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Saturday, March 13, 2004

Hyperflexion primary cause for late dislocations in THA

By Mary Ann Porucznik

Dislocation following total hip arthroplasty (THA) can be a formidable problem, regardless of when it occurs. Researchers for Poster Exhibit P088 contend that most late dislocations are due to hyperflexion and should be treated with closed manipulation and/or surgical intervention for persistant instability.

Reseachers initially identified 92 patients from a single institution who had a dislocation after primary THA between 1972 and 2000. In 13 patients, the dislocation occurred late-between 2 and 17 years after the primary procedure. The posterolateral approach to THA had been used with all patients, and the average age of the patients at dislocation was 63 years. The femoral component used in 10 patients (77 percent) had a 28-mm head; two patients (15 percent) needed components with 32-mm heads, and one patient (8 percent) had a component with a 22-mm head.

Investigators reviewed the etiology, epidemiological factors and management of these 13 patients with late dislocations. Radiographs and surgical observation were used to establish component positioning. The average follow-up was 56 months after the first dislocation (range: 28 months to 22 years). All dislocations were posterior.

The primary mechanism of dislocation was hyperflexion (10 patients). Other mechanisms included trauma, liner dislocation from the acetabular component and turning in bed. The two primary treatment options were closed reduction (seven hips, or 54 percent) and surgery to address the instability (six hips, or 46 percent). Intraoperative findings included femoral loosening, polyethylene wear, a dislocated liner and soft-tissue laxity.

Based on this data, researchers concluded that hyperflexion is the underlying cause for most late dislocations after primary THA. Gradual stretching of the periprosthetic soft tissues may play a role in eventual dislocation, but implant malposition is not a factor.

Investigators recommend closed reduction and bracing as initial management for late reductions. Surgically correctable causes such as component loosening and polyethylene wear also should be considered.

The research team consisted of Conjeevaram Maheshwer, MD, of West Lake, Ohio; Mihar Patel, MD, of New York City; and Hoang Bang and Victor Goldberg, MD, of Cleveland.

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Last modified 01/March/2004