Aronson D D, Stewart M C, Crissman J D
Department of Orthopaedic Surgery, Children's Hospital, Wayne State University School of Medicine, Detroit, Michigan 48201.
Clin Orthop Relat Res. 1990 Jun(255):61-7.
The etiology of valgus deformity after a seemingly innocuous fracture of the proximal tibial metaphysis in children is unknown. The purpose of this work was to identify the etiology of this deformity using a rabbit model. Twenty-two eight-week-old rabbits were divided into two groups. In Group I, the medial periosteum was excised from the left proximal tibial metaphysis. A partial osteotomy was created 5 mm distal to the epiphyseal plate, involving the medial one-half of the tibial metaphysis. Two 0.7-mm Kirschner wires were placed as markers on each side of the osteotomy. In Group II, the identical procedure was performed from the lateral side. Standard roentgenograms were obtained postoperatively and weekly until death by sodium pentobarbital overdose at six weeks. The angular deformity, medial growth, and lateral growth were calculated from the markers on the roentgenograms. All tibias were decalcified and analyzed under light microscopy. In Group I, all 11 rabbits developed valgus deformity averaging 12.2 degrees; asymmetric growth was statistically significant. In Group II, ten of 11 rabbits developed varus deformity averaging 9.8 degrees; asymmetric growth was not statistically significant. Despite obvious asymmetric growth in both groups, light microscopy failed to reveal any asymmetry of the physis. Valgus and varus deformities are secondary to asymmetric growth, which is not demonstrable by light microscopy.
