Your shoulder is a golf ball on a tee, held by four small muscles
The shoulder's ball sits in a socket so small and shallow that anatomists compare it to a golf ball balanced on a tee. Four muscles, the rotator cuff, clamp it in place so the big deltoid can lift the arm. Tear one of their tendons and reaching overhead turns painful and weak.
The cuff's members are the supraspinatus, infraspinatus, teres minor and subscapularis, four of the seven muscles linking shoulder blade to upper arm. Their tendons merge with the joint capsule and ligaments into one sheet that grips the humerus, and the supraspinatus and subscapularis wrap around the biceps tendon. Pressing the humeral head into the socket while the arm rises, a job called concavity compression, stops it riding upward and wasting the deltoid's pull. The front and back of the socket are shallower than its top and bottom, leaving those directions more exposed to shearing forces.
The division of labour is uneven. When the arm is raised in the plane of the shoulder blade, the infraspinatus and subscapularis generate two to three times the force of the supraspinatus, yet the supraspinatus has better leverage for general lifting. It is also the tendon most often torn, whether through sudden injury or gradual wear beneath the acromion. Repeated overhead or forceful pulling motions raise the risk, which is why pitchers, swimmers, tennis players, fast bowlers and even orchestra conductors and drummers turn up among the injured.
Diagnosis by examination alone is unreliable. The Hawkins-Kennedy test catches roughly 80% to 90% of impingement cases, but physical tests overall perform poorly. Much shoulder pain in impingement comes from tendinosis, an age-related problem that often settles by itself. Evidence for many treatments is modest: a single high-quality trial found hands-on therapy plus exercise beat a dummy treatment by only a small margin on function at 22 weeks, and a 2019 Cochrane review concluded with high certainty that subacromial decompression surgery does no better than a placebo operation for pain, function or quality of life.
Surgery still has a place for sudden traumatic tears causing substantial weakness, and keyhole repair has become far more popular than open operations. Rehabilitation proceeds in stages: a sling and no raising of the arm for 4 to 6 weeks so the tendon can knit, then therapist-guided passive movement, then active exercises, with free weights and resistance bands added at 8 to 12 weeks. A 2026 review also ties osteoporosis to tear development and poorer tendon-to-bone healing.
Source: Rotator cuff
