Growth direction in the mandibular condyle of pre-pubertal and pubertal monkeys (Macaca fascicularis) studied by morphometry and radioautography.

Eight male monkeys with prepubertal or pubertal skeletal maturity were used to assess age-related changes in anterior-posterior gradients of parameters which characterize growth velocity. The animals received single intravenous doses of 1 mCi/kg body weight of [3H]-proline at 24 h, and of 0.5 mCi/kg body weight [3H]-thymidine, 3 h before death. Four perichondral and chondral layers, and the subchondral zone of erosion of each condyle, were analysed morphometrically and radioautographically at 12 sampling sites distributed systematically over the joint surface. Values for cell density, cell proliferation, extracellular cartilaginous matrix production, cartilage resorption and subchondral bone formation produced characteristic curves which generally peaked in the central joint region. These peaks did not shift, either in relation to age or growth velocity, suggesting a uniform posterior-superior growth direction. Individual variability in both shape and prominence of the curves usually prevailed over the group effects attributable to skeletal maturity or growth velocity. Thus the gradual age-dependent shift in human condylar growth direction may be revealed only in longitudinal studies and would be masked by pronounced individual variation in cross-sectional studies of small samples.