The pronator teres is a muscle of the upper limb involved in forearm and hand movements. Understanding its location, function, and potential for causing pain provides insight into forearm mechanics.
Where the Pronator Teres Muscle Resides
The pronator teres muscle is situated in the anterior (flexor) compartment of the forearm. This means it is located on the front side, closer to the palm, and is considered one of the superficial muscles in this area.
The muscle originates with two separate heads. The larger humeral head arises from the medial epicondyle of the humerus (the inner side of the elbow), and the smaller ulnar head originates from the coronoid process of the ulna. The muscle travels obliquely across the forearm before inserting onto the lateral surface of the radius, the bone on the thumb side.
The Role of Pronator Teres in Forearm Movement
The primary function of the pronator teres is pronation of the forearm, a rotating movement that turns the palm downward or backward. This action is achieved because the muscle’s oblique path allows it to pull the radius across the ulna. Pronation is the motion used when turning a screwdriver.
The pronator teres works with the pronator quadratus, a smaller muscle near the wrist, to execute this rotational movement. The muscle also provides a secondary, minor contribution to flexion of the elbow joint. The median nerve controls these actions by supplying the pronator teres and initiating muscle contraction.
When the Muscle Causes Pain
The pronator teres is important because the median nerve, which controls its function, typically passes between the muscle’s two heads. This anatomical relationship can lead to Pronator Teres Syndrome (PTS), a condition where the median nerve becomes compressed by the muscle.
Symptoms often begin as an aching discomfort on the palm-side of the forearm, frequently accompanied by numbness or tingling. This compression can also reduce sensation in the thumb, index, middle, and part of the ring finger.
Repetitive, forceful movements involving pronation, such as assembly line work or sports like golf and tennis, can cause the muscle to become strained or overly developed, leading to nerve entrapment. Unlike carpal tunnel syndrome, which affects the median nerve at the wrist, PTS symptoms include pain that worsens when resisting forearm rotation.