Occipitocervical Instability After Far-Lateral Transcondylar Surgery: A Biomechanical Analysis.

Area of Science:

• Neurosurgery
• Orthopedic Biomechanics
• Anatomical Studies

Background:

• Far-lateral transcondylar approach can lead to delayed occipitoatlantal subluxation and neurological injury.
• Previous studies lack precise data on condylar resection extent and biomechanical consequences.

Purpose of the Study:

• Quantify bone removal in far-lateral transcondylar resection.
• Assess changes in range of motion and stiffness post-resection.
• Identify the threshold of condylar resection predicting occipitocervical instability.

Main Methods:

• Biomechanical testing of nine human cadaveric specimens before and after transcondylar resection.
• Volumetric analysis of computed tomography scans to quantify bone removal.
• Sensitivity analysis to determine the critical resection extent for biomechanical changes.

Main Results:

• Condylar resection into the hypoglossal canal (HC) involved 15.4%-63.7% of bone (mean 35.7%).
• Significant biomechanical alterations were predicted with as little as 29% occipital condyle resection.

Conclusions:

• Occipitocervical biomechanics can change with approximately one-third condylar resection.
• The hypoglossal canal may not be a reliable surgical landmark for resection limits.
• Close surveillance for instability is crucial in patients with condylar resections extending into or beyond the HC.