Ligament of Struthers: Location, Clinical Significance, and Management

Where is the Ligament of Struthers?

The Ligament of Struthers is an anatomical anomaly, a fibrous band located in the distal upper arm, specifically extending from an anomalous supracondylar process on the medial aspect of the humerus to the medial epicondyle.

Anatomical Location of the Ligament of Struthers

The Ligament of Struthers is a rare, accessory fibrous band found in the distal humerus, the long bone of the upper arm. Its precise location is critical to understanding its clinical significance:

• Origin: This ligament typically originates from an anomalous bony projection known as the supracondylar process (also called a supracondylar spur or beak-like process). This process, when present, projects anteromedially from the shaft of the humerus, approximately 5-8 cm proximal to the medial epicondyle.
• Insertion: From this supracondylar process, the Ligament of Struthers extends inferiorly and medially to insert onto the medial epicondyle of the humerus.
• Relationship to Neurovascular Structures: Crucially, this fibrous band, along with the supracondylar process, forms an arch or tunnel through which the median nerve and the brachial artery pass. This anatomical relationship is what gives the ligament its clinical importance, as it can predispose these structures to compression.

Embryological Origin and Clinical Significance

The Ligament of Struthers is considered a vestigial structure, meaning it is a remnant from an earlier evolutionary or developmental stage, analogous to a muscle or tendon found in some lower mammals.

• Developmental Anomaly: While the supracondylar process itself is present in approximately 0.7% to 2.7% of the population, the Ligament of Struthers is not always present even when the process exists. Its formation is thought to be an incomplete regression of an embryological structure.
• Asymptomatic Presence: In the vast majority of individuals who possess it, the Ligament of Struthers remains entirely asymptomatic, causing no issues throughout their lives.
• Potential for Compression: Its clinical significance arises when it acts as a constricting band, leading to entrapment neuropathy of the median nerve or, less commonly, compression of the brachial artery. This condition is often referred to as Struthers' Arch Syndrome or Supracondylar Process Syndrome.

Associated Conditions: Median Nerve Compression

When the Ligament of Struthers becomes symptomatic, it primarily affects the median nerve, leading to a specific set of signs and symptoms.

• Mechanism of Compression: The median nerve, along with the brachial artery, passes beneath the Ligament of Struthers. Repetitive arm movements, direct trauma, or hypertrophy of the pronator teres muscle (which also passes through this region) can cause the nerve to rub against the taut ligament or the underlying supracondylar process, leading to irritation, inflammation, and compression.
• Symptoms of Median Nerve Entrapment:
  • Sensory Deficits: Numbness, tingling, or pain (paresthesia) 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. Symptoms may be exacerbated by elbow extension and pronation.
  • Motor Weakness: Weakness in the muscles innervated by the median nerve, particularly those involved in pronation of the forearm (pronator teres, pronator quadratus) and flexion of the thumb and fingers (flexor pollicis longus, flexor digitorum profundus to digits 2 and 3, thenar muscles). This can lead to difficulty with fine motor skills or grip strength.
  • Pain: Localized pain in the distal arm or elbow, which may radiate down the forearm.
• Differential Diagnosis: It's crucial to differentiate Struthers' Arch Syndrome from other, more common median nerve entrapment sites, such as:
  • Carpal Tunnel Syndrome: Occurs at the wrist.
  • Pronator Teres Syndrome: Occurs more distally in the forearm, often involving the pronator teres muscle itself.

Diagnosis and Clinical Evaluation

Diagnosing Struthers' Arch Syndrome requires a thorough clinical assessment, as its symptoms can mimic other conditions.

• History and Physical Examination:
  • Detailed history of symptoms, including onset, duration, aggravating, and alleviating factors.
  • Palpation: Tenderness may be elicited over the supracondylar process or the course of the ligament.
  • Provocative Tests: Specific maneuvers that exacerbate symptoms, such as resisted forearm pronation with elbow extension, or direct pressure over the suspected compression site.
  • Neurological Examination: Assessment of sensation in the median nerve distribution and strength of median nerve-innervated muscles.
• Imaging Studies:
  • X-ray: Can identify the presence of a supracondylar process. This is often the first imaging modality used.
  • MRI (Magnetic Resonance Imaging): Can visualize the soft tissues, including the Ligament of Struthers and potential compression of the median nerve or brachial artery.
• Electrophysiological Studies:
  • Nerve Conduction Studies (NCS) and Electromyography (EMG): These tests measure the electrical activity of nerves and muscles and can pinpoint the exact location of nerve compression and assess the severity of nerve damage. A focal slowing of conduction velocity across the distal humerus, proximal to the elbow, is indicative of Struthers' Arch Syndrome.

Management and Treatment Options

Treatment for symptomatic Ligament of Struthers compression typically follows a conservative-to-surgical progression.

• Conservative Management:
  • Rest and Activity Modification: Avoiding activities that aggravate symptoms.
  • Non-Steroidal Anti-Inflammatory Drugs (NSAIDs): To reduce pain and inflammation.
  • Physical Therapy: May include nerve gliding exercises, stretching, and strengthening of surrounding musculature to improve nerve mobility and reduce tension.
  • Bracing or Splinting: To limit aggravating movements.
  • Corticosteroid Injections: In some cases, a corticosteroid injection near the site of compression may be used to reduce inflammation, though this is often a temporary measure.
• Surgical Intervention:
  • If conservative measures fail to provide relief, surgical decompression is often recommended.
  • The procedure involves surgical release (transection) of the Ligament of Struthers and, if present, excision of the supracondylar process. This effectively frees the median nerve and brachial artery from impingement.
  • Surgical outcomes are generally excellent, with significant relief of symptoms in most patients.

Implications for Fitness Professionals and Kinesiologists

Understanding the Ligament of Struthers, though rare, is valuable for fitness professionals and kinesiologists in a comprehensive assessment approach.

• Thorough Client Assessment: Be aware that persistent, unexplained median nerve symptoms (numbness, tingling, weakness in the thumb, index, and middle fingers) that don't respond to typical carpal tunnel or pronator teres syndrome interventions might indicate a more proximal entrapment.
• Consider Anatomical Anomalies: Recognize that anatomical variations can lead to atypical presentations of nerve impingement. While you won't diagnose, knowing these possibilities helps in appropriate referral.
• Exercise Modification: If a client presents with suggestive symptoms, advise on modifying exercises that involve repetitive or forceful elbow extension with pronation, as these could exacerbate nerve compression. Examples include certain pressing movements, throwing motions, or activities requiring sustained forearm pronation.
• Referral Pathway: Crucially, if you suspect nerve entrapment or any condition beyond your scope of practice, always refer the client to a qualified medical professional (e.g., physician, neurologist, orthopedic surgeon) for definitive diagnosis and treatment. Do not attempt to diagnose or treat such conditions.

Conclusion

The Ligament of Struthers is a fascinating, albeit rare, anatomical variation of the distal humerus. While often asymptomatic, its presence can lead to significant median nerve compression, known as Struthers' Arch Syndrome. A comprehensive understanding of its anatomical location, clinical presentation, and management strategies is vital for healthcare providers and provides valuable insight for fitness professionals and kinesiologists in guiding their clients toward appropriate care when symptoms arise. Awareness of such anatomical nuances underscores the complexity and individuality of the human musculoskeletal system.