Objective: To investigate the relation between localized pressure pain sensitivity and the amplitude and specificity of semispinalis cervicis muscle activity in patients with chronic neck pain.
Materials and Methods: Pressure pain detection thresholds (PPDTs) were measured over the C2-C3 and C5-C6 cervical zygapophyseal joints in 10 women with chronic neck pain and 9 healthy age-matched and sex-matched controls. Intramuscular electromyography (EMG) was acquired from the semispinalis cervicis at the levels of C2 and C5 during isometric circular contractions in the horizontal plane at 15 and 30 N, with continuous change in force direction in the range 0 to 360 degrees. The average rectified value and directional specificity of semispinalis cervicis muscle activity were computed and regression analyses were performed between measures of EMG and PPDT.
Results: Patients showed significantly lower PPDT compared with controls (P<0.01). Patients also displayed lower EMG amplitude of the semispinalis cervicis at both spinal levels during the circular contractions (average across spinal levels, mean±SD: 129.01±58.99 and 126.83±58.78 µV for the 15- and 30-N contractions, respectively) compared with controls (158.69±66.27 and 187.64±87.82 µV; P<0.05). Furthermore, the directional specificity of semispinalis cervicis muscle was lower for the patients during the circular contractions (P<0.05). The PPDT (C2 and C5 pooled) was positively correlated to both, directional specificity (R2=0.22, P<0.05) and amplitude (R2=0.15, P<0.05) of the EMG.
Discussion: In contrast to asymptomatic individuals, the semispinalis cervicis muscle displays reduced and less-defined EMG activity during a multidirectional isometric contraction in patients with chronic neck pain. The altered behavior of the semispinalis cervicis is weakly associated to pressure pain sensitivity.