The reliability of radiographic assessment of femoral neck-shaft and implant angulation in hip resurfacing arthroplasty.

Fifteen sets of patient radiographs were analyzed by 3 different observers on 2 occasions. Each observer measured the femoral neck-shaft angles (NSAs) of the preoperative digital radiographs and stem-shaft angles (SSAs) of the postoperative radiographs. The effect of femur position on SSA measured by digital radiographs was also investigated using a resurfaced synthetic femur. Radiographs were taken with the synthetic specimen positioned in 10 degrees increments of either flexion or rotation. Measurement by digital radiographs proved less than optimal in assessing preoperative NSA but was better in assessing the postoperative component SSA. External rotation of 30 degrees and flexion of 40 degrees resulted in a clinically significant disparity in SSA measurements. Patient malposition during radiographic imaging can contribute to erroneous NSA and SSA results.