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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