Fracture of an alumina femoral head used in ceramic-on-ceramic total hip arthroplasty.

A case report regarding the fracture of an alumina ceramic femoral head used in ceramic-on-ceramic total hip arthroplasty is presented. The patient, who was seen in the emergency room with pain, grinding, and instability in the hip immediately after a slip-without-fall event, also reported having fallen from a height of 8 ft 6 months earlier. Characterization of the alumina fracture surfaces by light and scanning electron microscopy suggests that the previous fall may have favored the nucleation and growth of subcritical cracks in the ceramic, which lead to fracture during the slip-without-fall event. The case report addresses the significance of impact trauma on the structural integrity of ceramic materials, which should not be ignored by patient or physician regardless of perceived severity.

Early failure of bioabsorbable anterior cervical fusion plates: case report and failure analysis.

STUDY DESIGN: Case report with forensic failure analysis. OBJECTIVE: To determine the failure modes of 3 explanted 70:30 PLDLA Mystique (Medtronic Sofamor Danek, Memphis, TN) graft containment plates retrieved from revision surgery for early device failure. SUMMARY OF BACKGROUND DATA: To reduce the problems of stress-shielding and radiopacity associated with metallic systems, bioabsorbable polymers have been used in anterior cervical discectomy and fusion procedures. Degradation of mechanical properties in vivo is a major concern when using bioabsorbable systems. Three of 6 patients who underwent anterior cervical discectomy with instrumented fusion, using Mystique graft containment systems experienced early failure requiring revision to alternate hardware. METHODS: Devices were retrieved after failure and analyzed by light microscopy and environmental scanning electron microscopy. Simulations were performed with an unused plating system to induce damage for comparison with the retrieved devices. A detailed case review was performed to identify possible sources of extraordinary loading or damage. RESULTS: One plating system failed at 6 weeks postimplantation due to fatigue fracture of the screws. Crack initiation sites were identified at the interface of the thread root and mold line of the screw. Another plating system failed at 16 weeks postimplantation due to the coalescence of radial microcracking between holes in the plate, leading to catastrophic failure of the plate. The final plating system failed during the implantation surgery, when the screw fractured in torsion. CONCLUSIONS: Stress concentrations at the screw head-shaft interface and thread-shaft interface reduce the fatigue performance of bioabsorbable screws. Hydrolysis of the polymer may also play a role in the reduction of resistance to crack initiation and propagation.