Introduction: The far lateral, transcondylar approach to the ventral foramen magnum requires partial resection of the unilateral occipital condyle. Early biomechanical studies suggest that occipital cervical (OC) fusion be considered at greater than fifty-percent condylar resection. However, in clinical practice, a joint sparing condylectomy has often been employed without the need for OC fusion. The biomechanics of the joint sparing technique have never been reported. We hypothesized that the clinically relevant joint sparing condylectomy would result in added stability of the craniocervical junction.

Methods: Multidirectional in vitro flexibility tests were performed using a robotic spine testing system on cadaveric specimens (occiput-C4) to assess the effect of sequential unilateral joint-sparing condylectomy in comparison to the intact state using a simulated head weight and follower load. Segmental range of motion (ROM) was recorded in the cardinal directions and in coupled motions in the following conditions: intact; C1 laminectomy; 25%, 50%, 75% and 100% joint-sparing condylectomy.

Results: We found the percent change in ROM following sequential condylectomy as compared to intact was 5.2, 8.1, 12.0 and 27.5% in flexion-extension (FE); 8.4, 14.7, 39.1 and 80.2% in lateral bending (LB); and 24.4, 31.5, 49.9 and 141,1 in axial rotation (AR). Only the values at 100% condylectomy were statistically significant (p<0.05). With coupled motions however, we found values for 75 and 100% condyle resection were statistically significant in AR with extension.

Conclusions: When tested in the traditional cardinal directions, the joint-sparing condylectomy did not create significantly increased motion until after seventy-five percent joint resection. However, when flexion-extension were coupled to axial rotation, we found significant increases in motion after fifty percent unilateral joint-sparing condyle resection.

Patient Care: The post-surgical stability of the craniocervical junction is an importnat consideration in the operative planning and treatment of patients following the far lateral approach to the ventral foramen magnum.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Discuss the stability of the craniocervical junction following joint-sparing condylectomy 2) Understand the biomechanical considerations, including headweight, that affect biomechanical studies

References: Vishteh AG, Crawford NR, Melton MS, Spetzler RF, Sonntag VK, Dickman CA: Stability of the craniovertebral junction after unilateral occipital condyle resection: A biomechanical study. J Neurosurg 90:91-98, 1999