Crossover Toe Deformity

Crossover toe deformity is a transverse-plane malalignment of the second toe, which deviates medially and dorsally to lie over the hallux. It is the end stage of lesser metatarsophalangeal (MTP) joint instability, driven by attritional failure of the plantar plate, the principal static stabiliser of the MTP joint. Podiatric authors describe the earlier, pre-deformity inflammatory stages as "predislocation syndrome".

Who. The patient is typically an older woman. In the largest surgical cohort 86% were women, the mean age at surgery was about 59, and incidence peaked in women over 50. The associations to ask about are hallux valgus, degenerative arthritis of the first MTP joint, inflammatory arthropathy such as rheumatoid arthritis, and high heels or other constrictive footwear.

Which toe. The second MTP joint is affected most commonly. The second is the longest lesser ray and carries the greatest plantar load.

The plantar plate. The plate is the primary plantar restraint of the lesser MTP joint, and its tear is the primary lesion. It inserts on the base of the proximal phalanx, and that distal insertion is its weakest point and the usual site of tearing.

The two stabilisers. The plantar plate holds the joint in the sagittal plane and the lateral collateral ligament, with the capsule, holds it in the transverse plane. The toe drifts medially once both have failed; the end result is dorsal subluxation, then dislocation, with the extensor digitorum longus (EDL) as the deforming force.

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The sequence. The deformity develops in order:

1. The great toe deviates laterally into valgus and pushes against the second toe, increasing the mechanical stress on the second MTP plantar plate.
2. Chronic overload causes microtrauma in the fibrocartilaginous plate, and partial tears develop, usually at its insertion on the proximal phalangeal base.
3. The plate ruptures full-thickness. With the plantar restraint lost, the proximal phalanx subluxes dorsally and the EDL overpowers the plantar structures.
4. The hallux pushes medially and the EDL pulls dorsally, so the second toe crosses medially over the great toe. Without treatment, capsular contracture makes it rigid in this position.

Other contributors. Three further factors add to the load or the imbalance:

• EDL overpull - the extensor overpowers the weakened plantarflexors and drives the dorsal subluxation; it requires lengthening
• Long second metatarsal - an anatomical variant that increases stress on the second MTP plantar plate and may need Weil shortening, though its causal role is disputed (below)
• Intrinsic muscle atrophy - the lumbricals and interossei lose function with age, weakening plantarflexion; an FDL transfer restores the balance

A recurring examiner trap is the causal role of a long second metatarsal (Morton foot). The biomechanical argument is intuitive: a relatively protruding second ray bears greater and more prolonged plantar load through late stance, chronically stressing the plate at its distal insertion. This is why metatarsal length is emphasised in generic metatarsalgia, and why a Weil shortening osteotomy is used to decompress the ray.

Why length explains little in crossover. Absolute length on a static radiograph is a weak predictor in crossover specifically. Relative dynamic loading and the integrity of the plate's insertion matter more, and overload during gait is not captured by a length measurement. The dominant transverse-plane driver is the loss of the hallux buttress, present in the majority of cases, and length alone cannot explain the medial drift it allows.

In practice. Do not rely on a long second metatarsal to make the diagnosis or to justify surgery. Diagnose from the drawer sign and the deformity, correct the hallux valgus, and shorten the metatarsal only to decompress the joint for the repair, not because length by itself caused the deformity.

Coughlin's clinical staging turns on reducibility, and the stage selects the treatment.

Staging at the bedside. Ask the patient to straighten the toe, then try to reduce it yourself:

• Stage 1 (flexible) - the patient can actively straighten the toe, passive reduction fully corrects it, and there is no fixed contracture of the capsule or EDL
• Stage 2 (semi-rigid) - active correction is lost and passive reduction is only partial; there is some capsular contracture, and the tight EDL needs forced plantarflexion to reduce
• Stage 3 (rigid) - the toe will not reduce even with passive force, the dorsal capsule is severely contracted, and there may be secondary arthritis

Associated pathology. Assess and address all of it:

• Hallux valgus - corrected by a bunionectomy performed with the crossover repair
• Second MTP synovitis - chronic inflammation from the plate injury adds pain and swelling; a synovectomy is performed at surgery
• Transfer metatarsalgia - if the third or fourth MTP joint becomes symptomatic, additional Weil osteotomies may be needed
• A widened first-second intermetatarsal angle - addressed by the hallux valgus correction

Anatomic grading. The tear itself is graded 0 to IV on the anatomy found at operation (Coughlin's cadaveric grading, below). The anatomic grade complements, but does not replace, the clinical assessment of reducibility and joint congruity.

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History. The pain is plantar, at the second MTP joint, and worse with walking, and the deformity comes on gradually over months to years. Ordinary shoes become difficult because the toe rubs dorsally, and push-off and balance suffer. The patient often reports a bunion and has usually tried pads and wider shoes without relief.

Examination. Look for the second toe crossing medially over the hallux with dorsal subluxation, and assess the severity of the hallux valgus and the intermetatarsal angle. Attempt passive reduction to stage the deformity, and ensure there is no digital nerve compression.

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The visible crossover is a late event. The reparable phase is the predislocation syndrome, the inflammatory, pre-deformity precursor, and catching it here is what separates a soft-tissue repair from a salvage fusion.

Definition and natural history. Predislocation syndrome is an acute, subacute or chronic inflammatory process of a lesser MTP joint, characteristically the second, that if untreated progresses to plantar plate and capsular attenuation, MTP instability, and ultimately dorsal subluxation and crossover (Mendicino 2001). It is the clinical face of an early, still-repairable plantar plate lesion, before any override of the hallux.

How it presents, before any crossover.

• Plantar second-MTP pain and swelling, worse on push-off and barefoot walking, often with a boggy synovitis palpable just distal to the metatarsal head
• A positive dorsal drawer sign, the earliest and most specific instability finding, often before radiographs show anything
• Loss of toe purchase on the paper pull-out test
• Frequent coexisting hallux valgus (seven of eight patients in Mendicino's series), reinforcing that the first ray must be assessed even at this early stage

Early management. Offloading, taping the toe into plantarflexion, stiff-soled footwear and activity modification come first, with a low threshold for surgery if instability progresses. Corticosteroid injection around an already-attenuated plate is avoided because it risks completing the rupture. A flexor-to-extensor (FDL) transfer reliably stabilises late-stage predislocation instability, albeit with a risk of residual MTP stiffness.

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Most cases are diagnosed clinically. Imaging confirms the severity and guides treatment.

Radiographs. Weight-bearing films are essential to assess the true deformity:

• AP weight-bearing - hallux valgus angle and second MTP alignment
• Lateral weight-bearing - dorsal subluxation of the second toe
• Oblique - additional detail of the MTP joints

What to measure. The hallux valgus angle (normally under 15°), the first-second intermetatarsal angle (normally under 9°), second MTP alignment (subluxation or dislocation) and the relative metatarsal lengths. The films also show the stage:

• Stage 1 - minimal subluxation, joint congruent
• Stage 2 - partial subluxation, joint surfaces losing contact
• Stage 3 - complete dislocation, the proximal phalanx dorsal to the metatarsal head

MRI. MRI is the imaging modality of choice for the soft tissues. A tear shows as high T2 signal at the insertion on the proximal phalangeal base, with discontinuity of the plate substance, surrounding oedema and inflammation, and sometimes retraction of the torn fibres. It may also show second MTP synovitis, collateral ligament injury and bone marrow oedema from stress reaction. The protocol uses T1, T2 and STIR sequences in axial, sagittal and coronal planes, with a small field of view on the forefoot. The indications:

• An uncertain diagnosis, to rule out other causes of pain
• Pre-operative planning for plantar plate repair
• Assessing the extent of a tear

Reading the scan. MRI confirms a tear in an uncertain case and guides surgical planning, but tears are also seen in asymptomatic feet (Gregg, below), so a reported tear is interpreted alongside the examination, not in isolation. Stress positioning can accentuate a true tear, but it can also miss a joint that is unstable on examination.

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Ultrasound. In experienced hands ultrasound can assess the plate and allows dynamic assessment during toe motion. It is less detailed than MRI and operator dependent.

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CT. Rarely indicated. It is useful for assessing bone quality before arthrodesis and gives better detail of arthritic change.

Transfer metatarsalgia. Excessive shortening at the Weil osteotomy transfers pressure to the adjacent third and fourth MTP joints. A patient who develops new pain at an adjacent joint after surgery may need further Weil osteotomies at those rays.

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What predicts a good result. Flexible or semi-rigid disease (Stages 1-2) treated early, before it becomes rigid, with the hallux valgus corrected at the same operation. Good bone quality for fixation, a non-smoker who complies with rehabilitation, and normal body weight all help.

What predicts a poor one. A rigid Stage 3 deformity, hallux valgus left unaddressed, inflammatory arthritis, previous failed toe surgery, obesity, smoking, and excessive metatarsal shortening.

Read this section knowing whose work it is. Coughlin is an author on five of the nine studies below — the 1987 description, the demographic review, the cadaveric grading study, the diagnostic-accuracy paper and the prospective protocol — and two of the remaining four come from the Weil Foot and Ankle Institute. So the description of the deformity, the grading system, the examination test, the treatment algorithm and the outcome data are substantially one investigator's programme and one closely linked practice, not a converging literature. The work is careful and it is the best available; a reader who counts nine citations should simply not infer nine independent confirmations.