At follow-up , the 90-N group had less pain than the 30-N group ( mean difference , 11.3 mm ; 95 % confidence interval : 0.1 , 22.6 mm ; P = .048 ) and lower stiffness than the placebo group ( mean difference , 17.5 % ; 95 % confidence interval : 4.2 % , 30.9 % ; P = .006 ) .