Performing Hip Replacement SurgeryWhen 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.
Leg Length DiscrepancyExactly 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 post-operative 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 experiences numbness or pain further down the limb.
What To Do When Leg Lengths Are DifferentYour 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.
Clark CR, et al. "Leg-Length Discrepancy After Total Hip Arthroplasty" J. Am. Acad. Ortho. Surg., January 2006; 14: 38 - 45.