Neurosurgical forum Letters to the editor
Occipital condyle to cervical spine screw and rod fixation To The Editor: We read with interest the article by Frankel et al.2 (Frankel BM, Hanley M, Vandergrift A, et al: Posterior occipitocervical (C0–3) fusion using polyaxial occipital condyle to cervical spine screw and rod fixation: a radiographic and cadaveric analysis. Technical note. J Neurosurg Spine 12:509–516, May 2010). Numerous conditions affect the occipitocervical junction, requiring treatment with occipitocervical fixation. In this paper, the authors present their technique of craniocervical fixation achieved with the cephalad extension of posterior C1–3 polyaxial screw and rods to polyaxial screws placed in the occipital condyles. They retrospectively analyzed occipital condyle morphology obtained from CT analyses of 40 patients with normal cervical spines, evaluated occipital condyle screw placement feasibility in 4 cadavers, and provided a case report of a 70-year-old woman with rheumatoid arthritis, basilar invagination, and atlantoaxial instability who was treated with this novel technique. Based on radiographic analysis of occipital condyle anatomy, they concluded that on average a 3.5-mm-diameter, 20- to 30-mm-long screw can be safely placed at an angle of 20°–33° from the sagittal plane. Overall, measuring the condylar heights (mean [± SD] 10.8 ± 1.5 mm, range 8.1–15.0 mm), widths (mean 11.1 ± 1.4 mm, range 8.5–14.2 mm), lengths (20.3 ± 2.1 mm, range 15.4–24.6 mm), and angles (mean 32.8° ± 5.2°, range 20.2°–45.8°) by using CT studies is an accurate and precise method. This finding correlates with the results of prior anatomical studies of occipital condyles and is important in the planning of craniovertebral junction surgery. We would like to make a few comments on this paper: First, the statement “This paper contains the first description and follow-up of this technique in a living patient” is inaccurate. The first description and follow-up of this technique was already published by our team.3 Our manuscript was submitted in March 6, 2008, and accepted for publication on March 6, 2009. Moreover, we have used our technique with success, and our first clinical series has already been published.1 Second, there are a few technical differences and similarities between our approach and that described by Frankel et al. In their approach, the occipital condyle entry point is usually lateral to the condylar canal (containing the occipital emissary vein) at the lateral edge of the condylar fossa. In our technique, the condylar entry point corresponds to the midcondylar area, 4 to 5 mm lateral to the foramen magnum on the axial plane and 1 to 2 mm J Neurosurg: Spine / Volume 21 / October 2014
rostral to the atlantooccipital joint.4 In the technique of Frankel et al., caudal-cranial angulation is determined by placing the hand drill in the pilot hole with its shaft tangential to and abutting the skull base. Depending on condylar, skull base, and hypoglossal canal anatomy, the overall trajectory of occipital condyle screws is usually 10° cranial or caudal to the horizontal plane. In our technique, the maximal superior screw angulation in the sagittal plane was 5° (limited by the angulation of the occipital bone). Frankel et al. used bilateral 3.5-mmdiameter, 20- to 30-mm-long, medially convergent occipital condyle screws, noting that they believe these screws should be placed at an angle preferably 20°–33° from the sagittal plane. In our technique, significant flexibility was found in terms of the screw angulation relative to the axial plane that would allow good bone purchase. Screw medialization ranged from 12° to 22° (mean 17°). We safely used 30- to 32-mm-length screws with 20 to 24 mm of bicortical condylar purchase, which may decrease complications related to unicortical screw purchase. Approximately 12 mm of the unthreaded portion of the screw remained superficial to the posterior cortex of the condyle, allowing the polyaxial portion of the screw to lie above the posterior arch of C-1 in order to avoid compression of the vertebral artery by the rods.5 We concur with the authors that it appears that anatomical reference points may be sufficiently reliable to guide screw placement. However, the use of fluoroscopy/ image guidance and intraoperative electromyographic nerve monitoring may be necessary, especially during the early phases of clinical trials, to ensure safe screw placement. This novel transcondylar screw placement is still in evolution, and we hope that others will work closely in collegiality to enhance its potential development in the future so that we can include this in our armamentarium when dealing with complex cases requiring occipital cervical fusion. Juan S. Uribe, M.D. Edwin Ramos, M.D. Sammy Youssef, M.D. Fernando L. Vale, M.D. University of South Florida Tampa, FL Ali A. Baaj, M.D. Johns Hopkins University Baltimore, MD
Disclosure Dr. Uribe reports a consultant relationship with NuVasive.
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Neurosurgical forum References 1. Ahmadian A, Dakwar E, Vale FL, Uribe JS: Occipitocervical fusion via occipital condylar fixation: a clinical case series. J Spinal Disord Tech 27:232–236, 2014 2. Frankel BM, Hanley M, Vandergrift A, Monroe T, Morgan S, Rumboldt Z: Posterior occipitocervical (C0–3) fusion using polyaxial occipital condyle to cervical spine screw and rod fixation: a radiographic and cadaveric analysis. Technical note. J Neurosurg Spine 12:509–516, 2010 3. Uribe JS, Ramos E, Baaj A, Youssef S, Vale FL: Occipital cervical stabilization utilizing occipital condyles for cranial fixation: technical case report. Neurosurgery 65:E1216–E1217, 2009 4. Uribe JS, Ramos E, Vale FL: Feasibility of occipital condyle screws placement for occipitocervical fixation: a cadaveric
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study and description of a novel technique. J Spinal Disord Tech 21:540–546, 2008 5. Uribe JS, Ramos E, Youssef AS, Levine N, Turner AW, Johnson WM, et al: Craniocervical fixation with occipital condyle screws: biomechanical analysis of a novel technique. Spine (Phila Pa 1976) 35:931–938, 2010
Response: No response was received from the authors of the original article.
Please include this information when citing this paper: published online July 18, 2014; DOI: 10.3171/2011.9.SPINE10327. ©AANS, 2014
J Neurosurg: Spine / Volume 21 / October 2014
Occipital condyle to cervical spine screw and rod fixation To The Editor: We read with interest the article by Frankel et al.2 (Frankel BM, Hanley M, Vandergrift A, et al: Posterior occipitocervical (C0–3) fusion using polyaxial occipital condyle to cervical spine screw and rod fixation: a radiographic and cadaveric analysis. Technical note. J Neurosurg Spine 12:509–516, May 2010). Numerous conditions affect the occipitocervical junction, requiring treatment with occipitocervical fixation. In this paper, the authors present their technique of craniocervical fixation achieved with the cephalad extension of posterior C1–3 polyaxial screw and rods to polyaxial screws placed in the occipital condyles. They retrospectively analyzed occipital condyle morphology obtained from CT analyses of 40 patients with normal cervical spines, evaluated occipital condyle screw placement feasibility in 4 cadavers, and provided a case report of a 70-year-old woman with rheumatoid arthritis, basilar invagination, and atlantoaxial instability who was treated with this novel technique. Based on radiographic analysis of occipital condyle anatomy, they concluded that on average a 3.5-mm-diameter, 20- to 30-mm-long screw can be safely placed at an angle of 20°–33° from the sagittal plane. Overall, measuring the condylar heights (mean [± SD] 10.8 ± 1.5 mm, range 8.1–15.0 mm), widths (mean 11.1 ± 1.4 mm, range 8.5–14.2 mm), lengths (20.3 ± 2.1 mm, range 15.4–24.6 mm), and angles (mean 32.8° ± 5.2°, range 20.2°–45.8°) by using CT studies is an accurate and precise method. This finding correlates with the results of prior anatomical studies of occipital condyles and is important in the planning of craniovertebral junction surgery. We would like to make a few comments on this paper: First, the statement “This paper contains the first description and follow-up of this technique in a living patient” is inaccurate. The first description and follow-up of this technique was already published by our team.3 Our manuscript was submitted in March 6, 2008, and accepted for publication on March 6, 2009. Moreover, we have used our technique with success, and our first clinical series has already been published.1 Second, there are a few technical differences and similarities between our approach and that described by Frankel et al. In their approach, the occipital condyle entry point is usually lateral to the condylar canal (containing the occipital emissary vein) at the lateral edge of the condylar fossa. In our technique, the condylar entry point corresponds to the midcondylar area, 4 to 5 mm lateral to the foramen magnum on the axial plane and 1 to 2 mm J Neurosurg: Spine / Volume 21 / October 2014
rostral to the atlantooccipital joint.4 In the technique of Frankel et al., caudal-cranial angulation is determined by placing the hand drill in the pilot hole with its shaft tangential to and abutting the skull base. Depending on condylar, skull base, and hypoglossal canal anatomy, the overall trajectory of occipital condyle screws is usually 10° cranial or caudal to the horizontal plane. In our technique, the maximal superior screw angulation in the sagittal plane was 5° (limited by the angulation of the occipital bone). Frankel et al. used bilateral 3.5-mmdiameter, 20- to 30-mm-long, medially convergent occipital condyle screws, noting that they believe these screws should be placed at an angle preferably 20°–33° from the sagittal plane. In our technique, significant flexibility was found in terms of the screw angulation relative to the axial plane that would allow good bone purchase. Screw medialization ranged from 12° to 22° (mean 17°). We safely used 30- to 32-mm-length screws with 20 to 24 mm of bicortical condylar purchase, which may decrease complications related to unicortical screw purchase. Approximately 12 mm of the unthreaded portion of the screw remained superficial to the posterior cortex of the condyle, allowing the polyaxial portion of the screw to lie above the posterior arch of C-1 in order to avoid compression of the vertebral artery by the rods.5 We concur with the authors that it appears that anatomical reference points may be sufficiently reliable to guide screw placement. However, the use of fluoroscopy/ image guidance and intraoperative electromyographic nerve monitoring may be necessary, especially during the early phases of clinical trials, to ensure safe screw placement. This novel transcondylar screw placement is still in evolution, and we hope that others will work closely in collegiality to enhance its potential development in the future so that we can include this in our armamentarium when dealing with complex cases requiring occipital cervical fusion. Juan S. Uribe, M.D. Edwin Ramos, M.D. Sammy Youssef, M.D. Fernando L. Vale, M.D. University of South Florida Tampa, FL Ali A. Baaj, M.D. Johns Hopkins University Baltimore, MD
Disclosure Dr. Uribe reports a consultant relationship with NuVasive.
685
Neurosurgical forum References 1. Ahmadian A, Dakwar E, Vale FL, Uribe JS: Occipitocervical fusion via occipital condylar fixation: a clinical case series. J Spinal Disord Tech 27:232–236, 2014 2. Frankel BM, Hanley M, Vandergrift A, Monroe T, Morgan S, Rumboldt Z: Posterior occipitocervical (C0–3) fusion using polyaxial occipital condyle to cervical spine screw and rod fixation: a radiographic and cadaveric analysis. Technical note. J Neurosurg Spine 12:509–516, 2010 3. Uribe JS, Ramos E, Baaj A, Youssef S, Vale FL: Occipital cervical stabilization utilizing occipital condyles for cranial fixation: technical case report. Neurosurgery 65:E1216–E1217, 2009 4. Uribe JS, Ramos E, Vale FL: Feasibility of occipital condyle screws placement for occipitocervical fixation: a cadaveric
686
study and description of a novel technique. J Spinal Disord Tech 21:540–546, 2008 5. Uribe JS, Ramos E, Youssef AS, Levine N, Turner AW, Johnson WM, et al: Craniocervical fixation with occipital condyle screws: biomechanical analysis of a novel technique. Spine (Phila Pa 1976) 35:931–938, 2010
Response: No response was received from the authors of the original article.
Please include this information when citing this paper: published online July 18, 2014; DOI: 10.3171/2011.9.SPINE10327. ©AANS, 2014
J Neurosurg: Spine / Volume 21 / October 2014
