Bupivacaine and morphine group had similar acute postoperative pain scores ( WMD : 0.07 ; 95 % CI , -0.18 to 0.32 ; P = 0.60 ) ; number of patients requiring supplementary analgesia ( relative risk : 0.74 ; 95 % CI , 0.42 to 1.31 ; P = 0.30 ) for the trials in this meta-analysis ( n = 13 ) ; and side effects ( relative risk : 0.63 ; 95 % CI , 0.39 to 1.02 , P = 0.06 ) .