Diagnosis: Plantar plate rupture.
Discussion: The plantar plate is a fibrocartilaginous structure that lies between the metatarsal head and the synovial sheath of the flexor digitorum (or hallucis) longus tendon. It is composed predominantly of collagen type I, which is the same type of collagen in the menisci of the knee. The plantar plate sustains longitudinal tensile loads and it can be torn either by acute trauma or chronic irritation.
The plantar plate is connected to the intracapsular collateral ligament complex (CLC), which is composed of two components, the main collateral ligament (MCL) and the accessory collateral ligament (ACL). The proximal attachments of both of these components are at the dorsal tubercles of the metatarsal heads, however their distal attachments are different: the distal MCL’s attach at either side of the base of the proximal phalanx whereas the distal ACL’s attach onto either side of the plantar plate.
When viewed sagittally, the MCL and ACL form a “V” that is lying on its side, with the apex of the V attaching to the metatarsal head, one limb (the MCL) of the V running straight towards the proximal phalanx, and the other limb (the ACL) running diagonally/inferiorly to attach to the plantar plate. A common metaphor is to describe this as a basket, where the ACL forms the handle (which runs diagonally/inferiorly, so the handle in this picture is really positioned at an angle) and the plantar plate forms the basket. Note that the MCL is not directly attached to the plantar plate.
The above describes the anatomy of the lesser metatarsophalangeal joints. In the great toe or first MTP joint, the plantar plate is positioned between the sesamoids. The plantar plate-sesamoid complex is connected to the first MTP joint CLC, which is also composed of two components: the MCL and the sesamoid ligament (SL). The SL (the “handle”) at the first MTP joint serves the same purpose as the ACL in the lesser MTP joints, which is to “hold up” the basket, except in this case the basket is not just the plantar plate but also includes two sesamoids. Therefore, the ACL attaches directly onto the plantar plate while the SL attaches onto the sesamoids – the SL is the ACL equivalent.
An example of acute plantar plate rupture is “turf toe,” or plantar capsular ligamentous sprain. This occurs in athletes such as football players who compete on hard, artificial surfaces while wearing soft, flexible shoes. With hyperdorsiflexion at the first MTP joint, the plantar portion of the MTP ligamentous complex stretches. This may result in disruption of the plantar plate proper and/or of the ligamentous attachments to the plantar plate.
Plantar plate disruption in the lesser MTP’s is usually due to chronic irritation/attrition, particularly in women who wear pointy, high-heeled shoes. Chronic dorsiflexion with increased weight bearing at the MTP joints lead to plantar plate degeneration and eventual rupture.
In the above figures, the plantar plate (see sagittal) and one side of its ligamentous attachment (the CLC – see coronal and axial) are ruptured. The intact but sprained/thickened CLC on the other side appears to tug on the proximal phalanx and remaining plantar plate. Thus, mild subluxation at the MTP joint and subluxation/deviation of the plantar plate can be visualized.
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