Three-dimensional spinal curvature in idiopathic scoliosis

Scoliosis is usually considered as a deformity of the spine in the frontal plane, without reference to curvatures in other planes. In this study, the three-dimensional shape of the spine of 104 patients with untreated idiopathic scoliosis (5-55 degrees Cobb) was studied by means of stereo radiographs to determine relationships between curvature of the spine in the frontal plane view, in the lateral view, and in the intermediate views. There was a weak but statistically significant correlation (r = 0.2) relating greater scoliosis with lesser kyphosis or greater lordosis. In the thoracic region, the sagittal plane spinal curvature was less than that measured in a population without scoliosis (mean difference, 7.72 +/- 9.9 degrees). Seventy-four of 76 scolioses in the upper region of the spine with lateral curvature greater than 5 degrees Cobb were kyphotic. Sixty-four of 84 curves greater than 5 degrees Cobb in the lower region were lordotic. Measuring curvatures in the plane of symmetry of the rotated apical vertebra altered these ratios to 69 of 76 kyphotic in the upper region and 68 of 84 lordotic in the lower region. The plane of maximum curvature of sections of the spine with scoliosis was not related to the plane of symmetry of the rotated apical vertebra, for in kyphotic regions of the spine the rotations of these two planes were in opposite directions. In all cases, the magnitudes of the rotations were quite different, i.e., by a factor of -0.22 for curves in thoracic region and by a factor of 0.24 for curves in the lumbar region. This implies that mechanical measures to correct this spinal deformity or to prevent progression should apply different rotations to the apex from those applied to the curve as a whole and, in opposite senses, in curves in kyphotic regions. There was no evidence of an abnormality of sagittal curvature of a magnitude to implicate it in the etiology or in the treatment.     

Distance-adjusted motor threshold for transcranial magnetic stimulation.

OBJECTIVE: To examine the relationship between coil-cortex distance and effective cortical stimulation using transcranial magnetic stimulation (TMS) in the left and right motor cortex. We also compare the effect of coil-cortex distance using 50 and 70 mm figure-eight stimulating coils. METHODS: Coil-cortex distance was manipulated within each participant using 5 and 10 mm acrylic separators placed between the coil and scalp surface. The effect of cortical stimulation was indexed by resting motor threshold (MT). RESULTS: Increasing distance between the coil and underlying cortex was associated with a steep linear increase in MT. For each additional millimetre separating the stimulating coil from the scalp surface, an additional approximately 2.8% of absolute stimulator output (approximately 0.062 T) was required to reach MT. The gradient of the observed distance effect did not differ between hemispheres, and no differences were observed between the 50 and 70 mm TMS coils. CONCLUSIONS: Coil-cortex distance directly influences the magnitude of cortical stimulation in TMS. The relationship between TMS efficacy and coil-cortex distance is well characterised by a linear function, providing a simple and effective method for scaling stimulator output to a distance adjusted MT. SIGNIFICANCE: MT measured at the scalp-surface is dependent on the underlying scalp-cortex distance, and therefore does not provide an accurate index of cortical excitability. Distance-adjusted MT provides a more accurate index of cortical excitability, and improves the safety and efficacy of MT-calibrated TMS.     

Acoustic myography of the human quadriceps muscle during intermittent fatiguing activity.

Integrated acoustic myography (IAMG) and electromyography (IEMG) were recorded over rectus femoris (RF) in six healthy subjects during a series of intermittent isometric contractions of quadriceps. Contractions were held for 10 sec with 10 sec rest between each, commencing at 75% maximum voluntary contraction (MVC) force and continuing to 40% MVC. The IAMG activity initially decreased (75%-60% MVC) in a linear relationship (r = 0.9) with fatigue (i.e. force loss) but then plateaued and increased once force fell below 52% MVC. The AMG/force relationship for the whole fatiguing protocol (i.e. 75%-40% MVC) was quadratic (r = 0.87). The IEMG also showed a quadratic relationship with force (r = 0.85) but activity initially increased before decreasing. The results of the present study quantify the relationship between AMG and force in quadriceps during fatigue from intermittent contractions commencing at 75% MVC. The findings confirm previous observations that AMG decreases with fatigue during strong contractions but the quadratic relationship found in the present study differs to that for other muscles during sustained contractions. The results also suggest that simultaneous recordings of AMG and EMG may help distinguish central and peripheral fatigue. Acoustic myography may therefore be a useful non-invasive monitor of force during early fatiguing activity using the present protocol but the need to study AMG during fatigue of different muscles and force levels is stressed.