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. - Singer BJ; Silbert PL; Song S; Dunne JW; Singer KP; Singer, Barbara J; Silbert, Peter L; Song, Swithin; Dunne, John W; Singer, Kevin P (British Journal of Sports Medicine, 2011)