Changes in apparent leg length”(leg retraction) have been used  by many as a means of locating subluxation in various Joints. The leg  assessment 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 assessment such  as: a) measurement error; b) subject positioning by the examiner  (expectancy bias) and; c) interference with die surface of the examining  table. There have been prior attempts to quantify the amount of leg  length changes that occur during a treatment session, but most have  suffered due to the lack of a measurement technique which provides the  necessary accuracy in the recording of slight changes in heel position.

The purpose of this study was to quantify involuntary, movements that  result from neck flexion and extension maneuvers. Five subjects  exhibiting involuntary leg reactions were tested using an optoelectric  motion analysis system. During each testing session, the subject lay  prone on an adjusting table while infrared light emitting diodes (IREDs)  were affixed to the heels of fracture boots. In the rest position, the  neck was in neutral flexion so the face rested on the surface of the  table. Prior to testing, the examination area was in neutral flexion so  the face rested on the surface of the table. Prior to testing, the  examination area was calibrated resulting in RMS errors of less than 0.3  mm. Data were collected for ten seconds by three cameras positioned to  record movement of the IREDs. During each testing session, each subject  preformed two movements; a head-up movement, during which the subject  extended the neck and then returned to a resting position, and a  chin-tuck movement, in which the subject flexed the neck and then  returned to a resting position. A testing session consisted of three  no-movement baseline trials, followed by three head-up trials and three  chin-tuck trials. Examination of output displacement histories showed  that during all trials, movement occurred at the heels in the direction  of the subject’s longitudinal axis. During the head-up trials, a  majority of cases showed a net shortening in heel position during head  movement.

Reference: John K. Dewitt. B.Sc.E, Paul J.  Osterbauer, D.C., George E. Stelmach, Ed.D., & Arlan W. Fuhr. D.C.;  Optoelectric Measurement of Leg Length Changes During Isolation Tests;  Proceedings of the CCR’s 8th Annual Conference on Chiropractic  Science in Health Policy and Research, Monterey, CA, June 18-20, 1993,  pp. 156-7.

Affiliation: Arizona State University, Phoenix. Arizona and National Institute for Chiropractic Research, Phoenix, AZ.