Dimensions of the Metacarpo-Phalangeal Joint with Particular Reference to Joint Prostheses

Abstract

Sixty metacarpo-phalangeal joints were dissected and investigated to determine the shape, size and position of the articular surfaces with respect to the medullary canals of the metacarpal and the phalanx. The results show that the articular surfaces of the metacarpo-phalangeal joint have a single centre of rotation in the sagital plane and in the transverse plane. The joints of the little and ring fingers have radii of curvature in the sagital and transverse planes, which are almost equal (within 1.6 per cent) while those radii of the middle finger varied by 9 per cent. The index finger had a variation in radius from the sagital to the transverse plane of almost 13 per cent; the sagital plane radius being the greatest. This observation is the opposite of the other joints where the transverse radius is the greater one. The overall widths of the metacarpal heads were seen to vary from 13 mm in the little finger of females to 17 mm in the index finger of males (average). The medullary canals had axes which were not coincident with the centre of rotation of the joint but up to 3 mm displaced from it. These dimensional differences have important implications in prosthesis design.