lesser tubercle of humerus

3 min read 18-03-2025

The lesser tubercle of the humerus is a crucial anatomical structure in the shoulder joint. Understanding its anatomy, function, and clinical significance is vital for healthcare professionals and those interested in human anatomy. This article provides a comprehensive overview of this important bony landmark.

Anatomy of the Lesser Tubercle

The humerus, the long bone of the upper arm, has several prominent features. The lesser tubercle, also known as the lesser trochanter, is a smaller, more medially positioned projection located on the anterior aspect of the humerus, just below the head. It's situated medial to the greater tubercle and separated from it by the intertubercular sulcus (bicipital groove). This groove houses the tendon of the long head of the biceps brachii muscle.

Relationship to Surrounding Structures:

Subscapularis Muscle: The subscapularis muscle, a rotator cuff muscle, originates from the subscapular fossa of the scapula and inserts on the lesser tubercle. This muscle plays a crucial role in medial rotation of the shoulder.
Biceps Brachii Muscle: While not directly attached, the lesser tubercle’s proximity to the bicipital groove significantly impacts biceps brachii tendon movement.
Glenohumeral Joint: The anatomical relationship between the lesser tubercle and the glenoid fossa of the scapula is key to the proper biomechanics of the shoulder joint.

Function of the Lesser Tubercle

The primary function of the lesser tubercle is to serve as an attachment point for the subscapularis muscle. The subscapularis, as mentioned, is critical for internal rotation of the humerus. This movement is essential for a wide range of upper limb activities, from throwing and swimming to simple everyday tasks. The lesser tubercle's robust structure provides a stable anchoring point for the powerful subscapularis muscle, enabling efficient force transmission during shoulder rotation.

Clinical Significance of the Lesser Tubercle

Several clinical conditions can affect the lesser tubercle and its surrounding structures:

1. Subscapularis Tears:

Tears of the subscapularis tendon are common rotator cuff injuries. These tears can result from trauma, overuse, or degenerative changes. Damage to the tendon's insertion point on the lesser tubercle can lead to pain, weakness, and decreased shoulder range of motion. Diagnosis often involves physical examination, imaging studies (MRI, ultrasound), and sometimes arthroscopy.

2. Fractures:

Although less common than greater tubercle fractures, lesser tubercle fractures can occur due to high-energy trauma. These fractures can disrupt the function of the subscapularis muscle and may require surgical intervention for optimal healing and functional recovery.

3. Impingement Syndrome:

While not directly impacting the lesser tubercle itself, impingement syndrome, a condition where the rotator cuff tendons are compressed within the subacromial space, can indirectly affect its function. The inflammation and irritation associated with impingement can lead to pain and dysfunction of the subscapularis, impacting the lesser tubercle's role in shoulder rotation.

4. Imaging and Diagnosis:

Radiographic imaging techniques like X-rays, CT scans, and particularly MRI scans are essential for visualizing the lesser tubercle and assessing for fractures, tears, or other pathologies. MRI provides detailed soft tissue imaging and is crucial for evaluating subscapularis tendon integrity.

Questions and Answers about the Lesser Tubercle

Q: What is the difference between the lesser and greater tubercle?

A: The greater tubercle is larger and more laterally positioned, serving as an attachment site for the supraspinatus, infraspinatus, and teres minor muscles. The lesser tubercle, smaller and medially situated, is the insertion point for the subscapularis. They are separated by the intertubercular sulcus.

Q: How is a lesser tubercle fracture diagnosed?

A: Diagnosis typically involves a physical examination revealing pain and limited range of motion, especially internal rotation. Imaging studies like X-rays, CT scans, or MRI confirm the fracture and assess its severity.

Q: What are the treatment options for a subscapularis tear affecting the lesser tubercle?

A: Treatment options range from conservative management (physical therapy, rest, anti-inflammatory medications) to surgical repair, depending on the severity of the tear and the patient's symptoms.

Conclusion

The lesser tubercle of the humerus, while seemingly a small bony prominence, plays a significant role in shoulder function. Understanding its anatomy, its relationship to the subscapularis muscle, and its clinical significance is crucial for healthcare professionals involved in the diagnosis and treatment of shoulder pathologies. Continued research into the biomechanics of the shoulder joint and its constituent structures, including the lesser tubercle, will undoubtedly lead to improved treatment strategies for a variety of musculoskeletal conditions.