The shoulder is a complex ball-and-socket joint. It relies on the rotator cuff, a coordinated group of muscles and tendons, for stability and movement. Because of the shoulder’s wide range of motion and repetitive use, these structures are frequently subject to injury. Tears to the supraspinatus tendon are the most common, and the interstitial tear presents a unique diagnostic and treatment challenge.
Defining the Supraspinatus and Interstitial Tears
The supraspinatus is one of the four muscles forming the rotator cuff. It is situated in the shallow depression of the shoulder blade (scapula), above the spine. Its tendon attaches to the upper arm bone (humerus). The primary function of the supraspinatus is to initiate arm abduction, which is the act of lifting the arm away from the side of the body, especially during the first 15 degrees of motion.
An interstitial tear is a partial-thickness tear, meaning the injury does not extend completely through the tendon. The tear is concealed within the tendon’s core, which is why it is termed “interstitial” or “intrasubstance.” Unlike other partial tears that communicate with the joint space or bursa, the outer layers of the tendon remain intact, covering the defect.
This configuration means the tendon’s surface appears normal during visual inspection, such as arthroscopic surgery, despite significant internal damage. On imaging, the tear typically appears as a fluid-filled slit or delamination within the tendon fibers. Because the tear is entirely contained within the tendon substance, it is often referred to as a concealed interstitial delamination.
Mechanisms of Injury and Primary Symptoms
Interstitial tears most frequently result from a combination of degenerative changes and repetitive strain, rather than a single acute traumatic event. The tendon tissue weakens internally over time due to microtrauma from activities involving repeated overhead movement. This chronic overuse, common in certain sports or occupational tasks, leads to a breakdown of the tendon’s internal structure.
The biological process involves the degradation of the collagen matrix that gives the tendon its strength, often due to an increase in specific enzymes. This causes the internal collagen fibers to thin and separate, creating the characteristic tear within the tendon substance. While acute trauma can cause any type of tear, the concealed nature of interstitial tears often points toward an underlying, long-term degenerative process.
The main symptom is a deep, aching pain felt within the shoulder joint, which can sometimes radiate down the upper arm. Patients experience increased pain when attempting to lift the arm, particularly in the initial arc of movement, or when reaching overhead. Nocturnal pain is also a common complaint, often severe enough to wake the person from sleep, especially when lying on the affected side.
How Doctors Confirm the Diagnosis
Diagnosis begins with a thorough physical examination where a doctor assesses the patient’s range of motion, strength, and tenderness. Specific maneuvers, such as the Jobe’s test, also known as the Empty Can Test, are used to isolate the supraspinatus muscle and tendon. This test involves positioning the patient’s arm in a specific way to simulate an “empty can” position.
A positive test result is indicated by noticeable weakness or pain when the doctor applies downward resistance to the arm. While X-rays are typically ordered, they will not show the tear itself as they visualize bone structure. X-rays are primarily used to exclude other conditions, such as fractures, bone spurs, or arthritis.
Definitive diagnosis relies on advanced imaging techniques because of the tear’s internal location. Magnetic Resonance Imaging (MRI) is the gold standard, as it provides detailed visualization of soft tissues and clearly shows the fluid-filled defect contained within the tendon substance. High-resolution ultrasound can also be used effectively to visualize the partial-thickness defect and confirm the tear’s intratendinous location.
Managing and Treating Interstitial Tears
Treatment for interstitial supraspinatus tears overwhelmingly begins with a non-operative approach, which is successful for most patients. This initial conservative management typically involves a period of rest or activity modification to avoid painful movements. Nonsteroidal anti-inflammatory drugs (NSAIDs) are also used to manage pain and swelling.
Physical therapy (PT) is a cornerstone of this non-operative treatment and is designed to address the underlying causes of the injury and restore function. The goals of PT focus on pain reduction, restoring the full, pain-free range of motion, and strengthening the entire shoulder girdle. Strengthening exercises target the supraspinatus, other rotator cuff muscles, and the scapular stabilizers to improve dynamic control and joint stability.
If pain persists despite several months of physical therapy, a doctor may suggest an injection, such as a steroid to reduce inflammation or platelet-rich plasma (PRP) to encourage healing. Surgery is usually reserved for cases where extensive conservative treatment (typically six to twelve months) has failed to relieve symptoms. Surgery may also be necessary if the tear is large (involving more than 50% of the tendon thickness) or shows signs of progression. The surgical goal is to repair the internal tear or debride the damaged tissue to prevent it from enlarging into a full-thickness defect.