Review Question - QID 211282

This patient has a displaced Salter-Harris I fracture of the distal femur and is treated with cast immobilization following successful reduction. These physeal fractures occur most commonly in the hypertrophic zone.

Physeal fractures can be difficult to diagnose given their lack of radiographic irregularities. Stress radiographs or an MRI scan have utility in making this diagnosis. Physeal anatomy is composed of the reserve zone, proliferative zone, hypertrophic zone, primary spongiosa, and secondary spongiosa. The hypertrophic zone is divided into the maturation zone, degenerative zone, and the zone of provisional calcification. These physeal fractures occur specifically through the zone of provisional calcification. The hypertrophic zone also plays a critical role in SCFE, rickets, enchondromas, and mucopolysaccharide diseases.

Zionts et al. review the traumatic forces applied to the immature knee which results in fracture patterns that differ from those in adults. They report on the difficulty of diagnosing physeal fractures in pediatric patients secondary to the abundance of cartilage. They conclude that there is utility of stress radiographs, computed tomography scan, or magnetic resonance imaging to establish this diagnosis when plain radiographs are unremarkable.

Salter et al. review injuries involving the epiphyseal plate. They reported that physeal fractures occur primarily on the diaphyseal side of the epiphyseal plate through the zone of hypertrophy. This fracture may deviate into the shaft contributing to a triangular fragment of the metaphysis attached to the epiphysis.

Figures A is the lateral radiograph of a pediatric distal femur fracture with obvious displacement. Illustration A shows the histology of the physis, which consists of the reserve zone, proliferative zone, hypertrophic zone, and spongiosa.

Incorrect Answers:
Answer 1: The reserve zone is important for cell storage of lipids, glycogen, and proteoglycan aggregates for later growth and matrix production
Answer 2: The proliferative zone is important for the proliferation of chondrocytes with longitudinal growth and stacking of chondrocytes. It is involved in gigantism and achondroplasia
Answer 4: The primary spongiosa is involved in metaphyseal “corner fractures” of child abuse, but is not the primary zone involved in physeal fractures
Answer 5: The secondary spongiosa is involved in internal remodeling including cartilage bar removal and the formation of lamellar bone