Review Question - QID 3335

The incidence of dislocation is highest in the first year after arthroplasty and then continues at a relatively constant rate for the life of the arthroplasty. At risk positions are based on component positioning and surgical approach. Post-operative hip instability can be caused by several factors including soft tissue imbalance, component malposition, and limb position.

Hip extension and external rotation put the hip at risk for anterior dislocation following an anterior approach. Hip flexion and internal rotation put the hip at risk for posterior dislocation following a posterior approach.

Soong et al review the common etiologies for hip dislocations following primary THA which can be divided into both patient and surgical factors. Patient factors include: neuromuscular and cognitive disorders, patient non-compliance, and previous hip surgery. Surgical factors include: soft-tissue tension, component positioning, impingement, head size, acetabular liner profile, and surgeon experience.

Mahoney et al also divides dislocation risks into patient and surgical factors. Critical factors under surgeon control include component orientation and restoration of soft-tissue tension. Prosthetic factors lowering the risk of dislocation include increasing femoral head size, maximizing the head neck ratio, and optimizing the placement of the acetabular component.