Lengthening up to 5mm is typical as lost cartilage is replaced. Patients will accommodate to lengthening up to 1 cm by pelvic tilt within 6 months after surgery. Lengthening greater than this is only rarely possible in certain cases of deformity.

Significant leg lengthening is defined as increasing the length of the leg more than 1 cm (3/8 inch) in surgery. This occurs in about 5% of stemmed THR. Most patients accommodate well to such minor changes in length. 1 cm is only 1% of the length of the leg. The pelvis is designed to shift and tilt over 2 cm from side to side to make up for minor leg length differences. No person is born with exactly equal leg lengths. In a study of healthy military recruits it was found that 25% have a difference of over 1cm from side to side.

There is no scientific evidence that a difference in leg lengths causes problems in other joints including in the back. Nevertheless chiropractors and physical therapist are prone to diagnose misalignment and prescribe lifts. There is no scientific basis for this. Just as there was no scientific basis for all the braces orthopedic surgeons historically used to prescribe kids with various deformities. It kind of made sense so it was done- but it has been largely abandoned by our profession because evidence of its ineffectiveness has accumulated.

Occasionally the length of a leg is inadvertently lengthened during standard stemmed total hip replacement surgery, especially in a patient with loose ligaments. Often the surgeon plans to slightly (<1cm) lengthen the leg to increase tissue tension and thereby reduce the chance of dislocation in a small bearing total hip replacement. If length is increased by more than 2 cm beyond the opposite leg, patients will often not accommodate to it with time and find it unpleasant. But it will not hurt other joints. The solution is to wear a 1cm (3/8) lift inside the opposite shoe. This does not affect appearance; other people cannot notice this. If more than 1 cm lengthening is required, the buildup is first put on the shoe, and then additional amount is placed on the sole if necessary.

With hip resurfacing it is only rarely possible to increase the leg length even if the surgeon tries to do it. This is because we are only cutting away a small layer of bone and replacing it with metal on both sides of the joint. Usually the leg is lengthened 0-0.5cm because lost cartilage is replaced. In certain cases of bone deformity length may be increased slightly more as the deformity is corrected. In patients who have a major leg length discrepancy, this cannot be corrected with resurfacing, but may be correctable with a stemmed total hip replacement. The patient must then decide what is more important to them, gaining up to 2 cm in length (THR), or preserving the top of the femur (HRA). We are unable to shorten the leg with either operation, because hip instability may develop.

Before surgery, with an arthritic hip most people have slight shortening due to loss of cartilage or bone. It is not uncommon for people to feel major shortening or even lengthening has occurred because of the arthritis. This sensation can be caused by pelvic tit associated with an arthritic hip. Sometimes this tilt is toward the hip and sometimes it is away. True change in length can be measured on the x-ray. On the other hand, measuring a patient’s leg length lying or standing is completely unreliable. After surgery, for up to 6 months, pelvic tilt as a response to the trauma of surgery can also occur. This can give the patient a false sense that major length change has occurred. The x-ray will again help the patient understand that this has not occurred. This sensation usually resolves by 6 months after surgery.