CHAPTER 18
METABOLIC DISTURBANCES OF THE
SKELETAL SYSTEM
In recent years, intensive research has been undertaken on biochemical and biophysical
problems of the catabolic and anabolic phases following transection of the spinal cord.
The spinal man offers, indeed, infinitely better possibilities in this respect than the spinal
animal, provided there exists the closest co-operation between the clinician and bio
chemist and the patient is kept under scientifically comparable conditions. For a proper
analysis of data, it is absolutely essential that the patient be kept on a standard diet and
that in series investigations the timing of taking blood samples and the hourly or 24-
hourly collection of urine be strictly observed.
Osteoporosis—'spontaneous' fractures
Bone formation and bone absorption are continuous reciprocal physiological activities
throughout life, although the rates of exchange vary with age and differ in various parts
of the skeleton. Bone formation consists of two processes which are under cellular
control: (a) laying down of a cellular matrix (osteoid) and (b) deposit of bone salts. Bone
formation is controlled by the single nuclear osteoblasts and their function is to lay down
calcifiable collagen fibrils in a suitable ground substance and produce alkaline phospha-
tase, but the precise role of this enzyme in bone formation is still obscure. The collagen
has the capacity to promote the formation of crystals on the surface of its fibrils. The
bone absorption is regulated by the multinuclear giant osteoclasts. The physiology and
pathology of these ground elements of the skeletal system, osteoblasts, osteoclasts,
osteocytes, collagen matrix and their relationship to the calcium, phosphate and protein
metabolism have been studied repeatedly in recent years (Bartelheimer, 1956, 1962;
Fourman, 1960; Glinebe, 1962; Norrdin, 1962; Eger, 1962; Paeslack, 1965). Although
there are still gaps in our knowledge of the complex mechanism, it is now a
well-established fact that prolonged bedrest, in particular when combined with immobi
lization, results in changes of the mineral metabolism associated with atrophy of soft
tissues, especially muscles, as well as of the skeletal system. This has been proved even
in non-paralysed individuals following fractures (Howard
et al. y
1945; Dietrick, 1948)
as well as in healthy volunteers. In spinal paraplegics this is the rule in the parts below the
level of the lesion, be it complete or incomplete (Guttmann, 1953,1971). The level of the
lesion is of importance in so far as the immobility of the motor apparatus in high lesions
involves larger parts of the body. Age plays a subordinate part and the writer has seen
considerable degrees of osteoporosis in spinal cord paralysed young children. It is also
agreed that chronic infections of the urinary tract or caused by osteomyelitis as a result
of pressure sores accelerate and greatly increase osteoporosis in paraplegics and tetra-
plegics. Even if these complications and other factors are absent it is still a matter of
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