Forensic anthropology 145
established rating scales that describe the degree to which growth
cartilages (metaphyses) have been replaced by bone, signaling the
completion of that skeletal element or an articulation.19,38 Likewise,
staging techniques have been developed for the ossification of
various symphyses, synchondroses, and sutures (e.g., sternal rib
cartilages, pubic symphysis, cranial sutures, basilar synchondrosis,
etc.). These techniques usually take the form of a semantic differen-
tial, which describes changes in the appearance characteristics of a
particular structure at known points in time based upon controls.^39
It is worth noting that the value of a technique is strictly limited
by the population sample upon which it is based. Thus, aging tech-
niques must be recalibrated as secular trends (e.g., improved public
health measures, available nutrition, antibiotics, etc.) modify matu-
rational rates and longevity.
Thirty years and beyond: As the last epiphyses (usually the medial
clavicles) complete development, skeletal age may still be estimated,
albeit with increasing error. Unlike the dentition, the skeleton under-
goes remodeling throughout life. As a result of endocrine-driven
cellular interactions that constantly remove bone and replace it, the
skeleton continues to “turn over” approximately every seven to ten
years, remodeling itself to accommodate gravity and the mechani-
cal habits of its owner. Alongside this process, the skeletal cartilages
that separate and cushion bones undergo increased hardening with
resulting grossly observable wear at the articulations, i.e., general-
ized osteoarthritic changes. Age-related changes in the weight-bearing
joints (ankle, knee, hip, sacroiliac, spine, etc.), as well as mineraliza-
tion of non articular connective tissues (e.g., thyroid, cricoid, arytenoid
cartilages, etc.), have been documented along with appropriate
caveats having to do with differential effects of lifestyle, disease, and
diet.^40 Other time-dependent structural changes may be appreciated
radiographically. For example, as the marrow of long bones assumes
a larger part of the hemopoetic burden with age, one can observe an
advance of the apex of the marrow cavities in femora and humeri. This
is seen as increasing radiolucency toward the proximal epiphyses. This
progression has been documented and timed.^41 Radiographs may a lso
complement and extend developmental staging techniques even after
epiphyseal completion by revealing remnants of growth plates that
have not yet reached uniform density.^42 Finally, as skeletal remod-
eling continues over the course of a lifetime, histological changes
in cortical bone may be correlated with age. As old cortical bone
is scavenged by osteoclasts to maintain mineral homeostasis, new
vascular pathways import osteoblasts that replace it. As the skeleton
moves through time, the amount of unremodeled lamellar bone seen