Biology Reference
In-Depth Information
Most of the other bones in the body develop via endochondral ossification. This develop-
ment does not initiate with a mesenchymal membrane but rather with a hyaline cartilage
model of the bone. The diaphysis (shaft) of long bones begins formation first (called the
primary ossification center) after vascularization of the cartilage. Ossification continues toward
one or both ends of the diaphysis, but a layer of cartilage (the metaphysis) persists until elon-
gation is finished (this timing differs within and between different bones; see the upcoming
section on epiphyseal fusion). This plate of cartilage is often called the growth plate. The
epiphyses (ends) of long bones begin ossification after the primary ossification center has
formed so they are called secondary ossification centers. When elongation is complete the
epiphyses fuse permanently to the diaphysis by replacement of the metaphyseal cartilage
with bone.
Scheuer and Black (2000)
and
Sadler (2004)
provide detailed and authoritative
accounts of bone development and growth.
The fragility of newly formed ossification centers makes them difficult to find in an archae-
ological context given taphonomic factors (see Marden et al. [Chapter 9], this volume);
however, sometimes they are encountered in a medicolegal context. Biological anthropolo-
gists are recognized as experts not only in constructing a biological profile from skeletal
remains but in the recovery of human remains and analysis of trauma to the skeleton. In these
contexts, forensic anthropologists may be asked for an assessment of fetal or infant skeletal
remains. Further, bioarchaeologists may have the opportunity to analyze fetal (rarely) or
infant remains from archaeological sites (e.g., see
Lewis, 2006
; May et al., 2012).
Fazekas and K´ sa (1978)
were the first to address the utility of fetal remains in the forensic
context. The next important tome to cover fetal and infant remains followed over 20 years
later: Developmental Juvenile Osteology by
Scheuer and Black (2000)
. The primary method of
age-at-death estimation for fetal and infant remains is via assessment of the development
of ossification centers because they begin formation in utero (
Scheuer and Black, 2000
). These
ossification centers can be difficult to recover or identify without soft tissue or anatomical
context, but standards do exist for age-at-death analysis, generally given in gestational
months (
Huxley, 2010
).
Timing of Epiphyseal Union
Timing of epiphyseal union is preferred as a method over appearance of secondary ossi-
fication centers due to the fragility of newly formed ossification centers. Differential timing of
epiphyseal fusion is found between bones and even within bones
d
for instance, bones with
multiple epiphyses (e.g., proximal and distal) usually show fusion of those epiphyses at
different times, such as the humerus and the femur. Some epiphyses, including many in
the skull, fuse in utero, while others do not even begin to fuse until very late adolescence
(
Schaefer et al., 2009
). The last epiphyses fuse in the early twenties; these include the medial
clavicle (
Langley-Shirley and Jantz, 2010
) and the first sacral segment (
Passalacqua, 2009
).
Studies have consistently shown that epiphyseal union happens earlier in females than
males (
Flecker, 1942; Fishman, 1982; Krogman and I¸can, 1986
). For example,
Crowder
and Austin (2005)
analyzed a large contemporary sample (North Americans born after
1969 and as recently as 1991) for fusion of the distal tibia and fibula. Their overall results
show some overlap, but even across varied ancestral populations females showed complete
fusion of these epiphyses sometimes as early as 13 years of age. The youngest males with
complete fusion were 15 years old. By 16 years old, all females showed complete fusion,
