A rotator cuff tear involves damage to one or more of the four tendons that stabilize the shoulder joint. While a torn tendon is the primary source of discomfort, this injury can also cause nerve damage, though this is not the most common outcome. This co-occurrence is often seen in larger, chronic tears due to the close proximity of major nerves to the damaged tendons and muscles.
Anatomical Relationship Between the Rotator Cuff and Shoulder Nerves
The shoulder’s architecture places several peripheral nerves in close contact with the rotator cuff muscles and bony structures. The two nerves most frequently implicated in injuries associated with a torn rotator cuff are the suprascapular nerve and the axillary nerve. The suprascapular nerve is particularly vulnerable due to its path.
This nerve supplies motor function to the supraspinatus and infraspinatus muscles, which initiate arm abduction and external rotation. It passes through the narrow suprascapular notch and the spinoglenoid notch, making it susceptible to mechanical irritation or compression. Changes in the surrounding anatomy from a tear can directly affect its function.
The axillary nerve also courses near the shoulder joint, supplying the deltoid muscle and the teres minor. It wraps around the surgical neck of the humerus, traveling through the quadrangular space. Although more distant from the primary tear site than the suprascapular nerve, the axillary nerve can be affected by severe trauma or structural changes. Damage to these nerves disrupts muscle signals and can cause abnormal sensation in the shoulder area.
Mechanisms Leading to Nerve Involvement
A torn rotator cuff can lead to nerve involvement through three primary mechanisms. The first is physical compression, or “mass effect,” where a large, retracted tendon or a fluid-filled sac, such as a ganglion cyst, presses on the adjacent nerve. The suprascapular nerve is often compressed as it passes through the narrow suprascapular or spinoglenoid notches, especially if a cyst forms nearby.
Another cause is traction injury, which occurs during a severe, acute tear. When a tendon tears suddenly and retracts significantly, the associated muscle belly pulls away, causing a stretching force on the motor nerve branches. This excessive stretching can damage the nerve fibers, impairing signal transmission. This is frequently observed with massive tears of the supraspinatus and infraspinatus muscles, placing tension on the suprascapular nerve.
The third mechanism involves the chronic inflammatory response accompanying a persistent tendon tear. Continuous inflammation within the shoulder joint creates a chemical environment that irritates or damages nearby nerves. This ongoing irritation can lead to neuropathy, where the nerve becomes dysfunctional. Inflammatory substances may sensitize nerve endings, contributing to chronic neuropathic pain that is disproportionate to the mechanical injury.
Differentiating Symptoms of Nerve Damage from Tendon Pain
Distinguishing between symptoms caused by a torn tendon and those caused by nerve damage is important for accurate diagnosis. Typical rotator cuff pain is a deep, dull ache localized to the shoulder, worsening with movements like lifting or rotating the arm. Patients often report pain that disrupts sleep, especially when lying on the affected side, and generalized weakness when moving the arm against resistance.
Symptoms related to nerve involvement are distinctly different. They may include burning, sharp, or shooting pain that radiates down the arm, often extending beyond the shoulder joint. Nerve compression can also cause altered sensation, such as tingling, “pins and needles,” or numbness (paresthesia). A key indicator of nerve damage is muscle weakness or atrophy following a specific nerve distribution, such as wasting of the deltoid muscle (axillary nerve) or the supraspinatus and infraspinatus muscles (suprascapular neuropathy).
Nerve-related weakness can be profound and unrelated to the mechanical ability of the remaining tendon. Tendon weakness, conversely, is a direct result of the torn tissue not transmitting force effectively. The presence of neuropathic symptoms suggests a complex injury involving structures beyond the tendon. If chronic pain does not respond to typical anti-inflammatory medications, a neuropathic component should be considered.
Diagnosis and Management of Co-Occurring Injuries
Diagnostic Tools
When nerve involvement is suspected alongside a torn rotator cuff, medical professionals use specific diagnostic tools. Magnetic Resonance Imaging (MRI) visualizes the torn tendon, assesses its size, and evaluates muscle atrophy or fatty infiltration. MRI can also reveal a ganglion cyst that may be compressing a nerve.
The standard for confirming nerve function is a combination of Electromyography (EMG) and Nerve Conduction Studies (NCS). NCS measures how fast electrical signals travel through the nerve. EMG assesses electrical activity within the muscles, identifying signs of denervation or nerve injury. These tests provide objective data, helping differentiate weakness caused by a purely mechanical tear from weakness resulting from neuropathy.
Treatment Approaches
Management of co-occurring injuries often begins with conservative approaches. These include targeted physical therapy to maintain range of motion and strengthen unaffected muscles, and medications to manage both types of pain. If symptoms persist or if the tear is massive and associated with confirmed nerve compression, surgical intervention may be necessary. Surgery often involves repairing the torn rotator cuff simultaneously with a procedure to decompress the trapped nerve, such as a suprascapular nerve release.