The prehensile ability of the human hand is largely due to the function of the unique saddle-shaped, multi axial carpometacarpal joint (CMC). This joint is commonly afflicted with debilitating osteoarthrosis (OA). Epidemiologic studies show that CMC joint OA is more prevalent in women, occurring in 116 of women older than 45 yrs. No basic study has been conducted to determine the details of biomechanical, biochemical and anatomic factors important for the cause of CMC joint OA, thus creating a significant gap in the literature. The hypotheses of this study relate specifically to joint anatomy, CMC joint cartilage material properties and biochemical composition: 1) CMC joints of females are less congruent than that of males. Also, other female and male anatomical differences exist, e.g., distribution of cartilage thickness (maps) over the joint surface. 2) CMC joint congruence changes with age, with the female joint becoming more incongruent than the male joint. 3) The material properties and biochemical composition of CMC joint cartilage vary with site, gender and age, and that the variations in joint congruence correlate with cartilage material properties and biochemical composition. 4) Due to subchondral bone remodeling, joints which show evidence of OA become more congruent than normal healthy joints. 5) Changes in cartilage material properties and biochemical composition associated with radiographic evidence of OA are more accentuated in the high load-bearing regions of the CMC surface than in the low load-bearing regions.
The specific aims have been designed to test these hypotheses. Three studies will be performed to test these hypotheses. Study A will focus on young (20-39 yrs) and middle-aged (40-59 yrs) non-OA samples, Study B will focus on middle-aged and old (60-79 yrs) OA samples, and Study C will be performed on OA and non-OA samples from middle-aged population to assess the effects of OA on joint topography, material properties and composition. In each study, experiments will be performed to determine: l) the precise topographies and curvature characteristics of the articular and calcified cartilage-subchondral bone surfaces using stereophotogrammetry; 2) the joint congruence index using principles of differential geometry; 3) a thickness map for each cartilage layer; and 4) cartilage material properties and biochemical composition. Statistical correlations will be made to determine: l) the effects of age and gender on these characteristics of normal CMC joints (Study A); 2) the effects of age and gender on the development of OA in CMC joints (Study B); and 3) the effects of OA on these characteristics of CMC joints (Study C). Thus, we will be able to contrast topographic, material and biochemical factors in young normal (controls), aging and OA in male and female joints. Using our new Silicon Graphics workstation, a procedure for """"""""least-square-error mutual surface overlays"""""""", similar to our contact area determination procedure, will be used to explore """"""""how accurately the two surfaces [could] potentially mate with one another."""""""" Interrelations between cartilage biomechanicaI properties and biochemical composition will be investigated and quantified with respect to the high and low load bearing regions within the joint.
