III. BONE, MUSCLE, ORGAN ASSOCIATIONS

        The evolution of the forelimbs and the evolution of the hind limbs in tetrapods (four-legged vertebrates) were homologous developments originating in identical genetic processes.³⁵ The homeobox-containing genes (hox genes) have been identified as the specific genes that control the morphogenesis of limbs.³⁶ According to molecular biology, the tretrapod limbs are also phylogenetically related to the pectoral and pelvic fins of their fish ancestors. During the evolutionary process, the pelvic fins appeared first, and the genetic program that occasioned the development of the latter was then reactivated and reoriented to induce the formation of the pectoral fins.

The above genetic encoding has also presided over the development of tetrapod limbs. In the case of tetrapods, however, the reorientation in the expression of the hox genes from the pelvic to the pectoral region (shoulder girdle) has resulted in an opposite orientation of the elbow and knee joints. While the knee joint flexes forward, the elbow joint flexes backward. During the course of evolution, this specific genetic encoding has been transmitted down to new generations of vertebrates. Modern man has been an integral part in this evolutionary process, and the association between bones and bones, joints and joints, and muscles and muscles, falls in line with this ancestral genetic print.

Structural association between bones, functional association between muscles, and functional association between organs are all part of the basic essence of life. When a given muscle or organ no longer responds to the functional needs of the partner muscle or organ, the entire body suffers. In our concept of health, a muscle or group of muscles is associated to other muscles for the purpose of locomotion, equilibrium, and postural reflexes. And this does not solely refer to antagonistic muscles like the flexors and extensors of the same body segment. In fact, the association between muscles may be between different segments of the body. For example, the right quadriceps femoris is associated with the right triceps brachii and the right biceps femoris is associated with the right biceps brachii to maintain proper posture. The right quadriceps femoris is also associated to the left biceps brachii during motion.

An organ is associated with another organ because of complementary functions or somatotopic organization in the central nervous system. For instance, the right mammary gland is associated with the right ovary, the right fallopian tube, and part of the uterus. A dysfunction of the right ovary is likely to produce a dysfunction at the level of the associated organ, that is, the right breast.

The same connection that we find in the functional association between muscles and between organs is also found in the structural association between bones. An examination of the hand and foot shows an equivalent structural arrangement. Associated bones of the carpus and tarsus have followed different paths of evolution due to their different functional purpose. Figure 3-1 shows the association between the bones of the carpus and the tarsus.

During the evolution of the foot, the calcaneus may have at one point in time resulted from the fusion of two original bones that corresponded to the os triquetrum and os pisiforme in the hand. Another plausible explanation for the development of the calcaneus is that the calcaneus is the matching bone for the pisiform and the talus is the product of the fusion of two bones, which correspond to the os lunatum and os triquetrum in the hand.³⁷

The fusion of bones is not an unheard of process, even in Modern Man.³⁸ One of the best known fusions of carpal bones is the fusion of the os triquetrum and the os lunatum. It is also not uncommon to find extra bones in the carpus. One of the most common extra bones is the central bone, located between the trapezium, trapezoideum, capitatum and scaphoid. It appears that a cartilaginous elementary form of the central bone is prevalent in humans and that it fuses with the scaphoid in the development of the carpal bones.³⁹

Bones, such as the os scaphoideum, os triquetrum, and os pisiforme, are also known to split up. It is thus evident that bones are not devoid of a natural plasticity; their size and shape can change as a result of a traumatic experience or some other form of bone pathology.

The calcaneus and the talus are of particular interest because of their intricate relationship to bipedalism. Bipedalism has forced these two bones to change drastically. Over the past 3 million years, the size of the human calcaneus has increased markedly along the antero-posterior axis when compared to the calcaneus of early hominids and Australopithecines (see Figure 3-2). The external side of the human calcaneus is parallel to the anterior-posterior axis. The posterior view of the bone shows a wide base of support and a slightly ovoid apex.⁴⁰ Standing posture and habitual bipedal locomotion have been responsible for this change.

At the same time, the pisiform has significantly regressed to become a pea-shaped bone. The pisiform of the Australopithecus afarensis was more elongated and rod-shaped just as its equivalent in apes and monkeys.⁴¹ Even though far more voluminous, the calcaneus of Modern Man presents the same general elongated shape as the pisiform and is parallel to the long axis of the foot.

The ipsilateral association between the pisiform and the calcaneus becomes more evident when we examine the tendon of the flexor carpi ulnaris and the tendon calcaneus (tendon of Achilles). Clinical experience with patients has shown that a trauma to the tendon of Achilles usually induces a concomitant imbalance in the tendon of the flexor carpu ulnaris. In other words, what will directly affect the tendon of Achilles will also affect the tendon of the flexor carpi ulnaris. The opposite, however, is not the case. An injury to the tendon of the flexor carpu ulnaris will not necessarily affect the tendon of Achilles, that is, unless the trauma or imbalance has an organic origin, such as one located at the level of the prostrate or urethra. If the prostrate or urethra demonstrates any kind of pathology, then not only will the tendons of Achilles and of the flexor carpi ulnaris be affected but also the extensors of the hand and feet and even the flexors and extensors of the neck.

In addition, it has been shown that among the muscles of the forearm, only the caput humerale of the flexor carpi ulnaris in the rhesus monkey contains a large number of slow contracting fibers (58%), which are typically found in anti-gravity muscles.⁴² This is another point of similarity between the caput humerale of the flexor carpi ulnaris and the muscles of the legs.

The talus is probably the product, for functional reasons, of the reshaping of the bone or, in greater probability, of the fusion of two bones in order to accommodate the tibia and the fibula. To make walking and running even more functional, the size of other bones in the foot naturally also had to regress, as for example the internal and external cuneiforms. Thus, the size and shape of bones in the tarsus have changed to adjust to the functions of bipedalism.

When the hand and wrist are resting on a flat surface in a natural prone position, the hand will show an ulnar deviation. On an X-ray picture, we can observe that the alignment of the bones of the carpus in this particular position is changed. The general alignment of the bones of the carpus will tend to be in the same direction as those of the tarsus (see Figure 3-3). The pisiform moves back to a position similar to the position of the calcaneus in the foot, while the os lunatum moves to a more internal position and the scaphoid of the hand to a position similar to the navicular bone in the foot.