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Degenerative disease

Osteoarthritis is among the oldest and most commonly known diseases afflicting humans. Measuring the amount of arthritic involvement with skeletal remains is sometimes difficult because of the potentially large number of areas to be assessed (each vertebra and all joint systems) and the range of variation in bony response among individuals (Figure 2.6). While many factors may contribute to the breakdown of skeletal tissue, the primary cause of osteoarthritis is related to biomechanical wear and tear and functional stress (Ortner and Putschar 1985). Biomechanical stress is most apparent at the articular surfaces of long bone joint systems and is referred to as degenerative joint disease (DJD). The patterning of DJD has been linked to behavioral factors, and individuals who habitually engage in activities that put strain on the joint system are more likely to demonstrate a breakdown in bone (Merbs 1983). There also may be a relationship between DJD and other health problems.

DJD is generally defined by changes in the articular surface areas of joint systems. Following the exposure of subchondral bone, the articular surface regions become pitted, with marginal lipping and erosion; eventually eburnation takes place. Eburnation is the formation of a very hard callus on bone surfaces that are rubbing together without being cushioned by lubricating fluids. DJD is not an inflammatory disease but develops with age and the breakdown of the cartilage and lubricating system. The condition is slowly progressive but is not found to occur in all older adults in the same form. Thus, the condition probably is the accumulation of years of alterations of the articular cartilage and breakdown of the joint and occurs with extreme variability across individuals. Lifestyle and activity play an important role in either buffering an individual from arthritis or enhancing the chance that the condition will appear. For instance, a professional athlete may begin to exhibit DJD at a far younger age than an individual who does not engage in consistent rigorous exercise and activity. The weight-bearing joints such as the lower back, hip, and knees and those exposed to chronic trauma such as the shoulder and elbow are most frequently affected (Jurmain 1991). The pattern, distribution, severity, and onset by age class and sex in adults can be used to interpret the role of cultural activity, as well in the overall understanding of quality of life for individuals within the community.

Vertebral osteophytosis is a form of degeneration that is characterized by lipping (extra bony growths usually in long spikes) on the vertebral bodies. This has been associated with changes in the intervertebral discs. Commonly found in ancient and modern populations, this degeneration typically begins at 30 years of age and affects almost all individuals by the age of 60. The lipping may range from a slight sharpness to complete fusion of contiguous vertebral bodies.

For analysis of the bony response to biomechanical wear and tear on both joint systems and vertebral elements, we scored for two basic morphological characteristics. These include the bony growth of osteophytes (hypertrophic osteogenesis) and the destruction of the joint surface (macroporosity and bone breakdown; Mann and Murphy 1990). On both joint systems and vertebral elements, the degenerative changes occur on the joint surface (where two bones articulate), the areas that are contiguous with but peripheral to the joint, and on various parts of the bone that come indirectly into contact with other bones in the movement of joint systems (such as vertebral spines and processes and various fossae and landmarks on long bones).

The systematic assessment of DJD and vertebral osteophytosis can provide an indicator of lifestyle and work habits in ancient populations. However, clinicians working in the area of gerontology and arthritis today caution the direct correlation of osteoarthritic changes and pain and dysfunction (Jurmain 1999). Any morphological changes less than total fusion of vertebral bodies or joint systems cannot be directly linked to inability of individuals to function nor can severity of osteoarthritis be linked directly to habitual use of the body in certain occupations (Merbs 1983).

 
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