The Biomechanical Study of the Bioabsorbable Plates in Finger Fracture Fixation

Abstract

Objectives: Plates and screws have been proven to be a strong construct for the treatment of finger fractures as it allows for immediate postoperative mobilization. However, plates made in metal can be high in profile and may lead to both adjacent tendons and soft tissue irritation. Meanwhile bioabsorbable plates and screws have the advantage of being more conforming and low in profile. Yet there are concerns on its biomechanical strength. This study aims to explore the biomechanical strength of bioabsorbable construct by comparing with its titanium counterpart. Materials and Methods: Fifty-four simulated bone models of hand with a transverse osteotomy were used to simulate a finger fracture. A control group of 18 bone models (group 0) were fixed with a standard 4-hole, 1.5-mm titanium straight plates. A second set of 18 bone models (group 1) were fixed by 1.5-mm bioabsorbable mesh plate which was fashioned to cover half of the circumference of the bone. For the remaining set of 18 bone models, similar fixation was employed using the bioabsorbable plates except that it covered two-third instead of half of the circumference of the bone. All bone models were mounted to the Servo-hydraulic MTS 858 Bionix testing machine for biomechanical testing. Six bone models from each group were tested for maximum bending force, maximum torsional force, and fatigue property. The fatigue property was to simulate the load that the fixation construct would encounter over a 6 weeks period, ie, a period that allows the bone to heal with callous. It was set at 100 000 cycles at a displacement rate of 1 mm/s. Results: The average maximum bending force for group 0, group 1, and group 2 were 67.0 ± 10.2 N, 40.8 ± 15.0 N, and 43.3 ± 15.0 N, respectively. There was a significance between the metal and both the bioabsorbable groups with P < .001. For the average maximum torsional force, group 0 was 0.66 ± 0.06 Nm, group 1 was 0.27 ± 0.06 Nm and group 2 was 0.32 ± 0.07 Nm. A significance difference between the metal and both the bioabsorbable groups was noted at P < .001. For the fatigue tests, all constructs, except 2 in group 1, were able to withstand 1 000 000 cycles. The subsequent force to failure of both the bioabsorbable constructs were only 10% of the titanium constructs (6.8 N vs 67.6 N) of which the P was <.001. No significant difference was noted in maximum bending strength, maximum torsion force, and fatigue stress between the 2 groups of bioabsorbable constructs. Conclusion: The biomechanical strength of the bioabsorbable plates is inferior to the titanium plates. Yet as the requirement of finger fracture fixation is mainly to provide a stable environment for finger mobilization, the fatigue property of a construct appears to be more important. Thus, the strength of bioabsorbable plate and screw construct may still be strong enough to allow the fracture to heal.