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@#Dislocation of meniscal bearing insert is a rare but wellrecognised 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.
RESUMEN
PURPOSE: The purpose of this study was to compare the results of posterior cruciate ligament retention and sacrificed total knee arthroplasties with mobile bearing design. MATERIALS AND METHODS: Between January 1992 and October 1997, the study consisted of two types of low contact stress(LCS) implants: a meniscal bearing implant(Group I) that retained the posterior crucaiate ligament(n=31), and a rotating platform implant(Group II) requiring sacrifice of this ligament(n=25). All patients were evaluated with pre-and postoperative range of motion and HSS(Hospital for Special Surgery)knee rating system and radiographic analysis at least five years following the knee replacement. RESULTS: The average active range of knee motion was 4 degrees-113 degrees (Group I), 5 degrees-109 degrees (Group II) preoperatively and 0 degrees-127 degrees (Group I), 0 degrees-118 degrees (Group II) at the final follow-up evaluation. The average HSS score was 61.7(Group I), 56.0(Group II) preoperatively and 90.1(Group I), 88.2(Group II) at the final follow-up evaluation. In group I, one patellar revision for patellar polyethylene breakage and one meniscal bearing change for medial meniscal bearing wear had been performed. In group II, one revision for infection and one rotating platform change had been performed for posterior instability during flexion. we had no dislocation of mobile bearing prosthesis, but 2 cases was required reoperation because of one traumatic periprosthetic fracture(Group 1) and one post. instability(Group 2). There was no significant progressive periprosthetic osteolysis on last follow-up radiographs in both groups. CONCLUSION: After five to ten years of follow-up, we found no signigicant difference between group I and II. However, it might be that subjective symptom is excellent in group I and surgical technique remains an important element of success with mobile bearing implants regardless of posterior cruciate ligament.
RESUMEN
PURPOSE: The mobile bearing, low contact stress, total knee replacement arthroplasty has proven successful with a high long-term survival rate and a low complication rate. Over 1,200 LCS knee has been successful with 97% survival. MATERIALS AND METHODS: However, we found fifteen knees showing early failure of mobile meniscal bearings with fracture, dislocation, and early wear, in some cases within three years. This caused the knee to subluxate and the bearings to dislocate. All fifteen knees had good surgical results with high HSS scores, normal valgus alignment, adequate sizing of the implants, lack of changes in the prosthese/bone interface as evidenced by the x-rays, and good ligament balancing. RESULTS: The reasons of the failure were: 1. Proportionately overweight patients. 2. Probable poor polyethylene quality due to air gamma radiation sterilization of the implant. 3. Overuse by the patients, causing undue load on the polyethylene. All patients with meniscal bearing failure had undergone revision surgery with good surgical results. CONCLUSIONS: We feel this merits further study to determine the relationship between the load and size of polyethylene mass in the rate of wear. While there are studies in the importance of thickness in relation to wear, we found no study on the effect that load has on the mass of polyethylene. We recommend a larger polyethylene tibial implant and rotating platform prostheses be used for an overweight patient and/or patient with high level of activity, both of which forecast a high load on the implant.