Sciatic nerve palsy is a troublesome complication of total hip arthroplasty, and may be caused by direct injury or over-traction at the time of the operation. We investigated the effects of over-traction on the blood flow of the sciatic nerve by placing the hip and knee joints in various positions. Twenty hip joints of 10 adult dogs were examined. Using a posterior surgical approach, the sciatic nerve was exposed and a site 1 cm distal to the greater trochanter was selected for blood-flow measurement. The blood-flow was measured using a Laser Doppler Flowmetry, with the hip and knee joints at various positions. Blood flow decreased as flexion angle increased and internal rotation angle of the hip joint increased, and decreased with as flexion angle of the knee joint decreased.

When we positioned the hip joint at 160 degrees of flexion and 30 degrees of internal rotation and the knee joint at 0 degrees of flexion, we found that the mean blood-flow decreased by 69% from the value measured when the hip joint was at 90 degrees of flexion and the knee joint was 90 degrees of flexion. When knee flexion was 90 degrees there was no significant difference in average blood flow between 30 degrees of internal rotation of the hip and 0 degrees internal rotation. When knee flexion was 0 degrees there was a significant difference in average blood flow between 30 degrees of internal rotation of the hip and 0 degrees of internal rotation.

Our results suggest that surgeons should pay attention to extension of the knee and the flexion and internal rotation positions of the hip to prevent sciatic nerve palsy as a complication of total hip arthroplasty