Efficacy of spinal manipulation and mobilisation on trunk flexibility and stiffness in horses: a randomised clinical trial

Reasons for performing the study: Spinal mobilisation and spinal manipulative therapy (SMT) are being applied to horses; however, there are limited objective measures of their effects on spinal mobility or stiffness in actively ridden horses. Objectives: To quantify passive spinal movements induced during dorsoventral mobilisation of the trunk and to identify any potential effects of SMT on measures of spinal mobility within the thoracolumbar region in standing horses. We hypothesise that displacement amplitudes will be significantly increased across vertebral levels after SMT, compared to spinal mobilisation only within the control group. Methods: Passive spinal mobility was assessed in 24 actively ridden mature horses once a week for 3 weeks. Peak vertical displacement, loading and unloading velocities, applied force, stiffness and the frequency of truncal oscillations induced during dorsoventral spinal mobilisation were measured at 5 thoracolumbar sites and compared between treatment (n = 12) and control (n = 12) groups. Each week, outcome parameters were measured pre‐ and post intervention, 10 min apart. Treatment consisted of manually‐applied, high‐velocity, low‐amplitude (HVLA) thrusts directed at the 5 intervertebral sites. Control horses received no additional intervention. A mixed‐effects linear regression model was used to assess the interactive effects of treatment group, vertebral level, week and pre‐/post intervention. Results: Post intervention displacement amplitudes of the trunk and applied forces were significantly higher in the SMT group, compared to the control group. A similar trend was found for increased spinal stiffness within the SMT group. Across vertebral levels, SMT induced a 40% increase in displacement, a 20% increase in applied force and a 7% increase in stiffness. Conclusions and potential relevance: SMT increased dorsoventral displacement of the trunk, which is indicative of producing increased passive spinal flexibility in actively ridden horses. Further clinical research is needed on the effectiveness of manual therapies in horses with objective measures of back pain, stiffness and poor performance.