Open Access
Roberson, Noah Richard
Area of Honors:
Biomedical Engineering
Bachelor of Science
Document Type:
Thesis Supervisors:
  • Stephen Jacob Piazza, Thesis Supervisor
  • William O Hancock, Honors Advisor
  • physis
  • ACL
  • outside-in
  • FlipCutter
Adolescents who undergo aggressive ACL reconstructive surgery, proven the most successful treatment for ruptured ACLs, can experience debilitating growth deformities due to violation of open femoral physes, with larger and more lateral violations increasing the chance of deformity. Compared to more traditional techniques, a newer outside-in (OI) technique using the Arthrex FlipCutter could reduce these physeal violations while maintaining high post-operative clinical scores due to independent tunneling and better recreation of the ACL anatomical footprint. Studying the effects of drill diameter and drill tunnel length on violation volume within the OI technique can give important information on the best surgical parameters to use on skeletally immature patients. Adolescent femoral Magnetic Resonance data were manually segmented on Avizo and 3D printed (n=17), and a single surgeon drilled through the models as if performing the OI technique using three commonly used guide angles (90˚, 100˚, and 110˚). A novel use of motion tracking was used to bring these drill axes into a CAD environment to simulate drilling through the femoral physes with three different drill diameters (8, 9, and 10 mm) and two different tunnel length options (20 mm max and 25 mm max). Data were collected using Boolean techniques in Rhinoceros 6.0 through custom written code. The physeal violation volumes were calculated for each guide angle, tunnel length, and drill diameter combination and compared through a four-way ANCOVA analysis with age as a covariate. The physeal violation location, the maximum tunnel length, and the overlapping areas and centroid differences between the drill aperture and ACL footprint were also calculated and compared through separate one-way ANOVAs with guide angle as the independent variable. The violation volume analysis showed the interaction of tunnel length option*diameter*age was significant (p = 0.005). Further analysis showed guide angle does not have a significant effect on violation volume and that larger diameter drills and longer tunnel lengths create larger violations, especially in patients under the age of 12. Also, guide angle did not have a significant effect on medial-lateral violation location (p = 0.228), anterior-posterior violation location (p = 0.262), or maximum tunnel length (p = 0.633). The 90˚ guide angle was superior to the 100˚ and 110˚ guide angles in all footprint recreation measurements, having significantly greater overlapping areas between the drill aperture and footprint normalized by the footprint area (p < 0.001) and drill area (p = 0.005), and significantly smaller centroid differences between the drill aperture and footprint (p = 0.001). The use of the 90˚ guide angle is recommended as this angle best recreates the original anatomical positioning of the ACL with similar violation volumes, leading to improved knee kinematics post-operation. Diameter drills of 9 and 10 mm should be avoided in patients under 12 years old.