Disrupted Bone Metabolism in Long-Term Bedridden Patients

Abstract

Background: Bedridden patients are at risk of osteoporosis and fractures, although the long-term bone metabolic processes in these patients are poorly understood. Therefore, we aimed to determine how long-term bed confinement affects bone metabolism.

Methods: This study included 36 patients who had been bedridden from birth due to severe immobility. Bone mineral density and bone metabolism markers were compared to the bedridden period in all study patients. Changes in the bone metabolism markers during a follow-up of 12 years were studied in 17 patients aged <30 years at baseline.

Results: The bone mineral density was reduced (0.58±0.19 g/cm3), and the osteocalcin (13.9±12.4 ng/mL) and urine N-terminal telopeptide (NTX) levels (146.9±134.0 mM BCE/mM creatinine) were greater than the cutoff value for predicting fracture. Among the bone metabolism markers studied, osteocalcin and NTX were negatively associated with the bedridden period. During the follow-up, osteocalcin and parathyroid hormone were decreased, and the 25(OH) vitamin D was increased. NTX at baseline was negatively associated with bone mineral density after 12 years.

Conclusions: Unique bone metabolic abnormalities were found in patients who had been bedridden for long periods, and these metabolic abnormalities were altered by further bed confinement. Appropriate treatment based on the unique bone metabolic changes may be important in long-term bedridden patients.

Fig 1. Bone mineral density and bone metabolism marker levels according to the period of bed confinement in all study patients.

Because all patients had been bedridden from birth, the period of bed confinement was equal to their age. A) Correlation between the bone mineral density of lumbar spine vertebrae 2–4 in the anteroposterior projection and the period of bed confinement. Correlation between the bone metabolism marker levels, including the serum osteocalcin levels (B), urine N-terminal telopeptide levels (C), serum 25 (OH) vitamin D levels (D), serum intact parathyroid hormone levels (E), serum calcium levels (F), serum phosphorus levels (G), and serum alkaline phosphatase levels (H), and period of bed confinement. Red lines indicate the cutoff value for osteoporosis (bone mineral density) and those for predicting bone fracture (osteocalcin and N-terminal telopeptide), as proposed by the guidelines for the prevention and treatment of osteoporosis [17].

Fig 2. Changes in the bone mineral density and bone metabolism marker levels during a 12-year follow-up period in patients whose baseline age was <30 years.

Red lines indicate the cutoff value for osteoporosis (bone mineral density) and those for predicting bone fracture (osteocalcin and N-terminal telopeptide), as proposed by the guidelines for the prevention and treatment of osteoporosis [17].

Fig 3. Association between the bone metabolism marker levels at baseline with the bone mineral density during a follow-up of 12 years in patients whose baseline age was <30 years.