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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.

A Guided Motion knee is one with features other than basic bearing surfaces, to guide or control the motion in prescribed ways, usually to provide some resemblance to anatomic knee motion. Among the earliest knees were those which allowed freedom of rotation of the femoral component on the tibia about a central axis, the UCI and the Variable Axis being two examples. These designs allowed for the axial rotation which occurs in function as well as anterior-posterior stability. Reproducing the function of the menisci was a logical goal in that they maintain a large area of contact, minimize contact stresses, and buffer the femur at the extremes of motion. Meniscal bearing knees were the result, including the Oxford and Minns. An evolution of this concept was the LCS rotating platform, which also provided freedom of internal-external rotation. Based on experimental data that the knee pivoted about the medial side, due to medial stability and lateral mobility, medial pivot knees were invented and have shown positive clinical feedback. Biomimetic knees, either imitating anatomic geometry or motion, have been challenging in that several designs have been invented, but there has been limited experience so far. This class of knee has a high but as yet unrealized potential.

In 2012-2014 total 67 unicompartmental arthroplasty surgeries with use of Oxford knee meniscal bearing were performed. The surgeries were performed by a single surgeon. Minimally invasive approach was used. All patients were evaluated clinically, radiographically and with Oxford Knee score scale, Knee Society score scale and functional scale. Obtained data was processed with nonparametric Mann-Whitney-Wilcoxon test. Results were processed using the statistical analysis application package SPSS, version 10.07. Analysis of of mid-term results showed that the average for Oxford Knee score increased from 16.4 (95% CI 9-23) to 41.3 (95% CI 29-47). Average for Knee Society score scale increased from 42.7 (95% CI 31-55) to 88.6 (95% CI 73-100). No occurrence of early postoperative complications have been reported. Statistically significant improvements of knee function in patients after unicompartmental arthroplasty have been observed. Unicompartmental arthroplasty currently can be considered as an advanced treatment option for medial knee joint pathology. Meniscal bearing cemented prostheses such as Oxford III are preferable.

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.

Meniscal bearing dislocation while rolling over in sleep has never been reported in Oxford unicompartmental knee arthroplasty (UKA). This study reports two cases of meniscal bearing dislocation into the intercondylar ridge while rolling over in sleep. In the case of one patient, closed reduction of the bearing was performed, and the use of a knee brace was effective in preventing re-dislocation. In the second patient, closed reduction was possible; however, bearing dislocation was repeated. Therefore, revision surgery was performed by replacing the tibial component and using a thicker bearing. The common features in dislocation during rolling over while sleeping in both cases were dislocation into the intercondylar ridge, the combination of small femur and AA-size tibia components, and osteonecrosis. As determined by intraoperative testing, valgus position of the knee while rolling over in sleep could induce bearing dislocation into the intercondylar ridge. LEVEL OF EVIDENCE: Retrospective case series, Level IV.

When the Oxford unicompartmental meniscal bearing arthroplasty (UCA) is used in the lateral compartment 10% of the bearings dislocate. A fluoroscopic study was performed to investigate if abnormal mid-sagittal plane kinematics was related to bearing dislocation. Video fluoroscopy is an accepted means of determining in-vivo knee kinematics in the sagittal plane. Video fluoroscopy was obtained of 5 Oxford lateral UCAs 10 years post-operatively and of five normal knees. Patellar tendon angle (PTA), derived from dynamic fluoroscopic images, was used to describe the joint kinematics. This in-vivo experiment demonstrated that the PTA/knee relationship for the Oxford lateral UCA is similar to the normal knee. Both the normal knee ( r 2 =0.99) and the Oxford lateral UCA ( r 2 =0.98) demonstrated a linear relationship between flexion angle and PTA. No significant difference in PTA was found between the normal knee and the Oxford lateral UCA. This study demonstrated normal kinematics, as indicated by PTA, ten years after implantation of the Oxford lateral UCA. It is therefore reasonable to suggest that abnormal kinematics is not a significant factor relating to meniscal bearing dislocation in the lateral compartment.

When the Oxford unicompartmental meniscal bearing arthroplasty is used in the lateral compartment of the knee, 10% of the bearings dislocate. A radiological review was carried out to establish if dislocation was related to surgical technique. The postoperative radiographs of 46 lateral unicompartmental arthroplasties were analysed. Five variables which related to the position and alignment of the components were measured. Dislocations occurred in six knees. Only one of the five variables, the proximal tibial varus angle, had a statistically significant relationship to dislocation. This variable quantifies the height of the lateral joint line. The mean proximal tibial varus angle for knees the bearings of which had dislocated was 9° and for those which had not it was 5°. In both groups it was greater than would be expected in the normal knee (3°). Our study suggests that a high proximal tibial varus angle is associated with dislocation. The surgical technique should be modified to account for this, with care being taken to avoid damage to or over-distraction of the lateral soft tissues.

Unicondylar knee arthroplasty (UKA) has become a popular alternative to total knee arthroplasty or high tibial osteotomy for unicompartmental knee conditions. This study investigated the effects of kinematics and femoral liftoff on the wear of fixed and mobile versions of a UKA design. The fixed bearing had lower wear than the mobile bearing under all conditions. Wear was higher in lateral bearings than medial bearings, indicating that the increased sliding distance laterally had a greater effect than the greater loading medially. Femoral condylar liftoff resulted in increased wear in the medial UKAs but reduced wear in the lateral UKAs for both the bearing designs. The reduced wear rates observed for the fixed UKA bearings highlight the potential for a longer osteolysis-free clinical outcome for these devices.

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.

Total knee arthroplasty (TKA) is considered as a standard procedure for the treatment of the severe degenerative knee joint. The outcomes of TKA have improved over the last few decades because of a better understanding of design features and surgical techniques. Contemporary tibial component designs in TKA can be subdivided into two groups (fixed or mobile-bearing) on the basis of different fundamental principles. The mobile-bearing knee is designed with better biomechanical concepts than the fixed-bearing knee, in terms of providing congruity and mobility of tibial bearing. It is expected that the mobile-bearing knee could resolve the problems of component wear and component loosening as seen in fixed-bearing knees. However, the long-term durability of mobile-bearing knees has not been extensively proven to have better outcomes than that of fixed-bearing knees. There are some potential clinical complications of mobile-bearing knees that must be addressed. On the basis of our previous clinical experience and a retrieval analysis, this article summarizes five specific complications including (1) early or late dislocation of the mobile-bearing component, (2) failure or dislodging of the meniscal bearing, (3) hemarthrosis associated with a failure of the meniscal-bearing knee, (4) failure of the patellar component, and (5) higher prevalence of osteolysis. Before taking advantage of mobile bearing, we should consider these specific clinical complications, which were not found in the fixed-bearing TKA.

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.

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.

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.

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.

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 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.

Anteroposterior (AP) joint translation is an important indicator of good clinical outcome following total knee arthroplasty (TKA). This study evaluated the in vivo relationship between changes in the degree of voluntary soft tissue tension and flexion angle versus simultaneous AP translation after TKA. A posterior cruciate ligament (PCL)-retaining meniscal-bearing design was investigated in 20 knees of 20 patients. AP translation was measured at 30° and 75° flexion with the KT-2000 arthrometer while patients were anesthetized and non-anesthetized. The mean translations at 30° and 75° were 10.5 and 10.4 mm, respectively, in non-anesthetized patients and 13.8 and 12.7 mm, respectively, in patients under anesthesia. AP translation showed a significant positive correlation with soft tissue tension (p

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.

Many mobile-bearing knees have been used since the late seventies. The most widely known include the Oxford (Biomet, USA), the LCS (De Puy), the Rotaglide (Corin), the T.A.C.K. (Link), and the S.A.L. (Protek). The concept of a meniscal-bearing knee appears attractive because it mimics the normal anatomy. With an adequate prosthetic design, the developers of these prostheses intend to achieve better joint kinematics and reduced polyethylene wear. Good midto longterm results have been published with the Oxford1 and LCS knee.2 The results obtained with these implants therefore represent the base line of comparison for other mobile-bearing knees being introduced. In 1992 a new design was developed and called the MBK prosthesis (meniscal-bearing knee, Zimmer, Warsaw, Ind, USA). The concept underlying the design of this prosthesis is to have complete congruency between the femoral component and the polyethylene insert at all degrees of flexion while allowing rotation between polyethylene and the tibial tray. The prosthesis was first implanted in October 1993. This chapter includes a description of the principles, technique, and preliminary results that were obtained with this implant.

The Low Contact Stress (LCS) knee system was introduced in 1977 as an attempt to improve the survivorship and clinical function of total knee replacement. From its outset, the design goals of this mobile bearing knee system were to decrease the prospect of polyethylene material damage, minimize constraint and optimize patient implant kinematics. The gait-congruent LCS design, in its origin, was proposed as a system inclusive of both cruciate-sparing meniscal bearing and PCL-sacrificing rotating platform variants, with the latter gaining the majority of popular usage over time. Both systems employ a dynamic tracking metal-backed rotating patellar component that articulates with the femoral sulcus.

The effect of a meniscal bearing on knee laxity in anterior cruciate ligament-sacrificing total knee arthroplasty was evaluated in 7 cadaver knees using a knee testing device that measured knee flexion angle as well as laxity to medial-lateral, anterior-posterior [AP], and rotational loads. A standard fixed tibial component and mobile tibial components (AP sliding, rotationally sliding, and AP and rotationally sliding) were used to evaluate AP, rotational, and varus-valgus stability and maximal flexion and extension with the neutrally positioned and malrotated tibial tray. The AP movable components increased AP laxity, and the fixed component decreased rotational laxity significantly when compared with the normal knees. The rotationally movable components did not change knee laxities significantly even when the tibial tray was malrotated. No significant difference among the components was detected when the maximal flexion and extension angles were compared in the neutrally positioned tibial tray. Malrotation of the tibial tray decreased the maximal extension angle in the fixed component. This study showed that the rotationally movable component can achieve near-normal laxity regardless of tibial tray rotation, but AP mobility of the bearing produces AP laxity that could lead to implant failure.

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 …

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.

A tribological study of a series of 27 retrieved Accord meniscal bearing knee joints has been carried out. The roughness of the articulating surfaces of the meniscal and the femoral components was investigated, and the penetration into the polyethylene meniscal component was determined. There was generally little damage to the highly polished metallic femoral components. A general polishing and smoothing of the ultra high molecular weight polyethylene meniscal components was observed, although there was some subsequent deterioration of the polyethylene surfaces in certain cases. The penetration rate of the femoral components into the menisci was low, and was found to be similar to that reported for other meniscal knee joints.

The first Ceramic knee implant in a human patient was used by Dr. G. Langer of the Orthopedic Clinic at the University of Jena, Germany in 1972 [1]. In 1980, Drs. Oonishi and Hasegave began using a Alumina femoral component on a polyethylene tibial component [2]. These early attempts all involve the search for solutions to the wear and degradation problems. The application of ceramics was limited by the demand of thin components. In the present feasibility study the in vitro wear behavior of a knee concept with a novel Alumina Matrix Composite (AMC) Ceramic was examined [3,4]. The wear behavior of the Ceramic components for the knee system were tested in accordance to ISO/WD 14243-3 for 5*106 cycles. Six samples were tested. The lubricant was calf serum diluted with deionized water. All tests have been performed with components made of the novel AMC Ceramic. The wear test performed showed an average gravimetric wear rate below 1 mg/1*106 cycles on each of the six components. A change of geometry was not measurable after 5 million cycles. No significant change of the surface structure was detectable with a conventional surface tracer. SEM and AFM pictures show traces of ultra mild abrasive wear at the surface. The performed investigation on the novel knee concept shows the following potential benefits for a Ceramic knee bearing: approx. 500 times lower volumetric wear low risk of tribologically induced failure no PE particle induced osteolysis The novel AMC Ceramic offers a solution to minimize the allergic and wear related problems of knee implants. New concepts on the basis of hard on hard combination are to be realized. The use of knee endo-prosthesis with Ceramic on Ceramic combination is an option for izeroi wear bearings in the knee. These first results motivate to start further R&D on Ceramic on Ceramic bearings for total knee implants.

Ten normal and ten patients with a posterior cruciate retaining meniscal hearing (having two articulating surfaces) TKA performed successive deep knee bends under fluoroscopic surveillance to determine the femorotibial contact positions. The purpose of this study was to analyze the kinematics of the meniscal bearing knee implant under in vivo, weightbearing conditions and to compare the obtained results to the kinematics of the normal knee. The fluoroscopic videos were analyzed using two techniques: (1) digitization and (2) image matching. For reference, a positive position is denoted as anterior and a negative position posterior to the midltne of the tibia. Total knee patients selected, had an excellent dinieal result (Avg. 96.0 New Jersey Knee Score) and had an average follow-up of 54 months. In contrast to normal knees, the femorotibial contact position for the meniseal bearing knee was posterior in full extension, similar to other posterior cruciate retaining designs analyzed using fluoroscopy. At full extension the average initial contact position for the normal and meniscal bearing knee groups was 6.2 (4.8 to 12.0ram), and 4.4 (3.9 to ll.Omm), respectively, ta 60 degrees of knee flexion, the average of the normal knee group rolled back to -5.8 (-2.5 to 13.2mm) and the meniseal hearing group roiled back to -9.2 (-4.0 to 17.0ram). From 60 to 90 degrees, the normal knee group continued to roll back to -7.8 m m (~5.8 to 13.8), but the meniscal bearing group slid in the anterior direction to an average position of -5.0mm (2.0 to 12.0). The normal knee group demonstrated a similar pattern for all subjects, but the meniscal bearing group demonstrated highly variable patterns. All meniscal bearing subjects demonstrated some form of roll back, but some slid anterior more than others. Five of the ten meniscal bearing knees demonstrated movement of the bearings during knee flexion, but the other five meniscaI heating knees had bearings that remained stationary during flexion. On average the meniscal bearing implant demonstrated femorotibial rollback from 0 to 60 degrees of knee flexion, but slid anterior from 60 to 90 degrees of flexion. The meniscal bearing implant is designed to slide in the A/P direction which may account for less wear at the femorotibial interface if the bearing motion occurs.

A comprehensive, interchangeable, low-contact-stress, mobile-bearing knee prosthesis system was developed and used over a 12-year period with both cemented and cementless fixation. Individual components of the system included a bicruciate-retaining meniscal bearing, a posterior cruciate-retaining me

Sixty-seven consecutive Oxford Meniscal total knee arthroplasties (TKAs) were compared prospectively with 66 Kinematic I TKAs. At follow-up examination an average of 5.5 (range, 5-8) years later, 20 (30%) of the Oxford Meniscal TKAs had been revised (nine due to aseptic loosenings, seven to aseptic loosening and patellofemoral syndrome, two to patellofemoral syndrome, one to meniscal bearing dislocation, and one to sepsis) and in 16% one or more of the remaining tibial components was radiographically at risk. Three (5%) Kinematic I TKAs had been reoperated upon (one for anterior dislocation, one for a loose patellar component, and one for sepsis) and no component was considered radiographically at risk. The remaining cases demonstrated good and excellent knee ratings (Oxford, 82 +/- 11; Kinematic I, 88 +/- 6; P less than .01; Hospital for Special Surgery). This study suggests that the results of Kinematic I TKA are superior to those of Oxford Meniscal TKA; that patellofemoral resurfacing is advisable; and that Kinematic I TKA yields 5-year data comparable to those of total hip arthroplasty.

Unicompartmental knee arthroplasty is an attractive concept, but some reports on its use are unfavorable. A meniscal bearing prosthesis has many advantages in this mode of arthroplasty. The authors present preliminary results of 25 unicompartmental knee replacements done with the Oxford Meniscal knee, with a follow-up period of 12-54 months (mean, 21 months). They discuss the scientific basis of unicompartmental knee arthroplasty, which they conclude may be the most appropriate treatment for selected cases of degenerative arthritis of the knee.

The Oxford method of knee arthroplasty replaces the femoral condyles with convex spherical metal components and relines the tibial plateaus with flat metal components. Free meniscal bearings of polyethylene, spherically concave above and flat below, lie between the fixed metal components, held in place by their geometry and ligamentous tension. Advantages of the design include: congruity of the articulating surfaces; unconstrained tibiofemoral movement; preservation of all the ligaments with facility to tension them accurately from a range of bearing thicknesses; minimal bone excision; applicability to unicondylar use. Laboratory studies showed that combined rolling and sliding at meniscofemoral and meniscotibial interfaces mimic normal joint kinematics and mechanics. One hundred twenty-five bicompartmental implants were followed for two to six years. Pain was relieved in 90%; mean flexion limit was 99 degrees and mean flexion deformity 7 degrees. Stability and alignment were recovered in nearly all joints. Six knees failed and were successfully arthrodesed (two) or converted to another prosthesis (four). Eight knees required revision to replace a dislocated bearing (five) or to recement a loose component (three). In knees with an intact anterior cruciate ligament, there were no failures and a low revision rate (4.8%). The prosthesis is proposed as a reliable and safe alternative to more invasive prostheses in rheumatoid and osteoarthritic joints in which the disease is still limited to the articular surfaces.