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OBJECT: The authors sought to determine the biomechanics of the occipitoatlantal (occiput Oc-C1) and atlantoaxial (C1-2) motion segments after unilateral gradient condylectomy. METHODS: Six human cadaveric specimens (skull with attached upper cervical spine) underwent nondestructive biomechanical testing (physiological loads) during flexion-extension, lateral bending, and axial rotation. Axial translation from tension to compression was also studied across Oc-C2. Each specimen served as its own control and underwent baseline testing in the intact state. The specimens were then tested after progressive unilateral condylectomy (25% resection until completion), which was performed using frameless stereotactic guidance. At Oc-C1 for all motions that were tested, mobility increased significantly compared to baseline after a 50% condylectomy. Flexion-extension, lateral bending, and axial rotation increased 15.3%, 40.8%, and 28.1%, respectively. At C1-2, hypermobility during flexion-extension occurred after a 25% condylectomy, during axial rotation after 75% condylectomy, and during lateral bending after a 100% condylectomy. CONCLUSIONS: Resection of 50% or more of the occipital condyle produces statistically significant hypermobility at Oc-C1. After a 75% resection, the biomechanics of the Oc-C1 and C1-2 motion segments change considerably. Performing fusion of the craniovertebral junction should therefore be considered if half or more of one occipital condyle is resected.
Vishteh et al. (Fri,) studied this question.