Simulations of rib cage surgery for the management of scoliotic deformities.

Costoplasties are surgical options to treat rib cage deformities. The main concern of rib resections is often for the cosmetic improvement of the back shape of the patient. Other experimental and clinical studies have shown that a costoplasty can also produce mechanical correction of the spine. Based on the assumption that surgery on the rib cage can alter the equilibrium of forces acting on the spine, this study aims to investigate the biomechanical role of the ribs during the surgical treatment of scoliosis using a finite element model of the spine and rib cage. The model was generated from patient-specific geometric data. Concave side rib shortening and convex side rib lengthening have been simulated and evaluated. Slight post-operative immediate geometrical correction of the spine was found in any of the simulations. However, both kinds of simulation induced similar loads on the vertebral endplates. Resulting torques in the frontal plane tended to correct the scoliotic spine in the frontal plane acting against vertebral wedging. Important torques were also found in the sagittal plane, increasing the physiological kyphosis, and derotational torques promoted the improvement of the transverse plane deformation. This biomechanical analysis showed that appropriate rib surgery may counteract the progression of the spine deformity depending on the remaining growth potential. These findings support the concept of early interventions on the rib cage that may be a new approach of treatment to prevent curve progression in small to moderate idiopathic scoliotic deformities.

Volumetric determination of normal and scoliotic vertebral bodies.

A new method is presented for stereological evaluation of the volume of the vertebral body in vivo. The height of the vertebral body is measured at three standardised points on an anteroposterior radiograph and at two other points on a lateral one. The area of the body is also measured using a special grid superimposed on a CT scan from the middle part of the vertebra. The volume of the vertebral body is then calculated using Cavalieri's principle for irregular objects: V = delta a x H, where V is the volume of the vertebral body, delta a is the mean cross-section surface area on the CT scan and H is the mean of the heights at the five points on the radiographs, computed as mean weighted circumferential height. The volume of one normal and one scoliotic vertebra was evaluated in vitro using this formula. The obtained values were compared with the values derived from serial CT scans of the two vertebrae. The results showed that the volume of the normal vertebra measured with our new method was 15.9 cm3 and measured with serial CT scans using the same grid it was 15.07 cm3. For the scoliotic vertebra the values were 17.6 and 17.3 cm3, respectively. The degree of accuracy of the measurements with the presented method as compared with the serial CT method was 95% for the normal and 98.5% for the scoliotic vertebra. To prove the clinical applicability of the method, the heights of the apical and of the upper and the lower end vertebrae of the curve and the volume of the apical vertebrae were evaluated in eight scoliotic girls (nine curves) before and 3 years after spinal instrumentation and posterior fusion. The results showed that the mean circumferential height of the three vertebrae had increased significantly at the last follow-up. The volume of the apical vertebra had also increased, but the difference was not significant. It is concluded that the described method is easy to apply and has satisfactory accuracy for in vivo longitudinal studies of the volume of the vertebral body on radiographs and CT scans.

A method for morphometric study of the intercostal muscles by high-resolution ultrasound.

Besides their main function of assisting in breathing, the intercostal muscles also play an important role in maintaining the balance of forces acting on the thoracic cage including the thoracic spine. Since it is virtually impossible to conduct a morphometric evaluation of these muscles, a study was undertaken to standardize an ultrasound method for accurate determination of the area of the intercostal muscles and hence, indirectly, their function. In a pilot study, the area of the intercostal muscles was determined on the torso of a fresh specimen of a grown-up lamb, using high-resolution ultrasound and CT, and by direct measurements of the intercostal space at two points equidistant from the midline on the left and the right sides of the back of the specimen. The size of the intercostal muscles was determined either by tracing or from the perpendiculars of the area of the muscles both on sonographs and on CT scans. The results showed that measurements derived from the perpendiculars of the muscle area on the sonographs give better estimates than those derived from CT scans, and were in good accordance with the direct measurements of the corresponding intercostal space on the specimen. To evaluate the applicability of the method in vivo the area of the intercostal muscles at maximal inhalation and exhalation was determined in one adult person. It was found that measurements at maximal inhalation were more accurate than those taken at maximal exhalation. It is concluded that ultrasonography is a reliable, safe, easy to apply and high-resolution method for measurements of the area and, indirectly, of the activity of the intercostal muscles in humans, and that the measurements are more accurate at maximal inhalation.

A physiological approach to surgical treatment of progressive early idiopathic scoliosis.

The results of previous clinical and experimental studies have provided accumulated evidence for the role of rib asymmetry in the pathogenesis of idiopathic scoliosis (IS). Moreover, it has been shown that scoliosis induced in rabbits can be corrected by elongation or growth stimulation of ribs on the side of the convexity. Taking these observations into consideration, a 7-year-old girl with right convex thoracolumbar IS was operated upon by 2-cm shortening of three concave ribs. The preoperative coronal Cobb angle was 46 degrees and the sagittal angle was 55 degrees. Twenty-seven months after the operation the curves were reduced to 21 degrees and 35 degrees, or by 54 and 36%, respectively. It is concluded that new, easy to perform and harmless interventions on the ribs may have vast implications for the overall treatment of young patients with early progressive, thoracic, IS.

Electrical muscle stimulation on the spine. Three-dimensional effects in rabbits.

We investigated the 3-dimensional effect of electrostimulation of the latissimus dorsi, the erector spinae and the intercostal muscles on spinal configuration in 16 New Zealand white rabbits. Electrostimulation on the right side of the spine resulted in a left convex, hypokyphotic curve and vertebral body rotation towards the convexity of the curve in all rabbits. The Cobb angle in the coronal plane increased with stimulation of each of the muscles examined. The kyphosis decreased with stimulation of the latissimus dorsi and the erector spinae. The vertebral rotation increased with stimulation of all muscles. Stimulation of the tested muscles resulted in the simultaneous occurrence of a 3-dimensional spinal deformity with the characteristics of idiopathic scoliosis.

In vitro opto-electronic analysis of 3-D segmental vertebral movements during gradual rib lengthening in the pig.

The effects of gradual rib elongation on the 3-D position of neighboring vertebrae were studied in vitro in two pig specimens. The ends of one osteotomized rib were gradually distracted and the micromovements of the numerically corresponding vertebra with the osteotomized rib were studied in relation to the subjacent and suprajacent vertebrae with an opto-electronic motion analysis device. The study showed that gradual lengthening of the rib resulted in micromovements of the central vertebra in relation to the neighboring vertebrae registered as a) lateral translation in the coronal plane, b) rotation in the horizontal plane (both a and b were movements towards the opposite side of the lengthened rib), c) ventral translation in the sagittal plane and d) tilt in the coronal and sagittal planes. All movements were registered simultaneously. There was a significant linear correlation with the degree of rib elongation. From the results of this study it is concluded that gradual elongation of one rib affects the position of the numerically corresponding vertebra in relation to the suprajacent and subjacent vertebrae in the three cardinal planes in the same way as the apex vertebra is affected in idiopathic scoliosis. Moreover, the registered tilt, i.e., the rotational movement of the central vertebra in the coronal plane, could explain the wedging of the disc space, and the ventral translation in combination with the tilt in the sagittal plane could account for the lordotic tendency of the scoliotic segment.

Accuracy and applicability of measurement of the scoliotic angle at the frontal plane by Cobb's method, by Ferguson's method and by a new method.

A new method for the measurement of scoliotic curves in antero-posterior (AP) radiographs is presented, in which the centre of the surface image of the vertebral bodies of the apical and two end vertebrae of the curvature are defined on the basis of geometric principles. Measurements using the Cobb, the Ferguson, and the new method were performed on ten AP radiographs from each of three groups of young patients with right convex thoracic idiopathic scoliosis with Cobb angles of between 7 and 15 degrees, 16 and 45 degrees and 46 and 80 degrees, respectively. Measurements using the Cobb method yielded significantly higher values than measurements using either the Ferguson method or the new method. In curves with Cobb angles of between 7 and 15 degrees, the values using Ferguson's method were significantly lower than those using the new method; the difference increased significantly in curves with a Cobb angle of 16 degrees or more. The level of significance of the intra- and interobserver differences between the new, the Cobb and the Ferguson methods was significantly higher in curves with a Cobb angle of 16 degrees or more. It is argued that measures of the scoliotic angle obtained by the new method are of greater clinical relevance than those obtained by the two other methods. Unlike the Cobb method, the new method takes into consideration the translation of the apical vertebra in relation to the end vertebrae and not only the tilt of the end vertebrae of the curve. As compared to the Ferguson method, the new method is based on standardised geometric principles, and is not influenced by changes in the shape of the vertebral body. Moreover, the repeatability of the new method is greater than that of both the Cobb method and the Ferguson method. Therefore, it is believed that the new method provides a more accurate measure of the scoliotic curve than do the two other methods, and it is to be preferred over the other two methods in longitudinal evaluation of the development of the curve.

Radiographic changes at the coronal plane in early scoliosis.

The development of structural skeletal changes was evaluated on 132 anteroposterior radiographs of spines from three scoliotic groups with a Cobb angle of up to 30 degrees and a reference control group. Significant wedging of the vertebral bodies and disks at the coronal plane was registered in-curves with a Cobb angle of 4 degrees or more. Asymmetry of the rib-vertebra angle was found in curves with a Cobb angle of 8 degrees or more and was most pronounced in the cranial part of the curves. The early simultaneous occurrence of vertebral and disk wedging suggests the involvement of an extraspinal factor rather than growth disturbance of the vertebral body or of the disk in the early pathomechanism of scoliosis.

Effects of intercostal nerve resection on the longitudinal rib growth in the growing rabbit.

Two, three, or four intercostal nerves with their vasoconstrictive sympathetic fibers were resected on the right side of 15 growing rabbits. Animals submitted to sham operations and intact animals formed two control groups. A scintigraphic study with 99mTc-methylene diphosphonate, performed on the test group 2 months after the resection, showed a significantly greater uptake of the isotope on the right than on the left costochondral junctions (p less than 0.05). Three months later the difference was still larger. There was no such significant difference in the rabbits of the two reference groups. In the rabbits of both these groups, the right and left ribs of each pair were almost equal in length. Of the denervated ribs of the rabbits composing the test group, the right ribs increased in length to a greater extent than the corresponding left ribs. The difference was statistically significant (p less than 0.05). As a consequence of this left-right difference in length, mild thoracic scoliosis convex to the left developed 2 months after the resection. The total weight and volume of the denervated right ribs increased significantly more than those of the corresponding control left ribs (p less than 0.05), but their mineral content per unit of weight or volume showed no significant difference.

Induction of scoliosis in the growing rabbit by unilateral rib-growth stimulation.

Growing rabbits were subjected to surgical resection of the intercostal nerves on the right side, posteriorly or anteriorly. Two other groups of animals were used as sham and as normal controls. Six months after the nerve resection, there was no electromyographic evidence of denervation of the involved muscles. Radiologic examinations revealed progressive development of a curve, convex to the left, in each animal of the two resection groups. Analysis of structural changes by computed tomography showed rotation of the apical vertebra about the longitudinal axis. Rib cage deformity was diagnosed in 82% of the rabbits. The experimental model developed for induction of scoliosis is simple. The surgical procedure involves just one selected and easily recognized anatomic structure, leaving the vertebral structures and their vicinity intact. Reliable analysis of the underlying mechanism of the developing scoliosis is thereby assured.

The symmetry of the breasts in normal and scoliotic girls.

Mammary asymmetry was estimated visually by different investigators in three series of scoliotic girls and in three control groups. The breasts of each girl were classified as being equal in size or as being obviously different in size, note being made of which breast was the larger. Breast asymmetry was significantly more common among the scoliotic than the normal girls. Moreover, the left breast was significantly more often larger in the scoliotic series of girls. On the other hand, there was no significant difference in the frequency of breast asymmetry in respect of the classifications according to curve type (right convex thoracic vs. other types) and to Cobb angle (35 degrees or less vs. more than 35 degrees).

Scoliosis. Experimental and clinical studies.

The hypothesis, advanced on the basis of experimental and clinical observations, that asymmetric growth of the ribs may be the primary cause of the thoracospinal deformity at least in some cases of right convex, thoracic, idiopathic scoliosis finds further support in the results of the anthropometric studies referred to below. There is also the possibility that asymmetric growth and more pronounced vascularization of the often larger breast may stimulate enough longitudinal growth at the underlying costosternal cartilage to upset the balance of forces acting on the normal spine. Muscular and other mechanical forces might be responsible for the further development of the deformity. Whether the data and evidence in this article will ultimately support or advance the hypothesis presented above remains to be seen. However, this hypothesis and the observations reported to date would seem to be capable of explaining the main characteristics of at least some cases of thoracic idiopathic scoliosis, i.e., the predominance in girls, the occurrence in the teens, and the predominant right convexity.

Osteoporosis. Experimental and clinical studies.

Combined experimental and clinical research illustrates not only the multiplicity of questions for research on osteoporosis but also the difficulty of penetrating such a complicated clinical problem as treatment and prevention of osteoporosis. Without thorough knowledge of the pathomechanisms responsible for the development of the condition and a rational working hypothesis, any attempt to develop a new approach seems unlikely to succeed.