Age estimation from bone ossification – The bones of the human skeleton are preformed in hyaline cartilage. This soft tissue model is gradually converted into hard osseous tissue by the development of osteogenesis, frequently in a central position, from which the process of transformation spreads, until the whole skeleton is ossified. The appearance of such centers of ossification is spread over a long period of time.
A large number are first seen in embryonic life, some appear much later in prenatal life, and others appear after birth. The earliest centers of bone ossification appear at the end of second month of pregnancy. At the eleventh intrauterine week, there are 806 centers of bone growth; at birth about 450; while the adult skeleton has 206 bones.
This shows that 600 centers of bone growth have disappeared, i.e., they have united with the adjacent centers to form the adult one. The process of appearance and union has a sequence and a time. As a rule, bone ossification begins centrally in an epiphysis and spreads peripherally as it gets bigger.
At first it is entirely amorphous, rounded and pinhead sized. As it grows, it takes on the osteological details of the bone. Some of them are ossified from a single centre, e.g. carpus and tarsus. The bone ossification centers in carpal bones appear as follows: capitate 1; hamate 2, triquitrum 3, lunate 4, scaphoid and trapezoid 5, trapezium 6, pisiform 11 years.
Most of them are ossified from several separate centers, one of which appears near the middle of the future bone. This center is concerned with progressive bone ossification towards the bone ends. In all such, their ends are cartilaginous at birth. These terminal regions are ossified by separate centres, sometimes multiple; they are said to be secondary centers.
Typically, the bone ossification of long bone such as the tibia has become ossified throughout its shaft (diaphysis) at birth; whereas its two ends (epiphyses), are later ossified by secondary centers. A layer of hyaline cartilage (epiphyseal plate) persists between the diaphysis and epiphysis.
It increases in length at this epiphyseal plate or disc (growth plate or growth cartilage), until its final dimensions are attained. The process of union of epiphysis and diaphysis is called fusion. Union is a process, not an event. The union in long bones is interpreted as non-united, uniting (1/4, 1/2, 3/4, etc.), recently united and united, depending on the stage of union.
The long limb bones show epiphysial arrangements at both ends, while metacarpals, metatarsals, phalanges, clavicles and ribs possess an epiphysis at one end only. In some, the epiphysial centres at one or both ends are more complex, e.g., in the proximal end of the humerus, which is wholly cartilaginous at birth, three separate centres appear during childhood. They soon unite to form a single epiphysial mass, which later fuses to the diaphysis.
Growth cartilages do not grow at the same rate at all points throughout their substance. By differential rates of growth, the two bony surfaces usually become reciprocally curved, commonly in such a way that the epiphysis fits like a shallow cap over the convex end of the shaft. There may be maturity imbalance between bones from different parts of the same individual.
For determining the age, skiagrams of the shoulder, elbow, wrist, hip, knee, ankle, pelvis and skull should be taken in anteroposterior direction.
In biology, stability is the exception, variability is the rule, i.e., there really is no average. There is only a central tendency with a normal range of variability. The variability increases with age. As a general rule, the aging of bones is more accurate with respect to the appearance of centres of bone ossification than it is with respect to the union of epiphyses. A study of various anatomical authorities shows that there is a considerable variation regarding the ages at which the various centers of bone ossification in the epiphyses fuse with their respective diaphyses.
As a general rule, the secondary centres of the limb bones that appear first are the last to fuse, whereas the late-forming epiphyses reach union with their primary centres in a shorter time period. In the long bones of upper limbs, the union occurs earlier in the elbow joint and later at the wrist. Head of the humerus is the last long bone epiphysis to unite. In the long bones of the lower limbs, the union occurs later at the knee joint and earlier at the hip and ankle joints.
The epiphyseal lines on the long bones of a young individual appear as circular grooves around the ends of the bones, and on radiographs as irregular lines resembling a fracture. In skeletal remains of a young person where the bones have become completely dry, the epiphyses often separate from the shaft, which should not be mistaken for fractures.
Too much reliance should not be placed on them, as variations occur depending on the health, hereditary, nutritional, endocrine and environmental factors. Multiple criteria of skeletal age should be employed whenever possible. The dentition may be used as a check during the first two decades of life.
An estimated skeletal age based on appearance of bone ossification centres and union of epiphyses must always be expressed in plus or minus terms, e.g., 10 ±1 (ten years, plus or minus one year). Skeletal development in the female can be in advance of the male up to one year, while dental development may differ only from one to four months.
Union of epiphyses in cartilaginous bone occurs slightly earlier (by about one year) in the female than in the male, but the reverse is seen in the closure of the sutures of the skull. Under tropical conditions bone ossification is observed earlier than in temperate areas.
The union of epiphyses as seen in radiographs appears earlier approximately about plus or minus six months than the periods of fusion indicated by anatomical evidence. This is due to the fact, that towards the end of the growth period, the epiphyseal plate of the cartilages becomes very thin and irregular in outline and may not show on radiograph. In a film, a persistent scar is not evidence of incomplete union or even of recent union.
In an individual bone, once union has begun, it will be completed in about 12 to 18 months. In radio graphs of growing long bones, one or more transverse lines are often observed at the diaphyseal ends. This is thought to be evidence of growth disturbance (e.g. scurvy, rickets), and are called “scars of arrested growth”.
The pubic symphysis is probably the best single criterion for determining age from third to fifth decades. It requires bones that are free of cartilage. The surface features are blurred, if there is erosion by drying and damage. The symphysial surface before 20 years has a layer of compact bone near its surface. At about 20 years, it is markedly irregular or uneven, and the ridges run transversely across the articular surface.
Between 24 and 36 years, the ridges gradually disappear and the surface has a granular appearance and ventral (outer) and dorsal (inner) margins are completely defined. Early in the fifth decade, the symphysial face has an oval, smooth surface with raised upper and lower ends.
Towards the end of the fifth decade, a narrow beaded rim develops on the margins. During the sixth decade, erosion of surface and breakdown of ventral margin begins. In the seventh decade, the surface becomes irregularly eroded. If the male criteria are used for females, the age would be underestimated by about ten years (Gilbert, 1973).
The four pieces of the body of the sternum fuse with one another from below upwards between 14 to 25 years. At about 40 years the xiphoid unites with the body. The manubrium fuses with the body in old age.
The greater cornu of the hyoid bone unites with the body between 40 to 60 years.
Bones of the calvaria are 8 in number: parietal 2, frontal one, temporal 2, occipital one, sphenoid one, and ethmoid one. Bones of the face and jaws are 14 in number : maxilla 2, zygomatic 2, nasal 2, lacrimal 2, palatine 2, inferior nasal concha 2, mandible one, and vomer one. The flexible cartilaginous joints of early life are replaced with interlocking connections between bones in maturity.
Lateral and occipital fontanelles usually close within the first two months. Posterior fontanelle closes in 6 to 8 months. The anterior fontanelle closes between 1.5 to 2 years. and the two halves of the mandible unite at the second year. The condylar portions of occipital bone fuse with the squama at the third year and with the basioccipital at the fifth year. The metopic suture closes about the third year, but in 5 to 10% cases it persists. The basioccipital fuses with the basisphenoid at about 18 to 21 years.
In the vault of the skull, closure of the sutures begins on the inner side 5 to 10 years earlier than on the outer side. The coronal, sagittal, and lambdoid sutures start to close on their inner side at about the age of 25 years. On the outer side, fusion occurs in the following order: posterior one-third of the sagittal suture at about 30 to 40 years; anterior one-third of the sagittal and lower half of the coronal at about 40 to 50 years; and middle sagittal and upper half of the coronal at about 50 to 60 years.
The lambdoid suture, starts closing near the lambda and the union is often completed at about 45 years. The squamous part of the temporal bone usually fuses with its neighbor by age of 60 years. Suture closure in skull occurs later in females than in males. Estimation of age of skull from suture closure is not reliable. It can be given only in a range of decade. Beginning union in the vault sutures may be identified by irregular radio-opacity on each side of the suture.
The most successful estimate is done from sagittal suture, next lambdoid and then coronal, A lateral head film is preferable for the observation of coronal and lambdoid sutures. Ectocranial suture closure is very variable. Sometimes, there may not be ectocranial suture closure. This is called “lapsed union”. This occurs most often in the sagittal suture. With lapsing there is slight bony elevation on either side of the incompletely closed suture. Bone ossification centre in the mandible appears at second month of intrauterine life.
OTHER AGE CRITERIA IN THE SKULL
A young adult skull is smooth and ivorine on both inner and outer surfaces. At about 40± 5 years, the surface begins to assume a “matted” granular, rough appearance. From 25 years onwards muscular markings become increasingly evident, especially on the side of the skull (temporal line), on the occiput (nuchal lines), and on the lateral side of the mandible (masseteric attachment).
On the inside of the skull, on either side of the sagittal suture, certain pits or depressions (pacchionian depressions) become more marked with age, both in depth and in frequency. The grooves of the middle meningeal artery become deeper. After 50 years, the diploe becomes less vascularly channeled and there is increasing replacement by bone. There is no consistent age change in the thickness of the vault bones.
The five sacral vertebrae are separated by cartilage until puberty, when the lateral portions grow together. After this, fusion of epiphyses takes place and bone ossification of intervertebral discs extends from below upwards. The sacrum becomes a single bone between 21 and 25 years. A gap may persist between S1 and S2, until 32 years due to “lapsed union”.
There is a close relationship between the development of cervical vertebrae and age. The immature vertebral body has a series of deep radial furrows both on the upper and lower surfaces. This feature increases in prominence up to the age of ten, and then gradually fades at from 21 to 25 years. After 45 years, osteoarthritic changes in the form of lipping of the vertebrae are seen.
Between 30 to 35 years, lipping starts on the ventral margin of the glenoid cavity. By 35 to 40 years, irregular lipping occurs around the clavicular facet and inferior surface of the acromion process. By 45 years. localised bony atrophy can be seen. Cristae scapulae occur by 50 years. Sternal end of fourth rib is an accurate and reliable method of estimating age.