Foot-type as a risk marker in chronic low back pain

 Foot function has been linked with various musculoskeletal pathologies. In recognition of the over-emphasised role of interventional trials and the underdeveloped role of observational studies in investigating such relationships, a case-control study was designed to examine the link with low back pain. Before this could proceed, several critical issues surrounding the validity and reliability of measures of 'foot-type' were examined to identify the optimal technique for use in observational research. Firstly, the ability of static measurements to reflect the dynamic state was investigated for two footprint and a calcaneal motion measure to examine a basic validity dimension. Although all measures differed between states, high correlations revealed a consistent dynamic increase. Subsequent content validity assessment involved examining the response of footprint and navicular motion measures to 50 changes in subtalar joint position. Navicular height was most sensitive (consistently changing value significantly with between 50 & 100 of calcaneal motion), whilst poor performance of footprint measures (requiring >150 of calcaneal motion to induce significant changes) compromised their further use. The original intention to categorise subjects according to subtalar axis orientation to increase the precision of this validity study was abandoned after its reliability was found to be poor. Finally, the optimal, motion-based, measures of foot-type identified were utilised in a case-control study, which recruited 64 cases with low back pain and 57 controls. A significantly higher magnitude of left-right asymmetry of calcaneal and navicular motion, and a significantly reduced score on a foot-health related quality of life assessment tool, the foot health status questionnaire, was found in cases. Despite concerns over the absolute reliability and validity of the motion-based measures used, and several limitations in the case-control design, the study implicates foot function with low back pain and suggests that further study to determine the extent of its involvement is warranted.