Response to Letter to the Editor: 'Is subchondral bone mineral density associated with nocturnal pain in knee osteoarthritis patients?'. Issue 12 (December 2015) - Burnett, W.D.; Kontulainen, S.A.; McLennan, C.E.; Hazel, D.; Talmo, C.; Hunter, D.J.; Wilson, D.R.; Johnston, J.D.