Anteroposterior radiograph of the injured left hand of a 7-year-old boy who fell off of his scooter shows a distal one-third radius fracture with plastic deformation.
Lateral radiograph of the patient
A 7-year-old boy injures his left arm and is brought to the emergency department a few hours later. He was riding on a scooter and fell forward, landing on his outstretched hand. On examination, a slight angular deformity to the left forearm is noted. Anteroposterior and lateral radiographs show a distal one-third radius fracture with plastic deformation.
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Plastic deformation, or traumatic bowing, is an irreversible change in the shape of bone after an injury. It occurs almost exclusively in pediatric forearm fractures.
Plastic deformation occurs when a large amount of force is placed on bone, and the bone stays in the deformed position (plasticity) even after the force is removed. The modulus of elasticity, or the measure of stiffness of a solid material, is higher in adult bone than in pediatric bone. Another example of modulus of elasticity is the use of metal implants in orthopedic surgery, which have a higher modulus of elasticity than bone.
Mineral content of bone plays a large role in its elastic properties. Pediatric cortical bone has lower mineral content than adult bone and therefore has weaker bending strength. With aging, the increased mineralization stiffens the collagen and hydroxyapatite in bone, which decreases the amount of deformity the bone will tolerate before fracture. Unlike adult bone, pediatric bone is able to absorb significant bending forces before fracturing because of its plastic deformation properties.1,2
Plastic deformity of the forearm can limit forearm supination and pronation, as the deformed radius and ulna encroach on the interosseous space. In general, plastic deformities are thought to have less remodeling potential and can be more difficult to reduce than other angulated pediatric forearm fractures. Therefore, the treatment approach is unique, as the threshold for closed reduction under anesthesia is less.
One recommendation includes using general anesthesia and performing closed reduction of plastic deformity that includes angulation greater than 10 degrees in all patients aged more than 6 years. In general, displaced forearm fractures (nonplastic deformity) require 15 to 20 degrees of angulation before closed reduction is attempted in patients aged less than 10 years.1,2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants (JOPA).
- Mabrey JD, Fitch RD. Plastic deformation in pediatric fractures: mechanism and treatment. J Pediatr Orthop. 1989;9:310-314.
- Wall EJ, Mehlman CT. Injuries to the shafts of the radius and ulna. In: Beaty JH, Kasser KR, eds. Rockwood and Wilkins’ Fractures in Children. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005:417-418.