Because protraction causes larger kinematic alterations than horizontal adduction it can be used to identify lesions in acromioclavicular injuries more clearly, a new study finds.
“Previous cadaveric kinematic studies on acromioclavicular injuries described mainly rotational difference during humerothoracic movements. Although isolated scapulothoracic movements are also often performed during activities of daily life and can be painful after acromioclavicular injuries, they have not been extensively studied,” wrote the researchers of the study, “Kinematic Alterations in the Shoulder Complex in Rockwood V Acromioclavicular Injuries During Humerothoracic and Scapulothoracic Movements: A Whole-Cadaver Study”.
The findings were published online in The American Journal of Sports Medicine on October 29, 2021.
The researchers conducted a cadaver study to test out the hypothesis that a kinematic analysis of joint motions in the intact shoulder versus a shoulder with Rockwood V injury would demonstrate different kinematic alterations during humerothoracic and scapulothoracic movements.
They performed a kinematic analysis in 14 cadaveric shoulders during 3 humerothoracic passive movements including coronal and sagittal plane elevations and horizontal adduction and 3 scapulothoracic passive movements including protraction, retraction, and shrug.
Rotational motions in the sternoclavicular, scapulothoracic and acromioclavicular joints were measured using an optical navigation system. And in the acromioclavicular joint, mediolateral, anteroposterior, and superoinferior translations were analyzed.
The researchers found that in a Rockwood V injury, there was a significant increase in clavicular elevation in the sternoclavicular joint during both humerothoracic and scapulothoracic movements. A decrease in posterior rotation of the clavicle only happened during humerothoracic movements.
Protraction caused the biggest change in scapular position in the scapulothoracic joint, they also reported.
In the acromioclavicular joint, there was also a significant inferior translation of the scapula during all movements, a significant anterior translation during protraction and horizontal adduction and a significant posterior translation during coronal plane elevation.
The acromial end of the scapula also slid further under the distal clavicle during protraction than it did during horizontal adduction.
“Large kinematic differences were seen between the intact state and a Rockwood V lesion not only during humerothoracic movements, but also during scapulothoracic movements in the cadaveric model,” the researchers wrote.
“During humerothoracic movements, rotational differences were mainly caused by alterations in the clavicular position. In contrast, during protraction, the alterations in the scapular position were the dominant factor,” they added.
“This study demonstrates that protraction induces larger kinematic alterations than horizontal adduction in acromioclavicular injuries and can therefore be included in both clinical examination and kinematic analyses to identify lesions more clearly.”
The authors of the study included Jan Peeters, M.D., Thomas Braeckevelt, M.D., and Alexander Van Tongel, M.D. of Ghent University Hospital in Ghent, Belgium, and Stijn Herregodts and Tanneke Palmans of Ghent University.
