Limitations of conventional radiographs in the assessment of acetabular defects following total hip arthroplasty

Background: Conventional radiographs are routinely used to evaluate acetabular bone loss as part of the follow-up in patients who undergo total hip arthroplasty (THA). The objective of this study was to examine the accuracy and specificity of conventional radiographs reviewed by arthroplasty surgeons in detecting acetabular bone loss in patients with prior THA. Methods: Using a cadaveric pelvic model, a defined percentage of bone was incrementally removed from the posterior acetabular column, followed by implantation of uncemented cups into both acetabula. Ten orthopedic arthroplasty surgeons, blinded to the defect sizes, assessed the percentage of bone defect using standard anteroposterior, Judet and oblique conventional radiographs. Results: Observers were unable to accurately grade bone defects using conventional radiographs. For defects less than 50%, observers reported on average a defect of 11%. Although observer estimates of defects 50% or more increased, these treatment-altering bone deficiencies remained grossly underestimated, with a sensitivity and specificity of 36.6% and 97.6%, respectively. Conclusion: Conventional radiographs reviewed by experienced arthroplasty surgeons do not reliably detect small bone lesions (< 50%). Although more successful in detecting larger bone lesions, surgeons tend to underestimate actual bone loss. Computed tomography scanning may be indicated if accurate estimation of acetabular bone loss is required in patients who have undergone previous THA.