Form and function of the musculoskeletal system as revealed by mathematical analysis of the lumbar spine. An essay.

Wolff's law describes the mechanical ultrastructure of tissue and indicates a design for minimal stress or minimal energy expenditure. Formation of this theory for the mechanism of the back reveals the critical design of members of this musculoskeletal system, which is comparable with other anthropoids. It also reveals that the pre-adaptations that enable the individual to lift heavy weights are the same adaptations that allow him or her to walk and run.

[Orthodontic-surgical treatment for correction of maxillary deficiency. LeFort I osteotomy]. / Tratamiento ortodóntico-quirúrgico para correción de deficiencia maxilar. Osteotomía Le Fort I.

Class III dentofacial deformities have been corrected by isolated orthodontic and/or surgical procedures, the facial a esthetics results of this approach are frequently less than optimal. The purpose of this article is to present our orthodontic-surgical approach, which has proved successful functional and esthetic results. Two representative cases are illustrated.

Dynamic EMG analysis of torque transfer in professional baseball pitchers.

Fifteen professional baseball pitchers underwent active pitching motion analysis of the abdominal oblique, rectus abdominis, lumbar paraspinous and gluteus maximus muscles bilaterally via surface electrode evaluation. Baseline resting and isometric maximum values were obtained and active data referenced against these for comparison. The muscle activity then was measured during the pitching sequence and analyzed in each of the five pitching phases. The abdominal oblique, lumbar paraspinous and rectus abdominis contralateral to the pitching arm and the ipsilateral gluteus maximus all had increases in activity level of 75 to 100% during the active pitching motion. Using these data indicating specific muscle group patterns with clinical and performance data, we hope to minimize injuries and maximize pitching performance.

The optimum spine.

System theory is used to describe the mechanism of the lumbar spine. The role of the spine in vertebrate evolution is presented. The importance of the intervertebral joint for the survival of the species is shown to be crucial. The mechanical behavior of the joint is derived, and from this the corresponding spinal motion and muscular responses is calculated. It is shown that physiologic behavior implies that the stress at the intervertebral joints is equalized and minimized. From this simple condition, the motion of the spine in the sagittal plane is calculated. From the analysis of sagittal plane motion together with a knowledge of the energy transfer through the intervertebral joint, a new theory of locomotion is derived. This theory of locomotion differs in important respects from current theories, but nevertheless explains available experimental data. This unified theory of the function of the human spine permits the determination of the level of safe loads that can be lifted and transported. It predicts the conditions of load transfer through a joint. It proposes a new approach to the mechanism of arthritis and to the repair of fractures.

The use of mechanical etiology to determine the efficacy of active intervention in single joint lumbar intervertebral joint problems. Surgery and chemonucleolysis compared: a prospective study.

A group of patients were matched for clinical diagnosis, severity of symptoms, and duration and type of preoperative management. The patients all had intractible sciatica. They were submitted to this study by nine participating authors working independently in various centers in North America. Of these patients, those with spondylolysis or spondylolisthesis or those who had had previous surgery were excluded. The patients were treated by chemonucleolysis or by surgery. The information in the various parts of the protocol allowed: (1) identification of the joint at risk, (2) the generic type of injury (torsion or compression), and (3) the procedure of choice for each patient. The outcome was predicted from the operation report using a demerit system for each deviation from the procedure of choice. It was possible to predict from this information only, with a high degree of accuracy (94%), the outcome 2 years later. It was also possible to compare the efficacy of the various types of intervention, especially chemonucleolysis versus a variety of surgical procedures.

The abdominal mechanism.

The abdominal mechanism, utilizing intraabdominal pressure, has been described and numericized. Simulations show that the lumbodorsal fascia under control of the abdominal muscles contributes to reduce the stress at the intervertebral joint. The musculature of the lumbar spine is of primary importance in the control of the efficiency of the spinal mechanism. The system of loading, which results in observable physiologic response, maintains the compressive load at virtually 90 degrees at the bisector of the disc for all weights and all angles of forward flexion.

Tolerance of the human cervical spine to high acceleration: a modelling approach.

A sagittal plane mathematical model for the cervical spine has been used to simulate the neck's response to loads due to high acceleration. The model is capable of simulating the muscular response of the cervical spine and the stress distribution between the joint levels. In order to obtain conservative estimates of the maximum acceleration that the neck can support, the neck was simulated using the assumption that the inertial load is supported primarily by the muscles. It was found that accelerations of up to 30 g can be supported with the appropriate posture and direction of acceleration. Estimates were also obtained using experimental results to approximate the role that the ligaments of the spine play in supporting the load. It was found that accelerations of up to 40 g can be supported for the appropriate posture and acceleration direction.

The nature of instability.

(Clinical) instability is that (symptomatic) condition where, in the absence of new injury, a physiologic load induces abnormally large deformations at the intervertebral joint.

The torsional injury of the lumbar spine.

Torsional injuries of the lumbar spine occur with load application accompanied by axial rotation. In these, damage occurs in both the annulus of the disc and the neural arch. Traumatic arthritis then develops, as do torsional deformities, and these lead to neural compromise. Myelographic defects arise as a result of torsional obliteration of the dural extensions.

The present status of spinal fusion in the treatment of lumbar intervertebral joint disorders.

Every type of fusion has its enthusiastic supporters. Unfortunately, the literature includes comparative analyses of various fusion procedures. Much of the effort spent in the clinical assessment of spinal fusion must be reinvested; neither the indications for diskectomy nor spinal fusion have been sufficiently clear-cut and accurately recorded. Moreover, spinal fusions often have not been applied to treat the disorder or to correct the deformity. It is essential at the outset to establish the mechanical fault; this is achieved only by a thorough understanding of the underlying pathologic lesion. Diagnosis follows a careful history and physical examination assisted by plain radiographs, lateral radiographs in flexion and extension, radiographs (anteroposterior in left and right lateral bending), and by information obtained from the CAT scan. We have designed a protocol for a prospective investigation wherein a specific fault with a specific etiology and pathologic anatomy is identified and submitted to a surgical procedure in a specified sequence. In future reviews, emphasis must be paid to selection of patients, the individual joint requiring stabilization and the type of fusion performed. Only then can we put this theoretically effective procedure to the acid test of objective clinical evaluation.

The mechanism of the lumbar spine.

The moments generated in the lumbar spine by a weight lifter are balanced by moments generated internally by muscles and by the intervertebral ligamentous structures including the disc. Unique real number solutions have been obtained by a optimization technique minimizing shear and penalizing excessive muscle power. The model faithfully reproduces the electromyographic responses and all known experimentally-determined values for muscle power and compression. The outputs can be used to calculate a realistic motion of the spine under various loads. The model suggests that in handling heavy loads, the stress at each intervertebral joint is identical and with maximal voluntary effort, the weight lifter does not exceed 67% of the ultimate strength of his tissues.

The pathological anatomy of degenerative spondylolisthesis. A cadaver study.

A variety of techniques were used to study the morbid anatomy of 19 spines demonstrating degenerative spondylolisthesis in order to define the precise changes which produce this lesion and its radiographic appearance. An association between this affliction and vascular disease is suggested. The studies indicate that the listhesis is basically a persistent rotary deformity and not a simple forward displacement. Furthermore, there is no construction of the neural canal at the site of the listhesis. These findings suggest that the myelographic defect and symptomatology arise from traction applied to the nerve root by the medially displaced pedicle.

A radiologic survey of various configurations of the lumbar spine.

This paper reports an investigation to determine whether or not human spine configurations can be categorized into types by which one could predict the possibility of disablement at one specific level more than another. Configurations of the lumbar spine, the shape of the lower two lumbar discs, the anterior and posterior heights of discs, the sizes of the transverse processes of L4-5, the presence or absence of rudimentery ribs, and the presence of transitional vertebrae were studied in roentgenograms of 554 subjects. They concluded that the probable criteria for development of L4-5 degeneration were 1) high intercrestal line passing through the upper half of L4, 2) long transverse process on L5, 3) rudimentary rib, and 4) transitional vertebra. Criteria for development of L5-S1 degeneration were 1) intercrestal line passing through the body of L5, 2) short transverse process on L5, 3) no rudimentary rib, 4) no transitional vertebrae. A high intercrestal line and long transverse process probably act as antitorsional devices protecting the L5-S1 disc; hence the likelihood of degeneration at L4-5 is increased.

The biomechanical advantage of lordosis and hip extension for upright activity. Man as compared with other anthropoids.

The mechanics of the muscle-ligament system for a weight lift in man is described. The adaptations of the human spine and the hip to this mechanism are indicated. The efficiency of this mechanism in the human is compared with other primates showing the vast superiority of man in this aspect over his nearest relatives.

The mechanical etiology of spondylolysis and spondylolisthesis.

There are 3 mechanisms that may result in failure of the neural arch with or without displacement of the vertebral body of the pathological vertebral: flexion overload, unbalanced shear forces and forced rotation. It is understood that all types of overload may be applied simultaneously and in various combinations. Of all the forces acting on the lumbar spine torsional violence is the most disruptive of the neural arch. Besides causing olisthesis, it is also capable of producing lysis of the pars especially if the dorsal spine has the added restraint of high tensile stresses in the posterior ligamentous system. Under normal conditions, the L5-S1 intervertebral joint is subject to the highest forces and it therefore receives the first damage. However, in the presence of antiverse process, damaging stress occurs in the next higher joint. While the antitorsional large transverse process may protect the L5-S1 joint from torsion, it may not protect the L5 vertebra from excessive flexional strains that may fracture the pars. Though lysis may occur in both instances, paradoxically spondylolysis and spondylolisthesis are mutually exclusive conditions. It has long been thought that shear force imbalance was the causative agent in olisthesis. This mechanism remains unconvincing except possibly in instances where there is a pathological condition affecting the skeletal tissue.