Therapeutic Effect of Botulinum Toxin A for the Treatment of Plantar Fasciitis.

Plantar fasciitis represents the most frequent cause of chronic heel pain, usually occurs in patients 40 years or older, overweight, sedentary or with intense physical activity.

The plantar fascia function is to prevent foot collapse by its anatomical orientation and by its tensile forces; It originates at the base of the calcaneus and extends distally to the phalanges. The plantar fascia stretching prevents the displacement of the calcaneus and the metatarsals and maintains the medial longitudinal arch. Simulates a cable attached to the calcaneus and metatarsophalangeal joints. The windlass mechanism described by Hicks, for the action of the plantar fascia is usually explained when a dorsiflexion of the fingers occurs, this leads to an effective shortening of the length of the plantar fascia causing an elevation of the arch. The extension of the fingers increases the arch of tension with the metatarsophalangeal joint as axis or anchor point. The shortening of the plantar fascia resulting from the dorsiflexion of the hallux is the essence of the windlass mechanism. When a fasciotomy is performed, this mechanism is lost, decreasing the stability of the arch and this does not allow a phase of stable terminal stay.

Historically the development of plantar fasciitis is attributed to biomechanical defects such as hyperpronation, this contributes to excesive mobility of the foot, which increases the stress applied to the musculofascial structures and soft tissue through an elongation of plantar fascia. There are other studies that have shown that one of the main factors for the appearance of this disease is the mechanical overload and it has been reported that the tension necessary for the rupture of the windlass mechanism ranges from 1.4 to 3.4 of the body weight of the subject.

There is a great variety of therapies reported for the treatment of this pathology, intralesional application of steroids, platelet-rich plasma, intralesional botulinum toxin A, treatments such as extracorporeal shock waves, all of which are assisted by stretching excercises of the gastrocnemius and sole muscles or stretching of the plantar fascia.

The clinical use of botulinum toxin A has expanded beyond the original indications by its effects on cholinergic neurons. The increased interest in the potential role to treat conditions of chronic pain is partially based on the effects of the toxin on the modulation of the release of substance P, on the calcitonin-related gene peptide and glutamate. On the other hand, the toxin has shown its effect on the inhibition of inflamatory pain and on the release of neurotransmitters from primary sensory neurons in a rat model. It also inhibits peripheral sensitization, which leads to an indirect decrease in central sensitization. It is unclear whether the treatment of chronic plantar fasciitis with botulinum toxin A works by causing muscle paralysis or by analgesic anti-inflamatory effects or by both mechanisms. A combined effect, induction of paresia of the muscles originating in the medial calcaneus process and direct analgesia due to analgesic anti-inflamatory properties.

We performed a previous study, where we compared the use of botulinum toxin A against intralesional steroids; The application of botulinum toxin A was performed in the twin and sole muscle wombs, while dexamethasone was applied in the area of greatest fascia pain. Patients who received botulinum toxin had a faster and more sustained improvement than patients who received steroids.

Another common form of treatment for plantar fasciitis is the application of intralesional steroids; however, there are reports of complications associated with these drugs and one of the main ones is the rupture of the plantar fascia, which ranges from 2.4% to 5.7% ; Despite pain relief due to rupture, many patients have other associated complications such as lateral plantar nerve dysfunction, stress fractures, among others, mainly after 2 applications.

Objective and originality: The aim of our study is to demonstrate that the use of botulinum toxin A for the treatment of plantar fasciitis is superior to treatment with intralesional steroids. We try to establish a safer and less painful treatment therapy for the patient, since the use of steroids is associated with complications. We believe that the botulinum toxin A can also be applied intralesional, since there is information that indicates that this toxin has analgesic and anti-inflammatory effect in its local application and not only by the action of muscle relaxation by blocking the release of acetylcholine at the neuromuscular junctions.

General objective:

To assess the therapeutic effect of botulinum toxin A in patients diagnosed with plantar fasciitis.

Hypothesis:

The application of botulinum toxin A presents better results in the treatment of plantar fascitis than the use of intralesional steroids.

Material and Methods:

All patients who are recruited for the study will be explained regarding the treatment protocol, and will also sign informed consent prior to inclusion in the study. Measurement of the plantar fascia using ultrasound and measurement of ranges of movement of ankle flexion, as well as measuring and weighing patients to know their body mass index. They will be randomized into one of three treatment groups. Group 1 (control) treatment with 5 ml of anesthetic (Ropivacaine 7.5%), Group 2 (steroids) application of 1ml of Betamethasone plus 3 ml of local anesthetic and Group 3 (botulinum toxin A) 250 U, in the insertion zone of the plantar fascia. All patients will receive a detailed explanation of the stretching exercises of the plantar fascia, as well as their frequency and duration. Afterwards, the patients will be evaluated by a blinded investigator, at 2 weeks, 1 month, 3 months and 6 months after infiltration; evaluation scales will be applied: Visual Analogue Scale (EVA), Maryland Foot \& Ankle Score, Foot \& Ankle Outcome Score (AOFAS), Foot \& Ankle Disability Index (FADI).