Shoulder Impingement Syndrome: Why Does It Hurt When You Raise Your Arm?

Shoulder impingement syndrome (subacromial pain syndrome) is the most common cause of shoulder pain, accounting for roughly half of all shoulder complaints. It occurs when the tendons of the rotator cuff and the bursa, a fluid-filled sac, become compressed between the bony roof of the shoulder (the acromion) and the head of the humerus as the arm is raised out to the side and overhead. It is common after age 40 and in people who work or play sports overhead.

Symptoms

• Pain in the front–outer shoulder that radiates down the outer arm

• Pain when raising the arm to the side between 60° and 120° (a "painful arc")

• Difficulty with overhead tasks and reaching behind the back, such as fastening a bra or reaching into a back pocket

• Night pain that worsens when lying on the affected side

• Weakness that develops over time

Marked weakness, complete inability to raise the arm, or a sudden onset after trauma suggest a tendon tear rather than impingement and should be evaluated separately.

What Causes It?

Current understanding holds that the problem is not only bone compressing the tendon but, in most cases, overuse-related wear of the tendon itself (tendinopathy). Contributing factors:

• Weakness and imbalance in the rotator cuff and scapular (shoulder-blade) muscles

• Poor posture: rounded shoulders, a stooped upper back

• Repetitive overhead activity, such as in painters, teachers, volleyball, and swimming

• Tightness of the posterior shoulder capsule

• Bony shape (a hooked acromion) — this contributes less than previously thought

Diagnosis

Diagnosis is made largely on examination. X-rays show bone shape and calcium deposits (calcific tendinitis). Ultrasound and MRI are ordered when a tendon tear is suspected or when there is no response to 6–12 weeks of treatment. It should be kept in mind that a substantial proportion of pain-free people over 60 also show tendon degeneration on MRI; an imaging finding alone does not determine treatment.

Treatment: An Evidence-Based Sequence

1. Exercise Therapy (the Strongest Evidence)

Programs that strengthen the rotator cuff and scapular stabilizers and correct posture are the mainstay of treatment. Large studies have shown that 12 weeks of structured exercise produces outcomes equivalent to surgery in the medium term. Exercises include:

• Resistance-band external and internal rotation

• Scapular retraction exercises

• Wall slides and prone Y–T–W exercises

• Posterior shoulder capsule stretches (sleeper stretch, cross-body stretch)

The program should be maintained for at least 8–12 weeks, 3–5 days a week. Mild pain, around 3–4 out of 10, during exercise is acceptable; pain that persists into the next day indicates the load was too high.

2. Load and Activity Modification

Temporarily reducing the overhead activities that trigger pain; complete inactivity is not recommended, as it can set the stage for a frozen shoulder.

3. Medication and Injection

• Short-term oral or topical anti-inflammatory medication

• Subacromial cortisone injection: provides 4–8 weeks of relief when severe pain is preventing exercise, making it easier to begin a rehabilitation program; it has no long-term advantage over exercise and is not recommended more than 2–3 times a year

• PRP injection: evidence in impingement syndrome is insufficient

4. Surgery

In selected patients who do not respond to at least 6 months of appropriate non-surgical treatment, arthroscopic bursa debridement and, if needed, bone shaving (subacromial decompression) may be performed. High-quality studies in recent years have shown that decompression alone does not produce a significant difference compared with placebo surgery, calling its routine use into question. Surgery is mainly meaningful when there is an accompanying structural problem, such as a tendon tear, calcium deposit, or bone spur.

Recovery Time

Most patients show significant improvement with 6–12 weeks of regular exercise; full recovery can take 3–6 months. Continuing strengthening exercises at a lower intensity is recommended to prevent recurrence.

This article is for general information purposes; a personal examination is required for an individual treatment plan.