Femoral head measurement in hemiarthroplasty: assessment of interobserver error using 3 measuring systems.

We have assessed the consistency of measurement of femoral head circumference using 3 standard measuring instruments used in hemiarthroplasty of the hip. Fifty femoral heads were independently sized by ten independent observers using a caliper, a half circular measuring template, each allowing measurement to the nearest millimeter. We found significantly greater variance of the results using the half-circular templates (p=0.001) and the calipers (p=0. 011) compared with the full circular measuring templates. Measurement with calipers underestimated femoral head size by 0.72 mm compared with full circular measuring templates (p=0.02). Insertion of an undersized hemiarthroplasty head is a cause of increased point loading of the acetabulum and may result in increased rates of acetabular erosion. The use of full circular measurement templates is recommended as the most consistent method for head sizing in hemiarthroplasty of the hip.