A bending fracture is a type of incomplete fracture where bone permanently deforms, or bows, without the outer shell of the bone actually cracking. The medical term is plastic deformation, and it sits on a spectrum alongside two closely related injuries: buckle (torus) fractures and greenstick fractures. All three are classified as bending injuries rather than full-thickness breaks, and they occur overwhelmingly in children.
How Plastic Deformation Works
When force is applied to a bone, the bone initially flexes and springs back to its original shape once the force is removed. This elastic phase is normal and happens constantly during everyday activity. But if the force exceeds the bone’s elastic limit, permanent deformation sets in. The bone bends and stays bent even after the force stops. If the force continues beyond that point, the bone eventually cracks or breaks completely.
Plastic deformation occupies that middle zone: enough force to permanently reshape the bone, but not enough to produce an actual fracture line. The outer layer of bone (the cortex) remains intact on all sides. This makes it fundamentally different from a greenstick fracture, where one side of the cortex breaks while the other side bends, and from a buckle fracture, where the cortex compresses and bulges outward on one side.
The Three Types of Bending Fractures
These three injuries form a continuum of severity, all caused by bending forces on immature bone:
- Plastic deformation (bowing): The bone curves permanently but has no visible fracture line. On X-ray, the bone looks bent but intact, with no crack and no new bone formation during early healing.
- Buckle (torus) fracture: The compressed side of the bone buckles outward, creating a small bulge in the cortex. These are the most stable of the three and typically heal in about three weeks with simple immobilization.
- Greenstick fracture: The tension side of the bone actually cracks, while the opposite (compressed) side undergoes plastic deformation and bends without breaking. Think of snapping a fresh twig: one side splinters while the other side folds. Greenstick fractures are the least stable of the group and carry a higher risk of re-fracturing or shifting out of alignment compared to buckle or plastic bowing injuries.
Why Children’s Bones Bend
Bone is roughly 60% mineral (mostly hydroxyapatite, a calcium-phosphate crystal), 30% organic material (primarily collagen protein), and 10% water. Collagen fibers give bone its flexibility and tensile strength. They can stretch 10 to 20% before breaking, which is substantial for a structural tissue.
Children’s bones contain a higher proportion of collagen relative to mineral compared to adult bones. Their skeleton is still mineralizing, so the collagen-to-crystal ratio is tilted toward flexibility. This is why a child’s forearm bone can bow like a green branch under force that would snap an adult’s bone cleanly in two. As bones mature through adolescence and into adulthood, increasing mineralization hardens the collagen and mineral complex, making bones stiffer and more brittle.
Can Adults Get Bending Fractures?
Rarely, but yes. A study of 30 adult cases of forearm plastic deformation found the average patient age was 21.3 years, with a range of 17 to 24. Nearly all injuries (97%) happened when the person’s arm became trapped in industrial machinery with rotating rollers, creating a sustained bending force over several minutes. The remaining case involved a skiing accident. Road-traffic collisions have also been reported.
Young adults in their late teens and early twenties still retain some of the flexibility that characterizes pediatric bone, which is why this age group accounts for almost all adult cases. In older adults, plastic deformation from trauma is exceptionally rare because fully mineralized bone tends to crack before it bows. The exception involves conditions that soften bone, such as osteomalacia (vitamin D deficiency affecting bone mineralization), though these cases are unusual.
Plastic deformation in adults is frequently missed on initial imaging because clinicians aren’t expecting it. The injury can cause significant loss of forearm rotation if the bowing goes undiagnosed and untreated.
How Bending Fractures Are Diagnosed
Plastic deformation is one of the trickiest fractures to spot on an X-ray. The hallmark features are a visible curve in the bone with no fracture line anywhere along its length and no new bone formation during early healing. Because there’s no obvious crack, radiologists and emergency physicians sometimes read the X-ray as normal, especially if the bowing is subtle.
Comparing X-rays of the injured limb to the uninjured opposite side can help reveal asymmetry. Clinical suspicion matters: if a child has pain, swelling, and difficulty using a limb after a fall, but the X-ray looks “clean,” plastic deformation should be considered. The bowing is often visible just by looking at the limb, even before imaging.
Treatment and Recovery
How a bending fracture is treated depends on the degree of angulation and the child’s age. Younger children have far more capacity to remodel bone over time, so mild bowing may simply be immobilized in a cast or splint and monitored as the bone gradually straightens itself through normal growth.
For forearm fractures in children under 9 or 10, angulation up to 15 degrees is generally considered acceptable without manual correction. In older children (girls over 8, boys over 10), the threshold drops to 10 degrees for the upper and middle portions of the forearm, though up to 15 degrees is still tolerated closer to the wrist. If the bowing exceeds these thresholds, the bone may need to be straightened under sedation or anesthesia before casting. Surgery is reserved for cases where adequate alignment can’t be achieved by manual correction alone.
Buckle fractures, being the most stable, typically need only a well-molded cast or a removable wrist brace for about three weeks. Greenstick fractures require more careful follow-up because of their tendency to shift or re-fracture. Some minimally angled greenstick fractures in young children can be managed with a splint rather than a full cast.
How Children’s Bones Remodel
One of the remarkable features of the growing skeleton is its ability to correct residual angulation over time. About 75% of the correction comes from the growth plates near each end of the bone, which gradually realign themselves perpendicular to the forces passing through them. The remaining 25% comes from the bone shaft itself, where new bone is deposited on the concave (compressed) side and reabsorbed from the convex (stretched) side.
This remodeling is not unlimited. It depends on the child’s age, the location of the injury, and the plane of the angulation (deformities in the same plane as joint motion correct better than those in other planes). In children up to age 10 to 12, even complete side-to-side displacement of a bone shaft can fully remodel in most locations. A study of 28 malunited femur fractures in children found that an average of 75% of the deformity corrected within three years, with complete remodeling by five years.
For older children and adolescents with less remaining growth, the remodeling window is narrower, which is why acceptable angulation thresholds become stricter with age.