Pediatric Femur Fractures

The embryonic development of the femur begins during week 4 of gestation, with the appearance of the limb bud. Rapid mesenchymal growth follows, and the endochondral ossification occurs during week 8. The femoral shaft is the primary ossification center. Secondary ossification, at the upper end, begins at the gestational age of 6 months. Ossification of the femoral head occurs at the age of 4-5 months. The distal femoral ossification center appears during month 7 of gestation.

At about 4 years of age, the single secondary ossification center at the upper end divides into two separate structures: the greater trochanter and the capital femoral epiphysis. The lesser trochanteric apophysis ossifies at the age of 10 years.

Proximal femur

The proximal femur has two growth centers: the proximal femoral epiphysis and the trochanteric apophysis. The proximal femoral epiphysis contributes 30% of the length of the femur and 13% of the length of the lower limb. Damage to the proximal femoral epiphysis leads to shortening of the extremity.

The trochanteric apophysis is a traction apophysis, and it contributes to the growth of the femoral neck. Injury to the trochanteric apophysis or paralysis of the muscles attached to it leads to shortening of the greater trochanter and coxa valga. Overgrowth of the greater trochanteric apophysis leads to apparent coxa vara and reduced articulotrochanteric distance.

Proximal femoral bone is very strong and is not easily fractured, except when the bone is affected by a pathologic condition. The proximal femoral epiphysis, however, is an area of structural weakness that can fail readily when subjected to shear forces.

The vascular anatomy of the proximal femur in children differs from that in adults. The artery of the ligamentum teres does not contribute any blood supply until the age of 8 years. The metaphyseal vessels do not contribute to the vascularity of the femoral head after the age of 3 years, and they contribute to the intraosseous blood supply to the femoral head only after the physeal closure, between the ages of 14 and 17 years, when the vascular anastomoses between the metaphyseal and epiphyseal blood vessels develop.

The lateral epiphyseal branches of the medial femoral circumflex system supply most of the femoral head throughout childhood (see the image below). The vascularity of the femoral head, therefore, is precarious in children, especially those between 3 and 8 years of age, and this arrangement renders children highly susceptible to AVN after proximal femoral injuries. ^[3]

Femoral shaft

The longitudinal growth and peripheral growth of the femoral shaft occur by endochondral ossification, which leads to the formation of woven bone. With maturation and development, the bone becomes more like adult bone, with remodeling of the trabecular bone into lamellar bone along the lines of stress.

The pediatric femoral shaft has an abundant blood supply that derives from both endosteal and periosteal blood vessels. The endosteal blood supply is from two nutrient vessels, which enter the medullary canal posteromedially at the junction of the proximal and middle thirds and the junction of the distal and middle thirds of the shaft. The periosteal blood supply comes from the large muscular cuff of the thigh. The periosteal vessels supply the outer one third of the cortex.

These two systems are interconnected and together provide the abundant blood supply that facilitates both the growth of bone and the healing of fractures in children.

Distal femur

The epiphyseal ossification center of the distal femur is usually present at birth in a full-term infant. This area is the largest and most active physeal system in the body, contributing almost 70% of the length of the femur and 40% of the length of the entire leg. It fuses with the metaphysis during the teen years (ages 14-16 years in girls and ages 16-18 years in boys).

At birth, the physis is essentially a transverse plane. As the infant commences walking, shearing forces across the knee cause the development of macroscopic undulations in the distal femoral physis; the physis also exhibits microscopic undulations and mammillary processes. This is a very important point: Because of the undulating nature of the distal femoral epiphysis, any type of fracture may lead to growth problems.

The circulatory supply to the epiphysis is multifocal. The main input and output are through the posterior femoral notch. There are watershed areas in the condyles, especially medially, that have limited circulation. ^[4]

The physis is completely extra-articular. The strong posterior capsule and the major ligaments are attached to the epiphysis. Normally, in an adult knee, ligaments fail when a bending stress is applied across the knee. In an immature skeleton, the bone fails through the growth plate because the ligaments are stronger than the cartilage of the distal femoral physis.

Nearly two thirds of femoral fractures in children and adolescents result from falls and motor vehicle accidents. Nearly 30% of fractures in children younger than 4 years are reported to be due to child abuse. Birth trauma can cause fracture of the femur in the newborn.

With increasing age from childhood to adolescence, the mechanism of injury goes from being a low-energy injury in young children to a high-energy injury in adolescents; as a result, there are increases in the complexity of injuries, the need for surgical intervention, the length of hospital stay, overall hospital costs, and mortality. ^[5]

Pathologic fractures of the femur in children account for just over 4% of cases and can occur after minor trauma. Underlying pathologic conditions include osteogenesis imperfecta, ^[6]  aneurysmal bone cyst, unicameral bone cyst, nonossifying fibroma, and generalized osteopenia due to neuromuscular disorders. Cerebral palsy and osteogenesis imperfecta are the most common associated pathologies. Typically, these patients experience femoral fractures between the ages of 6 and 12 years because they begin walking late. ^[5]

Proximal femoral injuries are produced by high-velocity trauma, such as occurs with falls from a height, motor vehicle accidents, and child abuse. In cases of distal femoral fracture, the cause in younger children is invariably severe trauma, whereas the usual cause in adolescents is a sports injury.

Classification of femoral fractures

Various classification systems have been developed for proximal femoral fractures, femoral shaft fractures, and distal femoral epiphyseal fractures.

Proximal femoral fracture (Delbet classification)

Proximal femoral fractures are most often categorized according to the Delbet classification (see the image below). ^[7]

Delbet type I injury is transepiphyseal separation—that is, acute traumatic separation of the proximal femoral epiphysis, similar to Salter-Harris type I epiphyseal injury. It is an uncommon injury, accounting for fewer than 10% of all pediatric proximal femoral fractures. This injury can occur in newborns after breech delivery and is often missed in these cases.

Type I injury has also been reported in children aged 5-10 years. In these patients, it occurs after high-energy trauma and has a high incidence of associated injuries, especially femoral head dislocations. This fracture type has the worst prognosis, and the reported rates of AVN range from 20% to 100%.

Delbet type II injury is a transcervical fracture and is the most common type, accounting for about 40-50% of proximal femoral fractures. These injuries are often displaced at the time of presentation. AVN rates as high as 50% have been reported with these injuries.

Delbet type III injury is a cervicotrochanteric fracture that occurs through the basicervical region; it accounts for 30-35% of proximal femoral fractures. AVN has been reported in 15-20% of cases.

Delbet type IV injury is a pertrochanteric or intertrochanteric fracture. This type accounts for 10-20% of proximal femoral fractures and is associated with the best prognosis; AVN is reported in fewer than 10% of cases. The involvement of the greater trochanter may lead to premature closure of the apophysis and coxa valga.

Femoral shaft fracture (Gustilo classification)

Femoral shaft fractures can be either open (with breach of the overlying soft-tissue envelope) or closed. The open fractures are further categorized according to the Gustilo classification. ^[8]  In this system, the fracture is classified on the basis of the following:

• Location (eg, proximal, middle, or lower third)
• Configuration (eg, spiral, oblique, or transverse)
• Degree of displacement or comminution

Distal femoral epiphyseal fracture (Salter-Harris classification)

Distal femoral epiphyseal fractures are categorized according to the Salter-Harris classification of epiphyseal injuries, with a modification by Ogden (see the image below).

Salter-Harris type I fracture involves the physis without an associated fracture through the adjacent epiphysis or metaphysis. It is an infrequent birth injury that occurs during delivery of a breech child, even in cases of cesarean section. ^[9]  The distal femur is also a common site of fracture in cases of child abuse. Metaphyseal beak fracture, a type I injury, is characteristic of child abuse but is not pathognomonic.

Salter-Harris type II fracture is characterized by physeal fracture, with extension of the fracture line into a corner of the adjacent metaphysis. This is the most common fracture and occurs in adolescents. The metaphyseal fragment remaining attached to the epiphysis is called the Thurstan Holland fragment. The periosteum is intact on the compression/concave side, and the torn periosteal sleeve on the tension side sometimes becomes interposed between the fracture ends.

Salter-Harris type III fracture involves the medial or lateral condyle. The fracture line usually exits through the intercondylar notch.

Salter-Harris type IV fracture is uncommon. A sagittal fracture line extends from the metaphyseal cortex down to the physis and enters the articular surface of the epiphysis.

Salter-Harris type V fracture is due to compression of the epiphyseal plate, which may be associated with an ipsilateral femoral fracture. Diagnosis is often retrospective when growth arrest is seen.

Salter-Harris type VI fracture is caused by glancing blows that lead to destruction of a small peripheral segment and formation of a physeal bridge.

Salter-Harris type VII fracture involves fracture of the femoral condyles. Bone bruising occurs within the substance of the epiphyseal trabecular plane. ^[4]

Salter-Harris type VIII fracture mainly consists of a metaphyseal fracture with extension into the metaphyseal-physeal junction.

Femoral head and neck fractures in children are rare injuries, accounting for fewer than 1% of all pediatric fractures and fewer than 1% of all hip fractures. Femoral shaft fractures account for 1-2% of all pediatric fractures.

Fractures of the femur have a bimodal age distribution. There is a high incidence in the first 2-3 years of life, when child abuse most commonly occurs and the femur is composed of weak woven bone. After the age of 5 years, the increase in lamellar bone, the greater cortical thickness, and the larger femoral diameter result in a stronger femur, and the incidence of femoral fractures falls. A second peak in incidence occurs in adolescence, when motor vehicle accidents account for the majority of fractures.

Femoral fracture is about 2.5 times more common in boys than in girls. Distal femoral physeal fractures account for 6-9% of all physeal injuries in children ^[10] and 15% of all lower-extremity physeal injuries. ^[11]