What Is Shoulder Impingement Syndrome?
Shoulder impingement syndrome is a common diagnosis among patients who seek medical care for shoulder pain. However, basing the treatment plan on this diagnosis alone makes it difficult to prevent recurrence. The subtype and structural cause must first be identified so that subsequent nonsurgical treatment can lead to actual functional recovery and long-term maintenance. This is because the direction of exercise therapy depends on knowing which structure is being compressed and where.
Shoulder impingement syndrome is not a single disease. It is an umbrella term for conditions in which tendons or bursae within the shoulder repeatedly rub against surrounding bony structures when the arm is raised or rotated, causing inflammation and pain. In clinical practice, even within the same patient's shoulder, the location and direction of impingement can vary considerably.
There are three subtypes. Subacromial impingement occurs when the rotator cuff (the four tendons that rotate the shoulder) and bursa are compressed in the space beneath the acromion. Internal impingement occurs when a tendon catches against the back of the glenoid inside the joint as the arm is raised to the side and externally rotated. Subcoracoid impingement occurs when the subscapularis is compressed beneath the coracoid process (a bony projection at the front of the shoulder blade). Subacromial impingement mainly occurs when the arm is raised overhead and is accompanied by inflammation of the bursa. By contrast, internal impingement results from the tendon striking the inside of the joint when the arm is externally rotated, as in a throwing motion, and the treatment approaches for the two conditions also differ.
Structural and functional causes are intertwined. If the acromion curves downward or a bone spur has developed, the space is anatomically narrow. In contrast, if the muscles that hold the shoulder blade in place are weak or a forward-head posture causes the shoulders to round forward, functional impingement can occur as the space narrows only during movement. The latter is seen much more often in clinical practice.
The term “impingement syndrome” has been criticized for being broad and nonspecific. This means that very different pathologies are grouped under the same diagnosis. The first step in treatment should not be merely diagnosing “impingement syndrome,” but determining the subtype and whether the problem is structural or functional.
What Symptoms Occur, and How Is It Diagnosed?
The most typical sign is a sudden stabbing pain between 60 and 120 degrees when raising the arm out to the side. In many cases, the pain decreases when the arm is raised higher beyond this range. This is medically known as a “painful arc,” and it corresponds to the angles at which the space beneath the acromion is narrowest.
Night pain is also characteristic. Rolling onto the painful side can wake you from sleep. Even when lying on the opposite side, the weight of the arm can cause a dull, heavy ache. You may also feel catching when reaching the arm behind your back to put on a shirt or place your hand in a back pocket. The pain may not remain limited to the top of the shoulder; it can radiate down to the deltoid region on the outer upper arm. Because of this radiating pain, quite a few patients seek medical care believing they have a cervical disc problem.
Diagnosis is not straightforward. The first step is a physical examination. The Neer test passively raises the arm to provoke contact between the acromion and the rotator cuff. The Hawkins–Kennedy test evaluates impingement from another direction by raising the arm to 90 degrees and rotating it inward. Because the two tests provoke impingement through different mechanisms, both should be performed. Even if the physical examination findings are positive, the tests have limited sensitivity and specificity, so imaging is used to supplement them.
X-rays are first used to assess the shape of the acromion (Type I flat, Type II curved, or Type III hooked) and the presence of bone spurs or calcium deposits. Ultrasound provides a more accurate assessment of the location and characteristics of rotator cuff calcification. Through real-time dynamic examination, ultrasound can detect changes in rotator cuff tendon thickness, partial tears, and bursal swelling. MRI provides the most detailed view of lesions within the joint and the extent of tendon tears, so depending on the situation, it plays an important role in deciding whether surgery is appropriate.
The importance of differential diagnosis cannot be overstated. Cervical C5–6 radiculopathy (a cervical disc problem) can cause pain on the outer shoulder and muscle weakness, so its symptoms overlap with those of impingement syndrome. Early-stage frozen shoulder, calcific tendinitis, and superior labral tears can all cause similar pain. Self-diagnosing based on symptoms alone can lead to repeatedly performing inappropriate exercises and making the condition worse.
Treatment Principles: Nonsurgical Treatment Comes First
Accurate differential diagnosis is the starting point for determining the direction of treatment. The treatment goals must first be clearly defined. Relieving pain is only the starting point; the key is to restore proper shoulder function and maintain it. Focusing only on eliminating pain quickly leaves the cause unresolved and allows the symptoms to recur.
Fortunately, most cases of shoulder impingement syndrome may improve without surgery. The first-line approach is nonsurgical treatment, with exercise therapy at its core.
Exercise therapy has two components. The first is rotator cuff strengthening, which restores the muscles that pull the humeral head downward to create space beneath the acromion. The second is scapular stabilization, which balances the muscles in the back and trains the shoulder blade to rotate at the proper time when raising the arm. Exercise-based rehabilitation plays an important role in preventing shoulder injuries and managing them over the long term. Even if an injection temporarily relieves pain, the likelihood of recurrence increases without exercise therapy.
During the acute phase, pain interferes with exercise. Nonsteroidal anti-inflammatory drugs (NSAIDs) are used to reduce inflammation, and medication is injected directly into the subacromial space. Image-guided injections may improve accuracy because the needle tip is visualized using ultrasound or a C-arm during the procedure, and the effects vary depending on the individual’s condition.
When tissue damage is also present, regenerative therapy may be considered as an adjunct. PRP (autologous platelet-rich plasma) may be considered for partial rotator cuff tears or tendon degeneration, but the evidence to date is heterogeneous. The clinical use of exosomes in South Korea remains limited. Therefore, these therapies are not necessary for every case of impingement syndrome and are selected by considering both imaging findings and the duration of symptoms.
When should surgery be considered? It should be limited to cases in which symptoms remain despite at least six months of adequate, systematic conservative treatment or imaging clearly shows structural damage such as a full-thickness tear or severe bone spurs. Acromioplasty is the final option, and the proper sequence is to first review the accuracy of the diagnosis and the quality of conservative treatment.
This content is provided for medical information purposes, and responses to treatment may vary from person to person. Outcomes may vary depending on the patient’s participation in exercise and use of the shoulder in daily life. Please consult a specialist for an accurate diagnosis and appropriate treatment.
References
- Horowitz Evan H, Aibinder William R (2023). Shoulder Impingement Syndrome.. Phys Med Rehabil Clin N Am. PMID: 37003655
- Chiou-Tan Faye Y (2022). Musculoskeletal mimics of cervical radiculopathy.. Muscle Nerve. PMID: 35466429
- Liaghat Behnam, Pedersen Julie Rønne, Husted Rasmus Skov (2023). Diagnosis, prevention and treatment of common shoulder injuries in sport: grading the evidence - a statement paper commissioned by the Danish Society of Sports Physical Therapy (DSSF).. Br J Sports Med. PMID: 36261251
Frequently Asked Questions
Q. How is shoulder impingement syndrome different from frozen shoulder?
With impingement syndrome, pain is concentrated only at certain angles or during specific movements, and the arm can move relatively freely outside that range. With frozen shoulder, the capsule surrounding the joint itself stiffens and limits the range of motion in all directions; the key difference is that the arm cannot be raised even when someone else tries to lift it.
Q. What happens if shoulder impingement syndrome is left untreated?
Even if it initially causes only mild inflammation, repeated impingement can gradually wear down the rotator cuff tendon, potentially progressing from a partial-thickness tear to a full-thickness tear. If a full-thickness tear is confirmed, surgery may need to be considered separately with a specialist, so it is important to identify the structural cause early in the course of symptoms.
Q. How long does treatment take?
Mild cases involving only functional problems without tendon damage often improve within 6–12 weeks. When a partial rotator cuff tear or calcium deposit is also present, the rehabilitation plan typically allows for 3–6 months or longer, although the actual course may vary depending on adherence to exercise and the amount of daily shoulder use.
Q. Can It Heal Without Surgery?
Most cases of shoulder impingement syndrome may improve with nonsurgical treatment, although outcomes may vary between individuals. Exercise therapy focused on strengthening the rotator cuff and stabilizing the shoulder blade is key. However, if there is severe structural damage, such as a full-thickness tendon tear, surgery should be considered separately.
Q. What should I keep in mind after treatment to prevent recurrence?
Even after the pain is gone, an imbalance in the muscles around the shoulder blade can recreate conditions that lead to impingement. After returning to your daily routine, consistently performing scapular stabilization exercises and reviewing any work or exercise habits that involve repeatedly raising your arms may help prevent recurrence over the long term.