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The Determination of the Age of the Individual from Skeletal Remains

by John A. Giacobbe
Class Lecture Outline for Human Osteology, ANT 601, Spring 1994,
Eastern New Mexico University, Portales

The determination of age relies on the assessment of the physiological age of the skeleton, as opposed to the chronological age of the individual. The physiological age is based upon relative growth patterns, and is hoped to give an accurate estimate of chronological age, but environmental, nutritional, and disease stresses often cause changes in the skeleton which will mask the true age of the individual. In addition, the accuracy with which age can be estimated varies inversely with the age of the individual at death. In younger years, with age being estimated primarily upon observed developmental changes, more precise estimates are possible, whereas in older individuals, age estimates are more often accomplished via the observation of degenerative changes, which offer less accuracy.

Age determination can be accomplished through many means, and a holistic analysis of all possible age-related attributes is best for an overall estimate. Some of the more typically utilized attributes include:

1. Dental Eruption and Occlusion
2. Cortical Bone Histology
3. Cranial Suture Closures
4. Postcranial Epiphyseal Unions
5. Pubic Symphyseal Face Morphology
6. Age-Related Degenerative Conditions
7. Phase Changes in the Sternal Rib
8. Potpourri

1. Dental Eruption and Occlusion

Age estimates are based on the age of eruption of the deciduous and permanent dentition. This method is useful in age estimates of up to about 15 years. The third molar (wisdom tooth) erupts after this time, but is so variable in age of eruption, if it erupts at all, that it is not a very reliable age indicator. See Bass pp. 289-290 for an illustration of Ubelaker's eruptive phases, noting the standard deviations. Occlusal wear has also been offered as an indicator of age, but this has been shown to be highly inaccurate, especially in archaeological context, where high-grit content diets (such as from the use of natural stone mano and metate) can wear down the occlusal surface of the tooth by the end of puberty - see Bass pp. 286-87, after Brothwell (1965).

2. Cortical Bone Histology

Kerley (1984) developed a system of aging based on osteon counts taken from midshaft long bone sections. This process involves counting the number of whole osteons and osteon fragments (which increase in number with age), and nonhaversion canals and the percentage of circumferential lamellar bone in the cortex (which decreases with age, completely disappearing around age fifty). These estimates are taken from the outer one third on the cortex, with a normal light microscope in four fields at 100X. A percentage estimate is calculated, and what is sought after is the rate of osteon turnover or replacement. These percentages are plugged into either a regression formula or a pre-calculated age\profile chart. Kerley has obtained a reliability of almost 90% with a standard deviation of +/- 5 years, with the best correlation coming from the fibula, then the femur and the tibia.

3. Cranial Suture Closures

This method bases age upon the degree of closure, union or ossification of the cranial sutures. These methods have until recently been considered inaccurate, but Meindel and Lovejoy (1985) have introduced new evidence to indicate parietal ectocranial sutures are reliable indicators of age over 40 years. In addition, Mann et al. (1987) have offered the four maxillary sutures and their rates of closure as reliable age estimators - see Bass pp.47-48.

4. Postcranial Epiphysial Unions

(see handout #1) Endochondral bones of the postcranium form via the union and ossification of cartilaginous bridges between growing bones. This process can be seen to occur along a growth algorithm, and can be used to estimate age at death. Handout #1, as well as Bass (1987), lists some of these locations of epiphyseal union, as well as the approximate age ranges for which these unions occur. This data can be used on a union/non-union basis, and McKern and Stewart have define five grades of epiphyseal union: unobservable (0), beginning (1), active (2), recent (3), and complete (4), and these offer a possibly more accurate estimate of age.

5. Pubic Symphyseal Face Morphology

(see handout #2) The pubic symphyseal face in the young is characterized by an undulating surface, such as the crennulated surface of a typical non-fused epiphyseal plate. This surface undergoes a regular progressive metamorphosis from age 18 onwards. The phase system diagrammed in the handout, was developed by Suchey and Brooks for the male pubic symphysis.

6. Age-Related Degenerative Changes in Skeletal Features

Many non-pathogenic conditions such as certain expressions of arthritis and osteoporosis become more prevalent and pronounced in old age, and can be used to give corroborative evidence in the determination of age. These occurrences are not entirely reliable in themselves, however, as injury and pathological expressions of these conditions can mimic the degenerative condition. An illustrative case can be seen in the osteophytic growths of the vertebral body (via osteoarthritis). These growths form on the outer margins of the centra, and Steward (1958) has computed an age progression histogram for humans over 21 years based on the percentage of extra-central lipping as a function of age for the lumbar and thoracic vertebra - see Bass pp. 20-21.

7. Phase Changes in the Sternal Ribs

Iscan and Loth have developed a system of age estimation based on sequential changes at the sternal end of the fourth rib. These changes are similar to those that occur on the pubic symphyseal face. They are of a specific morphological nature and occur on the costochondral joint between the rib and sternum. They consider that these phases are not as subject to variation due to sex, pregnancy and activity patterns as is the pubic symphyseal face. See Bass (pp. 135-142) for photos of Iscan and Loth's phases, with the general progression illustrated as an increase in the depth of the articular depression and the degenerative fragmentation, thinning and increased porosity at the edges of the articular surface over time.

8. Potpourri:

a. Note that generally females are more advanced than males with regard to physiological age, being about two years advanced at puberty, five years at maturity, and seven to ten years in old age.
b. The sacroiliac joint undergoes changes in morphology similar to those at the pubic symphysis, Lovejoy et al. (1985) offers a phase system based on these morphological changes.
c. Krogman (1949) offers a system of aging based on transillumination through the scapular body to chart the occurrence and amount of atrophic (thinning) centers, basically, the more that are present, the older the individual.
d. Various radiographic analysis techniques focus on age related changes to interior bone structures, such as at the costo-chondral juncture, the metaphyseal plates of the long bones, and Walker & Lovejoy's (1985) radiographic analysis of trabecular bone involution in the clavicle.
e. Bass (1987) and Ubelaker (1989) offer age estimates based on long bone lengths, but these have a wide range of variation even within a single relatively homogenous population.


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