What is the best course of action for a patient with a history of right total hip replacement and recurrent dislocations, despite a normal computed tomography (CT) scan?

Management of Recurrent Total Hip Arthroplasty Dislocations

For a patient with recurrent dislocations after total hip replacement despite a normal CT scan, proceed directly to surgical revision with component repositioning, dual mobility cup insertion, or constrained liner placement, as instability is the second most common cause of THA revision (17.4%) and conservative management fails in recurrent cases. 1

Initial Diagnostic Approach

Advanced Imaging Beyond Standard CT

• Obtain CT without IV contrast with metal artifact reduction (MAR) to assess component positioning, joint congruence, acetabular wall integrity, and detect intraarticular fragments that may contribute to instability. 2
• Standard CT has 87.3% sensitivity for detecting intraarticular fragments, but up to 43.3% of patients with negative CT may still have small fragments contributing to instability. 3, 2
• Add MRI without IV contrast specifically to evaluate abductor tendon tears, gluteal muscle insufficiency, or capsular disruption—soft tissue pathology that CT cannot adequately assess but frequently causes recurrent instability. 1, 2, 4

Critical Mechanical Factors to Identify

• Measure acetabular component anteversion and inclination on CT—excessive anteversion (>30°) or inclination (>50°) are primary mechanical causes of anterior dislocation. 5
• Assess femoral component anteversion (normal <25°) and combined anteversion—excessive combined anteversion predisposes to anterior instability. 5
• Evaluate offset reconstruction and leg length discrepancy—inadequate offset leads to impingement, reduced abductor tension, and instability. 4, 6
• Identify prosthetic or bony impingement zones using CT modeling techniques, as impingement is a major contributor to recurrent dislocation. 2, 4

Treatment Algorithm Based on Dislocation Pattern

For Posterior Dislocations (Most Common)

• Posterior dislocations have 79% success rate with surgical revision compared to only 54% for anterior dislocations. 6
• Cup augmentation (repositioning acetabular component) achieves stability in 90% of cases—the most successful single intervention. 6
• If posterior approach was used initially, consider posterior soft tissue repair with transosseous capsulotendinous reconstruction. 7

For Anterior Dislocations

• Anterior dislocations are more difficult to stabilize (54% success rate) and typically occur with transgluteal (Hardinge) approach. 6
• These cases require more aggressive intervention due to excessive anteversion (average 30° cup, 24° femoral). 5
• Component revision with correction of anteversion is necessary—conservative management with immobilization fails in recurrent cases. 5

For Recurrent Dislocations After Primary THA

• Primary THA instability achieves 75% stability after revision, significantly better than revision THA instability (50% success). 6
• First-line surgical option: dual mobility cup insertion, which reduces re-dislocation rate to 1.8% in recurrent cases. 8
• Alternative: constrained liner if dual mobility is contraindicated or unavailable. 7

Specific Surgical Interventions

Component-Based Solutions

• Increase femoral head size to larger diameter (≥36mm) to improve jump distance and stability. 7
• Exchange modular components to optimize offset and restore abductor tension—critical for stability. 4, 7
• Reorient acetabular component to safe zone: 40° inclination ± 10°, 15-20° anteversion. 9, 6

Soft Tissue Solutions

• If MRI demonstrates abductor tendon tears or gluteal insufficiency, perform trochanteric advancement or abductor repair concurrently with component revision. 1, 4
• Isolated soft tissue repair without addressing component malposition has poor outcomes. 4

Critical Pitfalls to Avoid

• Do not attempt prolonged conservative management with bracing for recurrent dislocations—this fails and delays definitive treatment. 6, 7
• Do not rely solely on radiographs—they miss component malposition, impingement zones, and soft tissue pathology in >50% of cases. 1, 2
• Do not revise components without assessing abductor integrity on MRI—unrecognized gluteal insufficiency causes persistent instability despite optimal component positioning. 1, 4
• Do not use bone scintigraphy, contrast-enhanced CT, or contrast-enhanced MRI—these add no diagnostic value for mechanical instability. 3
• Delayed surgical intervention increases morbidity and risk of secondary complications including femoral fracture and progressive soft tissue damage. 2

Expected Outcomes

• Dual mobility cups achieve 98.2% stability rate in recurrent dislocation cases with mean Harris Hip Score improvement from 76 to 87. 8
• Cup augmentation alone achieves 90% stability—highest success rate of single interventions. 6
• Revision for instability after revision THA has only 50% success rate, emphasizing importance of getting it right the first time. 6