Ligament of Struthers: Anatomy, Formation, Symptoms, Diagnosis, and Treatment

What is the Ligament of Struthers?

The Ligament of Struthers is an anatomical variant, a fibrous band found in the distal arm, which can be a site of median nerve and brachial artery compression, leading to a specific type of entrapment neuropathy.

Anatomy and Location

The Ligament of Struthers is an anomalous fibrous band located on the medial aspect of the distal humerus, typically found approximately 3-5 cm proximal to the medial epicondyle. It extends from a bony projection known as a supracondylar spur (or supracondylar process), which originates from the anteromedial surface of the humerus, down to the medial epicondyle. In cases where a supracondylar spur is absent, the ligament may arise directly from the medial supracondylar ridge. This ligament forms a tunnel or arch, beneath which the median nerve and the brachial artery pass as they descend into the forearm.

Formation and Embryological Origin

The Ligament of Struthers is considered a vestigial structure, meaning it is a remnant of an earlier developmental stage. It is believed to be a fibrous remnant of the medial head of the coracobrachialis muscle. During embryonic development, this muscular slip normally regresses, but in some individuals, it persists as a fibrous band. It is present in a small percentage of the population, with reported incidences ranging from 0.7% to 2.7%. Its presence is often, though not exclusively, associated with a supracondylar spur.

Clinical Significance: Median Nerve Compression

The primary clinical significance of the Ligament of Struthers lies in its potential to cause compression of the median nerve and, less commonly, the brachial artery. As the median nerve and brachial artery pass underneath this unyielding fibrous band, they can become entrapped, especially when the elbow is flexed and the forearm is pronated. This compression can lead to an entrapment neuropathy known as Struthers Ligament Syndrome or a proximal variant of Pronator Teres Syndrome.

• Median Nerve Entrapment: The inelastic nature of the ligament means that any increase in the volume of the contents passing beneath it (e.g., due to inflammation, swelling, or repetitive movements) or changes in elbow position can mechanically constrict the nerve. This can impair nerve function, leading to a range of neurological symptoms.
• Brachial Artery Compression: While less common than median nerve compression, the brachial artery can also be compressed, potentially leading to vascular symptoms such as diminished pulse, pallor, or coldness in the forearm and hand.

Symptoms of Median Nerve Compression at the Ligament of Struthers

Symptoms of median nerve compression at the Ligament of Struthers typically manifest in the forearm and hand, reflecting the distribution of the median nerve. These can include:

• Pain: Often described as aching or burning pain in the proximal forearm, sometimes radiating down into the hand.
• Sensory Disturbances: Numbness, tingling (paresthesia), or a pins-and-needles sensation in the median nerve distribution, which includes the thumb, index finger, middle finger, and the radial half of the ring finger. Unlike Carpal Tunnel Syndrome, nocturnal symptoms are usually absent.
• Motor Weakness: Weakness in the muscles innervated by the median nerve proximal to the wrist. This can include:
  • Pronator Teres: Difficulty with forearm pronation.
  • Flexor Carpi Radialis: Weakness in wrist flexion.
  • Flexor Digitorum Superficialis: Weakness in finger flexion.
  • Thenar Muscles: Weakness in thumb opposition and flexion, potentially leading to difficulty with fine motor tasks and a weakened grip.
• Aggravating Factors: Symptoms are often exacerbated by activities involving repetitive elbow flexion, forearm pronation, or direct pressure over the site of compression.

Diagnosis

Diagnosing Struthers Ligament Syndrome requires a thorough clinical evaluation and often involves specialized diagnostic tests:

• Clinical Examination: A detailed history of symptoms and a physical examination are crucial. The examiner may look for:
  • Tenderness: Palpation over the Ligament of Struthers may elicit pain.
  • Provocative Tests: Sustained elbow flexion and forearm pronation may reproduce symptoms.
  • Tinel's Sign: Tapping over the median nerve at the site of the ligament may cause tingling or pain.
  • Motor and Sensory Assessment: Evaluation of muscle strength and sensory perception in the median nerve distribution.
• Nerve Conduction Studies (NCS) and Electromyography (EMG): These neurophysiological tests are essential to confirm nerve entrapment, localize the site of compression, and assess the severity of nerve damage. They can help differentiate Struthers Ligament Syndrome from other median nerve entrapment sites, such as the pronator teres muscle or the carpal tunnel.
• Imaging:
  • X-ray: Primarily used to identify the presence of a supracondylar spur, which is often associated with the ligament.
  • Magnetic Resonance Imaging (MRI): Can visualize the fibrous band itself, the median nerve, and any signs of nerve compression or inflammation. It can also rule out other causes of arm pain.

Treatment Options

Treatment for Struthers Ligament Syndrome typically progresses from conservative management to surgical intervention if symptoms persist or worsen.

• Conservative Management:

  • Rest and Activity Modification: Avoiding activities that exacerbate symptoms, such as repetitive elbow flexion and forearm pronation.
  • Non-Steroidal Anti-Inflammatory Drugs (NSAIDs): To manage pain and inflammation.
  • Physical Therapy: May include nerve gliding exercises to improve median nerve mobility, stretching, and strengthening exercises for forearm muscles.
  • Splinting/Bracing: To keep the elbow in a position that reduces tension on the nerve.
  • Corticosteroid Injections: In some cases, an injection of corticosteroids around the nerve may provide temporary relief, although this is generally less effective for purely mechanical compression.

• Surgical Decompression:

  • If conservative measures fail to provide adequate relief after a reasonable period (typically 3-6 months), or if there is progressive motor weakness or severe sensory loss, surgical intervention is often recommended.
  • The surgical procedure involves an incision on the medial aspect of the distal arm to identify and transect (cut) the Ligament of Struthers. This releases the pressure on the median nerve and brachial artery, allowing them to glide freely.
  • Prognosis: Surgical decompression typically yields excellent results, with most patients experiencing significant improvement in symptoms and functional recovery.

Conclusion

The Ligament of Struthers is a relatively rare but clinically significant anatomical variant that can lead to median nerve and, occasionally, brachial artery compression in the distal arm. As an expert fitness educator, it's crucial to understand that persistent proximal forearm pain, numbness, and weakness in the median nerve distribution warrant a thorough evaluation to rule out this condition. Accurate diagnosis, often requiring a combination of clinical assessment and neurophysiological testing, is paramount for guiding effective treatment, which may range from conservative management to surgical decompression. Recognizing this potential site of nerve entrapment is vital for healthcare professionals and trainers working with individuals experiencing upper limb symptoms.