Effect of botulinum toxin injection on length and lengthening velocity of rectus femoris during gait in hemiparetic patients

BackgroundIn hemiparetic patients, rectus femoris spasticity is one of the main causes of reduced knee flexion in swing phase, known as stiff knee gait. Botulinum toxin is often used to reduce rectus femoris spasticity and to increase knee flexion during swing phase. However, the mechanisms behind these improvements remain poorly understood. The aim of this study was (1) to quantify maximal rectus femoris length and lengthening velocity during gait in ten adult hemiparetic subjects with rectus femoris spasticity and stiff knee gait and to compare these parameters with those of ten healthy subjects and (2) to study the effect of botulinum toxin injection in the rectus femoris muscle on the same parameters.Methods10 patients with stiff knee gait and rectus femoris spasticity underwent 3D gait analysis before and one month after botulinum toxin injection of the rectus femoris (200 U Botox®, Allergan Inc., Markham, Ontario, CANADA). Rectus femoris length and lengthening velocity were quantified using a musculoskeletal model (SIMM®, MusculoGraphics, Inc., Santa Rosa, California, USA).FindingsMaximal length and lengthening velocity of the rectus femoris were significantly reduced on the paretic side. There was a significant increase in muscle length as well as lengthening velocity during gait following botulinum toxin injection.InterpretationThis study showed that botulinum toxin injection in the spastic rectus femoris of hemiparetic patients improves muscle kinematics during gait. However maximal rectus femoris length did not reach normal values following injection, suggesting that other mechanisms are likely involved.