Familial relationships of normal spine shape

Sagittal balance of the spine

Spinal balance can be defined as the trade-off between outside forces acting on the spine and the muscle response of the trunk, under sensorineural regulation, to maintain stable upright posture, both static and dynamic. Homo sapiens developed sagittal alignment along with bipedalism. The upright posture was an important step in human evolution, to master the environment, at the price of some instability in postural control in the trunk, and to maintain horizontal gaze. To make upright stance energetically economical and thus sustainable, reciprocal sagittal curvatures developed. Sagittal spinal organization is governed by strict rules under physiological conditions, enabling alignment between the center of mass and the lower limb joint centers. In children and adolescents, morphologic changes related to skeletal growth and postural control centers maturation alter spinal alignment and hence spinal balance, with increases in pelvic incidence, sacral slope and consequently lumbar lordosis and thoracic kyphosis. Global cervical lordosis remains stable, at the cost of an increase of the inferior cervical lordosis angle in correlation with T1 inclination or T1 slope. In pathology, spinal alignment may induce certain spinal pathologies such as growth-related spinal dystrophy or spondylolisthesis. It can also be altered by spinal deformity such as scoliosis, a regional disorder inducing adjacent compensatory mechanisms. The management of spinal pathologies is indissociable from understanding and maintaining or restoring individual sagittal alignment so as to ensure physiological distribution of stresses and limit onset of complications or decompensation in adulthood.

A Description of Three-Dimensional Shape of the Posterior Torso Comparing Those with and without Scoliosis

Scoliosis results in a 3D asymmetry of the spine and torso. It is not clear what the variability in 3D shape is in a non-scoliotic population, how much that is altered by scoliosis and what surgery does to that. This study is a 3D analysis of the shape of the torso in a cohort of non-scoliotic children that is then compared with a cohort of those with scoliosis both pre- and post-operatively. Procrustes analysis is used to examine the mean 3D shape. There is variability in shape in the non-scoliotic cohort. Scoliosis increases this asymmetry, particularly around the most prominent areas of the torso. Surgery alters the torso asymmetry but increases the difference in height between the right and the left with regard to the most prominent points on the torso. There is a degree of asymmetry seen in a non-scoliotic cohort of children. Scoliosis increases that asymmetry. Surgery alters the asymmetry but causes an increase in some of the 3D elements of the most prominent areas of the torso.

Response of the Axial Skeleton to Bipedal Loading Behaviors in an Experimental Animal Model

Many derived aspects of modern human axial skeletal morphology reflect our reliance on obligate bipedal locomotion. Insight into the adaptive significance of features, particularly in the spine, has been gained through experimental studies that induce bipedal standing or walking in quadrupedal mammals. Using an experimental animal model (Rattus norvegicus), the present study builds on earlier work by incorporating additional metrics of the cranium, employing quantitative methods established in the paleoanthropological literature, and exploring how variation in mechanical loading regimes impacts axial anatomy. Rats were assigned to one of five experimental groups, including "fully loaded bipedal walking," "partially loaded bipedal walking," "standing bipedally," "quadrupedal walking," and "no exercise control," and engaged in the behavior over 12-weeks. From μCT data obtained at the beginning and end of the experiment, we measured foramen magnum position and orientation, lumbar vertebral body wedging, cranial surface area of the lumbar and first sacral vertebral bodies, and sacral mediolateral width. Results demonstrate that bipedal rodents generally have more anteriorly positioned foramina magna, more dorsally wedged lumbar vertebrae, greater articular surface areas of lumbar and first sacral vertebral bodies, and sacra that exhibit greater mediolateral widths, compared to quadrupedal rodents. We further document variation among bipedal loading behavior groups (e.g., bipedal standing vs. walking). Our experimental animal model reveals how loading behaviors and adaptations may be specifically linked, and implicates a potential role for developmental plasticity in the evolutionary acquisition of bipedal adaptations in the hominin lineage. Anat Rec, 2018. © 2018 American Association for Anatomy.

Variation in lifting kinematics related to individual intrinsic lumbar curvature: an investigation in healthy adults

Objective

Lifting postures are frequently implicated in back pain. We previously related responses to a static load with intrinsic spine shape, and here we investigate the role of lumbar spine shape in lifting kinematics.

Methods

Thirty healthy adults (18-65 years) performed freestyle, stoop and squat lifts with a weighted box (6-15 kg, self-selected) while being recorded by Vicon motion capture. Internal spine shape was characterised using statistical shape modelling (SSM) from standing mid-sagittal MRIs. Associations were investigated between spine shapes quantified by SSM and peak flexion angles.

Results

Two SSM modes described variations in overall lumbar curvature (mode 1 (M1), 55% variance) and the evenness of curvature distribution (mode 2 (M2), 12% variance). M1 was associated with greater peak pelvis (r=0.38, p=0.04) and smaller knee flexion (r=-0.40, p=0.03) angles; individuals with greater curviness preferred to lift with a stooped lifting posture. This was confirmed by analysis of those individuals with very curvy or very straight spines (|M1|>1 SD). There were no associations between peak flexion angles and mode scores in stoop or squat trials (p>0.05). Peak flexion angles were positively correlated between freestyle and squat trials but not between freestyle and stoop or squat and stoop, indicating that individuals adjusted knee flexion while maintaining their preferred range of lumbar flexion and that 'squatters' adapted better to different techniques than 'stoopers'.

Conclusion

Spinal curvature affects preferred lifting styles, and individuals with curvier spines adapt more easily to different lifting techniques. Lifting tasks may need to be tailored to an individual's lumbar spine shape.

Pelvic incidence variation among individuals: functional influence versus genetic determinism

Pelvic incidence has become one of the most important sagittal parameters in spinal surgery. Despite its great importance, pelvic incidence can vary from 33° to 85° in the normal population. The reasons for this great variability in pelvic incidence remain unexplored. The objective of this article is to present some possible interpretations for the great variability in pelvic incidence under both normal and pathological conditions and to further understand the determinants of pelvic incidence from the perspective of the functional requirements for bipedalism and genetic backgrounds via a literature review. We postulate that both pelvic incidence and pelvic morphology may be genetically predetermined, and a great variability in pelvic incidence may already exist even before birth. This great variability may also serve as a further reminder that the sagittal profile, bipedal locomotion mode, and genetic background of every individual are unique and specific, and clinicians should avoid making universally applying broad generalizations of pelvic incidence. Although PI is an important parameter and there are many theories behind its variability, we still do not have clear mechanistic answers.

Statistical shape modelling of hip and lumbar spine morphology and their relationship in the MRC National Survey of Health and Development

The anatomical shape of bones and joints is important for their proper function but quantifying this, and detecting pathological variations, is difficult to do. Numerical descriptions would also enable correlations between joint shapes to be explored. Statistical shape modelling (SSM) is a method of image analysis employing pattern recognition statistics to describe and quantify such shapes from images; it uses principal components analysis to generate modes of variation describing each image in terms of a set of numerical scores after removing global size variation. We used SSM to quantify the shapes of the hip and the lumbar spine in dual-energy x-ray absorptiometry (DXA) images from 1511 individuals in the MRC National Survey of Health and Development at ages 60-64 years. We compared shapes of both joints in men and women and hypothesised that hip and spine shape would be strongly correlated. We also investigated associations with height, weight, body mass index (BMI) and local (hip or lumber spine) bone mineral density. In the hip, all except one of the first 10 modes differed between men and women. Men had a wider femoral neck, smaller neck-shaft angle, increased presence of osteophytes and a loss of the femoral head/neck curvature compared with women. Women presented with a flattening of the femoral head and greater acetabular coverage of the femoral head. Greater weight was associated with a shorter, wider femoral neck and larger greater and lesser trochanters. Taller height was accompanied by a flattening of the curve between superior head and neck and a larger lesser trochanter. Four of the first eight modes describing lumbar spine shape differed between men and women. Women tended to have a more lordotic spine than men with relatively smaller but caudally increasing anterior-posterior (a-p) vertebral diameters. Men were more likely to have a straighter spine with larger vertebral a-p diameters relative to vertebral height than women, increasing cranially. A weak correlation was found between body weight and a-p vertebral diameter. No correlations were found between shape modes and height in men, whereas in women there was a weak positive correlation between height and evenness of spinal curvature. Linear relationships between hip and spine shapes were weak and inconsistent in both sexes, thereby offering little support for our hypothesis. In conclusion, men and women entering their seventh decade have small but statistically significant differences in the shapes of their hips and their spines. Associations with height, weight, BMI and BMD are small and correspond to subtle variations whose anatomical significance is not yet clear. Correlations between hip and spine shapes are small.

Concordance for curve type in idiopathic scoliosis among family members

OBJECTIVE:

To evaluate the concordance for the curve pattern, side and levels of the superior apical vertebrae, apex and inferior apical vertebrae of curves in patients and their relatives with idiopathic scoliosis.

METHODS:

Concordance according to the Lenke classification for curve pattern, side and levels of the superior apical vertebrae, apex and inferior apical vertebrae were evaluated comparative and prospectively in 243 pairs of patients and respective relatives with idiopathic scoliosis.

RESULTS:

The family concordance for the curve pattern and side was 51.4% (125 pairs). Among these pairs, the concordance of the levels of the vertebrae was 91.2% (114 pairs). The concordance rate for the curve pattern and side between parents/children was 51.6% and between siblings was 50.0% (p-value= 0.411). The concordance rates of the levels of vertebrae were 86.8% and 95.1%, respectively (p-value = 0.219).

CONCLUSION:

Curve shape in idiopathic scoliosis is related to family and degree of kinship, since the data showed a high concordance for the curve pattern, side and levels of the apical vertebrae and apex between patients and relatives with this deformity. The concordance was higher in those with a closer degree of kinship.Level of Evidence II, Lesser Quality Prospective Study.

Etiology of lumbar lordosis and its pathophysiology: a review of the evolution of lumbar lordosis, and the mechanics and biology of lumbar degeneration

The goal of this review is to discuss the mechanisms of postural degeneration, particularly the loss of lumbar lordosis commonly observed in the elderly in the context of evolution, mechanical, and biological studies of the human spine and to synthesize recent research findings to clinical management of postural malalignment. Lumbar lordosis is unique to the human spine and is necessary to facilitate our upright posture. However, decreased lumbar lordosis and increased thoracic kyphosis are hallmarks of an aging human spinal column. The unique upright posture and lordotic lumbar curvature of the human spine suggest that an understanding of the evolution of the human spinal column, and the unique anatomical features that support lumbar lordosis may provide insight into spine health and degeneration. Considering evolution of the skeleton in isolation from other scientific studies provides a limited picture for clinicians. The evolution and development of human lumbar lordosis highlight the interdependence of pelvic structure and lumbar lordosis. Studies of fossils of human lineage demonstrate a convergence on the degree of lumbar lordosis and the number of lumbar vertebrae in modern Homo sapiens. Evolution and spine mechanics research show that lumbar lordosis is dictated by pelvic incidence, spinal musculature, vertebral wedging, and disc health. The evolution, mechanics, and biology research all point to the importance of spinal posture and flexibility in supporting optimal health. However, surgical management of postural deformity has focused on restoring posture at the expense of flexibility. It is possible that the need for complex and costly spinal fixation can be eliminated by developing tools for early identification of patients at risk for postural deformities through patient history (genetics, mechanics, and environmental exposure) and tracking postural changes over time.

Lumbar lordosis

Lumbar lordosis is a key postural component that has interested both clinicians and researchers for many years. Despite its wide use in assessing postural abnormalities, there remain many unanswered questions regarding lumbar lordosis measurements. Therefore, in this article we reviewed different factors associated with the lordosis angle based on existing literature and determined normal values of lordosis. We reviewed more than 120 articles that measure and describe the different factors associated with the lumbar lordosis angle. Because of a variety of factors influencing the evaluation of lumbar lordosis such as how to position the patient and the number of vertebrae included in the calculation, we recommend establishing a uniform method of evaluating the lordosis angle. Based on our review, it seems that the optimal position for radiologic measurement of lordosis is standing with arms supported while shoulders are flexed at a 30° angle. There is evidence that many factors, such as age, gender, body mass index, ethnicity, and sport, may affect the lordosis angle, making it difficult to determine uniform normal values. Normal lordosis should be determined based on the specific characteristics of each individual; we therefore presented normal lordosis values for different groups/populations. There is also evidence that the lumbar lordosis angle is positively and significantly associated with spondylolysis and isthmic spondylolisthesis. However, no association has been found with other spinal degenerative features. Inconclusive evidence exists for association between lordosis and low back pain. Additional studies are needed to evaluate these associations. The optimal lordotic range remains unknown and may be related to a variety of individual factors such as weight, activity, muscular strength, and flexibility of the spine and lower extremities.

Sagittal spinal profile and spinopelvic balance in parents of scoliotic children

BACKGROUND CONTEXT

It is well known that spinal biomechanics and familial predisposition play an important role in the onset and evolution of idiopathic scoliosis. The relationship between the sagittal profile of the spine and spinal biomechanics has also been established in a number of studies. It has been suggested previously that a certain sagittal spinal configuration with implications for spinal rotational stiffness is inherited, thus providing a possible explanation for the well-known hereditary component in adolescent idiopathic scoliosis (AIS).

PURPOSE

To test the hypothesis that the familial trend in AIS may be partially explained by the inheritance of a sagittal spinal profile, which has been shown to make the spine less resistant to rotatory decompensation.

STUDY DESIGN

A prospective case controlled radiographic analysis of the sagittal profile of the spine and spinopelvic alignment.

PATIENT SAMPLE

One hundred two parents of scoliotic children, compared with 102 age-matched controls (parents of nonscoliotic children).

OUTCOME MEASURES

Physiologic measures: sagittal profile of the spine and spinopelvic alignment.

METHODS

Freestanding lateral radiographs of 51 parent couples of girls with severe (Cobb angle >30°) progressive AIS (AIS group) and 102 age-matched controls (control group) were taken. Parents with manifest spinal deformities or spinal pathology of any kind were excluded based on history or spinal X-ray to avoid distorted sagittal images with unreliable measurements. Values were calculated for thoracic kyphosis (T4-T12), lumbar lordosis (L1-L5), spinal balance (sagittal plumb line of C7 and T4, T1-L5 sagittal spinal inclination, T9 sagittal offset), curvature parameters (expressed in the area under the curve [AUC]), and pelvic parameters (pelvic tilt, pelvic incidence, and sacral slope). In addition, the height, offset, and length of the posteriorly inclined spinal segment, inclination of each vertebra, and normalized sagittal spinal profile were calculated. Differences in spinopelvic alignment between fathers and mothers of both groups were analyzed.

RESULTS

In the fathers of the AIS group, the plumb line of T4 was significantly less posteriorly positioned relative to the hip axis (79 mm vs. 92 mm; p=.009); the overall AUC and the lumbar AUC were significantly smaller (p=.002 and p=.008, respectively) as compared with the fathers in the control group. Vertebrae T11-L2 were significantly less backwardly inclined in the fathers of the AIS group (T11, L2: p<.05 and T12-L1: p<.01). An analysis of sagittal spinal profile showed a significantly flatter spine in the fathers of the AIS group (p=.01). No significant differences were observed in height, offset, and length of the backwardly inclined spinal segment. In the mothers of the AIS group, no statistically significant differences were observed in the spinopelvic parameters, spinal curvature, inclination of the vertebrae, and declive spinal segment parameters or sagittal spinal profile as compared with the mothers in the control group.

CONCLUSIONS

The sagittal spinal profile of the fathers of scoliotic children was significantly flatter than the sagittal spinal profile of fathers of nonscoliotic children. No difference was found in the sagittal spinal profile of the mothers of scoliotic children as compared with mothers of nonscoliotic children. Although it is well known that scoliotic mothers have an increased risk of having a scoliotic offspring, this study indicates that fathers may possibly contribute as well through their sagittal spinal profile to the inheritance of idiopathic scoliosis.

A Geometric Morphometric Assessment of Hand Shape and Comparison to the 2D:4D Digit Ratio as a Marker of Sexual Dimorphism

Twin studies are extremely useful for investigating hypotheses of genetic influence on a range of behavioral and physical traits in humans. Studies of physical traits, however, are usually limited to size-related biological characteristics because it is inherently difficult to quantify the morphological counterpart – shape. In recent years, the development of geometry-preserving analytical techniques built upon multivariate statistical methodologies has produced a new discipline in biological shape analysis known as geometric morphometrics. In this study of hand shape analysis, we introduce the reader already familiar with the field of twin research to the potential utility of geometric morphometrics and demonstrate the cross-discipline applicability of methods. We also investigate and compare the efficacy of the 2D:4D ratio, a commonly used marker of sexual dimorphism, to the fully multivariate approach of shape analysis in discriminating between male and female sex. Studies of biological shape variation utilizing geometric morphometric techniques may be completed with software freely available on the Internet and time invested to master the small learning curve in concepts and theory.

A new look at the geometry of the lumbar spine

STUDY DESIGN

A retrospective cohort study of the relationship between the structures that form the lumbar spine in humans.

OBJECTIVE

To investigate the relationship between the segmental wedging of the vertebral bodies and that of the intervertebral discs, and between the overall lordosis angle and each of the 5 lumbar segments.

SUMMARY OF BACKGROUND DATA

Little attention has been paid to the internal relationship between the structures that form the lumbar spine. Understanding these relationships is instrumental to our ability to restore and rehabilitate the lordotic curvature.

METHODS

Lateral radiographs of 101 adult lumbar spines were examined in patients at spinal clinics. The patients had no history of spinal surgery and no radiographic abnormality. The radiologic parameters are the lordosis angle (LA), the body wedge angle (B), the total segmental angle (S), and the intervertebral disc angle (D). Measurements B, S, and D were taken for each of the 5 lumbar segments. Measurements B and D were used to calculate ΣB, the sum of the B, and ΣD, the sum of the D.

RESULTS

The LA correlates with the sum of the vertebral body angles and with the sum of the intervertebral disc angles. Vertebral body wedging is negatively correlated with intervertebral disc wedging. The middle 3 lumbar segments are moderately-to-poorly correlated, among themselves and with the LA, while the upper and lower lumbar segments are poorly correlated with the LA and not correlated with any lumbar segment.

CONCLUSION

Three parts of the lumbar lordosis were identified: the upper part, formed by the first lumbar segment; the middle part, formed by the middle 3 segments; and the lower part, formed by the fifth lumbar segment. The statistical study shows an inverse relationship between vertebral body and intervertebral disc wedging.

The intrinsic shape of the human lumbar spine in the supine, standing and sitting postures: characterization using an active shape model

The shape of the lumbar spine in the sagittal plane varies between individuals and as a result of postural changes but it is not known how the shape in different postures is related. Sagittal images of the lumbar spines of 24 male volunteers were acquired using a positional magnetic resonance scanner. The subjects were imaged lying supine, standing and sitting. An active shape model was used to characterize shape in terms of independent modes of variation. Two modes were identified that described the total (mode 1) and distribution (mode 2) of the curvature. The spinal shape was found to be intercorrelated between the three postures for both modes, suggesting that the lumbar spine has an element of shape that is partially maintained despite postural alterations. Mode 1 values indicated that the spine was straightest when standing and curviest when sitting. Mode 2 values indicated that the distribution in the curvature was most even when sitting and least even when lying supine. Systematic differences in the behaviour of the spine, when changing posture, were found that suggest that the shape of the spine may affect its biomechanics.

Clinical etiological classification of scoliosis: report of 1289 cases

OBJECTIVE

With the development of diagnostic techniques and in-depth understanding of lateral curvature of the spine (scoliosis), it is possible to differentiate idiopathic scoliosis from other forms with various known etiologies. The present study was to analyze data collected at the authors' center according to the current etiological spectrum and classification of scoliosis.

METHODS

One thousand, two hundred and eighty-nine consecutive patients with different forms of structural scoliosis were reviewed. The average age at first visit was 18 years, ranging from 4 months to 79 years. Corrective surgery was performed on patients aged from 9 to 28 years; their clinical data were retrieved for independent statistical analyses, and further compared with those obtained from the whole group.

RESULTS

The prevalence of non-idiopathic scoliosis was 25.3% in the whole series, but it increased to 34% in the surgical group aged from 9 to 28 years. Thirty-nine percent of patients with congenital scoliosis presented at least one developmental spinal cord malformation.

CONCLUSION

The current study has shown that the etiological distribution of scoliosis has changed a lot from what was true decades ago. Developmental malformation related to scoliosis is one of the risk factors for neurological complications during corrective surgery, so it is important to make an accurate diagnosis and take appropriate prophylactic measures to avoid relative neurological complications.