Subacromial impingement syndrome is the reduction of the subacromial space caused by various reasons, mainly by tenderness at the acromion, pain during shoulder abduction, and loss or weakness of the shoulder girdle muscles and function. New perspectives suggest that "impingement" represents a cluster of painful symptoms and potential mechanisms, and the description of shoulder impingement has evolved into "impingement-related shoulder pain" rather than a pathological anatomical diagnosis itself. Further development can lead to the loss of normal shoulder joint function or substantial structural damage. Rotator cuff injury is characterized by substantial pathological changes that primarily occur in the shoulder cuff tendon portion, belonging to the category of bursa terminalis diseases, mainly due to the repetitive rotational movement of the greater tubercle of the humerus, especially abduction, and continuous friction with the coracoid and acromion ligaments. After rotator cuff injury occurs, the main clinical manifestations include pain, accompanied by limited shoulder function activity, affecting the shoulder joint function of the injured person, and causing an impact on routine work and life, with a relatively high recurrence rate. During shoulder joint movement, the tissue between the humeral head and the acromion may be repeatedly compressed, which may lead to damage and degeneration of the subacromial bursa and supraspinatus tendon, even tendon rupture, resulting in pain, weakness, and functional limitations. Rotator cuff injury may develop from degeneration of the supraspinatus tendon under shoulder impingement. In the non-surgical treatment of these two conditions, physical therapy is an important method, and a large number of studies have shown that physical therapy can improve symptoms of shoulder impingement syndrome and rotator cuff injury. By actively performing muscle strength training, stability training, and neuro-muscular control training, the goal is to alleviate pain and restore shoulder joint activity and function. When conducting physical therapy, assessing the scapulohumeral rhythm and adjusting exercise methods based on this rhythm are essential steps. Through the scapulohumeral rhythm, the balance of shoulder girdle muscle strength and the stability of neuromuscular control can be understood. When the coordination between the scapula and glenohumeral joint decreases, the scapulohumeral rhythm shows disruption and shoulder joint pain or dysfunction may occur. In Tomas et al.'s study, disruption of the scapulohumeral rhythm during shoulder impingement is manifested by insufficient upward rotation, external rotation, and abduction of the scapula, preventing the elevation of the acromion and increasing the pressure in the subacromial space. In Elizabeth et al.'s study, patients with shoulder cuff injuries exhibited disruption of the scapulohumeral rhythm, manifested by increased upward rotation angle and posterior tilt angle of the scapula, which was considered a compensatory mechanism for compressing the shoulder cuff tendon. When soft tissues under the acromion swell or fibrosis, the subacromial space may decrease relatively, and the body will adapt by changing the scapula's movement pattern to generate adaptive changes, making the scapula more prone to upward rotation or posterior tilt to raise the acromion, thereby compensatorily increasing the subacromial space, reducing the degree of soft tissue compression under the acromion, and alleviating shoulder joint pain symptoms.

To investigate the different scapulohumeral rhythm characteristics of patients with non-surgical treatment for shoulder impingement syndrome and rotator cuff injury to develop targeted rehabilitation exercises and to adjust the scapulohumeral rhythm to alleviate shoulder joint pain and restore movement function, providing a reference for non-surgical-treatment options for shoulder pain patients.

A total of 122 patients with shoulder joint pain were selected, including 43 cases of shoulder impingement syndrome, 40 cases of rotator cuff injury without surgical indications, and 39 cases in the control group. Targeted rehabilitation exercises were conducted for 12 weeks. The pre-and post-treatment data of scapulohumeral rhythm (scapular starting angle), Visual analogue scale (VAS), American shoulder and elbow surgeons' form (ASES), and shoulder joint abduction were recorded and statistically compared between the two groups.

(1) The scapulohumeral rhythm starting angle differed between the shoulder impingement syndrome group and the rotator cuff injury group, with the shoulder impingement syndrome group being later than the rotator cuff injury group (P<0.05). After adjusting the scapulohumeral rhythm, both groups showed significant improvement, while the control group showed no change. (2) After adjusting the scapulohumeral rhythm, there was a significant change in abduction angle in both the shoulder impingement syndrome group and the rotator cuff injury group (P<0.05), while the control group showed no change. (3) VAS and ASES scores significantly changed in all three groups after treatment (P<0.05) .

The scapulohumeral rhythm of shoulder impingement syndrome and rotator cuff injury exhibits inconsistent characteristics. Evaluating the scapulohumeral rhythm and implementing targeted scapulohumeral rhythm improvement and rehabilitation exercises can significantly alleviate shoulder joint pain and improve shoulder joint function.