Pain lifting the arm is usually the rotator cuffStrong evidence
Rotator cuff related shoulder pain, also called subacromial pain, impingement or bursitis, is "the most common reason for shoulder pain", NHS inform says. It is usually brought on by "lifting the arm above shoulder level and reaching behind the back, for example when putting a jacket on", and an NHS trust says the rotator cuff accounts for up to 70% of shoulder problems. The NHS describes pain "that's worse when you lift your arm, especially when you lift it above your head".
A review for GPs puts it at ages 35 to 75. Heavy lifting or repeated movements "especially above shoulder level" can play a part, though it often affects the non-dominant arm and people who don't do manual work. In studies of workers, working with the hands above shoulder level, repetition, force and vibration are the exposures most consistently linked with it. NHS inform adds age-related change, injury, smoking, obesity, high cholesterol and diabetes.
Sources 1, 2, 3, 4, 5, 6
The painful arc: a clue, not a diagnosisEmerging evidence
A painful arc is pain partway up as you lift your arm out to the side, roughly between 70 and 120 degrees, that eases as the arm goes higher or comes back down. A review for GPs says it "reinforces the diagnosis of a rotator cuff disorder", but "is neither specific nor sensitive".
The numbers agree. Pooled across studies, it picked up about half of cases of impingement (53%) and was absent in about three quarters of people without it (76%). In specialist clinics it was the only pain test that clearly raised the likelihood of rotator cuff disease, and a normal arc lowered it; in 55 people having surgery, it was a fair test, not a strong one. In the original series of 97 people, the trouble was spread across three different parts of the rotator cuff, so the arc doesn't point to one tendon, a tear or any particular treatment.
The old explanation, a tendon trapped under bone, is doubted: Arthritis UK says impingement is "nothing to do with your tendons being trapped by bones, as was previously thought".
Sources 4, 7, 8, 9, 10, 11
Other causes, and how they feelStrong evidence
Frozen shoulder makes the shoulder "painful and stiff for months, sometimes years", the NHS says, and it is linked with diabetes. A review for GPs puts it at ages 40 to 65, with movement lost in every direction, and the large UK trial of frozen shoulder took losing at least half of the ability to turn the arm outwards as its sign.
Pain on top of the shoulder, where the collarbone meets the shoulder, comes from the AC joint, the NHS says. It hurts to press there and to reach across the body, and arthritis of this joint often causes few or no symptoms. It's a minority: in 153 people with shoulder pain in primary care, 22 (14%) had AC joint pain confirmed by an injection, and the usual AC joint tests didn't pick them out.
Most rotator cuff tears come from wear over time and are often painless; a fall on an outstretched arm, or lifting something too heavy "with a jerking motion", can tear the cuff suddenly, with intense pain, sometimes a snapping feeling and immediate weakness, say the American Academy of Orthopaedic Surgeons' patient pages. Shoulder pain can also come from the neck, "even when you don't feel pain in your neck", NHS inform says, often with pins and needles or sharp, hot or burning pain.
Sources 12, 13, 4, 14, 15, 16, 17, 18
When a scan helpsStrong evidence
Usually not at first. The UK care pathway for this kind of shoulder pain says an ultrasound or magnetic resonance imaging (MRI) scan of the rotator cuff "is rarely indicated in primary care", and that a tear on a scan "does not always correlate with symptoms and does not imply a definite need for surgery in every case". Rotator cuff changes on scans become more common with age whether or not people have pain, from about 1 in 10 people aged 20 or under to 62% at 80 or over, and an NHS trust says the findings on a scan often don't explain the pain.
An X-ray can help if you aren't improving with treatment, and it shows arthritis and calcium deposits. A scan and an urgent specialist opinion are for an injury that leaves the arm suddenly weak.
Sources 19, 20, 2
How it usually goesEmerging evidence
NHS inform says a new shoulder problem or a flare should begin to settle within 6 weeks, and the NHS says self-care usually takes about 2 weeks to start helping and recovery can take 6 months or longer. With exercise, an NHS trust expects improvement over at least 12 weeks, sometimes up to 24, perhaps with little change in the first 6; the UK care pathway gives physiotherapy about 6 weeks, and a further 6 if it's helping.
In the trials, most people improved: both groups did in a large trial of 708 people, and in a trial of people already waiting for surgery, 69% reported a good result after 12 weeks of specific exercise. Frozen shoulder can take months or years. No one can promise a date.
Sources 18, 14, 2, 19, 21, 22, 12