What is the Evidence to Support Acetabular Dysplasia as a Cause of Osteoarthritis?

The term "acetabular dysplasia" suggests a smaller than normal acetabulum or one that is abnormally vertical. Acetabular dysplasia has been linked to the development of hip osteoarthritis over the last 90 years in 3 ways. First, it has been linked through the concept that biomechanical forces can cause osteoarthritis. A smaller than normal acetabulum will result in a smaller than normal contact surface between the femoral head and the acetabulum. This will generate increased pressure per unit of area, which will precipitate articular cartilage failure when the pressure reaches a critical point. Osteoarthritis will ensue in response to this cartilage failure. A more vertical than normal acetabulum will be associated with increased shear. When that shear reaches a critical level, articular cartilage will fail, leading that to osteoarthritis. This critical level, for a small or a steep acetabulum, may differ between individuals, based on their biology and their life styles. Second, it has been linked by multiple empirical studies. One of these is Wiberg's 1939 thesis entitled "Studies on Dysplastic Acetabula and Congenital Subluxation of the Hip Joint with Special reference to the Complication of Osteoarthritis." It is among the most quoted and most powerful works in the Orthopaedic literature connecting a disease entity with an antecedent. Third, the linkage is reenforced by an absence of glaring exceptions to the hypothesis that acetabular dysplasia causes osteoarthritis. Orthopaedic surgeons just do not report on dysplastic hips in the arthritis-free elderly. The inability of the Orthopaedic community to identify even 1 elderly, arthritis-free individual with significant hip dysplasia should not carry weight in establishing the concept that acetabular dysplasia causes osteoarthritis. However, the longer this case report goes unpublished, the more certain orthopaedic surgeons will be that the 2 are linked.