Precision of photon-counting detector CT compared to conventional CT for total wrist arthroplasty migration: a cadaveric and clinical study

OBJECTIVES: Implant loosening is a serious complication after total wrist arthroplasty. Radiostereometric analysis has been the gold standard for measurement of implant migration; however, the use of bead free computer tomography radiostereometric analysis (CT-RSA) has emerged as an alternative due to its higher precision. In this study, the precision of a novel photon-counting detector CT (PCD-CT) was compared to conventional energy-integrating detector CT (EID-CT) at different radiation doses. METHODS: One cadaveric wrist with total wrist arthroplasty (TWA) implant was scanned 40 times with EID-CT and PCD-CT at two radiation doses. Additionally, eight patients with the same implant were scanned with PCD-CT post-surgery, and after 6 and 12 months. PCD-CT scans were reconstructed with 0.2-mm and 1.0-mm slice thickness. Precision data for the cadaveric wrist and migration data for the patients were calculated using CT-RSA. RESULTS: The precision of total implant rotation was significantly better with PCD-CT at half the radiation dose (0.08°) compared to full-dose EID-CT (0.15°, p = 0.002). Similarly, translational precision at the implant tip was higher with half-dose PCD-CT (0.02 mm) than with EID-CT (0.03 mm, p = 0.04). For migration, the proximal component had moved (median) -0.04 mm distally at 6 months and 0.01 mm at 12 months. The rotation around the axis at these time points was 0.03° and 0.06°, respectively. CONCLUSIONS: In this cadaveric precision study, PCD-CT enabled CT-RSA measurements with high precision at a lower radiation dose than conventional EID-CT. The accompanying eight-patient in vivo cohort should be interpreted as a feasibility cohort and showed only small descriptive early migration values during the first postoperative year. Larger longitudinal studies are needed to determine clinically relevant migration thresholds and the value of this method for detecting implant loosening." RELEVANCE STATEMENT: Photon‑counting detector computed tomography and computed tomography micromotion analysis allow high-definition tracking of total wrist arthroplasty migration at half the radiation dose of conventional CT, offering a high‑precision, low‑dose tool for early detection of implant loosening.