Not at all: Plantar fasciitis is now a proven therapeutic target for onabotulinumtoxinA. Consider its potential value for your patients.
By Benn Jason Scott Boshell, MSc, BSc (Hons)
When people hear the word “Botox,”a their immediate associations might be with facial injection as an anti-wrinkle treatment or magazine gossip on the latest celebrity to suffer a “botch job” from one-too-many injections. Prior to the modern use of this acetylcholine-blocking neurotoxin, no one other than medical professionals who used it to treat their patients really knew what Botox is. Injections were originally used to treat neurological conditions that result in spastic paralysis, such as cerebral palsy.
In addition to managing neurological conditions and, more recently, for aesthetic enhancement, Botox is now being used to treat musculoskeletal disorders. One of these conditions is plantar fasciitis, the subject of this narrative review of the literature.b
a. Botox, the registered trade name of onabotulinumtoxinA, is used in this article for ease of reading.
b. Treatment of plantar fasciitis is not a US Food and Drug Administration-approved indication for Botox®.
How can Botox injection treat plantar fasciitis?
Botox is a neurotoxin that blocks release of the neurotransmitter acetylcholine in overactive muscles. Motor neurons release acetylcholine to activate muscles at the neuromuscular junction; Botox, when injected, causes relaxation of muscles and other local soft tissue.
A body of evidence identifies tightness in calf muscles as a causative factor in plantar fasciitis.1-5 Botox injection into the calf aims to relax contracture in calf muscles, thus reducing tensile strain on the plantar fascia as a result of muscle relaxation. Additionally, Botox can be injected into the muscles of the foot to achieve the same effect.
What is the evidence for Botox injection?
- Botox injection into the calf aims to relax contracture in calf muscles, thus reducing tensile strain on the plantar fascia. Botox can also be injected into muscles of the foot for the same effect.
- Improvement in plantar fasciitis pain after Botox injection has been reported to be sustained over the long term.
- Major adverse effects of Botox are uncommon when injections are administered by a qualified clinician.
Several clinical studies have looked at the effectiveness of Botox injection for treating plantar fasciitis.
Botox injection compared with corticosteroid injection (2013). Elizondo-Rodriguez and co-workers’ level-1, double-blind, randomized controlled trial compared Botox injection to corticosteroid injection for the treatment of plantar fasciitis.6The study randomized participants into 2 groups:
- Group 1 (19 participants) received a Botox injection and were instructed on performing plantar fascia stretching exercises.
- Group 2 (17 partcipants) received a corticosteroid injection and the same instructions on plantar fascia stretching exercises.
Results of treatment were recorded at 2 weeks and at 1, 2, 4, and 6 months. No significant improvement was seen in either group after the initial 2-week review. However, both groups showed significant improvement in pain scores at 1 month. At 2-, 4-, and 6-months follow-up, the Botox group had significantly better pain scores than the corticosteroid group. At the final, 6-month review, the average pain score in the Botox group was 1.1 (on a scale of 1 to 10, with 10 the “worst pain”), a reduction from 7.1 (difference of 6 points); in the corticosteroid group, the average pain score was 3.8, a reduction from 7.7 (difference of 3.9 points).
Elizondo-Rodriguez therefore concluded that Botox injection is superior to corticosteroid injection for the treatment of plantar fasciitis over the short term and mid-term. A limitation of this study is that patients were not followed over a longer period; it is not known, therefore, whether participants would have maintained their improved pain scores 12 months’ posttreatment. Longer follow-up would help ascertain whether Botox is also successful in the long-term management of plantar fasciitis.
A particular point of interest from the Elizondo-Rodriguez study is that Botox was not injected into or around the plantar fascia but into the gastrocnemius and soleus muscles. Following injection, calf muscles went into a state of relaxation, due to the effect of Botox. It is believed that this relaxation reduced additional strain on the plantar fascia that results from increased calf-muscle tension. One could argue that this approach seeks to address the purported cause of plantar fasciitis—unlike corticosteroid injection, which aims to treat symptoms.
Figure 1: Medial (a) and plantar (b) views of the injection entry point for study patients. This is at the distal aspect of the plantar-medial aspect of the calcaneus where the plantar fascia is proximal and the flexor digitorum brevis is adjacent. The X marks the most common spot injected for patients based on their maximum point tenderness. The circle around the X is a 1.5-cm radius where some patients received their injection based on their maximum point of tenderness (used with permission from reference 12).
Botox injection compared with corticosteroid injection (2012). Díaz-Llopis and colleagues also compared Botox injection with corticosteroid injection.7 Their study was likewise a randomized, controlled trial, with 28 patients in each group. As in the Elizondo-Rodriguez study,6 Díaz-Llopis found both that Botox and corticosteroid injections were successful at 1-month review; however, the difference between the 2 treatments grew at 6 months, with the Botox group continuing to improve while the steroid group grew slightly worse.
Long-term follow-up of sustained effects of Botox injection (2013). The lead Díaz-Llopis investigator and a different group of co-workers8 returned to the findings of the original Díaz-Llopis study,7 conducting a 12-month follow-up of the 2012 Botox group to determine whether reported improvements were sustained over the long term, which they were. Their findings provide evidence to support the use of Botox injection as a long-term treatment option.
(Notably, the site of the Botox injection in the 2012 Díaz-Llopis study differed from the site used in the Elizondo-Rodriguez study. Instead of injecting into calf muscles, Díaz-Llopis injected Botox into the plantar fascia attachment to the heel bone and further along the arch of the foot; they decided to use this technique based on a 2005 study by Babcock and co-workers.9 By using the same injection technique that Babcock used, Díaz-Llopis and colleagues were able to determine whether they would achieve similar success.)
Botox injection compared with corticosteroid injection (2018). In a randomized, controlled trial reported this year, Roca and co-workers found Botox superior to corticosteroid injection.10
Botox injection compared with placebo. Babcock and colleagues compared Botox injection and placebo in a double-blind, randomized, placebo-controlled study in 27 patients with plantar fasciitis.9 Results were recorded at 3 weeks and 8 weeks; improvement observed in the Botox group was significantly greater than in the placebo group. The strength of the study was limited by short-term follow-up.
Other studies have also compared Botox injection with placebo and found Botox to be significantly more effective.11,12 Ahmad and colleagues,12 in a double-blind, randomized, controlled trial of 50 patients (25 in each group) found Botox injection to be significantly superior to placebo at 6-month and 12-month reviews (Figure 1). The Botox group also showed significant reduction in plantar fascia thickness, which demonstrated healing of the degenerative plantar fascia—a finding not seen in the control group. A further benefit of Botox injection in this study was that it did not reduce heel fat-pad thickness, a commonly reported complication of corticosteroid injection.
Conversely, a similar study that compared Botox injection and placebo found only a marginal difference in improvement between the 2 groups:13 63.1% of the Botox group perceived improvement compared to 55% of the placebo group.
Botox injection compared with extracorporeal shockwave therapy (ESWT). Roca and co-workers’ study14 is interesting because ESWT has become an established, successful treatment option for plantar fasciitis.15 Because Botox injection is considered a novel treatment with less evidence of effectiveness, comparing it with an established treatment can be considered a good test of its effectiveness.
The Roca study randomized patients to 2 groups, 36 in each group. The researchers found both treatments effective—i.e., both demonstrated improved pain scores after treatment. However, ESWT came out on top, producing a greater reduction in pain than Botox injection.
A limitation of this study is that the researchers reviewed patients only 1 to 2 months after treatment. As noted, previous studies of Botox injection demonstrate continued improvement in pain score with more time. It is possible that the Botox group would have seen greater improvement in pain score if the researchers had reviewed that group at 6 and 12 months (although the same possibility can be considered for the ESWT group).
Are there risks to Botox injection?
Botox injection is generally safe; major adverse effects are uncommon when injection is administered by a suitably qualified clinician. There is a possibility (although highly unlikely) that the effect of botulinum toxin will spread to other parts of the body and cause botulism-like signs and symptoms, including:
- muscle weakness all over the body
- vision problems
- difficulty speaking or swallowing
- difficulty breathing
- loss of bladder control.
Can a verdict be brought?
Overall, it appears that the evidence for Botox injection as a treatment for plantar fasciitis is sufficiently strong to support its use. Nearly all current studies of moderate- to high-quality demonstrate significant success with this treatment option.
Despite that conclusion, Botox injection is not a commonly used treatment option and—in the United Kingdom—is not widely available for treating plantar fasciitis; in the United States, Botox injection is not indicated by the Food and Drug Administration for treating plantar fasciitis. Nevertheless, Botox injection deserves greater study and consideration for its applicability to clinical practice for treating plantar fasciitis. This therapy might replace commonly used corticosteroid injection for plantar fasciitis, which has 1) a lower success rate over the long term and 2) an increased risk of harmful effects, including plantar fascia rupture.
The most effective Botox injection technique remains in question. In most studies, plantar fascia and surrounding tissue were injected directly; in some, calf muscles were injected. To determine which technique is better, it will be necessary to conduct a head-to-head trial of these 2 techniques.
Benn Jason Scott Boshell MSc, BSc (Hons) is clinical lead podiatrist at Hatt Health & Movement Clinic, Devizes, United Kingdom.