P72. Biomechanical characteristics of physical therapists performing lumbar spine manipulation

Abstract

<h3>BACKGROUND CONTEXT</h3> Lumbar spinal manipulation (LSM) is a manual therapy procedure that has been validated for treatment of acute low back pain (LBP) and is commonly performed by physical therapists (DPT) and chiropractors. Although there is a great deal of literature on the efficacy, optimal performance of LSM is limited to expert opinion. Existing evidence is focused on forces exerted on the patient rather than movement of the practitioner. It is imperative to understand the biomechanics of optimal performance as this may have direct impact on efficacy and patient outcomes. <h3>PURPOSE</h3> The primary purpose of this study was to identify the biomechanical characteristics of LSM. We hypothesized that performance of LSM can be characterized by patterns in ground reaction forces (GRF) and pelvic kinematics of the DPT. The secondary purpose was to determine which characteristics are associated with expert performance by comparing these variables amongst DPT experts, residents, and students. <h3>STUDY DESIGN/SETTING</h3> Cohort study. Biomechanical laboratory setting. <h3>PATIENT SAMPLE</h3> A total of 44 DPT's (4 experts, 11 orthopedic DPT residents, 13 3rd year DPT students, 16 1st year DPT students). <h3>OUTCOME MEASURES</h3> Four analyses were completed: 1) analysis of peak GRF and rate of GRF unloading; 2) analysis of relationships between GRF of each foot using force-force plots to determine if feet were acting together or separately; 3) analysis of pelvic linear and angular velocity and center of mass (COM) linear acceleration; 4) regression analysis exploring variables that were most associated with expert performance. <h3>METHODS</h3> DPT's completed two LSM on 2 healthy models, a total of 4 trials per subject. Subject's vertical GRF (GRFv) data were captured through two force plates, one under each foot. 3-D kinematic data were captured with retro-reflective markers on: L5-S1 interspace, bilateral greater trochanters, and bilateral iliac crests. <h3>RESULTS</h3> 1) Experts had significantly greater rate of GRFv unloading than all other groups (p<0.05). 2) The force-force analysis demonstrated significantly greater use of "in-phase" patterns in experts compared to students (p=0.009). 3) The kinematic analysis demonstrated that experts performed left rotation and right side-bend of the pelvis, while students performed the opposite. Maximum absolute transverse plane pelvic angular velocity was also greater in experts compared to all students (p<0.03). Peak linear velocity of the pelvis was significantly greater in experts than in all students (p=0.012, p=0.001). 4) The regression analysis showed that practitioner years of experience, mediolateral GRF, rate of GRFv unloading, and lowest force on the back foot accounted for 73% of the variance in COM acceleration (R= 0.85, p<0.001). <h3>CONCLUSIONS</h3> To the authors' knowledge, this was the first study analyzing the biomechanical characteristics of LSM in DPTs at different experience levels. Performance of LSM can be characterized through biomechanical analysis, and certain variables changed with clinician experience level. Expert DPTs unload their feet more quickly, utilize both feet in a similar way, tend to rotate their pelvis more quickly and in the opposite direction compared to students. Finally, expert performance of LSM, which was associated with increased COM downward acceleration, is explained by kinetic variables and years of experience. These findings assist practitioners in understanding and teaching the optimal performance of LSM, which may have an impact on efficacy of the treatment and improved patient outcomes for patients with acute LBP. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.