THE PATHOLOGY OF ACUTE CHONDRO-OSSEOUS INJURY IN THE CHILD

Skeletal tissues from children sustaining acute skeletal trauma were a nalyzed with detailed radiologic and histologic techniques to assess t he failure patterns of the developing skeleton. In the physis- and epi physis-specific fracture propagation varied, usually going through the portion of the hypertrophic zone adjacent to the metaphysis. However, the physeal fracture in types 1 and 2 sometimes involved the germinal zone. There may also be microscopic propagation at oblique angles fro m the primary fracture plane, splitting cell columns apart longitudina lly. The cartilage canals supplying the germinal zone appear to be ''w eak'' areas into which the fracture may propagate, especially in infan cy. Incomplete type 1 physeal fractures, which cannot be detected by r outine radiography, may occur. Types 1, 2, and 4 physeal injuries may be comminuted. In type 3 injuries, discrete segments of physis that in clude the germinal zone may ''adhere'' to the metaphysis, separating t he cells from their normal vascularity. In types 2 and 3, comminution may occur at the site of fracture redirection from the physis. Direct type 5 crushing of the physeal germinal zone does not occur, even in t he presence of significant pressure-related changes within other areas of the epiphysis. Type 7 separation between cartilage and bone at any chondroosseous epiphyseal interface may occur, but is similarly impos sible to diagnose radiographically. In the metaphysis torus, fractures result from plastic deformation of the cortex, coupled with a partial microfracturing that may be difficult to visualize with clinical radi ography. Some of the energy absorption may also be transmitted to the physis, causing metaphyseal hemorrhage adjacent to the growth plate an d variable microscopic damage within the physis. In the diaphysis, the greenstick fracture is associated with longitudinal tensile failure t hrough the developing osteons of the ''intact'' cortex. The inability of these failure patterns to ''narrow'' after the fracture force dissi pates is the probable cause of retained bowing (plastic deformation). In bath torus and greenstick fractures, the fractured bone ends show m icro-splitting through the osteoid seams. In the diaphysis, metaphysis , and epiphyseal ossification center there may be areas of focal hemor rhage and microfracture that correlate with the reported MRI phenomeno n of ''bone bruising.'' Again, such injury cannot be diagnosed during routine radiography.