Biomechanical evaluation of the craniovertebral junction after unilateral joint-sparing condylectomy: implications for the far lateral approach revisited

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The far lateral transcondylar approach to the ventral foramen magnum requires partial resection of the occipital condyle. Early biomechanical studies suggest that occipitocervical (OC) fusion should be considered if 50% of the condyle is resected. In clinical practice, however, a joint-sparing condylectomy has often been employed without the need for OC fusion. The biomechanics of the joint-sparing technique have not been reported. Authors of the present study hypothesized that the clinically relevant joint-sparing condylectomy would result in added stability of the craniovertebral junction as compared with earlier reports.


Multidirectional in vitro flexibility tests were performed using a robotic spine-testing system on 7 fresh cadaveric spines to assess the effect of sequential unilateral joint-sparing condylectomy (25%, 50%, 75%, 100%) in comparison with the intact state by using cardinal direction and coupled moments combined with a simulated head weight “follower load.”


The percent change in range of motion following sequential condylectomy as compared with the intact state 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 values at 100% condylectomy were statistically significant (p < 0.05). With coupled motions, however, −3.9%, 6.6%, 35.8%, and 142.4% increases in AR+F and 27.3%, 32.7%, 77.5%, and 175.5% increases in AR+E were found. Values for 75% and 100% condyle resection were statistically significant in AR+E.


When tested in the traditional cardinal directions, a 50% joint-sparing condylectomy did not significantly increase motion. However, removing 75% of the condyle may necessitate fusion, as a statistically significant increase in motion was found when E was coupled with AR. Clinical correlation is ultimately needed to determine the need for OC fusion.

ABBREVIATIONS AR = axial rotation; CVJ = craniovertebral junction; FE = flexion-extension; HWL = head weight load; LB = lateral bending; O = occiput; OC = occipitocervical; ROM = range of motion; SOC+C1 = suboccipital craniectomy with C-1 laminectomy.

Article Information

Correspondence Varun R. Kshettry, Department of Neurological Surgery, Neurological Institute, Cleveland Clinic, 9500 Euclid Ave., S-40, Cleveland, OH 44195. email:

INCLUDE WHEN CITING Published online October 14, 2016; DOI: 10.3171/2016.7.JNS16293.

Disclosures Mr. Colbrunn receives royalties from the Cleveland Clinic Foundation Innovations Department.

© AANS, except where prohibited by US copyright law.



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    Testing setup. The specimen is rigidly fixed at the O and C-3. A navigation reference frame is rigidly fixed to the O, and titanium microscrew fiducial markers are registered. Optoelectric sensors are placed in the O, C-1, and C-2 to record relative ROM. A 6-axis robotic spine-testing system was used to apply head weight simulation and loading and unloading cycles of continuous moment. Figure is available in color online only.

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    A: Sagittal CT demonstrating occipital condyle anatomy with a rectangular main body (green) and concave articular surface (red). B: View of the foramen magnum. Yellow indicates the area of unilateral suboccipital craniectomy. Each condyle was divided into 4 quadrants along the anatomical transverse axis. Dotted lines indicate approximate location and course of the hypoglossal canal (HC). Figure is available in color online only.

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    Stereotactically guided joint-sparing condylectomy. Navigation plan (A and B) demonstrating 25% (green), 50% (red), and 75% (blue) resection lines. Navigation pointer on the lateral margin (C) and the medial margin (D) of the 25% condylar resection line. Blue dotted lines in the photographs (C and D) indicate the posterior O–C1 joint. Figure is available in color online only.

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    Occiput–C1 mean ROM (% change compared with intact state) in cardinal (A) and coupled (B) movements across various surgical conditions. Asterisks indicate statistical significance compared with the intact state.





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