The neuromechanics of idiopathic scoliosis is about the changes in the

bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...

s, muscles and

joints A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw- ...

in cases of spinal deformity consisting of a lateral curvature

scoliosis Scoliosis is a condition in which a person's spine has a sideways curve. The curve is usually "S"- or "C"-shaped over three dimensions. In some, the degree of curve is stable, while in others, it increases over time. Mild scoliosis does not ty ...

and a rotation of the

vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

within the curve, that is not explained by either

congenital A birth defect, also known as a congenital disorder, is an abnormal condition that is present at birth regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can ...

vertebral abnormalities, or neuromuscular disorders such as

muscular dystrophy Muscular dystrophies (MD) are a genetically and clinically heterogeneous group of rare neuromuscular diseases that cause progressive weakness and breakdown of skeletal muscles over time. The disorders differ as to which muscles are primarily af ...

. The

idiopathic An idiopathic disease is any disease with an unknown cause or mechanism of apparent spontaneous origin. From Greek ἴδιος ''idios'' "one's own" and πάθος ''pathos'' "suffering", ''idiopathy'' means approximately "a disease of its own kin ...

accounts for 80–90% of scoliosis cases. Its

pathogenesis Pathogenesis is the process by which a disease or disorder develops. It can include factors which contribute not only to the onset of the disease or disorder, but also to its progression and maintenance. The word comes from Greek πάθος ''pat ...

is unknown. However, changes in the

vestibular system The vestibular system, in vertebrates, is a sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating movement with balance. Together with the cochlea, a part of the auditory system, it constitut ...

, a lateral shift of the hand representation and abnormal variability of

erector spinae The erector spinae ( ) or spinal erectors is a set of muscles that straighten and rotate the back. The spinal erectors work together with the glutes ( gluteus maximus, gluteus medius and gluteus minimus) to maintain stable posture standing or ...

motor map location in the

motor cortex The motor cortex is the region of the cerebral cortex believed to be involved in the planning, control, and execution of voluntary movements. The motor cortex is an area of the frontal lobe located in the posterior precentral gyrus immediately ...

may be involved in this disease. A short spinal cord and associated nerve tensions has been proposed as a cause and model for idiopathic scoliosis. Besides idiopathic scoliosis being more frequent in certain families, it is suspected to be transmitted via

autosomal An autosome is any chromosome that is not a sex chromosome. The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosomal (sex chromosome) pairs, which may have different structures. The DNA in autosom ...

dominant inheritance.

Estrogens Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal acti ...

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 () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whol ...

intervertebral disc An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in the vertebral column. Each disc forms a fibrocartilaginous joint (a symphysis), to allow slight movement of the vertebrae, to act as a ligament to h ...

and muscle abnormalities have been suggested as the cause 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

menarche Menarche ( ; ) is the first menstrual cycle, or first menstrual bleeding, in female humans. From both social and medical perspectives, it is often considered the central event of female puberty, as it signals the possibility of fertility. Gir ...

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 pertains to any form of competitive physical activity or game that aims to use, maintain, or improve physical ability and skills while providing enjoyment to participants and, in some cases, entertainment to spectators. Sports can, ...

for

aerobic exercise Aerobic exercise (also known as endurance activities, cardio or cardio-respiratory exercise) is physical exercise of low to high intensity that depends primarily on the aerobic energy-generating process. "Aerobic" is defined as "relating to, inv ...

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

tennis Tennis is a racket sport that is played either individually against a single opponent (singles) or between two teams of two players each (doubles). Each player uses a tennis racket that is strung with cord to strike a hollow rubber ball cov ...

players, 16% of young swimmers and 24% in professional

ballet Ballet () is a type of performance dance that originated during the Italian Renaissance in the fifteenth century and later developed into a concert dance form in France and Russia. It has since become a widespread and highly technical form ...

companies. The exposure of the body to high repetitive mechanical constraints may influence the occurrence of idiopathic scoliosis.

Physiology

Cobb angle The Cobb angle is a measurement of bending disorders of the vertebral column such as scoliosis and traumatic deformities. Definition and method It is defined as the greatest angle at a particular region of the vertebral column, when measured from ...

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 density Bone density, or bone mineral density, is the amount of bone mineral in bone tissue. The concept is of mass of mineral per volume of bone (relating to density in the physics sense), although clinically it is measured by proxy according to optic ...

for the concave cortical bone is higher than for the convex cortical bone, and

cancellous bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, and ...

density is higher for the concave side than for the convex side. The concave side of a vertebra is less

porous Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...

and has a thicker cortical bone than the convex side, which is consistent with Wolff's law about bone remodeling.

Muscle

Scoliotic adolescents, at the apex vertebra, have a higher muscle activity (as measured by surface

electromyography Electromyography (EMG) 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 electromyo ...

) on the convex side than on the concave side in sitting or standing conditions. Because in scoliotic people wearing a

brace Brace(s) or bracing may refer to: Medical * Orthopaedic brace, a device used to restrict or assist body movement ** Back brace, a device limiting motion of the spine *** Milwaukee brace, a kind of back brace used in the treatment of spinal c ...

, the muscle activity of the

erector spinae muscles The erector spinae ( ) or spinal erectors is a set of muscles that straighten and rotate the back. The spinal erectors work together with the glutes ( gluteus maximus, gluteus medius and gluteus minimus) to maintain stable posture standing or ...

decreased on the convex side when

walking Walking (also known as ambulation) is one of the main gaits of terrestrial locomotion among legged animals. Walking is typically slower than running and other gaits. Walking is defined by an ' inverted pendulum' gait in which the body vaults ...

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.

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 column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordate ...

behaves like a torsional spring: while walking, the angular

momentum In Newtonian mechanics, momentum (more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. If is an object's mass ...

of the

shoulder The human shoulder is made up of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder mak ...

s compensates the angular momentum of the

pelvis The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...

(i.e. when the shoulders rotate

clockwise Two-dimensional rotation can occur in two possible directions. Clockwise motion (abbreviated CW) 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 up to the top. The opposite ...

, 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 In biology, a rachis (from the grc, ῥάχις [], "backbone, spine") is a main axis or "shaft". In zoology and microbiology In vertebrates, ''rachis'' can refer to the series of articulated vertebrae, which encase the spinal cord. In this c ...

flexion

range of motion Range of motion (or ROM), is the linear or angular distance that a moving object may normally travel while properly attached to another. It is also called range of travel (or ROT), particularly when talking about mechanical devices and in mechanic ...

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

gait 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 In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest joint in the ...

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, also called spondylodesis or spondylosyndesis, is a neurosurgical or orthopedic surgical technique that joins two or more vertebrae. This procedure can be performed at any level in the spine (cervical, thoracic, or lumbar) and pre ...

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 may refer to: Media Film and television * "Abduction" (''The Outer Limits''), a 2001 television episode * " Abduction" (''Death Note'') a Japanese animation television series * " Abductions" (''Totally Spies!''), a 2002 episode of an ...

) are observed and no changes occurred in lower extremities during gait (knee and

ankle The ankle, or the talocrural region, or the jumping bone (informal) is the area where the foot and the leg meet. The ankle includes three joints: the ankle joint proper or talocrural joint, the subtalar joint, and the inferior tibiofibular joi ...

References

External links

Research for this Wikipedia entry was conducted as a part of a Locomotion Neuromechanics course (APPH 6232) offered in the School of Applied Physiology at Georgia Tech
{{DEFAULTSORT:Neuromechanics Of Idiopathic Scoliosis Musculoskeletal disorders