Fig. 1.

Change scores in the ODI over time are displayed according to duration of symptoms. The surgery p value compares duration of symptoms ≤ 6 months with duration of symptoms > 6 months. The nonoperative p value compares duration of symptoms ≤ 6 months with duration of symptoms > 6 months. The interaction p value compares treatment effect (surgery versus nonoperative) between duration of symptoms ≤ 6 months and duration of symptoms > 6 months. All p values are time-weighted averages over 8 years (ie, area under the curve).