The goal of this pilot triple-blind randomized clinical trial is to determine the effectiveness of intra-muscular botulism injection for treatment of lower leg anterolateral chronic exertional compartment syndrome (CECS).

Primary Research Question: What is the effectiveness of intra-muscular botulinum injection, compared to normal saline placebo, for reducing pain related to painful sport activity in patients with lower leg anterolateral chronic exertional compartment syndrome (CECS), over a 24-week period?

Secondary outcomes will measure the time to initial onset and duration of pain during the painful sport activity, characterize the type of pain, foot paraesthesias, self-reported ankle instability, and ankle dorsiflexion and eversion muscle power. The Single Assessment Numeric Evaluation (SANE) score will provide a measure of overall leg function.

Adult patients with a confirmed diagnosis of anterolateral CECS, as determined by post-exertional compartment pressure measurements, will be invited to participate in the study. Using concealed, consecutively-numbered randomization envelopes, participants will be randomly assigned to receive either the botulinum (treatment) or the normal saline (control) injection. Participants will answer a web-based outcome questionnaire at Baseline (prior to receiving the injection) and at 2, 4, 6, 8, 12, 16, 24-weeks follow-up. Participants will be asked to do their painful sport activity the day before completing the questionnaire. Ankle dorsiflexion and eversion muscle power will be manually measured by a physiatrist in clinic at 6, 16 and 24-week follow-up visits.

Chronic exertional compartment syndrome (CECS) of the lower leg muscle compartments is a common problem in the active population. The condition often significantly restricts patients from participating in their desired activity to the best of their ability. The pathology of CECS is related to increased intra-muscular pressure related to a restrictive fascia (envelope around the muscle or muscle group). The current standard of care for definitive treatment of CECS is a surgical fasciotomy. However, there have been a number of case reports reporting successful reduction of the symptoms of CECS with intra-muscular botulinum injections. Intra-muscular botulinum injections may reduce the symptoms of CECS by potentially decreasing muscle activation, therefore diminishing blood flow, which may reduce intra-compartmental muscle expansion and pressure of the compartment during exercise. Thus botulinum injections might provide a non-operative method of treating CECS.

This study will determine the effectiveness of intra-muscular botulinum injection, compared to a normal saline placebo, for treatment of lower leg anterolateral CECS, over a 24-week period. Participants will answer a web-based questionnaire before receiving the injection (Baseline) and at regular follow-up intervals at 2, 4, 6, 8, 12, 16, 24-weeks post-injection. The questionnaires will ask the participant to provide detailed information about their painful sport activity, and the maximum level of pain that they experience during that activity. They will also characterize the type of pain experienced, record the time to initial onset and duration of pain during the painful sport activity, and provide an overall measure of their leg function using a Single Assessment Numeric Evaluation (SANE) score. Participants will also attend an in-person appointment in clinic at Baseline, and at 6, 16 and 24-weeks post-injection for assessment of numbness and/or tingling in the foot, ankle instability, and manual ankle muscle power.

Inclusion Criteria:

• Confirmed diagnosis of lower leg anterolateral chronic exertional compartment syndrome (CECS), as measured post-exertional compartment pressure measurements of greater than 30 mmHg for immediate post-exertional compartment pressure, and greater than 12 mmHg at 5 minutes after stopping exercise.

Exclusion Criteria:

• Female patients who are pregnant, trying to get pregnant or lactating
• History of keloidal scarring
• History of any significant neurologic disease (ie: amyotrophic lateral sclerosis, motor neuropathy, myasthenia gravis, Lambert-Eaton syndrome)

Requests for individual participant data will be considered upon request.

Participants will be blinded to the treatment they received until after the 24-week visit is completed. The physiatrist administering the injection and the physiatrist performing the manual muscle power assessments will be blinded to treatment allocation.