The Pronator muscles Are two muscles responsible for tilting the radius bone through the ulna bone or in a prone position (upside down).
There are two types of pronator muscles: the pronator round muscle (teres) and the pronator quadratic muscle.
The pronator word comes from the Latin Pronusm which means"leaning forward or lying face down." Pronation is a movement of the hand, wrist and forearm, which is unique in the human body.
While spinning at the top during supination, the radius bone circles half a circle at its distal end over the ulna bone as its axis point. Basically, the radius crosses over the ulna bone, when the hand and wrist move from the palm down.
The pronator muscle originates in the medial epicondyle of the humerus and is inserted in the axis of the radius. When traveling with the bone radius to the middle of its distance before inserting it, the pronator's muscle can take advantage of the leverage.
This means that half the radius of the bone is used as a lever to roll over the ulna bone, which gives one the ability to pronate with the power of the elbow. A capacity that comes from the pronator quadratic muscle.
Pronator muscles are innervated by the Median nerve . When the pronator muscles have spasms, they make pronation weak and Supination Be restricted.
Types of pronator muscles
Pronounced pronator muscle
The pronator teres muscle, also known as pronador teres, is a muscle of the human body that is mainly in the forearm, and that along with the pronator square, serves for the pronation of the forearm.
It is the strongest of the two pronator muscles, however, it only activates during rapid or resisted forearm pronation. The pronator round has two heads: humeral and ulnar.
The humeral head, the largest and superficial, arises from the medial supracondylar crest immediately superior to the medial epicondyle of the humerus and the common flexor tendon (arising from the medial epicondyle).
The ulnar head is a thin fascicle, arising from the medial side of the coronoid process of the ulna, and joining the anterior at an acute angle.
The pronator round has a tendency to be hyperactive and short due to its excessive use. This abuse can be caused by repetitive activities involving a pronounced forearm position or an active forearm pronation movement, including throwing, a few hits like playing tennis, swinging a golf club and turning a screwdriver or wrench.
Also, exercises that involve holding the forearm in a pronated position and contracting the pronator isometrically may contribute to its overuse.
As the pronator becomes shorter and shorter, the tension through the muscle increases and the quality of the tissue deteriorates, which often leads to injury.
Square pronator muscle
The pronator square is a rectangular muscle on the front of the forearm that connects between the radius and the ulna.
It is the main promoter of pronation of the forearm, receiving help of the pronator round during the rapid pronation. It is also known for its role in preventing separation of the ulna and the radius when the force is transferred to the forearm through the heel of the palm of the hand.
Classified as part of the deep anterior compartment of the forearm, the pronator square is the deepest of the muscles in the front of the forearm, and is deeply rooted to the mass of the flexor tendons of the wrist.
Its parallel muscle fibers extend laterally from its origin in the anterior distal ulna. The fibers cross over the interosseous membrane of the forearm before inserting into the distal anterior ulna, forming a flat form of square muscle.
The square pronator may become hyperactive and short due to excessive use of repetitive activities involving the movement of forearm pronation as well as activities involving excessive isometric contraction of the pronator muscles.
Pronator muscle syndromes
Some syndromes that can affect the pronator muscles are:
Carpal tunnel syndrome
Carpal tunnel syndrome is a common condition that causes a tingling sensation, numbness and sometimes pain in the hand and fingers. These feelings gradually develop and begin to worsen usually during the night. They tend to affect the thumb, index finger and middle finger.
Pronator syndrome round
Pronator syndrome (pronator syndrome) is a neuropathy by compression of the median nerve in the elbow.
It is not as common as compression on the wrist, which is carpal tunnel syndrome. It occurs most often in women over 40 years of age.
Compression of the medial nerve at the elbow can cause pain and / or numbness in the distribution of the medial distal nerve, and weakness may develop in the flexor of the long finger of the thumb and the deep flexor of the index finger and the quadratic pronator.
Symptoms include sensitivity to the pronator round muscle and pain with pronation of the forearm. Weakness may be present with abduction of the thumb, as well as deterioration of the caliper muscles. Feeling changes can also be experienced on the first three fingers and the palm.
Anterior interosseous nerve syndrome
Anterior interosseous nerve syndrome is a rare syndrome comprising less than 1% of all nerve palsies in the upper limbs. It is so named because it arises from the compression or inflammation of the anterior interosseous nerve of the forearm.
This syndrome innervates three muscles in the forearm: the square pronator, the long flexor of the thumb, and the radial half of the deep flexor of the finger.
Most people with this syndrome have localized pain in the forearm. The pain is sometimes described in the ulnar fossa and mainly causes pain in the elbow. What is characteristic is the deterioration in the movement of the thumb and forefinger.
References
- NHS Staff (2016). Carpal tunnel syndrome. GOV UK. Retrieved from: nhs.uk.
- Alex (2015). Pronator Teres: Functional Anatomy Guide. KOG. Retrieved from: kingofthegym.com.
- Royal Anatomy Team (2016). Pronator Muscles. Royal's Anatomy Book. Retrieved from: training.releasology.com.
- Anquain Sullivan (2014). Pronator Teres Syndrome. Physiopedia. Retrieved from: physio-pedia.com.