The extensor retinacular system at the metacarpophalangeal joint. Anatomical and histological study.

The anatomy of the sagittal bands was studied in 56 cadaver digits. The sagittal band is part of an extensor retinacular system which is integrated with the extrinsic and intrinsic musculotendinous structures. The extensor retinacular system is a single unit with radial and ulnar components and has transverse, sagittal and oblique fibres. The transverse-sagittal fibres, along with the palmar plate, form a closed cylindrical tube which surrounds the metacarpal head. The oblique fibres form the triangular lamina distal to the sagittal band. The radial component of the sagittal band is often thinner and longer than the ulnar component. The sagittal band envelops the extensor digitorum tendon and the superficial fibres are thinner than deep fibres, especially in the central digits. The central digits have palmar soft tissue confluence on each side consisting of the sagittal band, palmar plate, annular pulley and deep transverse metacarpal ligament. The sagittal band also appears to envelop the superficial interosseous tendons on both sides. Our findings explain the propensity for radial sagittal band injuries and suggest that the sagittal band is the primary stabilizer of the extensor digitorum at the metacarpophalangeal joint.