Study Design Cross-sectional cohort study. Objectives To describe: 1) the prevalence of suboptimal 25-hydroxy vitamin D status (Serum 25(OH)D <75nmol/L) and identify correlates of vitamin D deficiency; and, 2) the prevalence of secondary hyperparathyroidism (Serum intact PTH ≥ 7.0 pmol/L) and identify the relationships between serum parathyroid hormone (PTH) and 25(OH)D in adult men and women with chronic spinal cord injury (SCI). Setting Outpatient services, including an osteoporosis clinic at a tertiary spinal cord rehabilitation hospital in Ontario. Methods Serum levels of 25(OH)D and intact PTH were acquired at enrolment. Clinical correlates of suboptimal vitamin D status were collected via interview and chart abstraction, and identified by univariate logistic regression analysis. Pearson correlations were run to assess the relationships between serum PTH and 25(OH)D. Significance was p<0.05. Results Thirty-nine percent of the cohort, comprised of 62 adult men and women with chronic SCI, had suboptimal serum 25(OH)D levels. Factors associated with suboptimal vitamin D levels included having vitamin D assessed in the winter months (OR=7.38, p=0.001), lack of a calcium supplement (OR=7.19, p=0.003), lack of a vitamin D supplement (OR=7.41, p=0.019), younger age (OR=0.932, p=0.010), paraplegia (OR=4.22, p=0.016), and lack of bisphosphonate (OR=3.85, p=0.015). Significant associations were observed between serum PTH and 25(OH)D (r=−0.304, p=0.032) and between PTH and C-telopeptide of type I collagen (CTX-I) (r=0.308, p=0.025). Conclusions Disruption of the vitamin D-PTH axis may contribute to the bone loss seen in the chronic SCI population. The threshold for optimal serum 25(OH)D levels in the chronic SCI population may be higher than in the non-SCI population. Serum 25(OH)D level are likely important risk factors contributing to declining bone mass and increased fracture risk post-SCI.

In peripheral quantitative computed tomography scans of the calf muscles, segmentation of muscles from subcutaneous fat is challenged by muscle fat infiltration. Threshold-based edge detection segmentation by manufacturer software fails when muscle boundaries are not smooth. This study compared the test-retest precision error for muscle-fat segmentation using the threshold-based edge detection method vs manual segmentation guided by the watershed algorithm. Three clinical populations were investigated: younger adults, older adults, and adults with spinal cord injury (SCI). The watershed segmentation method yielded lower precision error (1.18%-2.01%) and higher (p<0.001) muscle density values (70.2±9.2 mg/cm3) compared with threshold-based edge detection segmentation (1.77%-4.06% error, 67.4±10.3 mg/cm3). This was particularly true for adults with SCI (precision error improved by 1.56% and 2.64% for muscle area and density, respectively). However, both methods still provided acceptable precision with error well under 5%. Bland-Altman analyses showed that the major discrepancies between the segmentation methods were found mostly among participants with SCI where more muscle fat infiltration was present. When examining a population where fatty infiltration into muscle is expected, the watershed algorithm is recommended for muscle density and area measurement to enable the detection of smaller change effect sizes.

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