Weight-Bearing CT Hounsfield Unit Algorithm Assessment of Calcaneal Osteotomy Healing: A Prospective Study Comparing Metallic and Bio-Integrative Screws
Authors: Mansur Nacime SB , Tazegul Tutku , Carvalho Kepler , Behrens Andrew , Iehl Caleb J. , Ahrenholz Samuel J. , Lalevée Matthieu , Netto Cesar de Cesar 
Published: November 2022

Category: Basic Sciences/Biologics; Hindfoot; Other Introduction/Purpose: The use of bio-integrative implants in orthopedic surgery is growing rapidly. While many biomechanical and histological studies have been able to demonstrate their structural and biological properties, few clinical reports are available to support their advantages, such as good osteosynthesis, lower rates of removal, and diminished implant-related artifact in imaging studies. This clinical information is vital to providers when choosing the proper material and planning postoperative treatment. Hounsfield Units (HU) algorithms have been used as an objective assessment of joint space width. This pilot data analysis intends to test the capacity of the bio-integrative screws in reaching similar radiographical outcomes of the current metallic screws when analyzing medial displacement calcaneus osteotomies (MDCO). Our hypothesis is that both types of implants would present similar results. Methods: In this prospective comparative IRB-approved study, three patients undergoing MDCO with bio-integrative screws were compared to two patients undergoing the same surgery with metallic screws. Surgeon, primary diagnosis, technique, and displacement were the same for both groups. Patients were assessed using weight-bearing computed tomography at weeks 2, 6, and 12 postoperatively. Using a dedicated software, a 40x40x40mm cube, which defines a volume of interest (VOI), is centered at the osteotomy site. Within the VOI, initial computational analysis focused on image intensity (Hounsfield Units) profiles along lines perpendicular to the osteotomy line, crossing the osteotomy line and spanning approximately 8mm on either side. The HU intensity profiles were recorded, and graphical plots of the HU distributions were generated for each line. The plots were then used to calculate the HU contrast, a proxy for bone healing at the osteotomy site. Results: At 2 weeks, mean HU intensity in the metallic and bio-integrative were respectively 403.25 and 416.28 at the centerline (p=0.312), 513.24 and 386.57 at the inferior (p<0.001), 438.97 and 487.92 at the superior line (p=0.020). With 6 weeks, a mean HU intensity of 318.40 and 414.22 was observed at the centerline (p<0.001), 340.41 to 356.86 (p=0.315) at the inferior, and 401.72 and 449.88 at the superior (p=0.018). At 12 weeks, HU intensity of -85.01 and 64.59 was found at the center (p<0.001), - 111.36 and 139.19 at the inferior (p<0.001), and 225.95 and 166.05 at the superior line respectively (p=0.010). Overall HU units decrease from the second to the twelfth week in both groups (ps<0.001). The contrast was higher in the metallic patients (0.66 to 0.26). Conclusion: Comparison among bone healing between metallic and bio-integrative screws through HU algorithms found similar results. The absence of valleys on the HU graphical plots at 2 weeks postoperatively could be a direct sign of osteotomy compression. Diffuse osteopenia might explain lower amounts at the 12-week evaluation. Maximum HU values were similar, indicating equivalent results at the osteotomy sites, a finding compatible with consolidation. Presence of metallic implants across the osteotomy site hindered both HU intensity and contrast evaluation, presenting a challenge when calculating bone healing through indirect and direct assessments.