Lower Extremity Injuries in Children

Epidemiology and Background

The prevalence of both acute traumatic and chronic overuse injuries of the lower extremity has increased in children for a number of reasons. Children are participating in athletics at earlier ages and a higher rate than in the past. Data from the last decade indicate that 30 million, or half, of all U.S. children engage in an organized sport, with children's sports injuries requiring 2.5 million Emergency department visits per year. Driven by societal expectations, participation has become more regimented; with children required to commit more time to a single sport, there is a greater level of conditioning and repetitive use or overuse. With a higher level of conditioning, greater forces act on the musculoskeletal system, causing biomechanical failure in modes typical for skeletally immature patients, but also in patterns more commonly seen in adults. Conversely, increasing rates of obesity also contribute to an increasing incidence of acute and chronic musculoskeletal lower extremity injuries. Finally, an increasing general awareness of athletic injury and increasing diagnostic capabilities have increased the rate of diagnosis.

Improper technique, training errors, muscle weakness and imbalance, and poorly fit protective equipment contribute to overuse injuries. The Centers for Disease Control and Prevention estimates that one half of all sports injuries in children are preventable with proper education and the use of protective equipment. These concerns have led to guidelines for sports participation by children and warnings about the increasing risk of injury in children competing in demanding athletic programs. Thankfully, when diagnosed expediently and accurately, most sports injuries in children can be managed conservatively.

This chapter discusses pediatric lower extremity injuries, with attention to those injuries that are unique to children. Physeal and apophyseal injuries are the starting point. Buckle, greenstick, and bowing fractures are described, as are fractures secondary to higher energy forces. Injuries of the knee form a significant portion of the chapter. The similarities and differences between acute and chronic injuries are noted; in many cases, this differentiation is made by history taking. Osteochondral injuries, from the slipped capital femoral epiphysis (SCFE) to osteochondritis dissecans (OCD) to the heterogeneous osteochondroses, also merit special attention.

Anatomy and Biomechanics of the Developing Skeleton

Fundamental differences between the developing skeleton and that of the mature adult lead to different patterns of injury resulting from the same force. The skeletally immature athlete differs in that cartilaginous growth centers are present around joints (epiphyses) and at attachments of tendon and ligament to bone (apophyses). These junctions between mature and growing bone are the weakest point in the kinetic chain. Distraction forces from the attached musculotendinous unit cause failure at the apophysis rather than injuring the muscle and tendon. Compressive and rotational forces preferentially damage the epiphyseal growth plate.

The lower limbs support the weight of the body and provide a stable foundation for standing, walking, and running. Muscles, tendons, ligaments, bones, and joints of the lower extremity are a cohesive kinetic chain that allows movement. Acute injury of the lower extremity is the response of tissues in this chain to excessive applied force and occurs in a reasonably predictable way. The site of failure will usually be at the weakest point within the kinetic chain. Damage can occur locally or distant from the site of trauma due to transmitted forces. Injury will be acute or chronic, depending on the nature and size of the force.

Sport-related injury frequently occurs after repetitive strain, where the force applied is sufficiently large to damage tissues without causing complete structural failure. Athletic training focuses on general fitness and technique and emphasizes repetitive motions. This uniformity of action focuses the stresses through the same area of the musculoskeletal system during training, increasing the likelihood of overuse injury. Repetitive strain occurs when the athlete is given insufficient recovery time from a partial injury. The initial tissue damage causes weakening, and, when force is reapplied to this weakened tissue, the same magnitude of force produces a greater degree of damage. This is termed cyclical failure. The less trained and conditioned incur more acute injuries, whereas prepared athletes experience repetitive strain or overuse injuries.

Compressive injuries cause more damage to osseous structures and are particularly seen in association with cyclical impaction (e.g., long-distance running). In the skeletally immature athlete, this usually occurs at the physes. In the very young, the diaphysis of long bones can fail because the bone has different mechanical properties. Examples are toddler's and bowing fractures. In those approaching skeletal maturity, fusing physes no longer represent the weakest point, and compressive forces again result in diaphyseal stress fractures.

Tension forces are secondary to contraction of the muscle-tendon unit. Failure under tension occurs at the apophysis in musculoskeletally immature patients and at the musculotendinous junction in older athletes. Muscle strain or tear commonly occurs in muscles crossing two joints such as the hamstring, quadriceps, and gastrocnemius because these are subject to greater forces.

Physeal Fractures

Growth plate, or physeal, injuries are unique to children, common, and usually acute. They are classified according to the Salter-Harris system ( Box 37-1 ). Damage to the physis can cause premature physeal closure and subsequent focal growth arrest. The Salter-Harris classification is used to assess the fracture's potential for growth disturbance. Type I injuries have little or no effect on growth with type V fractures causing the most growth disturbance. In general, the prognosis is worse in the lower extremities compared with upper limb injuries. The ankle is the most common site of physeal fracture in the lower extremity. Physeal injuries frequently occur during adolescence, perhaps due to increased exposure to high-energy trauma combined with temporary weakening of the growth plate around puberty. Although Salter-Harris fractures are usually secondary to an acute injury, subluxation at the proximal femoral physis, or the SCFE, is a relatively common distinct and multifactorial entity that usually occurs in the absence of an inciting event.

Most Salter-Harris fractures are apparent on radiographs, which may demonstrate epiphyseal displacement, widening of the physis, and loss of definition of the opposing surfaces of the epiphysis and metaphysis. Salter-Harris type I fractures involve only the radiolucent physis, and the finding of soft tissue swelling is helpful ( Fig. 37-1 ). Salter-Harris, type II physeal fractures extend into the metaphysis ( Fig. 37-2 ); type III fractures, the epiphysis ( Fig. 37-3 ); and type IV, both the metaphysis and epiphysis ( Fig. 37-4 ). The Salter-Harris, type V injury is also isolated to the physis ( Fig. 37-5 ) and frequently remains undiagnosed until bone shortening and joint deformity develop secondary to physeal injury. Diagnosis of nondisplaced Salter-Harris fractures can be difficult, and radiography of the opposite side for comparison may help. However, with knowledge of the typical fracture patterns, routine examination of the normal side is not necessary. CT is useful for further characterization of Salter-Harris fractures and for treatment planning. Magnetic resonance imaging may be used to diagnose radiographically occult fractures (see Fig. 37-2 ), as well as suspected Salter-Harris, type V injuries. The need for sedation is an obstacle to the use of MRI in children. When the cause of a child's limp cannot be localized, bone scintigraphy and/or whole limb radiographs can help.

Two distinctive forms of physeal fracture occur in the distal tibia because the physis closes from medial to lateral and posterior to anterior. When the physis is partially closed, the growth plate may fail anteriorly and laterally. A Tillaux fracture is a horizontal fracture of the anterolateral tibial physes and vertical epiphyseal fracture into the joint. The anterior-lateral corner of the epiphysis is avulsed by the strong anterior tibiofibular ligament in this Salter-Harris, type III fracture ( Fig. 37-6 ). Triplane fractures are Salter-Harris, type IV injuries with three fracture planes: a vertical fracture of the epiphysis, a horizontal plane within the physis, and an oblique fracture of the metaphysis. The metaphyseal fracture differentiates it from a Tillaux fracture ( Fig. 37-7 ).

In general, Salter-Harris, types I and II fractures are treated nonoperatively, types III and IV require fixation, and type V fractures are detected subsequently to growth arrest. All Salter-Harris fractures or high force axial injuries suspicious for type V fracture should be followed for 1 year to exclude growth arrest. CT and MRI are helpful for characterization of the physeal bony bridge in cases of growth arrest ( Fig. 37-8 ).

Salter-Harris, types I and II fractures are generally stable with an intact overlying periosteum and can be treated with 4 to 6 weeks of cast immobilization. Closed reduction is advised for most displaced Salter-Harris, types I and II fractures. When there is more than 2 mm of residual displacement of a Salter-Harris, type II fracture of the distal tibia, surgical treatment is recommended. Persistent physeal widening of greater than 3 mm at the distal tibia suggests interposed periosteum and requires surgical treatment.

Salter-Harris, type III and type IV injuries require precise anatomic reduction to minimize future joint degeneration or growth disturbance. Most require open reduction and fixation. Articular step-off of greater than 2 mm is a relative indication for operative treatment. Bone bridging across the injured physis is more frequently encountered with fracture displacement and may result in angular deformity or impaired growth.

Salter-Harris, type V fractures are relatively rare and often recognized retrospectively as a consequence of premature physeal closure. Common locations are the distal femur, proximal tibia, and distal tibia. At the time of the initial examination of the fracture, the physis may appear normal. On follow-up examinations, there is closure of the physis and deformity. Growth plate arrest arrest is usually partial and may be treated surgically by resection of the bone bridge and interposition of graft material.

Acute Apophyseal Injuries

Apophyseal injuries are also relatively frequent in young athletes. Caused by forceful muscular contraction, these apophyseal separations are characterized by their location and configuration. They are more common in sports requiring sudden powerful acceleration or change of direction such as football, soccer, dance, or gymnastics. Around the pelvis, it may be difficult to distinguish clinically between a muscle strain and an apophyseal avulsion. Apophyseal injuries occur most commonly around the pelvis, including the ischial tuberosity (hamstrings), anterior superior iliac spine (ASIS) (sartorius and tensor fascia lata), anterior inferior iliac spine (AIIS) (rectus femoris), iliac crest (abdominal obliques and latissimus dorsi), lesser trochanter (iliopsoas), greater trochanter (external hip rotators), and symphysis pubis (adductor muscles). At the knee, the tibial tuberosity (patellar tendon), anterior tibial eminence (anterior cruciate ligament [ACL]), or posterior tibial eminence (posterior cruciate ligament), may be avulsed.

Acute avulsion injuries are seen on plain radiographs as crescentic osseous fragments and irregularity of the underlying bone ( Fig. 37-9A ). Radiographic visualization of ACL avulsions can be difficult and may require additional tunnel view and oblique imaging (see Fig. 37-22 ). If the ossification center of the apophysis has not yet formed, radiographs may not be helpful and ultrasound or MRI will demonstrate the injury ( eFig. 37-1 ). Lazovic and colleagues described the use of ultrasound examination in 243 cases of suspected apophyseal avulsion and found it to be more sensitive than radiography. An advantage of ultrasound examination is that it allows dynamic examination for apophyseal instability (see Fig. 37-9B ). Follow-up, radiographs, and MRI will demonstrate healing of the avulsion site with productive bony callus that should not be mistaken for neoplasm ( e-Fig. 37-2 ).

The amount of separation and force exerted upon apophyseal avulsions is a consideration when planning treatment. ASIS and AIIS avulsions heal relatively quickly with conservative treatment. Ischial tuberosity avulsions require more bed rest, restricted activity, and a gradual return to activity over 6 to 12 weeks. Tibial tubercle avulsions of the patellar tendon frequently require operative anchoring. The majority of ACL avulsions are reattached surgically.

Buckle and Bowing Fractures

The biomechanical properties of immature bone lead to incomplete fractures that are peculiar to children. Immature bone is more porous and less dense than adult bone because of increased vascular channels and a lower mineral content. Increased plasticity and elasticity of young bone means that it is more likely to bow or buckle than to snap. This results in greenstick, buckle (torus), and bowing fractures. The periosteum is thicker, more elastic, and less firmly bound to bone so it will usually remain intact over an underlying fracture. Healing and remodeling is therefore more predictable than in adults, and nonunion is rare.

The classic greenstick fracture arises from bending forces that produce a complex break of the cortex on the tension side and plastic deformation of the opposite cortical border. An incomplete transverse fracture is produced in the convex cortex and usually extends to the middle of the shaft involving half of the circumference of the bone. The resulting fracture line may then extend longitudinally. The concave cortex remains bowed but is intact. These fractures are much more common in the upper limb but are also seen in the lower limb ( eFig. 37-3 ).

A torus or buckle fracture is produced by compressive forces that cause the cortex to buckle. They are seen in the metaphysis of the long bones and, again, are more common in the upper limb ( Fig. 37-10 ).

Bowing fractures result principally from compressive forces with an element of angulation producing a gradual curve across the length of the whole bone with no visible cortical break ( Fig. 37-11 ). These fractures may be difficult to diagnose on radiographs, and bone scintigraphy can be helpful by demonstrating longitudinal increased activity of the bone. In the lower limb, the fibula is the most commonly involved bone, frequently in association with a tibial fracture. Bowing is also seen in patients with reduced bone strength in diseases such as rickets, osteogenesis imperfecta, and osteopetrosis ( eFig. 37-4 ).

Mildly buckled or bowed fractures remodel rapidly in children. Treatment requires unloading of the lower extremity to allow remodeling. Bowing fractures of the lower extremity may show progressive angulation and poor remodeling when not recognized.

High-Energy Fractures

With high-energy injury mechanisms such as a fall from height or vehicular collisions, pelvic fractures, hip dislocations, proximal femur fractures, or femoral shaft fracture may occur in children, although these injuries are relatively rare.

These injuries are discussed in the online version.

Because of the relative elasticity of the bones and ligaments of the pelvic ring, displacement of pelvic fractures is often less severe in children than in adults. Fracture through the triradiate cartilage is an injury unique to children that is often difficult to visualize because displacement may be minimal. These injuries are important to identify because premature closure of the triradiate cartilage may result in deformity of the acetabulum and subluxation of the hip. Meticulous attention to radiographic positioning is necessary to identify medial displacement of the acetabulum, which typically involves the ischiopubic segment. Care must be taken because rotation may mimic displacement; an inlet view of the pelvis may be useful. Using CT examination, separate fragments of bone at the margins of the triradiate cartilage should be considered fractures in young children, because secondary centers of ossification do not occur at the margins of the triradiate cartilage until adolescence. MRI usefully demonstrates asymmetric edema-like signal involving the triradiate cartilage, which is indicative of injury. MRI has also been used to identify stress or overuse injuries of the triradiate cartilage.

Bucholz and colleagues described three different types of triradiate cartilage fracture: Salter-Harris, types I, II, and V. The diagnosis of a type I triradiate cartilage fracture is made by identifying displacement or widening of the cartilage without fracture of the bony margins. A type II injury is identified by a fracture through bone adjacent to the triradiate cartilage, the equivalent of a metaphyseal corner fracture. These fractures are better visualized using CT and should not be mistaken for free bone fragments within the joint or variants of ossification in younger patients.

Unlike hip dislocations in adults, femoral-acetabular dislocation in children can occur in the absence of high mechanism injury. Dislocations are usually posterior and often occur in children without associated fracture of the posterior acetabular wall. Potential complications include avascular necrosis, growth disturbance with enlargement of the femoral head, and degenerative arthritis.

In children, widening of the hip joint after reduction is most often due to interposed soft tissue, either the labrum or the joint capsule, or, less frequently, an entrapped osteochondral fragment. Widening of the joint should not be attributed to a simple hemarthrosis; fluid in the joint will depressurize anteriorly and stretch the capsule first; only the most massive hemarthrosis will disrupt the alignment of the joint. CT confirms widening of the joint space, but, because of the absence of bone in the labrum and joint capsule, the precise reason for the widening may not be evident. The entrapped joint capsule or cartilage may be seen on MRI or CT arthrography.

In contradistinction to injuries of the knee and ankle, traumatic physeal fractures of the proximal femur are rare. Those that do occur are almost always Salter-Harris, type I injuries, with the fracture line limited to the physis without extension into the metaphysis. These injuries occur as a result of falls, usually from a considerable height or vehicle-pedestrian accidents, and they are frequently associated with other injuries, particularly fractures of the pelvis. On the anteroposterior projection, the epiphysis may appear to be normally aligned with the femoral neck, even in comparison with the other side. Epiphyseal separation may not be obvious, but there is usually slight widening of the growth plate on the injured side. An oblique or frog-leg conventional radiograph is often required to demonstrate the epiphyseal displacement. The femoral epiphysis may remain in its normal position within the acetabulum, with the femoral neck displaced superiorly and the leg in the abducted position. Separation of the proximal femoral epiphysis may also occur in association with posterior dislocations of the hip.

Rarely, separation of the proximal femoral epiphysis occurs as the result of a birth injury. However, this may not be identified immediately because the proximal femoral epiphysis is not ossified. The superolateral displacement of the femur gives the appearance of congenital dislocation of the hip. The two are distinguished because the acetabulum is normally shaped in epiphyseal separation, but it is dysplastic in congenital dislocation and rarer forms of primary epiphyseal dysplasia. The combination of dislocation or subluxation and a shallow acetabulum is more accurately described as developmental dysplasia of the hip.

Neck or intertrochanteric fractures are more common than physeal injuries of the proximal femur. Again, the majority are caused by vehicular accidents or falls from a height. Transcervical fractures account for 50% of pediatric proximal fractures and are complicated by a high rate of displacement (80%) and avascular necrosis (40% to 50%). Basicervical fractures account for a third of hip fractures, and approximately half are displaced at the time of diagnosis. Intertrochanteric fractures are rare and usually uncomplicated. Radiographic diagnosis is usually sufficient.

Fracture of the shaft of the femur also occurs from higher-energy mechanisms. The most frequent site of femoral shaft fracture is in the middle third, where normal anterolateral bowing of the diaphysis is at a maximum. Greenstick fractures are more frequently seen in the distal third of the bone. Oblique fractures tend to result from more indirect forces, with transverse fractures due to high-energy direct trauma such as from vehicular accidents. These fractures often significantly displace and overlap because of muscular action on the fracture fragments ( eFig. 37-5 ).

Imaging of high mechanism of injury fractures of the lower extremity is usually completed with radiographs. Computerized tomography is helpful in anatomically complex areas such as the hip or when surgery is planned for complicated fracture patterns.

Anatomic rings are an important principle in musculoskeletal radiology. The tibia and fibula, joined at the proximal tibial-fibular joint and distal ankle mortise, form such a ring in the leg. They are nearly always disrupted at two sites ( eFig. 37-6 ). Single-site ring fracture is usually secondary to a rapid, focal, large force such as a ballistic injury.

Nonaccidental trauma is the primary differential consideration in all fractures in young children. Correlation of the reported injury mechanism with the type of fracture and age of the patient is necessary. Radiographic skeletal survey and whole body scintigraphy may be considered to evaluate for other sites of unreported fracture. The reader is directed to Chapter 39 .

In addition to fracture reduction, treatment of children's fractures requires consideration of physeal involvement and the potential for remodeling. In young children, there is great potential for spontaneous correction of displacement and angulation, but this decreases with maturation. Additionally, lower limb deformities are less well tolerated than upper limb injuries because of weight bearing. Pediatric femoral fractures have the potential for overlengthening when healing, so some overlap is acceptable. Remodeling is very effective in children. In general, children of all ages with stable lower-limb metaphyseal or diaphyseal fractures are treated conservatively with casting for approximately 3 to 5 weeks. Unstable fractures are treated with reduction and more extensive casting or surgery. Considerations of transphyseal fracture fixation include the potential for growth arrest and, in the case of the proximal femur, osteonecrosis. These must be weighed against the degree of deformity and instability and the patient's age.

Toddler's Fracture

Children between the ages of 1 and 3 years commonly present with an acute limp without a clear history of specific injury. While the differential includes nontraumatic etiologies such as synovitis, osteomyelitis, and tumor, the classic lesion is a nondisplaced oblique fracture of the distal tibia termed a toddler fracture. The toddler's fracture is frequently difficult to diagnose radiographically and is often demonstrated on one view only ( Fig. 37-12 ). Radiography of the whole leg is often performed. When the cause of a child's limp cannot be localized by history or clinical examination, bone scintigraphy can be extremely helpful to localize the injury, although at a significant radiation dose. However, osteomyelitis and tumors will also show increased uptake on bone scintigraphy. In toddler's fractures, a bone scintigram usually demonstrates diffuse increase in activity over the entire length of the bone even when radiographs demonstrate a fracture at the metaphysis only. With high-resolution techniques, the increased activity can be seen confined to an oblique band involving the diaphysis and metaphysis. The area of increased uptake on bone scintigraphy can then be further evaluated with plain radiographs, CT, or MRI. Despite the practical difficulties, to avoid radiation exposure, MR may be the preferred imaging technique in these patients.

Pathologic Fractures

Pathologic fractures through bone lesions may occur in children with minimal or no injury and are most commonly due to nonossifying fibromas and solitary bone cysts. Nonossifying fibromas are common benign lesions with a characteristic radiographic appearance. The lesion is cortically based with a narrow sclerotic zone of transition ( eFig. 37-7 ). This appearance in a child obviates the need for biopsy. Fractures associated with these lesions generally heal spontaneously.

Solitary bone cysts are also relatively common benign osseous lesions seen in children. This lesion is typically found centrally within the metaphysis of the humerus or femur. The calcaneus is another common site of occurrence in the lower extremity. An expanded well-defined lytic lesion is seen with a narrow sclerotic zone of transition without any matrix calcification. Fracture through these lesions is the most common presentation, and the fallen fragment sign is diagnostic because it can occur in purely fluid lesions only.