Post-Operative X-Ray Imaging After Total Hip Replacement
Baseline radiographs at 6-12 weeks post-operatively are essential for all patients to establish a reference for future comparison, but routine follow-up radiographs in asymptomatic patients with non-metal-on-metal (non-MoM) prostheses may be omitted as they rarely change clinical management. 1
Asymptomatic Non-MoM Hip Prostheses
Initial Post-Operative Imaging
- Obtain baseline radiographs at 6-12 weeks post-operatively to document initial prosthetic positioning, component alignment, and establish a reference for serial comparison 1
- Standard views include AP pelvis and lateral hip radiographs to assess component position, center of rotation, acetabular inclination, and femoral offset 2, 3
Routine Follow-Up Imaging
- Routine follow-up radiographs at 1 year in asymptomatic patients may be omitted, as a study of 423 patients found no cases where clinical management was changed by radiographic examination during this period 1
- Serial radiographs remain useful for identifying subtle changes when obtained, emphasizing the importance of baseline films for comparison 1
What to Assess on Radiographs
- Component position and alignment (acetabular inclination, anteversion) 2, 3
- Component loosening indicators 1
- Bone quality and osteolysis 1
- Fracture, dislocation, or subluxation 1
- Leg length discrepancy 3, 4
- Center of rotation and offset measurements 3, 5
Metal-on-Metal (MoM) Hip Prostheses
FDA-Mandated Surveillance
- The FDA recommends routine long-term follow-up every 1-2 years for all MoM hip implants, including appropriate radiographs 1
- This applies to both symptomatic and asymptomatic patients with MoM prostheses 1
Critical Radiographic Findings in MoM Prostheses
- Assess for femoral neck narrowing and medial femoral calcar erosion, which may indicate adverse reaction to metal debris (ARMD) with a positive predictive value of 0.83, warranting cross-sectional imaging 1
- Evaluate for component position, loosening, osteolysis, and metallosis 1
- High acetabular inclination, acetabular or femoral osteolysis, and acetabular loosening predict revision for pseudotumors 1
Important Caveat
- 20% of MoM hip resurfacing prostheses with pseudotumors at revision surgery had normal radiographic features, indicating radiographs alone are insufficient for complete surveillance 1
- Consider supplementing with ultrasound or MARS-MRI for comprehensive MoM surveillance 1
Symptomatic Patients (Any Prosthesis Type)
First-Line Imaging
- Radiographs are the first-line imaging modality for symptomatic hip prostheses to assess periprosthetic fractures, component loosening, dislocation, heterotopic ossification, and greater trochanter pathology 1, 2, 6
Advanced Imaging When Radiographs Are Negative/Equivocal
- Obtain non-contrast CT when radiographs are negative or equivocal but high suspicion exists for periprosthetic fracture, or when additional fracture characterization is needed for surgical planning 1
- MRI can demonstrate periprosthetic fractures and stress reactions, though susceptibility artifact from the prosthesis may obscure findings 1
- MRI is particularly valuable as seemingly isolated greater trochanter fractures on radiography frequently have occult intertrochanteric extension 6
Key Clinical Pitfalls
Positioning Matters
- Acetabular orientation changes significantly between supine and standing positions due to pelvic tilt alterations 7
- Components within the "safe zone" on supine radiographs may be outside the safe zone when standing 7
Radiographic Limitations
- Radiographs showing >2mm greater trochanter surface irregularities have only 24.7% positive predictive value for greater trochanteric pain syndrome, with 74.3% false-positive rate 1
- Component loosening assessment by CT when fracture is present shows inconsistent efficacy 1