Review Question - QID 219304

Zone D represents the hypertrophic zone of the physis, which contains the zone of provisional calcification, a weak point in the growth plate characterized by chondrocyte cell death allowing for calcium release and matrix calcification.

Salter-Harris fractures involve the pediatric physis and are classified based on whether they exit the metaphysis, epiphysis, or both (Illustration A). Because the zone of provisional calcification serves as a weak point in growing bone, abnormal injury forces, particularly shear forces, result in fractures that begin in the hypertrophic zone and propagate to create the patterns shown in Illustration A. Physeal injuries to the distal femur have a high rate of growth disturbance, which can result in limb length discrepancy or angular deformity.

Podeszwa and Mubarak reviewed physeal fractures of the distal tibia and fibula. The authors note that physeal fractures about the ankle are the second-most common physeal fractures, with only the distal radius being more common. They recommend that if gapping of the physis >3 mm exists after reduction, high suspicion should be held for the presence of entrapped periosteum that will increase the risk of premature physeal closure. They conclude that open reduction of displaced Salter-Harris type III and IV fractures is critical to maintaining joint congruity and minimizing the risk of physeal arrest.

Basener et al. performed a meta-analysis of growth disturbance after distal femoral growth plate fractures in children. The authors reviewed 564 fractures and found that 291 (52%) had a growth disturbance. They note that though fractures of the distal femoral growth plate are the third most common growth plate fracture in children (after wrist and ankle), they carry a risk of growth disturbance in up to 90% of cases. They concluded that the odds of a displaced fracture having a growth arrest was 4 times greater than that of a non-displaced fracture having a growth arrest.

Figure A is a radiograph demonstrating a salter-harris II fracture of the distal femur creating a large independent Thurston Holland fragment. Figure B represents the biology of the growth plate at the cellular level with Zone A representing the epiphyseal bone, Zone B the "resting" or reserve zone, Zone C the proliferative zone, Zone D the hypertrophic zone, and Zone E the primary spongiosa of the metaphysis.

Incorrect Answers:
Answer 1: Zone A represents the epiphyseal bone.
Answer 2: Zone B represents the reserve zone, an area of low oxygen tension and contains lipids, glycogen, and proteoglycan aggregates for later growth and matrix production.
Answer 3: Zone C represents the proliferative zone, an area of higher oxygen tension that prohibits calcification and is characterized by the proliferation of chondrocytes that become stacked to allow for longitudinal growth.
Answer 5: Zone E represents the primary spongiosa of metaphyseal bone that is characterized by vascular invasion and the presence of osteoblasts aligned along cartilage bars.