Bone metabolism in quadriplegia: dissociation between calciuria and hydroxyprolinuria

Relationships between duration of paralysis, recumbency, muscular activity, and urinary loss of calcium (Cau), phosphorus (Pu), and hydroxyproline (OHPu) were studied daily in 32 traumatic quadriplegic patients during comprehensive rehabilitation and randomly in those readmitted for treatment. Within days after onset, quadriplegic patients had increases in Pu, then OHPu, and finally, Cau. Patients actively engaged in rehabilitation exercises showed a steady fall in OHPu, whereas CAU remained high for up to 18 months. Patients paralyzed for over 18 months (late) had low Cau, Pu and OHPu; but if the patients were kept in bed, OHPu increased rapidly. Patients with early quadriplegia have an increased bone remodeling, suggesting that the excess OHPu and Cau are derived from resorbed bone. Patients with late quadriplegia have little bone remodeling, therefore the excess OHPu occurring during recumbency may be derived from the resorption of new collagen produced during the removal of weight bearing without further change in muscular activity. Resorbed new collagen is excreted in part as large, OHP-containing polypeptides; these were found in the urine of quadriplegic patients, and therefore were present in blood and may play a role in initiating ectopic bone and renal calculi. The presence of OHP in 11 bladder calculi from quadriplegic patients tends to support this hypothesis. These studies indicate that muscular activity and weight bearing influence the bone metabolism of quadriplegic patients and suggest that the presence in body fluids of increased catabolic products from bone may have a role in bone-related complications.