Struthers Ligament: Anatomy, Clinical Significance, and Treatment

What is the Struthers ligament?

The Struthers ligament is an anomalous fibrous band found in a small percentage of individuals, extending from the medial epicondyle of the humerus to an associated supracondylar process or the humeral shaft, and is clinically significant due to its potential to entrap and compress the median nerve and brachial artery.

Understanding the Struthers Ligament: An Anatomical Anomaly

The Struthers ligament is not a universal anatomical structure; rather, it is an accessory fibrous band, representing a developmental anomaly. While relatively rare, its presence can have significant clinical implications, primarily by serving as a potential site of entrapment for neurovascular structures in the upper arm, most notably the median nerve. Understanding this ligament is crucial for healthcare professionals and fitness specialists, as it can be a source of perplexing upper limb pain and neurological symptoms.

Anatomy and Location

The Struthers ligament typically originates from the medial epicondyle of the humerus or, more commonly, from an anomalous supracondylar process (also known as the supracondylar spur or epicondylar process) located on the anteromedial aspect of the distal humerus, approximately 5-7 cm proximal to the medial epicondyle. From this origin, it extends distally and laterally to insert onto the humeral shaft, usually just superior to the medial epicondyle.

When present, this ligament forms a fibrous arch beneath which critical neurovascular structures pass. The primary structures at risk of compression are the median nerve and the brachial artery. The ulnar nerve is typically located posterior to the medial epicondyle and is not directly affected by the Struthers ligament. The prevalence of the Struthers ligament, often in conjunction with a supracondylar process, is estimated to be between 1-2% of the population.

Embryological Origin

The existence of the Struthers ligament is explained by embryological development. It is considered a phylogenetic remnant of an accessory muscle, such as an aberrant head of the pronator teres muscle or a part of the latissimus dorsi. During normal development, these structures typically regress. However, in some individuals, this regression is incomplete, leading to the formation of the fibrous Struthers ligament, often associated with the presence of a supracondylar process of the humerus, which is itself an osseous remnant.

Clinical Significance: Median Nerve Entrapment

The primary clinical importance of the Struthers ligament lies in its potential to cause entrapment neuropathy of the median nerve. This condition, often referred to as a proximal median nerve entrapment, can mimic or occur concurrently with other median nerve compression syndromes, such as Pronator Teres Syndrome or even Carpal Tunnel Syndrome, making accurate diagnosis challenging.

The mechanism of compression involves the median nerve being squeezed as it passes under the taut fibrous band, especially during activities that involve elbow flexion and forearm pronation. This compression can lead to a range of symptoms:

• Sensory Symptoms:
  • Numbness, tingling, or pain in the distribution of the median nerve, which includes the palmar aspect of the thumb, index finger, middle finger, and the radial half of the ring finger.
  • Pain may radiate up the arm towards the shoulder.
• Motor Symptoms:
  • Weakness in forearm pronation (muscles like pronator teres and pronator quadratus).
  • Weakness in wrist flexion (e.g., flexor carpi radialis).
  • Weakness in thumb opposition and abduction (thenar muscles, e.g., abductor pollicis brevis, opponens pollicis).
  • In severe or chronic cases, thenar muscle atrophy (wasting of the thumb base muscles) may be observed.
• Vascular Symptoms:
  • While less common, compression of the brachial artery can lead to diminished pulses in the forearm and hand, pallor, or coldness of the hand, especially during provocative movements.

Diagnosis

Diagnosing median nerve entrapment due to the Struthers ligament requires a comprehensive approach:

• Clinical History and Physical Examination: A thorough history detailing the onset, nature, and aggravating factors of symptoms (e.g., repetitive arm movements, elbow flexion) is crucial. Physical examination includes:
  • Palpation: Tenderness over the distal humerus, particularly if a supracondylar process is present.
  • Tinel's Sign: Tapping over the presumed site of the ligament may elicit tingling or pain in the median nerve distribution.
  • Provocative Tests: Resisted forearm pronation with elbow extension, or sustained elbow flexion, may reproduce symptoms.
  • Motor and Sensory Testing: Detailed assessment of median nerve innervated muscles and sensory dermatomes.
• Electrophysiological Studies: Nerve Conduction Studies (NCS) and Electromyography (EMG) are essential to confirm nerve compression, localize the site of entrapment, and assess the severity of nerve damage.
• Imaging:
  • X-ray: Can identify the presence of a supracondylar process, which strongly suggests the potential for a Struthers ligament.
  • Magnetic Resonance Imaging (MRI): Can directly visualize the fibrous Struthers ligament and assess for median nerve edema or compression. It can also rule out other soft tissue pathologies.
  • Ultrasound: Can be used to visualize the nerve and surrounding structures, potentially identifying the ligament and any nerve swelling.

Treatment Approaches

Treatment for median nerve entrapment by the Struthers ligament can be conservative or surgical, depending on the severity and duration of symptoms.

• Conservative Management:
  • Rest and Activity Modification: Avoiding activities that exacerbate symptoms, particularly repetitive elbow flexion and forearm pronation.
  • Non-Steroidal Anti-Inflammatory Drugs (NSAIDs): To manage pain and inflammation.
  • Physical Therapy: Includes nerve gliding exercises to improve nerve mobility, stretching of forearm muscles, and strengthening exercises for muscles not affected by the compression.
  • Splinting: Elbow splints or braces may be used to keep the elbow in a slightly flexed or extended position to reduce tension on the nerve.
  • Corticosteroid Injections: Injections around the nerve can help reduce inflammation and provide temporary relief, and can sometimes be diagnostic.
• Surgical Intervention:
  • Indication: Surgical release is typically recommended when conservative measures fail to provide adequate relief, or in cases of severe or progressive neurological deficits (e.g., significant motor weakness or muscle atrophy).
  • Procedure: The surgical procedure involves an incision over the distal humerus, identification of the Struthers ligament, and its surgical division (neurolysis) to decompress the median nerve and brachial artery. If a supracondylar process is present, it may also be resected.
  • Rehabilitation: Post-surgical rehabilitation focuses on restoring range of motion, strength, and nerve mobility.

Prognosis

The prognosis for individuals with median nerve entrapment due to the Struthers ligament is generally good, especially with early diagnosis and appropriate intervention. Conservative management can be effective for mild cases. For more severe or persistent symptoms, surgical release typically provides excellent outcomes, leading to significant improvement or complete resolution of symptoms. However, if nerve compression has been long-standing or severe, some residual symptoms, particularly sensory deficits, may persist.

Conclusion

The Struthers ligament is an uncommon but clinically significant anatomical variant that can lead to median nerve and brachial artery compression in the upper arm. While not universally present, its recognition is vital for healthcare professionals when diagnosing unexplained upper limb pain, numbness, or weakness. A thorough clinical evaluation combined with electrophysiological and imaging studies is key to accurate diagnosis. With appropriate conservative or surgical management, individuals affected by the Struthers ligament can expect a favorable outcome and significant relief from their symptoms.