Crank Test: Purpose, Procedure, and Interpretation for Shoulder SLAP Lesions

What Is The Crank Test?

The Crank Test, also known as O'Brien's Test or the Active Compression Test, is a commonly utilized orthopedic special test designed to assess for superior labral anterior-posterior (SLAP) lesions of the glenohumeral joint, particularly in athletes involved in overhead activities.

Understanding the Crank Test

The Crank Test is a clinical examination maneuver employed by healthcare professionals, such as physical therapists, athletic trainers, and orthopedic surgeons, to help diagnose injuries to the superior aspect of the glenoid labrum in the shoulder. A SLAP lesion refers to a tear in the superior portion of the labrum, which is a rim of cartilage surrounding the glenoid (shoulder socket) that helps deepen the socket and stabilize the joint. This tear often involves the anchor point of the long head of the biceps brachii tendon, as it originates from the superior labrum.

The test's primary purpose is to provoke pain or other symptoms (like clicking or catching) that are characteristic of a SLAP tear by placing specific stress on the superior labrum and biceps tendon.

Anatomy and Biomechanics: What It Assesses

To understand the Crank Test, it's essential to grasp the relevant anatomy and biomechanics:

• Superior Glenoid Labrum: A fibrocartilaginous ring that attaches to the rim of the glenoid fossa. It enhances the depth and stability of the glenohumeral joint.
• Long Head of Biceps Brachii Tendon: This tendon originates from the supraglenoid tubercle and superior labrum, passing through the bicipital groove and attaching to the muscle belly. It plays a role in shoulder flexion, forearm supination, and contributes to glenohumeral stability.
• Glenohumeral Joint: The ball-and-socket joint of the shoulder, formed by the head of the humerus and the glenoid fossa of the scapula.

SLAP lesions often occur due to:

• Acute Trauma: Such as falling on an outstretched arm, direct blow to the shoulder, or sudden traction forces on the biceps (e.g., lifting a heavy object).
• Repetitive Microtrauma: Common in overhead athletes (e.g., baseball pitchers, volleyball players, swimmers) due to repetitive forceful eccentric contraction of the biceps or peeling forces on the labrum.

The Crank Test biomechanically stresses the superior labrum and biceps anchor by combining shoulder flexion, adduction, and specific rotational forces, aiming to reproduce the mechanism of injury or symptom provocation.

How to Perform the Crank Test

The Crank Test involves two distinct phases to help differentiate between intra-articular (SLAP) pain and other potential sources of shoulder discomfort.

Patient Position: The patient can be seated or standing.

Examiner Position: The examiner stands in front of the patient, supporting the arm being tested.

Test Procedure:

1. Phase 1 (Internal Rotation/Pronation):

   • The examiner flexes the patient's arm to 90 degrees of shoulder flexion.
   • The arm is then adducted approximately 10-15 degrees across the body.
   • The elbow is kept fully extended.
   • The forearm is placed in full pronation (thumb pointing downwards).
   • The examiner then applies a downward-directed force to the patient's arm, while the patient is instructed to resist this pressure.
   • The examiner observes for the patient's symptoms during this phase.

2. Phase 2 (External Rotation/Supination):

   • Without changing the shoulder position (still 90 degrees flexion, 10-15 degrees adduction, elbow extended), the examiner passively moves the patient's forearm into full supination (palm facing upwards).
   • Again, the examiner applies the same downward-directed force to the patient's arm, and the patient is instructed to resist this pressure.
   • The examiner observes for changes in the patient's symptoms compared to Phase 1.

Interpreting the Results

The interpretation of the Crank Test is crucial for its diagnostic value:

• Positive Test for SLAP Lesion: A positive test for a SLAP lesion is indicated by:

  • Pain or clicking inside the glenohumeral joint during Phase 1 (internal rotation/pronation).
  • This pain or clicking is then reduced or eliminated during Phase 2 (external rotation/supination).
  • The pain must be specifically intra-articular (deep within the shoulder joint), not superficial or at the AC joint.

• Positive Test for AC Joint Pathology: If the patient experiences pain on top of the shoulder (at the acromioclavicular joint) during Phase 1, and this pain is not relieved in Phase 2, it suggests an AC joint pathology rather than a SLAP lesion.

• Negative Test: If no pain or clicking is elicited in either phase, or if the pain/clicking does not change between phases, the test is considered negative for a SLAP lesion.

Clinical Significance and Limitations

The Crank Test serves as a valuable component of a comprehensive shoulder assessment, particularly when a SLAP lesion is suspected.

Clinical Significance:

• It helps guide further diagnostic steps, such as advanced imaging (e.g., MRI with arthrogram) or referral to an orthopedic specialist.
• It can help differentiate between various sources of shoulder pain, such as rotator cuff pathology, impingement, or AC joint issues.

Limitations:

• Not Definitive: Like most orthopedic special tests, the Crank Test is not 100% sensitive or specific. A positive test does not definitively confirm a SLAP lesion, and a negative test does not definitively rule one out.
• False Positives/Negatives: Other shoulder pathologies or patient apprehension can lead to false results.
• Examiner Skill: Proper execution, consistent application of force, and accurate interpretation of symptoms require experienced clinical judgment.
• Subjectivity: The test relies on patient reporting of pain and symptoms, which can be subjective.
• Pain Differentiation: It is critical for the examiner to distinguish between intra-articular pain and pain originating from other structures (e.g., AC joint, deltoid).

Integrating the Crank Test into Assessment

The Crank Test should never be used in isolation for diagnosis. It is one piece of a larger diagnostic puzzle that includes:

• Thorough Patient History: Understanding the mechanism of injury, onset of symptoms, activities that exacerbate or alleviate pain, and previous shoulder issues.
• Observation and Palpation: Assessing for swelling, deformity, muscle atrophy, and tenderness.
• Range of Motion Assessment: Active and passive range of motion in various planes.
• Strength Testing: Evaluating the strength of rotator cuff muscles and other shoulder girdle musculature.
• Other Special Tests: Employing a cluster of tests for various shoulder pathologies (e.g., Speed's Test and Yergason's Test for biceps tendinopathy, various impingement tests, instability tests).

A qualified healthcare professional, such as a physical therapist, athletic trainer, or orthopedic surgeon, is essential for accurate diagnosis and the development of an appropriate treatment plan based on a comprehensive assessment.