Lacertus Syndrome

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Lacertus syndrome (LS) is caused by compression of the median nerve at the lacertus fibrosus, often seen in athletes engaged in overhead throwing activities. It is frequently misdiagnosed as Carpal Tunnel Syndrome (CTS), with many patients having had unsuccessful carpal tunnel release. However LS may coexist with LS as a double crush phenomenon.

Anatomy and Pathophysiology

Illustration of the volar forearm and the compression that can occur by a thickened lacertus fibrosis of the underlying pronator teres.

The condition is caused by compression of the median nerve at the lacertus fibrosus, a fibrous band distal to the elbow joint.

The median nerve runs along the medial side of the brachial artery, situated between the biceps brachii and the brachialis muscle. It courses under the ligament of Struthers and often gives a branch to the pronator teres just distal to the elbow. The nerve remains medial to the biceps tendon and brachial artery throughout its course and is located deep to both the lacertus fibrosis (bicipital aponeurosis) and the pronator teres muscle. The lacertus fibrosis is not the primary fascia of the superficial volar compartment but acts as a constricting band around the pronator teres.

Risk Factors

The most commonly affected sports-people are baseball pitchers, American football quarterbacks, golf, tennis, or weightlifting. Occupational risk factors are dentistry and surgery.

Clinical Features

Lacertus notch - a deformity at the medial elbow. From Dr Jean Paul Brutus

Patients with lacertus syndrome typically present with a loss of hand strength (95.6%) and endurance (i.e. fatigue - 73.3%), forearm pain (35.4%), and occasional median nerve distribution numbness.

The syndrome has a diagnostic clinical triad (Hagert) that consists of weakness in the muscles innervated distally to the lacertus fibrosus, pain over the compression point at the lacertus, and positive scratch collapse test.

1. Weakness: muscle weakness distal to nerve compression - flexor carpi radialis (FCR), flexor policis longus (FPL), and 2nd ray flexor digitorum profundus (FDP-II).
2. Tenderness and/or positive Tinel's at the level of nerve compression. The examiner places their thumb over the medial epicondyle, the middle finger over the biceps tendon, and palpates the lacertus fibrosus with the index finger.
3. Positive scratch collapse test (See https://www.youtube.com/watch?v=OD7y-mrj7YQ and https://www.youtube.com/watch?v=eFTj9BlMOpA)

The Lacertus Antagonis Test is positive if FPL and FDP-II strength is restored when the elbow is compressed medially by the examiners hands or tape.

The Lacertus notch can be a helpful clinical sign with a sensitivity of 65.1% and specificity of 68.97% (Note these values were not specifically reported in the abstract, they were calculated manually from the figures provided in the study.)

Investigations

Electrophysiology studies are frequently negative. This is because the compression is typically mild or dynamic in nature, and hence there is insufficient axonal injury for detection.

Invasive pressure measurements, similar to those used for CECS in the legs, have been employed in the past, but they carry risks of injury to surrounding structures.

Pre- and post-exercise MRI has provided a less invasive and reliable diagnostic method.

Differential Diagnosis

Multiple distinct conditions can cause compression of the median nerve - Carpal Tunnel Syndrome, Lacertus Syndrome, Superficialis-Pronator Syndrome, and Struther's ligament syndrome. Struther's ligament syndrome is very rare.

Table 1. Clinical findings in carpal tunnel syndrome, lacertus syndrome, and superficialis-pronator syndrome. Table from Apard et al.

Feature	Carpal Tunnel Syndrome	Lacertus Syndrome	Superficialis Pronator Syndrome
Symptoms	Numbness, tingling in fingers	Forearm pain at elbow	Diffuse forearm pain
Sensory	Palmar side of fingers	Possible median nerve distribution	Generalized, less pronounced
Motor	Weakness in APB muscles	FPL, FDP2, FRC muscle weakness	FPL, FDP2-3, FRC muscle weakness
Night Symptoms	Common, worsen at night	Less common at night	Rare
Activities	Difficulty gripping, manual tasks	Fatigue with elbow flexion, forearm activities, difficulty in pinch	Discomfort with forearm movements
Provocative Tests	Positive Tinel's at wrist, Phalen's test	Elbow flexion, pain on LF	Provoked by pronation, repetitive movements, no pain on LF
Position	N/A	Worsens with wrist flexion, worsens in elbow pronation	Triggered by specific forearm activities
Onset	Gradual, repetitive strain	Abrupt or gradual, activity level dependent	Gradually, activity specific
Pattern	Swelling sensation	Elbow tenderness	Diffuse forearm tenderness

Treatment

Conservative management involves activity modification (reducing repetitive elbow flexion, forearm pronation, and foreceful gripping), taping, nerve gliding, and NSAIDs.

Injections can have a diagnostic and therapeutic role.

Surgical release of the lacertus fibrosis has been shown to provide excellent outcomes for lacertus syndrome.

Miscellaneous

Lacertus syndrome was first described by George Bennett in 1959 as a condition affecting overhead throwing athletes. It was originally described as compression of the median nerve between the two heads of pronator teres, but later the role of the lacertus fibrosus was discovered.

Resources

Lacertus Syndrome - Apard 2024.pdf - 1.27 MB (f)

Literature Review

Literature Review

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