Objectives 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. Selfreported 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 placeboinjected 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.
Conclusion 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.
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Funding Raine Medical Research Foundation at The University of Western Australia provided some funding support to the principal author (BJS); Ipsen supplied Dysport to Royal Perth Hospital at no cost and provided financial support for computed tomography costs.
Competing interests KPS and BJS have received travel support from Ipsen.
Ethics approval The study was approved by the institutional ethics committee and listed in the Australian New Zealand Clinical Trials registry (www.anzctr.org.au) ACTRN12605000775617.
Patient consent Obtained.
Provenance and peer review Not commissioned, externally peer reviewed.