Geometry of the first metatarsophalangeal joint

This study aimed to define the articular geometry of the metatarsophalangeal (MTP) joint of the great toe. Embedded in resin blocks, five pairs of cadaveric first MTP joints (all from men) were sequentially cut in the sagittal plane with a milling machine, removing 0.5 mm of bone in each cut. The photographed cartilaginous outline of each cut was digitized against reference markers, which enabled a computer system to superimpose each outline in three dimensions. The intersesamoidal ridge was found to be parallel to the lateral shaft. The peak of the ridge was just lateral to the midline of the MT head. The articular outline, through the ridge of each sample, was circular; however, other surface contours were noncircular. The undulating plantar aspect of the MTP head formed by the intersesamoidal ridge and related grooves was found to have symmetric relationships to the sesamoid bones and a consistent orientation to the shaft. The rounded distal dorsal aspect of the MTP head showed consistent differences to the concavity formed by the phalangeal base. The sample size is too small for the sizing of prostheses but it is adequate to study the geometry of the MTP joint. More data are needed for the accurate replication of a resurfacing prosthesis and understanding of joint kinematics.