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Saturday, March 13, 2004

Instability presents early in mobile-bearing TKA

By Jeannie Glickson

With mobile-bearing total knee arthroplasty (TKA), instability may present as either painful coronal plane instability accompanied by painful effusions or frank subluxation, dislocation, or fracture of the polyethylene-bearing elements. Researchers for Poster Exhibit P100 examined a series of 25 cases of postoperative instability following mobile-bearing TKA. Both menisical-bearing and rotating-platform implants were invoolved.

Between December 1987 and January 2002, 25 cases of clinical instability following mobile-bearing TKA with meniscal bearings or rotating platforms were brought to a single institution for evaluation. Researchers retrospectively identified these cases and reviewed all available charts and subsequent operative notes. The TKAs were performed at outside institutions by various surgeons.

Researchers were able to evaluate radiographs taken at the initial evaluation and at subsequent visits when appropriate. Stress radiographs were available in some cases to provide additional information. All clinical examinations were performed by the authors. Nine patients who had revision surgery at the same institution were also examined while under anesthesia, and the operative findings were available for review.

All 25 cases had clinical evidence of severe coronal plane instability and pain. Eight cases had polyethylene dislocation or subluxation evident both on radiographics and clinically. Four cases had extensor mechanism dysfunction or frank patellofemoral instability. Additionally, researchers identified one proximal tibial stress fracture that was secondary to severe coronal plane instability.

Patients began to experience symptoms at a mean of 9.2 months (standard deviation: 21.29 months; range 0-92 months) after the index procedure. In 18 cases, symptoms were evident immediately after the operation. Twenty-three of the 25 cases had symptoms within two years postoperatively.

The researchers found that instability in mobile-bearing TKA commonly presents within the early postoperative period. As a result, any potential long-term benefits of design innovations must be balanced with known problems that lead to these early failures.

Researchers included Joseph T. Moskal, MD, of Roanoke, Va., and Stephen R. Ridgeway, MD, of Greenville, S.C.

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Last modified 01/March/2004