Shoulder Pain: Rotator Cuff Injury and Impingement

The shoulder moves further than any other joint in the body, and it pays for that range with stability. The ball sits on a shallow socket roughly a third of its size, held centred by four muscles — the rotator cuff. Almost every common shoulder problem is a failure somewhere in that arrangement.

Pathophysiology: what is actually happening

Rotator cuff tendinopathy

The supraspinatus tendon runs through a narrow space between the humeral head below and the acromion above. Repeated loading, particularly overhead, produces degenerative change within the tendon: collagen fibres lose their normal parallel organisation, the matrix changes composition, and new vessels and nerve endings grow into the tissue. Those new nerve endings are part of why a degenerative tendon hurts despite little classical inflammation.

Blood supply matters here. The area of the supraspinatus tendon near its insertion is relatively poorly perfused, which is one reason it heals slowly and one reason it is the most common site of cuff pathology.

Subacromial impingement

When the space beneath the acromion narrows — through bony shape, thickening of the bursa, or more often through poor control of the shoulder blade allowing the humeral head to ride upwards — the cuff tendons and the bursa are compressed during elevation. This produces the characteristic painful arc, typically between roughly 60 and 120 degrees of abduction.

Impingement is better understood now as a consequence rather than a diagnosis in itself. The useful question is why the space narrowed.

Tears

Cuff tears are either traumatic — a single loading event in a younger person — or degenerative, where a tendon already changed by years of loading finally gives way. Partial-thickness tears involve part of the tendon depth; full-thickness tears extend through it. Degenerative tears are common with age and are frequently found on imaging in people with no symptoms at all, which is why imaging must be interpreted against the examination rather than in isolation.

Symptoms

• Pain reaching overhead, out to the side, or behind the back
• Night pain lying on the affected shoulder — very common, and often what finally prompts the appointment
• A painful arc through mid-range elevation
• Weakness that does not improve with rest, which suggests a tear rather than irritation

When to be seen sooner

Sudden weakness after a fall or heavy lift, an inability to lift the arm at all, or shoulder pain following a dislocation should be assessed promptly rather than managed at home.

First-line treatment

Most rotator cuff problems, including many partial-thickness tears, are managed without surgery. The programme addresses two things: the control of the shoulder blade, which is usually where the mechanical problem originates, and progressive strengthening of the cuff itself. Expect a course measured in months.

Injection options

Injections are not a treatment on their own. Used well, they reduce pain enough that you can do the rehabilitation that actually changes the outcome. Used as a substitute for that work, they buy time and little else. These are the options we discuss.

Corticosteroid

A strong anti-inflammatory placed directly into the painful structure. Onset is fast — usually within days — and for someone who cannot sleep or cannot work, that speed matters.

The limitation is duration. The effect fades over weeks to months, and repeated injections into the same tendon carry a real risk of weakening the tissue. In tendon problems specifically, the evidence is uncomfortable: corticosteroid outperforms doing nothing in the short term but does worse over a year. We use it deliberately and sparingly, and we will tell you if we think it is the wrong choice for your problem.

Platelet-rich plasma (PRP)

A sample of your own blood is spun in a centrifuge to concentrate the platelets, which carry the growth factors involved in tissue repair. The concentrate is injected into the injured tissue.

PRP works in the opposite direction to corticosteroid: onset is slower, often several weeks, but the effect tends to last longer. Preparation matters — leukocyte-poor systems, which remove most white cells, have performed better than leukocyte-rich ones in comparative studies. We use a leukocyte-reduced system.

PRP is a genuinely promising option and we are honest about where the evidence sits: the trials are smaller and less consistent than we would like, and some professional bodies still recommend against it on those grounds. We think it is reasonable for selected patients, and we will say so if we do not think you are one.

How the injection is given

Accuracy matters more than most people expect. Injections placed by landmark alone miss the intended target a meaningful proportion of the time, particularly in deep joints like the hip and in the small spaces around the shoulder and wrist. Ultrasound guidance lets us see the needle reach the structure we are aiming at, which improves both accuracy and safety.

The injection itself takes a few minutes. Most people feel some soreness for a day or two afterwards. We usually ask you to avoid heavy loading of the area for a short period, then start or resume the rehabilitation programme.

Where injection fits in the shoulder

The subacromial space is the usual target for corticosteroid in impingement and cuff tendinopathy. It can be very effective at breaking a cycle where pain prevents any meaningful rehabilitation. It is not a cure, and repeated injections around a degenerative cuff are approached cautiously.

PRP is used for cuff tendinopathy and selected partial tears, where the aim is to influence the tendon tissue rather than simply to suppress pain.

Complete tears in younger or more active people are more likely to need surgical repair, and that is a conversation with a surgeon rather than a reason for more injections. Dr Edwin Tan is our consultant orthopaedic surgeon.

When to see a doctor

Book an appointment if shoulder pain is waking you at night, if it has not settled after a few weeks, or if reaching overhead has become something you avoid. Sudden loss of power, or pain after a significant injury, warrants earlier assessment.

Part of the other joints we treat. See also elbow pain, wrist and hand pain.

Written by Dr Gerard Ee. Last medically reviewed and updated: September 2026.