Is it inevitable to have dynamic horizontal acromioclavicular joint instability with a single tightrope?

Background and purpose
Literature showed that single Tightrope fixation in acromioclavicular joint (ACJ) dislocation cases does not secure horizontal joint stability. A positive clinical cross-body adduction test is a usual outcome finding. We hypothesized that some cases might have some degree of horizontal stability, which might be confirmed with ultrasound examination.
Methods
This clinical study was performed on 27 patients who underwent single Tightrope application in acute ACJ dislocation. Patients were divided into group A which had an arthroscopic technique, and group B which had an open technique augmented with trans-ACJ fixation using two k-wires for 6 weeks. A clinical examination of the operated shoulders was done, and the results were compared with the sound shoulder examination in the same patient at the last 24 months postoperative follow-up visit. Besides, the results of the cross-body adduction test were correlated with ultrasound findings at the same visit. Records, operative details, and postoperative radiography were reviewed to assess if any factors would diminish the dynamic horizontal stability of the ACJ. Body mass index (BMI) was calculated per case.
Results
Group A had 17 patients (three patients had grade III dislocations, and 14 patients had grade V dislocations). Group B had 10 patients (four patients had grade III dislocations, and six patients had grade V dislocations). The clinical cross-body adduction test gave gross positive results in 14 patients out of group A patients while it gave gross positive results in six patients out of group B patients. Group A patients with negative results were 3, while group B patients with negative results were 4. By ultrasound, differences in horizontal translation of the clavicle within the ACJ in resting and cross-arm positions were more obvious in all operated shoulders than in all sound shoulders.
Conclusion
The less the Rockwood grading, the more potential to secure more horizontal stability. An open approach also gives more horizontal stability. With increased BMI, horizontal instability is usually masked. So, some factors may diminish, or mask clinical dynamic horizontal instability, which can be confirmed or rolled out with ultrasound usage.