Dual Energy X-Ray Absorptiometry of the Distal Femur May Be More Reliable than the Proximal Tibia in Spinal Cord Injury

Arch Phys Med Rehabil, 2009 · DOI: 10.1016/j.apmr.2008.12.004 · Published: May 1, 2009

Spinal Cord Injury Musculoskeletal Medicine

Simple Explanation

Spinal cord injury (SCI) often leads to fractures in the distal femur and proximal tibia. Current methods to assess bone density aren't designed for SCI patients, so this study checks how well DXA scans measure bone density at these knee sites. The study found that DXA scans are more precise at the distal femur than the proximal tibia in SCI patients. This suggests the distal femur is a better place to monitor bone density changes over time in this group. The researchers suggest using the distal femur for regular bone density scans in SCI patients to help diagnose and treat osteoporosis, a condition that increases fracture risk.

Study Duration

Not specified

Participants

20 subjects with chronic SCI

Evidence Level

Cross-sectional study

Key Findings

1
The root mean square coefficient of variation (RMS-CV) at the distal femur was 3.01%, and the root mean standard deviation (RMS-SD) was 0.025 g/cm2.
2
At the proximal tibia, the RMS-CV was 5.91%, and the RMS-SD was 0.030 g/cm2.
3
Precision at the distal femur is greater than the proximal tibia

Research Summary

This study evaluated the precision of dual energy x-ray absorptiometry (DXA) scanning at the distal femur and proximal tibia in individuals with spinal cord injury (SCI). The study found that precision at the distal femur is greater than the proximal tibia, suggesting it as the preferred site for longitudinal assessment of bone mineral density at the knee in chronic SCI. The authors conclude that the distal femur skeletal site can be used for SCI-specific DXA scanning protocols and the longitudinal assessment of BMD at the knee to determine the risk of fracture in chronic SCI.

Practical Implications

Preferred Site for Bone Density Assessment

The distal femur is recommended as the preferred site for longitudinal assessment of bone mineral density at the knee in chronic SCI.

Standardized DXA Scanning Protocols

The findings support the use of standardized DXA scanning protocols for the knee to advance the diagnosis and treatment of osteoporosis in SCI.

Improvement in Clinical Care

Improvements in the clinical care of SCI-induced osteoporosis will rely on the development of standardized protocols for BMD determination.

Study Limitations

1
The DXA scans were read consecutively and not read blindly, and due to SCI subject repositioning did not include complete dismounting and remounting of the scanning table, factors potentially increasing precision.
2
Internal rotation of the leg was limited by securing the limb at the ankle only, potentially decreasing precision.
3
In future work, we plan to explore additional methods of stabilizing the knee that may result in greater precision, particularly at the proximal tibia, and replicate our findings in additional persons.

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