Blood supply comes directly from the epiphyseal artery.
Cells store nutrients in preparation for proliferation.
Proliferative Zone
Chondrocytes proliferate, influenced by mechanical and hormonal factors.
Cells are disc-like and align into longitudinal columns.
Matrix becomes less organized.
The uppermost cell in the column is a progenitor cell.
Responsible for longitudinal growth, with the number of cell divisions proportional to growth.
High oxygen tension.
Epiphyseal artery terminates in the uppermost cells but does not penetrate into the zone.
Hypertrophic Zone
Chondrocytes enlarge, and extracellular matrix decreases, making this the weakest zone, prone to fractures.
Avascular and low oxygen tension.
Influenced by hormones and local growth factors like Indian hedgehog, parathyroid-related peptide, growth hormone, thyroid hormones, steroids, and sex hormones.
Provisional zone of calcification: matrix calcification begins here, and alkaline phosphatase and Type 10 collagen are secreted.
Programmed cell death of chondrocytes occurs.
Metaphysis
Primary Spongiosa
Capillary plexus brings osteoblasts, which lay down woven bone on the cartilage matrix (endochondral ossification).
Secondary Spongiosa
Osteoclasts and osteoblasts work together, resorbing woven bone and laying down lamellar bone.
Periphery of the Growth Plate
Groove of Ranvier: Contains osteoblasts, chondrocytes, and fibroblasts; responsible for circumferential growth of the physis.
Perichondral Ring of La Croix: Strong fibrous structure anchoring the physis to the epiphysis and metaphysis.
Physeal Blood Supply
Primary supply from the perichondrial artery.
Epiphyseal artery invades the reserve zone and ends in the proliferative zone.
Metaphyseal arteries invade the provisional zone of calcification.
The hypertrophic zone is completely avascular.
Growth Plate Biomechanics
The growth plate is the weakest part of a long bone.
The hypertrophic zone is the weakest part of the growth plate.
Heuter-Volkmann’s Law
Increased compression through the physis leads to decreased growth.
Growth plate shape is determined by the forces acting on it.
Normal Physeal Growth
Upper Limb
Most growth occurs away from the elbow.
80% of humeral growth is proximal, while 75% of radial growth is distal.
Leg grows 23 mm per year (femur 12 mm, tibia 9 mm).
Growth Rates in the Last 5-6 Years
Distal femur: 9 mm/year.
Proximal tibia: 6 mm/year.
Distal tibia: 5 mm/year.
Proximal femur: 3 mm/year.
Elbow Growth
CRITOL describes the order of ossification center appearance.
Capitellum appears between 1 month and 18 months, followed by each subsequent center at two-year intervals.
Ossification centers appear and fuse earlier in girls.
Fusion occurs in a different order, with the medial epicondyle and olecranon being the last.
Foot Growth
Foot bones are largely cartilage at birth, allowing for potential remodeling (e.g., Ponseti treatment).
All tarsal bones have one ossification center except the calcaneus, which has a secondary center posteriorly (appears around age 8).
Calcaneus anterior center, talus, and cuboid are present at birth.
Cuneiforms (lateral, then middle, then intermediate) and navicular appear each year after birth.
2nd to 5th metatarsals have primary centers in the shaft and secondary centers at the head.
1st metatarsal has its primary center in the shaft and secondary center at the base.
Acetabulum
The triradiate cartilage shapes according to stresses (Volkmann’s law). Developmental dysplasia of the hip (DDH) leads to dysplasia and a smaller femoral head.
Triradiate and femoral head epiphysis fuse by age 8, with corrective osteotomies being more effective before this age.
Acetabular fractures in children may cause traumatic arrest and secondary dysplasia.
Ilium
Crest fuses laterally to medially (used to assess the Risser stage in scoliosis).