Case Reports

Knee Mass From Severe Metallosis After Failure of a Metal-Backed Patellar Component Total Knee Arthroplasty

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Abstract not available. Introduction provided instead.

Failure of metal-backed patellar components in total knee arthroplasty has previously been reported.1-11 Developments in prosthetic design such as adding a
third peg to the metal baseplate and the use of a mobile-bearing patella have led to lower patellar revision rates.10,11

Bayley and colleagues2,3 reported on the failure of metal-backed patellar components in 25 patients after total knee arthroplasty. Mechanisms of failure included polyethylene wear, fracture, and dissociation.2,3 Wear or dissociation
of the polyethylene from the metal backing, enhanced by abnormal patellofemoral biomechanics or patellar malalignment, is followed by articulation of the patellar
metal backing against the femoral component.1,2,3,5,8 Patellar metallic wear against titanium surfaces causes much more severe abrasion and metallic debris generation in comparison with cobalt-chromium alloys.6,7,12

Over time, the abrasive metallic wear debris leads to synovitis.2,3,12,13 The patients generally experience any of a multitude of symptoms relating to the accompanying
synovitis, including pain, limitation of motion, or crepitus with knee motion. Weissman and colleagues9 introduced the “metal-line sign” as a preoperative aid in
radiographic detection of metal-induced synovitis from failure of the metal-backed patellar components after total knee arthroplasty. Breen14 reported on “titanium lines” as a manifestation of metallosis at the knee in the 3 patients following implantation of titanium tumor prostheses. The radiographic appearance of the titanium lines may mimic soft-tissue tumor recurrence.14

Our case report details a patient referred for a knee mass 9 years after primary total knee arthroplasty with a metal-backed patellar component.


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