Summary

Single-tunnel cortical button reconstruction of the CC joint significantly increases superior-inferior joint stiffness in a manner closely correlated with construct preload, while graft and suture augments and cyclic loading do not significantly alter SI-plane reconstruction biomechanics.

Abstract

Background

Coracoclavicular (CC) reconstruction is frequently performed with augments to help minimize clinical/radiographic failures without a thorough understanding of risks/benefits or preload effects.

Purpose

Compare single-tunnel (ST) cortical button (CB) CC reconstruction to augmentation with high-strength suture (CB + S) or tibialis anterior allograft (CB + G) under cyclic loading and load-to-failure conditions. Measure the effect of tensioning (preload) on superior-inferior (SI) and anterior-posterior (AP) load-displacements.
Study Design: Controlled laboratory study

Methods

Nine fresh-frozen cadaveric shoulders from five donors were disarticulated and potted for testing in a custom materials testing jig. Motion capture was used to measure scapular and clavicular displacements under physiologic loads: -10N to 70N SI and -25N to 25N AP for 10 cycles. Next, AC and CC ligaments were transected and CC ligaments were serially reconstructed with different techniques (CB, CB + S, and CB + G) in a randomized order, and exposed to 5,000 cycles of 10-70N superior-directed loading . Construct preload, and pre and post-cyclic testing displacements in SI and AP directions were recorded, followed by a superiorly directed load-to-failure.

Results

All reconstruction groups demonstrated significantly increased stiffness and reduced SI load-displacements vs intact state (p<0.04) before cyclic testing. Significant differences remained after cyclic testing, with average SI load-displacements of: 0.7+/-0.4mm, 0.5+/-0.3mm, and 0.7+/-0.4mm for the CB, CB + S, and CB + G groups respectively, compared to 2.3+/-1.5mm intact. SI loosening was minimal during cyclic loading, with 96% of reconstructed specimens loosening <0.5mm. Graft or suture augmentation did not significantly change SI load-displacements, but the CB alone group demonstrated significantly increased AP displacement vs intact and CB + S groups after cyclic testing. There were no significant differences in average failure loads between groups, all augmented groups failed at >700N. Across groups, preload tension was significantly inversely correlated with superior load-displacement p<0.005.

Conclusion

Single-tunnel cortical button-based CC reconstruction techniques significantly increase CC stiffness compared to native state, particularly in the SI direction (two-fold), in a manner highly correlated with preload tension. Suture augmentation may be beneficial to prevent AP creep and overload failures but does not significantly change superior force-displacements under cyclic loading.