Buckle (Torus) & Plastic Bowing — Paediatric Forearm Patterns

The paediatric forearm skeleton responds to mechanical loading in fundamentally different ways from the adult skeleton. The relative elasticity of the periosteum, the lower mineral density of immature cortical bone, and the presence of the physis create a spectrum of injury patterns unique to children — ranging from the incomplete buckle (torus) fracture, through the greenstick fracture, to the rare but important plastic bowing deformity. Understanding these patterns is essential because they require different management, carry different risks of re-fracture and malunion, and may be associated with overlooked or associated injuries (particularly the radial head dislocation in plastic bowing variants — see Monteggia equivalents).

• Why children`s bones fail differently: paediatric cortical bone has a higher proportion of organic matrix (collagen) relative to mineral (hydroxyapatite) compared to adult bone; this gives it greater flexibility (ductility) but lower stiffness; the periosteum is thick and firmly adherent — it can remain intact on one side of the bone even when the cortex is fractured on the other (tension vs compression failure asymmetry); the growth plate is a stress concentration site; these properties explain why children`s fractures are: (1) often incomplete; (2) may `bow` without fracturing; (3) may remodel significantly; and (4) may be missed because they do not have the complete fracture line expected on adult X-rays

• Definition and mechanism: a torus fracture (also called a buckle fracture — `torus` refers to the architectural term for a rounded convex moulding, reflecting the buckled cortical appearance on X-ray) is a compression failure of the cortex on the CONCAVE (compression) side of the bone; the cortex buckles outward under axial compression but does NOT breach; the periosteum and cortex on the tension (convex) side remain completely intact; the bone is not truly fractured through — there is no cortical disruption, no displacement, and no instability; the bone merely `buckles` under load; the typical mechanism is a fall onto an outstretched hand (FOOSH) — axial loading of the wrist driving compressive failure at the distal radial metaphysis; the distal radius is the most common site (90% of torus fractures in children involve the distal radial metaphysis)
• Radiological appearance: a subtle cortical buckling — a `puckering` or `wrinkling` of the metaphyseal cortex on one or both sides of the bone; no fracture line traverses the full cortex; no displacement; the normal parallel cortical lines are disrupted by a rounded outward buckle; the deformity is best seen on the lateral view of the wrist; comparison views of the contralateral wrist may help identify subtle changes; MRI is not required but would show a band of bone marrow oedema and the cortical buckling
• Management: the torus fracture is an inherently STABLE injury because the periosteum is intact and the bone is not truly disrupted; immobilisation is primarily for pain relief, not fracture stabilisation; a removable wrist splint (Futura-type or thermoplastic splint) for 3 weeks is the evidence-based treatment; multiple RCTs demonstrate equivalent outcomes with a removable splint vs plaster cast; the key advantage of a removable splint is that parents can remove it for bathing, it is adjustable for swelling, and it reduces the risk of pressure sores; a hard plaster cast is NOT required; no follow-up X-ray is needed for uncomplicated torus fractures if the injury has been correctly identified and immobilised; parents are given the splint and instructed to return if pain worsens (ruling out a missed greenstick or complete fracture)
• Re-fracture risk: very low for torus fractures; unlike greenstick fractures (which require completion at the time of reduction), torus fractures do not need any manipulation; return to sport at 4–6 weeks when pain-free

• Definition: a greenstick fracture is an incomplete fracture in which the cortex and periosteum are DISRUPTED on the TENSION (convex) side of the bone, but the cortex and periosteum remain intact on the COMPRESSION (concave) side; the bone breaks on the side under tension but bends rather than fracturing through on the compression side — like a green stick or twig that bends and breaks on one side but remains intact on the other; there is ANGULATION but typically no shortening; this is distinct from a torus fracture (which fails on the compression side) and a plastic bowing fracture (which does not breach the cortex at all)
• Radiological appearance: an angulated fracture with a fracture line on the convex (tension) side only; the concave (compression) cortex is intact (possibly buckled but not fractured through); the fracture line may appear as a short transverse fracture that does not cross the full bone width; angulation of the fracture is the key feature; often subtle on one view — always obtain two views perpendicular to each other
• Management — the `complete the fracture` principle: the most important and counterintuitive concept in greenstick fracture management; because the intact compression-side periosteum acts as a spring — it stores elastic energy and tends to spring back to the deformed position after reduction; if the fracture is simply reduced without completing it, the intact periosteum will gradually restore the angulation; therefore, at the time of closed reduction under general anaesthesia, the fracture should be COMPLETED (the compression cortex is deliberately broken through by applying a force in the direction of the deformity until a `crack` is felt) — this converts the greenstick fracture into a complete fracture; a complete fracture is more stable because neither periosteum is pulling the fragments back; after completion and reduction, an above-elbow plaster cast is applied; however, this principle is NOT universally agreed upon — many centres successfully manage displaced greenstick fractures without deliberate completion, relying on adequate reduction and moulded cast
• Acceptable angulation: depends on age and location; in the forearm, up to 15° of angulation may remodel in children under 8 years if in the sagittal plane and the physis has adequate growth remaining; rotational deformity does NOT remodel and must be corrected; more than 15° of angulation in the coronal plane or any significant rotational deformity requires reduction

• Definition and mechanism: plastic bowing (also called traumatic bowing or elastic deformation with permanent set) is a unique paediatric injury in which the bone is deformed beyond its elastic limit but the applied stress is insufficient to produce a discrete fracture line; the bone undergoes permanent plastic deformation — it is bent beyond its elastic range but never fractures; on X-ray, there is NO fracture line; the bone simply appears curved or bowed more than normal; the periosteum, cortex, and medullary canal are all visually intact; this is distinguished from a torus fracture (cortical buckling without angulation) and a greenstick fracture (tension-side cortical breach with angulation); plastic bowing is most common in the radius and ulna and occasionally the fibula
• Why this is clinically critical — the Monteggia equivalent: a plastically bowed ulna combined with anterior radial head dislocation is the most commonly MISSED Monteggia equivalent; because there is no discrete fracture line, the clinician may dismiss the ulnar deformity as normal or variant anatomy; the anterior radial head dislocation is the critical finding — apply the radiocapitellar line rule; a bowed ulna on ANY forearm X-ray should immediately trigger assessment of the radial head position; plastic bowing of the radius in isolation (without ulnar fracture) can also occur and causes restriction of forearm rotation
• Management: correction of plastic bowing deformity requires THREE-POINT BENDING MANIPULATION under general anaesthesia; unlike fractures, plastic bowing cannot be reduced by simple traction (there is no fracture plane); the examiner applies a three-point bending force to correct the deformity — counter-pressure at the apex of the bow and opposing forces at each end; the force required is substantial and must be applied progressively; the periosteum must plastically deform back beyond the elastic range to achieve a permanent correction; if reduction is inadequate (residual angulation >10°), forearm rotation will be restricted (the interosseous membrane space is narrowed); young children (<4 years) with mild deformity may remodel; older children and significant deformity require reduction

• Torus (buckle) fracture: compression side cortex buckles; periosteum intact; NO instability; removable splint 3 weeks; no manipulation; no follow-up X-ray needed; the most common paediatric wrist fracture; distal radial metaphysis
• Greenstick fracture: tension side cortex fractures; compression side intact; ANGULATED; the intact compression periosteum springs back → complete the fracture at time of reduction to prevent spring-back; above-elbow cast in supination for forearm greensticks (to maintain reduced position)
• Plastic bowing: NO fracture line; permanent plastic deformation of bone; ALWAYS check radiocapitellar line for associated radial head dislocation (Monteggia equivalent — the most commonly missed paediatric elbow injury); three-point bending manipulation under GA required for reduction
• Torus vs greenstick distinction: torus = compression side fails (buckles inward); greenstick = tension side fails (cracks outward); torus = stable + no reduction; greenstick = potentially unstable + reduction required
• Completing the greenstick fracture: deliberate completion of the intact compression cortex at the time of reduction converts greenstick → complete fracture → no spring-back tendency → more stable reduction; apply force in the direction of the deformity until a `crack` is felt; not universally practised but widely recommended for significantly angulated greenstick fractures
• Acceptable deformity in paediatric forearm fractures: age <8 years — up to 15° sagittal angulation may remodel; NO rotational deformity ever remodels (must correct); volar angulation of distal radius remodels better than dorsal angulation (matches the normal volar tilt); coronal plane angulation <10° acceptable in young children
• Follow-up X-rays for greenstick and complete forearm fractures: weekly for 2–3 weeks to detect loss of reduction; torus fractures do not need follow-up imaging (stable); greenstick and complete fractures need regular surveillance until union