Recognizing Hip Dislocation
Suspect hip dislocation in any patient with acute traumatic hip pain following high-energy injury (such as motor vehicle collision) who presents with a characteristic deformed limb position, severe pain, and inability to move the hip—and immediately obtain plain radiographs (AP pelvis with 15-degree internal rotation and cross-table lateral views) to confirm the diagnosis, as physical examination alone cannot reliably diagnose or exclude hip dislocation. 1
Key Clinical Presentation
Mechanism of Injury
- High-energy trauma is the typical mechanism in non-osteoporotic patients, most commonly motor vehicle collisions 1
- In contrast to hip fractures (which occur from low-energy falls in elderly patients), native hip dislocations require substantial force
Classic Physical Examination Findings
For Posterior Hip Dislocation (most common):
- Hip held in flexion, adduction, and internal rotation
- Shortened limb appearance
- Severe pain with any attempted movement
- Complete inability to bear weight or move the hip
For Anterior Hip Dislocation (less common):
- Hip held in extension, abduction, and external rotation
- Femoral head may be palpable anteriorly
Critical Limitation
Physical examination alone cannot definitively diagnose or exclude hip dislocation—imaging is essential for timely and accurate diagnosis 1. This is a crucial pitfall to avoid: never rely solely on clinical findings to rule out dislocation.
Immediate Diagnostic Approach
Initial Imaging (First-Line)
Plain radiography is the initial imaging modality of choice 1:
- AP view of pelvis with 15 degrees of internal hip rotation
- Cross-table lateral view of the affected hip (NOT frog-leg lateral, which risks fracture displacement)
- Can be performed portably in the trauma bay
- Rapidly confirms dislocation and detects associated fractures
Advantages of Rapid Radiographic Diagnosis
- Reduces morbidity by enabling prompt reduction (critical to prevent avascular necrosis)
- Avoids unnecessary patient movement before diagnosis 1
- Identifies associated acetabular fractures that affect management
Post-Reduction Evaluation
Confirming Successful Reduction
After closed or open reduction, obtain follow-up imaging to:
- Confirm successful reduction and joint congruence
- Detect intra-articular fracture fragments
- Characterize associated acetabular fractures (especially posterior wall fractures)
CT Scanning Indications Post-Reduction
CT hip without IV contrast is indicated when 1:
- Any radiographically visible acetabular fracture is present (to determine if surgical fixation is needed)
- Closed reduction fails (to identify entrapped fracture fragments)
- Concern exists for intra-articular fragments or inadequate joint congruence
Important caveat: CT has 87.3% sensitivity for intra-articular fragments, but 43.3% of patients with negative CT still had fragments at arthroscopy 1. Consider this limitation when clinical suspicion remains high.
Subtle or Delayed Presentations
CT Signs of Missed or Spontaneously Reduced Dislocation
If hip dislocation is suspected but not obvious on plain films, CT may reveal 2:
- Femoral head notching (sensitivity 56.7%, specificity 100%)
- Intracapsular air bubble (sensitivity 90%, specificity 100%)
These signs strongly suggest a history of hip dislocation even if currently reduced or if reduction history is unclear 2.
Time-Critical Nature
Hip dislocation is an orthopedic emergency:
- Prompt reduction (ideally within 6 hours) minimizes risk of avascular necrosis
- Delayed diagnosis increases morbidity, including risk of osteonecrosis and recurrent dislocation 1, 3
- In neglected cases (>3 weeks), complications include soft-tissue contracture, acetabular fibrous in-growth, and near-universal avascular necrosis 3
Common Pitfalls to Avoid
- Never rely on physical examination alone to exclude hip dislocation—always obtain imaging 1
- Avoid frog-leg lateral views in acute trauma—use cross-table lateral to prevent fracture displacement 1
- Don't miss associated injuries: up to 25% have sciatic nerve palsy; always assess neurovascular status 3
- Don't assume negative CT excludes all intra-articular fragments—maintain clinical suspicion 1