Quantitative histomorphometric analysis of the bone growth plate in infancy : a comparative study between SIDS and normal subjects

Bone elongation is achieved through the process of endochondral ossification, which involves the transition of growth plate cartilage into bone. The following study describes this sequence of events both spatially and temporally in ribs taken from normal infants and infants who have died of sudden infant death syndrome (SIDS). Growth plate hypertrophic (HZ) and proliferative (PZ) zone heights were measured in 26 normal (age range: ll - 344 days) and 24 SIDS (age range'. 9 - 342 days) growth plates and analysed using linear regression. In both groups FIZ heights were observed to decrease by more than half in the first 12 months following birth (normals: r = 0.63, P < 0.001, SIDS: r = 0.56, P < 0.003). PZ heights also declined significantly (r = 0.59, P < 0.001 ;r = 0.72, P < 0.0005) in normal and SIDS groups respectively. A more detailed histomorphometric analysis revealed a number of age dependent changes in each of the cartilaginous zones and adjacent bone in 43 normal infants aged between l1 and 791 days (mean age 203.4 + 182.6 days). In addition, a total of 34 normal infants, age, and sex-matched to SIDS infants, up to one year of age were analysed for age, sex and normaVSIDS differences using repeated measures analysis of variance. Cartrlage volume fraction was observed to increase significantly with age (P < 0.001), while chondrocyte lacunae diameter declined significantly with age (P < 0 0004). In the metaphysis, bone mineral volume (P < 0.00001) and trabecular thickness (P < 0.0001) showed a significant age increase. No significant differences between the morphometric variables were detected in males and females and between normal/SIDS groups. Thus, this study has demonstrated significant age related changes in cartilage and bone structure, which occurs in a well defined sequence spatially and temporally in both normal and SIDS infants. Longitudinal bone growth appears to be normal in SIDS infants. In contrast to previous reports, these results indicate that a growth abnormality is not always an associated factor in SIDS infants.Thesis (M.Med.Sc.)-- University of Adelaide, Dept. of Medicine, 199