Teres Minor Atrophy: Causes, Imaging, and Clinical Implications

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 Teres Minor Atrophy: Causes, Imaging, and Clinical Implications

Introduction

Teres minor atrophy is an uncommon but clinically significant radiologic finding that may indicate underlying neuromuscular pathology or chronic rotator cuff injury. As one of the four rotator cuff muscles, the teres minor plays an essential role in shoulder stability and external rotation. Although it is frequently overshadowed by larger muscles like the infraspinatus and supraspinatus, degeneration or atrophy of the teres minor can lead to impaired shoulder function and warrants careful assessment.

In this post, we explore the etiology, pathophysiology, imaging findings, clinical presentation, treatment, and prognosis of teres minor atrophy. We also include interpretive insights based on real imaging findings (Figure 1), quiz questions with answers, and a comprehensive literature reference.

Anatomy of the Teres Minor

The teres minor originates from the lateral border of the scapula and inserts onto the greater tuberosity of the humerus, adjacent to the infraspinatus. It is innervated by the axillary nerve, a branch of the posterior cord of the brachial plexus.

Functionally, the teres minor is a primary external rotator of the shoulder and works synergistically with the infraspinatus to stabilize the humeral head within the glenoid fossa.

Etiology and Causes of Teres Minor Atrophy

Teres minor atrophy may result from a variety of underlying conditions, including:

  • Quadrilateral (quadrangular) space syndrome (QSS)
    Compression of the axillary nerve within the quadrilateral space causes selective denervation.

  • Rotator cuff tears (especially massive tears)
    Chronic tears may lead to disuse atrophy or denervation changes in adjacent muscles.

  • Axillary nerve injury
    Due to shoulder dislocation, trauma, or iatrogenic causes during surgery.

  • Sarcopenia
    Age-related muscle degeneration affects the rotator cuff preferentially.

  • Neurogenic atrophy from cervical spine pathology
    C5/C6 radiculopathy may rarely affect the teres minor if the axillary nerve is involved.

Pathophysiology

Atrophy of the teres minor is characterized by muscle fiber loss and fatty infiltration, which may appear as hyperintense signal changes on MRI. Chronic denervation leads to progressive replacement of muscle fibers with fat and connective tissue.

Epidemiology

Teres minor atrophy is relatively rare when isolated. However, it is increasingly recognized in shoulder MRI reports due to improved imaging protocols. It is more commonly seen in:

  • Males aged 40–60

  • Overhead athletes (e.g., baseball pitchers)

  • Patients with chronic shoulder instability or trauma

  • Elderly patients with rotator cuff degeneration

Clinical Presentation

Isolated teres minor atrophy may be clinically silent, but patients can present with:

  • Posterior shoulder pain

  • Weakness in external rotation with the arm abducted (Hornblower’s sign)

  • Diminished performance in throwing or overhead activities

  • Discomfort during resisted lateral rotation

Imaging Findings

MRI is the gold standard for evaluating rotator cuff muscle quality. The following features are associated with teres minor atrophy:

MRI Findings

Figure 1: Marked absence of teres minor fibers with fatty replacement, consistent with chronic atrophy. No compressive lesion was observed near the quadratus radialis on the coronal PD view.

  • SAG T1: Reveals fatty infiltration with loss of normal muscle striation

  • COR PD: Shows preserved signal in the adjacent rotator cuff and no external compressive lesion

  • Axial T1 or T2 FS: May show volume loss and bright signal intensity due to fat replacement

  • Goutallier classification: Used to grade fatty degeneration from stage 0 to stage 4

Quadrilateral Space Syndrome (QSS)

The quadrilateral space is bounded by:

  • Teres minor (superior)

  • Teres major (inferior)

  • Long head of triceps (medial)

  • Humerus (lateral)

QSS involves compression of the axillary nerve and posterior circumflex humeral artery. Teres minor atrophy is often the only radiological evidence of this syndrome, especially when other cuff muscles are preserved.

Treatment

Conservative Management

  • Physical therapy (strengthening external rotators)

  • Activity modification

  • NSAIDs for pain relief

  • Neuromuscular retraining for posture and scapular stability

Interventional/Surgical

  • Surgical decompression in confirmed QSS

  • Nerve transfer in traumatic axillary nerve injuries

  • Rotator cuff repair if atrophy is secondary to a tendon tear

Prognosis

The outcome largely depends on the underlying cause:

  • In QSS, early decompression may reverse atrophy

  • In chronic cases or when caused by massive cuff tears, fatty infiltration is irreversible

  • Isolated atrophy without pain or functional limitation may require no intervention

Quiz

1. Which of the following nerves innervates the teres minor muscle?

A. Suprascapular nerve
B. Axillary nerve
C. Radial nerve
D. Musculocutaneous nerve

2. Which MRI finding is most indicative of chronic teres minor atrophy?

A. Fluid collection in the subacromial space
B. High T2 signal in the glenoid labrum
C. Fatty replacement on T1-weighted images
D. Labral tear with contrast leakage

3. Quadrilateral space syndrome is associated with compression of which structure(s)?

A. Axillary nerve and posterior circumflex humeral artery
B. Suprascapular nerve and supraspinatus tendon
C. Radial nerve and profunda brachii artery
D. Musculocutaneous nerve and brachial artery

Answer & Explanation

1. Correct Answer: B. Explanation: The axillary nerve provides motor innervation to both the teres minor and the deltoid.

2. Correct Answer: C. Explanation: T1-weighted images show increased signal intensity due to fat infiltration in atrophic muscles.

3. Correct Answer: A. Explanation: The axillary nerve and posterior circumflex humeral artery pass through the quadrilateral space and are prone to entrapment in QSS.

Conclusion

Teres minor atrophy, though often overlooked, can be a sentinel sign of deeper pathologies such as quadrilateral space syndrome, chronic rotator cuff injury, or axillary nerve entrapment. MRI is essential for diagnosis, and proper evaluation may guide both conservative and surgical interventions. Radiologists and sports medicine clinicians should remain vigilant for subtle signs of isolated muscle degeneration, particularly in overhead athletes and middle-aged patients with unexplained shoulder dysfunction.

References

[1] F. Goutallier et al., “Fatty muscle degeneration in cuff ruptures,” Clin Orthop Relat Res., vol. 304, pp. 78–83, 1994.
[2] S. Martin et al., “Isolated teres minor atrophy: Clinical significance,” J Shoulder Elbow Surg., vol. 15, no. 6, pp. 666–670, 2006.
[3] M. Blazar et al., “Quadrilateral space syndrome: MRI findings,” Skeletal Radiol., vol. 28, pp. 209–213, 1999.
[4] R. Frostick et al., “Axillary nerve injury,” J Bone Joint Surg Br., vol. 83, pp. 618–624, 2001.
[5] D. Fehringer et al., “Sarcopenia of the rotator cuff,” J Bone Joint Surg Am., vol. 90, pp. 230–240, 2008.
[6] C. Milgrom et al., “Prevalence of shoulder pathologies in asymptomatic individuals,” J Bone Joint Surg Am., vol. 80, pp. 768–780, 1998.
[7] A. Walch et al., “Muscle fatty degeneration and rotator cuff tears,” J Shoulder Elbow Surg., vol. 7, no. 4, pp. 349–355, 1998.
[8] T. Hashimoto et al., “Muscle degeneration and nerve injury in rotator cuff disease,” J Orthop Res., vol. 21, no. 3, pp. 556–563, 2003.

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