Pronator Teres: The Carpal Tunnel Pretender

Entrapment of the median nerve (MN) between the two heads of the pronator teres muscle (PTM) can lead to pain and functional disability in the arm and hand, and can lead to referred pain and neurological symptoms in the hand. This is known as Pronator teres syndrome (PTS). It is an uncommon condition suffered by athletes whose sports require strong grip in positions of forearm pronation – for example tennis players, rowers, bodybuilders and baseball batters. Its symptoms can mimic the more common carpal tunnel syndrome (CTS).

Anatomy and biomechanics

The PTM is attached proximally by two heads⁽¹⁾:

1. The humeral head attaches proximal to the medial epicondyle, and to the adjacent fascia or the medial intermuscular septum of the arm.
2. The ulnar head attaches to the medial side of the coronoid process of the ulna. The ulna head is more tendinous and may result in greater tension, which may compress the MN.

Both heads run diagonally downwards and merge to form a common flexor tendon, which inserts at the middle of the lateral surface of the radius (see figure 1). The MN enters the forearm from the cubital fossa between these two heads; the space between the two heads is called the pronator canal^(2,3). The passage of the nerve has some variation - e.g. passing through the ulna head or passing beneath both heads between the PTM and the flexor digitorum profundus^(3,4).