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A Comprehensive Animal Model to Evaluate Novel Sternal Closure Devices
Lishan Aklog1, Jaishankar Raman2, Edward Garrett3, Jeremy London4, Brian deGuzman5, John Pirris6, Kenneth Burkus7, Kyle Icke8, Brian Hatcher8.
1PAVmed Inc, New York, NY, USA, 2Rush University, Chicago, IL, USA, 3University of Tennessee Medical Center, Memphis, TN, USA, 4Savannah Vascular and Cardiac Institute, Savannah, GA, USA, 5Kaleidoscope Medical, Phoenix, AZ, USA, 6University of Florida, Jacksonville, FL, USA, 7The Hughston Clinic, Columbus, GA, USA, 8Zimmer Biomet, Jacksonville, FL, USA.
OBJECTIVE: Increased attention to sternal healing dictates the need for a useful model to compare new sternal closure devices (SCD). We report a model for evaluating sternal healing, biomechanical stability, biocompatibility and device removal with a novel titanium plate with integrated cerclage band SCD.
METHODS: Three skeletally mature sheep underwent median sternotomy followed by sternal closure with a combination of three SCD’s and two cerclage wires. Animals underwent sternal CT scanning at 6-weeks, and device removal force analysis, post-necropsy micro CT scanning, biomechanical, and histopathological analysis at 3-months. CT scans were scored on a 6 point scale at seven locations according to a validated method by an independent core laboratory (Figure 1). Sterna were sectioned into three dog bone-shaped segments and tested in lateral distraction until failure. Identical segments from intact sterna served as controls. Biocompatibility was characterized by independent histopathological assessment of thirteen inflammatory and healing markers at sixteen peri-implant sites.
RESULTS: Mean CT scan scores increased significantly from 6-weeks (3.4 ± 1.1) to 3-months (4.3 ± 0.9, p=0.003) confirming moderate to complete sternal healing at 3-months. Biomechanical properties of fixated sterna at 3-months approached those of intact controls with no significant difference in peak force (675 ± 327 N fixated, 880 ± 287 N intact, p=0.224) or stiffness (781 ± 210 N/mm fixated, 893 ± 204 N/mm intact, p=0.317). Histopathological assessment confirmed biocompatibility of the SCD with a relatively mild inflammatory response that did not differ from wire controls (p=0.23). The average force for SCD band removal (24.0 ± 15.1 N) was significantly less than wire removal (52.0 ± 22.2 N, p=0.014).
CONCLUSIONS: A comprehensive animal model for assessing sternal healing, biomechanical stability, biocompatibility and device removal performance of sternal closure devices has been established. At 3-months the SCD device showed sternal healing by CT scan, biomechanical stability approaching intact bone, biocompatibility and ease of removal. This model may be used to evaluate performance of sternal fixation devices outside of a clinical setting. 
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