• Patient's pain intensity score since the previous visit,using a visual analog scale(VAS) where 0 mm = no pain and 100 mm = extreme pain.
  

• Patient's current pain intensity VAS score
  
• Patient's global assessment
  
• Roland Disability Index
  
• Patient's sleep assessment
  

Immediate release (IR) tramadol has demonstrated efficacy in several pain conditions including: obstetrical, gynecological, orthopedic, abdominal, and oral surgery. The short elimination half-life of IR tramadol necessitates every 4-6 hour dosing in order to maintain optimum levels of analgesia in chronic pain. The study medication in this study is a once-daily, extended release (ER) tramadol formulation. This is a multicenter, double-blind, randomized, placebo-controlled, parallel-group study. At the Screening Visit, patients eligible for study participation by medical history, physical exam and other evaluations will enter a 2-7 day washout peroid during which time analgesics will not be allowed. At Visit 2, patients with a pain intensity >= 40 mm on a 100 mm visual analog scale (VAS) and who meet all other eligibility criteria will be admitted into a 3-week, open-label, run-in peroid during which time they will receive tramadol ER 100 mg once daily (QD) for at least 3 days. On Day 4, the dose will be increased to tramadol ER 200 mg QD, based on tolerability. Patients must be mainteained on a minimum dose of tramadol 200 mg QD by the beginning of Week-2 (Visit 3); the dose may be increased to tramadol ER 300 mg QD at Visit 3, based on tolerability. Patients must increase their tramadol ER dose to 300 QD by the beginning of Week - 1 (Visit 4); this dose must be maintained for one week. Patients with pain unresponsive to appropriate dose adjustments or with unacceptable side effects will be discontinued from the study and an alternative analgesic therapy will be initiated. Patients receiving tramadol ER 300 mg QD at the end of the run-in peroid (Visit 5, Week 0) will enter a 12-week, double-blind peroid during which they will be randomized to receive tramadol ER 300 mg, tramadol ER 200 mg, or placebo QD. No dose adjustments will be permitted during the double-blind peroid of the study. Patients will return for safety and efficacy evaluations at Weeks 1, 2, 4, 8 and 12 or early termination. Study medication will be discontinued at Week 12 and patients will return after one week for a post-treatment visit (Week 13).