By: 27 January 2014
Preventing and treating leg length differences with  total hip replacement

Vincent Y Ng, MD, et al. Limb-Length Discrepancy After Hip Arthroplasty.
In The Journal of Bone and Joint Surgery. August 7, 2013. Vol. 95A. No. 15. Pp. 1426-1436.

Many people don’t realise it, but one of their legs is longer (or shorter) than the other one. Over time, this can lead to degenerative osteoarthritis (OA) in the hip joint requiring a hip replacement. But the surgeon can’t just take the old hip joint out and put the new implant in. Careful planning, special surgical techniques, and adjusting of the implant component parts are important in preventing continuation or even worsening of the leg length discrepancy.
In this article, orthopaedic surgeons from Ohio State University offer their perspective and experience treating patients with a limb-length discrepancy. They define and categorise limb-length discrepancy and outline a plan-of-care that takes into consideration preoperative, intraoperative (during surgery), and post operative evaluation of this problem.

Some limb-length differences are caused by actual anatomic differences from one side to the other (referred to as structural causes). The femur is longer (or shorter) or the cartilage between the femur and tibia is thicker (or thinner) on one side. There could be actual deformities in one femur or hip joint contributing to leg length differences from side to side. Even a small structural difference can amount to significant changes in the anatomy of the limb.

A past history of leg fracture, developmental hip dysplasia, slipped capital femoral epiphysis (SCFE), short neck of the femur, or coxa vara can also lead to placement of the femoral head in the hip socket that is offset. The end-result can be a limb-length difference and early degenerative arthritis of the hip.

In other people, there are functional (rather than structural) reasons for the limb-length difference. Shortening or tightening of the soft tissues around the hip on one side can pull the pelvis or femur out of the proper alignment. Weight-bearing through the hip becomes uneven. Uneven compressive forces on the joint wear down the surface causing the degenerative changes associated with osteoarthritis.

Postural asymmetry of the legs can also occur as a result of changes in the lower leg. Stiffness and long-term loss of motion of the knee or ankle for any reason (muscle tightness or contractures, foot deformities) are examples of functional limb-length differences from postural asymmetry.

The body is often very good at compensating for off-centre alignment. Shifts and changes occur throughout the shoulders, trunk, pelvis, hips and legs to keep the head centred over the spine. But sometimes there are structural, functional, or a combination of both types of changes that make the leg length difference worse instead of better. The structures become rigid – no longer able to be corrected with a change in position or after a programme of stretching exercises.

When total hip replacement becomes the treatment of choice, the surgeon must evaluate any and all contributing factors, including functional and structural causes of leg length differences. X-rays such as teleoroentgenography and scanography, and more advanced imaging studies (CT scans) are taken preoperatively.

Careful review of imaging studies provides the surgeon with an appreciation of significant issues such as femoral neck shortening or lengthening, a large femoral offset, or excessive coxa vara. The authors point out that trying to lengthen or shorten the leg to correct deformities is not advised. The risk of nerve injury and creating an unstable hip is too great.

Replacing the hip joint will not change problems lower down in the knee or ankle or higher up in the spine. Patients must be made aware of what the hip replacement can and cannot do. Even with surgical release of tight soft tissues around the hip, correction of limb-length differences can’t be predicted or guaranteed.

In fact, it is possible that total hip replacement can actually result in major limb-length differences. As the authors point out, through careful evaluation and planning, surgeons make every effort to prevent this from happening. Educational articles such as this one aid in reviewing current concepts and guide surgeons through the process.

Measuring offsets, intraoperative assessment of limb length, selecting the best implant for each patient, specifics of surgical techniques, and postoperative care are additional areas of discussion in this article. The authors provide surgeons with many practical considerations when dealing with limb-length discrepancy in patients with osteoarthritis, especially those individuals planning to have a hip replacement.