Longitudinal study of bone demineralisation following spinal cord injury using peripheral Quantitative Computed Tomography (pQCT)

The motivation for this study was the clinical need to improve our understanding of the natural history of bone demineralisation in the paralysed limbs of patients with a complete Spinal Cord Injury (SCI), and to work towards developing clinical guidelines for the assessment and management of osteoporosis in this patient group. Ultimately, the goal would be to implement protocols which allow clinicians to identify and stratify those patients at highest risk of fast-progressing osteoporosis as early as possible post-injury, target them for treatment, and in the longer term reduce the lifetime risk of fracture. The chronic SCI population currently suffers from osteoporotic fractures in the long bones of the paralysed limbs at a rate far exceeding that of the general population. This has been the largest longitudinal bone mineral density (BMD) study in the acute SCI population that has used peripheral Quantitative Computed Tomography (pQCT) as the quantitative bone imaging tool, rather than the clinical densitometry system, Dual-Energy X-Ray Absorptiometry (DEXA), to describe patterns of bone loss after SCI in detail.

• When analysed together, pQCT data from the participants on this longitudinal study confirm that there are significant decreases in indicators of bone health (BMD, bone mineral content) within the first 8-12 months of a motor-complete SCI. This affects the paralysed limbs only, with no significant decreases observed in the upper limbs of paraplegic patients.
• The data confirm the patterns described by other studies performed in this patient group that have suggested an exponential decrease in bone parameters in the long bones of the legs after SCI, with the greatest bone losses occurring in the first 1-2 years post-injury.
• An additional contribution of this dataset relates to both scientific and clinical impact. The uniquely detailed temporal and spatial descriptions of individual patterns of bone loss in this patient cohort are suggestive of large inter-subject variability in bone adaptation to long-term immobilisation that is not easily attributed to age, gender or other known risk factors for fracture. The high variability in these spatio-temporal patterns of bone loss has led to the suggestion that some patients may be suffering much faster rates of bone loss than others. At some scan sites, rates of bone loss recorded in the study participants ranged from as low as 1% to more than 50% bone loss in the first year. This provides evidence for the possibility of stratifying SCI patients, based on early repeat pQCT scans, according to osteoporosis-progression (and fracture) risk. This approach will be key in achieving targeted treatment and personalised healthcare.