Diagnostic Evaluation for Persistent Thigh Pain After Hip Surgery
Begin with plain radiographs of the pelvis and hip, followed by MRI without IV contrast if radiographs are negative or equivocal, to systematically evaluate for the most common causes of post-surgical thigh pain including component loosening, infection, soft tissue pathology, and adverse local tissue reactions.
Initial Imaging Approach
First-Line: Plain Radiographs
- Obtain AP pelvis and dedicated hip views as the mandatory first imaging study 1
- Radiographs evaluate for:
Second-Line: Advanced Imaging When Radiographs Are Non-Diagnostic
For suspected soft tissue pathology (extra-articular):
- MRI hip without IV contrast (rating: 9/9 - "usually appropriate") 1
- Ultrasound hip (rating: 7/9 - "usually appropriate") 1
- MRI evaluates iliopsoas bursitis, abductor tendinosis/tears, trochanteric bursitis, and referred pain from spine 1
For suspected intra-articular pathology:
- MR arthrography (rating: 9/9) or CT arthrography (rating: 7-8/9) for labral tears, cartilage assessment, or ligamentum teres pathology 1
- These are particularly relevant if revision surgery is being considered 1
Clinical Examination Priorities
Key Physical Findings to Document
- Pain location and radiation pattern - distinguish intra-articular from extra-articular sources 4
- FADIR test (Flexion-Adduction-Internal Rotation) - positive suggests intra-articular pathology 1
- Hip range of motion - particularly flexion, abduction, and external rotation limitations 5
- Palpation of greater trochanter - for trochanteric bursitis 1
- Screen spine and pelvis - comprehensive examination required as diagnosis should never be made on imaging alone 1
Differential Diagnosis Framework
Prosthetic vs. Non-Prosthetic Pain Generators
The diagnostic algorithm follows a hierarchical approach 4:
Level 1: Is the hip the source?
Level 2: Prosthetic causes - Septic vs. Aseptic?
- Image-guided joint aspiration with fluid analysis/culture to exclude infection 1, 4
- Consider MRI without IV contrast (rating: 9/9) for non-invasive infection evaluation 1
Level 3: Aseptic causes - Well-fixed vs. Loose?
- Radiographic assessment of component position and fixation 2, 3
- Varus stem position with reactive bone at tip strongly suggests mechanical impingement 2
Level 4: Adverse Local Tissue Reaction (ALTR)
- Cross-sectional imaging (MRI or CT) is best for diagnosing ALTR to cobalt-chromium alloys 4
Diagnostic Injection Protocol
Image-Guided Anesthetic Injection
- Rating: 5-8/9 ("may be appropriate" to "usually appropriate") depending on clinical scenario 1
- Intra-articular injection relieving pain confirms joint as pain source 1
- Trochanteric injection for suspected bursitis 1
- Iliopsoas injection for anterior hip/groin pain 1
- All injections should be image-guided 1
Common Pitfalls to Avoid
- Never diagnose based on imaging alone - comprehensive clinical examination is mandatory 1
- Incidental findings are common in asymptomatic individuals - manage with appropriate clinical sensitivity 1
- Diagnostic imaging has only small shifts in post-test probability - positive or negative findings must be correlated clinically 1
- Thigh pain prevalence is 27% at 5 years post-THA - most strongly associated with poor functional scores and loose beads 3
- Consider stem design and press-fit issues - inadequate press-fit increases thigh pain risk 6
Special Considerations
When Conservative Treatment Fails
- If physiotherapy unsuccessful and surgery considered, MRI may be necessary for surgical planning 1
- For persistent pain with varus stem and reactive bone formation, distal femoral stem tip resection is a simple, effective treatment option 2