BACKGROUND CONTEXT Bone mineral density (BMD) is important as it may influence surgical decision-making particularly for fractures at C1 and C2 and C1-C2 instability cases. While the elderly population may be poor surgical candidates, they experience a high rate of fractures at C1 and C2 from low velocity falls and motor vehicle accidents. To stabilize these fractures, C1-C2 screws (pars, transpedicular) are commonly used. PURPOSE The present study tested the hypothesis that type 2 odontoid fracture occurs more commonly than Type I or Type III due to low BMD at the odontoid-C2 body interface compared to the other regions of the C2 vertebra. From mechanistic and bony structural architectural perspectives, external loads applied to this region of C2 is associated with the poor healing rate for type 2 odontoid fractures. STUDY DESIGN/SETTING Regional BMDs of C1 and C2 vertebra using quantitated computed tomography (QCT) were obtained from 10 cadaveric male spines (45-79 years, average 64). A QCT software (Mindways Inc., San Francisco, CA) was used. PATIENT SAMPLE Ten cadaveric cervical spines METHODS Regional BMDs of C1 and C2 vertebra using quantitated computed tomography (QCT) were obtained from 10 cadaveric male spines (45-79 years, average 64). A QCT software (Mindways Inc., San Francisco, CA) was used. For C2, BMDs were determined at six regions: top of odontoid, base of odontoid-body interface, mid body, bilateral lateral body and posterior spinous process. The eight regions for C1 were: anterior tubercle, bilateral anterior and medial lateral masses, bilateral posterior arches and posterior arch. Pairwise comparisons were performed, and correlations between different regions were evaluated using the one tailed t-test was performed to calculate the regional variations in BMD. The statistical significance was set at p < 0.05 level. RESULTS For C1, BMD was greatest at the anterior tubercle (607±205 mg/cc) and posterior ring (446± 133 mg/cc), and least at the anterior and medial lateral masses. For C2, there were no statistical differences (p>0.5) between left and right lateral mass BMDs, and hence averaged for analysis. BMD was significantly greatest (p < 0.05) at the top of the dens (402±83 mg/cc) compared to the other six regions (averages 263-319 mg/cc). It was the least at the midbody (263±54 mg/cc). The BMD was greater (p < 0.05) at the C2 lateral mass than interface or midbody). The C1 posterior arch (446 mg/cc) and C2 spinous process (283 mg/cc) had higher BMDs than C1 lateral mass (anterior 264.5 ± 40 mg/cc3). CONCLUSIONS The hypothesis that the BMD shows a regional response and decreases caudally from the top of the odontoid was proved. The lowest BMD was in the mid C2 body. For younger patients, the C1-C2 screw trajectory is through bone with better bone quality; however, care should be taken to avoid short screws as the distal portion may be in contact with softer bone (less BMD), which may potentiate screw loosening. Given the observed regional changes in BMDs of the C1 arch and C2 spinous process, the use of various C1-C2 wiring techniques (Sonntag and Brooks) should be considered particularly in the elderly, whose vertebral arteries may be ectatic. As BMD is directly related to bone strength, our study supports the use of these techniques that has a long track record of efficacy and safety with less blood loss and operative time. The present results offer supports these posterior wiring techniques in elderly patients. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs. Bone mineral density (BMD) is important as it may influence surgical decision-making particularly for fractures at C1 and C2 and C1-C2 instability cases. While the elderly population may be poor surgical candidates, they experience a high rate of fractures at C1 and C2 from low velocity falls and motor vehicle accidents. To stabilize these fractures, C1-C2 screws (pars, transpedicular) are commonly used. The present study tested the hypothesis that type 2 odontoid fracture occurs more commonly than Type I or Type III due to low BMD at the odontoid-C2 body interface compared to the other regions of the C2 vertebra. From mechanistic and bony structural architectural perspectives, external loads applied to this region of C2 is associated with the poor healing rate for type 2 odontoid fractures. Regional BMDs of C1 and C2 vertebra using quantitated computed tomography (QCT) were obtained from 10 cadaveric male spines (45-79 years, average 64). A QCT software (Mindways Inc., San Francisco, CA) was used. Ten cadaveric cervical spines Regional BMDs of C1 and C2 vertebra using quantitated computed tomography (QCT) were obtained from 10 cadaveric male spines (45-79 years, average 64). A QCT software (Mindways Inc., San Francisco, CA) was used. For C2, BMDs were determined at six regions: top of odontoid, base of odontoid-body interface, mid body, bilateral lateral body and posterior spinous process. The eight regions for C1 were: anterior tubercle, bilateral anterior and medial lateral masses, bilateral posterior arches and posterior arch. Pairwise comparisons were performed, and correlations between different regions were evaluated using the one tailed t-test was performed to calculate the regional variations in BMD. The statistical significance was set at p < 0.05 level. For C1, BMD was greatest at the anterior tubercle (607±205 mg/cc) and posterior ring (446± 133 mg/cc), and least at the anterior and medial lateral masses. For C2, there were no statistical differences (p>0.5) between left and right lateral mass BMDs, and hence averaged for analysis. BMD was significantly greatest (p < 0.05) at the top of the dens (402±83 mg/cc) compared to the other six regions (averages 263-319 mg/cc). It was the least at the midbody (263±54 mg/cc). The BMD was greater (p < 0.05) at the C2 lateral mass than interface or midbody). The C1 posterior arch (446 mg/cc) and C2 spinous process (283 mg/cc) had higher BMDs than C1 lateral mass (anterior 264.5 ± 40 mg/cc3). The hypothesis that the BMD shows a regional response and decreases caudally from the top of the odontoid was proved. The lowest BMD was in the mid C2 body. For younger patients, the C1-C2 screw trajectory is through bone with better bone quality; however, care should be taken to avoid short screws as the distal portion may be in contact with softer bone (less BMD), which may potentiate screw loosening. Given the observed regional changes in BMDs of the C1 arch and C2 spinous process, the use of various C1-C2 wiring techniques (Sonntag and Brooks) should be considered particularly in the elderly, whose vertebral arteries may be ectatic. As BMD is directly related to bone strength, our study supports the use of these techniques that has a long track record of efficacy and safety with less blood loss and operative time. The present results offer supports these posterior wiring techniques in elderly patients.