Cath Lab Digest

One of the most challenging disorders of the foot is the unstable second metatarsophalangeal joint (MPJ). Due to the specific anatomical and biomechanical conditions, the surgeon has to define the plane of deformity as he or she will encounter a wide range of mild and passively reducible to severe and fixed deformities.

Indeed, there are special considerations regarding second MPJ biomechanics. The seven interossei pass plantar to the axis of the metatarsal head and insert into the base of the proximal phalanx and the plantar plate respectively. They act as strong flexors of the MPJ and, according to their position lateral or medial to the central axis of the MPJ, as abductor or adductor in the transverse plane for the MPJ simultaneously.

The four lumbricales originate from the tendon of the flexor digitorum longus (FDL) and insert into the medial aspect of the proximal phalanx and extensor hood, passing the deep transverse metatarsal ligament plantarly. They function as strong flexors of the MPJ with extension of the proximal interphalangeal joint (PIPJ) and distal interphalangeal joint (DIPJ). It is important keep in mind that the second toe has two dorsal interossei and no plantar interossei. The medial insertion of the lumbricalis tendon exerts an unopposed adduction force to the second toe.
The plantar fascia, plantar plate and the collateral ligaments provide the static stabilization of the lesser toes. The plantar fascia centers the plantar plate under the metatarsal head. This trapezoidal plate has multiple attachments to the deep transverse and collateral ligaments, the tendon sheath of the flexors and the extensor hood. It serves as a strong deterrent against dorsal dislocation of the MPJ. The collateral ligaments stabilize the MPJ in the transverse plane and also contribute to the restraint against dorsal dislocation.

A Pertinent Primer On Possible Causes Of Second Toe Deformities

There are several disorders that lead to a dislocation of the second toe, whether it is isolated in the sagittal or transverse plane, or is part of a so-called multiplanar deformity.

Monoarticular synovitis of the second MPJ reveals a thickening of the synovia with a distended joint space. This results in a diminished range of motion with a deviation in the transverse plane. The reasons for this monoarticular synovitis still remain unclear. Some authors associate a long second metatarsal with consecutive changes in the stability of the plantar plate with increasing dislocating forces.1 Others describe some relation to first metatarsal instability in hallux valgus, which causes persistent inflammation in a constantly overloaded second MPJ.1

Sagittal instability may range from subluxation to complete dislocation.

Persistent inflammation causes the attenuation of the plantar plate. The effect of the ground reactive forces with a dorsally directed force vector also contributes to the subluxation in the sagittal plane and the rupture of the plantar plate.

Aside from the aforementioned factors, some have advocated localized trauma as one of the most frequent causes for this condition.2 The literature describes seronegative and seropositive rheumatoid arthritis as well as hypermobility (e.g. Ehlers-Danlos syndrome) as etiologic factors.3,4 High-heeled shoes in combination with a narrowed toe box can create a situation of persistent hyperextension at the MPJ, especially in the case of a long second metatarsal.

With the rupture of the lateral structures (e.g., the lateral collateral ligament and/or the tendon of the first dorsal interosseus muscle), a multiplanar instability (or crossover toe) will develop.

The differential diagnosis includes interdigital neuroma, stress fracture of the metatarsal neck, trauma, synovial cysts or Freiberg’s disease.

Essential Keys To The Clinical Examination

The typical patient is middle-aged and presents with painful swelling and tenderness of the second MPJ. The pain increases with passive flexion and the range of motion decreases, particularly in flexion. In the case of attenuation of the lateral ligamentous structures, the palpation of the lateral aspect of the MPJ is even more painful.