Radiology Case
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Radiographic findings: There
is moderate soft tissue swelling of the dorsomedial aspect of the distal
left antebrachium (arrow heads). There is a small gas opacity within the
swelling. There is medial closure of the distal radial physis with remodeling
of the surrounding adjacent metaphyseal and epiphyseal bone (arrows).
The right carpus included has no significant findings.
Radiographic impression: Closure of the distal medial radial physis most likely secondary to a non-displaced fracture (Salter V). The soft tissue swelling and lucency are consistent with the lick granuloma mentioned in the history.
Comments: Crushing injuries to the physis, as in this patient, are generally not radiographically detectable immediately following the injury, but become evident with time as the damaged physis closes. A brief review of the zones of the physis is helpful in developing an understanding of these fractures. There is a growth, maturation, transformation, and remodeling zone. Each of these zones consists of several structures (remember that the changes between these structures and zones are gradual). The first zone adjacent to the epiphysis is the growth zone that consists of a resting germinal cell layer (chondroblasts), a dividing layer (proliferative), and a columnating layer. As the chondrocytes proliferate, they will begin to align or stack which is called columnation. After columnation occurs, there is a transition to the maturation zone. Once columnated and in the maturation zone, the chondrocytes begin to hypertrophy and then calcify. Hypertrophy of the chondrocytes is responsible for most of the lengthening of the physis. Once calcified, the cells are in the transformation zone, and the chondroclasts and osteoblasts, carried into the region on metaphyseal capillaries, begin to remove the calcified cartilage and replace it with bone (endochondral ossification). The physis closes when proliferation of the chondrocytes is halted and the cells proceed to hypertrophy, calcify, and undergo endochondral ossification.
A crushing injury to the physis may destroy and halt the proliferation
of the chondrocytes allowing the physis to mature and close. If only one
of the bones of the antebrachium is affected, it will restrict the normal
growth of the damaged bone and alter the growth of the other bone leading
to an angular limb deformity. The physis, the bone that is damaged, and
the symmetry of the damage to the physis determine the subsequent limb
deformity. Elbow and radio-carpal incongruity can also be seen. If physeal
damage is suspected and not evident radiographically, follow-up radiographs
in 3 -4 weeks will usually demonstrate remodeling and/or early angular
deformity of the limb. In this case, since the medial portion of the distal
radial physis is prematurely closed, a varus angular deformity would be
expected.1,2
References
- Johnson KA, Watson ADJ, Page RL. Skeletal Diseases In: Ettinger SJ and Feldman EC, eds. Textbook of Veterinary Internal Medicine. 4th ed. Philadelphia: W.B. Saunders Co., 1995;2078-2079.
- Egger E. Fractures of the Radius and Ulna In: Slatter DH, ed. Textbook of small animal surgery. 2nd ed. Philadelphia: W.B. Saunders, 1993;1746-1757.
Dr. John Feleciano, DVM, DACVR
Dr. Renee Leveille, DVM, DACVR