Long-term changes in bone metabolism, bone mineral density, quantitative ultrasound parameters, and fracture incidence after spinal cord injury: a cross-sectional observational study in 100 paraplegic men

Zehnder, Yvonne ; Lüthi, Markus ; Michel, Dieter ; Knecht, Hans ; Perrelet, Romain ; Neto, Isolde ; Kraenzlin, Marius ; Zäch, Guido ; Lippuner, Kurt

In: Osteoporosis International, 2004, vol. 15, no. 3, p. 180-189

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    To study the time course of demineralization and fracture incidence after spinal cord injury (SCI), 100 paraplegic men with complete motor loss were investigated in a cross-sectional study 3months to 30years after their traumatic SCI. Fracture history was assessed and verified using patients' files and X-rays. BMD of the lumbar spine (LS), femoral neck (FN), distal forearm (ultradistal part=UDR, 1/3 distal part=1/3R), distal tibial diaphysis (TDIA), and distal tibial epiphysis (TEPI) was measured using DXA. Stiffness of the calcaneus (QUI.CALC), speed of sound of the tibia (SOS.TIB), and amplitude-dependent SOS across the proximal phalanges (adSOS.PHAL) were measured using QUS. Z-Scores of BMD and quantitative ultrasound (QUS) were plotted against time-since-injury and compared among four groups of paraplegics stratified according to time-since-injury (<1year, stratum I; 1-9years, stratum II; 10-19years, stratum III; 20-29years, stratum IV). Biochemical markers of bone turnover (deoxypyridinoline/creatinine (D-pyr/Cr), osteocalcin, alkaline phosphatase) and the main parameters of calcium phosphate metabolism were measured. Fifteen out of 98 paraplegics had sustained a total of 39 fragility fractures within 1,010 years of observation. All recorded fractures were fractures of the lower limbs, mean time to first fracture being 8.9±1.4 years. Fracture incidence increased with time-after-SCI, from 1% in the first 12months to 4.6%/year in paraplegics since >20years (p<.01). The overall fracture incidence was 2.2%/year. Compared with nonfractured paraplegics, those with a fracture history had been injured for a longer time (p<.01). Furthermore, they had lower Z-scores at FN, TEPI, and TDIA (p<.01 to <.0001), the largest difference being observed at TDIA, compared with the nonfractured. At the lower limbs, BMD decreased with time at all sites (r=.49 to .78, all p<.0001). At FN and TEPI, bone loss followed a log curve which leveled off between 1 to 3years after injury. In contrast, Z-scores of TDIA continuously decreased even beyond 10years after injury. LS BMD Z-score increased with time-since-SCI (p<.05). Similarly to DXA, QUS allowed differentiation of early and rapid trabecular bone loss (QUI.CALC) vs slow and continuous cortical bone loss (SOS.TIB). Biochemical markers reflected a disproportion between highly elevated bone resorption and almost normal bone formation early after injury. Turnover declined following a log curve with time-after-SCI, however, D-pyr/Cr remained elevated in 30% of paraplegics injured >10years. In paraplegic men early (trabecular) and persistent (cortical) bone loss occurs at the lower limbs and leads to an increasing fracture incidence with time-after-SCI