Biomechanical Evaluation of Different Fixation Methods for Percutaneous Extracapsular Transverse Cervical Metatarsal Osteotomy in a Hallux Valgus Sawbone Model

Background: There is limited literature available that provide information about fixation methods for minimally invasive hallux valgus osteotomies. Our objective was to evaluate the strength of different fixation methods for a percutaneous extracapsular transverse cervical metatarsal (PTCM) osteotomy in a sawbone model. Methods: Thirty solid foam sawbone foot models were used. Percutaneous extracapsular transverse cervical metatarsal osteotomies were performed and fixed in a standardized fashion in 6 different groups: (1) one 4.0-mm screw; (2) 2 (one 4.0-mm and one 3.0-mm) parallel screws; (3) 2 (one 4.0-mm and one 3.0-mm) divergent screws; (4) same as group 3, but with lateral metatarsal head cortex purchase with the 4.0-mm screw; (5) same as group 4, but with two 4.0-mm screws; (6) same as group 5, but with two 3.5-mm screws. Cyclic and load to failure testing were performed applying a plantar load to the metatarsal head. The measured variables were stiffness and force needed to create deformity using a Zwick Roell Universal Testing Machine. Results: Group 1 failed as a result of rotational instability in cyclic testing. In load to failure testing, group 3 did not achieve difference compared with group 2 (P =.09) (181 vs 131 N). Group 4 was stronger (P =.02) (250 N) than groups 1-3. Group 5 did not show differences relative to group 4 (P =.1) (223 N). Group 6 was stronger only than groups 1 and 2 (P =.01) (193 N). Conclusion: In this sawbones-based study, we found that the use of two 4.0-mm screws or use of a 3.0-mm screw and a 4.0-mm screw with lateral first metatarsal head cortical purchase was superior to other screw configurations.