Clinical biomechanics
-
Clinical biomechanics · Jul 2006
Clinical TrialSuprascapular nerve block disrupts the normal pattern of scapular kinematics.
Patients with full thickness rotator cuff tears typically demonstrate an increase in scapular motion, both in the clinic and under controlled laboratory conditions. To better understand the mechanisms behind this pattern of motion, we propose a suprascapular nerve block as an appropriate model of dysfunction of the supraspinatus and infraspinatus, which are the two tendons most commonly affected in cuff tear patients. ⋯ The nerve block resulted in no significant changes in clavicular rotations and scapular posterior tilting. However, there was a significant increase in scapular external rotation and upward rotation. While kinematic changes returned to baseline within 25 min of the block, force measurements did not return to baseline until 75 min post-block. Interpretation. The results of this study, especially those for upward rotation, are in general agreement with what has been found for patients with rotator cuff tears. While the supraspinatus and infraspinatus do not directly control the movement of the scapula, they appear to result in a compensatory change in scapular motion. Although more work needs to be done, it appears that abnormal scapular motion patterns observed in patients with cuff tears may therefore be compensatory in nature.
-
Clinical biomechanics · Jul 2006
Focal spinal arachnoiditis increases subarachnoid space pressure: a computational study.
Enlarging fluid filled cystic cavitations form within the spinal cord in up to 28% of spinal cord injured patients. These post-traumatic syrinxes can cause neurological deterioration and current treatment results are unsatisfactory. Localized scar tissue (arachnoiditis) within the subarachnoid space at the level of injury has been suggested to be involved in the pathogenesis of syrinx formation. This study tests the hypothesis that pressure pulses in the subarachnoid space are accentuated adjacent to regions of arachnoiditis, which may drive fluid into the spinal cord and contribute to syrinx formation. ⋯ Elevations in subarachnoid space pressures due to arachnoiditis may facilitate fluid flow into the spinal cord, enhancing syrinx formation. This suggests that it may be worthwhile to investigate strategies that inhibit arachnoiditis or minimize systolic pressure peaks for treating or preventing syringomyelia.
-
Clinical biomechanics · Jul 2006
The effect of foot position and chair height on the asymmetry of vertical forces during sit-to-stand and stand-to-sit tasks in individuals with hemiparesis.
The asymmetrical motor pattern of persons with hemiparesis influences the performance of activities that require interactions between the two sides of the body. ⋯ The time to execute the tasks ranged from 2.31 s to 3.69 s with higher values observed for the stand-to-sit task than for the sit-to-stand task. Overall, the asymmetry of vertical forces was greatest in the middle part of the tasks and was not influenced by the chair height. When the subjects were still in contact with the seat, the loading asymmetry originated from a difference between sides at both the thigh and the foot. The asymmetrical foot position with the affected foot backward promoted loading on the affected side during both tasks. Interpretation. This study shows that loading asymmetry was present before seat-off and after seat-on in sit-to-stand and stand-to-sit tasks, respectively. It shows that positioning the affected foot behind reduces the asymmetry whereas positioning the unaffected foot behind increases the asymmetry. Foot position should be taken into consideration when clinicians assess or train for these mobility tasks.
-
Bone healing is sensitive to the initial mechanical conditions with tissue differentiation being determined within days of trauma. Whilst axial compression is regarded as stimulatory, the role of interfragmentary shear is controversial. The purpose of this study was to determine how the initial mechanical conditions produced by interfragmentary shear and torsion differ from those produced by axial compressive movements. ⋯ This study found that the mechanical stimuli generated by interfragmentary shear and torsion differed from those produced by axial interfragmentary movements. The initial tissue formation as predicted by the mechanobiological theories was dominated by the deformation stimulus.
-
Clinical biomechanics · Jun 2006
In vitro fixator rod loading after transforaminal compared to anterior lumbar interbody fusion.
Cages are commonly used to assist lumbar interbody fusion. They are implanted from various approaches. In many cases internal fixators are added to provide sufficient stability. However, how the rods of these fixators are loaded and whether the kind of approach affects these loads is still unknown. The aim of this in vitro study therefore was to determine the loads acting on fixator rods and cages after anterior compared to transforaminal lumbar interbody fusion. ⋯ The loads acting on the rods of the fixator were small compared to the load that was applied. Thus, other structures such as the cages or the facet joints still play an important role in load transfer. The type of approach (anterior or transforaminal) had only little effect on the loading of the rods. This also applies to the local loading of the cages, which probably more depends on the fit between cage and endplates and on the local stiffness properties of the adjacent vertebral bodies.