Individual Skeletal Variation Notes

Individual Skeletal Variation

12.1 Principles of Skeletal Variation

Individual skeletal variation exists due to different genetic and environmental influences.
An individual's skeleton contains idiosyncrasies or individual variations in configuration or morphology.
These variants may be congenital, developmental, degenerative, or may result from disease processes or trauma.
Skeletal variation can provide valuable information for personal identification in forensic anthropology (Chapter 14).
Individual variants can reveal features of an individual’s health, lifestyle, or life history.
Rare individual variants may be useful for personal identification comparisons.
Certain conditions (e.g., those requiring medical treatment) increase the chance that a record may be available for comparison.
Skeletal variants or conditions (e.g., fatal diseases or injuries) may provide information relevant to circumstances surrounding death.
Forensic anthropologists should be familiar with possible skeletal morphological variants to avoid confusing them with trauma or taphonomic alterations (Chapter 13).
All variants discussed in this chapter result from in vivo processes (occurred while an individual was living).
Traumas are typically associated with fractures and recently exposed internal bone surfaces, whereas individual variants typically have a different appearance and bone quality.
A working knowledge of individual variants combined with a conservative analytical approach should prevent or minimize confusion with trauma or taphonomic alterations.
Individual skeletal variations typically fall into one of four categories:
- Normal anatomical variation
- Skeletal anomalies
- Pathological conditions
- Skeletal changes related to repetitive mechanical stress
The final conclusion as to which variant or condition is present on skeletal remains is ideally achieved through a process called differential diagnosis (Figure 12.1).
Differential diagnosis is a deductive process of elimination used to narrow down and identify a likely condition or a small number of possibilities that cannot be excluded.
A differential diagnosis begins with a description of the type of variant (i.e., normal, pathological), its location (i.e., the name of the bone or bones involved), and distribution (i.e., how much and which part or parts of the bone or bones is affected).
Additional descriptive information may include bone quality and radiologic appearance.
The diagnosis then proceeds by ruling out conditions that are inconsistent with the observations.
This may involve comparison with published clinical and research literature or exemplars such as photographs, casts, or documented pathological specimens.
If the condition is present on a paired bone or tooth, the normal antimere (the same bone or tooth from the other side) can be used as a reference.
Differential diagnosis of a particular skeletal variant or condition is not always possible.
In many cases, specialized methods such as radiology, stereomicroscopy, scanning electron microscopy, and histology may be useful.
When a differential diagnosis cannot be made, a detailed description of the variant including its pattern and distribution is recommended.
The analysis of skeletal variants should be amply supplemented with notes, diagrams, photos, etc., and all reasonable interpretations should be presented.

12.2 Normal Skeletal Variation

Normal skeletal variation refers to the range of morphological expression commonly observed in various skeletal regions.
Examples include differences in paranasal sinus configuration, cranial suture pattern, trabecular bone pattern, and external bone contour.
These features and characteristics are all present in normal bone anatomy but show differences between individuals.
Because these features are present in almost everyone and because they tend to show so much individual variation, they are often studied for their potential to facilitate personal identification (see Chapter 14).
Paranasal sinus shape is one example of a normal anatomical variant, with the frontal sinus being the most thoroughly studied in terms of its individual variation.
To a lesser extent, the individual variation in maxillary sinuses has also been studied, particularly in relation to uses in personal identification.
Because they are located within the cranial bones, the sinuses are usually only visible radiologically, which can reveal the dimensions, placement, configuration, and outline shape of the sinuses.
In traditional 2D radiographs, the variations in frontal sinus shape are quite apparent in an anterior/posterior view (Figure 12.2).
CT scanning is also an excellent method for visualizing the paranasal sinuses since the three-dimensional configuration can be seen (Figure 12.3).
Frontal sinuses usually appear as two irregularly shaped, asymmetric cavities that project a variable distance into the frontal bone.
Although some changes in adulthood have been noted (due to, for example, trauma, disease, or bone thinning with age), they typically complete growth by around age 20, after which their shape is stable.
The variation in frontal sinus shape has been attributed to various factors including craniofacial configuration, hormonal factors, biomechanical factors, genetics, ambient air pressure, or unknown factors.
The bones of the cranium join together along cranial sutures.
During the growth process, the margins of the bones of the cranium develop projections and recesses that eventually interlock with each other, resulting in suture lines that are jagged and seam-like on the ectocranial surface (remaining relatively straighter and less remarkable on the endocranial surface).
Because the growth of cranial bones is controlled largely by external stimuli (particularly neurocranial growth), cranial suture patterns are highly variable, and the inherent complexity of these projections and recesses (which are largely random) results in a nearly infinite number of possible patterns (Figure 12.4).
The exact paths of the lines, therefore, vary from person to person and have been shown to be highly individualistic; in fact, bilateral suture patterns within the same individual are also different (Sekharan, 1985).
It is also possible to quantify the variation in these patterns by examining the location, length, and slope of the lines of a suture’s components (Rogers and Allard, 2004).
Bone’s internal trabecular structure, which is visible radiologically, is also highly variable.
Normal internal bone structures have a nearly unlimited number of combinations of radiologically discernible features that show variability, including radiolucent vessel foramina and radiodense lines (Figure 12.5).
Although there is a normal overall pattern to bone’s external shape and contours, individual variation in these surfaces has also been demonstrated.
Sites studied include the clavicle and cervical spine, thoracic and lumbar vertebrae, and the hyoid.
Some studies have involved the examination of individual variation in multiple features such as external morphology/contour as well as trabecular patterns.

12.3 Skeletal Anomalies

Skeletal anomalies are characteristics that are considered deviations from normal skeletal anatomy, though they may not necessarily be rare or unique.
Anomalies are typically a product of disturbances to developmental fields at critical periods during morphogenesis, resulting in deviations from the normal outcome.
Anomalies may be caused by disturbances from genetic mutations, maternal conditions, exposure to detrimental environmental conditions, or nutritional disorders during a particular developmental event.
These variants are also sometimes called nonmetric (i.e., qualitative) or epigenetic variants.
Examples of skeletal anomalies include accessory or supernumerary (extra, or more than the normal number) bones or teeth, accessory foramina, and nonfusion anomalies.
Note that many accessory foramina and some accessory bones are technically the result of nonfusion anomalies, but certain cases will be addressed here as separate types of anomalies.
An accessory facet occurs when two bones articulate in a location in addition to their normal articulation.
Accessory bones can occur in many parts of the skeleton.
Examples of more commonly encountered accessory bones include having extra vertebrae, ribs, sesamoid bones, and cranial vault bones (for example, small bones located within sutures).
Other “extra” bones that are technically unfused portions of parent bones will be addressed with nonfusion anomalies.
Supernumerary vertebrae typically appear as transitional vertebrae at the thoracicolumbar, lumbosacral, or sacrococcygeal borders, with extra vertebrae at the cervical-thoracic border being extremely rare.
When an extra vertebra is located in the thoracic region, it is typically also associated with extra ribs.
In a forensic context, it may be difficult to detect the presence of a supernumerary vertebra or ribs unless the skeleton (or at least the thorax) is relatively complete.
Rather than complete extra vertebrae, sometimes a partial vertebra, or hemivertebra, is present, often resulting in misalignment of the spine (Figure 12.6).
Sometimes a vertebra takes on characteristics of another segment of the spine, a phenomenon called a vertebral shift.
For example, a 12th thoracic vertebra may have lumbar-like characteristics (articular facets, body shape, etc.), sometimes even resulting in the fusion of the 12th rib pair, which often appear as rudimentary structures (Figure 12.7).
Sesamoid bones are bones that are located within tendons where they pass over joints.
The patella and the pisiform are sesamoid bones, which are part of normal skeletal anatomy, but sesamoid bones can also be commonly found in other parts of the hand, particularly around the distal first metacarpal (Figure 12.5), and the foot, often at the junction of the first metatarsal and the first proximal pedal phalanx.
The number of sesamoid bones in these regions typically varies between zero and two.
Extra bones also occur in cases of accessory appendages.
Polydactyly (or polydactylism), for example, is the condition of having extra fingers or toes.
It is considered the most common congenital digital anomaly of the hand and foot and can occur either as part of a syndrome or in isolation.
Although rarely complete and functioning digits, accessory fingers and toes often do contain bones which may occur with or without joints.
They most commonly occur on the ulnar (little finger) side of the hand but can also occur on the radial (thumb) side.
Like accessory vertebrae, the identification of polydactyly in skeletonized forensic cases may be difficult unless the remains are complete, although in some cases it can be recognized by the shape of the adjacent metacarpal or metatarsal which may be broadened or bifurcated.
Another common location for accessory bones is along cranial sutures, where they are called extrasutural bones.
These tend to occur most often along the lambdoidal suture where they are also called Wormian bones but can be found along any suture of the cranium and are typically small and irregular in appearance (Figure 12.8).
Certain configurations occur regularly and have been studied more often including Inca bones, or os incae (so named because they were first studied in Peruvian crania), defined as a division of the squamous portion of the occipital bone (Hanihara and Ishida, 2001).
Inca bones typically appear as a single, large, triangular ossicle, but can vary in their divisions and number of extra ossicles.
While not an extra bone, hyperplasia (i.e., an increased amount of tissue) from the developing ossification centers in the maxillae or mandible can result in a unilateral torus or bilateral tori.
Tori can be found on the palatine process of the maxillae or the lingual surface of the mandible and can vary in size (Figure 12.9).
While these first occur during development, they can grow larger throughout adolescence and adulthood.
In the dentition, supernumerary teeth sometimes occur, a condition referred to as hyperdontia (Figure 12.10).
Extra teeth can occur anywhere within the oral cavity, but are most common in the anterior maxillary dentition, and more often found in permanent than primary dentition.
They typically result from anomalies in dental development and although they can be asymptomatic, they often lead to clinical problems such as failure of eruption, displacement, crowding, and pathology.
Accessory foramina (or extra holes in bone cortices where they typically would not be found) are seen in a number of locations throughout the skeleton including the cranium, long bones, and sternum.
They are commonly the result of nonfusion or incomplete fusion during skeletal development.
Perforations in bone can also result from trauma such as gunshot wounds, and taphonomic processes such as carnivore scavenging or weathering.
They should therefore always be assessed carefully to differentiate skeletal anomalies or conditions from those that result from other events or processes.
When there is incomplete ossification of the bony septum that separates the olecranon fossa from the coranoid fossa of the distal humerus, a septal aperture (sometimes also called a supratrochlear foramen) may be present (Figure 12.11).
This trait tends to occur more frequently in females, more often on the left side, and may be associated with joint hypermobility.
Although a septal aperture is expressed as an in vivo condition, a perforation in this region of typically thin bone can also result from taphonomic damage.
Nonfusion anomalies result from a failure of union between two ossification centers and can occur in virtually any part of the skeleton.
The result can be a cleft or perforation in the bone, or accessory bone portions.
They may be developmental anomalies but may also be linked to pathological conditions including trauma.
In cases where nonfusion may result in accessory bones, it is especially important that these regions are carefully assessed to differentiate them from traumas.
In forensic contexts, the failure to recover these (typically small) unfused portions can make the diagnosis particularly challenging.
Occasionally a hole is seen in the sternum, called a sternal foramen (Figure 12.12).
The sternum ossifies from a number of ossification centers, and a sternal foramen can result from incomplete union of any number of the sternebrae segments.
It is usually seen in the inferior sternal body but can also occur in the xiphoid process.
Although potentially mistaken for trauma (such as a gunshot wound) at first glance, careful inspection of a sternal aperture will reveal well-organized, mature bone and an absence of fractures around the margins.
Cleft neural arch occurs when the two sides of the neural arch of a vertebra fail to unite (Figure 12.13).
It typically affects only one or sometimes two presacral vertebrae and can range in appearance from a slight bifurcation of the vertebral laminae to cleft laminae with or without the spinous process, and can even involve complete aplasia of one-half of the neural arch.
Spina bifida, a defect of the developing spinal cord, also disrupts neural arch development, but can be distinguished from a cleft neural arch by its widened vertebral canal, distorted pedicles, and involvement of more than two presacral vertebrae.
Spina bifida occulta is a less severe, often asymptomatic, form of spina bifida (Figure 12.14).
The scapula has a number of secondary ossification centers which can fail to unite, resulting in additional ossicles.
The lateral end of the acromion process is a common location for nonfusion, resulting in a condition called os acromiale, where the lateral portion of the acromion is a small separate bone.
A bipartite patella, or segmented patella, occurs when the ossification centers of the patella fail to coalesce.
It usually appears as a notch in the superolateral border of the patella.
The smaller, separated ossicle may eventually partially unite, may be connected only by fibrocartilage, or may fail to ossify at all.
Nonfusion anomalies in the cranium often occur when parts of the cranial bones fail to coalesce prior to ossification, resulting in two ossification centers for the bone.
While extra sutures can arise in the parietals or occipital, the most commonly observed location is the frontal bone.
In normal growth and development, the frontal bone begins as two halves which unite along the midline or the metopic suture.
This union normally occurs by around age four with the suture line becoming completely obliterated, but occasionally the two halves fail to completely unite, resulting in a condition called metopism, or the retention of a visible metopic suture into adulthood (Figure 12.15).
The suture typically has the appearance of the other normal sutures of the cranium.
This feature also tends to show population differences, being more commonly seen in those of European ancestry.
Facial clefts such as cleft palate are also nonfusion anomalies and tend to result in significant facial deformities.
Another type of nonfusion anomaly is a pseudarthrosis, or “false joint,” which is created when two fractured portions of a bone fail to reunite.
It can result from repeated disruption of the fracture callus which impedes mineralization.
When a fracture occurs in infancy and fails to unite, it is referred to as a congenital or infantile pseudarthrosis.
While congenital pseudarthrosis can occur in any long bone in the body, it is most frequently seen in the tibia, is typically unilateral, and will usually also involve the fibula of the same limb.
It may be associated with disease, hereditary, or mechanical factors.
Another example of a common nonfusion anomaly at a fracture site is spondylolysis, also known as pars defect.
In this condition, the posterior portion of the neural arch is separated from the rest of the vertebra at the pars interarticularis (Figure 12.16).
Although sometimes attributed to a congenital defect, it most often results from a stress-fatigue fracture from low-grade repetitive stress in the lower back.
While it has been known to occur in any thoracic or lumbar vertebra, it is most common in the lower lumbar region, particularly at L5.

12.4 Pathological Conditions

Pathology refers to the study of disease, and a pathological condition is the abnormal anatomy which is a manifestation of a disease process.
These disease processes may be the result of infection, injury, or a disorder.
Not all diseases affect the skeleton, of course, but when they do, they manifest as localized bony alterations that are called lesions.
Pathological lesions on bone may be proliferative, lytic, or deformative.
Proliferative (or osteoproliferative) lesions are those that are characterized by excess deposition of bone, while lytic (or osteolytic) lesions involve a loss of bone.
Deformative lesions involve changes in overall bone shape.
As with other skeletal variants, pathological conditions and lesions must be examined carefully to distinguish them from other types of skeletal conditions that may be the result of traumatic or taphonomic processes.
Proliferative lesions are typically not confused with possible taphonomic alterations; naturally, in order to produce additional bone, the individual must have been alive.
Lytic lesions, on the other hand, may require closer examination since both pathological and taphonomic processes can both result in destruction of bone.
Likewise, bone deformation can be an in vivo process, but can also result from traumatic forces and taphonomic processes such as warping.
Certain pathological conditions, particularly some diseases, may provide information regarding medicolegal significance.
For example, certain diseases were much more prevalent in ancient or historic contexts and are rarely seen in modern populations due to improved hygiene and healthcare.
Proliferative lesions result from increased osteoblastic activity as a reaction to a disease (Figure 12.17).
They may involve a localized increase in bone density (osteosclerosis), or the projection of bony processes from the normal bone anatomy.
Common proliferative lesions include those that are associated with infections of the bone, or osteomyelitis.
Abnormal bone formation on the outer surface of a bone is commonly referred to as subperiosteal new bone formation (SPNBF), or as periostosis or periosteal reaction.
This bone formation often arises due to inflammation of the periosteum (often called periostitis) (Figure 12.18).
Inflammatory processes affecting the inner bone structures and the medullary cavity are called osteitis.
Some proliferative lesions are the result of ossification of other soft tissues such as cartilage and muscle.
With increasing age, many cartilaginous regions have a tendency to become calcified.
One such region is the costal cartilages (Figure 12.19), and as was discussed in Chapter 8, the pattern or progression of this ossification tends to vary between males and females.
In some cases, the attached connective tissue can become ossified in response to a trauma by producing bone directly within the soft tissue.
Generally, the condition is called heterotopic ossification (Figure 12.20); however, specifically in muscle the condition is called myositis ossificans, and in tendons is called ossific tendonitis.
This excess bone growth may be completely separated from the bone, or may become part of the bone, often appearing as a bony projection.
Diffuse idiopathic skeletal hyperostosis (DISH) is a pathological condition which results in proliferative ossification, primarily affecting the vertebral column and involving the ossification of the anterior longitudinal vertebral ligament (Figure 12.21).
DISH can often lead to the ossification of other connective and cartilaginous tissues including the thyroid (Figure 12.22) and cricoid which are cartilaginous laryngeal structures of the neck.
Other conditions can also result in the ossification of the laryngeal structures later in life, but the process is not strongly correlated with age.
Other proliferative lesions also take the form of bony projections.
Osteophytes are bony projections that form at the margins of joints and signify joint damage.
They are often associated with degenerative joint disease (also called osteoarthritis) and other degenerative joint conditions in older individuals.
Osteophytes are commonly found along the spine (Figure 12.23) but can be found in virtually any joint in the body (Figure 12.24).
Enthesophytes are bony projections that form at the site of ligament or tendon attachments (i.e., entheses) (Figure 12.25).
Osteoarthritis can also be associated with the wearing away of joint cartilage, exposing subchondral bone and resulting in the eburnation of joint surfaces, a form of sclerosis that gives the bone a hard and dense quality and sometimes a shiny surface.
Primary bone neoplasms (or tumors) are those that arise in bone and can result in prominent proliferative lesions.
Osteosarcoma, for example, can form prominent bone spicules or have the appearance of cauliflower.
Button osteomas are typically small benign growths found on the cranial vault (Figure 12.26).
If the nerve supply to a bone is damaged (often due to an injury), the lack of pain in that site can lead to continued use of the broken bone and affect healing.
The resulting exuberant bony response in these cases is called a Charcot joint (Figure 12.27).
Lytic lesions involve the destruction of bone.
The speed of bone destruction can affect the appearance of the lesion.
Lytic lesions that form very slowly will typically have reactive, normal density bone at their margins with more smooth or rounded margins.
If the pathological process destroys the bone more quickly, less reactive bone will form and the margins of the lesion will have more sharply defined borders.
These sharper borders could potentially be confused with trauma and should therefore be carefully examined.
Necrosis is a general term that refers to the death of any tissue.
In bone, necrosis (also called osteonecrosis) presents as a lytic lesion often resulting from a lack of blood supply to the bone.
This disrupted blood supply can result from a fracture or dislocation, especially in locations such as the shoulder, hip, and knee.
The resulting condition is called avascular necrosis which typically appears as a collapse or destruction of the joint surface.
Secondary bone neoplasms (also called metastatic tumors) are cancers that arise in other parts of the body and metastasize (spread) to the bone and are much more common than primary bone neoplasms.
In contrast with primary bone neoplasms which tend to produce proliferative lesions, many secondary neoplasms produce lytic lesions.
Examples include osteolytic sarcoma, metastatic carcinoma (Figure 12.28), and multiple myeloma.
A number of infectious diseases result in lytic bone lesions.
Brucellosis is an infectious disease that in humans presents as a chronic infection of the lungs and associated fever.
The disease also produces cavitating lytic lesions of the spine or sacroiliac joint (Figure 12.29).
It is rarely seen in modern populations, and its presence may suggest that the remains are ancient or historic rather than modern in origin.
Other infectious diseases including tuberculosis (Figure 12.30), leprosy, and syphilis also produce osteolytic lesions.
Osteoporosis (and its less severe manifestation, osteopenia) is a condition of lower than normal bone density.
Although these conditions also involve a loss of bone, they are not technically considered lesions since they are not localized.
Bones with osteoporosis and osteopenia retain the basic gross morphology of the bone but have a lower overall bone density and typically an associated loss in bone quality.
Prolonged immobility is also associated with a loss of bone density, as well as prolonged periods in low-gravity conditions of outer space, a condition referred to as spaceflight osteopenia.
Some lesions involve both proliferative and lytic processes.
These conditions, which normally result in proliferative periostitis, may also result in lytic necrosis if the bone in that area is deprived of blood supply and becomes necrotic.
In these cases, the dead bone can become separated from the surrounding bone and is called a sequestrum.
Hyperdeveloping reactive bone surrounding the sequestrum in the process of repair is called the involucrum.
Often there is an opening in the involucrum called a cloaca that allows debris and pus to leave the sequestrum.
One of the more widely studied pathological conditions in skeletal remains that involves both proliferative and lytic processes is porotic hyperostosis, or the porous enlargement of the bone tissue, which is often associated with megaloblastic and genetic anemias (for example, sickle-cell anemia and thalassemia) (Figure 12.31).
It is commonly seen in the skull as an enlargement of the diploe space, as the bone attempts to increase the available marrow space for increased red blood cell formation.
Radiographically, this condition has a moth-eaten or hair-on-end appearance.
When visible within the orbits, the condition often called cribra orbitalia (Figure 12.31).
Deformative lesions are those that involve pathologic changes in the overall bone contour or shape.
Some skeletal deformations may be the result of intentional cultural practices and are not considered pathological.
Examples include foot binding and head binding.
Others may be the result of trauma such as plastic deformation, or taphonomic processes such as warping.
Several skeletal deformities are recognized in the spine.
Lordosis refers to an abnormal degree of the inward curve of the lower spine (in the lordotic curve) resulting in a “saddleback” appearance.
Kyphosis is a condition of too much concave curvature of the thoracic spine (in the kyphotic curve) resulting in a “hunchback” appearance.
Scoliosis refers to lateral deviations of the spinal column from the midsagittal plane.
The factors leading to these deformations are varied, including compression fractures of the vertebrae, growth disturbances, or congenital defects such as hemivertebrae.
Inadequate bone mineralization caused by insufficient calcium and phosphorus can result in a softening of the bones due to defective mineralization called osteomalacia.
One common cause is a deficiency in vitamin D due to inadequate nutrition or any of a variety of disorders.
In adults it may lead to an increase in fracture potential, deformities of the pelvis, or lordosis of the spine.
In children (where the condition is called rickets) it can lead to significant bowing of the long bones (Figure 12.32).
Poliomyelitis (polio) is a viral disease that can cause paralysis and bone deformities.
Poliomyelitic paralysis affects bone growth and maintenance which can result in significant reduction in overall bone size (Figure 12.33).
Abnormalities of the development and fusion of the cranial sutures can result in the deformation of the cranium (Figure 12.34).
Craniosynostosis refers to premature fusion of the sutures of the cranium, resulting in significant cranial deformation because the normal growth of the head is altered.
The alteration of cranial shape depends on which sutures are involved and the age of onset, with the head typically expanding in the direction parallel to the closed suture.
The condition is also often associated with altered facial features.
Hydrocephaly is a condition involving the accumulation of fluid in the ventricles of the brain, usually causing an enlargement of the skull and a small face (Figure 12.35) and is typically associated with severe neurological symptoms.
Another form of skeletal pathology is a fracture, which may result in proliferative lesions such as calluses associated with healed fractures (Figure 12.36), lytic lesions such as necrosis from traumatic interruption of blood supply, or deformation such as misalignment from improper fracture reduction. Many of these conditions have been addressed in previous sections of this chapter, and fracture mechanics and healing are addressed in more detail in the next chapter. In addition to lesions at a fracture site, proliferative bone often forms around the sites of surgical implants (Figure 12.37).

12.5 Repetitive Mechanical Stress

Repeated mechanical stresses on the skeleton can cause the bones to adapt their morphology in response to these stresses.
These adaptations can result from work or cultural-related physical activities, but any repetitive skeletal stresses can produce changes in morphology, including those related to repetitive recreational activities or other frequent tasks or actions.
Examples of biocultural modifications include cradle boarding, dental wear, and other cultural activities performed repetitively.
Due to the many different types of activities that result in skeletal adaptations and modifications, it is not advisable to attribute any particular condition to a particular occupation or activity in forensic anthropological casework.
One adaptation to repeated mechanical stress is hyperdevelopment, or the increase in size of muscle attachments or the bone’s cortical area.
Many studies have demonstrated an increase in the cortical area of bones that are loaded in particular ways, especially in relation to various recreational activities and sports.
In addition, an increase in muscle size typically requires an increase in the size of the muscle attachment on the bone (larger muscles require greater surface area for attachment).
For example, well-developed deltoid muscles are often associated with pronounced deltoid tuberosities of the humerus.
If an activity is performed more frequently or more intensely on one side of the body (such as with a dominant limb), asymmetry can sometimes be seen in the size or shape of paired bones, with the dominant side being larger and/or more robust.
Various studies have examined the relationship between these asymmetries and handedness, but few have been successful in demonstrating good predictive value for forensic casework.
One reason for this is that the majority of people are right-handed (about 90%), and handedness therefore has relatively little importance in forensic applications.
Moreover, because of the prevalence of right-handedness, any method used to predict handedness must perform with a very high degree of accuracy in order to be useful; thus far, no methods have been found to perform satisfactorily.
Teeth also show signs of repeated mechanical forces including facets, grooves, notches, and attrition.
Occlusal attrition is typical with increasing age as the cusps become worn down over time from normal mastication forces.
This attrition can be more pronounced if the diet contains abrasive materials (either from the nature of the food itself or from methods used to prepare it).
Notches, grooves, and wear can occur from repeatedly holding things between the teeth or using teeth as tools.
This is commonly seen in long-term pipe smokers who hold the pipe between their teeth, also known as “pipe-mouth formation”, or seamstresses who hold needles between the teeth (Figure 12.38).

12.6 Case Study – Proliferative Lesions

In 2012, partially mummified human remains were discovered along a river bank in northern California.
The remains consisted of a complete skeleton of a White female, approximately 50–60 years of age.
The skeleton exhibited a number of individual variants such as ossification of costal cartilage, and several degenerative changes of the spinal column including osteophytic lipping of vertebral centra, eburnation and osteophytic lipping of articular facets, and ankylosis (fusion) of two pairs of vertebrae.
While the other variants of the vertebral column are relatively common among older individuals, ankylosis of vertebrae is somewhat rare.
Ankylosis was identified on C5 and C6 of the cervical spine, and on T5 and T6 of the thoracic spine.
Both fused pairs of vertebrae showed evidence of disc degeneration such as loss of disc height, bony bridging between vertebral bodies, and osteophyte projection beyond the normal anatomical margin (Figure 12.39).
This can result from trauma such as compression fractures of the spine, which is a common finding among older females with advanced signs of osteoporosis, or may also result from immune disorders which may be congenital.
Given the decedent’s age and the degenerative changes observed throughout the vertebral column, it is likely that the fused vertebrae are the result of disc collapse as opposed to a specific disease.
Identification of the skeletal variants in this case was relatively straightforward, but a precise diagnosis was more complicated.
In this case, the degenerative changes were an indication of relatively advanced age, and the ankylosis may be useful for identification if suitable medical records are available for comparison.

12.7 Case Study – Dental Anomalies

In 2012, decomposed remains were recovered from along a recently flooded river bank in northern California.
The remains consisted of a nearly intact skeleton of a Hispanic male, approximately 25–35 years of age.
Dental anomalies were identified including “winged” incisors and a supernumerary tooth (Figure 12.40).
Winged incisors are a dental feature involving a distinctive bilateral mesial rotation of the central maxillary incisors (making the incisor junction appear V-shaped in the occlusal view).
It is most often observed in individuals of Asian and Native American ancestry.
The extra tooth represented a rudimentary, nonfunctional tooth located distolingual to the left maxillary third molar.
Supernumerary teeth that form in this location are often impacted.
In this case, the tooth would likely have been considered impacted or unerupted and would have only been visible radiographically.
Dental anomalies such as these are relatively rare and can be useful in personal identification.

12.8 Case Study: Button Osteoma

An isolated bone fragment was found in a wooded area by geocachers (Figure 12.41).
Suspicious that it might be human, they contacted authorities.
The local police also were uncertain about the bone’s origin and requested assistance from an anthropologist.
They wanted to know if the bone was human in origin, and whether the “bump” on the bone was the reason for the person’s death.
The fragment was identified as a human cranial bone fragment, consisting of most of the frontal bone and part of the left parietal bone.
The margins were fractured, but the timing and cause of the fractures was undetermined.
The “bump” on the bone was identified as a button osteoma, and therefore was unrelated to the individual’s death.
Investigators were advised that this feature might be useful for identification since this feature is relatively rare, and may have been known to the individual and people they knew.
Since no other bones were recovered, no additional biological information could be provided.
A DNA sample was taken (from an area not affected by the button osteoma) and entered into CODIS, but the bone remains unidentified.

12.9 Summary

In addition to differences between sexes, across geographic groups, and throughout an individual’s lifetime, skeletal variation also exists on an individual level.
Skeletal variation can be useful for personal identification, and it is important to be familiar with possible skeletal variants so that they are not confused with