Themistocles S. Protopsaltis, MD. Currently Accepted Radiographic Measurements of Cervical Deformity

Transcription

1 Themistocles S. Protopsaltis, MD Currently Accepted Radiographic Measurements of Cervical Deformity The importance of sagittal alignment has been well established in the thoracolumbar deformity literature. 1-5 More recent studies are beginning to demonstrate that regional cervical sagittal alignment can also affect health related quality of life measures (HRQL). Primary cervical deformities need to be differentiated from compensatory cervical changes to malalignment in subjacent spinal regions. Studies have shown that deformities in the thoracic and lumbar regions can induce reciprocal changes in cervical spinal alignment which become compensatory mechanisms to maintain global standing alignment. 6-8 Differentiating these compensatory changes in the cervical spine from primary cervical deformities is the first step in the analysis of cervical deformity. Conditions such as spondylotic arthropathies, idiopathic cervical paraspinal myopathies and iatrogenic cervical kyphosis can create the most severe primary cervical deformities which can cause the chin-on-chest deformities that compromise horizontal gaze, swallowing, and breathing The majority of the literature on the subject of cervical deformity focuses on the subaxial cervical spine. A classic article demonstrating the link between cervical sagittal alignment and disability measures is that of Tang and colleagues; in a population of patients who underwent posterior cervical fusions, they showed that the postoperative C2-C7 sagittal vertical axis (csva) correlated with the Neck Disability Index (NDI) score and SF-36 Physical Component Score (PCS). 14 Using linear regression analysis they determined that a csva greater than 4 cm corresponds to a moderate disability threshold. 14 Likewise cervical kyphosis has been correlated with poor HRQOL outcomes. 6,12,15 Cervical kyphosis can be progressive resulting in neurologic deterioration, including progressive myelopathy. 15,16 1

2 A csva > 4 cm and cervical kyphosis have been the most commonly reported definitions of cervical deformity in the literature. 14,17 Using these definitions of cervical deformity Smith et al reported a 53% rate of cervical deformity in patients also meeting criteria for thoracolumbar deformity. 17 Ames et al recently proposed a standardized classification system of cervical deformity based on existing clinically relevant parameters within the context of global spinal alignment. 18 It has been shown to have moderate inter-observer and intra-observer reliability, and should provide a common language for studies on quantifying the severity of primary cervical deformity. 18 However, existing definitions of cervical deformity may not be sufficient. For one, cervical kyphosis can be a normal feature of physiologic standing alignment, particularly among younger people who stand with a negative SVA. 19,20 In a study on 106 subjects without neck pain, showed that 34% had cervical kyphosis. 20 Moreover, the csva can be affected by subjacent thoracolumbar mal-alignment. 7,8 Smith and colleagues demonstrated that thoracolumbar deformity patients can have increased csva and this cervical mal-alignment resolves spontaneously with correction of the underlying thoracolumbar deformity. 7 Recent literature on the subject of cervical deformity has begun to focus on the important relationship between T1 slope and cervical lordosis as a means of gauging the presence of cervical deformity The relationship between pelvic incidence and lumbar lordosis has been used effectively as a measure of lumbo-pelvic alignment and it is an effective perioperative tool for planning and executing corrections in lumbar flatback deformity. 3 In fact, sacral slope is more highly correlated with lumbar lordosis and this relationship is mirrored in the cervical spine where T1 slope has been shown to correlate with cervical lordosis, when this relationship is disrupted, subaxial cervical deformity is present or the underlying thoracolumbar deformity is so severe that it creates an excessively large T1 slope that outstrips the ability of cervical spine to balance alignment Protopsaltis et al demonstrated that even in the presence of underlying thoracolumbar deformity, if the mismatch between T1 slope and cervical lordosis (TS-CL) exceeded 17, then cervical deformity is present. 21 Ames and colleagues demonstrated that among patients who had 2

3 undergone cervical fusions, a mismatch exceeding 20 corresponded to a csva of more than 4 cm, the published threshold for cervical deformity. 22 Therefore, the TS-CL relationship can be used as preoperative planning tool to determine the amount of cervical lordosis necessary to improve regional cervical sagittal alignment. 21,22 Looking further into the TS-CL mesurement, the relationship distills down to the C2 slope. If TS-CL = T1 slope (C7 slope - C2 slope), and T1 slope approximates C7 slope in most cases, then TS-CL C2 slope. Protopsaltis et al., proposed C2-Slope as a singular cervical deformity parameter. 26 C2 Slope correlated with both upper cervical and subaxial cervical alignment parameters. C2-Slope has an extremely high correlation with TS-CL (R=0.98, p< 0.001) which is explained by the fact that C2-Slope is a mathematical approximation of TS-CL and therefore C2-Slope is a simple substitution for it (Figure 1). Significant correlations between the upper and lower cervical spine exist in patients with cervical deformities, confirming the existence of inherent compensatory mechanisms to maintain overall balance. The C2-Slope is a useful marker of overall cervical sagittal alignment, acting as a link between the occipitocervical and cervico-thoracic spine. The C2-Slope defines the presence of a mismatch between cervical lordosis and thoracolumbar alignment required to maintain horizontal gaze. 2 3

4 Figure 1: Depiction of the C2-Slope in a patient with flexible dropped head deformity. C2-Slope is a mathematical approximation of TS-CL and therefore C2-Slope is a simple substitution for TS-CL Surgical planning for cervical deformities begins with obtaining appropriate imaging. In addition to MRI and CT scan, long cassette x-rays provide an assessment of the full spine to identify concurrent thoracic and lumbar deformities that may be contributing to the cervical deformity. Smith and colleagues demonstrated the importance of full spine radiographs in a survey study in which 30% of spine surgeons would modify their surgical plan when presented with a long cassette radiograph showing thoracolumbar malalignment. 31 The C2-T1 Pelvic Angle (CTPA) and T1 Pelvic Angle (TPA) have been proposed as a means of determining the relative proportion of cervical and thoracolumbar deformity, respectively (Figure 2). 30 These measures require full-length radiographs with visualization from C2 to the pelvis. When planning cervical fusions, the clinical scenarios in which full spine radiographs should be obtained have not been well established. When the T1 tilt falls outside the range of 13 to 25 degrees, Knott et al recommended long 4

5 cassette radiographs in order to evaluate thoracolumbar malalignment. 32 Kleinberg and colleagues showed that when the T1 slope exceeds 32 degrees, underlying thoracolumbar deformity is likely to be present with a sensitivity of 69% and a specificity of 69%. 35 One potential reason for insufficient correction is the failure to recognize underlying thoracolumbar deformity that can contribute to the cervical malaligment. Sagittal malalignment may persist if the thoracolumbar malalignment is not recognized and addressed concurrently with cervical deformity. Similar to the problem of proximal juctional kyphosis in thoracolumbar deformity correction, unrecognized subjacent deformity may also contribute to distal junctional kyphosis which may further degrade the sagittal correction of the cervical spine. Figure 2: The C2-T1 Pelvic Angle (CTPA) is a global angular measure of cervical sagittal balance and a correlate of C2C7 plumbline. CTPA is the angle of a line from center of C2 to femoral heads (FH) and a line from FH to center of T1. The T1 Pelvic Angle (TPA) is a measure of global sagittal alignment and a 5

6 correlate of C7 SVA. CTPA and TPA account for the relative proportion of cervical and thoracolumbar deformity respectively. In surgical planning, the T1 slope cervical lordosis relationship can be utilized to determine the deficit of cervical lordosis in a given deformity If the T1 slope is greater than 30 degrees or if the T1 pelvic Angle is greater than 20 degrees then an underlying thoracolumbar deformity may need to be addressed concurrently which may be contributing to the cervical sagittal malalignment. 2,32 Kim and colleagues quantified the magnitude of angular and translational corrections obtained by common osteotomies in the cervical spine. 33 They showed that an anterior osteotomy combined with a posterior Smith Peterson osteotomy can provide a similar correction as a cervical pedicle subtraction osteotomy but with less blood loss. However, the determination of anterior or posterior approach requires an assessment of the stiffness of the cervical spine and whether there is anterior or posterior fusion. Hann and colleagues proposed an algorithm for planning the surgical approaches based on whether the cervical deformity is fixed or flexible. 34 Ames and colleagues described a reproducible cervical osteotomy classification based on increasing grades of osteotomy magnitude. 18 These studies provide a common language for communicating and planning cervical deformity corrections. Future directions in cervical deformity will require a reassessment of the clinical impact of these cervical deformities. While a handful of studies have demonstrated correlations between cervical alignment parameters and existing HRQoL measures such as the NDI and SF-36, more recent studies on cervical deformity have failed to corroborate these correlations. 29 Complicating this fact is the wide range of cervical deformities and their etiologic factors such as iatrogenic deformity after fusion, focal cervical kyphotic deformities, and flexible and fixed chin-on-chest deformities resulting from dropped head syndrome and ankylosing spondylitis. While existing measures such as the NDI have been shown to be relevant in common degenerative pathologies, they may not assess and capture the disabling features inherent in cervical sagittal deformity, such as loss of 6

7 horizontal gaze, dysphagia, dyspnea and walking difficulty. 29 Further study is warranted to define assessment domains that are specific to cervical sagittal malalignment. References 1. Glassman SD, Bridwell K, Dimar JR, Horton W, Berven S, Schwab F. The impact of positive sagittal balance in adult spinal deformity. Spine (Phila Pa 1976) Sep 15;30(18): Protopsaltis T, Schwab F, Smith JS, et al. The T1 Pelvic Angle (TPA), a novel radiographic measure of global sagittal deformity, accounts for both pelvic retroversion and truncal inclination and correlates with health-related quality of life. J Bone Joint Surg Am Oct 1;96(19): Legaye J, Duval-Beaupere G, Hecquet J, Marty C. Pelvic incidence: a fundamental pelvic parameter for three-dimensional regulation of spinal sagittal curves. Eur Spine J. 1998;7(2): Lafage V, Schwab F, Patel A, Hawkinson N, Farcy JP. Pelvic tilt and truncal inclination: two key radiographic parameters in the setting of adults with spinal deformity. Spine (Phila Pa 1976) Aug 1;34(17):E Terran J, Schwab F, Shaffrey CI, Smith JS, Devos P, Ames CP, et al. The SRS- Schwab Adult Spinal Deformity Classification: Assessment and Clinical Correlations Based on a Prospective Operative and Nonoperative Cohort. Neurosurgery Jul Protopsaltis TS, Scheer JK, Terran JS, et al. How the neck affects the back: changes in regional cervical sagittal alignment correlate to HRQOL improvement in adult thoracolumbar deformity patients at 2-year follow-up. J Neurosurg Spine In press. 7. Smith JS, Shaffrey CI, Lafage V, et al. Spontaneous improvement of cervical alignment after correction of global sagittal balance following pedicle subtraction osteotomy. J Neurosurg Spine. 2012;17(4):

8 8. Oh T, Scheer JK, Eastlack R, et al. Cervical compensatory alignment changes following correction of adult thoracic deformity: a multicenter experience in 57 patients with a 2-year follow-up. J Neurosurg Spine. 2015;22(6): Moore RE, Dormans JP, Drummond DS, Shore EM, Kaplan FS, Auerbach JD. Chin-on-chest deformity in patients with fibrodysplasia ossificans progressiva. A case series. J Bone Joint Surg Am. 2009;91(6): Lee JS, Youn MS, Shin JK, Goh TS, Kang SS. Relationship between cervical sagittal alignment and quality of life in ankylosing spondylitis. Eur spine J.2015 ;24(6): Gerling MC, Bohlman HH. Dropped head deformity due to cervical myopathy: surgical treatment outcomes and complications spanning twenty years. Spine (Phila Pa 1976) Sep 15;33(20):E Albert TJ, Vacarro A. Postlaminectomy kyphosis. Spine. 1998;23(24): Scheer JK, Tang JA, Smith JS, et al. Cervical spine alignment, sagittal deformity, and clinical implications: a review. J Neurosurg Spine. 2013;19(2): Tang JA, Scheer JK, Smith JS, et al. (2012) The impact of standing regional cervical sagittal alignment on outcomes in posterior cervical fusion surgery. Neurosurgery 71:662 9; discussion Smith JS, Lafage V, Ryan DJ, et al. Association of myelopathy scores with cervical sagittal balance and normalized spinal cord volume: analysis of 56 preoperative cases from the AOSpine North America Myelopathy study. Spine. 2013;38(22 Suppl 1):S Shamji MF, Ames CP, Smith JS, Rhee JM, Chapman JR, Fehlings MG. Myelopathy and spinal deformity: relevance of spinal alignment in planning surgical intervention for degenerative cervical myelopathy. Spine. 2013;38(22 Suppl 1):S Smith J, PhD; Shaffrey, Christopher, MD; Lafage, Virginie, PhD et al. Prevalence and Type of Cervical Deformity Among 470 Adults with Thoracolumbar Deformity. Spine (Phila Pa 1976) Aug 1;39(17):E Ames CP, Smith JS, Eastlack R, et al. Reliability assessment of a novel cervical deformity classification system. J Neurosurg Spine.In press 8

9 19. Kuntz Ct, Levin LS, Ondra SL, Shaffrey CI, Morgan CJ. Neutral upright sagittal spinal alignment from the occiput to the pelvis in asymptomatic adults: a review and resynthesis of the literature. Journal of neurosurgery. Spine. Feb 2007;6(2): Le Huec JC, Demezon H, Aunoble S. Sagittal parameters of global cervical balance using EOS imaging: normative values from a prospective cohort of asymptomatic volunteers. Eur Spine J Jan;24(1): Protopsaltis, T. S. et al. T1 slope minus cervical lordosis (TS-CL), the cervical answer to PI-LL, defines cervical sagittal deformity in patients undergoing thoracolumbar osteotomy. in Cervical Spine Research Society (CSRS) Annual Meeting; December 5-7 (2013). 22. Ames et al. T1 slope minus cervical lordosis. Cervical Spine Research Society (CSRS) Annual Meeting; December 5-7 (2013). 23. Kim TH, Lee SY, Kim YC, Park MS, Kim SW. T1 slope as a predictor of kyphotic alignment change after laminoplasty in patients with cervical myelopathy. Spine (Phila Pa 1976). Jul ;38(16):E Blondel BS, F; Ames, CP; LeHuec, JC; Smith; JS, Demakakos, J et a;. The crucial role of cervical alignment in regulating sagittal spino-pelvic alginment in human standing posture. Podium presented at 19th International Meeting on Advanced Spine Techniques; July , 2012; Istabul, Turkey. 25. Vialle R, Levassor N, Rillardon L, Templier A, Skalli W, Guigui P. Radiographic analysis of the sagittal alignment and balance of the spine in asymptomatic subjects. J Bone Joint Surg Am Feb;87(2): Protopsaltis TS, Ramchandran S, Lafage R, Smith JS, et al. The importance of C2-Slope as a singular marker of cervical deformity and the link between uppercervical and cervico-thoracic alignment among cervical deformity patients. Cervical Spine Research Society Annual Meeting (CSRS), December 2016, Toronto, Canada. 27. Zeidman SM, Ducker TB: Rheumatoid arthritis: Neuroanatomy, compression, and grading of deficits. Spine 1994;19:

10 28. Protopsaltis TS, Lafage R, Lafage V, Sciubba D, Hamilton K, Smith JS, et al. Novel cervical angular measures account for both upper cervical compensation and sagittal alignment. International Meeting on Advanced Spine Techniques (IMAST), July 2015, Kuala Lumpur, Malaisia 29. Protopsaltis TS, Lafage R, Lafage V, Sciubba D, Hamilton K, Smith JS, et al. Towards a Cervical Deformity Outcome Instrument: Principal Component Analysis of 89 HRQL Questions in 466 Patients with Cervical Deformity. International Meeting on Advanced Spine Techniques (IMAST), July 2015, Kuala Lumpur, Malaisia. 30. Protopsaltis T, Terran J, Smith J, Klineberg E, Mundis G, Kim HJ, et al. Cervical Sagittal Deformity Develops after PJK in Adult Thoracolumbar Deformity Correction: Radiographic Analysis Utilizing a Novel Global Sagittal Parameter, the CTPA. International Meeting on Advanced Spine Techniques (IMAST), July 2013, Vancouver, British Columbia, Canada. 31. Ramchandran S, Smith JS, Ailon T, Klineberg E, Shaffrey C, Lafage L, et al. Assessment of Impact of Long-Cassette Standing X-Rays on Surgical Planning for Cervical Pathology: An International Survey of Spine Surgeons. International Meeting on Advanced Spine Techniques (IMAST), July 2015, Kuala Lumpur, Malaisia 32. Knott PT, Mardjetko SM, Techy F. The use of the T1 sagittal angle in predicting overall sagittal balance of the spine.spine. 2010;10(11): Kim HJ, Piyaskulkaew C, Riew KD. Comparison of Smith-Petersen osteotomy versus pedicle subtraction osteotomy versus anterior-posterior osteotomy types for the correction of cervical spine deformities. Spine (Phila Pa 1976) Feb 1;40(3): Hann S, Chalouhi N, Madineni R, Vaccaro AR, Albert TJ, Harrop J, Heller JE. An algorithmic strategy for selecting a surgical approach in cervical deformity correction. Neurosurg Focus May;36(5):E Klineberg, Carlson, Protopsaltis et al. Can Measurements on Cervical Radiographs Predict Concurrent Thoracolumbar Deformity and Provide a 10

11 Threshold for Acquiring Full-Length Spine Radiographs? North American Spine Society (NASS), October 2015, Chicago. 11