A Biomechanical Study of 3 Types of Scaphoid Fixation in a Fracture Non-union Model: N/A - Not a clinical study

Abstract

Grant received from: AOA (Australian) Research Foundation Grant There is no financial information to disclose. Scaphoid fracture healing is related to inter-fragmentary displacement. In cases of non-union with bone resorption, this becomes more challenging to achieve. The null hypothesis of this study states there is no difference in the biomechanical stability of 3 different types of scaphoid fixation in a fracture non-union model. Thirty scaphoid cadaveric specimens were assigned to 3 different fixation groups: (1) Single 3.0mm cannulated compression screw, (2) 2 x 2.2mm cannulated compression screws and (3) scaphoid plate fixation. Standardized 3mm volar wedge osteotomies were used to create a scaphoid waist non-union model. All specimens were loaded using a servohydraulic axial force testing system at a rate of approximately 10N/s, from a dorsal to volar cantilever direction, oriented at 45 degrees to simulate physiologic loading. The primary outcome measure was load to failure. Secondary outcome measures were load to 2mm displacement, energy absorbed, construct stiffness and mode of failure, recorded by video and retrieval analysis. One-way ANOVA tests were used to analyze for differences between groups for parametric data and Kruskal-Wallis tests were used for non-parametric data. There was a significantly lower load to failure, in the single screw group compared to double screw fixation (mean difference: 187.2N, P = 0.005) and also in the single screw group compared to plate fixation (mean difference: 150.7N, P = 0.04). The mean load to 2mm displacement in the single screw group (91.5N) showed a trend towards being weaker than the double screw (181.8N, P = 0.08) and plate (197.2N, P = 0.06) fixation groups. There was a significantly lower stiffness in single screw compared with double screw (mean difference: 85.4N/mm, 95% CI [60.1,110.6], P = 0.03) and lower energy absorbed in single screw compared with double screw groups (mean 386.5mJ, P = 0.0042) and in single screw compared with plate fixation (mean difference: 270.8mJ, P = 0.02). The most common mode of failure was rotational failure (7/10), screw cut-out (7/10) and plate bending (6/10) in the single screw, double screw and plate fixation groups, respectively. •The null hypothesis is rejected: there is a difference in the biomechanical stability of 3 different types of scaphoid fixation in a fracture non-union model.•Double screw and plate fixation provides greater stability.•Single screw fixation is weakest due to rotational failure.•No significant differences between double-screws and plate groups.•The use of double screws or plate fixation in a non-union setting may allow accelerated rehabilitation without compromise to fracture stability and union.