Improving the Accuracy of Acetabular Component Orientation: Avoiding Malpositioning

Abstract

Many factors such as poor visualization, greater patient size, inaccuracies of mechanical guides, and changes in patient positioning during surgery can negatively impact acetabular component positioning1. Improper orientation contributes to an increased dislocation rate, limb-length discrepancy, component impingement, bearing surface wear, and revision surgery. Acetabular malpositioning also contributes to altered hip biomechanics, pelvic osteolysis, and acetabular component migration2-8. Despite the established definitions of acetabular safe zones, a recent analysis of United States Medicare total hip arthroplasty data revealed dislocation rates during the first six postoperative months to be 3.9% for primary arthroplasty and 14.4% for revision arthroplasty9. A recent report cited instability and dislocation as accounting for 22.5% of revision cases10. The use of larger femoral head sizes in primary total hip arthroplasty has increased dramatically in recent years with the introduction of alternative bearings and has reduced the short-term dislocation rate by almost one-half from 1998 to 2007 (from 4.21% to 2.14%)11. Dislocation rates have been lowered by increasing the femoral head-neck ratio, decreasing component impingement, increasing the range of hip motion until impingement, and increasing the jump distance when component impingement does occur12,13. Nevertheless, larger femoral heads are not a substitute for proper component placement and precise component orientation; inaccurate component positioning may be associated with alteration in soft-tissue tension and hip biomechanics leading to abnormal gait, trochanteric bursitis, and increased discomfort during walking. All total hip arthroplasty bearing couplings are intolerant of component malpositioning or variation in component positioning; specifically, they are intolerant of excessive lateral opening and anteversion—and implant survivorship and complications are directly related to component positioning8,14. Kurtz et al. forecast that the number of primary and revision hip arthroplasties will significantly increase over the …