PREVALENCE

The true prevalence of postoperative leg length discrepancy is difficult to quantify and remains unknown because of marked variation in definitions, measurement methods, and the interpretation of its clinical significance. Leg length discrepancy occurred after 14 of 85 hip replacements (17%) in one study,⁴ and a mean overlengthening (and standard deviation) of 15.9 ± 9.54 mm occurred in 144 of 150 hips (96%) in another study.⁵

ETIOLOGY

In the majority of cases of leg length discrepancy after THA patient symptoms can be attributable to “functional” causes and are not the result of true lengthening.⁶ In this situation the apparent discrepancy is secondary to a flexion or abduction contracture of the hip causing pelvic obliquity. The prognosis for “functional” leg length discrepancy is excellent, and in most instances the condition will improve with time and physical therapy.^6,7

True leg length discrepancy is more commonly related to overlengthening of the affected limb. In this situation the main cause is a component position that is not ideal. Common causes of incorrect component position include placement of the acetabular component inferior to the teardrop and placement of the femoral component with the center of the femoral head substantially proximal to the tip of the greater trochanter. Other, more subtle, but significant possible cause of lengthening include retroversion of the acetabular component resulting in intraoperative instability that causes the surgeon to improve the soft-tissue restraints by increasing the femoral neck length or the offset of the femoral stem, thus stabilizing the hip but causing limb-length discrepancy.

CLINICAL PRESENTATION

The majority of patients with minor leg length discrepancy after THA have few symptoms, and most patients with moderate leg length discrepancy have readily manageable symptoms. However, a small group of patients, mostly those with marked leg length discrepancy, may have substantial disability as a result of pain and functional impairment.¹ Common symptoms include pain, paresthesias, and instability of gait (Fig. 59-1).

FIGURE 59-1 Patients with marked leg length discrepancy with substantial disability as a result of pain and functional impairment.

Leg length discrepancy after THA has been associated with complications including sciatic, femoral, and peroneal nerve palsy; low back pain^6,8,9; and gait abnormalities.^10–14 Nerve injury is one of the most serious complications associated with leg length inequality.¹⁵ Edwards and colleagues,¹⁶ in a review of 23 THAs complicated by peroneal and sciatic nerve palsy, noted an average lengthening of 2.7 cm (range 1.9 to 3.7 cm) for peroneal palsy and 4.4 cm (range 4.0 to 5.1 cm) for sciatic palsy. Pritchett¹⁷

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