Objective
To evaluate the clinical utility of the dynamic gastrocnemius length, calculated with gait analysis after phenol or botulinum toxin block in spastic cerebral palsy.

Method
Gastrocnemius muscles were injected with phenol or botulinum toxin. Kinematic gait parameters including dynamic gastrocnemius length were surveyed with 3-dimensional gait analysis system before and after the procedure.

Results
The dynamic gastrocnemius lengths improved significantly after block of calf muscles, except 3 cases which showed severe genu recurvatum. The vertical displacement of the center of gravities and the maximal ankle dorsiflexion angles after the block were not significantly different from those before the block.

Conclusion
Dynamic gastrocnemius length calculated with gait analysis can be used as a tool to determine the efficacy of spastic calf muscle block, in the absence of severe genu recurvatum. In case of associated severe genu recurvatum, other parameters may be substituted.