Concomitant low back pain impairs outcomes after primary total knee arthroplasty in patients over 65 years: a prospective, matched cohort study - Collados-Maestre, I; Lizaur-Utrilla, A; Martinez-Mendez, D; Marco-Gomez, L; Lopez-Prats, F A (Arch Orthop Trauma Surg, 2016)