Abstract
Introduction Femoral offset is the perpendicular distance from the centre line of the femur to the centre of rotation of the femoral head. In total hip replacement this is important for maintaining the correct leg length and creating a stable hip with well balanced soft tissues.
We studied the effect of hip rotation on the measurement of femoral offset and its subsequent effect on choice of femoral stem.
Method A series of saw-bone models labelled with radio-opaque markers was prepared. Serial x-rays were taken as each model was rotated though +15° internal rotation, 0°, −15° and −30° external rotation. At 0° the model was in the anatomical position. The resultant offset was measured from each x-ray.
Results Offset was significantly different when measured at different angles of rotation (p< 0.0001 Fried-man 2-way analysis of variances). Offset was greatest when measured at +15°. The greatest difference was encountered at −30° (up to 14mm). For the Exeter hip system this could lead to the selection of a stem 2 sizes too small. Even between 0° and −15°, where rotation is not readily identified on x-ray, differences of up to 7mm were found, which could still lead to the selection of an incorrect stem.
The abstracts were prepared by Secretary Mr K Trimble.
