Leg Length Discrepancy After Hip Replacement

Hip replacement surgery is performed as a treatment for severe arthritis of the hip joint. During a hip replacement surgery, the ball and socket of the joint are replaced with an artificial implant, commonly made of metal and plastic. After hip replacement surgery, some patients notice one leg may be longer than the other, most commonly the leg that had surgery. Why are leg lengths sometimes different after surgery?

When a hip replacement surgery is performed, the hip joint is surgically opened. The top of the thigh bone (femur) is removed, and the socket of the pelvis is shaped. A metal cup is placed in the opened up socket, and a ball is placed on top of the thigh bone. It is important that the new ball-and-socket are stable, meaning they will not dislocate or come out of position. In order to prevent dislocation, your surgeon may adjust the tension between the ball and socket by placing larger or longer implants in the bone.

There are some surgical techniques that may lower the chance for developing a significant leg length discrepancy. With some surgical approaches, such as anterior hip replacement, surgeons may feel more comfortable restoring leg length, without having to worry about dislocation risk. In addition, surgical navigation and robotic assisted joint replacement are techniques that some surgeons are using to restore symmetric leg lengths.

Exactly how the hip replacement implants are placed, and the size of the implants will determine the length of the leg after surgery. If the hip is felt to be too loose, or unstable and prone to hip dislocation, your surgeon may elect to place larger or longer implants in the joint. The downside of placing these larger implants is lengthening of the limb. Ideally, your surgeon wants the leg lengths to end up being symmetric, but that is not always the final result.

To prevent a postoperative leg length discrepancy, your surgeon will template x-rays of your hip with overlay schematics of the hip replacement prosthesis. By doing so, your surgeon can determine the expected size of implant needed at the time of surgery, and how much bone to remove during the procedure. In addition, some doctors are now using computer-guided systems to help confirm position and size of the hip replacement implants. Computer-guided surgery is the operating room equivalent to a GPS system, showing your anatomy on a screen to help guide positioning of the implants.

When leg lengths are unequal, patients may experience increased pain and muscle fatigue. When the leg length is increased by more than a few centimeters, the nerves of the leg may become stretched to the point that patients experience numbness or pain further down the limb.

Interestingly, many people with severe degenerative arthritis of their hip joint develop a leg length discrepancy over time. Prior to undergoing hip replacement, it is not uncommon for people to have a leg length discrepancy as a result of cartilage and bone wearing away from the hip joint. When total hip replacement is performed, your surgeon may correct this deformity, leading to the sensation that the leg lengths are now asymmetric, when in fact they have been corrected. When this type of discrepancy is the case, most people gradually adapt to their new leg length.

Your surgeon can help you understand why your leg lengths are different. In some cases, a leg length difference may have been anticipated, and in others, unexpected. The usual treatment of a small leg length discrepancy is with a lift in the shoe of the shorter leg. If the discrepancy is more than about 2 centimeters, then a build-up of the sole of the shoe may be necessary.

In larger leg length discrepancies, surgery may be considered to re-size the implants or remove additional bone, but that is usually undertaken only in individuals severely affected. It is important to note that differences in leg length have not been shown to affect how long the hip replacement will last.

Leg length discrepancy following total hip replacement surgery is a possible complication of the surgical procedure. Most often, subtle leg length discrepancies are well tolerated and people can adapt to these differences.  In some situations, a more significant leg length discrepancy will not be well tolerated. In these situations there are ways to adapt footwear to help accommodate for the difference. If that is not well tolerated, there may be surgical options to correct a more severe leg length discrepancy. Some new surgical techniques are aimed to prevent this possible complication.