- 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.
