The Benefits of Progressive Occipital Condylectomy in Enhancing the Far Lateral Approach to the Foramen Magnum

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.