Pronator Teres Syndrome

What is Pronator Teres Syndrome?

Pronator teres syndrome also known as pronator syndrome, is a neurological disorder caused by the compression of the median nerve at the level of elbow (upper forearm). The possible sites where compression of the median nerve can occur are mentioned below

  • Between the two heads of the pronator teres muscle.
  • Due to the thickening of the bicipital aponeurosis.
  • By the Fibrous arch of the origin of Flexor Digitorum Superficialis muscle. We will discuss these things in detail.

Now, let’s understand the course of the median nerve (origin and insertion). How the median gets compressed, and the outcomes and treatment of the Pronator Teres Syndrome.

The course of the median nerve (origin and insertion)

  • The median nerve is formed by the lateral and medial cord of the brachial plexus. As you can see in the diagram, one branch is coming from the lateral cord, and one branch is coming from the medial cord, and together they form the median nerve.
  • The median nerve runs in the medial plane of the forearm. That’s why it is called the median nerve. Let’s discuss the origin of the median nerve.

Origin of the Median nerve

  • After originating from the brachial plexus, the median nerve enters the anterior compartment of the arm. The arm’s anterior (flexor) compartment contains three muscles (Biceps brachii, brachialis, and coracobrachialis).
  • In the arm initially, it lies lateral to the brachial artery, then it crosses in front (anteriorly) over the brachial artery to reach its medial side.
  • Then, it runs medial to the brachial artery, runs under the biceps muscles, and enters into the cubital fossa.
  • After that, it leaves the cubital fossa by passing between the two heads of the pronator teres muscle.

Anatomy of the pronator teres muscle – One head originates from the humerus, and the other head from the ulna. Both the heads fuse and go transversely to attach on the shaft of another major bone of the forearm, the Radius. The contraction of this muscle brings about pronation movement of the forearm.

  • After passing from the pronator teres muscle, it gives branches to the anterior compartment muscles of the forearm. Then it runs down the forearm between the two flexor digitorum muscles (flexor digitorum superficialis and flexor digitorum profundus).
  • Then it enters the palm through the carpal tunnel and supplies the radial 3½ digits.

Branches of the median nerve in the forearm area

1 – Anterior Interosseous branch – It supplies 2 ½ muscles

  • Flexor pollicis longus
  • Pronator quadrates
  • Lateral half of the flexor digitorum profundus.

2 – Palmar Cutaneous branch- Before entering the carpal tunnel, it gives off a palmar cutaneous branch. It is responsible for sensory supply over the thenar eminence and lateral part of the palm. This helps in differentiating between the pronator teres syndrome and the carpel tunnel syndrome.

How palmar cutaneous branch helps in differentiating between the pronator teres syndrome and the carpal tunnel syndrome?

As explained above just before entering the carpal tunnel, the median nerve gives off a palmar cutaneous branch, it provides sensory supplies over the thenar eminence and the lateral part of the palm.

So, if any sensory disturbances occur over the lateral part of the palm due to the involvement of the palmar cutaneous branch of the median nerve, it occurs proximal to (before) the carpal tunnel.

Therefore, sensory disturbances in the lateral part of the palm indicate a median nerve problem proximal to (before) the carpal tunnel. As if any sensory disturbance in the median nerve occurs after entering the carpal tunnel, Then it will indicate carpal tunnel syndrome. In this way, the palmar cutaneous branch helps in differentiating between the pronator teres syndrome and the carpal tunnel syndrome.

Median nerve Compression Sites

Possible sites of the compression of the median nerve include

Between the two heads of the Pronator Teres Muscle

This is the most important cause, as compression of the median nerve occurs between the two heads of the pronator teres muscle. Due to overuse, It occurs in the people who perform repetitive forceful pronation of the forearm.

Thus, increased tension in pronator heads leads to entrapment and compression of the median nerve near the elbow. This is the most common cause or location of compression in a patient with this Syndrome.

Compression due to Thickening of the bicipital Aponeurosis

While crossing from lateral to medial side over the antecubital fossa, the bicipital aponeurosis may irritate the median nerve. This is the potential sight for the compression of the median nerve.

Compression by the Fibrous Arch of the origin of the Flexor Digitorum Superficialis Muscle

Compression of the median nerve from the fibrous arch of the origin of the flexor digitorum superficialis muscle.

Bony spur and the Ligament of Struthers

In 1% of cases, there is a radiological finding called a medial supracondylar spur, about 5cm proximal to the medial epicondyle. This bony spur (medial supracondylar spur) is connected to the medial epicondyle by the Ligament of Struthers.

The median nerve gets compressed or entrapped by the bony spur (medial supracondylar spur) and ligament of the Struthers.

Causes of the Pronator Teres Syndrome

Pronator teres muscle functions as a “rotator” that turn your forearm into a “palm down” position (pronation). The main causes of pronator teres syndrome include

  • Prolonged or repetitive grasping or forceful pronation movement of the forearm, i.e., turning the forearm into a “palm down” position. This problem is common in mechanics, carpenters, tennis players, rowers, and weight lifters. This pronation movement can lead to the pronator teres muscle hypertrophy and compression of the median nerve. 
  • Other causes include compression of the median nerve from the fibrous arch of the origin of the flexor digitorum superficialis muscle. or thickening of the bicipital aponeurosis or by the bony spur (medial supracondylar spur) and ligament of the Struthers as explained above.
  • Nerve entrapment can occur due to local trauma or injury to the forearm. It also occurs in the patients who are going through renal dialysis and anticoagulation therapy.
  • The condition is often associated with the overdeveloped forearm muscles, and it is more common in the dominant hand.
  • The average age at which the condition develops is in the fifth decade. It is four times more common among women than it is in men.
  • Like other neuropathies, patients with diabetes, hypothyroidism, or alcoholism are also at risk for this condition.

Symptoms of The Pronator Teres Syndrome

Pronator teres syndrome is often present as an aching discomfort in the forearm’s volar (palm side) compartment and associated paresthesia in the lateral 3½ digits of the thumb, index finger, middle finger, and half of the ring finger. Pronator syndrome symptoms are similar to carpal tunnel syndrome, but some clinical findings help differentiate between pronator teres syndrome and carpal tunnel syndrome.

Radial 3½ digits paraesthesia – The median nerve innervates the muscles of the radial 3½ digits (thumb, index finger, middle finger, and half of the ring finger). Thus, its compression will weaken the muscles, causing failure to grip objects and the prickling sensation.

But this may occur as a result of the compression of the median nerve at the elbow or the carpal tunnel region. So it’s not a diagnostic criterion. So let’s understand the differences between the symptoms of pronator teres syndrome and carpel tunnel syndrome.

Difference Between Symptoms of Pronator Teres Syndrome and Carpel Tunnel Syndrome

  • Patients will complain of dull aching pain over the proximal (flexor compartment) of the forearm, i.e., over the pronator teres muscle and associated paresthesia in the 3½ digits (thumb, index finger, middle finger, and half of the ring finger). While in the carpal tunnel, syndrome symptoms will be only limited to 3½ digits.
  • In pronator teres syndrome, the pain worsens with prolonged or repetitive or forceful pronation of the forearm.
  • Night pain is not a common complaint in this condition. Tenderness may be noted over the pronator Teres muscle.
  • The most important thing is that isolated carpal tunnel syndrome symptoms don’t affect the palm. Pronator Teres syndrome often does affect the palm. As explained above, the palmar cutaneous branch arises just before the median nerve enters the carpal tunnel. So the loss of sensitivity of the skin of the palmar region can occur only if the median nerve is compressed in the forearm itself. Thus a sign of pronator teres syndrome.

Diagnosis of the Pronator Teres Syndrome

There’s no specific test as of yet to pinpoint the location of compression directly. But we can narrow down the sites of median nerve compression by certain tests.

Last year AAOS study has defined the sensitivity of two commonly used test to diagnose carpal tunnel syndrome.

  • The sensitivity of the Tinel sign (at the wrist) was 37.7 %
  • Phalen’s test sensitivity was 52.8%

These are the differences in clinical evaluations of isolated pronator teres syndrome patients.

Tinel’s Sign

Tinel sign is usually absent at the wrist but may be positive at the proximal anterior forearm.

  • In this test, we tap or percuss over the possible areas of the median nerve compression.
  • If the nerve is compressed in the area we percuss, then a tingling sensation or ‘pin and needle’ sensation is again felt at sites supplied by the nerve.
  • This is caused due to further irritation of the compressed nerve.
  • Thus in the case of proximal median nerve compression –

The Tinel’s sign is positive over the proximal forearm and abnormal sensation is felt in the palm of the hand.

Tinel-Sign-positive

While the Tinel’s sign is negative at the wrist. This helps in ruling out the carpal tunnel compression of the median nerve.

Phalen’s Test

  • The patient is in a sitting or standing position with shoulder relaxed, and elbow extended.
  • The patient is made to flex his hand from the wrist, not too forcefully.
  • In a positive test, there is a tingling or paresthesia sensation in at least one of the digits supplied by the median nerve 
  • This test will be negative for Pronator Teres Syndrome patients and positive for Carpal Tunnel Syndrome patients.

Orthopedic testing can be used to help identify the location of involvement. It involves generating tension at specific sites of median nerve compression.

Pronator Compression Test

If symptoms are reproducible within 30 seconds of applying deep, sustained compression of pronator muscles, the pronator compression test will be positive. However, do check that uninvolved arms should remain asymptomatic. Gainor conducted a small study and found that this test was 100% sensitive.  

Pronator Teres Syndrome Test

The examiners take the patient’s elbow in 90 degrees of flexion. The examiner then holds the elbow in 90 degrees of flexion and asks the patient to pronate his hand against the examiner’s resistance. While holding the resistance, the examiner extends the patient’s elbow. Reproduction of the symptoms indicates that there is a problem in the pronator Teres muscle.

Note – Similarly, compression at other sites can also be ruled out by tapping on the sites. For example, If tapping on the supracondylar spur worsens the tingling sensation, compression is at the spur.

There is a condition known as “Double Crush Syndrome”. In this syndrome, the nerve gets trapped at both or multiple locations. Therefore, a thorough examination becomes necessary. Nerve conduction tests, Physical examinations, and advanced imaging examinations are important to have an accurate diagnosis.

Pronator Teres Syndrome Treatment

At first, everyone goes for the conservative treatment as this includes rest, ice, splints, modification of activities that aggravate the symptoms, NSAIDs.

Rest  

As it becomes important to take a rest for some days and avoid using the affected arm for repetitive grasping and forceful pronation movement of the forearm. This is the most important aspect of the treatment, as repetitive movements will aggravate the symptoms. Instead, modify the activities that aggravate the symptoms.

In severe cases of pronator syndrome, an elbow splint can be used to maintain 90 degrees of flexion with the forearm in mid-rotation. The elbow splint provides rest and support to the elbow when it is bent and the forearm in neutral (or mid-rotation) position.

In addition, it prevents much movement and thus helps in preventing further compression of the nerve. The splint should be worn all the time for approximately two weeks and would be taken off for a range of motion activities.

Ice 

The application of ice helps in decreasing pain and swelling. You may find relief from pain and swelling by applying an ice massage or ice pack directly over the pronator teres muscle.

Pain killers and NSAIDs

They help decrease pain and swelling, as they are used for the symptomatic treatment (pain relief) of the pronator teres syndrome.

Physiotherapy Treatment 

Physiotherapy treatment includes modalities, therapeutic exercises, stretching, myofascial release, and Kinesio taping.

Modalities

Electrotherapy modalities such as ultrasound and TENS have shown benefits in the treatment of pronator teres syndrome. For example, a study has shown that the application of pulsed ultrasound daily for 15 minutes has shown benefits in reducing medial nerve compression (frequency – 1 MHz; intensity – 1 watt/cm).

Stretching and Myofascial Release and Kinesio taping.

It is important to have a good clinical judgment in deciding at which point performing the soft tissue mobilization cancels out the risks of symptoms aggravation.

When the symptoms are no longer severe, you can perform soft tissue mobilization, which includes stretching and myofascial release of the hypertonic pronator teres and wrist flexor muscles. Kinesio taping also provides relief in the symptoms of pronator teres syndrome.

One study has shown that 50% of pronator teres syndrome patients reported relief within four months after receiving conservative treatment. Surgical decompression of the median nerve is considered when conservative treatment gets fails i.e., rarely indicated. 

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