Residency · Residency · Orthopedic Surgery
Pediatric Forearm Fractures and Monteggia Lesions
Introduction
Forearm fractures are the most common fractures in the pediatric population, accounting for approximately 40% of all childhood fractures. The unique properties of the growing skeleton, including the thick periosteum and capacity for remodeling, allow many of these injuries to be treated nonoperatively. However, the orthopedic surgeon must recognize the specific patterns that require surgical intervention, particularly the Monteggia fracture-dislocation, which is frequently missed on initial evaluation.
Anatomy and Biomechanics
The radius and ulna function as a unit linked by the proximal and distal radioulnar joints and the interosseous membrane. The thick pediatric periosteum acts as a hinge during fracture, often preventing complete displacement and aiding reduction. The physis contributes to longitudinal growth, with the distal radius physis accounting for 75 to 80% of radial growth. The potential for remodeling is greatest in younger children, in fractures near the physis, and in the plane of joint motion.
Fracture Patterns
Plastic Deformation (Bowing Fractures)
In plastic deformation, bone bends beyond its elastic limit without a visible fracture line. The periosteum and cortex undergo microfractures without macroscopic failure. This pattern is more common in the ulna and can be challenging to diagnose, requiring comparison with the contralateral forearm. Treatment involves reduction if angulation exceeds 10 to 15 degrees and may require conscious sedation with sustained corrective force.
Buckle (Torus) Fractures
Buckle fractures represent compression failure of the cortex, typically at the metaphysis, where the cortex buckles on the compression side while the tension cortex remains intact. These are inherently stable fractures treated with a removable splint or short arm cast for 3 to 4 weeks. Follow-up radiographs are not needed for isolated torus fractures.
Greenstick Fractures
Greenstick fractures are incomplete fractures with disruption of the tension-side cortex and plastic deformation of the compression-side cortex. Significant angular deformity is common. Treatment involves closed reduction with correction of angulation, and completing the fracture to prevent re-angulation is sometimes performed but remains controversial. A long arm cast with three-point molding is applied for 6 to 8 weeks.
Complete Fractures
In complete fractures, both cortices are disrupted with variable displacement, angulation, and rotation. Both-bone forearm fractures are common, and the relationship between the radius and ulna must be carefully assessed. Treatment depends on age, location, displacement, and stability.
Acceptable Alignment Parameters
Distal Third Fractures
Distal third fractures have the greatest remodeling potential due to proximity to the physis. In children under 10, up to 15 to 20 degrees of angulation is accepted, while in children over 10, 10 to 15 degrees is the threshold. No malrotation is acceptable at any age.
Middle Third Fractures
Middle third fractures have less remodeling potential. Up to 10 to 15 degrees is accepted in children under 10, and less than 10 degrees in children over 10. Complete bayonet apposition with acceptable angulation may remodel in young children.
Proximal Third Fractures
Proximal third fractures have the least remodeling potential, requiring stricter reduction criteria of less than 10 degrees of angulation at any age. Rotational malalignment is poorly tolerated in this location.
Operative Treatment
Indications
Operative treatment is indicated for failed closed reduction or unacceptable alignment after reduction, open fractures, fractures with associated compartment syndrome or neurovascular injury, unstable fracture patterns that cannot be maintained in a cast, older adolescents near skeletal maturity with limited remodeling potential, and both-bone fractures in children over 10 years with significant displacement.
Flexible Intramedullary Nailing
Flexible intramedullary nailing is the preferred surgical method for pediatric diaphyseal forearm fractures. Titanium elastic nails or stainless steel nails are inserted retrograde through the distal radius (radial to Lister tubercle) and antegrade through the proximal olecranon apophysis. Advantages include a closed technique that preserves the periosteum and allows early mobilization. Nail diameter should be 40% of the medullary canal diameter for each bone. Nails are typically removed at 6 to 12 months after radiographic union.
Plate Fixation
Plate fixation is reserved for older adolescents near skeletal maturity, refractures, and complex fracture patterns. Standard AO compression plating techniques are used, providing more rigid fixation than flexible nailing.
Monteggia Fracture-Dislocation
Definition
A Monteggia fracture-dislocation is a fracture of the proximal ulna with dislocation of the radial head. It is the most commonly missed fracture-dislocation in pediatrics, underscoring the key principle that a radiograph of the forearm must always include both the elbow and wrist joints.
Bado Classification
Type I, the most common in children at 60 to 70% of cases, features anterior radial head dislocation with anterior angulation of the ulnar fracture. Type II, the most common in adults, involves posterior radial head dislocation with posterior angulation of the ulnar fracture. Type III has lateral or anterolateral radial head dislocation with lateral angulation of the proximal ulna. Type IV combines anterior radial head dislocation with fractures of both the radius and ulna.
Diagnosis
The radiocapitellar line should be applied on every lateral radiograph: a line drawn through the center of the radial shaft should pass through the center of the capitellum in every projection. If the radiocapitellar line is disrupted, a Monteggia lesion is present. A truly isolated ulna fracture with significant angulation in a child should be considered a Monteggia injury until proven otherwise.
Treatment
Closed reduction is typically successful in children. Anatomic reduction of the ulnar fracture usually results in concentric reduction of the radial head. Immobilization is maintained in 90 degrees of elbow flexion with the forearm in supination for Type I or pronation for Type II, using a long arm cast for 6 weeks. If the radial head does not reduce concentrically after ulnar reduction, interposed tissue such as the annular ligament should be suspected and open reduction pursued.
Chronic (Missed) Monteggia
Chronic Monteggia lesions present with progressive valgus deformity, limited forearm rotation, and posterior interosseous nerve palsy. Treatment requires ulnar osteotomy with angular correction, possible annular ligament reconstruction, and reduction of the radial head. Results are best when addressed within 3 to 6 months of injury, as late reconstruction is unpredictable.
Monteggia Equivalent Lesions
Monteggia equivalent lesions include radial neck fracture with ulnar shaft fracture and olecranon fracture-dislocation with radial head subluxation. These carry the same principles: restore ulnar length and alignment to achieve concentric radial head reduction.
Complications
Malunion with loss of forearm rotation is the most significant functional complication, as rotational malunion is poorly tolerated. Refracture occurs in approximately 5 to 7% of forearm fractures, typically within 6 months of cast removal. Compartment syndrome must be suspected with high-energy injuries, excessive swelling, or pain out of proportion to the injury. Posterior interosseous nerve palsy in Monteggia lesions is usually a neurapraxia that recovers spontaneously, though persistence beyond 3 to 6 months warrants exploration.
Clinical Pearls
Every forearm radiograph must include both the wrist and elbow joints, as failure to do so is the most common reason for missing a Monteggia fracture-dislocation. The radiocapitellar line must pass through the center of the capitellum on every view, and if it does not, a Monteggia lesion is present until proven otherwise. Pediatric forearm fractures have excellent remodeling potential, but rotational deformity does not remodel, so rotational alignment must be acceptable in every case. Flexible intramedullary nailing is the preferred surgical method for displaced diaphyseal forearm fractures in children, offering closed fixation with minimal periosteal disruption.
References
- Bado JL. The Monteggia lesion. Clin Orthop Relat Res. 1967;50:71-86.
- Flynn JM, Jones KJ, Garner MR, Goebel J. Eleven years experience in the operative management of pediatric forearm fractures. J Pediatr Orthop. 2010;30(4):313-319.
- Ramski DE, Hennrikus WL, Bae DS, et al. Pediatric Monteggia fractures: a multicenter examination of treatment strategy and early clinical and radiographic results. J Pediatr Orthop. 2015;35(2):115-120.
- Price CT, Scott DS, Kurzner ME, Flynn JC. Malunited forearm fractures in children. J Pediatr Orthop. 1990;10(6):705-712.