Despite the high prevalence and global burden of low back pain (LBP), the pathogenesis is poorly understood. Without a better understanding of what structures are involved in the development and chronicity of LBP, the value and efficacy of clinical assessments and physical therapy interventions are limited. Although there is a clear link between the lumbar spine, pelvis and hip extensors during movement in both LBP and healthy subjects, there is limited evidence regarding whether it is passive or active components that are influenced. There is a need for improved prognostic evaluation of patients with LBP, including whether altered hip biomechanics are the result of structural, passive elements, or neuromuscular, active components of movement. Such evaluations will be beneficial for researchers, clinicians and physical therapists.
The purpose of the present investigation is initially to demonstrate how a handheld measuring device can be adapted for use in measuring passive hip moments during supine leg raising. Comparisons are then made between subjects with LBP and healthy controls. A validated dynamic biomechanical model is used to calculate passive hip moments at a variety of knee angles, from which a predictive equation is derived, which is specific to each subject. Following a gait analysis protocol, the predictive equation is used to calculate passive hip extensor moments during the hip flexion component of gait. Comparisons are made between passive hip extensor moments, total hip moments, power and work done, in subjects with and without LBP.
The present investigation demonstrated the high accuracy of a handheld force transducer for the measurement of passive hip moments. There were no statistically significant differences in passive hip extensor biomechanical properties between subjects with LBP and healthy controls. However, assessment during walking demonstrated significant differences in passive hip extensor moments between subjects with LBP and controls. Further differences were identified in total hip moments, power and work done, despite no differences in gait parameters. It is plausible that the passive and active components of movement interact, although further research is required to determine whether such interactions are consistent and predictable.
It was observed that the passive contribution to hip biomechanics during the swing phase of gait is considerable, and should be incorporated into dynamic modelling. Differentiating between passive and active components may be particularly useful for researchers, clinicians and physical therapists, for evaluating which components are influenced by LBP and for assessing the efficacy of component-specific interventions. Future research should expand on this research to include a wider range of LBP patients, with different severity and disability of LBP, to develop a more complete range of data on how passive and active components are influenced and the range of interactions during common movements. Other research should attempt to determine which interventions are most appropriate for targeting changes to passive and active components independently, and in accordance with patient adaptations to LBP. The modelling, experimental procedures and customised equipment used in the present investigation are appropriate for use in assessing passive contributions to joint biomechanics during movement.