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Highlights • Medial Uni-compartmental Knee Arthroplasty (MUKA) is a newer minimally invasive procedure that gained recent spotlight. • Cheaper, less blood loss, faster hospitalization and less pain and makes it more favorable compared to the conventional TKA (Total Knee Arthroplasty). • Fewer studies compared to TKA have been reporting its complication. • Meniscal bearing dislocation is one of the most common complication in UKA. • We reported simple open reduction technique which is lest costly, effective with satisfying result., Introduction Dislocation of polyethylene insert is one of the most common complications of mobile bearing-medial unicompartmental knee arthroplasty (MUKA). Bearing dislocation was diagnosed by radiograph examination in these cases upon trivial injury. Case presentation We reported one case of meniscal bearing dislocation after an Oxford MUKA treated with a simple open reduction technique. Clinical discussion Simple open reduction surgery without change of the bearing and the use of knee brace for 6 months was effective in preventing re-dislocation. Conclusion Mobile bearing dislocation is one of the most common complications in mobile-bearing MUKA. Besides the prevention of technical errors, usage of UKA with a frequency of 10–15 per year is recommended to increase the surgeon’s learning curve.

Background National joint registries report increasing revision rates with decreasing patient age for all types of joint arthroplasty. This study aimed to explore the effect of age on function and revision risk in patients undergoing medial meniscal-bearing UKA. Methods A prospectively followed cohort of 1000 consecutive medial meniscal-bearing UKAs at a designer center was analyzed. All knees were implanted for recommended indications and had mean 10-year follow-up. Patients were grouped by age at surgery ( Results Mean patient age at surgery was 66.6 years (range, 33-88). All age-groups had significant (P < .001) improvement in OKS over time, and at 5 years achieved a median OKS of 44. At 10 years, median OKS, from youngest group to eldest, were 44, 45, 42, and 39, with the eldest group having a significantly lower OKS (P < .01). Ten-year implant survival rates were 97%, 94%, 94%, and 93%, respectively, and was not significantly associated with age at UKA. Conclusion Medial meniscal-bearing UKA provides good functional outcomes in all age-groups; however, in older patients (75+), the functional outcome deteriorated at 10 years presumably due to deteriorating health. Contrary to registry observations, the revision rate was not higher in younger patients. These results suggest that, with correct indications, patient age should not be considered a contraindication to medial meniscal-bearing UKA.

Background:Cemented unicompartmental knee arthroplasty (UKA) yields good clinical outcome but common revision reasons are loosening and pain. Cementless UKA may reduce the revision rate.Objective:The current study was designed to assess clinical and radiographic outcome of cemented and cementless UKA, using bone quality as determined by the Bone Hardness Test (BHT) as selection criterion for cementless implantation.Methods:In this prospective comparative cohort study we analyzed 50 cementless and 29 Oxford consecutive UKA cases. Patients with sufficient bone quality were eligible for cementless UKA. Bone quality was assessed with the BHT, which consisted of exercising pressure with the thumb on the bone surface created after resection of the tibia.Results:The average surgical times were 62.5 ± 12.6 and 78 ± 16 minutes in the cementless and the cemented group, respectively (p < 0.01). The average thickness of the polyethylene insert was 4.3 ± 1.2 (range, 3 – 9) and 3.7 ± 0.8 (range, 3 – 6) mm, respectively (p = 0.02). Both types of implants yielded excellent clinical and functional results. At an average follow-up time of seven years, we found non-significant differences between clinical results of cementless versus cemented implants.Conclusion:Shorter surgical time makes cementless implantation more attractive to surgeons when considering UKA options for their patients. The average thickness of the polyethylene insert in cementless group was 0.6 mm thinner than in the cemented group. The BHT is a simple and useful test to assess whether patients are eligible for cementless UKA.

Background: A new design of 3-part ankle replacement was developed to achieve compatibility with the natural ligaments by allowing certain fibers to remain isometric during passive motion. Methods: We evaluate 75 ankle prostheses implanted from July 2003 to December 2008, at a mean follow-up 6.5. ±. 1.1. years (range 5-9 years). The mean age at surgery was 62. ±. 13. years (range 29-82). Results: The mean AOFAS scores achieved at pre-op and at last follow-up were respectively 37. ±. 5 (23-45) and 78. ±. 8 (64-98). (p.

Dislocation of meniscal bearing insert is a rare but well-recognised complication in meniscal bearing unicompartmental knee arthroplasty (UKA). On the other hand, fracture of meniscal bearing insert of phase III Oxford UKA has only been reported once in the current literature. The authors report a case of fracture and posterior dislocation of one of the fragments of the meniscal bearing insert in a mobile bearing medial UKA. The fracture was only diagnosed during the revision surgery. The posteriorly dislodged fragment was subsequently retrieved through the same skin incision and a new polyethylene insert of the same size was implanted.

WOS: 000470771800002, PubMed: 31363444, Proximal fibular osteotomy (PFO) is a simple, easy and cheap procedure consisting of removing a 10 mm piece of fibula 6 to 9 cm below the fibular head. Proximal osteotomy of the fibula weakens the lateral fibular support and leads to a correction of the varus deformity and provides a widening on the medial joint space. Unicondylar knee arthroplasty (UKA) is intended to treat isolated medial compartment arthritis. However, knees with a varus deformity and tight medial joint space might cause both technical difficulties and poorer outcomes. A 68-year-old female with complaints of pain on the medial side of both knees for more than two years underwent bilateral UKA. While inserting the trial meniscal bearing was not easy due to the varus tight knee, at that stage, instead of performing a deeper cut, a PFO procedure was considered which provided widening of the medial joint space. We report, to our knowledge, the first simultaneous application of these two procedures. Despite being a single case with very short term results, our results suggest that the combination of PFO and UKA may reduce the loads over the implants on the medial compartment based on the widening of the joint space and varus deformity correction.

Mobile-bearing Oxford medial unicompartmental knee arthroplasty (UKA) has been widely used and has produced good results in the treatment of medial compartmental osteoarthritis. But it is associated with the potential risk of meniscal bearing dislocation. Symptoms caused by most meniscal bearing dislocations include acute pain, knee swelling, and locking. We report two unusual cases of meniscal bearing spinning of 180° without remarkable symptoms, which would have been easily missed if we had not watched carefully. Therefore, if there is sudden locking, pain, swelling, or a slight locking history, the possibility of meniscal bearing spin out as well as meniscal bearing dislocation should be considered and the direction of meniscal bearing markers should be confirmed, especially on lateral radiographs.

Polyethylene particulate wear debris continues to be implicated in the aetiology of aseptic loosening following knee arthroplasty. The Oxford unicompartmental knee arthroplasty employs a spherical femoral component and a fully congruous meniscal bearing to increase contact area and theoretically reduce the potential for polyethylene wear. This study measures the in vivo ten-year linear wear of the device, using a roentgenstereophotogrammetric technique. In this in vivo study, seven medial Oxford unicompartmental prostheses, which had been implanted ten years previously were studied. Stereo pairs of radiographs were acquired for each patient and the films were analysed using a roentgen stereophotogrammetric analysis calibration and a computer-aided design model silhouette-fitting technique. Penetration of the femoral component into the original volume of the bearing was our estimate of linear wear. In addition, eight control patients were examined less than three weeks post-insertion of an Oxford prosthesis, where no wear would be expected. The control group showed no measured wear and suggested a system accuracy of 0.1 mm. At ten years, the mean linear wear rate was 0.02 mm/year. The results from this in vivo study confirm that the device has low ten-year linear wear in clinical practice. This may offer the device a survival advantage in the long term.

Background The Oxford Medial Partial Knee Replacement (PKR) has been in clinical use for more than 20 years. The current surgical technique requires a number of judgements to be made, and even in the most experienced hands surgery can be challenging. We present an alternative surgical technique, which we believe addresses the unpredictability of the current method. The technique is based on precise femoral positioning prior to tibial resection. Method A prospective series of 125 Oxford Medial PKRs was performed using this new technique and a radiographical analysis was performed. We used meniscal thickness, meniscal position and femoral position as measures of reproducibility of the procedure. Results Variability in meniscal thickness has been minimised with a 3 mm meniscal bearing used in 21 knees (15%), 4 mm (the target thickness) in 73 knees (59%) and 5 mm in 30 knees (24%). The mean meniscal position relative to the tibial tray upright was 2 mm (SD 1 mm). Femoral component position relative to the tibial tray, which defines the excursion of the meniscus was also assessed. Mean coronal plane alignment was 2° of valgus (SD 2.8). Mean flexion/extension was 3.8° (SD 3.1). The mean rotation was 10° internal (SD 5°). Conclusion We believe this new technique makes this procedure more reproducible, and should be considered as a viable alternative to the current recommended technique. It may be a better technique for those surgeons who are relatively inexperienced with this prosthesis.

The Rotaglide knee arthroplasty has a highly congruent mobile meniscal bearing allowing both rotation and antero-posterior translation. We reviewed 137 consecutive primary arthroplasties in 120 patients at mean 11.1 years (10-12.9) following surgery. No cases were lost to follow-up. Hospital for Special Surgery (HSS) and American Knee Society (AKSS) scores were recorded at a review clinic. Radiographs were assessed using the Knee Society's roentgenographic evaluation system. Forty-two patients had died, leaving 78 patients (87 knees) available for review. Sixty-four patients (70 knees) were assessed at a clinic and in 14 (17 knees) clinical outcomes were obtained via telephone and their most recent radiographs were assessed. There were three cases of aseptic loosening and one deep infection requiring revision surgery. Two meniscal bearings were replaced with thicker inserts, one following bearing fracture and one following bearing dislocation. Survival at 11 years for aseptic loosening was 97.6% (95% CI 94.3 to 1.0) and survival using re-operation for any cause was 95.3% (95% CI 90.8 to 99.8). The Rotaglide mobile-bearing total knee replacement demonstrates good survivorship and outcome scores at 11 years following surgery.

Our initial experience with mobile bearing medial compartment unicompartmental arthroplasty (UKA) is presented to highlight lessons that have been learned to avoid short-term failures. Consecutive cases of the Oxford medial UKA performed between February 2001 and April 2006 were reviewed to derive those cases that were revised to total knee arthroplasty (TKA). There were 545 patients available with mean age and body mass index of 65.0 and 30.1, respectively. At final follow-up, 32 patients were revised for lateral compartment arthritis, aseptic component loosening, persisting medial or anterior pain and dislocated meniscal bearing. Revisions were performed with primary unconstrained TKA implants with no stems or wedges required. Our results seem to reflect those seen in registries confirming an earlier higher revision rate and highlight the technical issues of overstuffing the compartment, inadequate cementation technique, and strict adherence to patient selection.

Background: Most clinical studies on total ankle replacement (TAR) report assessments based on traditional clinical scores or radiographic analysis. Only a few studies have used modern instrumentation for quantitative functional analysis during the execution of activities of daily living. The aim of this study was to use gait analysis to compare the functional performance of patients who underwent TAR versus a control population. Methods: A retrospective analysis was performed of ten consecutive patients who had undergone meniscal-bearing TAR. Clinical and functional assessments were performed at a mean follow-up of 34 months with a modified Mazur scoring system and state-of-the-art gait analysis. Results: Gait analysis assessment of TAR at medium-term follow-up showed satisfactory results for all patients, with adequate recovery of range of motion. Because the literature reports unsatisfying long-term results, it is important to evaluate these patients over a longer follow-up period. Conclusions: This study showed that TAR yields satisfactory, but not outstanding, general functional results at nearly 3 years’ follow-up. These gait analysis results highlight the importance of integrating in vivo measurements with the standard clinical assessments of patients who underwent TAR while they perform activities of daily living. These results also emphasize the importance of evaluating the functional outcome of TAR over time. (J Am Podiatr Med Assoc 98(1): 19–26, 2008)

This study presents the survivorship data of a consecutive series of primary meniscal-bearing total knee replacements at one institution at 8 to 15 years followup. We reviewed 125 meniscal-bearing knee replacements in 93 patients at a minimum followup of 96 months (mean, 130 months; range, 96-191 months). The tibial and femoral components were cemented in 71 knees; uncemented femurs and tibias were used in 48 knees; and cemented tibias and uncemented femurs were used in six knees. One patient was lost to followup. Seventeen knees failed, three as a result of infection. Five knees were revised for loose tibial components and one for a loose femoral component. A second femoral component was identified as radiographically loose. All the loose components were uncemented. Five knees had reoperation for fractured bearings and one for a dislocated bearing. This knee was later rerevised for a loose uncemented tibia. One knee was revised for instability and a second knee was identified as grossly unstable but not revised. Kaplan-Meier survival analysis showed survivorship of approximately 90% at 9 years, which decreased to 71% at 15 years. Uncemented components had an increased aseptic loosening rate compared with cemented components. Meniscal-bearing replacements with cement fixation appeared successful, although bearing fracture seems to be a predominant failure mode at long-term followup.

To determine polyethylene deformation in well-functioning meniscal bearing PCL-retaining total knee prosthesis a quantitative stereophotogrammetric analysis was carried out over 5 years' follow-up. Polyethylene plastic deformation was obtained by tracking the intermarker distance variations of five tantalum beads inserted into the polyethylene prior to surgery in a known position. Plastic deformation occurred in the posteromedial part of the meniscal bearing. Radiostereometric analysis was a useful tool to monitor the load distribution in vivo on the polyethylene of this meniscal bearing prosthesis. This analysis revealed a very similar pattern of plastic deformation in the polyethylene insert of this prosthesis design to the wear pattern revealed with different methodologies in PCL-retaining fixed-bearing prosthesis.

Insertion of the bearing can be challenging due to patient body habitus or limited exposure when using a minimally invasive technique. We describe a novel way of inserting the bearing not previously described in the literature. The bearing is positioned on the femoral component in full flexion. Then, with a gentle extension of the knee, the bearing snaps into position and is seated correctly on a consistent basis.

We experienced two cases of atypical lateral dislocations of meniscal bearing in UKA (unicompartmental knee arthroplasty) without manifest symptoms. The dislocated bearing, which jumped onto the wall of tibial components, was found on radiographs in periodic medical examination although they could walk. Two thicker size bearing exchanges were promptly performed before metallosis and loosening of components. Continual examination is important to mobile bearing type of UKA because slight or less symptoms may disclose such unique dislocation. One case showed malrotation of the femoral component on 3D image. Anteroposterior view hardly disclosed the malrotation of the femoral component. Epicondylar view is an indispensable view of importance, and it can demonstrate the rotation of the femoral component. The the femoral distal end is wedge shaped and is wider posteriorly. If the femoral component is set according to the shape of medial condyle, the femoral component shifts to medial site compared with tibial component in flexion. It can account for such rare dislocation as follows. If excessive force applies on most medial side of the bearing during flexion, the lateral part of the bearing pops and the force squeezes it laterally simultaneously. Finally, the bearing jumps onto the lateral wall of the tibial component.

Summary Reconstructive surgery with an ankle prosthesis for a painful ankle joint is of extreme benefit for the rheumatoid patient. In contrast to ankle fusion, ankle arthroplasty maintains mobility with early remobilisation of the patient. The success of ankle arthroplasty depends on indication, implant design and surgical technique as well as postoperative treatment. The performance of the first ankle prosthesis generation, developed in the early 1970s, was poor, being plagued by high loosening and revisions rates up to 50%. The two main reasons for failure were constrained designs and cement fixation. Buechel and Pappas, with the BP-ankle prosthesis and H. Kofoed with the S.T. A.R.-prosthesis first developed the second generation of ankle prosthesis. The three-component type consists of amobile polymeric bearing that is interposed between the flat metallic tibial and the metallic talar component. The key of success has been the use of a meniscal bearing device that provides unconstrained motion and stability. In the last 10 years, the ankle prostheses currently used have achieved encouraging midterm results. Despite all the progress in ankle arthroplasty made over the last few years, there remain some drawbacks concerning malleolar fracture, stiff ankle joint and impingement. Based on their experience with the current ankle prosthesis designs, the authors developed a new ankle prosthesis design. The in vitro testing was promising and we hope to report our first clinical results soon.

Aim: A biomechanical study was conducted to determine the in-vitro modification of the posterior cruciate ligament tension following different types of total knee arthroplasty (TKA). Materials and methods: The Genesis CR (non-mobile tibial inlay, n =9) and LCS meniscal bearing prostheses (mobile meniscal bearings, n =8) were compared with the human cadaveric knee joint. Posterior cruciate ligament (PCL) tension was assessed with implantable force transducers. A six-degree-of-freedom manipulator was used to measure knee kinematics at 10° intervals from 0° to 120° of flexion with [300 Newton (N)] and without load application (0 N). Statistical analysis was performed with the Wilcoxon rank sum test. Results: Analysis of the PCL tension following TKA using the Genesis CR prosthesis revealed a non-significant ( P =0.20) decrease of transducer output with load (300 N) and a non-significant ( P =0.73) increase without load (0 N). Concerning the LCS meniscal bearing prosthesis a significant ( P =0.01) decrease of transducer output was assessed with load (300 N) whereas a non-significant ( P =1.0) modification was seen without load (0 N). Conclusion: The Genesis CR prosthesis allows PCL tension to be close to normal as the knee flexes, which is contradictory to the assumed evidence for a missing restorability of a regular PCL tension after TKA. Our results hence indicate, that the effected tension of the PCL strongly depends on the balance and interaction between design of the implant and the functional role of the retained PCL.

A prospective study of early clinical and radiologic outcome of the Motus (Osteo, Selzach, Switzerland) meniscal bearing total knee arthroplasty was performed. We reviewed the first 75 consecutive prostheses in 62 patients, implanted over a 4-year period. The mean follow-up was 2.5 years. Average preoperative knee score was 97 out of 200 (Knee Society score, 43; functional score, 54) and at 2-year review was 179 out of 200 (Knee Society score, 87; functional score, 92). Average postoperative flexion at 2 years was 113°. No meniscal bearing subluxation, dislocation, or breakages occurred. Radiologically, there was no evidence of subsidence or osteolysis. Our results support the continued use of this meniscal bearing knee prosthesis. It is important to confirm, however, an equal flexion and extension gap without proximal joint line migration. Copyright 2003, Elsevier Science (USA). All rights reserved.

From December 1991 to April 1995, 70 consecutive New Jersey low-contact stress (LCS) total knee arthroplasties (TKAs) were performed. Twenty two TKAs were done using rotating platform tibial component, and 48 were done using meniscal bearing tibial component. Two patients sustained bearing insert failure at eight years after primary TKA. Subluxation of tibiofemoral articulation occurred in one case, secondary to increased polyethylene wear and ligamentous instability. It was corrected easily by the insertion of a thicker bearing. The other case had patellar bearing breakage with delamination, but patellofemoral maltracking was not seen. The polyethylene of the patellar component was changed, improving the condition of both patients with relief of pain. Component failure, especially polyethylene wear and breakage were found to occur frequently.

Clinical results of the initial cemented and cementless series of 373 New Jersey Low Contact Stress total knee replacements in 282 patients surviving at least 10 years were analyzed using a strict knee scoring scale. The study showed excellent, good, fair, or poor results in 68.1%, 29.8%, 2.1%, or 0% of primary posterior cruciate-retaining meniscal bearing knee replacements, 46.7%, 53.3%, 0%, or 0% results in primary cemented rotating platform knee replacements, and 68.1%, 29.8%, 2.1%, or 0% results in primary cementless rotating platform knee replacements, respectively. Radiographic evaluation at minimum 10-year followup showed stable fixation of all components, no gross migration but significant osteolysis requiring bearing exchange and bone grafting in three cementless rotating platform knee replacements (1.8%) in three patients who underwent previous surgeries at an average of 10.2 years from the index surgery. Survivorship of the patients who underwent primary cementless posterior cruciate-retaining meniscal bearing knee replacements with an end point of revision for any mechanical reason was 97.4% at 10 years and 83% at 16 years; using an end point of a poor clinical knee score the survivorship was 98.9% at 10 years and at 16 years. Survivorship of the patients who underwent primary cemented rotating platform knee replacements with end points of revision for any mechanical reason or a poor clinical knee score was 97.7% at 10 years and at 20 years. Survivorship of the patients who underwent cementless rotating platform knee replacements with end points of revision for any mechanical reason or a poor clinical knee score was 98.3% at 10 years and at 18 years.

Buts de l'étude: Présentation d'une série de 21 prothèses totales de cheville non cimentées à ménisque et analyse des résultats à court terme. Matériel et méthode: 21 prothèses totales de cheville ont été implantées chez 21 patients d'un âge moyen de 63.5 ans. L'origine de l'arthrose était post-traumatique ou primaire. Notre recul moyen est de 21 mois. Résultats: Les résultats ont été évalués en utilisant le score de Koefod. 11 patients ont obtenu un excellent, 7 un bon résultat et 2 un résultat moyen. Un cas fut un échec et a nécessité une arthrodèse. Discussion: La prothèse totale de cheville non cimentée à ménisque permet d'obtenir à court terme une bonne indolence et une bonne fonction malgré un faible gain des amplitudes articulaires. Ces résultats apparaissent comme encourageants.

Summary We investigated the tibio-talar mobility clinico-radiographically in 11 ankle joint prostheses before surgery and after 6 and 12 months. The radiologist and the orthopaedic surgeon were not involved in the radiographic procedures. The total preoperative radiographic range of motion was median 16° (range 13–50). At 6 months after operation it had increased to median 22° (range 15–36) and at 12 months to median 27° (range 19–38). The difference at 6 and 12 months was significant compared to the preoperative value ( P = 0.05). The gain in motion took place in dorsiflexion that at 6 months had increased by 7° and at 12 months by 10°. There was no significant change in plantarflexion. The clinical measurements showed the same trend. However, the motion was significantly larger (45°, range 40–55). There was no correlation between clinical and radiographic measurements. True tibio-talar motion for ankle arthroplasty is determined best by radiography.

From January 1985 to December 1990, 598 consecutive New Jersey low-contact stress (LCS) total knee arthroplasties (TKAs) were performed for gonarthrosis. Among these 598 operations, 322 were with rotating platform elements and 276 were with meniscal bearing elements. During 5 to 8 years of follow-up, eight knees had severe symptomatic polyethylene failure that required revision surgery; all eight cases were meniscal bearing types. The failed polyethylene inserts were retrieved and studied. It was observed that there were four probable failure mechanisms associated with the catastrophic polyethylene wear. First, insufficient thickness of the meniscal bearing was the major reason for wear. Second, the malpositioning of the metal tibial tray in the transverse plane resulted in the breaking of the meniscal bearing. Third, the inability of the patellar to rotate due to tissue ingrowth made the polyethylene break. Last, yellowing of the subsurface of the meniscal bearing was a sign of polyethylene failure. These four possible failure mechanisms are all associated with the design of the meniscal bearing type of LCS knee prostheses. Therefore, it is suggested that the design of the LCS knee prosthesis should be modified.

The preliminary results of the Minns meniscal bearing total knee replacementare presented with an average follow-up of 62.5 months (range 38–78 months). A total of 90 cemented meniscal bearing total replacements of this design were performed on 67 consecutive patients. Three died of unrelated causes and four failed to attend for follow-up investigation. Consequently, 80 knees in 60 patients were reviewed with an average follow-up time of 62.5 months. Using the American Knee Society scoring system (see Appendix 1), 82% rated good or excellent, 11% were rated fair and 6% poor. There was a clinical improvement in all cases except one patient and pain relief was achieved in most cases (96%). Five knees had some mild pain on activity post-operatively. The average range of motion post-operatively was 98° and there were no cases of dislocation of the polyethylene bearings. There was a single case of radiological loosening which subsequently proved to be an infected prosthesis requiring revision surgery. Survivorship analysis (Kaplain-Meier survival curve) shows that 98.9% of the knees survived at five years follow-up.

We present the case of a 79-year-old man who dislocated the mobile bearing of a well-functioning Oxford unicompartmental knee replacement in a fall. The diagnosis was delayed by 14 days during which time the patient remained fully mobile. At the time of arthrotomy, there was some visible burnishing of the femoral articular surface where it had been rubbing on the tibial component. Both components were soundly fixed and had been functioning well for 7 years. The decision was made to leave the components in situ and simply replace the mobile meniscal bearing. The patient returned to full normal activity and has been followed-up for 3.5 years. Serial X-rays reveal no evidence of polyethylene wear and the knee remains pain free and fully functional. We conclude that it is safe to retain the components of an Oxford unicompartmental knee replacement despite some evidence of surface damage. Replacing just the mobile meniscus gave a good result in our patient.

A new design of 3-part ankle replacement was developed to achieve compatibility with the natural ligaments by allowing certain fibres to remain isometric during passive motion. From July 2003 to April 2008 we have implanted 70 ankle prostheses. The mean age at surgery was 61.5 years (range 29.7-82.5). Mean follow-u is 6,4 years (5-9 years). Radiographs showed good alignment, no loosening and little signs of progressive radiolucency. The preoperative AOFAS score was 38.4 and at last follow-up increased to77,9. Function and Range-of-motion scored better than previous total ankles. Two revisions necessitated component removal, neither for implant failure. These results demonstrate that non-anatomically shaped talar and tibial components, with a fully conforming interposed meniscal bearing, can provide satisfactory clinical results in the short term.

A complication of meniscal bearing total knee replacements is subluxation/dislocation of the rotating platform. In this article we describe two cases of platform dislocation occurring after several years, with no history of trauma.

We report the results of 53 knees with lateral compartmental osteoarthritis treated by unicompartmental arthroplasty with the Oxford Meniscal Knee. The mean follow-up was 5 years. Eleven knees required further surgery. Six of the revisions were for early dislocation of the meniscal bearing, three because of late infection, one because of loosening of the tibial component and one because of a stress fracture that occurred in the tibial plateau. Since introducing techniques to prevent bearing dislocation, 14 knees have been operated on and there has been one dislocation. This bearing was exchanged for one of a larger size, and the knee subsequently functioned well. Forty of the 42 knees that did not require further surgery had good relief of symptoms and restoration of function, and two had persistent pain. The risk of bearing dislocation in the lateral compartment with the Oxford Unicompartmental Knee replacement is greater than in the medial compartment. In other respects the results are similar. New techniques have reduced the risk of bearing dislocation but have not prevented the complication.

Summary A consecutive series of eight cases, five men and three women, of mean age 56 years (42–79) with unilateral meniscal-bearing total ankle arthroplasty was analysed with stabilometry in the standing phase in order to compare the in vivo stability of the artificial joint to that of the opposite normal ankle joint. The tests were performed as a one-legged balance test on a fully computerized static force plate, with or without shoes, and with open and closed eyes. The force plate registered the area used to keep balance, the length and direction of the corrective movements and their velocity. A system (maximum 100 points) with a pain score, normal daily-life ankle function score and ankle mobility score was used for clinical evaluation (excellent: 85–100 points, good 75–84, fair 70–74, and

In the Swedish Knee Arthroplasty Study, all 699 Oxford meniscal bearing cemented unicompartmental prostheses (Biomet, Bridgend, UK) were identified and analyzed regarding failure pattern and compared with all Marmor prostheses (Smith & Nephew Richards, Orthez, France) and with a time-, age-, and sex-matched subset of Marmor prostheses using survival statistics expressed as cumulative revision rates. After 1 year there was already a higher rate, and after 6 years the rate of the Oxford group was more than twice that of the Marmor group. There were 50 revisions in the Oxford group: dislocating meniscus in 16, loosening of the femoral component in 6, tibial component in 4, both components in 4, contralateral arthrosis in 10, infection in 4, and technical failure with instability, pain, and/or impingement of the meniscal bearing anterior in the femoral condyle in 6. It is still unclear if the design with the sliding menisci will, in the long turn, reduce wear and loosening, thereby compensating for the initially inferior results. It is recommended that until this question is clarified, the Oxford knee should be used on a limited scale for long-term comparative studies only.

The short-term results of 46 knees in 37 patients treated by LCS total knee systems were evaluated clinically and radiologically. The models used were the Rotating Platform type in 22 knees and the Meniscal Bearing type in 24 knees. Using the criteria described by three universities, the average clinical score after operation achieved by the Rotating Platform type was 88.9 points and 86.4 points for the Meniscal Bearing type. Component placement angle was good and follow-up revealed that the components remained in place. We found radiolucent lines in 69.6% and subsidence in 21.7% of the cases, but no further worsening was observed. The motion of the meniscal insert during bending fell into three groups; forward shift, backward shift and no shift. The range of motion was significantly wider in the backward shift group (flexion: average 132°), but there was no difference among the three groups in regard to clinical results.

Background An original total ankle replacement design was developed with the aim of establishing compatibility between the prosthetic articulating surfaces and the retained ligaments. This was achieved with a special shape of a conforming meniscal bearing, free to move forwards/ backwards on both metal components during dorsi/ plantar flexion. Careful kinematics analyses were carried out in patients after this replacement to assess the functional performance during activity of daily living. A thorough assessment shall include standard gait analysis (GA) and the more accurate motion tracking of the components by 3D fluoroscopic analysis (FA).

Meniscal bearing fracture is a rare complication of phase III Oxford unicompartmental knee replacement (UKR). We report a case of a meniscal bearing fracture that occurred 7 years after phase III Oxford medial UKR. The meniscal bearing showed uneven delamination of the polyethylene in the thinnest articular surface and an impingement lesion. This lesion initiated a fatigue crack that propagated to cause failure of the meniscal bearing. This is the first report of a meniscal bearing fracture without a posterior marker wire.

This study evaluated changes in the lower extremity 3-dimensional load-bearing mechanical axes in the anteroposterior and mediolateral directions before and at 3 weeks after mobile-bearing total knee arthroplasty. The effects of the degrees of anteroposterior constraint of the designs on the location of the load-bearing mechanical axis at the knee joint level were also assessed. We evaluated 151 knees from 134 patients with 74 knees receiving meniscal bearing-type and 77 knees receiving rotating platform-type prostheses. In the mediolateral direction, both designs showed significant improvements, whereas in the anteroposterior direction, they revealed no improvements postoperatively and were worsened significantly in meniscal bearing type. Differences in the degree of bone and soft tissue involvement for the correction of alignment may explain the findings.

The mobile meniscal bearing of unicompartmental knee arthroplasty is completely free moving, and dislocation of this bearing is a major concern for all mobile-bearing designs. Most dislocations are located in the intracapsular area; however, posterior dislocation of the polyethylene bearing to an extra-articular area of the knee after unicompartmental arthroplasty has not been previously reported. During a revision surgery, separate incision was necessary to remove a dislocated meniscal bearing in the popliteal fossa. The authors present a case of incarceration of a dislocated mobile bearing to the popliteal fossa after unicompartmental knee arthroplasty that was missed during initial diagnosis.

We recovered 23 meniscal bearings from 18 failed bicompartmental Oxford knee prostheses. They had been implanted for one to nine years. The minimum thickness of the retrieved bearings was measured and compared with the thickness of 25 unused bearings. The mean penetration rate, calculated by two methods, was either 0.043 or 0.026 mm per annum. This compares with 0.19 mm per annum reported for the Charnley hip. The use of a fully congruous meniscal bearing prosthesis can reduce wear in knee arthroplasty to a very low rate.

The purpose of this article is to review the early complications of minimally invasive mobile-bearing unicompartmental knee arthroplasty by analyzing the first 100 consecutive cases. All cases were medial unicompartmental arthroplasties with a follow-up of at least 24 months (range, 24-51 months). Seven revision procedures were performed due to 2 fractures of the medial tibial plateau, 1 loosening of the femoral component, and 4 dislocations of the meniscal bearing. The early results as determined by The Knee Society scores, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores and postoperative range of motion were satisfactory. However, there exists a high rate of early failures, which occurred during the initial learning curve. Therefore, surgeons must be aware that in order to minimize these complications, attention to detail is mandatory.

This study aimed to evaluate the clinical and radiographic results and to document the prevalence of osteolysis associated with fixed-bearing (anatomic modular knee) and mobile-bearing (low contact stress) total knee arthroplasties (TKAs) in 61 patients younger than 55 years who had bilateral simultaneous primary TKAs. Forty-five patients were female and 16 patients were male. The mean age of the patients was 48.3 years (range, 34-55 years). The mean postoperative Knee Society knee and functional score were similar in both groups (91 and 90 points and 85 and 86 points, respectively). Three knees (5%) in each group were revised for wear of the tibial bearing, and 1 knee (2%) in the mobile-bearing TKA was revised for dislocation of the meniscal bearing. Osteolysis was identified in both radiographs and computed tomography scans in 6 knees (10%) in the anatomic-modular-knee group and 4 knees (7%) in the low-contact-stress group.

Despite the fundamental value of wear simulation studies to assess wear resistance of total joint replacements, neither specialised simulators nor established external conditions are available for the human ankle joint. The aim of the present study was to verify the suitability of a knee wear simulator to assess wear rates in ankle prostheses, and to report preliminary this rate for a novel three-component total ankle replacement design. Four intact 'small' size specimens of the Box ankle were analysed in a four-station knee wear simulator. Special component-to-actuator holders were manufactured and starting spatial alignment of the three-components was sought. Consistent load and motion cycles representing conditions at the ankle joint replaced exactly with the prosthesis design under analysis were taken from a corresponding mechanical model of the stance phase of walking. The weight loss for the three specimens, after two million cycles, was 32.68, 14.78, and 62.28 mg which correspond to a linear penetration of 0.018, 0.008, and 0.034 mm per million-cycle, respectively for the specimens #1, #2, and #3. The knee wear simulator was able to reproduce load-motion patterns typical of a replaced ankle. Motion of the meniscal bearing in between the tibial and talar components was smooth, this component remaining in place and in complete congruence with the metal components throughout the test.

An example of a mobile meniscal bearing prosthesis design is the LCS Knee System (DePuy, Inc., Warsaw, IN). This prosthesis system provides a mobile bearing prosthesis for use when the posterior cruciate ligament (PCL) is retained and a rotating platform prosthesis for use when the PCL is sacrificed iatrogenically or has been lost to pathology. The purpose of the present study was to examine, in in-vitro models, the stability provided the knee by implantation of these two versions this mobile meniscal bearing prosthesis system. Following installation of the meniscal bearing PCL-retaining prosthesis, anterior/posterior tibial translation was significantly increased over that seen in the intact knee for the anterior drawer tests at both 90 and 30 degrees of flexion. The observations in this study of increased anterior/posterior laxity following installation of the meniscal bearing prosthesis are in qualitative agreement with those made by Schlepckow (1992). However, it would appear that the design of the rotating platform PCL-sacrificing prosthesis substitutes in some way for the roles played by the anterior and posterior cruciates in the restraint of anterior/posterior tibial motion. While the bearings of the meniscal bearing prosthesis allow unhindered anterior/posterior travel over a fairly long distance, the tibial condyle design of the rotating platform prosthesis may present anterior/posterior lips to restrain anterior/posterior motion after modest amounts of anterior/posterior tibial translation.

Several reports in the literature describe dislocation and fractures of the meniscal bearings as a result of polyethylene failure after total knee arthroplasty. In this case of an asymptomatic patient with a clinically uneventful 7-year follow-up, who died a year later of an unrelated cause, we found impressive damage of the polyethylene components. This damage, at the posterior corner of the meniscal bearing elements, was caused by regrowth of the posterior femoral osteophytes. The primary osteophytes had been resected adequately during the arthroplasty. These osteophytes are related to a bone–polyethylene impingement that occurs at >110° of knee flexion. The possible range of motion of an artificial joint, owing to its design, is less than the range of flexion sometimes reached clinically by the patient. This is a problem that should be solved by the industry in the near future. Copyright 2002, Elsevier Science (USA). All rights reserved.

As a first year orthopaedic surgery resident at New Jersey Medical School in Newark, New Jersey, I first met Michael J. Pappas, PhD, my biomechanics teacher from New Jersey Institute of Technology, (NJIT) (also in Newark, N.J.). It was early in 1974 when my orthopaedic chairman, Anthony F. DePalma, MD (a feisty, world renowned shoulder surgeon and founder of Clinical Orthopaedics and Related Research) decided that his orthopaedic residents needed to have an understanding of engineering principles as they applied to bone and joint surgery. To that end he enlisted two mechanical engineering volunteers from NJIT, Harry Herman, PhD and his junior associate Michael J. Pappas, PhD.

The effect of a mobile meniscal bearing on tibiofemoral contact stress was tested with a standard fixed tibial component and with movable tibial components (anteroposterior sliding, rotationally sliding, and anteroposterior and rotationally sliding). A digital electronic sensor was used to detect tibiofemoral contact location in five cadaver knees, then the location was reproduced while peak and mean stresses were measured under compressive load at 0 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion. Stresses were measured when the tibial component was normally aligned and at 15 degrees internal and 15 degrees external rotation. To evaluate the effect of excessive overhang of the polyethylene articular surface, undersurface stress of the rotationally sliding component was also measured with a 30 degrees and a 45 degrees malrotated tibial tray. Uppersurface stresses of the fixed-bearing components were significantly higher at full extension than those recorded in components with rotational mobility. Undersurface stresses were always lower than uppersurface stresses, but correlated with uppersurface stresses. Undersurface stresses of the rotationally sliding component gradually increased as the malrotation angle of the tray increased. A mobile meniscal bearing surface appears to offer an advantage over a standard fixed component when rotational malalignment of the tibial component occurs. However, with severe rotational malalignment, edge contact markedly increases undersurface stresses, which could cause deformity and subluxation.

A 54 year old man presented to the emergency department with an acutely locked left knee. He had had a unicondylar knee replacement done on this knee 18 months earlier. Plain x rays were taken (fig 1A) which confirmed the dislocation of the meniscal bearing. An attempt to reduce the knee under sedation in the emergency department was unsuccessful and an orthopaedic consultation was requested. An attempted manipulation under anaesthetic to reduce the …

Seven total knee arthroplasty systems were tested to determine contact stress patterns and contact areas using a calibrated Fuji film stress analysis technique. Knees were loaded to 2,000 N (204 kg) at 15 degrees, 60 degrees, 90 degrees, and 135 degrees flexion at 24 and 37 degrees C. Evaluation of stresses at 37 degrees C at 15 degrees and 60 degrees using an average contact stress assessment technique indicated that the LCS meniscal bearing knee system, (DePuy, Warsaw, IN), the AMK knee with a constrained insert (DePuy), and the PFC knee with a posterior-lipped insert (Johnson and Johnson, Raynham, MA) had the lowest average contact stresses (near or below 10 MPa). The PFC with a regular insert (Johnson and Johnson) the Ortholoc II (Dow Corning Wright, Arlington, TN), and the AMK with a regular insert (DePuy) had intermediate contact stresses. The AMK with a Hylamer-M insert (DePuy) and the MG II (Zimmer, Warsaw, IN) had the highest average contact stresses (near or above 20 MPa). A stress-calibrated Fuji film measurement technique has shown that an assessment of ranges of contact stress provides much more information about regions of expected wear than an assessment of average contact stresses. Testing of the tibiofemoral articulation of artificial knees revealed that all knees had some areas of contact with maximum stresses in excess of 15 MPa. As the yield strength of ultrahigh-molecular-weight polyethylene is approximately 15 MPa, all tibial inserts could wear to some extent. Peak contact stresses at four test angles of the AMK, Series 7000 (Osteonics, Allendale, NJ:) Genesis (Smith & Nephew Orthopaedics, Memphis, TN), and MG II patellofemoral articulations were high (above 30 MPa). Contact areas varied from line-shaped to bilateral circular or elliptical shapes. The LCS knee system experienced substantially lower patellofemoral contact stresses and larger contact areas. Changes in conformity of knee designs are warranted to overcome wear problems. Peak contact stresses measured from the LCS meniscal bearing tibiofemoral and patellofemoral joint were in excess of 30 MPa in some areas at low flexion angles. This design does create large areas of contact at very low contact pressures, however, and for this reason is expected to wear less than other designs.

Unicompartmental knee arthroplasty (UKA) is a well-established procedure for isolated medial compartment osteoarthritis. Meniscal dislocation is a well-recognized complication in mobile bearing UKA especially when performed for the lateral compartment. Dislocation in medial UKA is relatively uncommon and is usually anterior when encountered. We would like to report a case of posterior dislocation of the bearing insert in a mobile bearing medial UKA presenting as a Baker cyst, which was subsequently revised to total knee arthroplasty.