Are static and dynamic squatting activities comparable?

Background: Numerous studies have described 3D kinematics, 3D kinetics and electromyography (EMG) of the lower limb during quasi-static or dynamic squatting activities. However there is only little information on the comparison of these two squatting conditions. Only one study compared these activities in terms of 3D kinematics, but no information was available on 3D kinetics and EMG. The purpose of this study was to compare simultaneous recordings of 3D kinematics, 3D kinetics and EMG of the lower limb during quasi-static and fast dynamic squats. Methods: Ten subjects were recruited. 3D knee kinematics was recorded with a motion capture system, 3D kinetics was recorded with a force plate, and EMG of 8 muscles was recorded with surface electrodes. Each subject performed a quasi-static squat and several fast dynamic squats from 0° to 70° of knee flexion. Findings: Mean differences between quasi-static and dynamic squats were 1.6° for rotations, 1.8 mm for translations, 38 N ground reaction forces (2.1 % of subjects’ body weight), 6 Nm for torques, 13.0 mm for center of pressure, and 7 µV for EMG (6.3% of the maximum dynamic electromyographic activities ). Some significant differences (P < 0.05) were found in anterior-posterior translation, vertical forces and EMG. Interpretation: All differences found between quasi-static and fast dynamic squats can be considered small. 69.5% of the compared data were equivalent. In conclusion, this study show for the first time that quasi-static and dynamic squatting activities are comparable in terms of 3D kinematics, 3D kinetics and EMG.

Listed In: Biomechanical Engineering, Biomechanics, Gait, Orthopedic Research, Posturography

Impacts of Stifle Joint Remodeling on Vertical Ground Reaction Forces Following MCL Transection and Medial Meniscectomy

Functional demands placed on the human knee’s anterior cruciate ligament (ACL) vary with activity but remain impossible to measure directly in-vivo. Our lab is characterizing these demands in the sheep model by recording in vivo knee kinematics and ACL transducer voltages during activities of daily living (ADLs), reproducing these motions using the instrumented limb, and measuring the 3D forces in the ligament. However, up to 13% of patients sustaining ACL injuries will also sustain dual medial meniscus (MM) injuries and up to 10% will sustain dual medial collateral ligament (MCL) injuries. These structures are frequently left unrepaired, which may alter the ACL’s functional demands, resulting in inadequate ACL reconstruction outcomes for patients with dual injuries. Although these structures have been shown to alter ACL loading in cadaveric studies, the extent to which they impact ACL functionality during in vivo ADLs remains unknown. Moreover, changes in ACL functionality over time due to joint healing and remodeling have yet to be investigated. In this study, we aimed to track stifle joint remodeling in response to surgically imposed MCL transections and medial meniscectomies through monitoring vertical ground reaction forces (VGRFs) for three ADLs over 12 weeks. Results of this study may then be used in conjunction with future robotic studies as a tool to estimate in vivo load requirements for ACL reconstructions in patients with dual injuries.

Listed In: Biomechanical Engineering, Biomechanics, Gait, Orthopedic Research