Biomechanical Evaluation of Different Fixation Methods for a First Metatarsal Transverse Neck Osteotomy in a Hallux Valgus Sawbone Model

Abstract

Category: Bunion Introduction/Purpose: There are no studies available that provide information about fixation methods for minimally invasive Hallux Valgus osteotomies. Our objective was to evaluate different fixation methods' strength for a first metatarsal transverse neck osteotomy in a sawbone model. Methods: 30 sawbone foot models were used. Transverse neck first metatasal osteotomies were performed and fixed in a standardized fashion in 6 different configurations. Group 1 used one 4.0 screw; Group 2 used two (one 4.0 and one 3.0) parallel screws; Group 3 used two (one 4.0 and one 3.0) divergent screws; Group 4 used two divergent screws, one 4.0 with lateral metatarsal head cortex purchase, and one 3.0 screw; Group 5 was like Group 4, but with two 4.0 screws. Group 6 was like Group 4 and 5, but with two 3.5 screws. Cyclic and load to failure testing were performed, measuring stiffness and force needed to create deformity, using a Zwick Roell Universal Testing Machine. Results: Group 1 failed due to rotational instability. Group 2 showed increased stiffness (p < 0.05) against group 1. Group 3 did not achieve difference to group 2. Group 4 was stronger (p < 0.05) in all variables than groups 1-3. Group 5 did not show differences against Group 4. Group 6 was only stronger than Group 1-2. Conclusion: In this study, better biomechanical behavior is seen using divergent screws with lateral head cortex purchase. This is the first study that provides biomechanical information on first metatarsal transverse neck osteotomy fixation methods. Clinical studies are needed to evaluate the clinical impact of these findings.