Letter to Editor concerning “Comparative study of the efficacy of transdermal buprenorphine patches and prolonged-release tramadol tablets for postoperative pain control after spinal fusion surgery: a prospective, randomized controlled non-inferiority trial” by Kim HJ, Ahn HS, Nam Y, Chang BS, Lee CK, Yeom JS (2017) Eur Sp ine J 26:2961–2968