History of Spine Biomechanics

Pythagoras (580–500 bce )

Pythagoras defined the universe and the human body based on mathematical analysis. He stated that “all things have form, and all things can be defined by numbers.”

Hippocrates (460–377 bce )

Hippocrates was a priest-physician born on the island of Cos in 460 bce . He established an open-air school after he became prominent in the field of medicine. Hippocrates’ approach to medicine represented a watershed event for the development of medicine as a scientific discipline. His contributions span all subdisciplines of medicine. The Corpus Hippocraticum is a collection of 12 books authored by Hippocrates with contributions from his contemporaries.

Hippocrates carefully studied the anatomy and pathology of the spine ^. ( Fig. 2.1 ), separating the spinal vertebrae into three parts. The first part included the vertebrae lying above the level of the clavicle (including C7). The second part included the 12 vertebrae at the chest that articulated with ribs, the third part the five vertebrae between the chest and pelvis. He did not include the sacrum and coccyx as components of the spine. Hippocrates also described the natural curvature of the cervical and lumbar portions of the spine (although the terms lordosis and kyphosis were not introduced until Galen in second century ce ). He used the term ithioscoliosis to describe the natural curves of the spine in the sagittal plane.

Hippocrates classified spinal disorders as follows: (1) kyphosis, including both traumatic and nontraumatic etiologies; (2) scoliosis; (3) burst fractures; (4) vertebral dislocations; and (5) fractures of the spinous processes. He cited spinal tuberculosis as the most common cause for kyphosis, noting that the severity of deformity was greater when it occurred before puberty. Hippocrates was the first to relate traumatic spinal deformities to causative force mechanisms. He found that traumatic kyphosis could result from forceful falls on the shoulder or buttock. He correlated burst fractures with axial loading of the spine. Ventral vertebral dislocation was often secondary to a large force applied to the back, such as a fall from a height or a blow from a heavy object. Dorsal dislocations were rare, frequently fatal, and associated with severe abdominal injury. Given the spinal architecture, Hippocrates noted the extreme force needed to create a dislocation: “a great thrusting-out and rupture of the articulation of one or more of them does not very often occur, but is rare. Such injuries, indeed, are hard to produce.” ^, He also noted that dislocations (which he termed inward curvatures versus the outward curvatures seen in kyphosis) were associated with a poor prognosis:

In such cases, then, retention of urine and feces is more frequent than in outward curvatures; the feet and lower limbs as a whole more usually lose heat, and these injuries are more generally fatal. Even if they survive, they are more liable to incontinence of urine, and have more weakness and torpor of the legs; while if the incurvation occurs higher up, they have loss of power and complete torpor of the whole body. ^,

He noted that isolated spinous process fractures did not result in deformity, healed well, and did not result in clinical impairment.

Beyond his keen observations, Hippocrates also devised several innovative therapeutic interventions for spinal disorders, including the Hippocratic board and the Hippocratic ladder. As a first line of intervention, he recommended manual traction of the spine with application of focal pressure using one’s hand or foot over a kyphotic deformity. If this did not work, he recommended use of the Hippocratic board, by which spinal traction could be better obtained using two opposing axial force vectors in combination with manual perpendicular force over the kyphotic deformity ( Fig. 2.2 ). He liked this technique; he stated: “in accordance with nature; for the pressure forces the protruding parts into place, and the extensions according to nature draw asunder the parts that have come together.” ^,

Although he is credited with developing the Hippocratic ladder, his writings reflect less favorably upon this intervention. By this technique, a patient was fixed upside down on a ladder that was connected to a pulley system from which the ladder was raised, suddenly released, and allowed to fall to the ground; this was repeated several times ( Fig. 2.3 ). Hippocrates felt it was more difficult to control the direction and magnitude of force with this technique. Perhaps this is why he warned that this technique, which he called “succussion” (shaking), was better at pleasing the mob than correcting a deformity.

Plato (427–347 bce )

The great philosopher and mathematician Plato was founder of the Academy in Athens, the first institution of higher learning in the Western world. He suggested that mathematics, a system of pure ideas, was the best tool for the pursuit of knowledge. Plato’s contributions to mathematics are considered to be the origins and stimulus for the development of the science of mechanics and, consequently, spine biomechanics.

Aristotle (384–322 bce )

Aristotle provided treatises on many subjects, including physics, metaphysics, poetry, theater, music, politics, ethics, biology, and zoology. He should perhaps be considered the first biomechanist. As such, he recorded detailed information regarding the mechanical system of animals in his first book, De Motu Animalium (On the Movement of Animals). This work provides the first geometric analyses of isolated muscular movements such as flexion and extension. He commented on the rotational axes surrounding joints and how one type of motion, such as rotation, could be used to create another type, such as translation.

Aristotle discussed the problems of pushing a boat under various conditions from the standpoint of mechanics, describing, in a primitive form, Newton’s three laws of motion. Aristotle depicted a qualified understanding of the role of the center of gravity in his analyses of gait. ^, Of note, Aristotle’s findings were purely observational; he did not perform scientific experiments. Even though his work was not directly related to the spine, Aristotle’s work led to the birth of kinesiology and laid further groundwork for spinal biomechanics. ^,

Herophilus of Chalcedon (335–280 bce )

Medical science reached a high point during Greek civilization, but in the third century bce , the greatest medical minds were to be found in the Egyptian city of Alexandria. The effect of religion and mysticism on medicine in the city of Alexandria was prominent. Archimedes, Euclid, Praxagoras, Herophilus of Chalcedon, and Erasistratus are among the most prominent figures of this period.

Herophilus of Chalcedon, the world’s first anatomist, dominated the discussions of anatomic studies during this period. Although Herophilus carried out anatomic dissections on human cadavers, he did not comment on spine anatomy and biomechanics in his works. He did, however, make significant contributions to cerebral neuroanatomy and noted the consequences of spinal cord injuries, suggesting that direct surgical intervention on the spinal column should be avoided. ^,

Archimedes (287–212 bce )

Archimedes was a prominent mathematician, physicist, engineer, inventor, and astronomer of this age. He had the greatest influence on the future of spinal biomechanics through his contributions to theoretic mechanics in his work On the Equilibrium of Planes. He is known for his formulation of the hydrostatic principle (known as Archimedes’ principle) and the development of the Archimedes screw, a cylinder with an internal revolving screw that was built to pump water against gravity. Archimedes described fundamental theorems concerning the center of gravity and laws of leverage.

Galen of Pergamon (130–200 ce )

In the second century ce , as the Roman Empire rose to prominence, mysticism subsided, and scientific thought regained credibility and popularity, albeit under the strict oversight of the Church. Galen ( Fig. 2.4 ) was a physician to the Roman gladiators. More importantly, he made many significant discoveries in anatomy and physiology by performing anatomic dissections on animals and extrapolating his findings to humans. Galen’s anatomic studies and interpretations affected medicine for more than a thousand years, until the time of Vesalius. His own work corroborated the findings of Imhotep and Hippocrates on the neurological sequences of cervical trauma. ^{, ,}

Galen was the first to determine the reliance of muscular movements on supplying connections from nerves. He also demonstrated the neurological implications following transection of the spinal cord at several levels in live animals. He dealt with spinal tuberculosis, as well as an abundance of traumatic injuries to the spine and the spinal cord. He appreciated the structure of the spine in allowing an intersecting balance of neural protection and flexibility for mobility. Galen was able to detail the structure of the spine, in that the vertebrae were joined ventrally and had articulating components dorsally. He felt that the former allowed for motion and the latter provided greater stability. In addition, he was the first to describe the spinal canal, which contained the spinal cord—previously termed the spinal marrow in the Greek era. He noted that the spinal cord was an extension of the brain, “like a river having its springs in the brain.” He also used the Hippocratic board to treat kyphotic deformities, but, unlike Hippocrates, he advocated surgery in some cases to remove bony fragments impinging on the spine. ^,