THE RELATIONSHIP BETWEEN ABDUCTION CONTRACTURE AND LEG LENGTH DISCREPANCY FOLLOWING TOTAL HIP REPLACEMENT

Abstract

Introduction: Leg length discrepancy (LLD) following total hip replacement (THR) is not uncommon. Some patients are symptomatic, with problems such as gait imbalance or back pain. LLD is a potential cause of litigation following THR.

We have observed that some patients perceive their LLD to be much greater than the true LLD. A large LLD is sometimes reported by therapists, despite only a small true LLD.

We have found that abduction tightness is a potent cause of apparent LLD, and report our investigations into this phenomenon.

Method: We have identified a series of patients with abductor tightness and a significant apparent LLD. The LLD becomes apparent when the operated leg is adducted to the midline (or when the patient stands with their ankles together). This causes the contralateral pelvis to elevate and the un-operated leg to “shorten”.

Clinical photographs and videos have been produced to demonstrate this phenomenon.

A 2-dimensional model has been made to demonstrate how the degree of abduction, offset and over-lengthening affect this phenomenon.

A computer model has been used to quantify these effects.

Results: An abduction contracture after THR will cause the un-operated leg to be apparently and functionally short, even in the absence of a true discrepancy.

• Even with only minor abductor tightness, increasing the true length will disproportionately increase the apparent LLD.

• In the presence of tight abductors, increasing the offset will cause apparent shortening in the contra-lateral limb.

• Patients are who have adequate adduction are frequently unaware of true lengthening.

Conclusion: An abduction contracture is a potent cause of apparent LLD. Even a small degree of true over lengthening will be greatly magnified by this phenomenon. We recommend careful clinical assessment for abductor tightness when examining patients complaining of a LLD after THR.