Purpose of the study: To our knowledge, only qualitative data is available concerning the tension placed on the first carpometacarpal ligaments as a function of joint motion. The three articles published in the literature have provided discordant data. We conducted a quantitative study.
Material and methods:
Digitalized computed tomographies of the carpometacarpal joints magnified threefold were fed to a Stratasys® machine which created a rapid «polystyrene shock» prototype of the first and second metacarpals as well as the trapezium and the trapezoid.
After a preliminary study of the behavior observed with various materials, rubber with known consistency was used to simulate the different ligaments.
The first metacarpal was submitted to six movements in defined directions starting from the neutral position (in accordance with Pieron, 1973).
Ligament lengthening observed for each movement from the resting position of the first metacarpal was used to define the direction producing the greatest lengthening. This lengthening was measured directly with a graduated ruler under 2.5 x optical magnification.
Results: The anterior oblique ligament was under tension in the positions close to extension (positions L and D). The posterior oblique ligament was under tension in the position of ulnar finger opposition and in volar abduction (positions K and F). The inter-osseous ligament was under ension in volar abduction, opposition and flexion (positions F, K, J). A complex behavior was observed, best described by two portions, medial and lateral.
Discussion: This preliminary study on a model system depended on the interpretation of the ligament and joint surface anatomy. The method of creating joint motion described by Pieron enables comparison between two studies but does not correspond to the physiological position.
Conclusion: For a small-sized joint, magnification of the bony pieces and use of optical magnification facilitates apprehension of ligament lengthening during joint motion. This method can be used to better assess maximal range of motion according to ligament deformations observed in relation to joint solicitation.
