The crossover second toe is an extremely difficult problem for foot and ankle surgeons. Often, with the initial presentation, the deformity has progressed to the point where it is one subsection of a multitude of forefoot deformities. This makes the condition more challenging as you must treat the associated deformities at the same time in order to achieve a good outcome.
The etiology of crossover second toe syndrome is not fully understood. Although multiple theories have been suggested, the true underlying cause of the deformity is multifactorial and only some of these factors have been scientifically studied.
What is clear about the underlying deformity is an imbalance between the pull and position of the flexor and extensor apparatus. In a cadaveric dissection study done by Deland and Sung, the medial crossover second toe deformity was associated with an abnormal position of the long and short flexor tendons on the involved foot versus central position of the flexor tendons in the uninvolved foot.1 They found the flexor tendons to be medially deviated and sitting very close to the first interspace region.
Furthermore, Deland noted the plantar plate was medially and distally deviated on the plantar surface of the joint line. The researchers also noted poor continuity and thickness of the lateral plantar plate attachment to the proximal phalynx base.
Multiple studies have noted a second factor contributing to the deformity is a tear of the lateral collateral ligament structures.2-4, 6 The collateral ligament tears may include the metatarsophalangeal joint (MPJ) collateral, the accessory collateral which attaches to the plantar plate, or in most cases, both lateral collateral structures. With time, a shortening and overpowering of the medial collateral ligaments aggravates the underlying problem.
Although it’s essential to consider soft tissue deformity in such cases, there is a great deal of interest in the osseous deformity associated with crossover second toes. Inevitably, those who treat the condition commonly note there is a long metatarsal associated with the deformity. We must consider metatarsal length and possible wear and tear to the plantar soft tissue structures associated with prolonged periods of high peak pressures during gait.
A second area of concern is hypermobility of the first ray in association with high peak pressures plantar to the second metatarsal head region. It is possible that in those patients with laxity at the metatarso-cuneiform joint, there is poor plantar pressure distribution on the medial aspect of the foot resulting in high peak pressure values plantar to the second metatarsal head. Even in cases of hallux valgus deformity with minimal instability at the metatarso-cuneiform joint, there may be a decrease in direct pressure plantar to the first MPJ, resulting in increased peak pressure distribution plantar to the second MPJ capsule. This direct pressure coupled with adductus of the hallux, which may cause dorsal displacement of the second toe, may be one of the underlying causes of the crossover second toe.
Looking For Common Causes In Crossover Toe Cases
Presently, there is not one accepted cause for the problem of crossover toe. My impression is the problem often, if not always, involves a long second metatarsal, resulting in increased peak values plantar to the second MPJ. In most cases, surgeons note an associated hallux valgus deformity as well. This deformity is far worse in cases of severe crossover second toe deformity. However, since the problem does not present in its initial phase very often, it is difficult to consider if the hallux valgus deformity contributed to the cause or if the poor buttress function of the second toe resulted in the hallux valgus deformity increasing in severity.