Changes in apparent leg length (LL) (leg retraction) have been used by many as a means of locating subluxation in various joints. The leg check is based on the assumption that unequal muscular contraction (e.g. hyper irritable muscles) about the spine and pelvis have the ability to retract one leg relative to the other. Despite claims of usefulness, many problems are inherent in the prone leg check such as: a) measurement error; b) subject positioning by the examiner (expectancy bias); c) interference with the surface of the examination table; d) possible overwhelming effects of large muscles over smaller intersegmental muscles and; e) lack of information of the validity of subluxation (eg. segmental aberration) and it’s supposed neurological effects. While observation of leg retraction has not yet been correlated with patient outcome or health measures, it is implied that the phenomenon apparent changes in LL occur due to altered tonic neck and back reflexes which coordinate spinal movements and posture. A video recording has been made of a patient who exhibited an unusually large amount of leg retraction which appeared to be due to asymmetrical contraction of their supra-pelvic musculature upon maneuvers such as tucking their chin.
The purpose of this study is to quantify the involuntary movements which nave been observed about the spine, pelvis and extremities using a 2D motion analysis system.
A subject exhibiting a large involuntary leg retraction will be sought. The patient will be positioned prone on an adjusting table. Retro reflective markers will be placed about their spine, pelvis and extremities. The markers will be recorded by two video cameras during maneuvers which cause the leg to retract.
This data will yield 2D maker locations which will be used to quantify the amount and type of movement.
Despite claims of utility of the prone leg check to locate subluxation and treatment success, many confounders occur. Lack of objective documentation and theoretical basis of the leg retraction phenomena has hindered its acceptance as an examination procedure. Only indirect evidence exists for its validity in several small observational studies where it was used to determine were to adjust. Motion analysis, and EMG studies may help in understanding the physiology of this phenomena using. Further work is necessary to correlate the relationship of leg retraction to other methods of subluxation assessment, treatment outcome and patient health status, if any.
Reference: Paul J. Osterbauer,DC; Arlan W. Fuhr,DC. Proceedings of the California Chiropractic Foundation’s 7th Annual Conference on Research and Education, June 19-21,1992; pp.291-292.