Potential treatment effect modifiers for manipulative therapy for spinal pain in children Secondary analyses of a randomised controlled trial

Introduction
Spinal pain, i.e. back and/or neck pain, is recurrent and bothersome for a considerable subgroup of children. It is generally acknowledged that a particular intervention, e.g. manipulative therapy, may be more effective for a subgroup of people with certain characteristics, i.e. effect modifiers.

Objective
The aim of this study was to test whether five indicators of a potential increased need for treatment act as effect modifiers for manipulative therapy in the treatment of spinal pain in children, i.e. whether the most affected children may benefit more from manipulative therapy than the less affected children.

Five pre-specified, potential effect modifiers were explored
Number of weeks with spinal pain 6 months prior to inclusion
Number of weeks with co-occurring musculoskeletal pain (pain in more than one site) 6 months prior to inclusion
Expectations of the clinical course
Pain intensity at baseline
Quality of life at baseline

Outcomes
Number of recurrences of spinal pain
Length of episodes
Total number of weeks with pain
Global perceived effect after two weeks
Change in pain intensity after two weeks

Methods
This study was a secondary analysis of data from a randomised controlled trial comparing advice, exercises and soft tissue treatment with or without the addition of manipulative therapy in 238 Danish school children aged 9-15 years with spinal pain. A text message system (SMS) and clinical examinations were used for data collection.

Results
We found that children with long duration of spinal pain or co-occurring musculoskeletal pain prior to inclusion as well as low quality of life at baseline tended to benefit from manipulative therapy over non-manipulative therapy, whereas the opposite was seen for children reporting high intensity of pain.
However, most results were statistically insignificant, probably due to the limited sample size.

Conclusion
This secondary analysis indicates that children more effected by spinal pain have a greater chance to benefit from treatment that include manipulative therapy. However, these analyses were both secondary and underpowered, and therefore merely exploratory. The results underline the need for a careful choice of selection criteria in future investigations of manipulative therapy in children.