Reducing the Incidence of Leg Length Discrepancy After Total Hip Replacement
Leg length discrepancy is one of the most common complications after total hip replacement. A hip which has become arthritic is almost always short because it has lost the cartilage space of the joint, often resulting in shortening of the limb 3-5mm (1/8 – ¼ inch). Most often, we try to lengthen the hip this amount to equalize the leg lengths.
Sometimes, the leg must intentionally be over-lengthened; for instance, if the soft tissues are so lax that the only way to tighten the hip up to prevent a dislocation is to add length to the leg. However, with lateralized (high offset) femoral components and larger femoral heads, this is less often needed today. More often, the leg is inadvertently over-lengthened (or occasionally shortened). This is a known, accepted potential complication of total hip replacement, and discrepancies of up to ½ inch are considered within the accepted standard of care.
However, although most patients tolerate leg length discrepancies of up to ¼ inch quite well, ½ inch leg length discrepancies (or more) are not often well tolerated, and most will need a shoe lift on the opposite side to allow comfortable walking. Therefore, many methods to try to ensure equal leg lengths after total hip replacement have been devised and utilized over the years.
In 1997, we began working on a technique utilizing careful pre-operative templating to equalize leg lengths on the x-ray, then duplicate these measurements intra-operatively to attain equal leg lengths. However, no matter how carefully the x-rays were templated and the surgery performed, several patients still had over-lengthening of the leg without a good explanation.
A few years ago, we began looking critically at our x-ray templating to try to find the source of error. In the process, we began templating the NORMAL hip along with the ARTHRITIC hip. We soon found that if we used the x-ray templating of the NORMAL hip intra-operatively, we were more likely to achieve equal leg lengths. Since then, we have observed this to be true in approximately 75% of our patients.
We have now conducted a radiographic study scientifically showing that using templating measurements from the normal hip routinely gives more accurate restoration of equal leg lengths than using measurements from the arthritic hip. Utilizing this technique, we can equalize leg lengths to less than ¼ inch difference in almost all patients. Of course, we still see exceptions; for instance, when the soft tissues are so lax that the only way to reduce the risk of dislocation is to intentionally lengthen the leg, or when a large pre-existing leg length discrepancy exists, making accurate correction much more difficult.
Eventually, even more sophisticated methods of restoring equal leg lengths will be developed, particularly with the development computer navigation systems for total hip replacement. Technology will continue to move forward and minimize the problem of leg length discrepancies after total hip replacement. For now, we can come extremely close using these new templating techniques.