Introduction
The ossification of bones, which helps determine the age, can be used to establish skeletal age. Several ossification centers contribute to the formation of human bones. There are 806 ossification centers in the 11th and 12th weeks of gestation, which are decreased to about 450 at birth. There are 206 bones in an adult human.
The time of appearance of center of ossification and the process of union of the epiphysis with the diaphysis at the metaphysis has a sequence and time that is utilized towards determination of age. A radiological survey of ossification centers may provide considerable help in estimating the age of a person. However, we cannot place too much reliance on such a method as many factors affect the process of appearance and fusion of bone. Roughly this method provides one parameter in conjugation with others to deduce the age of a person and it cannot be superior criteria when considered in isolation. Similarly, it is important to note that bone fusion is a process rather than an event, therefore it is liable to variance.
The factors affecting the appearance and fusion of these centers are:
- Hereditary factors
- Growth and development
- Geographical variation
- Climate
- Dietary habits
- Association with diseases
Ossification of Bones
Up to the age of 20-22 years, ossification centers are analyzed, followed by skull vault sutures, union, and sternum activity; changes in the morphology of the mandible, and alterations in the pubic symphysis. The ossification begins centrally in an epiphysis that spreads peripherally and gradually takes up the osteological details of the bony part, it is going to constitute e.g., the upper end of the femur, lower end of radius and ulna, etc. The union of the epiphysis with a diaphysis in long bones is interpreted as united, recently united, uniting, and non-united, depending on the stage of union. When the epiphyseal lines persist, it is called recently united. The anatomical evidence of bony union differs from the radiological union by about three years and radiographs give an earlier time of union. The radiological examination of the bones is performed on living persons when determining their age to assist courts of law in cases of age disputes.
The Important Ossification Centers and Their Fusion
| Centers of bones | Appearance | Fusion |
| Clavicle-medial end | 15-19 years | 20-22 years |
| Sternum | 5 months IUL | 60-70 years |
| Manubrium body [first segment] | 5 moths IUL | 14-25 years from below upwards; 3 and 4-15 years |
| Second segment | 7 months IUL | – |
| Third segment | 7 months IUL | 2 and 3-20 years |
| Fourth segment | 10 months IUL | 1 and 2-25 years |
| Xiphoid process | 3 years | 40 years |
| Humerus [upper end] Head | 1 year | 18 years |
| Greater tubercle | 3 years | 4-5 years with head |
| Lesser tubercle | 5 years | 5-7 years |
| Humerus [lower end] Medial epicondyle | 5-6 years | Capitulum, trochlea and lateral epicondyle form conjoint tendon at 14 years, unites with shaft at 15 years medial epicondyle unites at 16 years. |
| Capitulum | 1 years | – |
| Trochlea | 9-10 years | – |
| Lateral epicondyle | 10-12 years | – |
| Radius Upper end Lower end | 5-6 years 1-2 years | 15-16 years 18-19 years |
| Ulna Upper end Lower end | 8-9 years 5-6 years | 16-17 years 18-19 years |
| Head first metacarpal Head other metacarpals | 2 years 1.5-2.5 years | 15-17 years 15-19 years |
| Hip bone Triradiate cartilage Iliac crest Ischial tuberosity Sacrum | 11-13 years 14-15 years 15-16 years 8 months IUL | 14-15 years 18-20 years 20-22 years 25 years |
| Femur [upper end] Head Greater trochanter Lesser trochanter | 1 years 4 years 14 years | 17-18 years 17 years 15-17 years |
| Tibia Upper end Lower end | 9 months IUL 1 year | 16-17 years 16 years |
| Scapula Coracoid base Acromion process | 10-11 years 14-15 years | 14-15 years 17-18 years |
Age of Ossification of Hand and Foot Bones
| Type of bone | Age of ossification |
| Capitate | 2 months |
| Hamate | 3 months |
| Triquetral | 3 months |
| Lunate | 4 months |
| Scaphoid | 4-5 months |
| Trapezium | 4-5 months |
| Trapezoid | 4-5 months |
| Pisiform | 9-12 years |
| Calcaneum | 5 months |
| Talus | 7 months |
| Cuboid | 10 months |
| Lateral cuneiform | 1 year |
| Medial cuneiform | 2 years |
| Intermediate cuneiform | 3 years |
| navicular | 3 years |
Individual variations for bony union tend to occur when establishing the age of a subject for medico-legal purposes. Hence the standard value derived thorough examination of a large number of subjects should be the major factor. The degree of growth and development of bones to some extent is affected by the dietary, environmental, hereditary, and endocrinal factors in different individuals belonging to different regions and cultures. Tropical climates develop ossification earlier than temperate zones. Epiphyseal union occurs 1-2 years earlier in females than males.
Maturation score for estimation of skeletal age
To minimize the errors of epiphyseal union, McKern and Stewart in 1957 suggested a scheme of scoring involving seven combinations of various segments. The total score is applied to the prediction equation for a more accurate age estimation.
| Degree of union | Scoring |
| No union | 1 |
| ¼ th union | 2 |
| ½ th union | 3 |
| ¾ th union | 4 |
| Complete union | 5 |
Suture Closure of Skull
The estimation of adult age based on cranial suture closure was one of the earliest methods of aging the skeleton to be developed. In the beginning, Todd and Lyon in the mid-1920s (Todd and Lyon, 1924–1925) conducted work on it. Since then, various scientists have examined the suture with ecto and endocranial anatomy macroscopically. While researchers describe sutural ossification as an age-related physiological process, age estimation for forensic purposes may find that it is highly variable and therefore unreliable as a method of age determination. Despite this, the closure of the sutures of the skull has some bearing on the milestone of life.
The absence of any signs of closure of any suture of the skull points to the strong possibility of the age has not exceeded 30 years. Evidence of commencing union of the sutures is always noticed first in the endo-cranial surface, then on the endo-cranial one. As a rule, the inner surface closes several years before the outer. The sutural closure occurs earlier in males than females. Estimation of age from the closure of sutures of the skull can be given within the range of 10 years between 30-60 years and even more in higher age groups.
The following are the ages at which sutural closure occurs chronologically:
- Lateral and occipital fontanelle closes at 2 months after birth
- Posterior fontanelle closes at 6-8 months of birth
- At 1½-2 years of birth Anterior fontanelle closes
- Metopic suture closes at 2-4 years but may extend up to six years.
- Basiocciput and basisphenoid fuses at 18-20 years.
- Sagittal suture is the first to start closing endo-cranially at about 25 years at its posterior portion close to parietal eminence. The fusion is complete both ectocranially and endo-cranially by 35-40 years.
- Coronal suture starts closing endo-cranially by 25-30 years in its lowest part, close to the junction with the sphenoid. It is closed completely at 40 years.
- Lambdoid suture starts closing endo-cranially at 25-35 years and terminal closure occurs by 45-50 years.
- At 40 years Pterion starts closing and completely closes by 65 years.
- At 45 years of age, the mastoid-occipital begins to close, and by 80 years of age, it has completely closed. The asterion closes after 80 years, and the Pareto-temporal suture in 70 years.
Adult Bone Changes
Scapula Changes
The scapula is a delicate bone that is often too injured to be of help. It takes skill to interpret, and the changes do not appear to be constant. The changes aren’t as strongly linked to age as one might think. The scapula changes are categorized into two categories:
a. Ossification-related changes after maturity:
i. Lipping of the glenoid fossa begins after 30-35 years of age.
ii. Lipping of the clavicular facet begins at the age of 35-40.
iii. At 35-40 years, the appearance of a ‘plaque’ or ‘facet’ on the bottom of the acromion process, thus extending the acromial tip from 2-8 mm.
iv. At 45- 50 years of age, the triangular area at the base of the scapular spine begins to demarcate more clearly.
v. With age, the crista scapularis tends to become broader at the base and more prominent at the apices.
b. After maturity, changes caused by the atrophic process include:
i. Surface vascularity
This appears as a series of fine lines in people under the age of 25 with time, this visibility fades and eventually vanishes.
ii. Deep vascularity
Deep vascularity appears as fine lines around the age of 25-30 years, but only under trans-illumination, and it tends to fade with age.
iii. Spots of atrophic growth
They are patches of bone atrophy that emerge around the age of 45 and usually begin in the infraspinous region.
iv. Infraspinous region ‘buckling’ and ‘pleating’
It is caused by irregular bone atrophy as a result of decreased vascularity. It starts around the age of 40 and is marked by the disappearance of cancellous tissue.
Rough Estimate of Age from Pubic Symphysis
1) Age is 20 years when the symphyseal surface is even.
2) The ridges run transversely across the articular surface when the surface is strongly ridged and irregular, a condition known as billowing; the age is 20-25 years.
3) By 25-35 years of age, the billowing has faded and the articular surface has become granular with distinct anterior and posterior edges.
4) By the age of 35-45 years, the articular surface is smooth and round.
5) By 45-50 years, narrow and beaded rims grow in and around the articular surface’s edges, and some surface degradation begins.
6) There is a varying degree of erosion, with the ventral margin breaking down by > 50-60 years.
7) After approximately 60 years, the surface becomes irregularly eroded.
Age Changes in the Vertebra
1) By the time the deciduous dentition is completed, the arch unites posteriorly and at the same time, the arches and bodies of the lowest lumbar vertebra begin to fuse.
2) The posterior parts begin to fuse by 6 years and at the same time, the arches of the first cervical vertebra unite posteriorly.
3) Up to ten years, the upper and lower surfaces of immature vertebrae show a series of radial furrows.
4) The furrows gradually fade on the upper and lower surfaces between 21-25 years.
5) Lipping of the vertebra is seen usually after 45 years.
6) By 40-45 years, osteophytes outgrowth from anterior and lateral margins becomes visible. The second cervical vertebra up to the age of about three years consists of three pieces that are two lateral portions that constitute the arch, the body, and the dens.
Age Changes in Internal Bone Structure
Two structural components are studied that is:
• Cancellous Tissue
For studying this, humerus and femur are mainly considered, and out of the two, humerus is used on a priority basis. The methods used are a radiological examination of bones and a longitudinal section of bones in which the resorption pattern of cancellous tissue is examined. The proximal end of the medullary cavity of the humerus assumes a cone shape, the tip of which gradually reaches the surgical neck of the bone during the period of 40-50 years and further ascends to the epiphyseal line by 60-75 years.
• Cortical Tissue
The cortical elements osteon, osteon fragments, lamellar bones, and nonhaversian canals are studied microscopically and the age could be ascertained within the margin of 5 years. By counting the osteons in the cross-section of bone, the age can be ascertained but it is not an accurate and reliable method.
