Abstract
Introduction
The anatomy of the first metatarsophalangeal (MTP) joint and, in particular, the metatarsosesamoid articulation remains poorly understood. The movements of the sesamoids in relation to the metatarsal plays a key role in the function of the first MTP joint. Although the disorders affecting the sesamoids are described well, the movements of the metatarsosesamoid joints and the pathomechanics of these joints have not been described. We have performed a cadaver study detailing and quantifying the three dimensional movements occurring at these joints.
Methods
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 positions ranging from 10 degrees of dorsiflexion to 60 degrees of plantarflexion using a Micro Scribe, enabling quantitative analyses in a virtual 3D environment.
Results
The sesamoids demonstrated excursion both in the sagittal and coronal plane. The tibial sesamoid had a mean saggital excursion of 14.2 mm; the mean excursion of the fibular sesamoid was 8.7 mm. The mean coronal excursion of the tibial sesamoid was 2.8 mm while that of the fibular sesamoid was 3.2 mm. We also describe the mean saggital and coronal excursion of the sesamoids during smaller, incremental motions of the MTP joint.
Conclusion
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.
Clinical relevance
The greater excursion of the tibial sesamoid could explain the higher incidence of pathology in this bone. The differential excursion of the sesamoids is also a factor that should be considered in the design and mechanics of an effective hallux MTP joint arthroplasty.
