Theforearm is the region of theupper limb between theelbow and thewrist.[1] The term forearm is used inanatomy to distinguish it from thearm, a word which is used to describe the entire appendage of the upper limb, but which in anatomy, technically, means only the region of the upper arm, whereas the lower "arm" is called the forearm. It ishomologous to the region of theleg that lies between theknee and theankle joints, thecrus.
The forearm contains two longbones, theradius and theulna,[2] forming the two radioulnar joints. Theinterosseous membrane connects these bones. Ultimately, the forearm is covered by skin, the anterior surface usually being less hairy than the posterior surface.
The forearm contains many muscles, including the flexors and extensors of thewrist, flexors and extensors of the digits, a flexor of the elbow (brachioradialis), andpronators andsupinators that turn the hand to face down or upwards, respectively. In cross-section, the forearm can be divided into twofascial compartments. The posterior compartment contains the extensors of the hands, which are supplied by theradial nerve. The anterior compartment contains the flexors and is mainly supplied by themedian nerve. The flexor muscles are more massive than the extensors because they work against gravity and act as anti-gravity muscles. Theulnar nerve also runs the length of the forearm.[3]
Theradial andulnar arteries and their branches supply the blood to the forearm. These usually run on the anterior face of the radius and ulna down the whole forearm. The main superficial veins of the forearm are thecephalic,median antebrachial and thebasilic vein. These veins can be used for cannularisation orvenipuncture, although thecubital fossa is a preferred site for getting blood.
Distally, it articulates with the ulna again at thedistal radioulnar joint. It forms part of thewrist joint by articulating with thescaphoid at its lateral aspect and with thelunate at its medial aspect.
"E/I" refers to "extrinsic" or "intrinsic". The intrinsic muscles of the forearm act on the forearm, meaning, across the elbow joint and theproximal anddistal radioulnar joints (resulting inpronation orsupination), whereas the extrinsic muscles act upon the hand and wrist. In most cases, the extrinsic anterior muscles areflexors, while the extrinsic posterior muscles areextensors.
The brachioradialis, flexor of the forearm, is unusual in that it is located in theposterior compartment, but it is actually in the anterior portion of the forearm.
See separate nerve articles for details on divisions proximal to the elbow and distal to the wrist; seeBrachial plexus for the origins of the median, radial and ulnar nerves.
The forearm can be brought closer to the upper arm (flexed) and brought away from the upper arm (extended) due to movement at theelbow. The forearm can also be rotated so that the palm of thehand rotates inwards (pronated) and rotated back so that the palm rotates outwards (supinated) due to movement at the elbow and thedistal radioulnar joint.[5]
Afracture of the forearm can be classified as to whether it involves only the ulna (ulnar fracture), only the radius (radius fracture), or both radioulnar fracture.
For treatment of children withtorus fractures of the forearm splinting appears to work better than casting.[7]Genetically determined disorders likehereditary multiple exostoses can lead to hand and forearm deformities. Hereditary multiple exostoses is due growth disturbance of the epiphyses of the radius and ulna, the two bones of the forearm.[8]
^WebMD (2009)."forearm".Webster's New World Medical Dictionary (3rd ed.). Houghton Mifflin Harcourt. p. 166.ISBN978-0-544-18897-6.
^"Forearm".The Lecturio Medical Concept Library. Retrieved2021-06-22.
^Mitchell, Brittney; Whited, Lacey (2020-08-15)."Anatomy, Shoulder and Upper Limb, Forearm Muscles".National Center for Biotechnology Information, U.S. National Library of Medicine. StatPearls Publishing LLC. Retrieved22 June 2021.
^Jiang N, Cao ZH, Ma YF, Lin Z, Yu B (November 2016). "Management of Pediatric Forearm Torus Fractures: A Systematic Review and Meta-Analysis".Pediatric Emergency Care.32 (11):773–778.doi:10.1097/pec.0000000000000579.PMID26555307.S2CID25796224.
