Role of inferomedial supporting screws for secondary varus deformity in non?osteoporotic proximal humerus fracture: A biomechanical study

Abstract

Introduction The purpose of this study was to evaluate the efect of a medial support screw through a proximal humerus fracture. For this purpose, we verifed whether the biomechanics are diferent according to the position of the screw while using the same number of screws. In addition, we tried to verify whether the insertion of additional inferomedial screws would make a diference in stability. Materials and methods Twenty-four proximal humerus bones were included in the study. A two-part fracture was created and fxed using a locking plate. Cyclic loading and load-to-failure test were applied to three groups: group A (proximal 6 screws+calcar screws), group B (proximal 6 screws), and group C (proximal 4 screws+calcar screws). Interfragmentary gaps were measured following cyclic loading and compared. The failure was defned when the bone breakage or medial gap closing was observed during ultimate failure load applied. The load-to-failure, maximum displacement, stifness, and yield load were recorded and compared. Results The interfragmentary gap was diferently reduced by 0.29±0.14 mm, 0.73±0.25 mm, and 0.53±0.09 mm following 1000 cyclic loading for groups A, B, and C, respectively. The load-to-failure was 945.22±101.02 N, 941.40±148.90 N, and 940.58±91.78 N in groups A, B, and C, respectively. The stifness of group A (214.76±34.0 N/mm) was superior when compared to that of group C (171.12±23.0 N/mm; p=0.025). The maximum displacement prior to failure, yield load, showed no signifcant diference between comparative groups. Conclusion Our study did not show any additional biomechanical efects with the use of inferomedial supporting screws in non-osteoporotic proximal humerus fracture, besides making the fracture-plate construct stif. The role of the inferomedial supporting screw was also unclear. However, the groups that used increased screw fxation and inferomedial screw insertion seemed to be more resistant to cyclic loading.