Biomechanical comparison of two biplanar and one monoplanar reconstruction techniques of the acromioclavicular joint

The purpose of this proof-of-concept study was to investigate the biomechanical performance of two surgical techniques, namely (1) the double Tight-Rope fixation with an additional acromioclavicular FiberTape fixation (DTRC) and (2) the fixation of the clavicle to the acromion and coracoid in a bipodal manner (Bipod) using a Poly-Tape and FiberTape. Both techniques intend to address vertical and horizontal instability after acromioclavicular dislocation. They were compared with the commonly used (3) double Tight-Rope (DTR) technique, which only stabilizes the clavicle to the coracoid.

The acromioclavicular joint (ACJ) of 18 composite Sawbone shoulder specimens (6 per reconstruction group) were tested for posterosuperior elongation (70N cyclical load, 1500 cycles), load-to-failure and stiffness.

After 1500 cycles, the DTRC, Bipod and DTR group showed an elongation of 0.45 mm (SD 0.14 mm), 1.19 mm (SD 0.54 mm), and 0.46 mm (SD 0.15 mm), respectively. Although the elongation of the Bipod group was increased when compared to the other two groups (Bipod versus DTRC p = 0.008; Bipod versus DTR p = 0.006), the difference was less than 0.7 mm. The DTRC showed a higher load-to-failure of 656.1N (SD 58.1 N) compared to the Bipod [531.1 N (SD 108.2N) (p = 0.039)] and DTR group [522.8 N (SD 32.8 N) (p = 0.033)].

The DTRC and the DTR group resulted in similar low elongation, while the elongation in the Bipod technique was slightly higher. Even though this difference of 0.7 mm shows statistical significance, it most likely has no clinical relevance. When testing in posterosuperior direction, which is the clinically relevant load vector, an additional fixation of the clavicle to the acromion did not reduce elongation in this study. It is, furthermore, questionable if the benefit of an increased load-to-failure in combination with no improvement in elongation and stiffness as seen in the DTRC group outweighs the possible risks and increased costs coming with the DTRC refixation.