Ethiopathogeny, biomechanics and physiopathology aspects in idiopathic scoliosis

The scoliosis is an evolutive disease, in which are one or more lateral curves of the vertebral column, that we can see in a frontal plane; also , there is present the rotation of the vertebrae. The curves are compensate at superior and inferior level, but don’t exist reductibility in suspension or in decubitus.

Ethiologycal factors of the idiopathic scoliosis

Growth factors

The importance of growth in the development of idiopathic scoliosis is known since the XIX th century.

There have been established 3 phenomens.

The growth is necessary for the apparition of scoliosis

The progression of the deformity is important at the age of rapid growth (pubertary age)

The minor scoliosis(with low angle) are relatively stable at the end of the bone maturity.

Tissue and metabolic factors

Many authors have observed the existence of scoliosis in diseases that affect the connective tissue(Marfan disease, Ehler-Dunlos disease, imperfecta osteogenesis). These aspects suggests that the collagen and the proteoglicans are important in the apparition of scoliosis. It is difficult to say if these alterations of the two main components of the connective tissue are preexistent or are secondary to the deformity of the vertebral column.

Neurological and balance factors

There are many clinical and experimental factors that are important for the nervous regulation and the postural balance in the development of idiopathic scoliosis. The purpose of the balance system is to resist in front of gravitational forces and to control the movement and the eyes position. The afferences are generate in the proprioceptors (tendons, ligaments, joints surfaces, muscles), in the ocular and vestibular system. The impulses are integrate in the cerebral trunk and cerebellum and the efferences will be transmitted to the skeleton through the vestibulo-spinal and the reticulo-spinal ways.

Yamada had observed in 150 cases of idiopathic scoliosis that in 79% of cases there were anomalies of the balance function, proprioception and oculomotor reflexes. In the witness group were only 5% of cases with such anomalies it is very interesting that these anomalies disappear at maturity(20 years). So we can suppose that there is a delay in the maturation of the nervous system, not a disease of the nervous system.

The authors also observed that the central otholitic function is altered in idiopathic scoliosis. The primary or the secondary character of this alteration cannot be asserted.

In conclusion, the alteration of the vestibular function is evident in idiopathic scoliosis, but it is very hard to define the neurological level of the disfunction. But the most important thing is that this neurological disfunction is transitory.

Muscular factors

There have been made many studies to asses the muscular ethiology of the idiopathic scoliosis. Many authors have observed that the ATP-azical activity in the paravertebral muscular fibers is low and the intracellular calcium level is high. For that reason, has been proposed a general anomaly of functioning of the cellular membrane.

From that point of view, we can consider that the idiopathic scoliosis is a consequence of a genetically transmitted miopathy.

Melatonine

Melatonine is a hormone of the pineal gland. In 1959, Marie-Jeanne Thillard(3) discovered that the pineal ablation produces scoliosis. In 1993, Machida(4) and Dubousset(5) published an experimental study in which reimplantation of the pineal gland has a protective effect in the development of a scoliosis.

Melatonine is a neuro-hormone that acts on the central nervous system (proprioceptive pathways in medular thalamus, cerebral trunk, medular spine). Another role of melatonine is hormonal, in growth. From this point of view, we can try the treatment with melatonine in the case of evolutive scoliosis at the age of adolescence.

The biomechanic of idiopathic scoliosis

In the scoliotic curve, all the vertebral are in extension if the vertebral rotation is greater than 90°, the vertebral column become pseudo-kyphosis, but in that case , too, the vertebres are in extension.

The thoracic and the rib deformations(the gibosity at the level of the convexity of the curve), that are so important clinically, are the consequences of the vertebral dislocations.

The progression of the scoliosis

Mechanical factors

The structural alterations(vertebral, ligamentar, muscular) are moderate until the scoliosis has a lower angle(20°-30°) and the curves may regress with a correct treatment. The angle of 30° represents a mechanical level because an elevated value means the presence of a deformity and progression of the scoliosis

Growth factors

The idiopathic scoliosis is progressive until the age of bone maturation and then it is stabilize. But Ponsetti observed that if the curve is greater than 30°-40° in the end of the growth, the aggravation of the scoliosis is possible(1°/year).s.

The Natural and Evolutional History of idiopathic scoliosis

Historical

The concept of aggravation for the pubertary growing period it was known before Ponsetti (6) and Friedman, who described in 1950 two possibilities of scoliosis aggravation:

If the scoliosis arise before the age of 10, this remains often constant and slow evolutional for a period of few years, further abruptly aggravates.

If scoliosis arise after the age of 10, it will aggravate on a regular basis, so that a prognosis can be adopted after 2-3 succeeding radiological examinations.

If the aggravation is slow after more radiological examinations, prognosis is good.

The reserved prognosis appears if aggravation is fast.

For the curves more than 10 degrees, RISSER test is a good part of prognosis: if RISSER is 0 the aggravation risk is 68 %, and if RISSER is 3-4 the aggravation risk is lower 18%.

In 1984, Lonstein assessed 727 patients with idiopathic scoliosis, whom initial curve range between 5 and 29 degrees, and he is looking to find the identifiable risk factors.

For him, the progress risk of scoliosis depends on the topography curve, the age it has been discovered, the initial grade of amplitude, RISSER phase, and the first time of menses. The aggravation risk is lower if the RISSER test arises an aging boned, (aging osseous) more advanced. So, for a RISSER phase that is 0, the aggravation risk of one curve inferior to the 20 degrees angle is 22 %, and for a curve superior to the 20 degrees angle is three times higher. It is a direct correlation between COBB angle, RISSER test, and the chronological age, turned into the following equation by Lonstein:

The risk quotient = (COBB angle – 3) x RISSER test/ chronological age

The evolutional ways

Perdriolle and Vidal described three evolutional possibilities, according to the scoliosis type:

Infantile scoliosis aggravate immediately, sometimes brutally, and they can be to 90 degrees:

For juvenile curves, the aggravation is different. If the angle appears before 6 year old, this remains constant and inferior to the 30 degrees angle. Aggravation appears between 6 years old and the age of pubertary, and the angle gain could range between 25-30 degrees on year.

The pubertary scoliosis presents a large evolutional type, the angle at the end of development ranging between 10 and 90 degrees.

Assessment of evolutional risk

The role of debut age

In 1962 Cotrell proposed a classification on 5 groups:

The infantile scoliosis diagnosed before 3 years old exceed frequently 100 degrees ageing boned, (osseous ageing).

Juvenile scoliosis break down in 3 age groups, between 3 and pubertary – the percent cases, that are increasing to an angle more than 50 degrees, decreases in the same time with the debut age, ranging between 83% and 55%.

The adolescent scoliosis, from pubertary to the ageing boned, (osseous ageing) – rarely are exceed the 50 degrees angle.

Ageing boned, (osseous ageing) and the residual growing

Risser test is easily recognize and differentially Risser 0 and Risser 1, but it’s more difficult to say that RISSER is 5, without having a global picture of basin.

RISSER 1 and RISSER 2 appear in the majority of cases between 13-14 years old to the girls, and 14-15 years old to the boys, referring to the osseous age. For RISSER 2 the scoliosis risk decreases, and practically it will become null for a curve lesser than 20 degrees. If RISSER is 3 or 4, the child is on the descendent part of his pubertary growing, and the growing peak is on the thoracic chest.

The rib circumference the growing of thoracic chest may produce the curve decrease.

The osseous age of vertebres can be assesse by Ring test, which correspond to the vertebeas ossification, and take the aspect of a “leaf” seen from front and lateral, then a more regular track, going to complete seam in anterior part, which correspond to the closure of aging osseous.

The initial angle

Weinstein in 1985 demonstrated parallelism between the risk progression of scoliosis and the initial angle. This confirms Stagnara’s researches, which considers that 30 degrees angle as being critical, because if this is bigger then all scoliosis are evolutional, if it’s less than 30 degrees than one from two cases evoluate before pubertary period.

The topography of the curve

In 1950, Ponsetti and Friedman had shown the evolutional differences connected to the type of the curve, break them down in thoracic curves, double-major, thoracic – lumbar, and lumbar.

The thoracic scoliosis represents the most deformed curves at the adult age, and also the result of the precociously forms, with a large evolution. Stagnara described them as being the most powerful forms, because they go beyond 90 degrees, induct a thoracic deformation and a restrictive respiratory syndrome, which aggravates the vital prognostic for the adult age.

The thoracic – lumbar scoliosis have a better prognostic, but induct an important esthetically prejudice.

The double major scoliosis are often lumbar and dorsal, producing an esthetic prejudice relatively smaller for the angles that are exceed 40 degrees This is not happening in the thoracic double dorsal deformations and dorsal – lumbar, which involve a severe esthetic prejudice by shoulders’ unbalance.

The lumbar scoliosis, from statistical point of view are the less evolutional in development period, the angle and the esthetic prejudice being moderate, but the degradation risk for the adult age being important. At this level, the spinal segment is more mobile because the relative inflexibility effect attached to the thoraces , disappears, the scoliosis can grow in three-dimensional sides. The right deformations are two times more evolutional then the left ones and a satisfactory explanation can not be given.

The scoliosis evolution after osseous aging

Spinal pain

Weinstein demonstrated that spinal pain frequency for people with scoliosis is 80% comparing to the general population. The pains frequency is more important in lumbar scoliosis or dorsal – lumbar, because of the lateral dislocations from the inferior extremity of the curve. In lumbar scoliosis and dorsal – lumbar cases, the pains can also appear at the compensatory curves. In most cases these pains emerge at the end of the work day. They are calm down by rest, and have a variable topography, which generally is not correlated location and amplitude of deformation.

The most frequent causes of these pains are ligament distensions and the dyscopathy lesions

The cardio – respiratory deficit

Exclusively appear in the dorsal scoliosis. The major thoracic scoliosis straitens the back circulatory system and can involve the occurrence of one chronic pulmonary heart and right cardiac insufficiency.

The scoliosis patients’ longevity

In 1968, Nachmson did a research on 130 patients with scoliosis, who had the major thoracic curves more than 90 degrees. In this group at the age of 50 the mortality was three times more than normal, and the reduction of the vital capacity was 50 %.

The gestation

The gestation dosen’t go up the risk of progressive scoliosis. This risk dosen’t correlate with the patient’s age at the first gestation or with the number of gestations.

The prognostic determination at the first clinical examination

The problem of prognosis appears before the scoliosis is close to 30 degrees. The most powerful aggravations appear in the cases of short thoracic curves, while the long curves have less risks of further deformation.

The clinical exam is the most important, and the appearance of lumbar unbalance, or shoulders unbalance are not that relevant prognosis signs.

The Cobb angle dosen’t have by itself predictive value, because it must be compare with the three-dimensional deformation, and with residual growing.

The most important is to evaluate the residual growing, which can aggravate the risks factors.

The global clinical exam is necessary to eliminate the presence of a secondary scoliosis, and morphological exam can show signs with an adverse character of the curve global hypotrophy, amyotrophy, balance disorders, ligamentars laxity, without forget to verify the intelectual capacity and the adaptation to a possible treatment.

The clinical and radiological exam leads to a right prediction of 92% from cases. Is important to understand that 8% from cases are errors and incertitude, and so we must to try solving the mystery of ethiopatogeny scoliosis.

References :

1. Wynne-Davies R (1968). Familial (idiopathic) scoliosis Bone Joint Surg, 50, pp24-39.

2. Cowell HR, Hall JN, MacEwen GD.(1969). Familial patterns of idiopathic scoliosis. J Bone Joint Surg [Am] 1969; 51: 1236.

3. Dubousset, J.; Queneau, P.; and Thillard, M. J.(1983). Experimental scoliosis induced by pineal and diencephalic lesions in young chickens. Its relation with clinical findings in idiopathic scoliosis. Orthop. Trans., 7: 7.

4. Machida, M., Dubousset, J., Imamura, Y., Iwaya, T., Yamada, T.,Kimura, J.(1995). Role of melatonin deficiency in the development of scoliosis in pinealectomised chickens. J. Bone and Joint Surg., 77-B(1): 134-138, 1995.

5. Pedrini, V. A., Ponseti, I. V.,Dohrman, S. C.(1973) Glycosaminoglycans of intervertebral disc in idiopathic scoliosis. J. Lab. Clin. Med., 82: 938-950.

6. Bushell G.R. , Taylor T.K., (1979). Intervertebral disc colagen in adolescent idiopathic scoliosis, J. Bone Joint Surg.

7. Burwell RG, Cole AA, Cook TA.(1992). Pathogenesis of idiopathic scoliosis: The Nottingham Concept. Acta Orthop Belg.; 58 (Suppl 1): 33-58.

8. Duval-Beaupere G., Barhel F. (1983). La croissance des scoliotiques. Revue de Chirurgie Orthopedique, 69, 201-206.

9. Garland, H. G.(1934). Hereditary scoliosis. British Med. J., 1: 328-334, 1934

10. Sahlstrand, T., and Petruson, B.(1979). A study of labyrinthine function in patients with adolescent idiopathic scoliosis. I. An electro- nystagmographic study. Acta Orthop. Scandinavica, 50: 759-769.