Implant failure after biodegradable screw fixation in osteochondritis dissecans of the knee in skeletally immature patients.

PURPOSE The primary purpose of this study was to retrospectively assess the incidence of bioabsorbable screw failure in skeletally immature patients treated for osteochondritis dissecans (OCD) of the knee. The second purpose was to assess implant degradation, focusing on differential breakdown of the intraosseous and extraosseous parts of the screw on magnetic resonance imaging (MRI). METHODS In this retrospective study, 24 patients (30 knees) with MRI-confirmed OCD were treated with a total of 61 biodegradable screws and followed up for a minimum of 2 years or until the onset of new symptoms. MRI scans were performed every 6 months to assess differences in signal intensity between the head and body of the screw. The angle between the surface of the head and the body of the screw was measured, with an angle greater than 90° interpreted as indicating a broken screw (i.e., failed implant). RESULTS Seven screws (all 2.7 mm, 11.5% of all screws) in 5 patients were considered broken screws. The implant failed completely in an additional 4 patients with breakage of 7 of 9 screws; 3 patients were considered late failures, occurring after more than 6 months. Altogether, 14 of a total of 61 screws (23%) were broken. CONCLUSIONS Screw breakage is a surprisingly frequent cause of failure in resorbable OCD fixation in skeletally immature patients. MRI data showed differential decomposition of the screw within and outside of bone as a possible cause. LEVEL OF EVIDENCE Level IV, therapeutic case series.