LAUSR

Objectives: Biomechanical testing supports anatomic reconstruction for high-grade acromioclavicular injuries to achieve improved stability, however, clavicle fractures have been reported following reconstruction. Thus, this study used laboratory experiments and finite element models to investigate the influence of tunnel parameters on the clavicle biomechanical performance. Methods: Composite synthetic clavicles were subjected to four-point bending on a servohydraulic load frame. Two established surgical techniques were compared; a single 3 mm tunnel technique and a double 6 mm tunnel technique. Finite element (FE) models were validated against experimental findings. Subsequent FE models explored a broad range of tunnel parameters to determine their biomechanical consequences. Results: The single tunnel (3 mm) specimens exhibited a stiffness of 19.9 ± 1.55 Nm2 and failed at 686 ± 45.2 N through the tunnel. The double tunnel technique exhibited a stiffness of 15.8 ± 1.18 Nm2 and failed at 390 ± 31.7 N through the medial tunnel. In FE models of the experiments (Fig. 1), the double tunnel technique has 69% of the strength of the single tunnel (vs 57% in the experiments) and failure was predicted at the medial tunnel. In 200 variations of tunnel configuration, the double tunnel technique exhibited increased stress concentration relative to a single tunnel. Larger tunnels exhibited higher stresses than smaller tunnels. Fig. 1: FE models exhibit greater stress concentration of the double 6 mm tunnel (right) technique compared to the single 3 mm tunnel (left) and technique. Conclusion: Experimental and FE results demonstrate that the double 6 mm tunnel reconstruction has a higher stress concentration than the single 3 mm tunnel technique when subjected to four-point bending. The validated FE model supports the use of small tunnels and suggests that a double tunnel configuration may have biomechanical disadvantages that must be weighed against the perceived advantages of “anatomic” reconstruction.