The Thickness of the Medial Wall of the Acetabulum Prevents Acetabular Fracture during the Insertion of a Cementless Cup in Total Hip Arthroplasty: A Biomechanical Study

Intra-operative acetabular fracture is a total hip arthroplasty complication that can occur during cementless cup insertion, especially in osteoporotic patients. We conducted this biomechanical study to investigate the impact resistance of the acetabulum with simulated bones of different density by drop-weight impact testing. Low- and high-density polyurethane foam blocks were used as osteoporotic and healthy bone models, respectively. Polyurethane blocks were used as the acetabular cancellous bone. Composite sheets were used as the acetabulum's medial cortex. The testing revealed that the osteoporotic bone model's impact resistance was significantly lower than that the healthy bone model'. In the healthy bone model, even thin acetabular cancellous bone with > 1 mm acetabulum medial cortex was less likely to fracture. In the osteoporotic bone model, fracture was possible without > 1 mm medial cortex of the acetabulum and thick acetabular cancellous bone. Although impaction resistance differs due to bone quality, the impaction resistance in this osteoporotic bone model was equivalent to that healthy bone model's when a thick medial wall was present. To avoid intra-operative acetabulum fracture, surgeons should consider both the bone quality and the thicknesses of the medial cortex and acetabular cancellous bone.