Rotator Cuff Arthropathy: Given the presence of multiple complete rotator cuff tears (subscapularis, biceps, and supraspinatus), along with associated findings like bony irregularity and capsular thickening, this diagnosis is highly probable. The clinical presentation of multidirectional reduced range of motion (ROM) and the ultrasound findings strongly support this condition.

Adhesive Capsulitis: Although the assessment of the inferior glenohumeral ligament (IGHL) and capsule was limited, the possibility of adhesive capsulitis cannot be ruled out, as suggested by the report. This condition is characterized by pain and stiffness in the shoulder, which could be contributing to the limited patient movement observed.
Subacromial Bursitis: The presence of pathological sheath fluid and the suboptimal visualization of the subacromial bursa due to tendon tears suggest that bursitis could be a contributing factor to the patient's symptoms.
Osteoarthritis of the AC Joint: Bony irregularity and capsular thickening of the acromioclavicular (AC) joint are indicative of degenerative changes, which could be contributing to the patient's shoulder pain and limited mobility.

Infection (Septic Arthritis or Osteomyelitis): Although less likely given the information, infection must always be considered in cases of joint pain and limited mobility, especially if there are systemic symptoms or a history of trauma. Infection in the shoulder joint or surrounding bone could lead to severe consequences if not promptly diagnosed and treated.
Tumor: A tumor affecting the shoulder region could cause pain, limited mobility, and the observed ultrasound findings. While rare, this possibility should not be overlooked, especially if the patient's symptoms do not improve with conservative management or if there are atypical findings on imaging.

Rheumatoid Arthritis or Other Autoimmune Disorders: These conditions can cause shoulder pain, limited mobility, and inflammatory changes that might be visible on ultrasound. However, they are less common causes of the specific ultrasound findings described.
Neurogenic Causes: Conditions affecting the nerves supplying the shoulder, such as a brachial plexus injury, could potentially cause some of the observed symptoms and signs, including muscle atrophy. However, these would not directly explain the ultrasound findings related to the rotator cuff and bursa.