A "responder" is a participant in the study that: 1. completed 28 days of the maintenance phase 2. had a numeric rating scale score below 5 on the 11 point scale (where 0 indicates no pain and 10 indicates worst possible pain. This twice daily current pain score was averaged over Day 18 to Day 43. 3. did not use more than 20 mg of rescue medication per day on average in the 28 day maintenance period (from Day 18 to Day 43). A participant that met all 3 of the above-mentioned criteria is counted as a responder, in other words the participant benefited from the assigned drug treatment. A participant that failed to meet only 1 of the 3 criteria is not counted as a responder.

For this twice daily pain assessment, the participants were required to indicate the level of pain experienced over the previous 12 hours on an 11-point Numeric Rating Scale (NRS) where a score of 0 indicated "no pain" and a score of 10 indicated "pain as bad as you can imagine". The lower the value the less pain in the treatment group. Negative values indicate a reduction in pain.

Pain control was considered to be achieved for participants who met both of the following criteria for any consecutive 3 days during the first week of treatment period: a) Change from baseline of mean 24 hour numerical rating scale (NRS) (an 11-point NRS is used to measure the pain level where 0=no pain to 10=pain as bad as you can imagine) score less than +1.5, and b) when the frequency of rescue medication was twice or less per day.

For this twice daily pain assessment, the patients were to indicate the level of pain experienced over the previous 12 hours on an 11-point Numerical Rating Scale (NRS) where a score of 0 indicated "no pain" and a score of 10 indicated "pain as bad as you can imagine".

SPID5 was calculated as the weighted (weights is taken as the number of hours elapsed since the previous measurement) sum of the PID collected up to 5 days. Pain intensity (PI) score is calculated as the average PI over the past 12 hours using an 11-point (0 to 10) numerical rating scale (NRS) where "0" is no pain and "10" is pain as bad as you can imagine. The difference between baseline PI at the qualifying period and current PI is pain intensity difference (PID).

The number of SBM over the 14-day IR treatment phase was determined from the Bowel Function Patient Diary and factored to enable a per week value to be used. An SBM is defined as any BM that has occurred without the use of a laxative, enema, suppository, or manual manipulation within the previous 24 hours.

The SPID score incorporates the cumulative analgesic effects of tapentadol IR on pain intensity over an extended period (48 hours) allowing for an evaluation of multiple doses of drug, even when dosing frequency may vary. Scoring is derived from the Numerical Rating Scale (NRS) from 0 = No pain to 11 = Pain as bad as you can imagine. A positive difference between the mean SPID48 for an active study drug and placebo would indicate a numerically larger analgesic effect for subjects dosed with active study drug than in the placebo group. A higher value in SPID indicates greater pain relief.

The number of subjects who reported a TEAE during the treatment period. TEAE was defined as any adverse event that started or worsened on or after the start of the study medication and up to 3 days after the discontinuation of the study medication.

For this twice daily pain assessment, the subjects were to indicate the level of pain experienced over the previous 12 hours on an 11-point Numerical Rating Scale (NRS) where a score of 0 indicated "no pain" and a score of 10 indicated "pain as bad as you can imagine".

For this twice daily pain assessment, the subjects were to indicate the level of pain experienced over the previous 12 hours on an 11-point Numerical Rating Scale (NRS) where a score of 0 indicated "no pain" and a score of 10 indicated "pain as bad as you can imagine".

The number of participants who reported a TEAE during the treatment period. TEAE was defined as any adverse event that started or worsened on or after the start of the study medication and up to 3 days after the discontinuation of the study medication.

Participants were asked to assess the average pain intensity on an 11-point NRS ranging from 0 (no pain) to 10 (maximum pain imaginable) by selecting a number on the scale applicable to their pain. Baseline pain score is defined as the average pain intensity score over the last 3 days prior to the randomization. Change from Baseline in NRS score is the mean NRS score at Week 12 minus mean NRS score at Baseline.

Participants were asked to assess the average pain intensity on a 11-point NRS ranging from 0 (no pain) to 10 (maximum pain imaginable) by selecting a number applicable to their pain on the scale. The mean pain intensity during the past 74 hours (3 days) was evaluated at Baseline and the mean pain intensity during the past 12 hours was evaluated at subsequent study visits.

The Cmax is the maximum plasma concentration.

The tmax is time to reach the maximum observed serum concentration.

The AUC (0-last) is the area under the serum concentration-time curve from time zero to last quantifiable time.

The AUC (0-infinity) is the area under the serum concentration-time curve from time zero to infinite time, calculated as the sum of AUC(last) and C(last)/lambda(z), wherein AUC(last) is area under the serum concentration-time curve from time zero to last quantifiable time; C(last) is the last observed quantifiable concentration; and lambda(z) is elimination rate constant.

Percentage of AUC (0-infinity) will be obtained by extrapolation and calculated as: difference between AUC (0-infinity) and AUC (0-last)/AUC (0-infinity) multiplied by 100.

Elimination half-life (t \[1/2\] Lambda) is associated with the terminal slope (lambda \[z\]) of the semi logarithmic drug concentration-time curve, calculated as 0.693/lambda(z).

Lambda(z) is first-order rate constant associated with the terminal portion of the curve, determined as the negative slope of the terminal log-linear phase of the drug concentration-time curve .

The t (last) is the time to last quantifiable serum concentration.

The Cmax,ss is the observed maximum serum concentration during a dosing interval at steady-state (time at which serum concentration does not change with time).

The C trough is the trough serum concentration before each dose of the multiple-dose treatment.

The Tmax,ss is the time to reach the maximum serum concentration after the fifth dose of the multiple-dose treatment.

The AUC (0-tau) is the area under the serum concentration-time curve during a dosing interval (tau).

The Cavg,ss is the average serum concentration at steady-state, calculated as AUC (tau) divided by tau.

The FI is percentage fluctuation that is, variation between peak and trough at steady-state, calculated as difference between Cmax and Ctrough divided by Cavg,ss and multiplied by 100.

Accumulation Ratio calculated for AUC as AUC (x, ss) divided by AUC (x, sd) and for Cmax as C(max,ss) divided by C(max,sd).