The shoulder joint is a ball joint with only very loose bony tracking; it derives its stability almost completely from the complicated interaction of ligaments, capsule and muscles. This makes possible the vast range of movement of the upper extremity, which is one of the reasons for our outstanding position in the evolutionary history of life. On the other hand, this also make the shoulder very prone to injury and wear.
The most common disorders amongst the many that may affect the shoulder joint include:
- Instability of the shoulder as the result of an accident after luxation (dislocation) or congenitally caused by weak ligaments.
- Impingement syndrome of the shoulder (entrapment pain) caused by anatomic crowding between the upper arm bone (humeral head), the rotator cuff tendon and the summit of the shoulder (acromion, acromioclavicular joint, coracoid process). Complaints can be caused by the following:
- Arthrosis of the acromioclavicular joint or a bony spur at the lower end of the shoulder summit, thus further decreasing the sub-acromial space between the humeral head and the shoulder summit.
- Tears of the rotator cuff (supraspinatus and infraspinatus tendon, subscapularis tendon). The supraspinatus tendon in particular is prone to early signs of degeneration with the formation of tears (ruptures). The rupture disturbs the biomechanics of the shoulder joint and results in painful impairment to mobility with a loss of strength.
- Calcification of the rotator cuff tendon (tendinitis calcarea), particularly around the supraspinatus tendon.
- Inflammations of the lubricating sac (synovial bursa), mainly as an accompanying symptom.
- Frozen shoulder, occurring spontaneously or after injuries.
- Arthrosis of the shoulder joint.
- Fractures in the shoulder region, particularly a fracture of the humeral head in older patients.
- Acromioclavicular (AC) joint disruption after falls, particularly in younger patients.