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

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OBJECTIVE

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.

METHODS

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.”

RESULTS

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.

CONCLUSIONS

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: varunkshettry@gmail.com.

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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Figures

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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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