Use of CT for Assessing Bone Mineral Density
Use of CT for Assessing Bone Mineral Density
The technique described has excellent intraobserver and interobserver reliability, with interclass correlation coefficients of 0.964 and 0.975, respectively. This reliability has been confirmed in other investigations. Using the average of 3 measurements at each vertebra compared with a single measurement appears to offer little advantage in terms of reliability. No differences are seen at different levels within the vertebral body (Figure 2).
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Figure 2.
No differences were observed between HU values obtained at different locations within lumbar vertebral bodies.
The HU values decrease linearly by decade of life, with a significant correlation observed between age and HU ( Table 2 ; Figure 3). The mean HU in females ranged from 250 in young adults to less than 79 in those in their 9th decade. As expected in females, there was a notable decrease in HU around the time of menopause (Figure 3 left). Normative male data demonstrated a more linear decrease in HU with age (Figure 3 right). The mean HU in males ranged from 270 in young adults to 85 in those in their 9th decade.
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Figure 3.
Normative data of HU values in females (left) and males (right) stratified by decade of life.
These findings were corroborated by a subsequent investigation of 128 patients, which also demonstrated strong correlations between HU values of the lumbar spine and T-scores from DXA scans, with a trend toward decreasing HU values with increasing age.
The control data from previous studies provide normative data for HU values from the T-1 vertebral body to the S-1 vertebral body. In addition, we evaluated 280 healthy female patients who underwent thoracic CT scanning to rule out spinal injury after trauma. Normative data, which can be useful for both clinical and research purposes, are shown in Table 2 .
There was good correlation of HU value to DXA for both BMD and T-score. The Pearson correlation coefficients were 0.44 and 0.48 for BMD and T-score, respectively. The correlation for both parameters was highly statistically significant (p < 0.001, Figure 4).
(Enlarge Image)
Figure 4.
Correlation between BMD assessed via DXA (in g/cm) and HU measurements in the lumbar spine. Adapted with permission from Schreiber JJ et al: J Bone Joint Surg 93:1057–1063, 2011. www.jbjs.org.
Patients were grouped as normal, osteopenic, and osteoporotic based on DXA T-score and the WHO criteria (Figure 5). The mean HU values were 133.0 (95% CI 118.4–147.5) for the normal group, 100.8 (95% CI 93.1–108.8) for the osteopenia group, and 78.5 (95% CI 61.9–95.1) for the osteoporotic group ( Table 3 ).
(Enlarge Image)
Figure 5.
Mean HU values (± SD) in the lumbar spine representative of normal bone, osteopenia, and osteoporosis. Error bars depict 95% CI.
In the 20 patients with adjacent-segment fracture following spinal fusion surgery, HU measurements at the fractured vertebral body were significantly lower in the fracture group compared with matched controls (145.6 vs 199.4, p = 0.006). Global HU measurements throughout the thoracic and lumbar spines were also significantly lower in the fracture group (139.9 vs 170.1, p = 0.032). This study also provided normative data for HU from T-1 to S-1 ( Table 2 ).
In the investigation assessing the association between HU with fusion success, the successful fusion cohort (n = 38) had significantly higher HU measurements than the nonunion cohort (n = 14) both adjacent to the fusion (203.3 vs 139.8, p < 0.001) and globally throughout the noninstrumented spine (133.7 vs 107.3, p < 0.05).
Results
Reliability
The technique described has excellent intraobserver and interobserver reliability, with interclass correlation coefficients of 0.964 and 0.975, respectively. This reliability has been confirmed in other investigations. Using the average of 3 measurements at each vertebra compared with a single measurement appears to offer little advantage in terms of reliability. No differences are seen at different levels within the vertebral body (Figure 2).
(Enlarge Image)
Figure 2.
No differences were observed between HU values obtained at different locations within lumbar vertebral bodies.
Normative Data
The HU values decrease linearly by decade of life, with a significant correlation observed between age and HU ( Table 2 ; Figure 3). The mean HU in females ranged from 250 in young adults to less than 79 in those in their 9th decade. As expected in females, there was a notable decrease in HU around the time of menopause (Figure 3 left). Normative male data demonstrated a more linear decrease in HU with age (Figure 3 right). The mean HU in males ranged from 270 in young adults to 85 in those in their 9th decade.
(Enlarge Image)
Figure 3.
Normative data of HU values in females (left) and males (right) stratified by decade of life.
These findings were corroborated by a subsequent investigation of 128 patients, which also demonstrated strong correlations between HU values of the lumbar spine and T-scores from DXA scans, with a trend toward decreasing HU values with increasing age.
The control data from previous studies provide normative data for HU values from the T-1 vertebral body to the S-1 vertebral body. In addition, we evaluated 280 healthy female patients who underwent thoracic CT scanning to rule out spinal injury after trauma. Normative data, which can be useful for both clinical and research purposes, are shown in Table 2 .
Correrlation of HU Value to DXA
There was good correlation of HU value to DXA for both BMD and T-score. The Pearson correlation coefficients were 0.44 and 0.48 for BMD and T-score, respectively. The correlation for both parameters was highly statistically significant (p < 0.001, Figure 4).
(Enlarge Image)
Figure 4.
Correlation between BMD assessed via DXA (in g/cm) and HU measurements in the lumbar spine. Adapted with permission from Schreiber JJ et al: J Bone Joint Surg 93:1057–1063, 2011. www.jbjs.org.
Threshold for Diagnosis of Osteoporosis
Patients were grouped as normal, osteopenic, and osteoporotic based on DXA T-score and the WHO criteria (Figure 5). The mean HU values were 133.0 (95% CI 118.4–147.5) for the normal group, 100.8 (95% CI 93.1–108.8) for the osteopenia group, and 78.5 (95% CI 61.9–95.1) for the osteoporotic group ( Table 3 ).
(Enlarge Image)
Figure 5.
Mean HU values (± SD) in the lumbar spine representative of normal bone, osteopenia, and osteoporosis. Error bars depict 95% CI.
HU Value and Fracture Risk
In the 20 patients with adjacent-segment fracture following spinal fusion surgery, HU measurements at the fractured vertebral body were significantly lower in the fracture group compared with matched controls (145.6 vs 199.4, p = 0.006). Global HU measurements throughout the thoracic and lumbar spines were also significantly lower in the fracture group (139.9 vs 170.1, p = 0.032). This study also provided normative data for HU from T-1 to S-1 ( Table 2 ).
HU Value and Fusion Success
In the investigation assessing the association between HU with fusion success, the successful fusion cohort (n = 38) had significantly higher HU measurements than the nonunion cohort (n = 14) both adjacent to the fusion (203.3 vs 139.8, p < 0.001) and globally throughout the noninstrumented spine (133.7 vs 107.3, p < 0.05).
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