Interpretation of cervical passive accessory intervertebral movements: From thumbs to outcomes

Abstract

PURPOSE: To describe the specific characteristics of passive accessory intervertebral movements (PAIVMs) to the cervical spine that relate to patient symptoms and segmental mobility. RELEVANCE: PAIVMs are common manual therapy techniques. The interpretation of PAIVM findings is often described using force-displacement curves contained in movement diagrams, but it has not been clear what aspects of the force-displacement curves are related to patient symptoms or to intervertebral mobility. DESCRIPTION: Contrary to the initial concepts of PAIVMs, the intervertebral movements produced are neither accessory nor localized, but rather physiological and involve the entire cervical region. Nonetheless, specific, measurable characteristics of PAIVMs have been shown to be related to patient outcomes and to local tenderness. This paper will discuss how these specific characteristics compare to simulations using computer- based modeling. EVALUATION: Experimentally determined changes in PAIVMs at symptomatic locations that occur with symptom improvement are similar to differences between tender and less tender locations. The relevant differences are easier to visualize using stiffness-displacement curves than the forcedisplacement curves that are typically used in movement diagrams and become apparent at levels of force starting at less than those required to click a retractable pen (4-5 N). Computer-based modeling indicates that similar differences in PAIVM stiffness to those found in the clinical studies would be expected to occur with a reduced lax zone of the underlying motion segment. CONCLUSIONS: The behaviors of PAIVM stiffness related to patient symptoms (1) are more clearly visualized with stiffness curves than force-displacement curves, (2) occur from low levels of force, and (3) are consistent with a smaller lax zone at the underlying intervertebral motion segment. IMPLICATIONS: The early parts of PAIVM movements contain clinically important information. Simple linear approximations of force-displacement curves of PAIVMs may not be sufficient to detect the specific characteristics that are related to patient symptoms.