Mean values of wedge ratio (WR) and wedge angle (WA) equivalent to an anterior vertebral height (Ha) of 1.0 mm in grade 1-3 vertebrae of 3.5% and 1.5 ˚, respectively, may be reliably used in clinical practice as cutoff values to diagnose fresh osteoporotic vertebral fractures (OVF) and make bone union determinations, according to research results published in the Journal of Bone and Mineral Metabolism.
Through a retrospective, observational study, researchers sought to clarify the values of WR and WA equivalent to Ha of 1.0 mm and to compare the reported vertebral mobility cutoff values. They also sought to evaluate how radiographic magnification resulting from different tube-to-film distances (TFD) influence vertebral mobility cutoff values in clinical practice.
Vertical mobility, the study authors explained, is defined as the difference in shape of vertebral bodies between lateral radiographs taken in weight-bearing and non-weight bearing positions. Plain lateral radiographs show vertebral bodies in OVFs are most severely collapsed or deformed in weight-bearing positions—such as sitting or standing. They are restored to individually different extents in non-weight-bearing positions, such as laying on one’s side or back. More advanced radiographic pictures can benefit diagnosis.
Investigators obtained lateral radiographs from thoracolumbar vertebrae T11 to L2 from 183 women aged 60 or older (mean age, 77 years; height, 149.5±5.9 cm; and a body mass index (BMI) of 23.2±3.9 kg/m2) who received treatment in a single center. Fifteen prevalent OVFs were found in patients with spine disorders; those with deformed vertebrae with spondylosis, severely collapsed burst fractures, and other spinal disorders, were excluded.
Radiographs were taken in with patients lying in non-weight-bearing positions (lateral decubitus, or DEC) with knees bent and the x-ray beam centered over the thoracolumbar vertebrae, except for patients with spine disorders, where the beam was centered on the lumbar spine. Radiofluorenscence radiography and computed radiography were used.
The images were also magnified and magnification was considered in the analysis.
Mean patient thickness was 15.6±1.4 cm in 30 patients with a mean age of 81 years. With a 10 cm decrease in TFD, investigators noted a 3% decrease in vertebral dimensions, with a difference in radiographic magnification of 3% between 2 radiography models. Values measured on computed radiographs were therefore reduced by 3%, then added to values measured on radiofluorescence radiographs.
Coefficients of variation for normal and deformed vertebrae were 1.2±0.5% and 2.2±1.0% for Ha, 1.2±0.4% and 1.3±0.6% for posterior vertebral height (Hp), and 1.4±0.5% and 1.3±0.5% for vertebral depth (VD). Intraobserver reliability assessed by intraclass correlation coefficients for both normal and deformed vertebrae were 0.980 and 0.987 for Ha, 0.953 and 0.989 for Hp, and 0.962 and 0.946 for VD.
Mean Ha, Hp, and VD values increased significantly on moving caudally from T11 to L2 in grade 0 fractures; in grade 1, and 2, these values increased significantly at each level of the spine. No increases were noted in grade 3. Mean values from T11 to L2 were 28.0±30 mm, 31.5±2.9 mm, and 34.7±2.7 mm for Ha, Hp, and VD, respectively, in grade 0; 24.5±1.8 mm, 31.3±2.2 mm, and 34.4±2.2 mm in grade 1; 19.2±2.7 mm, 28.6±3.3 mm, and 34.4±2.2 mm in grade 2; and 13.0±3.8 mm, 27.1±3.3 mm, and 35.9±3.3 mm in grade 3.
Mean Ha values for each vertebrate decreased from grade 0 to grade 3 with a significant difference between each grade of vertebral deformity, noted the study authors.
Wedge ratio and WA values presenting the extent of vertebral deformity were calculated through Ha, Hp, and VD. Wedge ratio increased significantly moving caudally from T11 to L2 in grade 0, but not in grades 1 through 3, while WA decreased significantly at the same grades.
Wedge ratio/Ha was “absolutely dependent” on Hp; as mean Hp value increased moving caudally, wedge ratio/Ha decreased significantly moving caudally from T11 to L2 in grades 0, 1 and 2. Mean WR/Ha values for T11 through L2 in each vertebral deformity grade were 3.2±0.3%, 3.2±0.2%, 3.5±0.5%, and 3.7±05%.
Calculations indicated an intraclass correlation coefficient between WA values via trigonometric function and radiographs was 0.989, demonstrating high reliability for calculated WA values. WA/Ha decreased significantly moving caudally from T11 to L2 in grades 0, 1 and 2, but not grade 3; mean values of WA/Ha for grades 0 and 1 were 1.6˚±0.1˚, and 1.5˚±0.1˚ and 1.4˚±0.1˚ for grades 2 and 3. Researchers emphasized this showed that WA/Ha decreased with advancing V-deformity, particularly in grade 3.
The mean values of the vertebral dimensions in grade 0 vertebrae were obtained from 446 vertebrae, in comparison to 146 vertebrae obtained in grades 1-3, which researchers considered a limitation of the analysis.
“This study clarified the values of WR and WA equivalent to Ha of 1.0 mm,” the researchers concluded. “The values of WR of 3.5% and WA of 1.5˚ equivalent to Ha of 1.0 mm, which were the mean values in grades 1-3 vertebrae, may be recommended as representative values to secure a reliable value of vertebral mobility in daily clinical practice, and to set cutoff values to diagnose fresh OVFs and to determine bone union.”
Disclosure: The authors declare no conflicts of interest.
Sato K, Kogawa M, Yamada Y, Yamashiro M, Kasama F, Matsuda, M. . Equivalent values between anterior vertebral height, wedge ratio, and wedge angle in osteoporotic vertebral fractures. J Bone Miner Metab. Published August 22, 2021. doi: 10.1007/s00774-021-01264-9