PubMed · 8343792
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R W Bohannon. 1993. Sphygmomanometer vs. dynamometer.. https://doi.org/10.2519/jospt.1993.17.6.320
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The aim of the present study was to analyze the organization of aiming movements in right-handed children aged 5 years, depending on gender and hand used to perform the task. We first tested the hypothesis that aiming movements are predominantly organized in a feed-forward manner before the age of six. Using a direction pre-cueing protocol, we analyzed the effect of gender and hand used to perform the task on reaction time (RT), movement time (MT), spatial accuracy (SA) and acceleration profiles (APs) in children aged 5 years. Differences in RT between the uncued and pre-cued conditions suggest that the direction is actually specified prior to the execution of the movement at the age of five. However, the results also show significant hand and gender effects on MTs, spatial error and APs. Specifically, in girls, MT and kinematics profiles vary as a function of hand and target localization, whereas this is not the case in boys. In addition, SA is lower when aiming with the non-dominant hand in boys, but not in girls. These results suggest that multiple movement strategies are already available to the child at the age of five. Girls appear to be able to change movement strategy as a function of the constraints of the task, resulting in a stability of spatial accuracy (SA). On the contrary, the functional advantage of the right hand on MT and SA generally reported in right-handed males is not present in the boys at the age of five.
STUDY DESIGN: The finite element technique was used to predict changes in biomechanics that accompany the application of a novel instrumentation system designed for use in the upper cervical spine. OBJECTIVE: To determine alterations in joint loading, kinematics, and instrumentation stresses in the craniovertebral junction after application of a novel instrumentation system. Specifically, this design was used to assess the changes in these parameters brought about by two different cervical anchor types: C2 pedicle versus C2-C1 transarticular screws, and unilateral versus bilateral instrumentation. SUMMARY OF BACKGROUND DATA: Arthrodesis procedures can be difficult to obtain in the highly mobile craniovertebral junction. Solid fusion is most likely achieved when motion is eliminated. Biomechanical studies have shown that C1-C2 transarticular screws provide good stability in craniovertebral constructs; however, implantation of these screws is accompanied by risk of vertebral artery injury. A novel instrumentation system that can be used with transarticular screws or with C2 pedicle screws has been developed. This design also allows for unilateral or bilateral implantation. However, the authors are unaware of any reports to date on the changes in joint loading or instrumentation stresses that are associated with the choice of C2 anchor or unilateral/bilateral use. METHODS: A ligamentous, nonlinear, sliding contact, three-dimensional finite element model of the C0-C1-C2 complex and a novel instrumentation system was developed. Validation of the model has been previously reported. Finite element models representing combinations of cervical anchor type (C1-C2 transarticular screws vs. C2 pedicle screws) and unilateral versus bilateral instrumentation were evaluated. All models were subjected to compression with pure moments in either flexion, extension, or lateral bending. Kinematic reductions with respect to the intact (uninjured and without instrumentation) case caused by instrumentation use were reported. Changes in loading profiles through the right and left C0-C1 and C1-C2 facets, transverse ligament-dens, and dens-anterior ring of C1 articulations were calculated by the finite element model. Maximum von Mises stresses within the instrumentation were predicted for each model variant and loading scenario. RESULTS: Bilateral instrumentation provided greater motion reductions than the unilateral instrumentation. When used bilaterally, C2 pedicle screws approximate the kinematic reductions and instrumentation stresses (except in lateral bending) that are seen with C1-C2 transarticular screws. The finite element model predicted that the maximum stress was always in the region in which the plate transformed into the rod. CONCLUSIONS: To the best of the authors' knowledge, this is the first report of predicting changes in loading in the upper cervical spine caused by instrumentation. The most significant conclusion that can be drawn from the finite element model predictions is that C2 pedicle screw fixation provides the same relative stability and instrumentation stresses as C1-C2 transarticular screw use. C2 pedicle screws can be a good alternative to C2-C1 transarticular screws when bilateral instrumentation is applied.
STUDY DESIGN: The three-dimensional flexibility of six human lumbar functional spinal units was measured after the anterolateral insertion of an interbody cage. OBJECTIVES: To determine whether an interbody cage inserted from an anterolateral direction stabilizes the spine with respect to the intact state and to compare the finding with that from the same cage inserted from an anterior direction. SUMMARY OF BACKGROUND DATA: Several biomechanical studies have shown that interbody cages do not stabilize the spine in extension. It is suspected that this may be caused by the destruction of the anterior longitudinal ligament and anterior anulus fibrosus. METHODS: Six human cadaveric lumbar functional spinal units were tested under pure moments of flexion, extension, bilateral axial rotation, and bilateral lateral bending to a maximum of 10 Nm. The relative intervertebral motions were measured by an optoelectronic camera system with the spinal units in the intact condition, after discectomy, after anterolateral interbody cage stabilization, and with additional translaminar screw fixation. The implant used was a central, porous, contoured implant with endplate fit. The results were compared with those of a previous study, which used the same implant inserted from an anterior direction. RESULTS: The anterolateral cage insertion significantly decreased the motion in comparison with the intact situation in flexion and lateral bending, but not in extension or axial rotation. No differences were found between the anterior and anterolateral insertion approaches in flexion or extension, but differences were observed in axial rotation and lateral bending, in which the anterolateral approach resulted in more motion. Additional translaminar screw fixation reduced motion to below intact levels in all loading directions. None of the surgical procedures introduced asymmetrical behavior. CONCLUSIONS: Anterolateral cage insertion did not stabilize the spine in extension or axial rotation and was not different from the anterior approach in flexion and extension. Additional translaminar screw fixation stabilized in all directions.