Results of changes in oswestry disability index. a) Functional status. The Oswestry disability index (ODI; 0–100, with lower scores indicating less disability) values are presented as a single-subject design study graph of 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 ODI of each individual patient is presented, together with the regression line from the mixed model (ODI = 54.2 - 5.7 × time).