A 78-year-old woman underwent right total hip arthroplasty using a posterolateral approach 4 years before she was referred to our center. During that time, she sustained two posterior hip dislocations that were treated successfully by closed reduction. She also reported sensations of the hip clicking, for which she had to “turn” it back into place. Infection was ruled out by negative serology results. Radiographs showed well-fixed components without obvious malposition ( Fig. 68.1 ). Computed tomography showed a slightly decreased degree of acetabular anteversion.
Instability after total hip arthroplasty (THA) is a serious complication that results in patient dissatisfaction and frequently necessitates revision surgery. For approximately 60% of patients, closed reduction can successfully treat the first dislocation if it occurs soon after the THA. Patients who experience multiple dislocations frequently need revision surgery. Determination of the cause of instability is essential for a successful revision.
In the setting of well-fixed and well-positioned components, use of modular components can ease the adjustment of soft tissue tensioning.
If component positioning or the clinical track record is poor, revision of the components should be considered even when they are well fixed.
A definitive surgical plan is essential before a revision operation.
Soft tissue tension and competency should be thoroughly evaluated during revision.
Adequate exposure during the index surgery is essential to avoid impingement and component malposition as underlying causes of instability.
Modern techniques should be used for well-fixed femoral (i.e., extended trochanteric osteotomy) and acetabular (i.e., explant systems) component removal when necessary.
Dislocation is second only to aseptic loosening as the most common cause of failure of total hip arthroplasty (THA). The incidence of dislocation is approximately 2% (Scottish and Kaiser Registries) after primary THA and between 5% and 20% after revision THA. The causes of instability after THA are often multifactorial and include component malposition, impingement, inappropriate soft tissue tensioning, and noncompliance with hip precautions ( Figs. 68.2 and 68.3 ). In some patients, the exact cause of dislocation is not clear. The key to optimizing the outcome of revision THA for recurrent dislocation is preoperative determination of the cause of dislocation.
When presented with an unstable THA, a thorough history, physical examination, and radiographic evaluation should be performed. The history should include the mechanism of dislocation (i.e., activity and position of the limb at the time of dislocation) and descriptions of previous episodes of subluxation or dislocation. The patient’s history of infection should be obtained. Both lower extremities should be examined for gait, range of motion, strength (particularly of the abductor musculature), neurovascular status, leg lengths, position of previous incisions, and leg position at rest.
Radiographic examination should include an anteroposterior view of the pelvis centered over the pubis and anteroposterior and cross-table lateral views of the affected hip. Component alignment and rotation can be delineated from radiographs. If component alignment remains unclear, computed tomography (CT) should be considered. Full serology, including a complete blood cell (CBC) count with a differential count, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) level, should be performed. ESR and CRP values are used to diagnose indolent infection, which may be the cause of instability. If any value is out of the normal range, preoperative hip aspiration with or without an intraoperative frozen section biopsy should be done to rule out infection as a cause of dislocation.
Indications and Contraindications
The indications for revision THA are straightforward because dislocation is typically a traumatic event. First-time dislocations warrant an attempt at closed reduction with placement of a hip abduction brace. The brace should be worn full time for 4 to 6 weeks. For a posterior dislocation, the hip abduction brace should limit hip flexion to 40 degrees, with 10 degrees of abduction and no internal rotation. For an anterior dislocation, the limitations include maintenance of hip flexion to avoid hip extension and external rotation.
The position of the components should be thoroughly evaluated. If there is malpositioning, particularly of the acetabular component, revision THA should be considered because recurrent dislocations are likely. If component positioning is acceptable, a conservative course of hip abduction bracing should be considered.
After a second dislocation, closed reduction and bracing may be attempted again, but the patient should be counseled that revision surgery may be necessary if another dislocation occurs. Typically, revision THA is performed when a third dislocation takes place.
Contraindications for revision THA are few but include active periprosthetic infection, which requires treatment with a two-stage procedure. Any form of patient morbidity may be a contraindication to further surgical intervention.