Treatment of refractory anterior knee pain using botulinum toxin type A (Dysport) injection to the distal vastus lateralis muscle: a randomised placebo controlled crossover trial.
OBJECTIVE
This randomised controlled crossover trial examined the efficacy of botulinum toxin type A (BoNT-A) injection, plus an exercise programme, to remediate chronic anterior knee pain (AKP) associated with quadriceps muscle imbalance.


METHODS
24 individuals with refractory AKP received either BoNT-A (500 U Dysport) or the same volume saline injection to the vastus lateralis (VL) muscle and performed home exercises focusing on re-training the vastus medialis (VM) muscle. All subjects were offered open-label injection at 12 weeks. Knee-related disability (anterior knee pain scale; AKPS) and activity-induced pain (10 cm visual analogue scale) at 12 weeks were the primary outcomes. Peak isometric extensor force was recorded and normalised VL:VM ratios were derived from simultaneous surface electromyography. Self-reported pain and disability measures were collected at six time points to a mean of 20±8 months.


RESULTS
14 subjects received BoNT-A and 10 placebo injection. Improvement at 12 weeks was significantly greater for BoNT-A compared with placebo-injected subjects for the AKPS (p<0.03), pain on kneeling (p<0.004), squatting (p<0.02) and level walking (p<0.04). At week 12, five placebo subjects crossed over to open-label injection. At 24 weeks, 16 of 19 BoNT-A-injected and two of the remaining five placebo-injected subjects were either satisfied or very satisfied with treatment outcomes. Improvements were maintained in 11 of 14 BoNT-A-injected and two of five placebo subjects available at longer-term follow-up.


CONCLUSIONS
BoNT-A injection produced a greater reduction in pain and disability than placebo injection in carefully selected patients with chronic AKP related to quadriceps muscle imbalance.
Singer
Barbara J
BJ
Centre for Musculoskeletal Studies, School of Surgery, The University of Western Australia, Perth, Western Australia. barbara.singer@uwa.edu.au
Silbert
Peter L
PL
Song
Swithin
S
Dunne
John W
JW
Singer
Kevin P
KP
D000293:Adolescent; D000328:Adult; D018771:Arthralgia / Q000188:drug therapy*; D019274:Botulinum Toxins, Type A / Q000008:administration & dosage*; D018592:Cross-Over Studies; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007273:Injections, Intramuscular; D007719:Knee Joint; D008297:Male; D008875:Middle Aged; D009465:Neuromuscular Agents / Q000008:administration & dosage*; D010147:Pain Measurement; D010148:Intractable Pain / Q000188:drug therapy*; D017060:Patient Satisfaction; D052097:Quadriceps Muscle; D016896:Treatment Outcome; D055815:Young Adult
D009465:Neuromuscular Agents; D019274:Botulinum Toxins, Type A; C542869:abobotulinumtoxinA