A New Method to Measure Congruence of the Thumb Carpometacarpal Joint: Maximum Contact Area Criterion

A new criterion based on maximum contact area is proposed to describe the congruence of the thumb carpometacarpal (CMC) joint. An optimization algorithm was developed to calculate the maximum contact area of the CMC joint based on the articular surface topography, and using a proximity-based contact area determination. The relationship between the maximum contact area and curvature-based congruence index defined in a previous study (Ateshian et al., 1992) was investigated using 17 human thumb CMC joints with an average age of 70 years. The results showed that the maximum contact area criterion gave consistent congruence measures of saddle surfaces compared to the curvature-based congruence criterion. The results also indicated that the five male specimens had a greater maximum contact area (74 ± 11 mm2) than the twelve females (49 ± 9 mm2) at a significance level p < 0.05. This disparity is believed to contribute to etiologic factors which lead to a greater incidence of CMC osteoarthritis in females over the age of 45.