CHAPTER OUTLINE
Prevalence 437
Etiology 437
Clinical Presentation 438
Treatment 438
Specific Situations 439
Acetabular Retroversion 439
Inferior Position of the Acetabular Component 439
Proximal Position of the Femoral Head 439
Summary 439
Patient’s perception of leg length inequality in the early postoperative period is relatively common. Fortunately, in the majority of patients this symptom resolves with time and physical therapy. However, a minority of patients, mostly those with marked leg length discrepancy, may have substantial disability as a result of persistent pain and functional impairment. This situation is a disturbing problem for both the surgeon and the patient. Although revision arthroplasty usually is considered to be a last resort in these cases, continuing recurrent instability, profound functional impairment (abductor weakness, dysfunctional gait, or low back pain), and failure of conservative treatment may necessitate surgical intervention. Also, it is important to realize that patient dissatisfaction with leg length discrepancy after total hip arthroplasty (THA) is one the most common reasons for litigation against orthopedic surgeons.
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, and a mean overlengthening (and standard deviation) of 15.9 ± 9.54 mm occurred in 144 of 150 hips (96%) in another study.
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. 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.
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. Common symptoms include pain, paresthesias, and instability of gait ( Fig. 59-1 ).
Leg length discrepancy after THA has been associated with complications including sciatic, femoral, and peroneal nerve palsy; low back pain ; and gait abnormalities. Nerve injury is one of the most serious complications associated with leg length inequality. Edwards and colleagues, 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. Pritchett reported severe neurologic deficit and persistent dysesthetic pain after THA in patients with leg lengthening of 1.3 to 4.1 cm. Although some authors have documented ranges of lengthening of the lower extremity of 15% to 20% of the resting length that may be safe with regard to the sciatic nerve, neurogenic pain and nerve palsy may occur with any degree of lengthening.
TREATMENT
Conservative Treatment
Functional Leg Length Discrepancy
In cases of functional leg length discrepancy, patient education, reassurance, time, and physical therapy will most likely improve the symptoms. One should resist the temptation to use a shoe lift in the first 6 months after THA, because this may jeopardize the possibility of abductor musculature recovery. Ranawat and Rodriguez studied a series of patients with functional limb length discrepancy and showed that it resolved in all cases by 6 months with proper physical therapy, despite an initial high prevalence ( Fig. 59-2 ).
True Leg Length Discrepancy
As with functional leg discrepancy, initial treatment consists of patient education and physical therapy. In most cases it is desirable to delay the use of a shoe lift for 6 months postoperatively to prevent permanent soft-tissue contractures and to determine whether the perceived leg length discrepancy will resolve.
The initial treatment for true leg length discrepancy is the use of a shoe lift for the extremity that seems to be shorter. Friberg described a series of more than 1000 cases in which a shoe lift to correct leg length inequality resulted in alleviation of lower back symptoms ( Fig. 59-3 ).
