Studies investigating posteroanterior (PA) forces in spinal stiffness assessment have shown relationships to spinal level, body type, and lumbar extensor muscle activity. Little objective evidence is available discerning variation in PA stiffness and its clinical significance. The aim of this prospective clinical study was to determine the stiffness index and neuromuscular characteristics of the asymptomatic and symptomatic low back. Twenty-two subject underwent physical examination and completed outcome VAS, Oswestry, and SF-36 questionnaires. A hand-held spinal manipulation instrument, equipped with a load cell and accelerometer was used to deliver high rate (<0.1 sec) PA manipulative thrusts (450 N) to several common spinal landmarks including the posterior superior iliac spine (PSIS), sacral base, and L5, L4, L2, T12, T8 spinous (SP) and transverse processes (TP). Surface, linear enveloped, electromyographic (sEMG) recordings were obtained during the trusts from electrodes (8 leads) located over the L3 and L5 erector spinae. The accelerance (peak acceleration/peak force, kg.sup.-1) or stiffness index and composite sEMG response was calculated for each of the trusts. Significantly increased SP stiffness (7.0 kg.sup.-1) (P<0.05) and a more positive sEMG response was found in subjects with frequent or constant LBP symptoms in comparison to SP stiffness (6.5 kg.sup.-1) of subjects with lesser symptom frequency. A positive sEMG response was associated with a significant increase (P<0.05) in the TP stiffness response to PA thrusts in comparison to negative neuromuscular responders. The average SP stiffness was 6.6% greater (P<0.05) and 19.1% greater (P<<0.001) than the average SI stiffness and average TP stiffness, respectfully.

Les études étudiant des forces du posteroanterior (PA) dans l'évaluation spinale de rigidité ont montré des rapports avec le niveau spinal, le type de corps, et l'activité lombaire de muscle d'extenseur. Peu d'évidence objective est disponible discernant la variation dans la rigidité de PA et sa signification clinique. Le but de cette étude clinique éventuelle était de déterminer l'index de rigidité et les caractéristiques neuromusculaires du dos asymptomatique et symptomatique du bas. Vingt-deux soumis a subi l'examen physique et a accompli des résultats VAS, Oswestry, et questionnaires SF-36. Un instrument spinal tenu dans la main de manipulation, équipé d'une cellule et d'un accéléromètre de charge a été utilisé pour fournir le taux élevé (