The Teres Minor is a spindle-shaped muscle located deep within the posterior shoulder, forming one of the four muscles of the rotator cuff. This muscle group stabilizes the humerus (upper arm bone) within the glenoid cavity (shoulder socket). Functionally, the Teres Minor is a stabilizer and mover, maintaining the integrity of the glenohumeral joint during various arm movements. Assessing the strength of this specific muscle is an important step in evaluating overall shoulder function and stability.
Understanding the Muscle’s Primary Action
The Teres Minor originates along the lateral border of the scapula and inserts onto the greater tubercle of the humerus. This anatomical path dictates the muscle’s primary function: external rotation of the arm at the shoulder joint. This outward rotation turns the palm forward when the elbow is bent and held close to the side. The Teres Minor collaborates closely with the larger Infraspinatus muscle, contributing significantly to the shoulder’s total external rotation strength. Additionally, the muscle helps pull the head of the humerus into the glenoid socket, preventing the joint from sliding upward during arm elevation.
Positioning and Safety Before Assessment
Proper body positioning is necessary before any strength assessment to ensure the Teres Minor is effectively isolated. The individual should be seated or standing upright with the shoulders relaxed and the spine straight, avoiding slouching or leaning that could engage accessory muscles. The arm being tested must be raised to shoulder height (90 degrees of abduction), with the elbow bent 90 degrees so the forearm points forward. This specific position is adopted for the Hornblower’s Sign, a clinical test variant that maximizes Teres Minor activation. Individuals should stop the test immediately if they feel sharp, debilitating pain, as this indicates a potential acute injury requiring medical attention.
Executing the Teres Minor Strength Test
The Teres Minor strength test uses a resistance method, requiring the individual to attempt external rotation against an opposing force. Starting with the arm abducted 90 degrees and the elbow flexed 90 degrees, the individual prepares to rotate the forearm upward. Resistance is provided by a partner or clinician, applying force to the forearm just above the wrist. The partner pushes the forearm downward and inward, attempting to force the arm into internal rotation.
The goal is to resist this opposing force, maintaining the forearm’s position so the hand remains level with the shoulder. This is an isometric resistance test, meaning the individual is holding a fixed position against resistance without moving through a range of motion. Resistance should be gradually increased to a maximum tolerance level over a few seconds to fully challenge the muscle.
Strength is evaluated by the maximum resistance the muscle can withstand before the arm gives way and moves into internal rotation. Comparing the tested side to the opposite, unaffected side helps establish a baseline. A significant difference in resistance ability, or a noticeable tremor, indicates a deficit in muscle strength or function.
Interpreting Weakness and Pain
A positive result is indicated by an inability to resist the applied external rotation force, causing the arm or forearm to drop into an internally rotated position. This suggests muscular weakness, potentially caused by a strain, partial tear, or injury to the axillary nerve supplying the Teres Minor. If the arm cannot be held in the starting position against gravity before resistance is applied, it suggests substantial weakness or a full-thickness tear of the external rotators.
The presence of pain during the test is also significant, even if strength is maintained. Pain localized to the posterior shoulder during the maneuver often points toward tendonitis or a partial tear of the Teres Minor or adjacent Infraspinatus tendon. Weakness accompanied by pain may indicate a mechanical issue like impingement or a degenerative process. Persistent weakness or sharp, unmanageable pain requires professional evaluation from a physical therapist or medical doctor to accurately diagnose the underlying cause.