Detaillierte Beitrags-Information
| Beitragstitel | Metal wear in metal-on-metal total hip arthroplasty is not always caused by the bearing: a case report. |
|---|---|
| Beitragscode | P037 |
| Autoren | |
| Präsentationsform | Poster |
| Themengebiete |
|
| Abstract |
INTRODUCTION Local adverse reaction to metal debris and systemic toxicity of metal ions are common causes of failure after metal-on-metal (MoM) total hip arthroplasty (THA). We report a case with an uncommon mechanical complication with massive metal wear. METHODS A 81-year-old man underwent MoM THA 20 years ago. Only 2 years later, the cup was revised, due to delamination of the titanium mesh, with reconstruction with a reinforcement ring and a cemented metal-polyethylen sandwich cup and a 28 mm metal head. During further follow-up, the treating orthopaedic surgeon documented a migration of the cup, but no additional revision was performed. Finally, the patient was referred due to progressive leg shortening. The cup had migrated cranially and was dislocated, causing an extraarticular impingement. The blood levels of Cr, Co and Ti were increased. RESULTS Transfemoral revision THA was performed. Massive metallosis was present, with solid tumours and viscous fluid. The neck of the stem had a deep posterior notch due to impingement with the metallic inlay. Retrospectively, this could also be identified on the preoperative CT-scan. Reconstruction was performed with acetabular porous tantalum augments, an anti-protrusion ring, a cemented polyethylene cup and an uncemented modular stem. Histology showed massive proliferation of macrophages, due to phagocytosis of metal particles, and necrosis within the solid tumours. Now 6 months postoperatively, the patient showed an unproblematic recovery. Ti blood levels however remain high. DISCUSSION In this case, massive metallosis after MoM THA had an uncommon cause, which might easily be overlooked and thus probably also is underreported. The harder CoCr alloy of the bearing can easily notch into the softer Ti alloy of the stem. In case of cup malposition, component impingement has to be looked for, but was missed preoperatively in this case. A precise analysis of the components with CT-scan could detect critical material defects and might be essential for accurate planning of any revision. Phagocytosis of metal particles by macrophages lead to voluminous tissue reactions, even if the total amount of metal is small. Histology is crucial in revision to identify the reason of failure, both in septic and in aseptic situations. The determination of metal ion blood levels is recommended too, because it can indicate metal wear and as increased levels might also cause systemic toxicity, which has to be identified properly. |