Rotator Cuff Impingement: What Is Happening and What the Evidence Supports

The rotator cuff is four muscles: supraspinatus, infraspinatus, teres minor and subscapularis. Supraspinatus initiates shoulder abduction; the other three are primarily external and internal rotators, but their deeper function is compressing the humeral head into the glenoid socket during movement, keeping it centered under load [5]. When any of these muscles is weak or inhibited, the humeral head migrates superiorly during arm elevation, and the supraspinatus tendon runs into the underside of the acromion.

That is impingement: not primarily an injury, but a mechanical problem. The supraspinatus tendon is being pinched because the muscles responsible for keeping the humeral head centered are not doing their job well enough. This means the solution is usually not rest, not stretching, and often not surgery. It is restoring the strength and coordination of the muscles that keep the humeral head where it belongs.

What Is Happening

Subacromial impingement syndrome describes pain caused by compression of the supraspinatus tendon and the subacromial bursa between the humeral head and the acromion during arm elevation. The traditional explanation, proposed by Neer in the 1970s, was that acromial bone shape caused the compression. This led to decades of acromioplasty surgery, in which the underside of the acromion was shaved down to make more room.

The evidence no longer supports that explanation as the primary cause. A 2018 Lancet trial (the CSAW trial) randomized 313 participants to arthroscopic subacromial decompression, sham surgery (arthroscopy without the bone shaving), or no treatment. At one year, there was no significant difference in shoulder pain between the real surgery and the sham procedure [1]. The mechanical shaving of bone did not produce better outcomes than putting the patient under anesthesia and pretending to do it.

What does cause the compression, in most cases, is muscular. The rotator cuff muscles are not centering the humeral head adequately, often because of disuse, fatigue, or compensatory patterns from thoracic spine stiffness. The scapula may also be part of the problem: if the scapula does not upwardly rotate and tilt posteriorly during arm elevation, the subacromial space narrows regardless of how strong the rotator cuff is [4].

The Scapula’s Role

The shoulder joint does not operate in isolation. Every degree of arm elevation above about 60 degrees involves coordinated movement between the glenohumeral joint and the scapulothoracic articulation. The scapula must upwardly rotate, posteriorly tilt and externally rotate as the arm rises. This is called scapulohumeral rhythm, and it depends on the coordinated action of several muscles: the serratus anterior for upward rotation and protraction, the lower trapezius for upward rotation and posterior tilt, and the middle trapezius for retraction and stabilization.

When these muscles are weak or poorly coordinated, the scapula does not rotate adequately, the acromion does not clear out of the way, and the supraspinatus tendon gets pinched regardless of rotator cuff strength [2]. This is scapular dyskinesis, and it is a common finding in people with impingement symptoms. Clinically, it often presents as the scapula winging (medial border lifting off the rib cage) or the shoulder hiking (upper trapezius substituting for lower trapezius and serratus anterior during arm elevation).

The practical implication is that rotator cuff strengthening alone is sometimes insufficient. If the scapula is not moving properly, restoring rotator cuff strength addresses the force couple at the glenohumeral joint but not the one at the scapulothoracic articulation. Both need to work for impingement to resolve [4].

The Thoracic Spine Connection

The thoracic spine sits directly beneath the scapula. If the thoracic spine is stiff in extension (a common finding in people who sit at desks for prolonged periods), the scapula starts from a more anteriorly tilted, downwardly rotated position. This narrows the subacromial space before the arm even begins to move. A person with a stiff, kyphotic thoracic spine may have perfectly strong rotator cuff and scapular muscles and still develop impingement because the starting position of the scapula is compromised.

This is the mobility-stability framework in action. The thoracic spine is a mobility segment: it needs adequate extension and rotation for the stability segments above and below it (the scapula, the lumbar spine) to function properly. When thoracic mobility is lost, the scapula compensates, and the shoulder pays the price.

Conservative Treatment: What the Evidence Supports

A 2017 systematic review of 36 randomized controlled trials found that exercise-based interventions produced significant improvements in pain and function for shoulder impingement, with effects comparable to or better than corticosteroid injection and substantially better than doing nothing [3]. The exercises that showed the strongest evidence were:

• Rotator cuff strengthening, particularly external rotation
• Scapular stabilization exercises
• Graduated loading of the shoulder in functional ranges

Passive stretching of the shoulder, on its own, does not have strong trial support for impingement. In some cases, aggressive stretching of the posterior capsule can increase anterior humeral head translation and worsen the problem. The emphasis in current evidence-based protocols is on strengthening and motor control, not flexibility [5].

Corticosteroid injection has evidence for short-term pain relief (weeks to months) but no evidence for long-term improvement in function. Its role, when used, is to reduce pain enough to allow engagement with an exercise program. It is not a treatment on its own, and repeated injections carry risks to tendon integrity.

The distinction between exercise and injection is worth understanding clearly. An injection reduces inflammation and pain in the subacromial space, which can be valuable when pain is preventing the person from doing the exercises that will address the cause. But the injection does not change the muscular weakness or scapular dyskinesis that produced the impingement. Once the injection wears off, the mechanical problem remains. Exercise addresses the cause. Injection addresses the symptom. The two can work together, but exercise is the treatment that produces lasting change.

It is also worth noting that the term “impingement” itself has come under scrutiny in the research literature. Some clinicians now prefer “rotator cuff related shoulder pain” as a broader descriptor, because the traditional impingement model (bone pinching tendon) is too narrow to capture the range of mechanisms that produce subacromial pain [5]. The rotator cuff may be deconditioned, the scapula may be dyskinetic, the thoracic spine may be stiff, or the tendon may have intrinsic degenerative changes. In most cases, several of these factors coexist. The exercise-based approach addresses them collectively, which may be part of why it outperforms interventions that target a single factor.

Exercises to Try

Side-lying external rotation. Lie on your uninvolved side with the affected arm on top, elbow bent to 90 degrees. Hold a light weight (1 to 3 kg). Rotate the forearm upward, keeping the elbow pinned to your side. Pause at the top for two seconds. Lower slowly. Three sets of 12 to 15 repetitions. You should feel the back of the shoulder working. You should not feel a pinch at the top of the shoulder; if you do, reduce the range. The slow lowering phase is where most of the tendon adaptation occurs, so control the descent rather than letting gravity do the work.

Prone Y raise. Lie face down on a bench or the edge of a bed, one arm hanging straight down. Raise the arm at roughly a 45-degree angle from the body (forming a Y shape), thumb pointing up. Lift only to horizontal. Hold two seconds. Lower slowly. This targets lower trapezius, which assists scapular upward rotation [2]. Three sets of 10. No weight initially. Start without weight and add 0.5 to 1 kg only when the movement can be completed with the shoulder blade drawing down before the arm lifts.

Wall slide. Stand with your back against a wall, elbows bent at 90 degrees, backs of hands touching the wall. Slide your arms upward as far as you can without the hands or elbows losing contact with the wall. This trains scapular upward rotation under controlled conditions. Three sets of 10, slow and controlled. The point where you lose contact with the wall is the point where your scapular control runs out. Work to extend that range gradually rather than forcing the arms higher.

Thoracic extension over a foam roller. Sit on the floor with a foam roller across your mid-back. Support your head with your hands. Extend backward over the roller, aiming for 10 to 15 degrees of extension. This addresses thoracic spine stiffness, which is a common contributor to impingement because a kyphotic thoracic spine forces the scapula into a position that narrows the subacromial space. Ten repetitions, holding each for three seconds. Move the roller to different levels of the thoracic spine across sets to address the full range.

Scapular push-up plus. Start in a push-up position on your knees. Lower the chest slightly, then push up, and at the top push further by protracting the shoulder blades (rounding the upper back). The “plus” at the end specifically targets the serratus anterior, which is the primary muscle responsible for scapular upward rotation and keeping the scapula flat against the rib cage. Three sets of 10. If this provokes shoulder pain, perform it against a wall at an incline rather than on the floor.

When to See a Doctor

Most impingement responds to exercise-based rehabilitation within 6 to 12 weeks. See a doctor or physical therapist if:

• Pain is worsening despite consistent exercise over 6 weeks
• There is significant weakness in lifting the arm (which may indicate a rotator cuff tear)
• Pain followed a specific injury or fall (possible fracture or labral tear)
• Night pain is severe and persistent (may indicate a different pathology)
• You have numbness or tingling in the arm (may indicate cervical radiculopathy rather than a shoulder problem)

When to see a doctor. If joint pain follows a significant injury, is accompanied by swelling, giving way, locking, or loss of range of motion, or if you have neurological symptoms (numbness, tingling, weakness), see a doctor or physical therapist. They can assess whether imaging or specialist input is appropriate.