Hereditary sensorimotor peripheral neuropathies (HSMN)

Hereditary sensorimotor peripheral neuropathies (HSMN) in children: what orthopedic problems?

Hereditary sensorimotor peripheral neuropathies are a group of genetically determined , progressive peripheral neuropathies ; the most common neuropathy in this group is Charcot-Marie-Tooth disease (CMT). In this article, we summarize the main clinical features of peripheral neuropathies of orthopedic interest.

Most patients with peripheral neuropathy present for observation in the second decade of life , although earlier or later presentations are possible. Peripheral neuropathy causes reduced strength and muscle atrophy , which initially affect the muscles of the feet and hands (with varying degrees of involvement of different muscles): this results in muscle imbalances, calf wasting, and atrophy of the intrinsic muscles of the feet and hands . Most patients also experience sensory impairment . Progressive deformities generally affect the feet, but the hands, spine, and hips may also be affected. Due to the deformities and strength deficits, gait changes occur , which are more or less evident depending on the severity of the patient’s involvement, leading to full-blown difficulties in walking, running, getting up from the ground, and climbing stairs. In case of marked involvement of the tibialis anterior muscle, the patient progressively loses the ability to keep the foot raised during the phase in which the limb advances ( drop foot ) and will adopt compensatory mechanisms to avoid tripping (generally excessive flexion of the hip and knee: stepping gait or steppage).

In case of clinical suspicion of peripheral neuropathies , further diagnostic tests are necessary (electromyography, electroneurography, motor conduction velocity, nerve biopsies, genetic tests, etc.).

Cavus varus foot

The most common orthopedic manifestation of peripheral neuropathy is pes cavus-varus .
It is not uncommon for patients to be evaluated for idiopathic (i.e., without a known cause) pes cavus (or cavovarus) and for these tests to ultimately lead to a diagnosis of peripheral neuropathy.
The denervation typical of this condition leads to retraction of the intrinsic musculature of the foot and the plantar fascia, resulting in a raised arch of the foot (pes cavus).
Muscle imbalances (between the tibialis posterior and peroneus longus on one side and the tibialis anterior and peroneus brevis on the other) cause flexion of the first metatarsal, equinus of the forefoot, and varus ( pes varus ). Similarly, claw deformities of the toes are produced secondary to muscle imbalances.

The orthopedic surgeon’s task is to identify existing deformities through careful clinical and radiographic examination and treat them appropriately. For example, the surgeon will be required to distinguish varus due to a forefoot deformity from rigid varus of the hindfoot ( Coleman test, Andreasi test ) to avoid errors when planning the surgery.

The treatment will initially use orthotics (insoles, insoles, Codivilla springs), and subsequently surgical solutions.

Depending on the severity of the condition (correctability/stiffness of the deformity, early intervention), the interventions may address only the soft tissues (soft tissue release or tendon balancing interventions) or the correction of the bone deformities or both.

Interventions on soft tissues

• Plantar fascia release (or “plantar fasciotomy”) : consists in the detachment of the plantar fascia at its proximal insertion to treat the retraction of the fascia itself
• Tendon balancing: these include interventions on the lateral side of the foot, i.e. on the peroneal tendons (peroneal recovery, transfer of the peroneus longus to the peroneus brevis) and on the internal side of the foot ( posterior tibial lengthening, transfer of the posterior tibial to the dorsum of the foot )
• Achilles tendon lengthening : indicated only in cases of hindfoot equinus. Avoid when equinus is due to a deformity of the midfoot or forefoot.

Bone correction interventions

Depending on the deformity, the following may be associated:

• 1st metatarsal lifting osteotomy : indicated in case of flexion deformity of the 1st metatarsal
• multiple metatarsal or midtarsal osteotomy : indicated in cases of global equinus of all metatarsals
• corrective osteotomy of the calcaneus : for structural deformity at this level

Procedures for claw fingers

• arthrodesis of the interphalangeal joints : indicated in cases of rigid flexion deformity with footwear-related problems
• Jones procedure: this involves transferring the extensor hallucis longus tendon with the aim of lifting the metatarsal and reducing the claw deformity of the toe itself.

Double arthrodesis surgery

• In cases of rigid cavus varus foot that cannot be corrected with any of the previous options, it may be necessary to perform a double arthrodesis, a corrective procedure in which certain joints of the foot (subtalar, talonavicular, and calcaneocuboid) are resected, corrected, and locked in the corrected position. These procedures should be avoided in younger children, as they arrest the growth of the bone structure.

Hip dysplasia and dislocation in peripheral neuropathies

Another problem to keep in mind in patients suffering from peripheral neuropathy is developmental dysplasia of the hips , that is, the onset during adolescence of a progressive alteration (acetabular dysplasia, subluxation) affecting the hips.

It is essential that affected children be screened for this condition, which is often poorly understood, even in orthopedics.
If pathological changes are detected, bone correction procedures ( femoral osteotomies, acetabular osteotomies ) will need to be scheduled after appropriate radiographic and CT studies.