Results of changes in pain using the visual analogue scale. a) Pain intensity. Visual analogue scale (VAS; 0-no pain, 100-worst pain) values of evening pain, presented as a single-subject design study graph for each individual patient. Repeated measurements in each of the four different phases — baseline (pre-operative) and 3 months, 6 months and 12 months post-operatively — are presented (black line). The mean value of each phase is indicated by a dotted line. b) The mean VAS of each patient is presented, together with the regression line from the mixed model (VAS = 81.7 - 8.4 × time).