Immediate effects on pressure pain threshold following a single cervical spine manipulation in healthy subjects

DESIGN: A placebo, control, repeated-measures, single-blinded randomized study. OBJECTIVES: To compare the immediate effects on pressure pain threshold (PPT) tested over the lateral elbow region following a single cervical high-velocity low-amplitude (HULA) thrust manipulation, a sham-manual application (placebo), or a control condition; and to analyze if a different effect was evident on the side ipsilateral to, compared to the side contralateral to, the intervention. BACKGROUND: Previous studies investigating the effects of spinal manual therapy used' passive mobilization procedures. There is a lack of studies exploring the effect of cervical manipulative interventions. METHODS: Fifteen asymptomatic volunteers (7 male, 8 female; aged 19-25 years) participated in this study. Each subject attended 3 experimental sessions on 3 separate days, at least 48 hours apart. At each session, subjects received either the manipulation, placebo, or control intervention provided by an experienced therapist. The manipulative intervention was directed at the posterior joint of the C5-6 vertebral level. PPT over the lateral epicondyle of both elbows was assessed preintervention and 5 minutes postintervention by an examiner blinded to the treatment allocation of the subject. A 3-way analysis of covariance (ANCOVA) with intervention, side, and time as factors, and gender as covariate, was used to evaluate changes in PPT RESULTS: The analysis of variance detected a significant effect for intervention (F = 31.46, P <.001) and for time (F = 33.81, P <.001), but not for side (F = 0.303, P >.5). A significant interaction between intervention and time (F =15.74, P <.001) was also found. Gender did not influence the comparative analysis (F = 0.252, P >.6). Post hoc analysis revealed that the application of a HVLA thrust manipulation produced a greater increase of PPT in both elbows, as compared to placebo or control interventions (P <.001). No significant changes in PPT levels were found after the placebo and control interventions (P >.6). Within-group effect sizes were large for PPT levels in both elbows after the manipulative procedure (d > 1.0), but small after placebo or control intervention (d < 0.1). CONCLUSIONS: The application of a manipulative intervention directed at the posterior joint of the C5-6 vertebral level produced an immediate increase in PPT over the lateral epicondyle of both elbows in healthy subjects. Effect sizes for the HVLA thrust manipulation were large, suggesting a strong effect of unknown clinical importance at this stage, whereas effect sizes for both placebo and control procedures were small, suggesting no significant effect.