CT-based Implant Motion Analysis for diagnosing loosening of megaprostheses

Megaprostheses are commonly used in patients with primary bone tumours or metastases. The identification of loosening of megaprostheses in these patients using conventional radiography can be difficult. The use of CT-based Implant Motion Analysis (IMA) has been shown to identify loosening of conventional hip prostheses with great accuracy. The aim of this study was to investigate the accuracy of its use in the identification of loosening of the components of megaprostheses. This was a retrospective, observational study in which we analyzed its efficacy for the investigation of loosening in 12 patients who underwent 13 IMA examinations, and compared the results with subsequent perioperative findings. A total of ten IMA examinations in nine patients were positive, and loosening was subsequently verified at operation in eight patients. The positive predictive value of the method was 90% and the negative predictive value was 100%. The sensitivity was 100% and the specificity was 75%. We recommend the use of this method in the investigation and diagnosis of patients with a megaprosthesis with symptoms suggestive of loosening, and in the preoperative planning of revision surgery.