Posterior instrumentation for laminar screw of C2: a dimensional anatomic study of axis

Abstracts

INTRODUÇÃO: A articulação atlantoaxial possui mecanismos estabilizadores C1-C2, ligamentares, ósseos e capsulares, mantendo a relação anatômica adequada entre C1 e C2. A falha, traumática ou atraumática, isolada ou um conjunto destes mecanismos leva à instabilidade atlantoaxial, podendo culminar em alterações neurológicas, dor e limitação da mobilidade cervical. Casos com déficit neurológico e de instabilidade moderada a grave, são passíveis de tratamento cirúrgico. Desde 1910 inúmeras técnicas de estabilização cirúrgica C1-C2 são praticadas e mesmo recentemente novas técnicas de estabilização C1-C2 vêm sendo desenvolvidas. Novas técnicas foram desenvolvidas utilizando parafusos bilaterais na massa lateral de C1 e na lâmina de C2, conectados por barras. OBJETIVO: Mensurar as dimensões da lâmina de C2 para avaliar a segurança e dimensão do parafuso a ser utilizado, pela técnica de Wright. MÉTODOS: Estudo anatômico com 29 cadáveres adultos dissecando a lâmina de C2, aferindo medidas externa e interna da lâmina no plano sagital, coronal e axial. RESULTADOS: A média das medidas das porções médias externas das lâminas de C2 foi 5,83 mm, das quais 8,93% foram abaixo de 3,5mm. CONCLUSÃO: Sugerimos um estudo tomográfico pré-operatório, para identificar pacientes com lâminas menores e logo em maior risco.

Axis; Parafusos ósseos; Coluna cervical; Articulação atlanto-axial; Instrumentação

ORIGINAL ARTICLE

Posterior instrumentation for laminar screw of C2: a dimensional anatomic study of axis

Luiz Sorrenti; Mauricio Masasi Iamaguchi; Rafael Barban Sposeto; Marcelo Poderoso de Araújo; Alexandre Sadao Iutaka; Tarcisio Eloy Pessoa de Barros Filho; Ivan Dias da Rocha

LIM 41 - Laboratory of Medical Investigation of the Musculoskeletal System, Department of Orthopaedics and Traumatology-HC/FMUSP

Correspondences to

ABSTRACT

INTRODUCTION: The atlantoaxial joint has stabilizing mechanisms (bones, ligaments and capsules) keeping the anatomic relation between C1-C2. When one or more of those mechanisms fail, in a traumatic or non-traumatic way, an instability atlantoaxial occurs leading to neurologic impairment, pain and cervical mobility limitation. Neurologic impairment and moderate to severe instability may need surgical treatment. Since 1910, a great number of C1-C2 stabilization techniques have been developed, and, even recently, new methods have been developed. New techniques using bilateral screws on C1 lateral mass and C2 laminar screws connected by rods were developed.

OBJECTIVE: To measure C2 lamina size in order to evaluate the safety and the dimension of the screw used in Wright´s technique.

METODS: We conducted an anatomic study with 29 human adult cadavers whose C2 laminas were dissected and measured, in sagittal, coronal and axial planes.

RESULTS: The average measure of the external middle portion of C2 lamina was 5,83mm, and 8,93% were below 3,5mm.

CONCLUSION: We suggest a tomographic study prior to surgery in order to identify patients with smaller laminas, thus presenting a higher risk.

Keywords: Axis. Bone screws. Spine. Atlanto-axial joint. Instrumentation.

INTRODUCTION

Atlanto-axial joint stability is provided by C1-C2 stabilizing mechanisms, which include: alar ligaments, Atlas cross-like ligament (transverse, upper and lower longitudinal), apical ligament, tooth of Axis, joint capsule, anterior and posterior Atlanto-axial membrane, tectorial membrane, joint facets, C1 and C2 bone integrity, among other passive and active mechanisms. If one or more fail, atlanto-axial instability of traumatic, non-traumatic or congenital etiology would result, ultimately leading to neurological changes, pain, and/or restricted cervical motion.

Surgery is usually reserved for patients with neurological deficit and in cases of moderate to severe instability.¹ Indications for posterior C1-C2 stabilization are numerous and include type-II and type-III odontoid process fractures (when associated to Jefferson fracture or atlanto-axial joint fracture and failure of other treatment methods), congenital C2 malformations (e.g., odontoideum and odontoid agenesia), degenerative diseases, inflammatory diseases, tumors, infections associated to atlanto-axial instability, postoperative instability (laminectomies and joint facet removal), C1-C2 ligament laxity with augmented atlanto-dental interval (e.g., rheumatoid arthritis).

The assessment of currently available C1-C2 arthrodesis techniques suggest that fixation with intralaminar screws on C2 may reduce the risk of neurological injuries, while increasing success rates in arthrodeses and reducing the risk of pseudoarthrosis.

The objective of this study was to measure, by dissecting cadaver's posterior C2 elements, the internal and external dimensions of C2 lamina in order to assess the safety and size of screws to be used.

MATERIALS AND METHODS

An anatomical study on 29 adult (> 18 years old) cadavers sourced by the Death Examination Service of University of São Paulo's Medical School, as approved by the committee of ethics of University of São Paulo's Hospital das Clínicas. The pieces were randomly selected between June 2006 and June 2007.

Exclusion criteria included the following:

- cervical surgery;

- history of cervical trauma;

- osteometabolic diseases;

- rheumatic diseases;

- immature skeleton, and;

- congenital cervical abnormalities.

The cadavers were preserved, and no decomposed cadavers were used.

The study starts with the body in pronation with a head support, providing a posterior longitudinal access port (approximately 10 cm) to the high cervical spine. The posterior arch of the second cervical vertebra is carefully dissected, as well as the arches of the first and third cervical vertebrae. The spinous process, the laminae and C3 pedicles are resected in situ, favoring an appropriate positioning of the instrumentation and the osteotomy of C2 pedicles. The block, including a portion of the pedicles, lateral masses, laminae and the spinous process is resected with delicate chisel and saws.

Any adhered soft part is carefully resected from posterior C2 arch, leaving the anatomical piece composed only by bone. These are measured with an accurate pachymeter and goniometer, with the following parameters being checked:

1. Total laminar length (C), at cross-sectional plane, measured between the center of the spinous process and the beginning of lateral masses (Figure 1a)

2. Laminar thickness (cross-sectional plane) measured at three points: close to spinous process (medial - M), close to lateral mass (lateral - L) and at mid-distance between these two measurements (mid - m). (Figure 1b)

3. Laminar height (sagittal plane) measured at three points: close to spinous process (medial - M), close to lateral mass (lateral - L) and at mid-distance between these two measurements (mid - m). (Figure 2)

4. Interlaminar angle (β) formed by anterior portions of C2 laminae, the vertex of which is the base of spinous process (Figure 3).

After measuring these points, the pieces are cross-sectioned (Figure 4) at the center of its height using a delicate saw. Then, the following parameters are measured:

5. Internal laminar thickness (cross-sectional plane), measured from the thickness of laminar spongy bone, inner interval between bone tables forming laminae, measured at three points, close to spinous process, close to lateral mass and at half distance between these two measurements.

6. Internal laminar length (cross-sectional plane) distance between spinous process base and the union between lamina and contralateral paars.

After measuring these points, a statistical analysis is carried out with the interlaminar angle, length and width of C2 lamina (both intramedullar and extracortical) comparing these values to available laminar screws, showing if there is enough intramedullary space for this kind of fixation.

The descriptive statistical analysis was carried out with the mean and standard deviation values for the measurements taken on pieces.

RESULTS

Twenty-eight cadavers were assessed, after one case was excluded for presenting C2-C3 vertebrae fusion. In this sample, there were 20 men and nine women, including eleven Caucasians, ten non-Caucasians and eight African-descendents.

The mean age of the cadavers was 58.71 years (range: 31-91). The mean height was 1.71 meters, ranging from 1.60 to 1.90. They weighted, in average, 67.10 kilos (49.9 to 85) and all deaths were resultant from clinical factors, without associated trauma.

The mean angle between C2 laminae was 88.61 degrees (range: 72 -110) and other measurements are shown on tables 1 to 5.

DISCUSSION

Since 1910, countless surgical C1-C2 stabilization techniques have been practiced for treating C1-C2 instabilities, and, recently, new C1-C2 stabilization techniques are being developed. In 1910, Mixter and Osgood² described the ligation technique for C1-C2 spinous processes with silk; in 1939, Gallie³ described the ligation of C1-C2 laminae; in 1978, Brooks and Jenkins⁴ described an alternative C1-C2 laminae ligation method, which was subsequently modified by Dickman and Sonntag.⁵ In 1980, interlaminar clamps⁶ became popular. Posterior fixation with transarticular C1-C2 screws and screws on C1 lateral mass, on C2 pedicle and lamina were more recently developed.

All these techniques are susceptible to failure, complications and technical challenges. Sublaminar ligation techniques, passing through C1 arch³, or double passing through C1 and C2⁴ present risks of neurological injuries inherent to the act of passing sublaminar wires, in addition to the need of a stiff external orthosis and a high rate of arthrodesis non-union, which can range from 9% to 20%.^7-9 Some authors state that non-union is related to little mechanical stability, especially rotational, provided by techniques using ligation alone (Gallie or Brooks-Jenkins).^10-14

The technique described by Magerl¹⁵ shows good stability and several clinical studies evidenced its effectiveness in obtaining arthrodesis and good clinical outcomes. It uses a three-point fixation system, with two transarticular C1-C2 screws (right and left) associated to ligation, similarly to the technique by Gallie. No stiff orthosis is required, and arthrodesis rates are high.^15,16 However, anatomical studies showed that vertebral artery can be damaged by that technique, especially when anatomical changes are present on its path close to C2 paars (medial or superior migration of the artery), preventing the use of this technique in up to 20% of the cases.^16-20 This technique becomes unfeasible when a non-reducible C1 sub-dislocation > 50% occurs over C2.²¹ The verticalized screw insertion angle may represent an additional technical challenge, preventing its use in patients with severe thoracic kyphosis and potentially leading to the need of an enlarged access port up to C6-C7 in order to get the right screw insertion angle.²²

In this situation, we can use the technique described by Harms^13,20,23, using a fixation system with screws on C1 lateral masses connected by means of nails to screws inserted on C2 pedicle. In this technique, there is a potential to reduce the sub-dislocation, and, in most cases, inserting the screw on C2 pedicle is possible, because it presents a more medial and inferior position to the transarticular screw in the technique described by Magerl.^13-15 Several studies report few little problems in inserting screws on C1 lateral mass, as in the technique by Harms^24-26, but some patients have a C2 pedicle not enabling screws to be passed through^22,24-27 due to the same changes described for Magerl's technique.

Wright et al.²⁸ developed a fixation technique between C1 and C2 using bilateral screws on C1 lateral mass and on C2 laminae, connected by nails. In a series of 10 cases, a low complication rate and an appropriate stability of the fixated segment are reported. These good results have been attributed to a reduced risk of iatrogenic injuries when inserting screws, since the insertion sites are not so close to vascular or neural structures.^20-22,24-28

The biomechanical resistance in the technique by Wright was reported in a study with anatomical cadaver pieces, showing high synthesis stability.²⁰

Wright et al.²³ and Cassinelli et al.²⁹ in anatomical studies with dried cadaver bones showed the feasibility of inserting screws on C2 laminae. Cassinelli et al.²⁹ in their study on 420 dried cadaver bones found a mean laminar thickness of 5.7 mm, 70.5% of which presenting thickness above or equal to 5 mm, 92.6% above or equal to 4 mm, and 96.7% above or equal to 3.5 mm, which is consistent to our study data, where the mean external thickness measurements of the mid laminar portions was 5.83 mm, with 76.78% showing thickness above or equal to 5 mm, 91.07% above or equal to 4 mm, and 91.07% above or equal to 3.5 mm. This small percentage variation is probably due to a reduced number of anatomical pieces.

CONCLUSION

Our study corroborates the conclusion of previous studies, showing the feasibility of inserting intralaminar screws on C2 vertebra.

As we detected 8.93% of specimens with external laminar thickness below 3.5 mm (diameter of screws usually employed), we suggest that a preoperative tomographic study is conducted for identifying patients at higher surgical risk.

REFERENCES

• 1. Szpalski M, Gunzburg R. The degenerative cervical spine. J Bone Joint Surg Br. 2001;83:933-4.
• 2. Mixter SJ, Osgood RB. Traumatic lesions of the atlas and axis. Ann Surg. 1910;51:193-207.
• 3. Gallie WE. Fractures and dislocations of cervical spine. Am J Surg. 1939;46:495-9.
• 4. Brooks AL, Jenkins EB. Atlantoaxial arthrodesis by the wedge compression method. J Bone Joint Surg Am. 1978:60:279-84.
• 5. Dickman CA, Sonntag VK, Papadopoulos SM, Hadley MN. The interspinous method of posterior atlantoaxial arthrodesis. J Neurosurg. 1991;74:190-8.
• 6. Holness RO, Huestis WS, Howes WJ, Langille RA. Posterior stabilization with an interlaminar clamp in cervical injuries: technical note and review of the long term experience with the method. Neurosurg. 1984;14:318-22.
• 7. Hamilton JD, Gordon MM, McInnes IB, Johnston RA, Madhok R, Capell HA. Improved medical and surgical management of cervical spine disease in patients with rheumatoid arthritis over 10 years. Ann Rheum Dis. 2000;59:434-8.
• 8. Kolen ER, Schmidt MH. Rheumatoid arthritis of the cervical spine. Semin Neurol. 2002;22:179-86.
• 9. Clark CR, Goetz DD, Menezes AH. Arthrodesis of the cervical spine in rheumatoid arthritis. J Bone Joint Surg Am. 1989;71:381-92.
• 10. Richter M, Schmidt R, Claes L, Puhl W, Wilke HJ. Posterior atlantoaxial fixation: biomechanical in vitro comparison of six different techniques. Spine. 2002;27:1724-32.
• 11. Oda I, Abumi K, Sell LC, Haggerty CJ, Cunningham BW, McAfee PC. Biomechanical evaluation of five different occipito-atlanto-axial fixation techniques. Spine. 1999;24:2377-82.
• 12. Puttlitz CM, Melcher RP, Kleinstueck FS, Harms J, Bradford DS, Lotz JC. Stability analysis of craniovertebral junction fixation techniques. J Bone Joint Surg Am. 2004;86:561-8.
• 13. Melcher RP, Puttlitz CM, Kleinstueck FS, Lotz JC, Harms J, Bradford DS. Biomechanical testing of posterior atlantoaxial fixation techniques. Spine. 2002;27:2435-40.
• 14. Henriques T, Cunningham BW, Olerud C, Shimamoto N, Lee GA, Larsson S et al. Biomechanical comparison of five different atlantoaxial posterior fixation techniques. Spine. 2000; 25:2877-83.
• 15. Abou Madawi A, Solanki G, Casey AT, Crockard HA. Variation of the groove in the axis vertebra for the vertebral artery. Implications for instrumentation. J Bone Joint Surg Br. 1997;79: 820-3.
• 16. Madawi AA, Casey AT, Solanki GA, Tuite G, Veres R, Crockard HA. Radiological and anatomical evaluation of the atlantoaxial transarticular screw fixation technique. J Neurosurg. 1997;86:961-8.
• 17. Neo M, Matsushita M, Iwashita Y, Yasuda T, Sakamoto T, Nakamura T. Atlantoaxial transarticular screw fixation for a high-riding vertebral artery. Spine. 2003;28:666-70.
• 18. Farey ID, Nadkarni S, Smith N. Modified Gallie technique versus transarticular screw fixation in C1-C2 fusion. Clin Orthop Relat Res. 1999;(359):126-35.
• 19. Wright NM, Lauryssen C. Vertebral artery injury in C1-C2 transarticular screw fixation: results of a survey of the AANS/CNS section on disorders of the spine and peripheral nerves. American Association of Neurological Surgeons/Congress of Neurological Surgeons. J Neurosurg. 1998;88: 634-40.
• 20. Gorek J, Acaroglu E, Berven S, Yousef A, Puttlitz CM. Constructs incorporating intralaminar C2 screws provide rigid stability for atlantoaxial fixation. Spine. 2005;30:1513-8.
• 21. Song GS, Theodore N, Dickman CA, Sonntag VK. Unilateral posterior atlantoaxial transarticular screw fixation. J Neurosurg. 1997;87:851-5.
• 22. Resnick DK, Lapsiwala S, Trost GR. Anatomic suitability of the C1-C2 complex for pedicle screw fixation. Spine. 2002;27:1494-8.
• 23. Harms J, Melcher RP. Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine. 2001;26:2467-71.
• 24. Wang MY, Samudrala S. Cadaveric morphometric analysis for atlantal lateral mass screw placement. Neurosurgery. 2004;54:1436-9.
• 25. Currier BL, Todd LT, Maus TP, Fisher DR, Yaszemski MJ. Anatomic relationship of the internal carotid artery to the C1 vertebra: A case report of cervical reconstruction for chordoma and pilot study to assess the risk of screw fixation of the atlas. Spine. 2003;28:E461-7.
• 26. Tan M, Wang H, Wang Y, Zhang G, Yi P, Li Z et al. Morphometric evaluation of screw fixation in atlas via posterior arch and lateral mass. Spine. 2003;28:888-95.
• 27. Bozbuga M, Ozturk A, Ari Z, Sahinoglu K, Bayraktar B, Cecen A. Morphometric evaluation of subaxial cervical vertebrae for surgical application of transpedicular screw fixation. Spine. 2004;29:1876-80.
• 28. Wright NM. Posterior C2 fixation using bilateral, crossing C2 laminar screws: case series and technical note. J Spinal Disord Tech. 2004;17:158-62.
• 29. Cassinelli E, Lee M, Skalak A, Ahn N, Wright N. Anatomic considerations for the placement of C2 laminar screws. Spine. 2006;31:2767-71.

Publication Dates

• Publication in this collection
  11 Sept 2009
• Date of issue
  2009

History

• Accepted
  14 Sept 2008
• Received
  11 June 2008