Wrist flexion is a fundamental movement of the hand that involves bending the hand downward, bringing the palm closer to the inner forearm. It is one of the four primary movements occurring at the wrist joint, alongside extension and the side-to-side motions of radial and ulnar deviation. Understanding wrist flexion requires looking at the anatomy of the joint and the muscles that power this motion.
Defining the Movement and Range
Wrist flexion is mechanically defined as the movement of the hand in the sagittal plane, which is an imaginary line dividing the body into left and right halves. The action effectively decreases the angle between the palm and the front of the forearm.
The typical healthy range of motion for wrist flexion is measured between 75 and 90 degrees. This total movement is a coordinated effort shared between two main joint complexes: the radiocarpal joint and the midcarpal joint. During full flexion, the midcarpal joint contributes slightly more to the overall motion than the radiocarpal joint. The movement is ultimately limited by the compression of the soft tissues on the anterior side of the wrist and forearm.
The Musculature Behind Wrist Flexion
The force behind wrist flexion is generated by a group of muscles located primarily in the anterior compartment of the forearm, known as the wrist flexors. The three principal muscles responsible for this movement are the Flexor Carpi Radialis, the Flexor Carpi Ulnaris, and the Palmaris Longus. These muscles share a common origin on the medial epicondyle of the humerus.
The Flexor Carpi Radialis (FCR) inserts onto the base of the second and third metacarpal bones. This positioning allows it to flex the wrist and assist in radial deviation (movement toward the thumb side). Conversely, the Flexor Carpi Ulnaris (FCU) inserts on the pisiform bone, the hook of the hamate, and the base of the fifth metacarpal, enabling it to contribute to ulnar deviation while flexing the wrist.
Lying between these two main flexors is the Palmaris Longus (PL), which is absent in a significant portion of the population. When present, its tendon runs superficially and inserts into the palmar aponeurosis, the thick connective tissue layer of the hand. Other muscles, such as the Flexor Digitorum Superficialis and Profundus, also assist in wrist flexion when the fingers are not fully extended.
Common Conditions Impairing Flexion
Conditions can limit the range of motion and cause pain in the tendons and nerves responsible for wrist flexion. One common issue is flexor tendonitis, which involves inflammation of the flexor tendons, typically resulting from repetitive strain or overuse. This irritation can make the act of bending the wrist painful, especially under load.
A more complex impairment is Carpal Tunnel Syndrome (CTS), where the median nerve is compressed as it passes through the narrow carpal tunnel. Since the median nerve supplies many flexor muscles, compression can lead to weakness, numbness, and pain that makes gripping and forceful wrist flexion difficult. The pain is often aggravated by activities requiring sustained or repetitive wrist flexion, such as prolonged typing.
Traumatic injuries, such as fractures of the distal radius, also frequently impede normal wrist flexion. Even after healing, resulting scar tissue and joint stiffness can significantly restrict the available range of motion. Furthermore, non-cancerous lumps called ganglion cysts can develop near the joint and sometimes grow large enough to physically block the smooth movement of the tendons, leading to limited and painful flexion.