There are many causes of inflammation around the shoulder joint. Generally speaking, degenerative changes in the soft tissues around the shoulder, shoulder trauma and reduced shoulder activity, long-term strain on the ligaments and tendons around the shoulder joint, the effects of other diseases, and psychological factors can cause acute and chronic aseptic inflammatory reactions in the soft tissues around the shoulder joint. 1. Degenerative changes of the soft tissues around the shoulder. Degenerative diseases of the shoulder joint itself, especially local soft tissue degenerative changes, can cause frozen shoulder due to painful restriction of shoulder joint movement. The most common degenerative soft tissue diseases that lead to frozen shoulder are tendonitis and tenosynovitis, followed by impingement syndrome and subacromial damage. These diseases can lead to frozen shoulder due to further formation of damage, adhesions, contractures and other pathological changes in the musculature, rotator cuff, bursa and joint capsule. In addition, injuries to the shoulder, sometimes even minor ones, are also very likely to be the cause of frozen shoulder. 2. Shoulder trauma and reduced shoulder activity. Reduced activity of the shoulder joint, especially with the upper limb leaning against the body and hanging on the side for a long time, is considered to be the most important trigger of frozen shoulder. Fractures of the shoulder or upper arm, improper braking for too long after trauma can cause frozen shoulder, and sometimes even reduced shoulder joint activity due to the application of a neck and wrist sling after a forearm or wrist fracture, or immobilization in a chest cast can also cause frozen shoulder. In addition, heart surgery, thoracic surgery, female mastectomy, and sometimes even hepatobiliary surgery can also cause frozen shoulder on the same side of the shoulder. Frozen shoulder caused after this surgery may be related to postoperative pain and reduced shoulder activity. 3. Long-term strain on the ligaments and tendons around the shoulder joint. A considerable number of patients with frozen shoulder occur in occupations with poor posture, such as manual work and sedentary work, and excessive posterior thoracic spine protrusion. （Patients who have a hunchback are significantly more likely to develop frozen shoulder. This may be due to long-term poor posture or postural disorders that cause tilting of the scapula, and changes in the position of the scapula and humerus due to abnormal stress, gradually forming rotator cuff injury and potentially leading to frozen shoulder. 4.The influence of other diseases . (1) Neurological diseases
There are more clinical observations that show a higher incidence of frozen shoulder in patients with neurological disorders such as hemiplegia and nerve paralysis. This may be related to reduced muscle strength and movement, such as the incidence of frozen shoulder in patients with Parkinson’s disease, which is 12.7%.
The reason for the high incidence is clearly related to reduced movement. (2) Neighborhood diseases
A common adjacent site disorder is cervical spine disorders. There are many studies that show that patients with cervical spine disorders are significantly more likely to develop frozen shoulder, and that patients with frozen shoulder are often associated with a significant decrease in ipsilateral cervical lateral flexion and rotation. Therefore, caution should be exercised when making the differential diagnosis or determining whether a cervical spine disorder is responsible for frozen shoulder. Other adjacent disorders include heart disease, pulmonary tuberculosis, and subphrenic disease. (3) Endocrine system disorders
Endocrine system diseases such as diabetes mellitus, hyperthyroidism or hypothyroidism are also closely related to frozen shoulder, especially in patients with diabetes mellitus, where the incidence of combined frozen shoulder can reach 10%-20%.
Therefore, endocrine dysfunction may also be associated with frozen shoulder. Therefore, endocrine dysfunction may also be one of the triggering factors for frozen shoulder. 5. Psychological factors. A significant number of patients with frozen shoulder can have a history of emotional instability and trauma. Or they may be depressed due to long-term illness and socioeconomic pressure. They are more sensitive to pain, i.e. people with lower pain threshold tend to suffer from frozen shoulder easily. The possible reason for this is that once shoulder pain and inflammation has occurred, these individuals tend to have a harder time regaining motor function because they are overly sensitive to pain.