This is a randomized, outpatient, multicenter, double-blind study (blinded to patient and to study doctor) comparing NUCYNTA to oxycodone IR in the treatment of patients with acute (new onset) low back pain who also have associated leg pain that radiates (travels down) below the knee. Patients will be screened for study eligibility at Visit 1. The study will be explained and informed consent will be obtained. Potential patients must satisfy all eligibility criteria to be enrolled in the study. Eligible candidates will proceed to the Double-Blind Treatment Phase. At the time of study entry, all prohibited medications will be discontinued and will be disallowed throughout the study. All patients will call into an interactive voice response system (IVRS) to complete a pain assessments twice daily throughout the study. Patients who discontinue early for any reason will be instructed to contact the study site to complete final assessments, prior to taking supplemental pain medication if applicable, and to schedule a final study visit. All patients will return to the study site on Day 5 (Visit 2) where they will be evaluated by study personnel and, as appropriate, continue with study treatment for an additional 5 days. Patients will return to the study site for the final visit on Day 10/End of Study (Visit 3) when they will have all final study assessments. The treatment duration will be up to 10 days. The sponsor will collect adverse events starting with the signing of the informed consent form. Adverse events will be reported by the subject for the duration of the study. Any clinically significant abnormalities persisting at the end of the study will be followed by the investigator until resolution or until a clinically stable endpoint is reached. Blood samples for serum chemistry and hematology and a urine sample for urinalysis will be collected. The investigator will review the laboratory report, document this review, and record any clinically relevant changes occurring during the study. The following tests will be performed by the central laboratory: Urine Pregnancy Testing for women of childbearing potential only, Urine Drug Screen, Vital Signs (pulse rate and blood pressure), Physical Examination, Neurological Examination, and Vomiting Assessment. The study will be conducted at approximately 80 sites in the United States (US). Patients will be randomized to one of the two following treatment groups: NUCYNTA 50, 75 or 100 mg every 4 to 6 hours up to 10 days as needed for pain. Oxycodone IR 5, 10 or 15 mg every 4 to 6 hours as needed for pain. Patients will begin treatment on Day 1 with one "lower dose" capsule of study drug (NUCYNTA 50 mg or oxycodone IR 5 mg). Subsequent dose adjustments will be made by study patients, as needed, to achieve a dose that provides a meaningful improvement in their pain intensity