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Infraspinatus muscle atrophy is a condition that causes severe atrophy and fatty degeneration of the infraspinatus muscle. It is usually caused by a chronic rotator cuff tear but can also be caused by suprascapular nerve entrapment at the spinoglenoid notch. Isolated infraspinatus muscle atrophy is uncommon and typically occurs alongside suprascapular nerve entrapment distal to the spinoglenoid notch. In some cases, infraspinatus muscle atrophy can be caused by an insertional tear of the infraspinatus tendon. This condition can lead to severe pain and weakness in the affected area. Magnetic resonance imaging (MRI) is often used to diagnose infraspinatus muscle atrophy and identify any underlying causes of nerve impingement. Treatment options include both conservative and surgical approaches, with most patients able to return to full activity. However, recovery of muscle bulk is less common, even with isokinetic testing showing a full or near-full return of strength.
| Characteristics | Values |
|---|---|
| Cause | Acute traumatic events, such as a fall onto an outstretched hand |
| Compression on the suprascapular nerve near the scapular notch | |
| Overhead athletic activities | |
| SLAP lesions | |
| Acute muscle trauma | |
| Rupture of the infraspinatus muscle | |
| Fibrosis and contracture | |
| Labral tears | |
| Diagnosis | MRI |
| Electromyography | |
| Nerve conduction velocity studies | |
| Treatment | Labral repair with or without nerve decompression |
| Neuromuscular electrical stimulation | |
| Progressive walking | |
| Wheel-barrowing | |
| Aquatic therapy |
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What You'll Learn
- Infraspinatus muscle atrophy is caused by isolated infraspinatus tendon tears
- It can also be caused by compression on the suprascapular nerve
- Suprascapular nerve entrapment at the spinoglenoid notch can cause atrophy
- Chronic injuries such as entrapment can cause wasting of the infraspinatus muscle
- Conservative and surgical treatment can relieve pain and restore function
Infraspinatus muscle atrophy is caused by isolated infraspinatus tendon tears
The infraspinatus is one of four muscles that make up the rotator cuff, which helps the arm and shoulder move and stay stable. It is located at the back of the shoulder and attaches the top of the humerus (upper arm bone) to the shoulder blade. It is responsible for assisting in shoulder extension and providing the primary muscle force for external rotation of the shoulder.
Infraspinatus muscle atrophy refers to the severe wasting away and fatty degeneration of the infraspinatus muscle. This condition is usually caused by a chronic rotator cuff tear, which can be the result of repetitive motion involving the shoulder. Athletes in sports such as swimming and tennis are particularly susceptible to this type of injury. However, atrophy of the infraspinatus muscle can also be caused by an isolated infraspinatus tendon tear, as seen in some rare cases.
Isolated infraspinatus muscle atrophy is uncommon and typically associated with suprascapular nerve entrapment distal to the spinoglenoid notch. The suprascapular nerve innervates the supraspinatus and infraspinatus muscles, and compression of this nerve can lead to muscle atrophy. While nerve compression is uncommon, it can occur in athletes who perform overhead motions, such as throwing a ball. In these cases, the nerve can be compressed or pinched, resulting in infraspinatus muscle atrophy.
The diagnosis of infraspinatus muscle atrophy involves a physical examination to assess the range of motion, muscle weakness, and painful motions. Magnetic resonance imaging (MRI) is often used to visualise muscular atrophy and identify underlying causes of nerve impingement. Electromyography and nerve conduction velocity studies are considered the gold standard for confirming nerve compression. Treatment options depend on the severity of the injury and may include non-surgical methods such as rest, ice, and exercises, or surgical intervention for more severe cases.
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It can also be caused by compression on the suprascapular nerve
Infraspinatus muscle atrophy can be caused by compression on the suprascapular nerve. The suprascapular nerve innervates the supraspinatus and infraspinatus muscles. Compression of the nerve is uncommon and often presents as poorly explained shoulder pain, suspicious for a rotator cuff injury.
In a reported case, a 23-year-old male hockey player presented with right shoulder pain and weakness after falling onto an outstretched hand during a game. Examination revealed severe atrophy of the right infraspinatus muscle, with significant loss of strength in external rotation. Further investigation with magnetic resonance imaging (MRI) showed a superior labrum anterior and posterior (SLAP) tear and a large paralabral cyst compressing the suprascapular nerve at the spinoglenoid notch. This compression can be caused by paralabral cysts, which are accumulations of synovial fluid escaping the glenohumeral joint through a labral tear.
The O'Brien compression test, involving resisted shoulder flexion with adduction and a pronated forearm, can be useful in evaluating suspected suprascapular nerve compression. This test elicited deep glenohumeral pain in the aforementioned case, suggesting a superior labral lesion. While MRI is valuable for visualizing muscular atrophy and nerve impingement, electromyography (EMG) and nerve conduction velocity studies are the gold standard for confirming nerve lesions.
Treatment of labral tears with associated suprascapular neuropathy typically involves labral repair with or without nerve decompression. Early surgical intervention is crucial, as delaying treatment for more than six months can result in permanent muscle bulk and strength damage. Conservative and surgical treatments can relieve pain, but recovery of muscle bulk is less common, even with near-full return of strength.
It is important to be aware of other potential causes of infraspinatus atrophy, such as concomitant rotator cuff tendon or muscle pathology, which should be ruled out during the diagnostic process.
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Suprascapular nerve entrapment at the spinoglenoid notch can cause atrophy
The infraspinatus muscle assists in shoulder extension and provides the primary muscle force for external rotation of the shoulder. Along with the rest of the rotator cuff muscles, it provides stability to the shoulder complex. Atrophy in the infraspinatus muscle is usually caused by a chronic rotator cuff tear but may also be caused by suprascapular nerve entrapment at the spinoglenoid notch.
Suprascapular nerve entrapment is a rare but significant cause of posterior shoulder pain and weakness. The suprascapular nerve innervates the supraspinatus and infraspinatus muscles. When the nerve is entrapped at the suprascapular notch, patients present with weakness and atrophy of both the supraspinatus and infraspinatus. However, when entrapment occurs at the spinoglenoid notch, these symptoms are isolated to the infraspinatus. Compression at the suprascapular notch affects both muscles, whereas compression at the spinoglenoid notch affects the infraspinatus alone.
Suprascapular nerve entrapment at the spinoglenoid notch can be caused by a variety of factors, including anomalous transverse scapular ligaments, ganglion cysts, abnormal bony morphology, direct trauma, and traction injury. The most commonly encountered cause of this condition is a ganglion, usually arising from a posterior labral tear. Other causes include trauma to the scapula, varicosities, and tumours.
MRI is an indispensable tool for evaluating rotator cuff and labral pathology at the shoulder and diagnosing other surgically correctable causes of shoulder pain. It is also effective in diagnosing other surgically correctable lesions that may result in nerve entrapment at the shoulder. Electromyography and nerve conduction velocity studies are the gold standard in confirming the diagnosis of nerve entrapment.
Treatment of labral tears with associated suprascapular neuropathy involves labral repair with or without nerve decompression, typically resulting in substantial pain relief and cyst resolution within 2–3 months. However, if surgical intervention is delayed for more than 6 months and major atrophy has occurred, muscle bulk and strength may be permanently damaged.
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Chronic injuries such as entrapment can cause wasting of the infraspinatus muscle
The infraspinatus is one of the four muscles that make up the rotator cuff, which is responsible for the movement and stability of the shoulder joint. It is a thick triangular muscle located at the back of the shoulder, attaching the upper arm bone (humerus) to the shoulder blade (scapula).
Infraspinatus muscle atrophy refers to the wasting or degeneration of the infraspinatus muscle. This condition can be caused by various factors, including chronic injuries such as entrapment. Chronic injuries can lead to the compression or entrapment of the suprascapular nerve, resulting in atrophy of the infraspinatus muscle. This nerve supplies the infraspinatus muscle, and trauma to the shoulder or other chronic injuries can cause compression, leading to muscle atrophy.
Chronic injuries, such as entrapment, can cause wasting of the infraspinatus muscle through various mechanisms. One common cause is suprascapular nerve entrapment, which occurs when the nerve becomes compressed or pinched. This compression can happen due to trauma, overuse injuries, or other shoulder dysfunctions. In the case of a 23-year-old male hockey player, a fall onto an outstretched hand during a game resulted in severe atrophy of the right infraspinatus muscle. The O'Brien compression test revealed deep glenohumeral pain, suggesting a superior labral lesion, and magnetic resonance imaging showed a tear and a cyst compressing the suprascapular nerve.
Another way that chronic injuries contribute to infraspinatus muscle wasting is through rotator cuff injuries. These injuries can lead to disuse atrophy of the infraspinatus muscle, as seen in a study where 31% of patients with shoulder pain had atrophy originating from this muscle. Repetitive motions involving the shoulder, common in sports like swimming and tennis, can also cause infraspinatus pain and contribute to chronic injuries. Tendinopathy, including tendonitis and tendinosis, can result in inflammation and small tears in the tendon, leading to potential atrophy over time.
Chronic injuries can also cause wasting of the infraspinatus muscle through mechanisms such as trigger points and ganglion cysts. Trigger points are hard, tender spots in a muscle that can restrict motion and cause muscle weakness. Ganglion cysts in the suprascapular nerve area can compress the nerve and lead to atrophy. Treatment for labral tears and cysts typically involves repair with or without nerve decompression, resulting in pain relief and cyst resolution. However, delayed surgical intervention may result in permanent damage to muscle bulk and strength.
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Conservative and surgical treatment can relieve pain and restore function
Infraspinatus muscle atrophy is a rare condition that typically affects athletes, especially those involved in overhead sports such as hockey, baseball, and volleyball. It is characterised by severe pain and weakness in the shoulder, which worsens with activities involving external rotation and abduction. The infraspinatus muscle is responsible for only 30-40% of the throwing power of the shoulder, so a deficit affecting this muscle alone may go unnoticed.
The condition is usually caused by a chronic rotator cuff tear or suprascapular nerve entrapment at the spinoglenoid notch. In some cases, it can also be caused by trauma to the shoulder or falling on an outstretched arm. The pain associated with infraspinatus muscle atrophy can be treated through both conservative and surgical means, and most patients are able to return to their full range of activities.
Conservative treatments include rest, icing, heat therapy, physical therapy, and steroid injections. Resting the injured shoulder in a sling and avoiding activities that cause pain can give the muscle a chance to heal. Icing the shoulder can help reduce inflammation, especially in the early stages of injury or after exercise and stretching. Applying heat before stretching or exercising can help relax the infraspinatus muscle. Physical therapy, including specific stretches and exercises, can improve flexibility and range of motion, as well as strengthen the muscles to prevent further injury. Steroid injections, which contain a mix of local anaesthetic and anti-inflammatory steroids, can be administered directly into the infraspinatus or bursa, depending on the specific condition. These injections provide temporary pain relief but can damage the muscle if done too frequently.
Surgical treatment is typically considered if conservative treatments are ineffective or in cases of severe injuries. Surgery is usually a first-line treatment for acute injuries, such as a complete tear from a fall. Different types of surgical procedures can be performed, and a doctor will discuss the most suitable options for the patient's specific condition.
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Frequently asked questions
Infraspinatus muscle atrophy is the severe wasting away and fatty degeneration of the infraspinatus muscle. This is usually caused by a chronic rotator cuff tear but may also be caused by suprascapular nerve entrapment at the spinoglenoid notch.
Infraspinatus muscle atrophy is caused by isolated infraspinatus tendon tears. Compression of the suprascapular nerve is uncommon, but when it occurs, it affects both the infraspinatus and supraspinatus muscles.
Infraspinatus muscle atrophy can be treated conservatively or surgically, and most patients are able to return to full activities. However, recovery of muscle bulk is uncommon, and muscle bulk and strength may be permanently damaged if surgical intervention is delayed for more than 6 months.
