the measured extension and flexion gaps. Results. The selected bearing size was 3 mm: 3 knees, 4 mm: 20 knees, 5 mm: 15 knees and 6 mm: 2 knees. The mean flexion gap in the medial compartment was 25N: 8.4 ± 1.6 mm, 50N: 9.4 ± 1.6 mm, 75N: 10.4 ± 1.5 mm, 100N: 11.0 ± 1.4 mm, 125N: 11.6 ± 1.5 mm, 150N: 11.9 ± 1.4 mm. The mean extension gap was 25N: 7.8 ± 1.6 mm, 50N: 8.8 ± 1.6 mm, 75N: 9.7 ± 1.6 mm, 100N: 10.4 ± 1.5 mm, 125N: 11.1 ± 1.5 mm, 150N: 11.4 ± 1.5 mm. The mean flexion interplay gap was 25N: 0.5 ± 1.2 mm, 50N: 1.5 ± 1.2 mm, 75N: 2.4 ± 1.1 mm, 100N: 3.1 ± 1.0 mm, 125N: 3.6 ± 1.1 mm, 150N: 4.0 ± 1.1 mm. The mean extension interplay gap was 25N: −0.2 ± 1.2 mm, 50N: 0.8 ± 1.1 mm, 75N: 1.7 ± 1.2 mm, 100N: 2.5 ± 1.2 mm, 125N: 3.1 ± 1.2 mm, 150N: 3.5 ± 1.2 mm. When flexion and extension of the interplay gap were compared, the extension interplay gap was shown to be significantly smaller compared with the flexion interplay gap at every joint distraction force (p < 0.05). Conclusion. The mean extension interplay gap was shown to be significantly smaller compared with the flexion interplay gap at every joint distraction force even though the extension gap was adjusted to the flexion gap using the spacer block. This suggests that in the actual UKA operative technique using a spacer block there is a potential that the extension gap will be smaller than the flexion gap. Surgeons should be aware of this fact and adjust the flexion and extension gaps with caution when performing mobile-bearing UKA

Introduction. Posterior cruciate ligament (PCL) preservation in total knee arthroplasty (TKA) is adovocated on the grounds that it provides better restoration of knee joint kinematics as opposed to PCL sacrifice. Mobile-bearing (MB) total knee prostheses have been in the market for a long time, but the PFC-Sigma Rotating Platform (RP) prosthesis (DePuy Orthopaedics, Inc, Warsaw, Ind) has been introduced in the market since 2000. Since, little is known about the in vivo kinematics of MB prostheses especially with cruciate retaining (CR). The objective of this study is to investigate the in vivo kinematics of MB RP-CR total knee arthroplasty during weight-bearing deep knee bending motion. Patients and methods. We investigated the in vivo knee kinematics of 20 knees (17 patients) implanted with PFC-Sigma RP-CR. All TKAs were judged clinically successful (Hospital for Special Surgery scores >90), with no ligamentous laxity or pain. Mean patient age at the time of operation was 78.0 ± 6.0 years. Mean period between operation and surveillance was 15.0 ± 9.0 months. Under fluoroscopic surveillance, each patient did a wight-bearing deep knee bending motion. Femorotibial motion was analyzed using 2D/3D registration technique, which uses computer-assisted design (CAD) models to reproduce the spatial position of the femoral, tibial components from single-view fluoroscopic images. We evaluated the range of motion, axial rotation, and antero-posterior (AP) translation of the nearest point between the femoral and tibial component. Results. Between the femoral and tibial components, the mean minimum flexion angle was on average 2.1±5.5 °. The mean maximum flexion angle was 118.0±9.9 °. The average range of motion was 115.8±12.8°. The femoral component relative to the tibial component demonstrated 5.5±3.7° external rotation for 0–120 degrees flexion. At full extension, the medial nearest point was −2.4±2.7 mm, and the lateral nearest point was −8.4±3.4 mm. The medial nearest point moved 1.3 mm anteriorly from full extension to 90° of knee flexion, and then moved 1.5mm posteriorly until maximum flexion. On the other hand, the lateral nearest point moved 0.4mm posteriorly from full extension to 90° of knee flexion, and then moved 3.6mm posteriorly until maximum flexion. At maximum flexion, the medial nearest point moved posteriorly to a final position of −2.6±3.3 mm and the lateral nearest point moved posteriorly to a final position of −12.5±3.6 mm [Fig.1]. From the results of bilateral contact positions at each flexion angle, patterns of kinematic pathways were determined. The kinematic pathway pattern was externally rotated due to a central pivot pattern from extension to 90° knee flexion. Subsequently from 90 to 120°, bilateral condyles moved backward. Discussion and conclusion. In this study, we have evaluated the in vivo kinematics of MB prostheses with cruciate retaining motion during deep knee bending motion under weight-bearing condition. The results in this study demonstrated that the kinematic pathway pattern was externally rotated due to a central pivot pattern from extension to 90° knee flexion. Subsequently from 90 to 120°, bilateral condyles moved backward. This indicated that PCL functions

INTRODUCTION. Mobile-bearing knee prostheses have been designed in order to provide less constrained knee kinematics compared to fixed-bearing prosthesis. Currently, there is no evidence to confirm the superiority of either of the two implants with regard to walking performances. It has been shown that subjective outcome scores correlate poorly with real walking performance and it has been recommended to obtain an additional assessment of walking ability with objective gait analysis. OBJECTIVES. We assessed recovery after total knee arthroplasty (TKA) with mobile- and fixed-bearing between patients during the first postoperative year, and at 5 years follow-up, using a new objective method to measure gait parameters in real life conditions. METHODS. 56 patients with mobile- and fixed-bearing of the same design were included in this randomised controlled double-blinded study and evaluated pre- and post-operatively at 6 weeks, 3 months, 6 months 1 year and 5 years. At each visit a WOMAC and Knee Society Score were calculated and each participant completed an EQ-5D questionnaire. To assess the patients' gait five miniature angular rate sensors mounted respectively on the sacrum and each shank and thigh measured lower limb movement and rotation. The patients walked 30 metres on a flat surface and gait parameters were recorded with a small ambulatory device in order to carry out an objective gait analysis. RESULTS. Objective recovery was strongly correlated with patients' age. When the whole population was considered, there was no significant difference between groups at any time in objective gait parameters. After separating the population according to their age (less than 71 years old, compared to those of more than 71 years old) a secondary analysis showed that the bearing type can lead to opposite results in different age groups. At five years follow-up, most of the recorded gait parameters (stride length, knee max rotation speed, shank and thigh range of motion, and limp) showed better results for mobile bearing in younger patients, while better gait performances were found systematically with fixed-bearing TKA in older patients. CONCLUSION. To our knowledge, this is the first study where similarly designed posterior-stabilised knee replacements with fixed- and mobile-bearing have been compared with gait analysis in real-life conditions. We observed systematically differences between mobile and fixed bearing groups, which are confirmed by multivariate analysis. Our results suggest that older patients might not benefit from a mobile bearing TKA and that extended age controlled study should be performed to identify an age, above which fixed bearing should not be the recommended choice. Before choosing the bearing type, surgeons should take into account the age of the patient

Aims

Medial unicompartmental knee arthroplasty (UKA) is undertaken in patients with a passively correctable varus deformity. Our hypothesis was that restoration of natural soft tissue tension would result in a comparable lower limb alignment with the contralateral normal lower limb after mobile-bearing medial UKA.

We prospectively reviewed a consecutive series of 101 patients with mobile bearing total knee replacement (TKR) and 72 patients with the fixed bearing cruciate retaining TKR. Patients were assessed for diagnoses, range of motion, pre- and post-operative Oxford knee scores and complications. In the mobile bearing group of 113 knees in 101 patients, 97 had minimum 10-year follow up. By ten years, 16 patients had died of unrelated causes. Mean Revised Oxford Knee score improved from 16 pre-operatively to 42 at last follow up. The mean range of flexion was 115 degrees (75 – 130). One patient dislocated the bearing and needed manipulation. One patient reported superficial infection which resolved with antibiotics. One patient had deep vein thrombosis and one had non-fatal pulmonary embolism. In the fixed bearing group, 89 TKR's were performed in 72 patients. The mean age was 71.9 years and the mean follow up was 12.1 (10–14.1) years. 19 patients died during this study period. The mean range of flexion was 111.2 (80–135) degrees of flexion at latest follow- up. There was an improvement in the mean Oxford knee score from 16.2 preoperatively, to 42.5 to date. One patient required revision surgery at 12 years for polyethylene wear. One patient developed deep infection 10 years after the primary procedure but declined revision surgery. At ten years no revisions were performed in either group. This series has highlighted excellent results with both fixed and mobile bearing CR knees with hundred percent survival at ten years.

Introduction

Mobility at insert-tray articulations in mobile bearing knee implant accommodates lower cross-shear at polyethylene (PE) insert, which in turn reduces wear and delamination as well as decreasing constraint forces at implant-bone interfaces. Though, clinical studies disclosed damage due to wear has occurred at these mobile bearing articulations. The primary goal of this study is to investigate the effect of second articulations bearing mobility and surface friction at insert-tray interfaces to stress states at tibial post during deep flexion motion.

Purpose

The purpose of this study was to evaluate the complications related to the prosthesis design in patients managed with cemented total knee arthroplasty (TKA) with the anterior-posterior glide (APG) mobile bearing prosthesis.

Introduction

Unicompartmental knee arthroplasty (UKA) is a successful procedure for medial compartment osteoarthritis (OA). Recent studies using the same implant report a revision rate of 2.9%. Other centers have reported revision rates as high as 10.3%. The purpose of this study was to retrospectively review the clinical results of Oxford Phase 3 UKA's performed in the setting of isolated medial compartment OA and to compare our results to the previous mid-term studies. Our secondary goal was to determine reasons for revision and evaluate selected independent predictors of failure.

Introduction. Comparative studies examining Fixed-Bearing (FB) and Mobile-Bearing (MB) Total Ankle Replacement (TAR) designs have demonstrated similar results and successful long-term outcomes for both. To date there has been no study directly comparing FB and MB designs of the same prosthesis. We present the first prospective randomised trial comparing patient satisfaction, functional outcomes and radiographic results of the Salto Talaris Fixed-Bearing and the Salto Mobile-Bearing Total Ankle Replacement in the treatment of end-stage ankle arthritis. Methods. A total of 108 adult patients with end-stage ankle arthritis were enrolled in the study between November 2014 and October 2021 with similar demographic comparison. Prospective patient-reported outcomes and standardised weightbearing ankle radiographs were performed preoperatively, at 6 weeks, 6 months and 12 months post-operatively, followed by yearly intervals. All surgeries were performed by a single non-design orthopaedic foot and ankle specialist with experience in over 200 Salto and Salto Talaris TAR prior to the study. Radiographs were examined independently by two clinicians. Complete patient data and radiographs were available for 103 patients with an average follow up of 2 years. Results. Both groups demonstrated statistically significant improvement from preoperative evaluation to most recent follow up with no statistically significant difference between the two groups in all outcome measures. Radiographic incidence of subchondral cyst formation was 8.9% and 38.2% for FB and MB, respectively. Talar subsidence occurred in 2.2% and 5.5% of FB and MB, respectively. Discussion. Our study demonstrates a higher than previously reported rate of cyst formation in the MB TAR and comparatively higher talar subsidence in the MB TAR vs FB however this did not correlate with clinical outcome measures which were favourable for both groups. Conclusion. Fixed-Bearing and Mobile-Bearing Total Ankle Replacement demonstrate comparable favourable

Introduction. The mobile-bearing (MB) total knee arthroplasty (TKA) design was introduced with the aim of reducing polyethylene wear and component loosening seen in the fixed-bearing (FB) design. A recent joint registry study has revealed increased risk for all-cause revision, but not revision for infection, in MB-TKA. We used the New Zealand Joint Registry (NZJR) to compare all-cause revision rates, and revision rates for aseptic loosening of MB-TKA compared with fixed bearing (FB) TKA. Methods. All patients who underwent a primary TKA registered in the NZJR between the 1st January 1999 to 31st December 2021 were identified. Analysis compared MB to FB designs, with sub analysis of implants from a single company. We identified 135,707 primary TKAs, with 104,074 (76.7%) FB-TKAs and 31,633 (23.3%) MB-TKAs recorded. We examined all-cause revision rates, reasons for revision and performed survival analyses. Results. For all-comers, MB-TKA had an all-cause revision rate of 0.43/100-component-years (OCY) compared with 0.42/OCY for FB-TKA (p=0.09). The all-cause revision rate was higher for those age < 65 years (MB TKA 0.60/OCY vs. FB-TKA 0.59/OCY) compared to those > 65 years at time of primary TKA (MB-TKA 0.29/OCY vs. FB-TKA 0.32/OCY), however there was no statistically significant difference between implant design in either age group (p=0.16 and p=0.64; respectively). Similarly, there was no difference in revision rates for aseptic loosening between implant designs. Kaplan-Meier survival analysis demonstrates no statistically significant difference in revision-free survival of implants, with both MB-TKA and FB-TKA demonstrating ∼93% revision free survival at 23 years. Conclusions. Both FB- and MB-TKA demonstrated excellent survivorship, with no significant difference in all-cause revision rates or revision for aseptic loosening between implant designs

Introduction. The mobile-bearings were introduced in total knee arthroplasty (TKA) to improve the knee performance by simulating more closely ‘normal’ knee kinematics, and to increase the longevity of TKA by reducing the polyethylene wear and periprosthetic osteolysis. However, the superiority between posterior-stabilized mobile-bearing and fixed-bearing designs still remains controversial. The objective of the present study was to compare the mid-term results of Scorpio + Single Axis system (Stryker Howmedica Osteonics, Allendale, New Jersey) for the mobile-bearing knees and Duracon system (Stryker Howmedica Osteonics, Allendale, New Jersey) for the fixed bearing design with regard to clinical and roentgenographic outcome with special reference to any complications and survivorship. Methods. Prospective, randomized, double-blinded controlled study was carried out on 56 patients undergoing primary, unilateral total knee arthroplasty for osteoarthritis, who were divided into two groups. Group I received mobile-bearing knee prosthesis (29 patients) and Group 2 received fixed-bearing prosthesis (27 patients). The patients were assessed by a physical examination and knee scoring systems preoperatively, at a follow-up of three months, six months, and one year after surgery by independent researcher who was not part of the operating team, and was blinded as to the type of implant inserted. We used the Oxford knee score (OKS) and Knee society score (KSS), with Knee Society Knee Score (KSKS) and Knee Society Functional Score (KSFS) being the subsets. The questionnaire for OKS was printed in our national language, and handed over to the patient at each visit. Results. The Knee Society knee scores, pain scores, functional scores and Oxford knee scores were not statistically different (P > 0.05) between the two groups. Mean postoperative range-of-motion of mobile-bearing knees was significantly greater than that of fixed-bearing knees (127º versus 111º, P = 0.011). 72% of patients could sit cross legged, 48% could sit on the floor, and 17% could squat. Kaplan–Meier survival rate was 100%. No spin-out of mobile bearing was observed. The radiological analysis showed no osteolysis or implant loosening. Conclusion. Mobile-bearing, and fixed-bearing knees demonstrated no statistically significant difference in the Oxford knee score, Knee society score, and radiological outcome with 100% survivorship, at 4 to 6.5 years (mean: 5.5 years) follow up. However, the post-operative range-of-motion of mobile-bearing knees was significantly higher than the fixed-bearing designs (mean, 127° versus 111°; range, 95° to 145° versus 80° to 125°)

Introduction. Forward solution joint models (FSMs) can be powerful tools, leading to fast and cost-efficient simulation revealing in vivo mechanics that can be used to predict implant longevity. Unlike most joint analysis methods, mathematical modeling allows for nearly instantaneous evaluations, yielding more rapid surgical technique and implant design iterations as well as earlier insight into the follow-up outcomes used to better assess potential success. The current knee FSM has been developed to analyze both the kinematics and kinetics of commercial TKA designs as well as novel implant designs. Objective. The objective of this study was to use the knee FSM to predict the condylar translations and axial rotation of both fixed- and mobile-bearing TKA designs during a deep knee bend activity and to compare these kinematics to known fluoroscopy evaluations. Methods. The knee joint is modeled mathematically using Kane's dynamics, incorporating muscle controllers to predict the muscle forces, contact detection algorithms to compute the knee joint forces, and nonlinear ligaments at the knee joint. The tibiofemoral kinematics data for 20 subjects implanted with fixed-bearing (FB) PS TKA and 20 subjects implanted with mobile-bearing (MB) PS TKA were collected using fluoroscopy data during a deep knee bend (DKB) activity from full extension to 120° of flexion. All subjects were implanted by the same surgeon. The same CAD models for these implanted were incorporated in the FSM to predict the tibiofemoral kinematics. The average component placement from fluoroscopy data were used as an initial condition for the placement of the component in the mathematical model. Results. Overall, fluoroscopy results showed patients experienced 6.8 mm and 6.4 mm posterior rollback of the lateral femoral condyle for FB and MB PS TKA groups, respectively. The FSM predicted 5.9 mm and 6.3 mm of lateral posterior rollback for FB and MB PS TKA models, respectively (Figure 1). On average, media condyle translated posteriorly −2.9 mm and −2.5 mm, for FB and MB subjects, respectively. The mathematical model prediction for FB and MB models was −1.4 mm and −2.4 mm, respectively (Figure 2). The overall axial rotation was 5.1° and 4.5°, for FB and MB subjects from fluoroscopy, respectively. The axial rotation prediction using the FSM was 6.0° and 4.2°, for FB and MB models, respectively (Figure 3). Conclusion. Overall, it is clear that the FSM can accurately predict both the patterns and magnitudes of fixed- and mobile-bearing TKA condylar translations and axial rotations, showing consistent rollback of the lateral condyle, less translation of the medial condyle, and consistent axial rotation throughout flexion, all of which were also observed in the fluoroscopy data. The correlation between the theoretically predicted and experimentally confirmed kinematic patterns demonstrates the viability of forward solution modeling as a valuable and accurate method to evaluate total joint replacement mechanics. For any figures or tables, please contact the authors directly

The mobile-bearing variant of a single-radius design is assumed to provide more freedom of motion compared to the fixed-bearing variant because the insert does not restrict the natural movements of the femoral component. This would reduce the contact stresses and wear which in turn may have a positive effect on the fixation of the prosthesis to the bone and thereby decreases the risk for loosening. The aim of this prospective randomized study was to evaluate early migration of the tibial component and kinematics of a mobile-bearing and fixed-bearing total knee prosthesis of the same single-radius design. According to a prospective randomized protocol 20 Triathlon single-radius posterior- stabilized knee prostheses were implanted (9 mobile-bearing and 11 fixed-bearing). Fluoroscopy and roentgen stereophotogrammetric analysis were performed 6 and 12 months post-operatively. The 1 year post-operative roentgen stereophotogrammetric analysis results showed considerable early migrations in 3 mobile-bearing patients and 1 fixed-bearing patient. The range of knee flexion was the same for the mobile-bearing and fixed- bearing group. The mobile insert was following the femoral component during motion. This study showed no apparent distinction in early migration and kinematics between mobile-bearing and fixed-bearing single-radius total knee prostheses. Des- pite the mobile insert was following the femoral component during motion, and therefore performed as intended, no kinematic advantages of the mobile-bearing total knee prosthesis were seen. It is concluded that a mobile insert in single-radius total knee prostheses is redundant and will not lead to additional benefits

Background. The patterns and magnitudes of axial femorotibial rotation are variable due to the prosthesis design, ligamentous balancing, and surgical procedures. LCS mobile-bearing TKA has been reported the good clinical results, however, knee kinematics has not been fully understood. Therefore, we aimed to investigate the effects of the weight-bearing (WB) condition on the kinematics of mobile-bearing total knee arthroplasty (TKA). Methods. We examined 12 patients (19 knees) implanted with a low contact stress (LCS) mobile-bearing TKA system using a two- to three-dimensional registration technique as previously reported [1]. All 12 patients were diagnosed with medial knee osteoarthritis. The in vivo kinematics of dynamic deep knee flexion under WB and non-WB (NWB) conditions were compared. We evaluated the knee range of motion, femoral axial rotation relative to the tibial component, anteroposterior translation, and kinematic pathway of the femorotibial contact point for both the medial and lateral sides. Results. Under the WB condition, the mean range of motion was 117.8° ± 16.7°. Under the NWB condition, the mean range of motion was 111.0° ± 4.4°. No significant difference in this value was apparent between the 2 conditions. The mean range of axial rotation from full extension to maximum flexion was 3.0° ± 1.5° under the WB condition and 2.2° ± 1.0° under the NWB condition. No significant difference in this value was apparent between the 2 conditions. With regard to the anteroposterior translation, the LCS mobile-bearing TKA system showed the same kinematic patterns under both conditions, except for axial rotation at 0°, 10°, and 110°. From hyperextension to maximum flexion, the kinematic pattern reflected a central pivot under both conditions (Figure 1). Conclusions. In conclusion, this study demonstrated that, in an LCS mobile-bearing TKA system, knee kinematics showed the same patterns under NWB and WB conditions, except for axial rotation at the early phase. Further understanding of knee kinematics could provide us with useful information for future design concepts of TKA implants

Introduction. Unicompartmental knee arthroplasty (UKA) is becoming an increasingly popular option in single compartment osteoarthritis. As a result, diverse re-operations including revisions to total knee arthroplasty (TKA) has also increase. The objective of this study is to investigate the distribution of causes of re-operations after UKA and to analyze the types of re-operations. Method. We retrospectively reviewed 691 UKAs performed on 595 patients between January 2003 and December 2011. Except in one case, all UKAs were performed for medial compartment osteoarthritis of the knee. The UKAs were performed in 487 (81.8%) women and 108 (18.2%) men. The mean age at the time of UKA was 61.5 years (47 to 88 years). Mobile-bearing designs were implanted in 627 (90.7%) knees (626- Oxford knee and 1- Scorpio knee) and fixed designs were implanted in 64 (9.3%) knees (42- Tornier and 18- Zimmer). The mean interval between UKA and second operation was 15.4 months (10 days to 10 years) and between second and third operation was 7.7 months (5 weeks to 17 months). In the re-operation group, there were 50 knees (48 patients) with 38 female and 10 male patients. Results. In our study, the burden of a re-operation after the initial UKA was 8.7%with, the total number of re-operation of 60. There was 50 cases of second operations (n = 45 mobile, n = 5 fixed), and 10 cases of second re-operation. The most common cause of a second re- operation after a mobile-bearing UKA was the dislocation of the meniscal bearing (32%), followed by component loosening (20%), the formation of a cement loose body (14%), unexplained pain (12%), infection (6%), periprosthetic fracture (4%), and others (2%). For the fixed-bearing UKA, the causes of a second operation were loosening (4%), unexplained pain (4%), and bearing wear (2%). 10 cases required a 3rd operation at mean time interval of 7.7 months, of them 7 cases (70%) had liner exchange at their 2nd operation. Discussion and conclusion. The most common cause of a second re-operation after a mobile-bearing UKA was the dislocation of the bearing, followed by component loosening and the formation of a cement loose body. After a fixed-bearing UKA, component loosening and unexplained pain were the most common causes of re-operation. In cases which underwent a third operation, 70 percent had liner exchange with or without some minor procedure at the time of the 2ndoperation. All were converted to TKA at their 3rd operation at a mean time interval of only 7.7 months. Based on our observations, we recommend a cause-based approach to the management of primary and failed UKA to help minimize the possibility of second and third operations. Furthermore caution should be undertaken when contemplating liner exchange as treatment option in cases involving mobile-bearing UKA