The prone comparison of  changes in leg alignment is commonly used to identify musculoskeletal  dysfunction by chiropractors. Despite its widespread use as a diagnostic  tool, confusion exists about the reliability of these measures. A  possible problem is this methods dependence upon the clinician to  accurately assess leg length asymmetries by visual inspection. The  purpose of this investigation was to utilize a precise optoelectric  device to determine 1) Leg length asymmetries prior to and after a  random series of isolation tests, and 2) Heel trajectories during the  performance of these isolation tests.


-Four subjects were tested in the Motor Control  Laboratory at ASU. During each testing Session the subjects lay prone on  a portable adjusting table with infrared light emitting diodes affixed  with adhesive to their posterior heels, and posterior occiput.  Additional markers were placed on a moveable reference bar placed near  the subject’s feet. The reference bar was aligned to be perpendicular to  the body, and was independent of the adjusting table. Prior to any data  ‘Collection, each patient was assessed visually by a chiropractor for  the incidence of any leg length inequality, which was recorded for later  use. After the visual assessment, the reference bar was placed at its  permanent location, and a second leg length measurement was made by a  second investigator by measuring marker location of each heel from the  bar with a scale marked in millimeters. Each measurement (visual and  from the bar) were kept blind from the other respective investigator.  Data collection then proceeded with the optoelectric device. 

Data were  collected for 8 seconds at 50 Hz during the following conditions: no  movement, head-up, chin-tuck, pressure test right transverse process of  C-1, or pressure test left transverse process of C-1, The initial 5  trials were in the order mentioned in the prior sentence; 5 trials of  each condition were then collected in a randomized order for a total of  30 trials. After all data were collected, leg length assessments were  carried out by the two investigators as was completed prior to data  collection. After data collection was complete, digital data were  filtered at 2 Hz and 0′ rotated mathematically into a local reference  frame within which the bar represented one axis in a 3-D frame. This  allowed measurements to be examined along an axis perpendicular to the  bar, the expected axis of lengthening or shortening of each leg. Two types of analyses were completed for each subject. Leg  length difference analysis consisted of examining the heel positions at  the; beginning and end of the entire testing session and comparing the  data to the investigator’s manually measured reports.

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 Inequalities Before, During, and  After Isolation Tests; Proceedings of the 1994 International  Conference on Spinal Manipulation. Palm Spring, CA, June 10-11, 1994, p.  24-25.

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