Pronator Teres Syndrome - An Overview

What Is Pronator Teres Syndrome?

Pronator teres syndrome (PTS), originally detailed by Henrik Seyffarth in 1951, stems from the compression of the median nerve (MN) within the forearm by the pronator teres (PT) muscle. The PT muscle is a rounded muscle responsible for pronating the forearm. In most instances (66 percent), it comprises two unequal heads: a giant humeral head originating from the upper portion of the medial epicondyle and a smaller ulnar head arising from the coronoid process of the ulna. These heads descend into the forearm, merge into a common flexor tendon, and attach to the radial shaft. Before their fusion, the median nerve traverses between them in 74 to 82 percent of cases, providing innervation to both heads from C6 to C7 roots. The absence of the ulnar head is uncommon (14 percent) and may mitigate the risk of median nerve entrapment. Many individuals exhibit additional fibrous bands within the PT muscle's two heads. Subsequently, the anterior interosseous nerve (AIN) branches from the MN approximately two to three inches distal to the medial epicondyle.

What Are the Causes of Pronator Teres Syndrome?

• Repetitive Motion and Overuse: Frequent and repetitive grasping or pronation movements, such as hammering, ladling food, cleaning dishes, or playing tennis, can lead to hypertrophy of the pronator teres muscle. This hypertrophy (enlargement of an organ) can compress the median nerve.

• Anatomical Variations: Individuals with additional fibrous bands within the pronator teres muscle are more prone to median nerve entrapment.

• Local Trauma: Injury or trauma to the forearm can lead to swelling or scar tissue formation that compresses the median nerve.

• Tumors: Compression of the median nerve by a schwannoma, a type of nerve sheath tumor, can cause PTS.

• Medical Treatments and Conditions: Patients undergoing anticoagulation therapy or renal dialysis may develop PTS, possibly due to increased bleeding or swelling in the forearm region.

• Tight Lacertus Fibrosis (Bicipital Aponeurosis): A tight lacertus fibrosis can exacerbate the compression of the median nerve, worsening the symptoms of PTS.

What Are the Signs and Symptoms of PTS?

The symptoms of Pronator teres syndrome are:

• Pain: Pain in the volar forearm region, which is aggravated by resisted pronation of the forearm and flexion of the elbow.

• Positive Tinel Sign: Tinel sign over the proximal edge of the pronator teres muscle may be positive.

• Weakness: Patients may report significant weakness, although wasting of the median nerve-innervated muscles is rare. Mild weakness of the flexor pollicis longus (FPL) and abductor pollicis brevis (APB) is common, with some involvement of the flexor digitorum profundus (FDP) to digits 2 and 3 and opponens pollicis (OP).

• Muscle Sparing: The pronator teres muscle is usually spared because it receives innervation before the median nerve pierces it.

• Sensory Loss: Sensory loss is variable and may involve the palm or mimic carpal tunnel syndrome, affecting the thenar eminence, thumb, index, middle, and ring fingers.

• Positive Phalen Test: A positive Phalen test (a diagnostic test) over the pronator teres muscle can be present in 50 percent of cases.

These symptoms are critical for distinguishing PTS from other conditions, such as carpal tunnel syndrome.

How to Diagnose PTS?

Pronator teres syndrome is diagnosed through:

1. Nerve Conduction Studies (NCS): It is essential to rule out other neuropathies, though abnormalities are rare in PTS.

2. Electromyography (EMG): It shows abnormalities in specific muscles, notably the flexor pollicis longus (FPL) and flexor digitorum profundus (FDP) to digits 2 and 3.

Rarely affects the pronator teres muscle directly.

3. Imaging Studies:

• Ultrasound: Ultrasound offers dynamic imaging at a lower cost and can correlate median nerve size with symptom severity.

• Magnetic Resonance Imaging (MRI): It is also used for diagnosis but is typically more expensive.

These methods confirm PTS and exclude other upper limb conditions.

What Is the Differential Diagnosis of PTS?

Pronator teres syndrome shares similarities with various conditions, including:

• Ligament of Struthers Entrapment: Compression by a ligament from the medial epicondyle to the distal medial humerus, worsened by forearm supination and elbow extension.

• Median Nerve Entrapment by Hypertrophied Lacertus Fibrosis: Compression by the bicipital aponeurosis, exacerbated by resisted elbow flexion with the forearm supinated.

• Median Nerve Compression by Sublimus Bridge of Flexor Digitorum Superficialis Muscle: Exacerbated by resisted flexion of the middle finger's proximal interphalangeal joint.

• Carpal Tunnel Syndrome (CTS): Common wrist entrapment syndrome presenting with sensory loss sparing the thenar eminence.

• Anterior Interosseous Nerve (AIN) Syndrome: Demonstrated by pronation with the flexed elbow, without sensory loss.

• Brachial Plexus Injury or Cervical Radiculopathy: This may involve weakness beyond the median nerve territory, with neck pain radiating to the arm in cervical radiculopathy.

• Neuralgic Amyotrophy: Involves multiple nerves, with shoulder pain being more typical than forearm discomfort.

How to Treat Pronator Teres Syndrome?

The treatment for pronator teres syndrome treatment typically involves:

• Rest: Rest helps the affected area heal in time.

• Activity Modification: Adjusting activities that worsen symptoms.

• Physical and Occupational Therapy: Exercises and techniques to strengthen muscles and improve function.

• Medication: Nonsteroidal anti-inflammatory drugs (NSAIDs) for pain and inflammation management.

• Local Injections: Corticosteroids or local anesthetics may be injected to reduce inflammation and pain.

Patients can usually continue working unless they experience significant motor or sensory deficits that affect their job performance. Conservative treatment should be pursued for at least six weeks. If conservative methods fail, surgery may be necessary.

• Surgical intervention is recommended if the patient exhibits symptoms, objective findings of weakness or motor atrophy on examination, and abnormal electrodiagnostic studies. Surgery typically involves exploring the median nerve in the forearm and releasing the pronator teres muscle, along with other compressive structures such as the ligament of Struthers, lacertus fibrosis, or fascia of the flexor digitorum superficialis. Although decompression at multiple sites may be performed, it is considered a single procedure.

• Endoscopic release surgery offers advantages over open surgery, including preserving the nerve's blood supply, reducing scar formation, and yielding excellent results. Open surgery may be necessary in cases of recurrent symptoms.

Complications after surgical treatment for pronator teres syndrome are rare. In a study of 72 patients, no complications were reported during operations, with a 59 percent overall postoperative satisfaction rate. Theoretical risks include infection, seroma or hematoma formation, nerve injury, and scar formation.

Conclusion:

Pronator teres syndrome, though often misdiagnosed due to its symptoms overlapping with carpal tunnel syndrome, can be effectively managed with a comprehensive, interprofessional approach. Early and accurate diagnosis by primary care physicians, sports physicians, physiatrists, neurologists, and radiologists is essential for successful treatment. Conservative treatments, guided by physical and occupational therapists, often lead to significant improvement. In cases where surgery is necessary, patients generally experience good recovery outcomes. With collaborative care, individuals affected by pronator teres syndrome can look forward to resuming their normal activities and enjoying an improved quality of life. Continued research and awareness are vital to enhance diagnosis and treatment strategies for this condition.