Deforming Forces: in Both Bone Forearm Frx




- Deforming forces:
    - Biceps brachii and Supinator inserts into the proximal1/3 of the radius;
         - these muscles are the supinators of the forearm;
    - Pronator Teres, originating above the elbow medially, inserts into the middle third of the radius;
         - when frx is distal to insertion of pronator teres, proximal fragment lies in neutral rotation, and the distal fragment is pronated;
    - Pronator Quadratus, located on the anterior aspect of the lower forearm, inserts into the distal third of the radius;
         - when the fracture is distal to the insertion of the pronator teres muscle, the proximal fragment lies in neutral rotation, and the distal fragment is pronated;
    - Brachioradialis
         - assists in elbow flexion & is also semipronator & semisupinator of forearm of forearm, bringing it from supine or prone position to neutral rotation;
    - extensors and abductors of the thumb act with Brachioradialis muscle in fractures of the distal third of the radius and pull the distal fragment of the radius proximally;
    - Flexor muscles of the forearm:
         - tend to pull the distal fragments anteriorly and produce dorsal bowing of the radius and ulna during healing;

- Proximal Third Frx :
    - see pediatric proximal 1/3 forearm frx
    - above insertion of pronator teres;
    - proximal fragment of radius is supinated & flexed because of unopposed action of biceps brachii & supinator, and the distal fragment is pronated by the action of the pronator teres & pronator quadratus muscles;
    - to obtain alignment of the fracture, the distal fragment should be supinated;

- Middle Third Fractures:
    - below pronator teres teres;
    - proximal fragment is held in neutral rotation, as action of supinator is countered by the pronator teres;
    - proximal fragment is drawn into flexion by action of biceps;
    - distal fragment is pronated & drawn toward ulna by pronator quadratus;
    - to achieve anatomic reduction, distal fragment is brought into neutral rotation;

- Lower 1/3 of Forearm Fractures:
    - distal fragment of the pulled radius is pronated & pulled inward by pronator quadratus;
    - overriding & shortening are caused by obliquity of frx & pull of muscles


The effects of angular and rotational deformities of both bones of the forearm. An in vitro study.



Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Friday, August 3, 2012 11:02 am