Jack Cy Cheng

The effect of backpack load on the gait of normal adolescent girls

Concerns regarding the effects of load carriage have led to recommendations that backpacks be limited to 10 – 15% of body weight, based on significant changes in physical performance. However, gait responses to backpack loads are not entirely consistent and there is a particular lack of data regarding load-bearing gait in adolescent females. Gait patterns of 22 normal adolescent girls were recorded at backpack loads of 0, 7.5, 10.0, 12.5 and 15.0% body weight. Temporal-distance, ground reaction force and joint kinematic, moment and power parameters were analysed by repeated measures ANOVA with factors of backpack load and side (left or right). Walking speed and cadence decreased significantly with increasing backpack load, while double support time increased. Kinematic changes were most marked at the proximal joints, with a decreased pelvic motion but a significant increase in the hip sagittal plane motion. Increased moments and power at the hip, knee and ankle showed increasing demand with backpack load. Parameters showed different responses to increasing load, and those that suggested a critical load indicated this to be approximately 10% body weight. While this may be due to a change in gait due to increased demand, further work is required to verify this and also to examine the cumulative effects of backpack load on the musculoskeletal system, which may be more appropriate in determining recommended load limits.

Biomechanical analysis and modeling of different vertebral growth patterns in adolescent idiopathic scoliosis and healthy subjects

BackgroundThe etiology of AIS remains unclear, thus various hypotheses concerning its pathomechanism have been proposed. To date, biomechanical modeling has not been used to thoroughly study the influence of the abnormal growth profile (i.e., the growth rate of the vertebral body during the growth period) on the pathomechanism of curve progression in AIS. This study investigated the hypothesis that AIS progression is associated with the abnormal growth profiles of the anterior column of the spine.MethodsA finite element model of the spinal column including growth dynamics was utilized. The initial geometric models were constructed from the bi-planar radiographs of a normal subject. Based on this model, five other geometric models were generated to emulate different coronal and sagittal curves. The detailed modeling integrated vertebral body growth plates and growth modulation spinal biomechanics. Ten years of spinal growth was simulated using AIS and normal growth profiles. Sequential measures of spinal alignments were compared.Results(1) Given the initial lateral deformity, the AIS growth profile induced a significant Cobb angle increase, which was roughly between three to five times larger compared to measures utilizing a normal growth profile. (2) Lateral deformities were absent in the models containing no initial coronal curvature. (3) The presence of a smaller kyphosis did not produce an increase lateral deformity on its own. (4) Significant reduction of the kyphosis was found in simulation results of AIS but not when using the growth profile of normal subjects.ConclusionResults from this analysis suggest that accelerated growth profiles may encourage supplementary scoliotic progression and, thus, may pose as a progressive risk factor.

Whither the etiopathogenesis (and scoliogeny) of adolescent idiopathic scoliosis? Incorporating presentations on scoliogeny at the 2012 IRSSD and SRS meetings

This paper aims to integrate into current understanding of AIS causation, etiopathogenetic information presented at two Meetings during 2012 namely, the International Research Society of Spinal Deformities (IRSSD) and the Scoliosis Research Society (SRS). The ultimate hope is to prevent the occurrence or progression of the spinal deformity of AIS with non-invasive treatment, possibly medical. This might be attained by personalised polymechanistic preventive therapy targeting the appropriate etiology and/or etiopathogenetic pathways, to avoid fusion and maintain spinal mobility. Although considerable progress had been made in the past two decades in understanding the etiopathogenesis of adolescent idiopathic scoliosis (AIS), it still lacks an agreed theory of etiopathogenesis. One problem may be that AIS results not from one cause, but several that interact with various genetic predisposing factors. There is a view there are two other pathogenic processes for idiopathic scoliosis namely, initiating (or inducing), and those that cause curve progression. Twin studies and observations of family aggregation have revealed significant genetic contributions to idiopathic scoliosis, that place AIS among other common disease or complex traits with a high heritability interpreted by the genetic variant hypothesis of disease. We summarize etiopathogenetic knowledge of AIS as theories of pathogenesis including recent multiple concepts, and blood tests for AIS based on predictive biomarkers and genetic variants that signify disease risk. There is increasing evidence for the possibility of an underlying neurological disorder for AIS, research which holds promise. Like brain research, most AIS workers focus on their own corner and there is a need for greater integration of research effort. Epigenetics, a relatively recent field, evaluates factors concerned with gene expression in relation to environment, disease, normal development and aging, with a complex regulation across the genome during the first decade of life. Research on the role of environmental factors, epigenetics and chronic non-communicable diseases (NCDs) including adiposity, after a slow start, has exploded in the last decade. Not so for AIS research and the environment where, except for monozygotic twin studies, there are only sporadic reports to suggest that environmental factors are at work in etiology. Here, we examine epigenetic concepts as they may relate to human development, normal life history phases and AIS pathogenesis. Although AIS is not regarded as an NCD, like them, it is associated with whole organism metabolic phenomena, including lower body mass index, lower circulating leptin levels and other systemic disorders. Some epigenetic research applied to Silver-Russell syndrome and adiposity is examined, from which suggestions are made for consideration of AIS epigenetic research, cross-sectional and longitudinal. The word scoliogeny is suggested to include etiology, pathogenesis and pathomechanism.

Abnormal functional responses of osteoblasts to leptin in adolescent idiopathic scoliosis

Objective Leptin has been postulated as one of the etiologic factors of AIS because of its important physiological functions in neuro-osseous development affecting skeletal growth, the onset of puberty, energy expenditure and body composition. Previous studies on the relationship between leptin and HR-pQCT derived bone quality parameters had found abnormal correlations in AIS girls, and suggested possible abnormalities in the leptin regulated bone metabolic pathways. Another study on AIS patients showed hyposensitivity to leptin in bone marrow derived mesenchymal stem cells This study aimed to investigate the effect of leptin on the functional responses of osteoblasts in AIS girls, and compare with that of controls.

Spine velocity provides more accurate assessment of curve progression than height velocity in progressive female idiopathic scoliosis undergoing bracing treatment

of growth velocity curves. Multiple linear regression analysis was used to analyze the contributions of each maturity assessments to AV, while logistic regression model was constructed to identify the high risk factors of AV more than 5° per year. Results Thirty IS girls were included in this study. Correlation was found between SV and HV (r=0.314, P=0.001). AV was significantly correlated with SV (r=0.414, P<0.001) and HV (r=0.275, P=0.005), respectively. The multiple linear regression analysis showed that AV was influenced by SV (B=0.199, P=0.001) instead of HV (B=0.187, P=0.354). The logistic regression analysis demonstrated that PSV (OR=5.052, P=0.001) rather than PHV (OR=1.979, P=0.144) was the high risk indicator for the occurrence of AV more than 5° per year. Conclusions Variations of curve progressive velocity were influenced more directly by SV rather than HV, and congruously onset of PSV were endowed with the high risk of the occurrence of AV more than 5° per year in IS girls with curve progression of 10° or more, indicating the high clinical value of measurement of spinal growth in the treatment of IS.

Morphological and bone strength indices in girls with adolescent idiopathic scoliosis and their correlations with leptin and soluble leptin receptor

Results Compared with controls, AIS subjects had higher sOB-R level (p=0.006), higher SMI value (p=0.020) reflecting more rod-like structures within the trabecular compartment, and numerically lower stiffness (-2.03%) and estimated failure load (-3.07%). Significant negative correlation was found between SMI and serum total leptin level in AIS (r=-0.325; p=0.003) but not in controls (p=0.533). Significant positive correlations were found between stiffness, estimated failure load, and serum total leptin in both AIS (r=0.278, p=0.003; r=0.268, p=0.004 respectively) and controls (r=0.462, p<0.001; r=0.468, p<0.001 respectively). Conclusion

Normative Standards for HRpQCT Parameters in Chinese Men and Women: NORMATIVE STANDARDS FOR HRpQCT PARAMETERS

Assessing bone architecture using high‐resolution peripheral quantitative computed tomography (HRpQCT) has the potential to improve fracture risk assessment. The Normal Reference Study aimed to establish sex‐specific reference centile curves for HRpQCT parameters. This was an age‐stratified cross‐sectional study and 1072 ambulatory Chinese men (n = 544) and women (n = 528) aged 20 to 79 years, who were free from conditions and medications that could affect bone metabolism and had no history of fragility fracture. They were recruited from local communities of Hong Kong. Reference centile curves for each HRpQCT parameter were constructed using generalized additive models for location, scale, and shape with age as the only explanatory variable. Patterns of reference centile curves reflected age‐related changes of bone density, microarchitecture, and estimated bone strength. In both sexes, loss of cortical bone was only evident in mid‐adulthood, particularly in women with a more rapid fashion probably concurrent with the onset of menopause. In contrast, loss of trabecular bone was subtle or gradual or occurred at an earlier age. Expected values of HRpQCT parameters for a defined sex and age and a defined percentile or Z‐score were obtained from these curves. T‐scores were calculated using the population with the peak values as the reference and reflected age‐ or menopause‐related bone loss in an older individual or the room to reach the peak potential in a younger individual. These reference centile curves produced a standard describing a norm or desirable target that enables value clinical judgements. Percentiles, Z‐scores, and T‐scores would be helpful in detecting abnormalities in bone density and microarchitecture arising from various conditions and establishing entry criteria for clinical trials. They also hold the potential to refine the diagnosis of osteoporosis and assessment of fracture risk.

Factors favoring regain of the lost vertical spinal height through posterior spinal fusion in adolescent idiopathic scoliosis

Height gain is a common beneficial consequence following correction surgery in adolescent idiopathic scoliosis (AIS), yet little is known concerning factors favoring regain of the lost vertical spinal height (SH) through posterior spinal fusion. A consecutive series of AIS patients from February 2013 to August 2015 were reviewed. Surgical changes in SH (ΔSH), as well as the multiple coronal and sagittal deformity parameters were measured and correlated. Factors associated with ΔSH were identified through Pearson correlation analysis and multivariate regression analysis. A total of 172 single curve and 104 double curve patients were reviewed. The ΔSH averaged 2.5 ± 0.9 cm in single curve group and 2.9 ± 1.0 cm in double curve group. The multivariate regression analysis revealed the following pre-operative variables contributed significantly to ΔSH: pre-op Cobb angle, pre-op TK (single curve group only), pre-op GK (double curve group only) and pre-op LL (double curve group only) (p < 0.05). Thus change in height (in cm) = 0.044 × (pre-op Cobb angle) + 0.012 × (pre-op TK) (Single curve, adjusted R2 = 0.549) or 0.923 + 0.021 × (pre-op Cobb angle1) + 0.028 × (pre-op Cobb angle2) + 0.015 × (pre-op GK)-0.012 × (pre-op LL) (Double curve, adjusted R2 = 0.563). Severer pre-operative coronal Cobb angle and greater sagittal curves were beneficial factors favoring more contribution to the surgical lengthening effect in vertical spinal height in AIS.

Effect of upright posture on tonsillar level in adolescent idiopathic scoliosis

Results In AIS patients, the cerebellar tonsil position was significantly lower in the upright than the supine position (-0.7 +/-1.5 vs +1.2+/-1.7, p<0.00001) while in normal subjects, there was no change in cerebellar tonsil position between upright and supine positions (mean +2.1+/-1.7 vs +2.2 +/-1.8, p = 0.93). AIS patients also had a greater degree of tonsillar excursion between upright and supine positions compared to normal subjects (mean -1.9 +/-1.6 vs -0.1 +/-1.7, p<0.00001). More AIS patients tended to have tonsillar descent in the upright position rather than the supine position though this did not reach statistical significance (28% in supine position vs 48% in standing position, p=0.15). There is slightly better correlation between tonsillar level and Cobb angle in upright position (r = 0.45, p = 0.01) than those in supine position (r= 0.31, p=0.03) in AIS patients. Conclusion AIS patients have more tonsillar descent in the upright position and a greater degree of tonsillar excursion between supine and upright positions compared to matched control subjects. Apart from supporting the hypothesis of relative cord tethering in AIS, the results also enhance the likelihood of more significant chronic dynamic compression of the brainstem and upper cervical cord in AIS. Whether this will lead to chronic insult with subclinical neurophysiological disturbance, affecting both dynamic postural balance and SSEP, and contributing to the etiopathogenesis of AIS, warrants further study.

Quantitative analysis of structural abnormality of the vestibular system in progressive and non-progressive adolescent idiopathic scoliosis (AIS) using MRI techniques.

Previous studies suggested that asymmetric growth of vestibular system (VS) is related to the development of AIS. It provided a possible direction to resolve the unclear etiopathology of AIS and to reveal the difference in vestibular system morphology between progressive and non-progressive AIS patients.