Fig. 2.

The effect of the operated level on headache relief. The highest levels (C3–4 and C4–5) were combined for analysis, since the number of operations at these levels was low (5 and 13, respectively). The pre- and postoperative NDI headache scores, respectively, were 2.8 and 1.6 for levels C3–4/C4–5, 2.6 and 1.2 for C5–6, and 2.1 and 0.9 for C6–7. Higher levels (those more proximal to the head) were associated with greater preoperative pain. There was no difference, however, in degree of postoperative pain relief as a function of what level was surgically treated (p = 0.45 for quantitative approach, p = 0.38 overall for categorical approach).