Objectives: When the clinical efficacy of spinal manipulative treatment for spinal pain has been assessed, high-velocity low-amplitude thrust (HVLAT) manipulation and mobilization have been regarded as clinical interventions giving identical and equivalent biologic effects. The objective of this review is to critically discuss previous theories and research of spinal HVLAT manipulation, highlighting reported neurophysiologic effects that seem to be uniquely associated with cavitation of synovial fluid. Data Source: The biomedical literature was searched for research and reviews on spinal manipulation. MEDLINE and EMBASE databases were used to help find relevant articles. Study Selection: All articles relevant to the objectives were selected. Data Extraction: All available data were used. Data Synthesis: The main hypotheses for lesions that respond to HVLAT manipulation were critically discussed: (1) release of entrapped synovial folds or plica, (2) relaxation of hypertonic muscle by sudden stretching, (3) disruption of articular or periarticular adhesions, and (4) unbuckling of motion segments that have undergone disproportionate displacements. Results: There appear to be 2 separate modes of action from zygapophyseal HVLAT manipulation. Intraarticular "mechanical" effects, of zygapophyseal HVLAT manipulation seem to be absolutely separate from and irrelevant to the occurrence of reported "neurophysiologic" effects. Cavitation should not be an absolute requirement for the mechanical effects to occur but may be a reliable indicator for successful joint gapping. Conclusions: It is hoped that identification of these unique neurophysiologic effects will provide enough theoretical reason for HVLAT manipulation and mobilization to be assessed independently as individual clinical interventions.
