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Class Notes: Human Osteology

Thursday: January 5, 2012

Week 11: Paleopathology

Tuesday:

The study of ancient skeletal alterations due to processes that are deleterious to health is known as paleopathology. Paleopathologists use differential diagnoses; that is, they list all the possible causes for what is observed on the skeleton, then rule out cases and narrow in on the likely cause. Unlike medical practitioners who rightly treat the individual rather than observing the bigger picture, bioarchaeologists examine the pathological evidence within the scope of the entire population and track the history of diseases. Therefore, the study is epidemiological and correlates human action with disease. That is, do certain cultural traits promote or hinder pathological conditions? The study is limited however: there is no communication between the affected and the examiner as in the medical field; there is no evidence of soft tissue involvement (unless in the rare cases of mummies); and chronic diseases are better understand rather than acute ones, which would have killed the afflicted before the skeleton had time to react in the diagnostic ways.

There are several classifications of paleopathology that can be recorded in a skeleton. These are: arthritic changes; trauma; infections; tumors/neoplasms; and congenital, metabolic, endocrine, and circulatory disorders.

A readily observable pathology is that of arthritis, otherwise known as osteoarthritis or degenerative joint disease. In fact, it is the most common condition found in ancient bones and results from activity-related breakdown of the synovial joints. As the cartilage protecting the joint wears down and disintegrates, the end of one bone will contact the end of another. Bone, being a living tissue, will react first with resorption (seen as pitting), then the bone will expand the joint to disperse the stress (seen as lipping, or extra growth of bone), and followed by eburnation (when the bones physically polish each other to a shiny sheen). Furthermore, some lipping can become extreme and fuse the joint together (ankylosing, or stiffened joint) – a trait seen in toes commonly, I’m told. Typically, this type of reaction is from secondary arthritis, or that cause from a traumatic event. Lipping of the spine has a special classification and is known as osteophytosis (osteoarthritis is a term used strictly for synovial joints; therefore a vertebra may have osteoathritis on the zygopothesis and osteophytosis on the body). Generally, arthritis is age related and the pattern shown on a skeleton can give evidence of activities. For instance, a population with a high percentage of arthritis showing its effect on left shoulder + right knee may mean that percentage of people were doing a similar activity – other clues found through archaeology or history can aid in interpretation. So it has been documented then that agricultural populations tend to show less arthritis than pre-agricultural groups (though not always) and that Eskimos show the highest levels of arthritic changes proving the intensity of their labor in such a harsh environment.

Trauma is the second most common pathology recorded. Patterns found in the fractures of bone indicate terrain topography, occupation activities, violence, and disease. Colle’s fractures (distal end of the radius) are associated with falling (when you throw your arm down to stop yourself) – high percentages likely related to the type of terrain. On the other hand, parry fractures (found on the unla) are associated with self-defense (when you throw your arm up to block something from hitting your head). In that same vein, depressed fractures of the skull often are interpreted for violence but these can also be caused by falling. Pseudoarthritis is also found in the archaeological record – a pathology resulting from a broken bone which never heals together but rather heals apart, creating a false joint. Collapsed vertebrae and vertebral psuedoarthritis are other forms of trauma that is related to disease and will be covered later.The rates of healing and correct versus incorrect alignment are taken into account to interpret medical skill/knowledge/technology of past populations as well.

Speaking of medical knowledge, some populations extensively used trepination and it is thought that they understood this would relieve endocranial pressure. Trepination is when a part of the skull is removed – either through drilling, cutting, or scraping. Fascinatingly, 90% of known trepination cases shows healing which means that the individuals were surviving this type of surgery without modern tools, medicine, or even anesthesia!

Thursday:

Some pathology can share resemblance with osteoathritis. The first is Diffuse Idiopathic Skeletal Hyperostosis, or DISH for short. It’s cause is still unknown and tends to occur in older male adults (those beyond 50 years). It involved fusion of four or more consecutive vertebral bodies, but does not affect the zygopotheses or the cortovertebral joints, nor does it affect the sacroilliac joint. It also preserves the intervertebral space (between each vertebral body). DISH involve excessive bone growth along the anterior longitudinal ligament – so much boney growth that it has been likened to a melted candle stick.

Ankylosing spondylitis is similar but note the differences. It affects almost only males who are young (under 40 and as early as childhood). It effects all parts of the vertebrae and can create fusion with the sacroilliac joint. The annulus fibrous between each vertabrae ossifies, syndesmophytes grow (similar to osteophytes) and complications can make this disease fatal.

Sometimes confused with gout, rheumatoid arthritis is different than osteoarthritis because instead of being related to age and activity, it is an autoimmune disease. Found mostly in females, it affects the hands and knees most commonly. Because it is inflammatory in nature, it causes osteoporosity and cyst formation. It can also lead to ankylosing of a joint.

Gout, on the other hand, is caused by the buildup of uric acid and typically is found in people over 40 years old. Sodium urate crystals can inflame the bone and cartilage. Because it also affects the hands (and commonly the feet), it can be mistaken for rheumatoid arthritis. However, the pitting created by gout can be huge – up to an entire centimeter whereas rheumatoid arthritic pitting is typically only a few millimeters in diameter.

Infection conditions are caused by an external pathogen, which is almost always microbial (parasitic infections from worms is another form). Viruses, bacteria, and fungi can all infect an individual, wreaking havoc on the body and leaving scars on the skeleton. The most easily recognized infections are caused by bacteria though. Periostitis and osteitis are terms used for when there has been evident periosteal reaction to something, but that something is too vague to diagnose (in fact, it may not have been caused by an infection at all).

One of the most prevalent bacterial infections recorded in bioarchaeology is that of tuberculosis. TB has been impacting human lives for thousands of years – dating back 2000 in India, 5000 in Egypt, and up to 9000 in Europe. Contrary to popular belief, it did exist in the Americas before “contact”, although it was rare. Caused by Mycrobacterium tuberculosis, this pulmonary disease (involving the soft tissue of the lungs) will eventually spread to the inside surface of the ribcage and the spine in chronic conditions. Thoracic vertebrae can show smooth walled pitting, which leads to collapse. If TB progresses this far and the verts show this characteristic wedging, it is known as Pott’s disease. TB often causes changes within the midface as well, resorbing the bones around the nasal aperture and sinuses; it can also affect the knees and hips. TB proves an important case for considering the osteological paradox: for TB to be seen on the skeleton, the individual must have lived a long time with the illness in a chronic state. Therefore, when the skeleton is studied, how should that individual’s health be considered? Surely being able to survive the disease long enough to have skeletal changes means your body was more robust against it than the person who died quickly before these changes occurred, leaving a healthy looking skeleton. But alas, there is no way to know if that healthy looking skeleton belonged to an individual who even ever had TB to begin, so perhaps that person may have indeed been healthier. Or perhaps they did both have it, but they suffered from different strains of M. tuberculosis with different virulences. At this point, with DNA studies few and far between due to preservation and resources, who can say. The osteological paradox just needs to keep a researcher on their toes and not leap to interpretations.

Moving on, another common infection found in the bioarchaeological record is that of osteomyelitis.It is a favorite for researchers because the bacteria acts upon the human body today just as it did in the past so it is easily diagnosed in skeletons. It is cause by Staphylococcus aureus bacterium – aka the well known Staph infection. In fact, in recent times there has been a renewed interest in public media due to its drug-resistant form, MRSA (Methicillin-resistant or multidrug-resistant S. aureus). The bacteria on the skin spreads to the bone in the local area of infection due to a build up of pus formation. This can cause a resorptive reaction of the bone, creating lytic lesions. In fact, the bone often reacts so intensely that it literally tries to cut out the infection. Bone resorbs around the infection, boring a hole (termed cloaca) through to the medullary cavity, thus leaving an island of affected bone in the center (the sequestra) . The healthy bone reacts by building up around the hole, forming what is known as an involucrum.

Yikes, right?

Friday:

Another infectious disease common to the archaeological record is  treponemal disease. It has two forms: syphilis (a sexually transmitted disease) and congenital (mother-child at birth). This too has been rumored to not have existed until the time of “contact” but archaeology has proven this not to be the case. Because the illness is slow, it is a chronic condition which leaves evidence on the body in the same manner as TB. Tibias will show a pronounced apposition of bones along the anterior crest, giving the saber shin appearance. This differs from that of rickets- the bones do not bend, but merely appear so. A skull will show lytic lesions in a diagnostic stellate shape, which sometimes progresses into pitting with bump formations, known as caries sicca. If a child contracts the disease during gestation or at birth, it can affect tooth formation. This results in characteristic Hutchinson’s incisors (notched edge) and mulberry molars (where the cusps are poorly developed).

Metabolic diseases are also recognized in past populations. For instance, a vitamin D deficiency can lead to rickets in children, or osteomalacia if extended into adulthood. A lack of vitamin D disrupts the roles of calcium and phosphorus in the body, which means that the rigidity of bone is lessened. Particularly in weight bearing long bones, this causes bones to bend, giving the characteristic bowed leg effect. It is common in people with terribly poor diets, and also in areas with low sunlight, as the sun triggers skin to produce the vitamin. Interestingly, low sunlight is not just an effect of where you are in the world (less light further from the equator, and the problem is exaggerated with darker skin colors), but also the culture. Industrializing cities with long days spent in factories, or religious communities that prefer clothing that covers much of the skin can both be causal factors for rickets and osteomalacia.

Porotic hyperostosis and cribra orbitalia are two other commonly found metabolic diseases, involving what is thought to be a response to low iron levels. PH affects the outer table of the crania, resorbing until the diploe is exposed, giving a “hair-on-end” appearance. CO, on the other hand, affects the orbital roof, sometimes growing spicules.Both are non-specific; that is the cause is unknown. Are the iron levels low due to a poor diet, a parasitic infection, a congenital susceptibility, a protection from worse symptoms, all or none of these? What is known, however, is that they are diseases of childhood. This is because the role of bone in blood production lessons with age and therefore both PH and CO are typically scored as healing/healed in adults.

Briefly covered were some congenital disorders. Pituitary gigantism results from a tumor of the pituitary gland. Because it begins in children prior to fusion of all the epishyses, the body will grow porpotionatly. Also affected is the shape of the sella turcica, or the boney saddle that the gland sits in, which will be enlarged and diagnosable. In addition, gigantism is hard to miss – in the archaeological record, people have been found to have grown 8 feet tall. A more common form of gigantism is that of acromegaly. Because of its later onset, fusion has already been taking place. This leads to only some bones allowed the extra growth: the mandible, clavicle, ribs, etc. You can recognize this form on “smaller giants”, with big chins, wide shoulders, and heavy brows. The opposite of these is achondroplastic dwarfism. It occurs when the growth plates do not form correctly, causing early fusion. It only affects endochondral bones, which is why people affected with this disorder will have a normal size torso and head, but shortened limbs.

And to round things out, a few mischellaneous bits. Myostitis ossificans is a mineralization of tendons at the muscle attachment point. It can form as a result of trauma, which need not be particularly detrimental, or it can from as a result of a congenital disorder which can be more severe, limiting movement and such. A button osteoma is a benign bone tumor. It is fairly common – you may know someone who has one. It is simply a small button-like growth on the skull. Feel around your own head, maybe you even have one yourself!

 

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