Forearm pronation mechanism

The human forearm consist of two bones: the ulna and the radius.

The ulna connects to the humerus at the proximal end, forming the elbow joint. At the distal end, both the ulna and radius connect to the hand. [1] Stability of this joint is maintained by the dorsal and palmar radioulnar ligaments (DRUL and PRUL) and the interosseous membrane (IOM). [2] The head of the radius is discoid, and the radial neck, within the circular annular ligament, attaches the proximal radius to the ulna.

The ulna and the radius are sometimes parallel and sometimes cross, edenabling movements at the proximal and distal radioulnar joints called pronation and supination. This is extra important ability in daily activities, essential for gripping and hand movements. Without it, tasks such as eating, writing, and personal hygiene would be difficult. People rotate their forearms almost constantly.

When the forearm is pronated, with the palm facing downwards, the radius rotates around the ulna. This movement is governed by the pronator teres and pronator quadratus muscles. The pronator teres muscle’s action is weak, especially when elbow is extended. The pronator quadratus is stronger. This muscle wraps around the distal part of the ulna and acting by “unwinding”. [3]

When forearm is supinate, palm facing upwards. The supination muscles (brachioradialis and supinator muscle) originate from lateral part of the humerus. Additionally, the biceps brachii acts as a supinator of the forearm. All these muscles insert on the radius. During pronation, the supinator muscle wraps around the radius, enabling the opposite movement, supination.

Both pronation and supination of the forearm occur within a range of 80-90 degrees from the neutral position. [4]

  1. Youm, Y., i in. „Biomechanical Analyses of Forearm Pronation-Supination and Elbow Flexion-Extension”. Journal of Biomechanics, t. 12, nr 4, january 1979, s. 245–55. DOI.org (Crossref), https://doi.org/10.1016/0021-9290(79)90067-8
  2. Kihara, Hitoshi, i in. „The Stabilizing Mechanism of the Distal Radioulnar Joint during Pronation and Supination”. The Journal of Hand Surgery, t. 20, nr 6, november 1995, s. 930–36. DOI.org (Crossref), https://doi.org/10.1016/S0363-5023(05)80139-X
  3. Kapandji, Adalbert. „Biomechanics of pronation and supination of the forearm”. Hand Clinics, t. 17, nr 1, febuary 2001, s. 111–22. DOI.org (Crossref), https://doi.org/10.1016/S0749-0712(21)00605-3
  4. Laksanacharoen, S., i S. Wongsiri. „Design of apparatus to study human elbow joint motion”. IEEE EMBS Asian-Pacific Conference on Biomedical Engineering, 2003., IEEE, 2003, s. 236–37. DOI.org (Crossref), https://doi.org/10.1109/APBME.2003.1302670
forearmpronationradioulnar jointradiussupinationulna
Muscles