Horizontal stability of the acromioclavicular joint for intact, disrupted and reconstructed coracoclavicular ligaments.

Abstract

INTRODUCTION: The acromioclavicular (AC) joint serves a vital role in suspending the upper limb from the axial skeleton. Injuries to the AC joint represent 9-12% of all acute shoulder injuries. This number increases up to 40-50% in those involved in contact sports. Failure to treat these injuries adequately can lead to debilitating pain, scapula dyskinesia, skin tenting and deformity. Biomechanical and clinical studies have proven the superiority of anatomical reconstruction of the coracoclavicular (CC) ligaments with AC joint vertical stability, but horizontal stability has been somewhat neglected. The study aimed to investigate the effect of the position of the coracoid tunnel on horizontal (anterior) displacement during the arthroscopic assisted CC ligaments reconstruction. The hypothesis was that the horizontal (anterior) displacement would increase with a more anterior coracoid process tunnel position. MATERIALS AND METHODS: Fifteen fresh frozen shoulder specimens were included. Shoulders with visible AC joint pathology and/or surgery were excluded. Horizontal displacement was performed determined with a Universal Testing Machine (Hydropuls® UTS, 100 kN) and an IDT NX8-S2 camera was used to capture displacement during testing. 2D motion analysis was then performed on the captured images using the TEMA motion analysis. The following conditions were tested: intact and disrupted CC ligaments; repair with Tightrope single tunnel coracoid and clavicle (ST); repair with double tunnel clavicle (DT) and single tunnel coracoid. For all repair test occasions the coracoid tunnel was placed at base (0), 1:9 and 1:5 anterior to the base. One way ANOVA with post hoc comparisons were used for within and between group differences. RESULTS: The displacement for intact CC ligaments was 1.6 ±0.9mm and 3.6 ±1.1mm for the disrupted ligament. The mean AC joint horizontal (anterior) displacement for ST-0 was 1.9 ±0.8mm, while the ST-9 and ST-5 demonstrated 36% more displacement than the native state. The mean AC joint horizontal (anterior) displacement for DT-0, DT-9 and DT-5 were 1.2 ±0.7, 2.0 ±1.2mm and 1.9 ±1.2mm. DISCUSSION: The present study used the displacement-controlled load testing method with a 100kN Hydropuls® Universal testing machine. To test the hypothesis of the present study, the coracoid tunnel location had to be modified. During testing, the coracoid tunnel was located at the base of the coracoid, 1:9 and 1:5 from the coracoid base. The results of this study demonstrated that disruption of the coracoclavicular (CC) ligaments resulted in 100% displacement of the clavicle when compared to the intact condition. CONCLUSION: There was no statistically significant difference in the horizontal (anterior) displacement between the three tunnel positions for both ST and DT surgical techniques. However, DT-0(Base) demonstrated the least horizontal (anterior) displacement of the tested tunnel positions. The position of the coracoid tunnel has no effect on the horizontal (anterior) stability during AC joint reconstruction. Keywords: acromioclavicular joint; coracoclavicular ligaments repair; biomechanical testing; horizontal instability; clavicle tunnel; coracoid process tunnel; coracoclavicular ligament reconstruction; Hydropuls® machine; Tightrope.