Locking Mechanism Failure after Distal Femoral Reconstruction with Modular Universal Tumor and Revision System (MUTARS) Tumor Prosthesis / 대한정형외과학회잡지

PURPOSE: We have used Modular Universal Tumor and Revision System (MUTARS) tumor prosthesis to reconstruct segmental resection defect of the distal femur. The purpose of this study was to evaluate the incidence and pattern of locking mechanism breakage and its correlation with other clinical variables. MATERIALS AND METHODS: We retrospectively reviewed 94 patients who were followed-up for more than one year after tumor prosthesis replacement (MUTARS) between 2008 and 2013. We examined the incidence and timing of locking mechanism (PEEK-OPTIMA) failure. We also evaluated the clinical characteristics of patients experiencing locking mechanism failure and compared them with those of other patients. RESULTS: At a mean follow-up of 55 months, we observed locking mechanism failure in 10 of 94 patients (10.6%). The mean age of patients with locking mechanism failure was 29 years (range, 13-54 years); the mean weight and height were 169 cm (range, 151-181 cm) and 67 kg (range, 53-89 kg), respectively. The mean body mass index was 23.5 kg/m² (range, 20.5-29.4 kg/m²). The median time interval between replacement and locking mechanism failure was 26.5 months (range, 12-72 months). The mean body weight of patients with failure was higher than that of patients without failure (p=0.019). CONCLUSION: The incidence of locking mechanism (PEEK-OPTIMA) failure after distal femoral reconstruction with MUTARS was 11%, and there was a correlation between failure and body weight of patients. Advancements in the design and material of locking mechanisms are warranted to reduce the complication.

Late dissociation of the polyethylene liner from a modular acetabular metal shell after primary total hip arthroplasty: a report of five cases

Modular designs of hip prostheses have become popular recently. Along with complications inherent in all hip arthroplasty systems, modular systems have the additional potential for dissociation of components. Five male patients underwent total hip arthroplasties, in which all of the acetabular components were Harris-Galante II porous acetabular cups. Many years after the operation, the polyethylene liners were dissociated without any previous trauma or dislocation of the femoral heads, these dissociations and dislodgements were managed with open reduction. This complication can be predicted from clinical symptoms and signs. Roentgenograms must be taken and carefully compared to previous roentgenograms. We postulated two causes for the dissociation. First, the polyethylene liner was not fixed securely within the acetabular metal shell at the time of operation. Second, the locking mechanism of the acetabular metal shell was not strong enough to firmly hold the polyethylene liner within the acetabular metal shell. It does warrant that certain precautions must be taken when implanting modular components. The locking mechanism of the harris-Galante II porous acetabular component is mechanically weak and fails easily, therefore its design must be improved in an attempt to prevent postoperative dissociation of the polyethylene liner.