Computed Tomography With Implant Movement Analysis in the Work-Up of Painful Total Hip Prostheses

Background: Diagnosing aseptic loosening following total hip arthroplasty is challenging. Computed tomography (CT)–guided implant movement analysis (CT-IMA) overlays two CT scans of a stressed total hip prosthesis to evaluate for micromotion. The purpose of this study was to evaluate this technology in identifying clinically stable and unstable total hip prostheses. Methods: Plain radiographs and CT-IMA scans of 80 patients with painful total hip prostheses were evaluated. Standard radiographs demonstrating 1- to 2-mm circumferential radiolucent lines within the modified Gruen, or Delee and Charnley zones, or subsidence were considered loose. A CT-IMA scan demonstrating implant motion > 0.5 mm was generally considered loose. Patients were categorized by implant stability based on plain radiographs and CT-IMA scans. Hip Dysfunction and Osteoarthritis Outcome Score for Joint Replacement (HOOS, JR) scores were calculated for each group from the initial to the final follow-up. Statistical analysis was performed with two-tailed paired t-tests. Results: There were 66 patients who were categorized into the radiographically Stable–IMA Stable group (Group 1), six into the radiographically Loose–IMA Stable group (Group 2), and eight into the radiographically Loose–IMA Loose group (Group 3). Within Group 1, HOOS, JR scores improved from 49.5 ± 18.4 to 64.2 ± 18.9 (P = 0.004). The 14 patients who underwent revision surgery had well-fixed components. Within Group 2, HOOS, JR scores improved from 57.7 ± 19.7 to 69.1 ± 21.5 (P = 0.01). The two patients who underwent revision surgery had well-fixed components. Within Group 3, HOOS, JR scores improved from 45.5 ± 18.1 to 71.8 ± 15.4 (P = 0.04). The seven patients who underwent revision surgery had loose components and one patient was lost to follow-up. Conclusions: A CT-IMA better identified patients who had stable total hip prostheses than standard radiographs, demonstrating its value in the workup of a painful total hip prosthesis.