Brachymetatarsia / Congenital Short Metatarsal

Brachymetatarsia is a congenitally short metatarsal, most often the result of premature closure of the metatarsal physis (growth plate). The fourth metatarsal is the one most commonly affected.

Who. The condition is more common in females and is frequently bilateral. It has recognised syndromic associations, among them pseudohypoparathyroidism and pseudo-pseudohypoparathyroidism, Down syndrome, Turner syndrome and Apert syndrome.

The disrupted parabola. The metatarsal heads normally form a smooth cascade of lengths, the metatarsal parabola. A short metatarsal breaks it: the affected head sits proximal to the parabola, and the corresponding toe is shortened and typically rides dorsally, sitting up out of the line of the other toes.

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Symptoms. Most patients present with cosmetic concern and difficulty with footwear, and the dorsally displaced toe can rub in shoes. Some develop transfer metatarsalgia, pain under the adjacent metatarsal heads, because the short ray does not share the weight-bearing load.

Diagnosis. The diagnosis is clinical, with a weight-bearing AP radiograph of the foot showing the short metatarsal, its head proximal to the parabola and the cascade disrupted. The same film is used to measure the shortening and plan the lengthening, below.

The operation is elective, technically demanding and carries a real complication burden, so who is offered it matters as much as how it is done. The asymptomatic short metatarsal needs only reassurance and shoe modification; surgery is for symptoms or significant cosmetic distress, not for the radiograph alone.

The indication. It is usually a combination rather than appearance alone: difficulty with footwear, a transfer lesion or metatarsalgia under the adjacent heads, a dorsally riding or non-functional toe, and distress about the appearance of the foot. A purely cosmetic request deserves a frank discussion of the complication rate, the months in a fixator and the realistic aesthetic result.

Non-operative management. This is legitimate and often chosen, and many patients prefer it once the alternative is explained. The options are accommodative footwear with a wide toe box, metatarsal padding or a bar to offload the transfer lesion, and a toe prop or sleeve for a floating toe.

Timing. Lengthening is generally deferred until skeletal maturity. The causative physis has usually closed prematurely, and operating earlier risks further growth of the adjacent rays altering the parabola again.

Two strategies lengthen the ray: a one-stage lengthening with an interpositional bone graft, or gradual distraction osteogenesis (callotasis) through a mini-external fixator after a metatarsal osteotomy. The choice turns mainly on how much length is needed.

The soft tissues set the limit. The soft tissues and the neurovascular bundle limit how much length can be gained acutely. A one-stage graft stretches them all at once, which restricts the safe gain and risks neurovascular and soft-tissue compromise and MTP stiffness, so it suits cases needing only limited lengthening. When greater length is required, callotasis is preferred, because lengthening the bone slowly allows the soft tissues to lengthen with it.

How much length. The target is to restore the affected head to the metatarsal parabola, judged on the weight-bearing AP against the adjacent metatarsals and the contralateral normal foot. That defines the required lengthening, which in brachymetatarsia is often substantial, commonly more than a centimetre.

The acute limit. What constrains one-stage grafting is acute stretch of the digital nerves and vessels. Acute gains beyond roughly 15% of the metatarsal length, a small absolute amount, risk neurovascular compromise and stiffness, so one-stage grafting suits small deficits only. Set this against the Lee series in the evidence below, where the one-stage group gained a mean of 13.9 mm (27.1%), from a fourth ray that was longer before surgery, and had the most dissatisfaction of the three groups.

Callotasis in the short metatarsal. The sequence is:

• A low-energy osteotome osteotomy
• A latency of about a week
• Distraction at roughly 0.5 to 1 mm per day, in divided increments
• Consolidation in the fixator until the regenerate corticates

The healing index, the time in the fixator per centimetre gained, is higher (slower) for first than for fourth brachymetatarsia, attributed to the larger osteotomy surface and to weight-bearing. The general principles of distraction osteogenesis are covered in the Distraction Osteogenesis and Limb Lengthening topics, and the parabola in the Metatarsalgia topic.

The joint at risk. During lengthening the MTP joint is dragged distally, and the toe, already riding dorsally, is at real risk of dorsal subluxation or dislocation and stiffness. The joint is commonly protected with a temporary axial Kirschner wire across the MTP joint, and sometimes down the toe, through distraction and consolidation. It holds the reduction and resists subluxation, and is removed afterwards.

Soft-tissue adjuncts. A dorsal capsulotomy with extensor (sometimes flexor) lengthening or release may be needed if the ray will not come out as it lengthens, and any associated syndactyly, webbing or toe deformity is addressed. Gradual distraction itself reduces the need, by lengthening the soft tissues with the bone. Associated toe deformities are covered in the Lesser Toe Deformities topic.

After surgery. The patient follows a supervised distraction schedule with pin-site care, and starts early MTP range-of-motion physiotherapy to combat stiffness. Weight-bearing is modified during consolidation.

Protect the MTP joint and lengthen within safe limits, and consent for the complications in the order they actually occur:

• MTP stiffness, the commonest
• Dorsal MTP subluxation
• Pin-site infection
• Premature consolidation or a poor or insufficient regenerate (failure of bone formation), requiring re-osteotomy or grafting
• Malunion or axial deviation of the lengthened ray
• Nonunion
• Neurovascular compromise if distraction is too rapid
• Floating toe
• An aesthetic result the patient does not consider worth it

Floating toe. This is the characteristic functional disappointment. The lengthened toe sits clear of the ground and takes no load, because tendon length and MTP mechanics have not kept pace with the bone. It is more likely after large gains and deserves a specific warning, because the foot may look better while the toe still does nothing.