Preoperative botulinum toxin test injections before muscle lengthening in cerebral palsy

Muscle weakening is a well-known side effect of muscle-tendon lengthening. Botulinum toxin A (BTX-A) weakens the muscle temporarily by blocking the neuromuscular junction. Hence application of the drug is a logical step to test whether weakness deteriorates function prior to an operation. In the present study, BTX-A application is used to test preoperatively whether the gait pattern depends on the strength of the tested muscle. Since 1999, instrumented gait analysis, including kinematic, kinetic, and dynamic electromyographic data, is routinely used to define the individual surgical program.

In our series of 110 consecutive patients with cerebral palsy (CP) considered for surgical muscle lengthening from 1999 to 2008, BTX-A was applied to identify patients at risk for functional deterioration. Gait analysis was repeated 6 weeks (maximum effect of BTX-A) and 12 weeks (follow-up) after the test injection to check for loss of joint control (excessive ankle dorsiflexion, knee flexion, increased anterior pelvic tilt).

In all, 20.9% (n = 23) showed deterioration in gait after preoperative BTX-A test injections (n = 112, two patients had two test trials) in all muscles considered for lengthening. As a consequence, their lengthening surgery was canceled. A total of 68 patients underwent surgery as planned, and in none of them did gait function deteriorate. These clinical data were compared to those of a historical group (n = 105) before this test, where 18% showed functional deterioration after surgery. The similar percentage of patients filtered out by the test suggests that there could be a context to the number of poor results in the historical group.

We conclude that preoperative BTX-A test injection is a reliable tool for filtering out patients with risk of deterioration after muscle lengthening surgery in patients with CP and can be helpful to avoid poor outcomes.