Too Many Bones to Pick - from Overproduction to Refinement: Evidence for Trabecular Pruning in Early Postnatal Development as a Distinct Phase of Skeletal Functional Adaptation.

purposeWhile bone functional adaptation has been previously documented in adults and adolescents, the developmental trajectory of trabecular bone during early postnatal life remains poorly characterized. We investigated whether trabecular bone development follows a biphasic pattern analogous to synaptic pruning in neural development: initial selective trabecular elimination ("trabecular pruning") followed by architectural refinement.

methodsWe conducted a systematic review synthesizing data from 14 human studies and 11 animal studies examining trabecular bone ontogeny from birth through the early juvenile period across multiple skeletal sites.

resultsFollowing initial in-utero trabecular overproduction, available evidence suggests that altricial mammals (including humans) undergo trabecular pruning during the perinatal period, characterized by decreases in trabecular bone volume fraction (BV/TV, 10-65%) driven primarily by a reduction in trabecular number (Tb.N) rather than trabecular thinning. In long bones directly involved in locomotion, where evidence is clearest, Tb.N decreases from 3-4/mm to below 2/mm while trabecular thickness (Tb.Th) increases modestly from approximately 100 µm to 150 µm. Trabecular pruning timing coincides with independent locomotion onset, and concurrent increases in the degree of anisotropy suggest mechanically guided elimination of minimally loaded trabeculae. Evidence from precocial animals (horses, pigs) is currently limited, but is broadly consistent with the absence of a perinatal trabecular pruning phase, in line with their immediate weight-bearing requirements at birth.

conclusionTrabecular pruning represents a specific manifestation of "developmental sculpting"-a suggested fundamental biological principle whereby systems achieve functional optimization through initial overproduction followed by activity-dependent elimination. Recognizing trabecular pruning as a distinct skeletal functional adaptation phase provides new insights into bone development within broader principles of biological organization.