Abstract
The anatomy of the first metatarsophalangeal (MTP) joint and, in particular, the metatarsosesamoid articulation remains poorly understood. Its effect on sesamoid function and the pathomechanics of this joint have not been described.
Fresh frozen cadaveric specimens without evidence of forefoot deformity were dissected to assess the articulating surfaces throughout a normal range of motion. The dissections were digitally reconstructed in various positions of dorsiflexion and plantarflexion using a MicroScribe, enabling quantitative analyses in a virtual 3D environment.
In 75% of specimens, there was some degree of chondral loss within the metatarsosesamoid articulation. The metatarsal surface was more commonly affected. These changes most frequently involved the tibial metatarsosesamoid joint.
The tibial sesamoid had an average excursion of 14.2 mm in the sagittal plane when the 1st MTP joint was moved from 10 degrees of plantarflexion to 60 degrees of dorsiflexion; the average excursion of the fibular sesamoid was 8.7 mm. The sesamoids also move in a medial to lateral fashion when the joint was dorsiflexed. The excursion of the tibial sesamoid was 2.8 mm when the joint was maximally dorsiflexed while that of the fibular sesamoid was 3.2 mm.
There appears to be differential tracking of the hallucal sesamoids. The tibial sesamoid has comparatively increased longitudinal excursion whilst the fibular sesamoid has comparatively greater lateral excursion.
This greater excursion of the tibial sesamoid could explain the higher incidence of sesamoiditis in this bone. The differential excursion of the 2 metatarsosesamoid articulations is also a factor that should be considered in the design and mechanics of an effective hallux MTP joint arthroplasty.
