Inverted Acetabular Labrum Causes Insufficiency-type Stress Fracture of the Femoral Head: A Biomechanical Study

Purpose: Subchondral insufficiency-type fracture is associated with rapidly progressive osteoarthritis of the hip, but are these fractures caused by a single load event such as an injury from a fall or by stress (fatigue) from repeated loading during the activities of daily life? Our biomechanical study applied repeated loading to a simulated osteoporotic bone model to investigate the relationship between an inverted acetabular labrum and the incidence of subchondral insufficiency-type fracture of the femoral head. Methods: : We performed fatigue load testing on 15 osteoporotic composite femurs, applying 2000 N at 1 Hz, 1 million times or to failure, on 5 composite femurs without silicone rubber and 10 with 10x5 mm silicone rubber. Silicone rubber was inserted as a surrogate for inversion of the acetabular labrum between the acetabulum and femoral head. Results: : No breakage was noted in the 5 specimens without silicone rubber, even after the application of 1 million individual loads at 1 Hz. Fractures appeared in the anterior femoral head in all 10 specimens with 10×5 mm silicone rubber, and mean number of loads to fracture was 6389. Conclusion: Our research selected an osteoporotic bone model to investigate the effects of loading tests that were designed to mimic typical repeated loads in daily activities, using silicone rubber as a surrogate for inversion of the acetabular labrum and resulting in the development of insufficiency-type stress fracture on the femoral head.Concept diagram or graphical abstract