Patients with multiple sclerosis (MS) are encouraged by their health care providers to remain active and exercise to maintain strength and agility of their musculoskeletal system. Foot and ankle conditions can interfere with mobility and affect balance. Presented below is a listing of some of the more common foot and ankle problems encountered in the general population.

Hallux valgus, more commonly known as a bunion deformity, is a condition in which the first metatarsal abducts from the midline of the foot and the hallux adducts toward the midline of the foot.¹ It is often a combination of joint contracture and incongruity, combined with structural boney changes or adaptation that is present in this and many other developmental foot
deformities. In MS, one limb is often more supinatory and the other more pronatory.² The side that pronates more is also more likely to develop a hallux valgus deformity.³ This condition is generally a progressive deformity, worsening and becoming more painful over time, as the adductor hallucis and extensor tendons gain a mechanical advantage. Conservative treatments such as foot orthoses, strappings, shoe gear modifications, anti-inflammatories, physical therapy, and ultrasound-guided corticosteroid injections are indicated. Surgical options are available to correct the deformity when conservative therapy fails. These include a wide variety of metatarsal osteotomies, musculotendinous and capsular balancing, and first metatarsophalangeal joint (MTPJ) or first metatarso-cuneiform fusions.

In hallux varus, the hallux abducts away from the midline of the foot at the first MTPJ. The first MTPJ and hallux may become painful owing to joint incongruity, positional deformity, and from direct shoe pressure on the hallux. The development of hallux varus in MS and other neurologic conditions is attributed to the neurologic deficits and biomechanical alterations associated with these conditions.⁴ The neurologic deficits can cause an imbalance of the musculotendinous structures around the first MTPJ that lead to development of the deformity. As the adductor hallucis tendon gains a mechanical advantage, the condition continues to progress and increase in severity. Conservative treatments specific for this condition are categorically similar to those used for hallux valgus are indicated. In severe case, tendon transfers and capsulotendinous rebalancing, with or without osteotomy, are necessary to restore the integrity of the joint and eliminate pain. First MTPJ fusion is also an option, although should be considered a last resort until all conservative measures are exhausted.

A plantar-flexed first ray is a sagittal plane deformity. This condition is also a hallmark of neurogenic disorders such as MS. It is related to the progressive equinus or equinovarus attitude that the foot frequently assumes as the disease progresses.⁵ Increase stress and strain on the peroneus longus tendon, one of the major invertors of the foot, may also contribute to the deformity. The musculotendinous imbalance caused by the neurologic deficit that leads to the plantar-flexed first ray is then exacerbated by the progressive deformity leading to increased mechanical advantage and eventually a rigidly plantar-flexed first ray.⁶ A hammering of the hallux, with extension at MTPJ and flexion at the interphalangeal joint (IPJ), is often a sequela.

A plantar-flexed first ray is associated with sesamoiditis and submetatarsal bursitis/metatarsalgia.⁷ In sesamoiditis of the first metatarsal, the tibial sesamoid is more commonly affected.³ Stress fractures of this small bone are also known to occur. Nonunion or malunion of sesamoid fractures is not uncommon owing to their small size, location, and relatively poor blood supply. In addition, damage to the ligaments and tendons in this area is a common presentation that can best be visualized using magnetic resonance (MR) and diagnostic ultrasound.

Metatarsalgia is a general term that describes a number of conditions that cause pain underneath or around one or more of the metatarsal heads.⁷ These conditions can be associated with the anterior cavus foot (anterior equinus) or global cavus foot associated with many central nervous system (CNS) conditions including MS. Hyperpronation in one foot, associated with MS, can also lead to imbalance and overloading of one or more MTPJs, causing metatarsalgia.² There may be an associated metatarsal bursitis or capsulitis and, in more extreme cases, degeneration and partial tearing of the plantar ligament. One or more of the lesser metatarsal phalangeal joints may also be involved in cases of global and/or forefoot equinus. Conservative care includes NSAIDs, orthoses, bracing, padding, corticosteroid injections, and physiotherapy. Surgery is indicated when conservative therapy fails and may involve metatarsal osteotomies to shorten or elevate the metatarsals and tendon balancing procedures. In the case of unresolved sesamoiditis, removal of the involved sesamoid may be indicated. Surgery for the hammered hallux includes fusion with or without tendon lengthening or transfer.³

A variety of lesser toe deformities can be related to or caused by MS. The specific causation and progressive nature of the deformities dictate the type of deformity observed. Hammertoes can be seen from hyperpronation and also in the earlier stages of supinatory conditions and equinovarus associated with MS.⁸ With hammertoes, there is extension at the MTPJ and flexion at the proximal IPJ. Clawing of the toes is generally seen in both early or late stage supinatory conditions, the equinovarus foot, and conditions caused by CNS deficits such as MS.⁶ In this condition, there is extension at the MTPJ and flexion at the proximal and distal IPJs. These deformities initially present as flexible deformities and may progress to semirigid or rigid deformities. Clinodactyly is a transverse plane deformity of the toes that may or may not coexist with hammertoes, clawtoes, and plantar plate tears. The presence of clinodactyly can be an indicator of neurologic deficit when not solely associated with a biomechanical cause or trauma. Shoe gear changes, strappings, paddings, orthoses, and
debridement of associated hyperkeratotic lesions over a bony prominence are indicated as conservative treatments for all of these digital deformities. Surgical correction is often needed that includes arthroplasty, toe fusions and tendon balancing, lengthening, releases or transfers, and joint capsulotomy.