The architecture of the 6-month-old gastrocnemius: a 3D volumetric study

Gastrocnemius is essential in normal gait, contributing to the control of ankle plantar flexion and knee flexion. However, there is a paucity of literature on the architecture of the infant gastrocnemius muscle prior to the onset of weight-bearing and gait. This study investigates the three-dimensional (3D) musculoaponeurotic architecture of the gastrocnemius in a six-month-old infant. One six-month-old cadaver was used in this study (The University of Toronto Health Sciences Research Ethics Board, #32679, and The University of Auckland Human Participants Ethics Committee, #016164). Medial (MG) and lateral (LG) heads of the gastrocnemius were serially dissected and a Microscribe G2X(TM) digitizer used to digitize fiber bundles, aponeuroses and tendons. Data were then exported to Autodesk(R) Maya(R) to create 3D models. Custom software quantified architectural parameters, including fiber bundle length, pennation angle, physiological cross-sectional area, and muscle volume. The intramuscular architecture was assessed to determine whether musculoapo-neurotic partitions were present. Muscle volume was <1cm3 for both MG and LG. Three architectural partitions, proximal, middle, and distal, were identified for both MG and LG. Notably, the proximal partitions of both MG and LG had mean fiber bundle length at 2.21 ± 0.41 cm and 2.22 ± 0.27 cm, significantly greater (p < 0.05) than the middle and the distal partitions. The results of this study suggest that both MG and LG have architectural partitions before the commencement of gait. Further longitudinal studies with larger sample sizes are needed to confirm the presence of these architectural partitions, as well as to investigate their growth across the developmental spectrum

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Hemodynamic changes in women with symptoms of supine hypotensive syndrome.

INTRODUCTION: Supine positioning during late pregnancy causes the gravid uterus to compress the inferior vena cava, resulting in dramatic hemodynamic changes. The maintenance of placental perfusion requires maternal circulatory and autonomic adaptations. Women with supine hypotensive syndrome (defined as a drop in systolic blood pressure of anything between 15 and 30 mmHg or an increase in heart rate of 20 bpm, with or without symptoms) may have reduced ability to compensate for the effects of supine positioning. MATERIAL AND METHODS: Twelve women with uncomplicated pregnancies and no symptoms of supine hypotension (normal) and 10 women with uncomplicated pregnancies who reported symptoms of supine hypotension between 34 and 38 weeks' gestation underwent magnetic resonance imaging in the supine and left lateral positions. Phase contrast images were evaluated to measure blood flow through the aorta, inferior vena cava, superior vena cava and azygos vein. RESULTS: Women with symptoms of supine hypotension showed significant reductions in azygos venous flow rate compared with the normal group (-0.15 (-0.30 to -0.01) L/min). Those with symptoms showed no statistically significant compensatory changes in heart rate compared with the normal group (heart rate change 4.5 (-3.1 to 12.1) bpm). Hemodynamic changes in response to positioning were similar across both groups including: a reduction in inferior vena cava blood flow, reduction in cardiac output and an increase in azygos blood flow. CONCLUSIONS: Maternal hemodynamic adaptations were found to be consistent across groups irrespective of whether the women had symptoms of supine hypotension. In both groups a reduction in blood flow through the inferior vena cava occurred in the supine position with a subsequent reduction in cardiac output. Both groups showed a compensatory increase in blood flow through the azygos vein in order to partially compensate for this. Taking into account the effect of maternal position, women with symptoms were found to have reduced azygos flow compared with asymptomatic women. There was a significant increase in heart rate when the women were supine than when they were in the left lateral position.

Closure of the anterior and posterior fontanelle in the New Zealand population: A computed tomography study.

AIM: Significant ethnic variation has been demonstrated in the closure of the anterior fontanelle (AF); however, to date, this has not been investigated in the Maori/Pasifika population. METHODS: The computed tomography scans of 163 individuals (116 Maori/Pasifika and 47 New Zealand (NZ) European) aged between birth and 4 years were retrospectively analysed to investigate the surface area (SA) and time of closure of the anterior and posterior fontanelles in New Zealand. RESULTS: The Maori/Pasifika group showed clinical AF closure (SA < 114 mm2 ) rates of 25% at 4-6 months, increasing to 47% at 10-12 months and 80% at 13-18 months. The posterior fontanelle was clinically unfused in 17% of the Maori/Pasifika group aged <1 month and in 7% of the 1-3-month-old group. No cases of posterior fontanelle non-fusion were identified in the NZ European population. CONCLUSION: This study establishes normal values for AF size and closure frequency for the first time in the paediatric Maori/Pasifika population.

Ultrasound visualization of the spinal accessory nerve in vivo.

BACKGROUND: Inadvertent injury of the spinal accessory nerve during surgical procedures is a cause of significant morbidity with medicolegal repercussions. Surface anatomy is an unreliable guide to the nerve's location. We suggest that ultrasound can be used to map the course of the nerve in the posterior triangle of the neck. MATERIALS AND METHODS: Fifty healthy subjects (28 females, mean age 37 y) were scanned using a VF13-5 linear probe and a Siemens Sonoline Antares ultrasound machine (Siemens Medical Solutions USA Inc., Malvern, PA). The caliber, course, and distribution of the nerve in the posterior triangle of the neck were recorded. RESULTS: The nerve was visualized bilaterally in all subjects, running superficially across the posterior triangle with either a straight (56%) or tortuous (44%) course at a depth of about 3 mm beneath the skin surface. It had a mean caliber of 0.76 ± 0.12 mm. It exited the posterior border of sternocleidomastoid at a mean of 6.7 (4.0-9.4) cm below the mastoid process and 1.1 (0.1-2.1) cm above the great auricular point and penetrated the anterior border of trapezius 5.4 (2.1-9.2) cm above the clavicle. Importantly, 58% of nerves divided into 2-4 branches before penetrating trapezius; the nerve branched on at least one side in 49 of 50 individuals. CONCLUSIONS: The spinal accessory nerve and its anatomical variants can be consistently and reliably demonstrated by ultrasound in normal individuals. Surface anatomical landmarks are not a reliable guide to the position and course of the nerve in the posterior triangle. Preoperative mapping of the nerve with ultrasound may reduce the risk of iatrogenic injury.