The Milk Test for Shoulder: Purpose, Performance, and Interpretation

What is the milk test for the shoulder?

The Milk Test for the shoulder is a specialized orthopedic clinical examination maneuver primarily used to assess for posterior shoulder instability, often indicating posterior labral pathology or capsular laxity, particularly in athletes involved in overhead or throwing sports.

Introduction to the Milk Test

The shoulder joint, or glenohumeral joint, is the most mobile joint in the human body, relying heavily on surrounding soft tissues—the joint capsule, ligaments, and rotator cuff muscles—for stability. When this complex system is compromised, instability can arise, leading to pain, dysfunction, and apprehension. While anterior shoulder instability is more commonly recognized, posterior instability, though less frequent, can be a significant cause of shoulder complaints, especially in athletes. The Milk Test is one of several clinical maneuvers developed to help clinicians identify and evaluate this specific type of instability.

What is the Milk Test?

The Milk Test, sometimes referred to as the "Milk Maneuver" or "Milk Sign," is a provocative test designed to stress the posterior capsule and labrum of the glenohumeral joint. It aims to reproduce symptoms such as pain, apprehension, or a palpable clunk that would suggest a posterior labral tear (e.g., a reverse Bankart lesion) or excessive posterior capsular laxity. The test involves a specific positioning of the arm combined with an axial compression and rotational force applied by the examiner.

Purpose of the Milk Test

The primary purpose of the Milk Test is to aid in the diagnosis of posterior glenohumeral instability. This condition occurs when the humeral head translates excessively in a posterior direction relative to the glenoid fossa. It is often seen in:

• Overhead Athletes: Such as baseball pitchers, volleyball players, or swimmers, due to repetitive forceful internal rotation and adduction movements.
• Individuals with Traumatic Injuries: Direct blows to the anterior shoulder or falls onto an outstretched arm in adduction and internal rotation.
• Individuals with Generalized Ligamentous Laxity: Contributing to hypermobility.

By selectively stressing the posterior structures, the test helps differentiate posterior instability from other common shoulder pathologies, such as rotator cuff tendinopathy, subacromial impingement, or other labral tears.

How to Perform the Milk Test

Performing the Milk Test requires a trained examiner and a cooperative patient.

• Patient Positioning: The patient lies supine (on their back) on an examination table.
• Examiner Positioning: The examiner stands beside the affected shoulder.
• Procedure:
  1. The examiner grasps the patient's affected arm and abducts it to approximately 90-120 degrees.
  2. The elbow is flexed to 90 degrees, and the shoulder is then externally rotated to its end-range.
  3. The examiner's thumb is placed over the posterior aspect of the humeral head, near the glenohumeral joint line, to monitor for posterior translation or clunking.
  4. With the other hand, the examiner applies a posterior-directed force along the shaft of the humerus, effectively "pushing" the humeral head posteriorly into the glenoid.
  5. While maintaining this posterior force, the examiner then slowly and gently internally rotates the patient's arm.

Interpreting the Results

The interpretation of the Milk Test is based on the patient's subjective response and the examiner's objective findings.

• Positive Test: A positive Milk Test is indicated by:
  • Reproduction of Posterior Pain: The patient experiences pain deep in the posterior aspect of the shoulder.
  • Apprehension: The patient expresses a feeling of impending subluxation or dislocation, often resisting the movement.
  • Palpable or Audible Clunk: The examiner may feel or hear a clunk as the humeral head translates posteriorly, which can be indicative of a labral tear or significant capsular laxity.
  • Increased Posterior Translation: Compared to the unaffected side.
• Negative Test: A negative test would involve the absence of pain, apprehension, clunking, or excessive translation during the maneuver.

Clinical Significance and Limitations

Clinical Value

When positive, the Milk Test adds to the clinical picture suggesting posterior shoulder instability. It is often performed as part of a comprehensive shoulder examination, alongside other tests for instability (e.g., the Jerk Test, Posterior Apprehension Test) and impingement. In particular, it can be useful in identifying subtle posterior instability that might be missed by less provocative tests, especially in athletes with repetitive overhead movements.

Limitations and Considerations

• Sensitivity and Specificity: Like many orthopedic special tests, the Milk Test is not 100% sensitive or specific in isolation. A positive test indicates a likelihood of posterior instability but requires confirmation with a thorough clinical history, physical examination, and potentially diagnostic imaging (e.g., MRI with arthrogram).
• Subjectivity: Patient apprehension and pain are subjective, requiring careful interpretation.
• Examiner Skill: The accuracy of the test relies heavily on the examiner's experience and ability to correctly position the patient, apply the forces, and interpret the findings.
• False Positives/Negatives: Other shoulder pathologies might elicit similar symptoms, or significant instability might exist without a strongly positive test.
• Not a Standalone Diagnostic Tool: It should always be used as one piece of the diagnostic puzzle, not the sole determinant.

When to Seek Professional Advice

If you experience persistent shoulder pain, instability, apprehension, or a feeling of "looseness" in your shoulder, especially after an injury or during athletic activity, it is crucial to consult with a qualified healthcare professional. This could include an orthopedic surgeon, sports medicine physician, or physical therapist. They can perform a comprehensive evaluation, which may include the Milk Test and other diagnostic procedures, to accurately diagnose your condition and recommend the most appropriate treatment plan.

Conclusion

The Milk Test is a valuable clinical tool used by healthcare professionals to assess for posterior glenohumeral instability. By intentionally stressing the posterior structures of the shoulder, it helps to identify posterior labral tears or capsular laxity, particularly in populations prone to such injuries. While a positive test provides strong indicators, it is one component of a thorough musculoskeletal assessment and should always be interpreted within the broader context of a patient's history and other clinical findings.