Anatomy
There are 4 muscles in the muscle sheath (rotator cuff) surrounding the shoulder joint that control, coordinate and assist movement in the shoulder: M supraspinatus (upper scapular muscle), M infraspinatus (lower scapular muscle), M subscapularis and M teres minor. When the arm is brought out from the body and up over the head (abducted), the supraspinatus muscle slides under the upper shoulder blade projection (acromion).
Right shoulder blade muscles, from behind:
A. Acromion
B. Tuberc. majus (humeri)
C. M. infraspinatus
D. Spina scapulae
E. M. supraspinatus
Cause
The muscle can rupture if it is suddenly subjected to a load that exceeds the muscle’s strength, such as falling on an outstretched arm, lifting or throwing heavy objects. The vast majority of ruptures are partial muscle ruptures. With age and repeated loading with the arm above head level (tennis, swimming, throwing), the upper scapula muscle (M supraspinatus) becomes more rigid and inflexible and, together with the bursa above the muscle (bursa subacromiale), can easily become pinched between the humeral head (caput humeri) and acromion.
This can weaken the tendon and put it at risk of rupture. Most total ruptures occur in the elderly with degeneration (wear and tear changes) in the muscle tendon. In the elderly, total ruptures are particularly common. It is rare for healthy tendons to rupture.
Symptoms
In mild cases, a localised soreness is felt after the load (‘muscle strain’, ‘threatening fibre’). In more severe cases, a sudden shooting pain is felt in the muscle (‘partial muscle rupture’, ‘fibre rupture’) and in the worst case, a violent snap is felt, after which it is impossible to use the muscle (‘total muscle rupture’).
In muscle injuries, the following three symptoms are characteristic: Pain on pressure, stretching (the hand is moved in the lower back) and activation against resistance (the arm is lifted out to the side and up over the head, abduction). The pain is localised on the top and outside of the shoulder. After a longer period of time, you can see the shrinkage of the muscle at the back of the shoulder blade. In many older people, the tear is asymptomatic and has probably developed slowly so that other muscles have had time to take over the function.
Examination
The diagnosis is usually made through a general clinical examination where there is pain and reduced strength when lifting the arm. For more pronounced, sudden pain and difficulty lifting the arm away from the body, an ultrasound scan (or MRI scan) should be performed to detect even minor injuries.
See the ultrasound scan of the shoulder where a ‘collapsed socket’ is visible.
Treatment
Only in cases of almost total rupture of the supraspinatus muscle can surgery be considered, especially in younger patients. Surgery should be performed within 3 months of rupture, although the evidence for this is limited (Lapner P, et al. 2023), but re-rupture after surgical treatment is frequent (Routledge JC, et al. 2023) and the difference between surgery and conservative treatment (rehabilitation) is modest (Brindisino F, et al. 2021).
For partial tears and total tears in the elderly, treatment is short-term relief and gentle exercise (Dickinson RN, Kuhn JE. 2023).
Complications
If the progress is not smooth, you should consider whether the diagnosis is correct or if there are complications.
In particular, the following should be considered:
