Background: The portion of the occipital condyle that is “safe” to remove remains controversial
in the transcondylar approach. We aimed to correlate the gain in exposure with incremental
removal of the occipital condyle to determine if there is a point where further drilling
yields diminishing gains.
Methods: Virtual reality (VR) rendering of the skull was generated from 25 subjects with no
pathology in the posterior fossa. A suboccipital far lateral craniotomy was done in
VR space, stopping at the posterior edge of the occipital condyle. Angular measurements
in the surgical corridor were taken at this point, as well as after removal of 25
and 50% of the condyle. Two surgical targets were used in this study: at the anterior
midline of the foramen magnum (MFM) and the vertebrobasilar junction (VBJ).
Results: Progressive removal of the occipital condyle increased the angular exposure to both
targets in a linear fashion. For the MFM, the working angle increased from 12 to 18
degrees for quarter condylectomy and then to 25 degrees for half condylectomy. The
corridor to VBJ was much tighter, and the angle increased from 5.5 to 9 degrees for
quarter condylectomy and then to 12 degrees for half condylectomy. The gain in exposure
for low target was greater than for the high target (p < 0.001).
Conclusion: Progressive removal of the occipital condyle yielded a linear increase in exposure,
and there was no “sweet spot” beyond which the drilling was futile. However, the impact
of condylectomy was greater for the low target at the level of the foramen magnum.
For the high target at VBJ, the gain may be clinically irrelevant.
