Forearm Fractures – General Principles

Forearm Fractures – General Principles

Anatomy
– distal radial physis closes about age 17 in girls, 18 in boys
– proximal radial physis closes about age 17-18
– because the radius and ulna are not completely cylindrical, you can tell malrotation by the width of the proximal and distal fragments at the fracture site.
– the annular ligament is most responsible for maintaining the proximal radioulnar joint – most stable in supination
– the TFC complex and ligaments is responsible for maintaining the DRUJ

Rotational Considerations
– supination tends to shorten the ulna on the radius (ulnar minus) while pronation tends to lengthen the ulna relative to the radius (hence, if looking for ulnar variance, must do it in neutral)
– interosseous membrane and space is narrowest in pronation, widest in neutral to 30 of supination
– 10 degrees of angulation in the midshaft limites rotation 20-27 degrees
– bayonet apposition does not limit rotation as long as the interosseous space is maintained

Deforming Forces
– biceps and supinator flex and supinate the proximal radius fragment
– pronator teres pronates the mid-radius fragment
– pronator quadratus pronates distally
– it is hard to predict how to immobilize the arm based on these deforming forces and the level of the fracture. Just be aware of them!

Remodeling Potential
– the amount of spontaneous correction is dependent on age, amount of residual angulation, the fracture to epiphyseal plate proximity, and relationship of deformity with plane of motion
– don’t depend on remodeling after age 11; best remodeling is seen in kids less than 8
– average rate of remodeling at the distal radius is .9 degrees per month, or 10 degrees per year
– volar and ulnar angulation result in a higher rate of correction than do dorsal angulation
– increased correction takes place when there is greater deformity
– bayonet apposition is acceptable and will remodel in a child less than 8-10 if rotation is correct, if interosseous space is preserved, and there is no angulation!

In general:
Accept no more than 10 degrees of angulation (maybe 20 in a child less than 8)
Accept no malrotation
Accept bayonet apposition only in a child less than 10.

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