Accuracy of cut-off acetabular reamers for minimally invasive THA

Cut-off reamers have been introduced for minimally invasive hip replacement to make reamer insertion through the small incision easier. However, the accuracy of cut-off reamers in comparison to traditional hemispherical reamers has not been documented. We reamed four human cadaveric hips using a cut-off reamer and three hips using a standard reamer. We started with smallest size reamer to remove subchondral bone, and the size was progressively increased until breaching the acetabular floor. We performed computed tomography scans for each reamer size to digitally determine the true dimensions and sphericity of the reamed acetabula. The cut-off reamers breached the acetabulum at a smaller size than with a standard reamer in two specimens, and at the same size as the standard reamer in one specimen. The accuracy of each reamer size was determined by quantifying the percentage of the reamed acetabular surface that was within 0.5 mm of the hemispherical reamer size. The average accuracy of the cut-off reamers was 70% compared with 81% for the standard reamers. The cut-off acetabular reamers showed a trend toward decreased accuracy that may be attributable to a tendency of the reamer to wobble in use.