Final answer:
The absolute measurement indication for a C1/C2 fusion in rheumatoid atlantoaxial instability is typically based on imaging findings, such as the atlantodens interval (ADI) and the space available for the spinal cord (SAC).
Step-by-step explanation:
In the context of rheumatoid atlantoaxial instability, a C1/C2 fusion is a surgical procedure that aims to stabilize the atlantoaxial joint between the C1 (atlas) and C2 (axis) vertebrae.
The absolute measurement indication for a C1/C2 fusion in this condition is typically based on imaging findings, specifically the presence of certain measurements that indicate instability in the atlantoaxial joint. Some of the measurements that may be considered in this context include:
- The atlantodens interval (ADI), which measures the distance between the anterior arch of the atlas and the dens of the axis. A value greater than 3mm is typically considered abnormal.
- The space available for the spinal cord (SAC), which measures the distance between the posterior aspect of the dens and the posterior arch of the atlas. A value less than 14mm is typically considered abnormal.
It's important to note that these measurements may vary depending on the specific guidelines or protocols used by healthcare providers.