INTRODUCTION
ANATOMY
The infraspinatus muscle is one of the four rotator cuff muscles in the shoulder joint. It is located in the posterior part of the shoulder. Infraspinatus connects the top of the humerus and the shoulder, helping arm rotation and shoulder stability.
As infraspinatus is essential for everyday functions of the shoulder and arm, it can become overworked, injured, or otherwise stressed, leading to muscle pain.
SYMPTOMS AND CAUSES OF PAIN
Repetitive motions of the shoulder usually cause infraspinatus muscle pain. It is, therefore, not uncommon that tennis players, swimmers, carpenters, painters, box players, or handball players often suffer from infraspinatus pain. Other possible causes include different pathologies.
Infraspinatus muscle pain is, in most cases, caused by muscle overuse, wear and tear, and some minor muscle strains. However, other pathologies and injuries can cause pain in the infraspinatus muscle.
Some of them include tendinopathy, muscle sprain, infraspinatus tear, impingement, bursitis, pinched nerve, trigger points etc.
Infraspinatus tendinopathy is a pretty common cause of infraspinatus muscle pain. It represents a minor injury to the muscle and can be divided into tendinitis and tendinosis. Tendinitis is characterized by tendon inflammation, while tendinosis means a small tear in the tendon without severe inflammation. Infraspinatus tendinopathies are usually caused by overuse, especially with repetitive overhead or throwing movements, the trauma of the shoulder joint, arthritis, or other joint inflammatory diseases, and usual “aging” wear and tear.
The infraspinatus pain caused by the tendinopathy is usually dull, increases with the shoulder movement and at night, localized in the shoulder and upper arm. Furthermore, the shoulder joint feels weak and stiff, and the range of motion can be reduced.
Another cause of infraspinatus pain is partial and complete tendon tears. The partial tear damages one part of the tendon and mostly develops through aging and repetitive stress. On the other side, a complete tear represents a full-thickness tear and is usually caused by the injury. Pain is present at rest and night, and it worsens with arm movements. Arm weakness and crackling sensation in the arm may also be present.
Infraspinatus impingement represents tendon compression and usually develops with a bone spur or inflammation. Impingement is quite common in athletes performing sports that involve overhead throwing. The infraspinatus pain caused by the impingement involves the whole shoulder, spreads down the arm, and worsens as time passes.
Bursitis can also cause infraspinatus pain. It occurs when the bursa (a fluid-filled sac between the arm bone and the shoulder joint) gets inflamed. Besides causing pain, muscle movements can be restricted. Bursitis is, in most cases, caused by overuse. Still, it can also be caused by arthritis, injury, diabetes, gout, thyroid disorders, or tendonitis.
Pinched nerves are generally well-known causes of pain. In the case of the infraspinatus muscle, the pain may arise when the suprascapular nerve gets pinched. The nerve can become pinched by the trauma, overuse, or shoulder dysfunction, producing pain located posteriorly and at the top of the shoulder joint, unresponsive to most usual treatments. Shoulder weakness is also quite common. Furthermore, in rare cases, it can lead to muscle atrophy.
Trigger points in the infraspinatus are quite common and sometimes underestimated causes of infraspinatus pain. These spots are thought to be muscle knots whose activation triggers pain. Active trigger points can cause pain even in rest, restrict movements and lead to muscle weakness.
The pain may be localized, but referred pain in other body parts is also not uncommon. So, what activates the trigger points? Usually, any stress on the muscle can lead to trigger point activation. Trigger points in the infraspinatus muscle may cause pain in the shoulder and down the arm.
DIAGNOSTIC EVALUATION
In order to determine the cause of infraspinatus pain, the first step is taking a detailed medical history. Important information for diagnosis is related to the symptoms, their onset, potential injuries, sports activity and so on.
Following the history taking, the doctor will perform a physical examination and test your range of motion and location of pain, and look for muscle weakness and motion-causing pain. If medical history and physical examination are insufficient for diagnosis setup, other tests like X-rays or MRI can be required.
TREATMENT
Treatment options, of course, depend on the cause of infraspinatus pain and can include the following:
- Rest (temporarily avoiding activities or resting the arm in a sling),
- Ice/heating (ice reduces inflammation, and heat relaxes the muscle),
- Nonsteroidal anti-inflammatory drugs (NSAIDs) (usually ibuprofen),
- Anesthetic or steroid injections (applied on the pain site, depending on the cause),
- Dry needling,
- Massage,
- Muscle stretching and exercise (physical therapy is usually recommended), and, in some cases,
- Surgery (for severe injuries).
Usually, nonsurgical treatments are recommended first, when possible. However, sometimes the combination of the nonsurgical treatment options is necessary. Furthermore, if other underlying diseases cause infraspinatus pain, that disease should also be treated. All of the mentioned treatment options should be discussed with the doctor.
MD, PhD. Physical Medicine & Rehabilitation Physician from São Paulo - Brazil. Pain Fellowship in University of São Paulo.