The proportion of patients ( Proximal : Distal : Placebo ) who experienced moderate-to-severe posterior knee pain was 18 % :22 % :89 % ( P < 0.00001 ) at 2 h , 24 % :28 % :72 % ( P < 0.01 ) at 4 h , and 12 % :17 % :78 % ( P = 0.00003 ) at 6 h postoperatively .