Neuromechanics of idiopathic scoliosis
Encyclopedia
The neuromechanics of idiopathic scoliosis is about the bone
s, muscles and joints changes in people having a spinal deformity consisting of a lateral curvature and a rotation of the vertebrae within the curve that is not explained by congenital (e.g. vertebral abnormality) or neuromuscular (e.g. muscular dystrophy) reasons.
The idiopathic
scoliosis
accounts for 80–90% of scoliosis cases. Its pathogenesis
is unknown. However, changes in the vestibular system
, a lateral shift of the hand representation and abnormal variability of erector spinae motor map location in the motor cortex
may be involved in this disease. Besides, idiopathic scoliosis being more frequent in certain families, it is suspected to be transmitted via autosomal dominant inheritance. Estrogens could also play a crucial part in the progression of idiopathic scoliosis through their roles in bone formation, growth, maturation and turnover. Finally, collagen
, intervertebral disc
and muscle abnormalities have been suggested as etiologic factors in idiopathic scoliosis, although these are perhaps results rather than causes.
status and the magnitude of the curve are used to foresee the idiopathic scoliosis curve progression. However, the relative importance of each factor and how they may interact is not clearly defined. The earlier the scoliosis appears, the more likely it will progress. Though it is recommended that idiopathic scoliotic people should practice a sport
for aerobic exercise
and development of a positive body image, practice of a sport at a competitive level is to be avoided.
players, 16% of young swimmers
and 24% in professional ballet
companies. The exposure of the body to high repetitive mechanical constraints may influence the occurrence of idiopathic scoliosis.
Cobb angle
is a common measure to classify scoliosis. The greater the angle, the more serious is the disease but the smaller is the number of patients. One to three out of every hundred people have idiopathic scoliosis curves greater than 10° with an equal proportion of boys and girls. One to three out of every thousand people have idiopathic scoliosis curves greater than 30° with a ratio of eight girls for every one boy.
Scoliosis is also classified according to the region(s) they affect. The vertebral column can be deformed at the thoracic level, at the lumbar level or at both. In the lumbar region, scoliosis induces perturbations to standing balance. The thoracic region is the location that most impacts movement strategies. Scoliosis impedes on the movement of the ribs, places the respiratory muscles at a mechanical disadvantage and displaces the various organs of the thoracic cavity.
for the concave cortical bone
is higher than for the convex cortical bone, and cancellous bone density is higher for the concave side than for the convex side. The concave side of a vertebra is less porous and has a thicker cortical bone than the convex side, which is consistent with Wolff’s law
about bone remodeling
.
) on the convex side than on the concave side in sitting or standing conditions. Because in scoliotic people wearing a brace
, the muscle activity of the erector spinae muscles decreased on the convex side when walking
with the brace and because after spinal arthrodesis
surgery, idiopathic scoliotic people showed a significant decrease in paravertebral muscle activity on the convex side but not on the concave side, the muscular asymmetry in idiopathic scoliosis is thought to be a biomechanical consequence of the scoliotic curvature rather than its cause.
behaves like a torsional spring
: while walking, the angular momentum
of the shoulder
s compensates the angular momentum of the pelvis
(i.e. when the shoulders rotate clockwise
, the pelvis rotates counterclockwise; when the pelvis rotates clockwise, the shoulders rotate counterclockwise). As scoliosis perturbs the architecture of the shoulders, spine and pelvis, gait also differs between patients and non-scoliotic people.
and a narrower hips extension range of motion than non-scoliotic people. The range of motion for rachis extension, hips flexion, left and right lateral flexions are similar to non-scoliotic people.
After arthrodesis, all rachis ranges of motion decrease because of surgery but hips extension range of motion is comparable to the one of non-operated scoliotic people.
, while walking at a constant speed of 4 km/h for a few minutes until a steady state is reached, relative to non-scoliotic people, idiopathic scoliotic people have a frontal (i.e. coronal) pelvis, hip, and shoulder, transversal hip and sagittal knee
motion restriction. The step length is reduced and the stance phase duration is also reduced.
Surgical treatment of thoracolumbar/lumbar adolescent idiopathic scoliosis, whether performed with anterior spinal fusion
or posterior spinal fusion arthrodesis, results in overall positive changes that lead to partial normalization of some gait parameters. After surgery, a slight reduction of trunk rotation, a decrease in shoulder rotation, an increase in frontal motion of pelvic and hips (pelvic tilt and hip abduction
) are observed and no changes occurred in lower extremities during gait (knee and ankle
).
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
s, muscles and joints changes in people having a spinal deformity consisting of a lateral curvature and a rotation of the vertebrae within the curve that is not explained by congenital (e.g. vertebral abnormality) or neuromuscular (e.g. muscular dystrophy) reasons.
The idiopathic
Idiopathic
Idiopathic is an adjective used primarily in medicine meaning arising spontaneously or from an obscure or unknown cause. From Greek ἴδιος, idios + πάθος, pathos , it means approximately "a disease of its own kind". It is technically a term from nosology, the classification of disease...
scoliosis
Scoliosis
Scoliosis is a medical condition in which a person's spine is curved from side to side. Although it is a complex three-dimensional deformity, on an X-ray, viewed from the rear, the spine of an individual with scoliosis may look more like an "S" or a "C" than a straight line...
accounts for 80–90% of scoliosis cases. Its pathogenesis
Pathogenesis
The pathogenesis of a disease is the mechanism by which the disease is caused. The term can also be used to describe the origin and development of the disease and whether it is acute, chronic or recurrent...
is unknown. However, changes in the vestibular system
Vestibular system
The vestibular system, which contributes to balance in most mammals and to the sense of spatial orientation, is the sensory system that provides the leading contribution about movement and sense of balance. Together with the cochlea, a part of the auditory system, it constitutes the labyrinth of...
, a lateral shift of the hand representation and abnormal variability of erector spinae motor map location in the motor cortex
Motor cortex
Motor cortex is a term that describes regions of the cerebral cortex involved in the planning, control, and execution of voluntary motor functions.-Anatomy of the motor cortex :The motor cortex can be divided into four main parts:...
may be involved in this disease. Besides, idiopathic scoliosis being more frequent in certain families, it is suspected to be transmitted via autosomal dominant inheritance. Estrogens could also play a crucial part in the progression of idiopathic scoliosis through their roles in bone formation, growth, maturation and turnover. Finally, collagen
Collagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...
, intervertebral disc
Intervertebral disc
Intervertebral discs lie between adjacent vertebrae in the spine. Each disc forms a cartilaginous joint to allow slight movement of the vertebrae, and acts as a ligament to hold the vertebrae together.-Structure:...
and muscle abnormalities have been suggested as etiologic factors in idiopathic scoliosis, although these are perhaps results rather than causes.
Demographic data
The patient’s age at presentation of scoliosis, the remaining growth, the menarcheMenarche
Menarche is the first menstrual cycle, or first menstrual bleeding, in female human beings. From both social and medical perspectives it is often considered the central event of female puberty, as it signals the possibility of fertility....
status and the magnitude of the curve are used to foresee the idiopathic scoliosis curve progression. However, the relative importance of each factor and how they may interact is not clearly defined. The earlier the scoliosis appears, the more likely it will progress. Though it is recommended that idiopathic scoliotic people should practice a sport
Sport
A Sport is all forms of physical activity which, through casual or organised participation, aim to use, maintain or improve physical fitness and provide entertainment to participants. Sport may be competitive, where a winner or winners can be identified by objective means, and may require a degree...
for aerobic exercise
Aerobic exercise
Aerobic exercise is physical exercise of relatively low intensity that depends primarily on the aerobic energy-generating process. Aerobic literally means "living in air", and refers to the use of oxygen to adequately meet energy demands during exercise via aerobic metabolism...
and development of a positive body image, practice of a sport at a competitive level is to be avoided.
Age
Idiopathic scoliosis can appear at different ages. Infantile idiopathic scoliosis that appear from the birth to 3 years old, account for 0.5% of idiopathic scoliosis. Juvenile idiopathic scoliosis that appear from the 4 to 10 years old, account for 10.5% of idiopathic scoliosis. Adolescent idiopathic scoliosis that appear after the age of 10 years, account for 89% of idiopathic scoliosis. From these statistics, it seems that individuals are at highest risk of developing idiopathic scoliosis during adolescence.Physical activity level
Because scoliotic people have higher joint laxity compared to non-scoliotic people, they are drawn toward gymnastics but the practice of gymnastics for less than 20 hours training per week does not cause scoliosis. Based on populations that had more than 20 hours training per week, idiopathic scoliosis has been observed among 10% of tennisTennis
Tennis is a sport usually played between two players or between two teams of two players each . Each player uses a racket that is strung to strike a hollow rubber ball covered with felt over a net into the opponent's court. Tennis is an Olympic sport and is played at all levels of society at all...
players, 16% of young swimmers
Swimming (sport)
Swimming is a sport governed by the Fédération Internationale de Natation .-History: Competitive swimming in Europe began around 1800 BCE, mostly in the form of the freestyle. In 1873 Steve Bowyer introduced the trudgen to Western swimming competitions, after copying the front crawl used by Native...
and 24% in professional ballet
Ballet
Ballet is a type of performance dance, that originated in the Italian Renaissance courts of the 15th century, and which was further developed in France and Russia as a concert dance form. The early portions preceded the invention of the proscenium stage and were presented in large chambers with...
companies. The exposure of the body to high repetitive mechanical constraints may influence the occurrence of idiopathic scoliosis.
Physiology
Cobb angle
The Cobb angle, named after the American orthopedic surgeon John Robert Cobb , was originally used to measure coronal plane deformity on antero-posterior plain radiographs in the classification of scoliosis...
is a common measure to classify scoliosis. The greater the angle, the more serious is the disease but the smaller is the number of patients. One to three out of every hundred people have idiopathic scoliosis curves greater than 10° with an equal proportion of boys and girls. One to three out of every thousand people have idiopathic scoliosis curves greater than 30° with a ratio of eight girls for every one boy.
Scoliosis is also classified according to the region(s) they affect. The vertebral column can be deformed at the thoracic level, at the lumbar level or at both. In the lumbar region, scoliosis induces perturbations to standing balance. The thoracic region is the location that most impacts movement strategies. Scoliosis impedes on the movement of the ribs, places the respiratory muscles at a mechanical disadvantage and displaces the various organs of the thoracic cavity.
Skeleton
In a scoliotic patient, the vertebral column experiences extension forces on the convex side and compression forces on the concave side. At the apical vertebra, average bone densityBone density
Bone density is a medical term normally referring to the amount of mineral matter per square centimeter of bones. Bone density is used in clinical medicine as an indirect indicator of osteoporosis and fracture risk.This medical bone density is not the true physical "density" of the bone, which...
for the concave cortical bone
Cortical bone
Cortical bone, synonymous with compact bone, is one of the two types of osseous tissue that form bones. Cortical bone facilitates bone's main functions: to support the whole body, protect organs, provide levers for movement, and store and release chemical elements, mainly calcium. As its name...
is higher than for the convex cortical bone, and cancellous bone density is higher for the concave side than for the convex side. The concave side of a vertebra is less porous and has a thicker cortical bone than the convex side, which is consistent with Wolff’s law
Wolff's law
Wolff's law is a theory developed by the German Anatomist/Surgeon Julius Wolff in the 19th century that states that bone in a healthy person or animal will adapt to the loads it is placed under. If loading on a particular bone increases, the bone will remodel itself over time to become stronger...
about bone remodeling
Bone remodeling
Bone remodeling is a lifelong process where mature bone tissue is removed from the skeleton and new bone tissue is formed...
.
Muscle
Scoliotic adolescents, at the apex vertebra, have a higher muscle activity (as measured by surface electromyographyElectromyography
Electromyography is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph, to produce a record called an electromyogram. An electromyograph detects the electrical potential generated by muscle...
) on the convex side than on the concave side in sitting or standing conditions. Because in scoliotic people wearing a brace
Orthotics
Orthotics is a specialty within the medical field concerned with the design, manufacture and application of orthoses. An orthosis is an orthopedic device that supports or corrects the function of a limb or the torso...
, the muscle activity of the erector spinae muscles decreased on the convex side when walking
Walking
Walking is one of the main gaits of locomotion among legged animals, and is typically slower than running and other gaits. Walking is defined by an 'inverted pendulum' gait in which the body vaults over the stiff limb or limbs with each step...
with the brace and because after spinal arthrodesis
Arthrodesis
Arthrodesis, also known as artificial ankylosis or syndesis, is the artificial induction of joint ossification between two bones via surgery. This is done to relieve intractable pain in a joint which cannot be managed by pain medication, splints, or other normally-indicated treatments. The typical...
surgery, idiopathic scoliotic people showed a significant decrease in paravertebral muscle activity on the convex side but not on the concave side, the muscular asymmetry in idiopathic scoliosis is thought to be a biomechanical consequence of the scoliotic curvature rather than its cause.
Effects on movement
Since idiopathic scoliosis and its surgery affect the vertebrae and the joints along the spine, the range of motion is expected to be different between patients and non-scoliotic people. There is a hypothesis that states that the vertebral columnVertebral column
In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...
behaves like a torsional spring
Torsion spring
A torsion spring is a spring that works by torsion or twisting; that is, a flexible elastic object that stores mechanical energy when it is twisted. The amount of force it exerts is proportional to the amount it is twisted. There are two types...
: while walking, the angular momentum
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
of the shoulder
Shoulder
The human shoulder is made up of three bones: the clavicle , the scapula , and the humerus as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder make up the shoulder joints. The major joint of the shoulder is the glenohumeral joint, which...
s compensates the angular momentum of the pelvis
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
(i.e. when the shoulders rotate clockwise
Clockwise
Circular motion can occur in two possible directions. A clockwise motion is one that proceeds in the same direction as a clock's hands: from the top to the right, then down and then to the left, and back to the top...
, the pelvis rotates counterclockwise; when the pelvis rotates clockwise, the shoulders rotate counterclockwise). As scoliosis perturbs the architecture of the shoulders, spine and pelvis, gait also differs between patients and non-scoliotic people.
Range of motion
Independently of the Cobb angle, the affected vertebra and the age, idiopathic scoliotic people have a larger rachis flexion range of motionRange of motion
Range of motion , is the distance that a movable object may normally travel while properly attached to another object. It is also called range of travel, particularly when talking about mechanical devices and in mechanical engineering fields...
and a narrower hips extension range of motion than non-scoliotic people. The range of motion for rachis extension, hips flexion, left and right lateral flexions are similar to non-scoliotic people.
After arthrodesis, all rachis ranges of motion decrease because of surgery but hips extension range of motion is comparable to the one of non-operated scoliotic people.
Gait
In terms of gaitGait
Gait is the pattern of movement of the limbs of animals, including humans, during locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on speed, terrain, the need to maneuver, and energetic efficiency...
, while walking at a constant speed of 4 km/h for a few minutes until a steady state is reached, relative to non-scoliotic people, idiopathic scoliotic people have a frontal (i.e. coronal) pelvis, hip, and shoulder, transversal hip and sagittal knee
Knee
The knee joint joins the thigh with the leg and consists of two articulations: one between the fibula and tibia, and one between the femur and patella. It is the largest joint in the human body and is very complicated. The knee is a mobile trocho-ginglymus , which permits flexion and extension as...
motion restriction. The step length is reduced and the stance phase duration is also reduced.
Surgical treatment of thoracolumbar/lumbar adolescent idiopathic scoliosis, whether performed with anterior spinal fusion
Spinal fusion
Spinal fusion, also known as spondylodesis or spondylosyndesis, is a surgical technique used to join two or more vertebrae. Supplementary bone tissue, either from the patient or a donor , is used in conjunction with the body's natural bone growth processes to fuse the vertebrae.Fusing of the...
or posterior spinal fusion arthrodesis, results in overall positive changes that lead to partial normalization of some gait parameters. After surgery, a slight reduction of trunk rotation, a decrease in shoulder rotation, an increase in frontal motion of pelvic and hips (pelvic tilt and hip abduction
Abduction (kinesiology)
Abduction, in functional anatomy, is a movement which draws a limb away from the median plane of the body. It is thus opposed to adduction.-Upper limb:* of arm at shoulder ** Supraspinatus** Deltoid* of hand at wrist...
) are observed and no changes occurred in lower extremities during gait (knee and ankle
Ankle
The ankle joint is formed where the foot and the leg meet. The ankle, or talocrural joint, is a synovial hinge joint that connects the distal ends of the tibia and fibula in the lower limb with the proximal end of the talus bone in the foot...
).