Predicting Cervical Spine Compression and Shear in Helicopter Helmeted Conditions Using Artificial Neural Networks.

OCCUPATIONAL APPLICATIONSMilitary helicopter pilots around the globe are at high risk of neck pain related to their use of helmet-mounted night vision goggles. Unfortunately, it is difficult to design alternative helmet configurations that reduce the biomechanical exposures on the cervical spine during flight because the time and resource costs associated with assessing these exposures in vivo are prohibitive. Instead, we developed artificial neural networks (ANNs) to predict cervical spine compression and shear given head-trunk kinematics and joint moments in the lower neck, data readily available from digital human models. The ANNs detected differences in cervical spine compression and anteroposterior shear between helmet configuration conditions during flight-relevant head movement, consistent with results from a detailed model based on in vivo electromyographic data. These ANNs may be useful in helping to prevent neck pain related to military helicopter flight by facilitating virtual biomechanical assessment of helmet configurations upstream in the design process.

TECHNICAL ABSTRACTBackground: The use of night vision goggles (NVGs) has been linked to a high prevalence of neck pain and injury in military helicopter pilots. Next generation helmet designs aim to mitigate NVG related consequences on cervical spine loading. Currently, in vivo human-participant experiments are required to collect necessary data, such as electromyography (EMG) to estimate joint contact forces in the cervical spine as a result of unique helmet designs. This is costly and inefficient. Digital human models, which provide inverse dynamics, coupled with artificial neural networks (ANNs), can provide a surrogate for musculoskeletal joint modeling to predict joint contact forces.Purpose: We developed ANNs to predict C6-C7 compression and anteroposterior shear during flight-relevant head movements with sufficient sensitivity to differentiate between candidate helmet designs in terms of associated biomechanical exposures.Methods: Motion capture and EMG data were collected from 26 participants who performed flight-relevant reciprocal head movements about pitch and yaw axes while donning one of four helmet configurations. These data were input into an EMG-driven musculoskeletal model of the neck to generate time series of C6-C7 compression and shear. Rotation-specific ANNs were trained to predict the EMG-driven model outputs, given only the head-trunk kinematics and C6-C7 moments as inputs.Results: ANNs for pitch rotations were successful in estimating peak and cumulative compression and shear, with an absolute error that was lower than absolute differences in joint contact forces between relevant helmet conditions. ANNs for yaw rotations were similarly successful in differentiating between C6-C7 compression and cumulative C6-C7 shear, but less so for peak C6-C7 shear.Conclusions: When combined with biomechanical data readily available from digital human modeling software, use of an ANN surrogate for joint musculoskeletal modeling can permit evaluation of joint contact forces associated with novel helmet designs during upstream design. Improved consideration of joint contact forces during a virtual helmet design process will assist in identifying helmet designs that reduce biomechanical exposures of the cervical spine during helicopter flight.

Strain of the facet joint capsule during rotation and translation range-of-motion tests: an in vitro porcine model as a human surrogate.

BACKGROUND CONTEXT: Prior data about the modulating effects of lumbar spine posture on facet capsule strains are limited to small joint deviations. Knowledge of facet capsule strain during rotational and translational intervertebral joint motion (ie, large joint deviations) under physiological loading could be useful as it may help explain why visually normal lumbar spinal joints become painful. PURPOSE: This study quantified the strain tensor of the facet capsule during rotation and translation range-of-motion tests. STUDY DESIGN/SETTING: Strain was calculated in isolated porcine functional spinal units. Following a preload, each specimen underwent a flexion/extension rotation (F/E) followed by an anterior/posterior translation (A/P) range-of-motion test while under a 300 N compression load. METHODS: Twenty porcine spinal units (10 C3-C4, 10 C5-C6) were tested. Joint flexion/extension was imposed by applying a ±8 Nm moment at a rate of 0.5°/s, and translation was facilitated by loading the caudal vertebra with a ±400 N shear force at a rate of 0.2 mm/s. Points were drawn on the exposed capsule surface and their coordinates were optically tracked throughout each test. Strain was calculated as the displacement of the point configuration with respect to the configuration in a neutral joint position. RESULTS: Compared to a neutral posture, superior-inferior strain increased and decreased systematically during flexion and extension, respectively. Posterior displacement of the caudal vertebra by more than 1.3 mm was associated with negative strains, which was significantly lower than the +4.6% strain observed during anterior displacement (p≥.199). The shear strain associated with anterior translation was, on average, -1.1% compared to a neutral joint posture. CONCLUSIONS: These results demonstrate that there is a combination of strain types within the facet capsule when spinal units are rotated and translated. The strains documented in this study did not reach the thresholds associated with nociception. CLINICAL RELEVANCE: The magnitude of flexion-extension rotation and anterior-translation may glean insight into the facet capsule deformation response under low compression (300 N) loading scenarios. Further, intervertebral joint motion alone, even under low compression loading, does not appear to initiate a clinically relevant pain response in the lumbar facet capsule of a nondegenerated spinal joint.

Total Parenteral Nutrition During Pregnancy in a Patient Requiring Long-Term Nutrition Support.

BACKGROUND: Total parenteral nutrition (TPN) has been used successfully in preventing intrauterine growth retardation, premature labor, and perinatal morbidity and mortality associated with poor maternal nutrition. Parenteral nutrition support is provided in most instances for short intervals during pregnancy when oral intake is compromised, eg, hyperemesis gravidarum or during complications from comorbid conditions that develop or are exacerbated during pregnancy. Few reports describe continuous parenteral nutrition support from conception through labor and delivery. OBJECTIVE: To support successfully a 19-year-old woman on long-term TPN since age 8 years because of short bowel syndrome complicated by chronic pancreatitis. METHODS: Estimated energy requirements were based on indirect calorimetry and current recommendations for maternal weight gain for optimal fetal growth and development. A strategy was formulated to improve her low maternal weight during early pregnancy. RESULTS: The fetus grew normally throughout pregnancy. There were no significant metabolic or obstetric complications as a result of the parenteral support. CONCLUSIONS: Patients on long-term TPN can conceive successfully and carry a pregnancy to term without any adverse outcome for the mother or the fetus. TPN feeding during pregnancy and recommendations for maternal weight gain are reviewed.