The effect of joint loading on acetabular wear measurement in total hip arthroplasty

All radiographic calculations of acetabular wear assume concentric reductio n of the prosthetic articulation. To date, no studies have shown thar the f emoral head is fully reduced on standard radiographs, and we have seen case s on early postoperative radiographs in which this assumption is not met. U sing our computerized radiographic technique, 78 paired anteroposterior pel vic radiographs in 46 patients at a mean of 14 months after surgery (range, 1-92 months) were evaluated with and without joint loading. Displacement w ith loading was analyzed against time since surgery, a surrogate for acetab ular wear. Regression analysis found a statistically significant increase i n femoral head displacement after loading with longer duration of follow-up , but the rate of this increase was small (0.027 mm/y). This difference aff ects calculated wear values by <15%, We conclude that in a low-wear cohort, joint loading does not affect radiographic calculations of acetabular poly ethylene wear in a clinically important way.