Gravitational forces and sagittal shape of the spine. Clinical estimation of their relations

The sagittal morphology of the pelvis determines the amount of lordosis needed for each individual. The proper harmony of the sagittal spinal curves allows a stable balance, economical in terms of mechanical effects and muscular energy. A previous barycentremetrical laboratory study allowed us to demonstrate that the axis of gravity of the upper body segment was located behind the lumbar vertebrae and the femoral heads, thus ensuring economy and stability. The determination of the anatomical connection of the individual gravity is thus of primary importance for the evaluation of sagittal balance. Data for 42 patients without spinal pathology, previously evaluated by barycentremetry, were used to establish a predictive equation for the application point of the gravity at the level of the third lumbar vertebra (L3). This equation, using anthropometric and radiographic pelvic and spinal parameters, was integrated into a software program called Similibary. It was applied to the same 42 subjects. These results were compared in order to validate the method. No significant difference was observed between the two techniques. This easy-to-use tool allows a personalised evaluation of the sagittal balance of the spine, both through the evaluation of the harmonious relationship between the spinal curves and the pelvis, and through the location of gravity supported by the vertebral structures in L3.

Threshold values for supine and standing Cobb angles and rib hump measurements: prognostic factors for scoliosis

Seven parameters recorded at the first clinical examination of 326 growing scoliotic patients were correlated with the speed of progression of the scoliotic curve during a natural history survey period. The parameters were: age; bone age (according to Greulich and Pyle); pubertal and Risser stage; curve shape; rib hump, measured in forward bending in a sitting patient and supine and standing radiographic Cobb angles of the scoliotic curve. The speed of progression of the scoliotic curve was expressed as the annual increase in Cobb angle. It was quantified graphically after plotting the measurements taken from all the radiographic examinations made during the survey. The survey period ranged from 6 months to several years, depending on the rate of progression. It was 6 months only if the scoliotic curve demonstrated worsening of more than 3 degrees at two successive examinations performed at least 3 months apart. The authors aimed to identify the minimum values of curve angle and rib hump, identified at first examination in 95-100% of patients whose parameters at follow-up were above these values (supine angle: 17 degrees; standing angle: 24 degrees; rib hump: 11 mm), therefore demonstrating curve worsening. Then, they analysed how the other parameters such as age, bone age, state of maturation and curve shape influenced these threshold values of rib hump and supine and standing angles. The authors present the threshold values for the whole sample according to the sexual state of maturation and also for each curve shape. They demonstrate that a combination of states of maturation, several measures of the scoliotic curve and curve shape provides the best basis for individual prognosis.

Upward displacement of the centre of gravity in paraplegic patients

The centres of gravity of 44 complete chronic spinal cord injured patients and 24 normal subjects were measured using a gamma ray scanner (Barycentremetre). The results are expressed as a percentage of body length and as anatomical level. The mean weight of paraplegic patients was 12kg less than the controls. The centre of gravity was 5% of body length higher in the paraplegic patients than in the controls, equivalent to 3 to 4 vertebrae level. The importance of such changes in the centre of gravity for the design of stable wheelchairs is discussed.

Age-dependent responsiveness of rabbit and human cartilage cells to sex steroids in vitro

Rabbit epiphyseal cartilage tissue has been shown to convert testosterone (T) to dihydrotestosterone (DHT). In this report, the metabolic conversion of T into DHT is shown to be age-dependent, being most active in cartilage from animal at the age of gonadal maturation. Human cartilage from newborn and prepubertal children is also shown to convert T into DHT and--to a lesser extent--to estradiol. Low concentrations of DHT and 17 beta-estradiol (E2) (10(-11)-10(-9) M) were also shown to stimulate in vitro cartilage cells from boys and girls respectively. As previously shown for cultured rabbit chondrocytes, the stimulating effects of both hormones on human chondrocytes was age-dependent. Cartilage cells derived from children up to one year old did not respond, while cells from boys and girls in the early phase of puberty responded best. These data indicate that human cartilage tissue in vivo, contains both 5 alpha-reductase and aromatase activities during post-natal skeletal growth. Androgens may act on cartilage after their metabolic conversion to estrogens. The mechanism of age-dependency of both cartilage androgen enzymatic activities and chondrocyte responsiveness to sex steroids in vitro remains to be explained.

Trunk and leg growth in children with paraplegia caused by spinal cord injury

After a survey of the bibliography on the subject of clinical and experimental data on retarded growth in children affected by lesions of the peripheral nervous system, the authors present a semi-longitudinal analysis of the anthropometric values obtained by spinal cord section in the case of young paraplegics. By this means, they demonstrate an average growth defect of the order of two standard deviations which only affects the body distal to the neurological lesion in cervical or dorsal injuries. The lower the level of the cord lesion and the earlier the paralysis the greater the growth defects.

Pathogenesis of scoliosis

Scoliosis often occurs in otherwise normal individuals or it may be associated with many widely differing diseases. The curve patterns are fairly uniform and the vertebrae always rotate in the frontal and horizontal planes producing convex side rotation with little displacement of the spinuous processes. Many small curves do not increase. Progressive scoliosis increases linearly and the rate of increase accelerates at puberty. No endocrine abnormalities have been observed in these patients. Usually the deformity is not caused by abnormal vertebral growth nor by abnormal collagen in verterbral ligaments. The glycosaminoglycans of nucleus pulposus are decreased in patients with idiopathic scoliosis. We speculate that loss of proteoglycans will affect the viscoelastic properties of the intervertebral discs which may result in permanent deformation. The etiology of scoliosis appears to be multifactorial with a genetic tendency to the deformity which is triggered in different individuals by different factors, some medical, some mechanical and some genetic.