Morrey, Bernard F MD
Hip instability remains a costly complication of primary (3%) and revision (10%) procedures. In those with well-oriented components, instability may be anticipated in about 70% from advancement of the trochanter. Articular reorientation readily is affected by the use of modular cups with elevated rims. This has proven to be an effective strategy both to lessen the likelihood of an initial dislocation after both primary and revision procedures. It has also proven to be an effective strategy to treat the unstable implant, especially if cup orientation has been defined as the primary problem. Larger head sizes in the range of low-friction arthroplasty, such as 32 mm, are not any more stable than 22-mm diameter implants. Anatomic-sized heads as used in bipolar devices are effective in treating established instability in up to 90% of instances. The most popular current option is that of the constrained head/cup articulation. Good short-term results have revealed success in more than 90%. However, the effectiveness is design dependent, and the long-term effectiveness understandably is questioned as reports of mechanical failure begin to emerge.
Clinical Orthopaedics & Related Research. (429):94-101, December 2004.