Botulinum toxin dilution and endplate targeting in spasticity: a double-blind controlled study

Arch Phys Med Rehabil. 2009 Jan;90(1):9-16.e2. doi: 10.1016/j.apmr.2008.04.030.


Objective: To determine the effects of botulinum neurotoxin type A (BTX-A) dilution and endplate-targeting in spastic elbow flexors.

Design: Double blind randomized controlled trial; 4-month follow-up after a 160-unit injection of BTX-A into spastic biceps brachii (4 sites). Randomization into: group 1: 100 mouse units (MU)/mL dilution, 0.4cc/site, 4-quadrant injection; group 2: 100MU/mL dilution, 0.4cc/site, 4 sites along endplate band; group 3: 20MU/mL dilution, 2cc/site, 4-quadrant injection (n=7 per group).

Setting: Institutional tertiary care ambulatory clinic.

Participants: Referred sample of 21 adults with spastic hemiparesis. No participant withdrew due to adverse effects.

Intervention: A 160-unit injection of BTX-A of different dilutions and locations into biceps brachii.

Main outcome measures: Primary: agonist and antagonist (cocontraction) mean rectified voltage (MRV) of elbow flexors/extensors during maximal isometric flexion/extension; secondary: maximal voluntary power of elbow flexion/extension; spasticity angle and grade in elbow flexors/extensors (Tardieu Scale); active range of elbow extension/flexion.

Results: BTX-A injection overall reduced agonist flexor MRV (-47.5%, P<0.0001), antagonist flexor MRV (-12%, P=.037), antagonist extensor MRV (-19%, P<.01), flexion maximal voluntary power (-33%, P<.001), elbow flexor spasticity angle (-30%, P<.001) and grade (-17%, P=.03), and increased extension maximal voluntary power (24%, P=.037) and active range of elbow extension (5.5%, 8 degrees , P=.002). Agonist and antagonist flexor MRV reductions in group 3 (-81% and -31%) were greater than in groups 1 and 2, whereas increase in active range of elbow extension was greater in group 2 (10%) than in groups 1 and 3 (P<.05, analysis of covariance [ANCOVA]). Elbow flexor spasticity was significantly reduced in groups 2 and 3 only (P<.05, ANCOVA).

Conclusions: In spastic biceps, high-volume or endplate-targeted BTX-A injections achieve greater neuromuscular blockade, cocontraction and spasticity reduction, and active range of elbow extension improvement, than low volume, nontargeted injections.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Botulinum Toxins, Type A / administration & dosage
  • Botulinum Toxins, Type A / therapeutic use*
  • Dose-Response Relationship, Drug
  • Double-Blind Method
  • Female
  • Follow-Up Studies
  • Humans
  • Male
  • Middle Aged
  • Motor Endplate / drug effects*
  • Muscle Spasticity / rehabilitation*
  • Neurotoxins / administration & dosage
  • Neurotoxins / therapeutic use*
  • Paresis / rehabilitation*
  • Range of Motion, Articular


  • Neurotoxins
  • Botulinum Toxins, Type A