A quantitative method to measure maximal workspace of the trapeziometacarpal joint--normal model development

A reliable and quantitative method for measuring motion of the thumb is lacking. In particular, review of the previous methods of motion analysis of the thumb joints shows that there is no objective method for clinicians to assess the impairment of the thumb trapeziometacarpal (TMC) joint. Based on the concept of the three-dimensional (3-D) space within which the first metacarpal can move relative to the trapezium (a concept of defining and measuring the workspace of the TMC motion), we present a quantitative method for measuring motion and impairment (loss of function) of the TMC joint.

Twenty normal subjects were recruited in this study. An electromagnetic device was placed over the thumb metacarpal and long finger metacarpal, the 3-D relationship between them previously established. We measured the position and orientation of the TMC motion in space. Maximum movements of the thumb TMC joint in circumduction, flexion-extension and abduction-adduction were used to construct the 3-D maximal workspace of the TMC joint. Mathematical methods were used to verify the model and calculate the maximal workspace.

The results of this study demonstrate accurate and repeatable measurement of 3-D TMC motion with high statistical reliability and low variability of the maximal TMC workspace. A statistically significant linear correlation between the maximal surface area and the square of the first metacarpal length was obtained.

We conclude that a quantitatively comparative measurement of the range of motion of the TMC joint can be obtained with potential to measure motion in joints affected by arthritis or trauma and measured in both dynamic and static positions of the thumb.