Citations

The purpose of this study was to validate a commercially available inertial measurement unit (IMU) system against a standard lab-based motion capture system for the measurement of shoulder elevation, elbow flexion, trunk flexion/extension, and neck flexion/extension kinematics. The validation analyses were applied to 6 surgical faculty members performing a standard, simulated surgical training task that mimics minimally invasive surgery. Three-dimensional joint kinematics were simultaneously recorded by an optical motion capture system and an IMU system with 6 sensors placed on the head, chest, and bilateral upper and lower arms. The sensor-to-segment axes alignment was accomplished manually. The IMU neck and trunk IMU flexion/extension angles were accurate to within 2.9 ± 0.9 degrees and 1.6 ± 1.1°, respectively. The IMU shoulder elevation measure was accurate to within 6.8 ± 2.7° and the elbow flexion measure was accurate to within 8.2 ± 2.8°. In the Bland-Altman analyses, there were no significant systematic errors present; however, there was a significant inversely proportional error across all joints. As the gold standard measurement increased, the IMU underestimated the magnitude of the joint angle. This study reports acceptable accuracy of a commercially available IMU system; however, results should be interpreted as protocol specific.

ABSTRACTIntroductionRegional variability in interstitial fluid pressure confounds use of intramuscular pressure measurement to assess muscle force. It is hypothesized that interstitial flow is dependent on intramuscular pressure. The goal of this study was to assess the feasibility of using fluorescent microspheres to evaluate movement of interstitial fluid in skeletal muscle.MethodsTwo diameters of fluorescent microspheres were injected into the rat tibialis anterior during both static (n = 6) and passively lengthened (10% strain) experimental conditions (n = 6). Microsphere dispersion was evaluated using confocal imaging of transverse muscle sections.ResultsFluorescent microspheres tracked interstitial fluid while not penetrating the muscle fiber. When compared with the static condition, significantly greater dispersion (P = 0.003) was seen with passively lengthened conditions (17 ± 9% vs. 31 ± 7%, respectively). Dispersion did not differ for the 2 microsphere sizes (P = 0.811).ConclusionsFluorescent microspheres track movement of interstitial fluid, and dispersion is dependent on passive lengthening. Muscle Nerve 54: 444–450, 2016

Repeated durations of dynamic activity with high ground reaction forces (GRFs) and loading rates (LRs) can be beneficial to bone health. To fully characterize dynamic activity in relation to bone health, field-based measurements of gait kinetics are desirable to assess free-living lower-extremity loading. The study aims were to determine correlations of peak vertical GRF and peak vertical LR with ankle peak vertical accelerations, and of peak resultant GRF and peak resultant LR with ankle peak resultant accelerations, and to compare them to correlations with tibia, thigh, and waist accelerations. GRF data were collected as ten healthy subjects (26 [19–34] years) performed 8–10 walking trials at velocities ranging from 0.19 to 3.05 m/s while wearing ankle, tibia, thigh, and waist accelerometers. While peak vertical accelerations of all locations were positively correlated with peak vertical GRF and LR (r2 > .53, P < .001), ankle peak vertical accelerations were the most correlated (r2 > .75, P < .001). All peak resultant accelerations were positively correlated with peak resultant GRF and LR (r2 > .57, P < .001), with waist peak resultant acceleration being the most correlated (r2 > .70, P < .001). The results suggest that ankle or waist accelerometers give the most accurate peak GRF and LR estimates and could be useful tools in relating physical activity to bone health.

ABSTRACTFor total knee arthroplasty (TKA), neutral mechanical alignment produces balanced static knee loading. Dynamically, knee loading is affected by more than limb static alignment. We compared static and dynamic knee loading following TKA. Fifteen TKA patients were evaluated pre‐operatively and 2 months and 2 years post‐operatively. Tibiofemoral angles and medial tibial plateau loading were calculated. Pre‐operatively, static medial load was greater for varus than valgus knees. Post‐operatively, no relationship existed between tibiofemoral angle and static medial plateau load. Pre‐operatively and post‐operatively, dynamic medial load was not dependent on tibiofemoral angle. While all patients achieved equal static plateau load distributions at 2 years, only 47% had dynamic medial load distributions of 50 ± 10%. Static tibiofemoral alignment alone does not predict dynamic tibial loading. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:???–???, 2014.

Since Blix noted that force varies with muscle length [1], many investigators have worked to characterize the passive length-tension properties of skeletal muscle in the tissue’s fiber direction [2]. However, few reports have examined the properties of muscle in either transverse extension or in longitudinal shear [3–4]. Material properties in these three directions are needed to fully characterize computational models, which generally describe muscle as being transversely isotropic, hyperelastic, and isovolumetric [3–6]. Further, previous studies reporting tri-planar material properties indicate that muscle tissue is stiffer in the transverse direction compared to the longitudinal direction [3–4]. This counters conventional notions of transversely isotropic materials, which are generally stiffer in the fiber direction.

Mathematical models are non-invasive tools used for analyzing biomechanical conditions. Various models of the knee using the finite element analysis technique [1–6] and rigid body spring model (RBSM) [7] have been developed to predict pressure distribution in articulating joints, although the RBSM is considered the simplest of the modeling techniques, while still effectively predicting load distribution. These models can be used to study altered joint loading, which causes a degeneration of the articular cartilage, in order to gain an understanding of the etiology of osteoarthritis (OA). The purpose of this study is to develop a subject-specific analytical knee model using the RBSM approach that incorporates subject-specific geometry, joint health, and loading patterns to predict tibiofemoral load distributions.