Tibialis Posterior Dysfunction

Patients usually present with medial foot pain, decreased function and flattening of the arch.  Often described as “acquired flat foot”, this condition is most commonly a result of overuse and damage to the structures supporting the medial longitudinal arch. Tibialis posterior’s main function is to stabilise the mid foot and control contact phase pronation, with a lesser role in contributing to propulsive phase supination.

Tibialis posterior dysfunction can be defined in 4 different stages which serve as a guide to management.

• Stage I: The tendon is still intact and functioning but inflamed
• Stage II: The tendon has become dysfunctional and the foot has developed acquired flat foot. The deformity is passively correctable.
• Stage III: The foot deformity has become fixed and degenerative changes are seen in the subtalar joint.
• Stage IV: The foot deformity has become fixed and degenerative changes and loss of congruency are also seen in the ankle joint.

Differential Diagnosis

Painful flatfoot can have other causes such as tarsal coalition, severs disease, degenerative changes, fractures or inflammatory conditions. Key indicators which suggest tibialis posterior dysfunction include pain and/or swelling around the medial malleolus, along the arch and instep, along with a low arch axis, over pronating foot type.

Biomechanical Causes

A medially deviated low axis foot type, where the arch profile when non weightbearing is low, is predisposed to Tibialis Posterior dysfunction. In these patients, tibial posterior attachment is close the rearfoot axis and therefore has a shorter lever arm, which renders it less efficient. If the patient also has instability issues, it can exacerbate the situation. The inefficient Tibialis Posterior is unable to counteract the excessive contact phase pronation, which results in micro trauma and tendon degeneration. The poorly resisted hyper-pronation often leads to Forefoot Inversion deformity, a blocking of the windlass mechanism, functional hallux limitus and often 1^st MPJ deformity. In more severe cases subluxed deformity at the navicular, and talar/ankle mortice loss of congruency is observed

Management

Management strategies are totally dependent on the stage of progression. Identification of Rearfoot and Midfoot deformity and if there is mobility or rigidity is key. Early and appropriate conservative intervention is considered essential to prevent progression of the deformity.

Stage I & II:

If condition is acute:

• Reduce pain, inflammation and promote healing.
• Immobilisation by means of a removable boot (Aircast)

When symptoms settle:

• A combination of Orthotic management and Tibialis Posterior Rehabilitation exercises is imperative
• Eccentric exercise program to activate & strengthen Tibialis posterior
• Orthotic management to control the progressive rearfoot eversion of the calcaneus, addressing the causes and consequences of the flatfoot deformity
• Choose an off the shelf device with high medial borders/deep heel cups such as the X-line TPD, Salford Insole, Vasyli custom
• Custom made devices such as the Evolve will provide a closer fit to the arch and better cupping at the heel for stability

Stage III & IV:

• Orthotic management depends on the flexibility of the deformity;
  • FLEXIBLE: control the progressive rearfoot eversion of the calcaneus through orthoses
  • RIGID: immobilisation of the rearfoot & accommodation of any bony abnormalities
• As foot shape is abnormal, often partial subluxation and deformity around the navicular is evident, so a custom device is generally indicated. PPL often recommend using a CADCAM EVA total contact for this foot type. Frequently bony forefoot eversion is evident therefore total forefoot wedging is often indicated
• Generally normal 1^st MPJ function cannot be re-established therefore a rocker bottom soled shoe such as X-Diab can assist
• If the ankle joint has lost congruency then bespoke/modular orthopaedic boots and possiblly an AFO may be required to accommodate the deformity and facilitate gait
• Surgery such as triple arthrodesis may be required to correct deformity and alleviate pain