Restoration of Leg Length, Offset, and Center of Rotation in Total Hip Replacement

Background:

Leg length inequality following total hip replacement is the leading cause of patient dissatisfaction and subsequent litigation after total hip replacement. A change in the total offset of the hip (lateral translation of the femur relative to the pelvis) may also cause significant discomfort and hip instability. Before surgery, patients are informed that their leg may be lengthened and a shoe lift may be required in the opposite shoe to equalize the leg lengths. Although much less frequent, the leg can accidentally be shortened following total hip replacement. In one recent study, 62% of patients had a mean leg lengthening of 9 mm and one third of these patients complained about this lengthening.

Limb length inequality can occur for two reasons. First, significant inaccuracies exist in current leg length measurement techniques. Second, the surgeon may deliberately lengthen a patient in order to gain hip stability. Increasing leg length and/or hip offset decreases the occurrence of bony impingement and increases myofascial tension, both of which improve hip stability and prevent hip dislocation.

Current methods of determining leg length and offset during surgery include pre-operative templating, intra-operative measurements, intra-operative x-rays, and computer navigated surgery. From the pre-operative x-rays, surgeons typically determine which size implant will best fit the patient's anatomy and best recreate the same leg length. During surgery, surgeons may attempt to palpate both the operative and the contra-lateral knee and/or ankle to estimate leg lengths. Surgeons may measure the length of the femoral head and neck that were removed and the length of the femoral head and neck that were replaced. Surgeons may insert a long pin into the pelvis (typically the ilium bone) and measure the length from this pin to some reference point on the femur. This pin in the pelvis method is probably considered the most accurate, but the leg must be repositioned in exactly the same position for the measurement to be accurate; 5° of hip abduction results in an 8 mm error in leg length.3 An intra-operative x-ray that shows both hips can also help estimate leg length and hip offset. Surgical navigation can determine leg length but is not widely availability and requires a significant financial commitment by an institution. Surgeons typically determine the appropriate amount of hip offset from their pre-operative templating. Current leg length guides have shown even greater errors in their attempts to measure hip offset.

Hypothesis: