Aims. The mobile bearing Oxford unicompartmental knee arthroplasty (OUKA) is recommended to be performed with the leg in the hanging leg (HL) position, and the thigh placed in a stirrup. This comparative cadaveric study assesses implant positioning and intraoperative kinematics of OUKA implanted either in the HL position or in the supine leg (SL) position. Methods. A total of 16 fresh-frozen knees in eight human cadavers, without macroscopic anatomical defects, were selected. The knees from each cadaver were randomized to have the OUKA implanted in the HL or SL position. Results. Tibial base plate rotation was significantly more variable in the SL group with 75% of tibiae mal-rotated. Multivariate analysis of navigation data found no difference based on all kinematic parameters across the range of motion (ROM). However, area under the curve analysis showed that knees placed in the HL position had much smaller differences between the pre- and post-surgery conditions for kinematics mean values across the entire ROM. Conclusion. The sagittal tibia cut, not dependent on standard instrumentation, determines the tibial component rotation. The HL position improves accuracy of this step compared to the SL position, probably due to better visuospatial orientation of the hip and knee to the surgeon. The HL position is better for replicating native kinematics of the knee as shown by the area under the curve analysis. In the supine knee position, care must be taken during the sagittal tibia cut, while checking flexion balance and when sizing the tibial component

Aims: The purpose of this report is to present the short-term clinical performance of total knee arthroplasties performed with the Scorpio+ posteriorly stabilized mobile bearing knee. Methods: 100 Scorpio+ knees were implanted in 96 patients consecutively by the same surgeon and evaluated at one year of follow-up. All patients were assessed clinically using the IKS Score, Western Ontario McMaster Score (WOMAC), a chair rise evaluation6 and radiographically with long leg radiographs, standard A/P, lateral and patellar skyline views. Results: At one year of follow-up the average Range of Motion was 123° with an IKS Score averaging 191, an average knee score of 94, an average functional knee score of 97, and an average WOMAC score of 92. Furthermore, 95 out of 96 patients were able to arise from a chair without using their arms at 1 year of follow-up. Radiographically no radiolucent lines were visible and all patellar components were centered. Conclusions: Patients with the Scorpio+ MBK demonstrated satisfactory clinical outcomes especially regarding overall stability, range of motion (average flexion 123°) and extensor mechanism function with 98% of patients being able to arise from a chair without the use of their arms at three months of follow-up

The aim of this prospective cohort study is to compare the early results in a single surgeon series of the mobile and fixed bearing versions of the Preservation UKR for lateral OA. Lateral UKRs were only considered for patients with isolated lateral compartment osteoarthritis with a functioning anterior cruciate ligament. Mild patellofemoral osteoarthritis was not considered a contraindication. If there was any doubt over the condition of the medial compartment or patellofemoral joint, single photon emission computed tomography was performed. Significant uptake it the medial or patellofemoral joint was considered a contraindication. Patients were assessed preoperatively and at 1 and 2 years postoperatively with the American Knee Society Score (AKSS), Oxford Knee Score (OKS) and with anteroposterior, lateral and Rosenberg radiographs. Between 29. th. May 2001 and 15. th. May 2003, the senior author (GK) performed 233 consecutive Preservation UKRs. 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. Patients in the mobile bearing group were significantly younger (t test; p< 0.0001) and had better AKSS knee (Mann-Whitney U test; p=0.05) and AKSS function scores (Mann-Whitney U test; p=0.005). The patients were reviewed after a minimum of 2 years (range 2 to 3.4 years). There was no significant difference between the 2 groups. There had been 3 revisions in the mobile bearing group for tibial loosening and none in the fixed bearing group (chi squared test; not significant). There was 1 tibial periprosthetic fracture in the fixed bearing group. This study shows that the choice of bearing type makes little difference in clinical outcome or range of motion over the first 2 years when using the Preservation Knee. A similar good functional result was obtained with a fixed bearing despite the mobile bearing group being younger and having significantly better preoperative AKS knee and function scores. The 3 revisions for tibial loosening in the mobile bearing group are a concern. However, these results are short-term and there may be improved implant longevity in the long-term with mobile bearing tibial components due to reduced polyethylene wear

The objective was to assess and compare polyethylene-bearing mobility patterns and magnitudes in various total knee arthroplasty(TKA) types of mobile bearing TKA. In vivo kinematics were determined for 38 subjects implanted with either a PCL-retaining (PCR) mobile bearing TKA, which allows both rotation and antero-posterior (AP) translation (n=20), aposterior stabilized rotating platform (PS) TKA (n=9) or a PCL-sacrificing (PCS) rotating platform TKA (n=9) using video fluoroscopy. Using a 3D model-fitting technique, kinematics were determined during a weight-bearing deep knee bend. The femoral and tibial components and mobile bearing polyethylene insert (implanted with four tantalum beads) were overlaid onto the fluoroscopic images to determine bearing mobility. AP bearing translation was determined for subjects implanted with a PCR mobile bearing TKA. Subjects implanted with PCR and PCS TKA were evaluated at a single interval. Those with a PS TKA were evaluated at two postoperative intervals, (12 months apart) to assess changes in bearing mobility over time. All subjects experienced polyethylene bearing rotation relative to the tibial tray and minimal rotation relative to the femoral component. The average maximum amount of bearing rotation was 10.3o (3.0o to 20.8o), 8.9o (5.3o to 14.1o), and 8.5o (3.3o to 12.9o) for subjects implanted with a PCR, PS, and PCS mobile bearing TKA, respectively. For subjects implanted with a PS mobile bearing TKA, bearing mobility increased to 9.8o (4.8o to 14.1o) one year later post-operatively. All subject shaving a PCR mobile bearing TKA experienced AP bearing translation, averaging 5.6 mm (1.0 mm to 12.5 mm). These results demonstrate that the polyethylene bearing is rotating and translating relative to the tibial tray in all subjects. Minimal motion occurred between the femoral component and the polyethylene insert. Magnitude and direction of bearing motion varied among subjects. Paradoxical anterior translation of the bearing during deep flexion was observed in the PCR TKA group. The presence of bearing mobility should result in lower contact stresses, reducing the potential for polyethylene wear

UKA with mobile bearing is a one of the treatment of medial osteoarthritis. However, some reports refer to the risk of dislocation of the mobile bearing. Past reports pointed out that medial gap might be enlarged in deep flexion position (over 120 degrees), and says that it will lead to instability of the mobile bearing. The purpose of this study is to research the risk factors of enlargement of medial gap in deep flexion position. We performed 81 UKAs with mobile bearing system from November 2013 to December 2015, and could evaluate 41 knees. This study of 41 knees included 9 males and 32 females, with average operation age of 75.4years(63–89years). The diagnosis was osteoarthritis in 39 knees and osteonecrosis in 2 knees. The UKA(Oxford partial knee microplasty, Biomet, Warsaw, IN) was used in all cases. We performed distal femur and proximal tibia osteotomy using CT-Free navigation system(Stryker Navigation System II/precision Knee Navigation ver4.0). And we inserted femoral and tibial trial component, then we placed an UKA tensioner on the medial component of the knee. Using tensioner under 30 lbs, we measured joint medial gap at 0,20,45,90,130(deep flexion) degrees. When we compared medial gap at 90 degrees position with at 130 degrees, we defined it as ‘instability group’ if there was gap enlargement more than 1mm, and defined it as ‘stability group’ if there wasn't. We compared this two groups with regard to age, BMI, femoro-tibial angle (FTA), the diameter of anterior cruciate ligament (ACL), tibial angle and tibial posterior slope angle of the implant. We evaluated preoperative and postoperative FTA by weightbearing long leg antero-posterior alignment view X-rays. We measured ACL diameter at its condyle level in coronal view of MRI. Also we evaluated tibial component implantation angle by postoperative CT using 3D template system. These measurement were analyzed statistically using t test. The stability group contained 26 knees, and the instability group contained 15 knees. Compared with the stability group, the instability group indicated higher FTA (p=0.001). Between 20 and 90 degrees flexion position, there was no change of medial gap. Dislocation of the mobile bearing is one of the complications of UKA and it will need re-operation. It is said to be caused by impingement of the bearing and osteophyte of femur. However, some reports said that dislocation was happened when the knee was flexed deeply or twisted, and there was no impingement. We think it may means that dislocation could be caused by medial gap enlargement. This study indicates that higher FTA could be risk factor of dislocation of mobile bearing. It is important to evaluate preoperatively FTA by X-ray

There is ongoing debate on the benefits of fixed versus mobile bearing Unicompartmental Knee Replacement (UKR). We report the results from a randomised controlled trial comparing fixed and mobile bearing of the same UKR prosthesis. Forty patients were randomized to receive identical femoral components and either a fixed or mobile bearing tibial component. At 6.5 years follow-up 37% of the mobile bearing design had been revised and 14% for the fixed bearing design. The main reasons for revision were pain and loosening. These results were compared with data from The Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) that show a cumulative percent revision of 24.2% for the mobile bearing Preservation UKR at 6.5 years. All locally explanted mobile bearings were examined microscopically, and 83% demonstrated significant backside wear. Constraint on the undersurface of the bearing coupled with a congruent upper surface may have contributed to the excessive revision rate. This is the first randomised controlled trial examining mobile and fixed variations of the same UKR prosthesis and shows this design of UKR with the mobile bearing has an unacceptably high revision rate and patients with this knee design should be closely monitored

Introduction. Previous fluoroscopy studies have been conducted on numerous primary-type TKA, but minimal in vivo data has been documented for subjects implanted with revision TKA. If a subject requires a revision TKA, most often the ligament structures at the knee are compromised and stability of the joint is of great concern. In this present study, subjects implanted with a fixed or mobile bearing TC3 TKA are analyzed to determine if either provides the patient with a significant kinematic advantage. Methods. Ten subjects are analyzed implanted with fixed bearing PFC TC3 TKA and 10 subjects with a mobile bearing PFC TC3 TKA. Each subject underwent a fluoroscopic analysis during four weight bearing activities: deep knee bend (DKB), chair rise, gait, and stair descent. Fluoroscopic images were taken in the sagittal plane at 10 degree increments for the DKB, 30 degree increments for chair rise, and at heel strike, toe off, 33% and 66% cycle gait and stair descent. Results. The average weight bearing maximum flexion for the fixed bearing TKA group was 104 degrees (SD = 18.2 degrees). The average medial and lateral anterior-posterior (AP) translation for these subjects from full extension to maximum weight-bearing flexion was −6.74 mm and −8.0 mm in the posterior direction, respectively. The average femorotibial axial rotation was 1.27 degrees from full extension to maximum flexion. The average medial and lateral AP translations respectively from full extension to maximum flexion are shown in Figures 1 and 2 and the corresponding average femorotibial axial rotation pattern is shown in Figure 3. Subjects implanted with a mobile bearing device are presently being analyzed. Discussion. The fixed bearing device, on average, does not allow for much axial rotation when compared to less constrained or mobile bearing TKA designs. Previous studies have mobile bearing rotating platform primary posterior stabilized devices have documented that the bearing does rotate with the femur. Therefore, it is assumed subjects having a mobile bearing TC3 TKA may achieve greater axial rotation. Subjects having the fixed bearing TC3 TKA did achieve posterior femoral rollback of both condyles, revealing that a fixed bearing revision TKA may act more like a hinged device

Aim. The aim of the study was to assess the impact of a self aligning unidirectional mobile tibial bearing and the use of a patella button on lateral patella release rates within a knee system using a common femoral component for both the fixed and mobile variants. Methods and results. A total of 347 patients undergoing TKR were included in the study and randomly allocated to receive either a Mobile Bearing (171 knees) or a Fixed Bearing (176 knees) PS PFC Sigma TKR. Further sub-randomisation into patella resurfacing or retention was performed for both designs. The need for lateral patella release was assessed during surgery using the ‘no thumbs’ technique. The lateral release rate was similar for fixed bearing (9.65%) and mobile bearing (9.94%) implants (p=0.963). Patella resurfacing resulted in lower lateral release rates when compared to patella retention (5.8% vs 13.8%; p=0.0131). This difference was most marked in the mobile bearing group where the lateral release rate was 16.3% with patella retention compared to 3.5% with patella resurfacing (p=0.005). Conclusion. The addition of a rotating platform tibial component had no impact on the lateral release rate in this study. Optimising patella geometry by patella resurfacing appears more important than tibial bearing deisgn per se. The combination of a mobile bearing design and patella resurfacing appears to optimise the lateral release rate and patello-femoral tracking in the PS PFC Sigma design which has a deeply radiused trochlea on the femoral component. The results with a patella resurfacing confirm the results with this prosthesis reported by Pagnano et al in Clin Orthop 428 pp221-227

Aseptic loosening is one of the most frequent cause of total knee arthroplasty (TKA) failure; it is related to a fatigue-type wear which can rapidly break up a tibial polyethylene (PE) inlay. PE debris production is the result of this wear and depend on contact stress between the components. This crucial parameter is more related to conformity than to load tranfer. That is why mobile bearing TKA seems to represent a valid solution to the PE debris production. In fact this implant offers great tibio-femoral conformity without an increased risk of loosening due to increased axial torque. Mobile bearing TKA also eneables the surgeon to self correct tibial component malrotation. On the other hand this implant could lead to new problems such as bearing dislocation or breakage and a possible new wear pattern at the PE-tibial metal tray interface. We performed 100 consecutive cemented posterior stabilised TKA using randomly in 50 cases a mobile bearing and in 50 cases the same implant with a fixed bearing. The mean follow up was 15 months. The results in mobile bearing group are the following. Hospital for Special Surgery (HSS) score improved from 38 to 91 after the surgery. Preoperative Range of Movement (ROM) was 71 while the post op value was 107. No lucencies > 1 mm were observed. There were no statistically significant differences among the mobile bearing group and the fixed bearing one. Despite our short follow up, this implant offers the same good clinical results if compared to other devices, and allows the surgeons to correct errors in positioning the implant. In future we have to consider that this possibility will lead to an abnormal load stresses distribution and to a higher risk of late loosening

Purpose: Mobile Bearing TKA has been reported to improve patellofemoral tracking due to the self-aligning impact of the mobile bearing. However, limited rotation of the mobile bearing may be insufficient to impact patellar tracking in an otherwise well-balanced TKA. Methods: Between December 1998 and October, 2003, 445 primary TKAs were performed via transpatellar arthrotomy. The same posterior stabilized femoral component was implanted in all knees. There were 312 fixed bearings and 133 rotating platforms implanted. In order to optimize patellar tracking, a neutral mechanical axis was established, femoral components were lateralized and externally rotated, patellar buttons were medialized, tibial components were externally rotated, and gaps and ligaments were meticulously balanced. Lateral release was performed based on intraoperative assessment of patellar tracking. Results: Lateral releases were performed in 47 of 312 (15%) fixed bearing knees, and in 14 of 133 (11%) mobile bearing knees (p=NS). Average preoperative alignment in the fixed bearing knees was –5 degrees (R-7 to 20), and in the mobile bearing knees was 0 degrees (R-10 to 20). Conclusions: Careful surgical technique with attention to the details of optimizing patellar tracking may be the most important factor determining the rate of lateral release. The self-aligning ability of mobile bearing TKA, which has been postulated to improve patellar tracking, may not reduce the need for lateral release in the cohort of patients in whom lateral tilt and subluxation of the patella persist even after other factors affecting patellar tracking have been surgically addressed

Introduction: Polyethylene wear of the prosthetic knee tibial component is currently the main cause of medium and long term failure of total knee arthroplasty. The use of a mobile bearing knee prosthesis is intended to decrease the rate polyethylene wear and therefore delay medium and long term failure. We present our five year clinical results of a mobile bearing knee prosthesis. Material and methods: 150 mobile bearing knee arthroplasties implanted between 1993 and 1996 in our institution were followed. 15 knees were lost to follow up. All knees followed up were operated on for osteoarthritis. The British Orthopaedic Association knee function score was used to access the clinical results and the Knee Society Radiographic evaluation was used for radiological evaluation. Results: 33% of patients achieved an excellent result, 52% a good result, and only 3% were not satisfied with the end result. Flexion was greater than 90 degrees in 97% of the patients. Three knees required re-surgery, 1 for deep sepsis, 1 for patello femoral problems and 1 for a fractured polyethylene component. No knee required revision for polyethylene were or loosening. Conclusions: Our mid term results are comparable to those of other prosthesis both mobile and fixed bearing knees as far as revision and radiological and functional scores are concerned. We noted that patient satisfaction in the face of good radiological and functional scores is less than would be expected

OBJECTIVES. The use of a mobile bearing has been suggested to decrease the rate of patellar complications after total knee arthroplasty (TKA). However, to resurface or retain the native patella remains debated. Few long-term results have been documented. The present retrospective study was designed to evaluate the long-term (more than 10 years) results of mobile bearing TKAs on a national scale, and to compare pain results and survivorship according to the status of the patella. The primary hypothesis of this study was that the 10 year survival rate of mobile bearing TKAs with patella resurfacing will be different from that of mobile bearing TKAs with native patella retaining. METHODS. All patients operated on between 2001 and 2004 in all participating centers for implantation of a TKA (whatever design used) were eligible for this study. Usual demographic and peri-operative items have been recorded. All patients were contacted after the 10 year follow-up for repeat clinical examination (Knee Society score (KSS), Oxford knee questionnaire). Patients who did not return were interviewed by phone call. For patients lost of follow-up, family or general practitioner was contacted to obtain relevant information about prosthesis survival. TKAs with resurfaced patella and TKAs with retained native patella were paired according to age, gender, body mass index and severity of the coronal deformation (with steps of 5°). Pain score, KSS and Oxford knee score were compared between two groups with a Student t-test at a 0.05 level of significance. Survival curve was plotted according to the actuarial technique, using the revision for mechanical reason as end-point. The influence of the patella status was assessed with a logrank test at a 0.05 level of significance. RESULTS. 1,604 TKAs were implanted during the study time-frame. 849 cases could be paired according to age, gender, BMI and severity of the pre-operative coronal deformation (2/1 ratio) into two groups: resurfaced patella (496 cases) and retained patella (243 cases). There was no difference in any baseline criteria between both groups. 150 patients deceased before the 10 year follow up (18%). Final follow-up was obtained for 489 cases (58%). 31 reoperations (prosthesis exchange or patellofemoral revision) were performed during the study time frame (4%), with 17 reoperations for mechanical reasons (3%). KSS and Oxford knee score were significantly higher for TKAs without patella resurfacing, there was a significant difference between the 13 year survival rates of TKAs with resurfaced patella (97%) and TKAs with retained native patella (93%). CONCLUSIONS. The primary hypothesis was confirmed: 10 year survival rate of mobile bearing TKAs with patella resurfacing was better than mobile bearing TKAs with native patella retaining. Patella resurfacing may lead to a better survival after mobile bearing TKA. However, the clinical results were better after patella resurfacing when the index TKA was not revised

Background: In the UK 80% unicompartmental knee replacements(UKRs) and 10% of total knee replacements(TKRs) use mobile bearings. It is suggested that mobile bearings are more physiological and wear less, however it is still unclear whether patients tolerate mobile bearing knee replacements as well. Patients and methods: We report four prospective studies,. Two compared fixed with mobile bearings in TKR and two in UKR. The prostheses involved were fixed and mobile variants of the Rotaglide (TKR), Kinemax (TKR) and Uniglide (UKR). In addition the Oxford and St. George Sled UKRs were compared. All except the Uniglide study were randomized prospective trials (RCTs). 611 patients were involved with a mean age of 68 years. Residual pain following surgery was assessed with either the Oxford Knee Score (OKS) or the WOMAC score. The patients were followed up at one and two years postoperatively by a Research nurse and the findings recorded prospectively on the Bristol Knee database. Results:. Study 1:. Rotaglide. Prospective RCT. 171 patients. Mean pain score (OKS) Fixed bearing 15.4 v Mobile bearing 13.2. P= 0.012. Fixed bearing prosthesis caused significantly less pain. Study 2:. Kinemax. Prospective RCT. 198 patients. Mean pain score (WOMAC) Fixed bearing 8.9 v Mobile bearing 8.3. P = 0.443. Trend favouring fixed bearing. Study 3:. Uniglide Non-randomised trial. 184 patients. Mean pain score (WOMAC) Fixed bearing 7.6 v Mobile bearing 10.1. P < 0.001. Fixed bearing caused significantly less pain. Study 4:. St. George Sled v Oxford. Prospective RCT. 94 patients. Mean pain score (OKS) 15.8 v 13.9 . P= 0.058. Strong trend suggesting the Sled caused less pain. Conclusion: Our data suggests that the fixed bearing knee replacements result in less residual pain than their mobile bearing counterparts, at least in the first two years following surgery

Background. Total ankle arthrpoplasty (TAA) was performed frequently for ankle deformity caused by rheumatoid arthritis (RA) and osteoarthritis (OA). TAA has some advantages over ankle arthrodesis in range of motion (ROM). However, loosening and sinking of implant have been reported with several prostheses, especially constrained designs. Recently, we have performed mobile bearing TAA and report short term results of this prosthesis followed average 3 years. Method. 20 total ankle prostheses were implanted in patients with RA (n=14) or OA (n=6) in 19 patients (5 male and 14 female, one bilateral), between 2005 and 2009. We used FINE total ankle arthroplasty that is mobile bearing system (Nakashima Medical Co., Ltd, Okayama, Japan). All patients were assessed for American Orthopaedic Foot and Ankle Society (AOFAS) score, ROM in plantar flexion and dorsiflexion at the point of pre-operation and final follow-up. We evaluated radiolucent line, sinking, and alignment of prostheses at final follow-up. Results. At the operation, patients were, on average, 64.1 years old. The mean follow-up period was 34.0 (6∼55) months. We found excellent satisfaction and a significant improvement of AOFAS score. Plantar flexion and dorsiflexion also improved compared with the preoperative state, but not significantly (table 1). At final follow-up, five ankles (25%) showed radiolucent line around the components or sinking of prostheses. Three ankles (15%) was performed reoperation, due to early infection, progressive medial OA change by sinking, and loosening of the talus component. Discussion. Radiolucent line around the components or sinking of prostheses occurred at high frequency (25%). But, only two ankles (10%) were had to reoperation, cause by pain. We take account of the fact that the symptom was lack in spite of radiological changes. Good clinical results can be achieved with FINE total ankle arthroplasty system. However, this series was short term of follow-up. We need to evaluate mid- and long- clinical results. Mobile bearing total ankle arthroplasty is a treatment option for RA and OA

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. 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 100 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°, the difference between range of movement as well as dislocation rate being significant. Conclusions. The improved surgical technique and implant design have reduced the dislocation rate to an acceptable level and therefore a mobile bearing can now be recommended for lateral UKR

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

Objective. Mobile bearing unicompartmental knee arthroplasty (UKA) is an effective and safe treatment for osteoarthritis of the medial compartment. However, mobile-bearing UKA needs accurate ligament balancing of flexion and extension gaps to prevent dislocation of the mobile meniscal bearing. Instability can lead to dislocation of the insert. The phase 3 instruments of the Oxford UKA use a balancing technique for the flexion gap (90° of flexion) and extension gap (20° of flexion), thereby focusing attention on satisfactory soft tissue balancing. With this technique, spacers are used to balance the flexion and extension gap. However, gap kinematics in another flexion angle of mobile-bearing UKA is unclear. We developed UKA tensor for mobile-bearing UKA and we assessed the accurate gap kinematics of UKA. Materials and Methods. Between 2012 and 2013, The Phase 3 Oxford Partial Knee UKA (Biomet Inc., Warsaw, IN) were carried out in 48 patients (71 knees) for unicompartmental knee osteoarthritis or spontaneous osteonecrosis of the medial compartment. The mean age of patients at surgery was 71.6 years and the mean follow-up period was 1.7 years. The mean preoperative coronal plane alignment was 7.4° in varus. The indications for UKA included disabling knee pain with medial compartment disease; intact ACL and collateral ligaments; preoperative contracture of less than 15°; and preoperative deformity of <15°. Each surgery was performed by using different spacer block with 1-mm increments and the meniscal bearing lift-off tests according to surgical technique. We developed newly tensor for mobile bearing UKA which designed to permit surgeons to measure multiple range of the joint medial compartment/joint component gap, while applying a constant joint distraction force (Figure 1). We assessed the intra-operative joint gap measurements at 0, 20, 60, 90 and 120 of flexion with 100N, 125N and 150N of joint distraction forces. Results. The gaps measured were 0°: 8.6 ± 1.6, 20°: 9.2 ± 1.4, 60°: 9.6 ± 1.2, 90°: 11.1 ± 1.3, 120°: 11.6 ± 1.8 in 100 N, 0°: 9.7 ± 1.7, 20°: 11.2 ± 1.3, 60°: 11.4 ± 1.3, 90°: 11.9 ± 1.5, 120°: 10.4 ± 1.6 in 125 N, 0°: 11.3±1.4, 20°: 11.8 ± 1.3, 60°: 11.1 ± 1.2, 90°: 12.5 ± 1.3, 120°: 11.9 ± 1.6 in 150N (Figure 2). There was a significant difference between full extension to extension (20° of flexion) and flexion (90° of flexion) to full flexion (120° of flexion). Conclusion. Mobile bearing UKA instrumentation using a balancing technique by spacer block for the flexion gap (90° of flexion) and extension gap (20° of flexion), full extension gap was significantly smaller than extension gap and flexion gap was significantly smaller than full flexion gap in 100N, 125N and 150N of joint distraction forces

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

Introduction. The results of the original mobile bearing Oxford unicompartmental knee replacement (UKR) in the lateral compartment have been disappointing because of high dislocation rates (11%). This original implant used a flat bearing articulation on the tibial tray. To address the issue of dislocation a new implant (domed tibia with biconcave bearing to increase entrapment) was introduced with a modified surgical technique. The aim of this study was to compare the risk of dislocation between a domed and flat lateral UKR. Methods. Separate geometric computer models of an Oxford mobile bearing lateral UKR were generated for the two types of articulation between the tibial component and the meniscal bearing: Flat-on-flat (flat) and Concave-on-convex (domed). Each type of mobile bearing was used to investigate three distinct dislocation modes observed clinically: lateral to medial dislocation, with the bearing resting on the tray wall (L-M-Wall); medial to lateral dislocation, out of the joint space (M-L); anterior to posterior dislocation, out of the joint space (A-P). A size C tray and a medium femoral component and bearing were used in all models. The femoral component, tibial tray and bearing were first aligned in a neutral position. For each dislocation the tibial tray was restrained in all degrees of freedom. The femoral component was restrained from moving in the anterior-posterior directions and in the medial-lateral directions. The femoral component was also restrained from rotating about the anterior-posterior, medial-lateral and superior-inferior directions. This meant that the femoral component was only able to move in the superior-inferior direction. Different bearing sizes were inserted into the model and the effect that moving the femoral component medially and laterally had on the amount of distraction required to cause bearing dislocation was investigated. Results. The average femur distraction to allow bearing dislocation in the A-P, M-L and L-M-wall directions was 1.62 mm (27%), 0.51 mm (26%) and 1.2 mm (24%) greater respectively for the domed bearing. There was a 3% increase in femoral distraction required to cause L-M-Wall dislocation, per increment of bearing thickness for both the domed and lateral bearings. There was on average a 7% increase in femoral distraction required to cause L-M-Wall dislocation per mm increment of medial femoral component movement. Discussion. Dislocation over the tray wall is a particular clinical problem and using a domed bearing can lead to an increased required femoral distraction of between 25% and 37%. This may be significant during everyday activities and demonstrates that the new domed design should reduce the incidence of bearing dislocation by increasing the amount of entrapment. Increasing the thickness of the bearing has a small effect on the distraction required to allow bearing dislocation. Lateral placement of the femoral component markedly reduced the femoral distraction required for bearing dislocation over the tray wall. Medial placement of the femoral component is advisable so long as impingement with the tray wall is avoided

Introduction: Recently, many different mobile bearing TKA designs are being implanted throughout the world. Also,fluoroscopy has been used to evaluate variousTKA under in vivo conditions to determine the kinematics. The objective of this study was to utilize a randomized prospective study to evaluate the kinematic patterns, for Japanese subjects implanted with two different mobile bearing TKA. Methods: Twenty Japanese subjects were entered into a prospective study. Ten subjects were implanted with a mobile bearing TKA, which is free to rotate around the longitudinal axis of the tibia (MB1). The other ten subjects were implanted with a mobile bearing TKA that allows for unrestricted translation and rotation (MB2). Femorotibial contact positions were analyzed using video fluoroscopy. Each subject, while under fluoroscopic surveillance, was asked to perform gait. Video images were downloaded to a workstation computer and analyzed at varying degrees of gait stance. Femorotibial contact paths for the medial and lateral condyles were then determined using a computer automated model-fitting technique. Femorotibial contact anterior to the tibial midline in the sagittal plane was denoted as positive and contact posterior was denoted as negative. Results: During gait, on average, subjects implanted with MB1 experienced minimal A/P translation of either condyle. Also, all subjects having MB1 experienced similar motion patterns throughout the stance phase of gait. Axial rotation was evident in these subjects, as one condyle would move in the anterior direction, a similar amount to the other condyle moving posterior. On average, subjects implanted with MB2 experienced both translation and rotation. The amount of translation for subjects with MB2 was greater than subjects with MB1. The kinematic patterns for subjects having MB2 were also more variable than subjects having MB1. Axial rotation was also evident for subjects having MB1. Discussion: This study has shown that the kinematic patterns for subjects having two different mobile bearing TKA designs differed considerably. Subjects implanted with a mobile bearing TKA that only allows for free rotation, experienced minimal A/P motion and significant axial rotation (MB1). Subjects implanted with a mobile bearing TKA that allows for free translation and rotation did experience both types of motions (MB2). There was minimal variability in the kinematic patterns for subjects implanted with MB1, while subjects implanted with MB2 experienced more variable kinematic patterns