How Good is the Evidence Linking Acetabular Dysplasia to Osteoarthritis?

BACKGROUND: A common claim in the orthopaedic literature is that acetabular dysplasia (AD) exists when the center-edge angle of Wiberg (CE angle) is <20 degrees and that AD leads to osteoarthritis (OA). Our purpose is to evaluate the validity of the linkage between AD and OA.
METHODS: We assess and discuss the theories and the empirical evidence relating AD to OA. Moreover, we test the rule that hips with a CE angle <20 degrees will develop OA by 65 years of age, by looking for exceptions to this rule.
RESULTS: Wiberg and Cooperman and colleagues present 30 ideal patients for assessing the relationship between AD and OA. Each was arthritis free, with stable AD, CE angle <20 degrees, without signs of subluxation. They were all followed and all developed OA. In the studies by Stulberg and colleagues, and Jacobsen and colleagues, every patient presented with OA, making it difficult to be certain about the appearance of the hip before the onset of OA. In the study by Murphy and colleagues, we have the same problem, as an unknown number of patients already had OA at first assessment. All of these studies used different schemes for diagnosing OA, making the studies difficult to compare. Most of the patients in the studies were of Northern European ancestry, making the results difficult to generalize to other populations. Four patients had CE angles <20 degrees and did not develop severe arthritis by 65 years of age.
CONCLUSIONS: Our conclusions apply directly to patients of Northern European ancestry. A few patients with stable, mild AD (CE angle 15 to 19 degrees) will be arthritis free at 65 years of age. Almost all patients with stable AD develop OA by 65 years of age. Unstable AD (CE angle <20 degrees, with subluxation) always leads to OA by 65 years of age. It is probably reasonable to extend these conclusions to other populations, but the reader must be prepared to re-evaluate them, as more data accumulates.