Determining the gluonic gravitational form factors of the proton.

The proton is one of the main building blocks of all visible matter in the Universe1. Among its intrinsic properties are its electric charge, mass and spin2. These properties emerge from the complex dynamics of its fundamental constituents-quarks and gluons-described by the theory of quantum chromodynamics3-5. The electric charge and spin of protons, which are shared among the quarks, have been investigated previously using electron scattering2. An example is the highly precise measurement of the electric charge radius of the proton6. By contrast, little is known about the inner mass density of the proton, which is dominated by the energy carried by gluons. Gluons are hard to access using electron scattering because they do not carry an electromagnetic charge. Here we investigated the gravitational density of gluons using a small colour dipole, through the threshold photoproduction of the J/ψ particle. We determined the gluonic gravitational form factors of the proton7,8 from our measurement. We used a variety of models9-11 and determined, in all cases, a mass radius that is notably smaller than the electric charge radius. In some, but not all cases, depending on the model, the determined radius agrees well with first-principle predictions from lattice quantum chromodynamics12. This work paves the way for a deeper understanding of the salient role of gluons in providing gravitational mass to visible matter.

Measured proton electromagnetic structure deviates from theoretical predictions.

The visible world is founded on the proton, the only composite building block of matter that is stable in nature. Consequently, understanding the formation of matter relies on explaining the dynamics and the properties of the proton's bound state. A fundamental property of the proton involves the response of the system to an external electromagnetic field. It is characterized by the electromagnetic polarizabilities1 that describe how easily the charge and magnetization distributions inside the system are distorted by the electromagnetic field. Moreover, the generalized polarizabilities2 map out the resulting deformation of the densities in a proton subject to an electromagnetic field. They disclose essential information about the underlying system dynamics and provide a key for decoding the proton structure in terms of the theory of the strong interaction that binds its elementary quark and gluon constituents. Of particular interest is a puzzle in the electric generalized polarizability of the proton that remains unresolved for two decades2. Here we report measurements of the proton's electromagnetic generalized polarizabilities at low four-momentum transfer squared. We show evidence of an anomaly to the behaviour of the proton's electric generalized polarizability that contradicts the predictions of nuclear theory and derive its signature in the spatial distribution of the induced polarization in the proton. The reported measurements suggest the presence of a new, not-yet-understood dynamical mechanism in the proton and present notable challenges to the nuclear theory.

Static standing, dynamic standing and spasticity in individuals with spinal cord injury.

STUDY DESIGN: This was a cross-over efficacy study design. OBJECTIVE: To determine spasticity differences between static and dynamic standing training in individuals with spinal cord injury (SCI). SETTING: Vancouver, Canada. METHODS: Ten individuals with SCI who could stand with or without bracing or supports participated in both dynamic and static standing training (one session each, 2 days apart) using a Segway. The primary outcome was spasticity as measured by Visual Analog Scale (VAS), Modified Ashworth Scale (MAS) and electromyography (EMG) of the quadriceps, hamstrings, adductors and gastrocnemius. RESULTS: There was no statistically detectable difference in spasticity between dynamic and static standing training in individuals with SCI as measured by VAS, MAS or EMG, although there was a trend towards decreased spasticity after the dynamic training. CONCLUSION: There is no significant difference in spasticity outcomes between static and dynamic standing training on a Segway for individuals with SCI. SPONSORSHIP: This research was funded by Natural Sciences and Engineering Research Council of Canada and International Collaboration on Repair Discoveries.

Relationships between wheeling parameters and wheelchair skills in adults and children with SCI.

STUDY DESIGN: Cross-sectional. OBJECTIVES: To determine the relationships between (1) wheeling parameters using the SmartWheel Clinical Protocol (SCP) and wheelchair skills (wheelchair skills test 4.1 (WST)) and (2) push effectiveness (m per push) and the WST, among individuals with spinal cord injury. SETTING: Biomechanics Laboratory, Canada. METHODS: Sixteen adults and eight children participated in this study. Multiple regression analyses were used to determine significant SCP predictors (that is, weight-normalised peak force, speed, push frequency and mechanical effectiveness) of WST score. To determine relationships between push effectiveness and WST scores, Pearson's correlations were calculated. RESULTS: SCP-TILE: speed and mechanical effectiveness explained 36% of the variance in the WST score. SCP-RAMP and SCP-CARPET: speed explained 58% and 37% of the variance in the WST score, respectively. Push effectiveness was significantly correlated with the WST score on all three surfaces (tile, ramp and carpet). CONCLUSION: Wheeling speed was a significant predictor of the WST score for all surfaces tested. Regression analyses demonstrated that SCP-RAMP had the strongest relationship with WST score. Therefore, when time is restricted, the SCP-RAMP may be the most predictive test and speed may be the most useful variable to evaluate. However, the authors do not believe that one single variable should ever replace a full assessment of skills.

Spasticity changes in SCI following a dynamic standing program using the Segway.

STUDY DESIGN: A pilot prospective pre- and post-intervention study. OBJECTIVES: To determine whether a dynamic standing program using the Segway Personal Transporter results in any measurable physiological effects in individuals with spinal cord injury (SCI) using both qualitative and quantitative measures of spasticity, pain and fatigue. SETTING: International Collaboration of Repair Discoveries (ICORD) Research Centre, Vancouver, BC, Canada. METHODS: Eight individuals with SCI ASIA (American Spinal Injury Association) A-D, who could stand with or without the assistance of bracing or supports, participated in a 4-week dynamic standing program using a Segway (3 per week, 30-min sessions). The main outcome was spasticity as measured by the Modified Ashworth Scale (MAS). Secondary measures included the SCI-Spasticity Evaluation Tool, Pain Outcomes Questionnaire, and Fatigue Severity Scale. RESULTS: The dynamic standing sessions were associated with immediate improvements in spasticity (MAS) (P<0.001) and self-reported pain (P<0.05). Fatigue levels decreased, however this was not significant. There is little evidence to suggest that these beneficial outcomes may have lasting effects. CONCLUSIONS: Dynamic standing on the Segway may be effective for short-term spasticity reduction and decreased pain and fatigue. Future work should examine a larger sample size and help to propose mechanisms for potential reductions in spasticity.

Classification and measurement of pain in the spinal cord-injured population.

STUDY DESIGN: Comprehensive review and systematic analyses. OBJECTIVES: The purpose of this review was to summarize studies reporting on the psychometric properties of measures commonly utilized in spinal cord injury (SCI) pain research to better inform clinicians and researchers on the selection of appropriate pain-related instruments. SETTING: Vancouver, British Columbia, Canada. METHODS: A detailed literature search was completed to extrapolate articles that described the psychometric properties of pain measures specifically used in SCI populations. Psychometric properties data of the identified measures such as reliability coefficients, type and magnitude of validity correlations, responsiveness as well as logistical factors (that is, interpretability, acceptability and feasibility) were extracted from manuscripts in accordance with similar projects designed to review outcome measures. RESULTS: Five different pain classification schemas, six self-report measures of pain, and two measures of pain impact on functioning were selected based on our inclusion criteria. The majority of the studies identified in these areas reported inter- and intra-rater reliability information. Of the little validity data found for pain screening measures, it was difficult to compare due to the variability of the descriptors used. No data on sensitivity was identified. CONCLUSION: We propose a call to SCI researchers to consistently apply psychometric analyses to SCI pain data measures. Greater rigor for assessing psychometric information in SCI pain studies will better inform the SCI research community of the applicability of generic measures to SCI pain investigations.

Measuring energy expenditure using heart rate to assess the effects of wheelchair tyre pressure.

OBJECTIVE: To investigate the effects of wheelchair tyre pressure on mechanics and energy and explore the use of heart rate as a measurement of energy expenditure. DESIGN: A single factor repeated measures design was used. Four tyre pressures (100, 75, 50, 25 psi) represented a change of workload. Each subject wheeled at a constant self-selected wheeling velocity for 8 min. A total of four trials were completed with a 10-min rest between trials. Oxygen consumption, heart rate and distance travelled were collected during each trial. SUBJECTS: Three women and 11 men with spinal cord injury. The mean age for the whole group was 34.5 years. The range of lesion level was T4-L1. RESULTS: There was a significant increase is energy expenditure when tyres were deflated to 50 psi from 100 psi. The mean correlation between heart rate and oxygen consumption was 0.74 for all subjects. For the subjects with lesions above T6 and T6 and below the correlations were 0.55 and 0.82, respectively. CONCLUSIONS: Tyre pressures below 50% inflation add an additional 25% increase in energy expenditure during wheeling. This could be detected using oxygen consumption or heart rate, as heart rate was shown to have a good correlation with oxygen consumption in the spinal cord injured with lesions below T5. Heart rate does have its limitations and it should only be used to measure within-subject differences.

Rotations of a helix as a model for correction of the scoliotic spine.

STUDY DESIGN: A prospective study using intraoperative stereophotogrammetry to analyze helical motion of the spine during the correction of scoliosis. OBJECTIVE: To determine whether derotation systems rotate the scoliotic helix. SUMMARY OF BACKGROUND DATA: Scoliosis is a complex three-dimensional deformity that is difficult to visualize on standard radiographs. The use of stereophotogrammetry has allowed study of the deformity in three dimensions during surgical correction. METHODS: Thirty-five patients with right thoracic adolescent idiopathic scoliosis were studied using a stereophotogrammetry technique during surgical correction. Changes in vertebral unique rotations and spinal plane of maximum deformity were measured during three sequential stages of the surgery. RESULTS: The mean preoperative and postoperative Cobb angles were 58 degrees and 19 degrees, respectively. Most rotation occurred at the top and bottom vertebrae in the curve, averaging 10 degrees each but in opposite directions. The apical vertebra rotated the least in the structural curve, with an average rotation of 5 degrees. Much of the rotation occurred during the derotation maneuver with additional rotation occurring during the final distraction. The plane of maximum deformity changed from a mean of 50 degrees before instrumentation to 19 degrees at the end of the procedure. CONCLUSIONS: Multiple rotations of the scoliotic curve occur, and it can be shown when maximum rotations occur during surgery. Posterior derotational systems unwind or rotate the scoliotic helix and reposition the resultant sine wave toward the sagittal plane as described by the change in the plane of maximum deformity.

Effects of three-dimensional assessment on surgical correction and on hook strategies in multi-hook instrumentation for adolescent idiopathic scoliosis.

STUDY DESIGN: A prospective study using intraoperative stereophotogrammetry to analyze change during the correction of scoliosis. OBJECTIVE: To examine the relation between the number of hooks used during segmental instrumentation and the amount of correction achieved. SUMMARY OF BACKGROUND DATA: An intraoperative stereophotogrammetric technique was developed at our center. Vertebral translations and rotations can be measured at several stages during scoliosis surgery. METHODS: Thirty-two patients with right thoracic adolescent idiopathic scoliosis were studied using our stereophotogrammetry technique during surgical correction. Correlations were determined between apical vertebral movements and the hook ratio (number of vertebrae/number of hooks used). RESULTS: Mean curve Cobb angle correction was 66%. Correction occurred in all three planes but primarily along the x and y axes. Scoliotic deformity was corrected by translation of the vertebra along the y axis and rotation about the x; physiologic kyphosis was restored by translation along the x axis and rotation about the y. The plane of maximum deformity as compared with the sagittal plane of the patient corrected from 57 degrees to 25 degrees as an indication of detorsion of the scoliotic deformity. CONCLUSIONS: Increasing the number of hooks per vertebral segment significantly enhances the correction of the coronal scoliotic deformity and enhances the z axis derotation, but does not significantly change the reestablishment of the kyphosis, nor does it result in significant elongation of the spine.

The effects of labor and delivery on spinal cord function and ambulation in patients with meningomyelocele.

Two hundred and eight patients with meningomyeloceles were reviewed to assess the role of birth trauma in the pathogenesis of their neurological deficit. Vaginal breech-delivered patients appeared to have poorer neurological function in the newborn period. The factors responsible include: (1) a mid or upper lumbar level, that by sparing hip flexors and knee extensors, predisposes to breech presentation; (2) limb posturing due to residual neurological function and intrauterine positioning that limits the accurate neurological assessment of the newborn; (3) nervous system or soft tissue injury due to labor and delivery. Regardless of the mechanism, vaginal breech-delivered patients showed improvement in function, and eventually exhibited ambulatory function comparable to those infants born by cesarian section or vaginally after vertex presentation and labor. In our patient population, elective cesarian section did not offer a spinal cord or ambulatory advantage over vaginal delivery for those pregnancies presenting in a vertex fashion. Thus, it should be reserved for fetuses who are presenting breech or who have other obstetrical indications for operative delivery.

Soft tissue anatomy of proximal femoral focal deficiency.

The soft tissue anatomy of Aitken types A, B, C, and D proximal femoral focal deficiency (PFFD) was examined by magnetic resonance imaging (MRI). A characteristic pattern of soft tissue abnormalities is described. All muscles were present, but most were smaller than their normal counterparts. The exception was the obturator externus muscle, which was elongated and remained muscular almost up to its insertion. In type A PFFD, it is straight; in types B, C, and D PFFD, it is L-shaped. The sartorius is hypertrophied.

The use of fibrin sealant to reduce blood loss during Cotrel-Dubousset instrumentation for idiopathic scoliosis.

The increased complexity of Cotrel-Dubousset instrumentation has, as an unexpected side effect, a potential increase in blood loss. A prospective randomized study was undertaken to test the hypothesis that application of a fibrin sealant to exposed cancellous bone can significantly reduce blood loss during Cotrel-Dubousset instrumentation for idiopathic scoliosis. A significant difference was demonstrated in total body loss, loss per level fused, and loss per kilogram of body weight when comparing the sealant group with random controls. A significant difference was demonstrated in loss per level fused when comparing the sealant control with a historical control group. Thirty-three patients were randomly assigned to the fibrin sealant or nonsealant groups; another 10 patients operated on before planning the study were included as historical controls. The sealant was used to control bleeding at the bone graft donor site and in the spine after decortication. All patients underwent Cotrel-Dubousset instrumentation for idiopathic scoliosis. There were no significant differences between groups with respect to degree of curvature, number of levels fused, age or weight of patient, or operating time. Total blood loss in the sealant group averaged 672 ml compared with 894 ml in the sealant control group. No patient in the sealant group required homologous blood. Given the increasing awareness of the complications of blood transfusion, the authors conclude that fibrin sealant is a useful adjunct to spinal surgical technique.

Undiversion in patients with meningomyelocele.

Since 1981, 12 patients with neurogenic bladder due to meningomyelocele who had had previous ileal conduit urinary diversions underwent assessment for undiversion. Two important criteria for undiversion were motivation and a reconstructable bladder. Four patients either did not fulfil these criteria or refused surgery. Eight patients (six females and two males) underwent undiversions. Uretero-ureteral anastomosis was achieved in 13 ureters and ureteroneocystostomy in 2; transureteroureterostomy was necessary in 1 ureter. Augmentation cystoplasty and vesicourethropexy were important in establishing continence postoperatively; these procedures were not performed in two patients whose undiversion failed early in the series. The evolution of an investigation protocol, surgical technique and final approach to this complex problem are discussed.

Bladder-outlet reconstruction in neurogenic bladder due to myelomeningocele.

In a subgroup of children with myelomeningocele, urinary incontinence cannot be managed by clean intermittent catheterization and anticholinergic medication. The authors report on 24 such children who required bladder-outlet reconstruction. Twelve boys underwent the Young-Dees/Leadbetter procedure, 8 girls underwent the Burch procedure and the remaining 4 had a combination of the two. Augmentation cystoplasty was also carried out in seven girls and one boy. Results were most favourable in the girls, with improvement in 92%, in contrast to the boys in whom only 58% were improved. Artificial sphincter placement may be a more beneficial alternative for boys.