Relationships between T-scores at the hip and bone mineral density at the distal femur and proximal tibia in persons with spinal cord injury

Abstract

Objective: To identify T-score values at the total hip (TH) and femoral neck (FN) that correspond to the cutoff value of <0.60 g/cm² for heightened risk of fracture at the distal femur (DF) and proximal tibia (PT).

Design: Retrospective analysis of data in a research center’s database.

Setting: Community-based individuals with spinal cord injury (SCI).

Participants: 105 unique individuals with SCI.

Outcome Measurements: DXA derived areal BMD (aBMD) and T-score of the DF, PT, TH, and FN.

Results: The aBMD at the DF and PT regions were predictors of T-scores at the TH (R² = 0.63, P < 0.001 and R² = 0.65, P < 0.001) and FN (R² = 0.55, P < 0.001 and R² = 0.58, P < 0.001). Using the DF and PT aBMD of 0.60 g/cm² as a value below which fractures were more likely to occur, the predicted T-score was −3.1 and −3.5 at the TH and −2.6 and −2.9 at the FN, respectively. However, when the predicted and observed T-score values disagree outside the 95% limit of agreement, the predicted T-score values are lower than the measured T-score values, overestimating the measured values between −2.0 and −4.0 SD.

Conclusion: The DF and PT cutoff value for aBMD of 0.60 g/cm² was a moderate predictor of T-score values at the TH and FN, with considerable inaccuracies outside the clinically acceptable limits of agreement. As such, the direct measurement of knee aBMD in persons with SCI should be performed, whenever possible, prior to prescribing weight bearing upright activities, such as robotic exoskeletal-assisted walking.

Keywords:

• Spinal cord injury
• Dual energy X-ray absorptiometry
• Bone mineral density
• T-score
• Distal femur
• Proximal tibia

Acknowledgments

The authors wish to thank the James J Peters VA Medical Center, Bronx, NY, the Department of Veterans Affairs Rehabilitation Research & Development Service, the Kessler Institute for Rehabilitation and the Kessler Foundation, West Orange, NJ, for their support.

Disclaimer statements

Contributors None.

Funding This material is from work supported by the Department of Veterans Affairs, Veterans Health Administration, Rehabilitation Research and Development Service National Center for the Medical Consequences of Spinal Cord Injury (B9212-C), [DOD/ CDMRP Award: W81XWH-14-2-0170], New Jersey Commission on Spinal Cord Research [CSCR131RG013], Craig H. Neilsen Foundation [297267], the New York State Department of Health Spinal Cord Injury Research Board [DOH01-PART3-2019-00002], and the National Institute on Disability, Independent Living, and Rehabilitation Research (NIDILRR) [90SI5026]; Congressionally Directed Medical Research Programs.

Conflicts of interest Authors have no conflict of interests to declare.

Ethics approval This study was approved by the James J. Peters VA Medical Center, Rutgers University, and Kessler Foundation Institutional Review Boards and all participants gave their informed consent to participate.