Internal Fixation Bone Mass Index (IFBM) and Biomechanical Performance of Different Fixation Methods for Herscovici Type B and Type C Medial Malleolar Fractures.

BACKGROUND

Optimal fixation for Herscovici type B and type C medial malleolar fractures because of debated due to differences in fragment size and loading conditions.

PURPOSE: This study introduces the theoretical concept of Internal Fixation Bone Mass Index (IFBM) and compares three fixation methods under multidirectional loading.

STUDY

DESIGN

Biomechanical study using Synbone® artificial tibia models.

METHODS

Synbone® tibia models simulated type B (small fragment, n=27) and type C (large fragment, n=27) fractures. Three fixation methods-cannulated screws (CS, 4.0 mm), fully threaded cancellous screws (FTCS, 4.0 mm), and Kirschner wires (KW, 1.5 mm)-were tested under axial, transverse, and traction loading using an Instron® 5969 machine. IFBM was defined as A_implant/A_bone.

RESULTS

For type B fractures, KW showed a higher 2 mm displacement load under traction than CS (65 ± 11 N vs. 31 ± 9 N; post-hoc p = 0.008) and FTCS (65 ± 11 N vs. 36 ± 12 N; post-hoc p = 0.012), with no statistically significant difference under axial and transverse loading (ANOVA p = 0.231 and p = 0.501). For type C fractures, CS and FTCS showed higher stability than KW under transverse and traction loading (ANOVA p = 0.004 and p = 0.003); no statistically significant difference was detected under axial loading (ANOVA p = 0.167).

CONCLUSIONS

Fixation performance differed by fracture type. KW showed favorable performance for type B fractures, whereas screw fixation (CS or FTCS) demonstrated superior performance for type C fractures. IFBM is a theoretical metric that requires clinical validation.