infraspinatus pain test

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19-03-2025

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The Infraspinatus Pain Test: A Comprehensive Guide

The infraspinatus muscle, one of the four rotator cuff muscles, plays a crucial role in shoulder stability and external rotation. Pain originating from the infraspinatus can significantly impair shoulder function, limiting activities of daily living and participation in sports. Accurate diagnosis is crucial for effective treatment, and the infraspinatus pain test forms a cornerstone of the clinical examination. This article delves into the infraspinatus pain test, exploring its mechanics, variations, limitations, and its role within a comprehensive shoulder examination.

Anatomy and Function of the Infraspinatus:

Before discussing the test itself, understanding the infraspinatus muscle's anatomy and function is essential. The infraspinatus muscle originates from the infraspinous fossa of the scapula (shoulder blade) and inserts onto the greater tubercle of the humerus (upper arm bone). Its primary function is external rotation of the shoulder, a movement crucial for activities such as throwing, reaching, and lifting. It also contributes to shoulder stability and helps to prevent excessive upward movement of the humeral head within the glenoid fossa (the socket of the shoulder joint). Injury or dysfunction of the infraspinatus can lead to pain, weakness, and instability of the shoulder.

The Infraspinatus Pain Test: Methodology and Interpretation:

The infraspinatus pain test, also known as the external rotation lag sign, is a relatively simple yet informative clinical assessment. The procedure involves the following steps:

1. Patient Positioning: The patient sits or lies supine (on their back) with their arm relaxed at their side. The examiner supports the patient's elbow, ensuring comfort and stability.

2. Passive External Rotation: The examiner passively externally rotates the patient's affected arm to its maximal range of motion. This is crucial to ensure that any pain elicited is indeed from the infraspinatus, not just from the end range of movement. The patient’s arm should be held at about 90 degrees of abduction from the body.

3. Release and Assessment: The examiner slowly releases their hold on the patient’s arm. If the arm remains in the externally rotated position due to the patient’s active muscular control, this is interpreted as a negative result. If, however, the arm falls into internal rotation, indicating weakness of the infraspinatus, the test is considered positive. The examiner should note the point at which the arm falls and whether the patient experiences pain. Pain accompanying the fall is a strong indicator of infraspinatus pathology.

Variations of the Infraspinatus Pain Test:

While the standard infraspinatus pain test is widely used, variations exist to enhance sensitivity and specificity. These include:

• Resisted External Rotation Test: This test assesses the strength of the infraspinatus muscle. With the arm in a similar position as the lag sign, the patient is asked to resist the examiner’s attempt to internally rotate the arm. Weakness or pain during this resisted movement suggests infraspinatus involvement.

• Belly Press Test: This test indirectly assesses the infraspinatus by asking the patient to press their belly against the examiner's hand while attempting to externally rotate their shoulder. The premise is that the infraspinatus needs to contract to stabilise the scapula and humerus for efficient belly pressing.

• Empty Can Test: While primarily assessing the supraspinatus muscle, the empty can test can indirectly reveal infraspinatus involvement if pain is experienced during the test. This is because both muscles are synergistic and often affected concurrently.

Limitations of the Infraspinatus Pain Test:

Like all clinical tests, the infraspinatus pain test has limitations:

• Specificity: The test's specificity is not perfect. Pain can be elicited from other structures, such as the posterior deltoid, teres minor, or even the glenohumeral joint itself. A comprehensive examination is crucial to differentiate between these possibilities.

• Sensitivity: The sensitivity of the test can vary depending on the severity and location of the infraspinatus pathology. Minor injuries might not produce a positive result.

• Subjectivity: The test relies on the patient’s subjective report of pain, which can be influenced by factors such as pain tolerance and previous experiences.

• Patient Cooperation: The patient's ability to actively cooperate and follow instructions is crucial for accurate interpretation.

Integrating the Infraspinatus Pain Test into a Comprehensive Shoulder Examination:

The infraspinatus pain test should not be used in isolation. A thorough shoulder examination should incorporate other tests to assess range of motion, strength, stability, and palpation of the affected area. Other tests often employed include:

• Apley Scratch Test: Assesses shoulder range of motion.
• Neer and Hawkins-Kennedy Impingement Tests: Evaluate subacromial impingement.
• Apprehension Test: Assesses anterior shoulder instability.
• Sulcus Sign: Assesses inferior shoulder instability.
• Drop Arm Test: Evaluates rotator cuff tears, particularly of the supraspinatus.

Imaging and Other Diagnostic Tools:

In cases where the clinical examination is inconclusive, imaging studies such as MRI or ultrasound can provide more definitive information about the infraspinatus muscle and surrounding structures. These techniques can help to identify tears, tendinopathy, or other pathologies.

Conclusion:

The infraspinatus pain test is a valuable tool in the clinical assessment of shoulder pain. However, its limitations must be considered. The test should be integrated into a comprehensive shoulder examination that incorporates other clinical tests and, when necessary, imaging studies. Accurate diagnosis is crucial for developing an effective treatment plan that addresses the underlying cause of the pain and restores optimal shoulder function. Early diagnosis and appropriate management can significantly improve patient outcomes and reduce long-term disability associated with infraspinatus injuries. It’s important to remember that this information is for educational purposes only and should not replace the advice of a qualified medical professional. If you experience shoulder pain, it is crucial to seek professional medical evaluation for proper diagnosis and treatment.