Implant Related Artifact Around Metallic and Bio-Integrative Screws: A CT Scan 3D Hounsfield Unit Assessment

CATEGORY: Basic Sciences/Biologics; Hindfoot INTRODUCTION/PURPOSE: Implant-related artifact (IRA) represents an important limitation in Computed Tomography (CT) assessment of osteotomy and fracture healing, bone-implant integration, and success of fusion procedures. Metallic implants are the most used in foot and ankle surgery and are recognized as important IRA generators. Absorbable and bio-integrative (BI) implants are attractive options for bone fixation when postoperative CT imaging is likely, particularly in procedures with higher risk for nonunion. However, the literature comparing IRA with metallic and BI implants is scarce. The objective of this study was to assess the degree of IRA around metallic and BI cannulated screws. Our hypothesis was that BI implants would demonstrate significantly decreased IRA around the inserted screws. METHODS: In this cadaveric/CT imaging study, 2 below-knee specimens were used. Medial displacement calcaneal osteotomy was performed through a 5-cm long lateral heel approach. Calcaneal tuberosity was displaced medially by 10mm and fixed provisionally with 2 parallel K-wires under fluoroscopic guidance. Specimens were fixed with two headless 4.0 millimeters cannulated screws, either metallic or BI. Cone-beam CT imaging of both specimens was acquired following osteotomy screw fixation (120kVp, 5.5mA, 0.25mm isotropic). Using a dedicated software, the overall dispersion of Hounsfield units (HU) in a 3D cube of 30mm edge length was assessed. Four HU lines were then traced parallel to the screws, crossing the osteotomy site. Lines 1, 2, 3 and 4 were positioned respectively: In close proximity, over, inside the cannulation and away from the implant. The HU dispersion in these lines was measured and compared between metallic and BI implanted specimens, using T-tests/Wilcoxon analysis. P-values<0.05 were considered significant. RESULTS: When compared to the BI implant, the average HU was pronouncedly and significantly increased around metallic implants in the lines with more close proximity (Line 1), over the screw wall (Line 2) and inside the screw cannulation (Line 3), when considering both the whole line extension inside the 3D cube as well as in a selected 8mm line-segment across the calcaneal osteotomy line: Line 1 (entire, 7.26 vs -159; selected, -5 vs -249) Line 2 (entire, 4.846 vs 108; selected, 6286 vs 151.2); Line 3 (entire, 1664 vs 144; selected, -277.7 vs 198.7) selected). However, across Line 4 (away from the implant), the HU dispersion was interestingly and significantly decreased around the metallic implant (entire, -49 vs 178.5; selected, -110 vs 221), potentially as result of beam hardening artifact, concentrating HU close to the metal, and shielding the surrounding cancellous bone from being accurately reconstructed. CONCLUSION: In this cadaveric imaging study, we compared Implant-related artifact (IRA) around metallic and bio-integrative (BI) implants utilized to fix medial displacement calcaneal osteotomies. We found metallic implants to demonstrate significantly and pronouncedly increased HU dispersion in in close proximity with the implants and significantly decreased dispersion more distantly from the implant, shielding the surrounding cancellous bone, and potentially hindering the assessment of bone density quality and bone/osteotomy/fusion healing in its neighborhood. BI implants represent an alternative to decrease these IRA effects. Additional clinical studies are needed to confirm and expand our findings.