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Cervical Radiographical Alignment: Comprehensive Assessment Techniques and Potential Importance in Cervical Myelopathy

Ames, Christopher P., MD*; Blondel, Benjamin, MD†,‡; Scheer, Justin K., BS§; Schwab, Frank J., MD; Le Huec, Jean-Charles, MD, PhD; Massicotte, Eric M., MD, MSc, FRCS(C); Patel, Alpesh A., MD, FACS**; Traynelis, Vincent C., MD††; Kim, Han Jo, MD‡‡; Shaffrey, Christopher I., MD§§; Smith, Justin S., MD, PhD§§; Lafage, Virginie, PhD

doi: 10.1097/BRS.0b013e3182a7f449
Influence of Spinal Deformity on Management and Outcome of Cervical Spondylotic Myelopathy
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Study Design. Narrative review.

Objective. To provide a comprehensive narrative review of cervical alignment parameters, the methods for quantifying cervical alignment, normal cervical alignment values, and how alignment is associated with cervical deformity and myelopathy with discussions of health-related quality of life.

Summary of Background Data. Indications for surgery to correct cervical alignment are not well-defined and there is no set standard to address the amount of correction to be achieved. In addition, classifications of cervical deformity have yet to be fully established and treatment options defined and clarified.

Methods. A survey of the cervical spine literature was conducted.

Results. New normative cervical alignment values from an asymptomatic volunteer population are introduced, updated methods for quantifying cervical alignment are discussed, and describing the relationship between cervical alignment, disability, and myelopathy are outlined. Specifically, methods used to quantify cervical alignment include cervical lordosis, cervical sagittal vertical axis, and horizontal gaze with the chin-brow vertical angle. Updated methods include T1 slope. Evidence from a few recent studies suggests correlations between radiographical parameters in the cervical spine and health-related quality of life. Analysis of the cervical regional alignment with respect to overall spinal pelvic alignment is emerging and critical. Cervical myelopthay and sagittal alignment of the cervical spine are closely related as cervical deformity can lead to spinal cord compression and tension.

Conclusion. Cervical deformity correction should take on a comprehensive approach in assessing global cervical-pelvic relationships and the radiographical parameters that effect health-related quality of life scores are not well-defined. Cervical alignment may be important in assessment and treatment of cervical myelopathy. Future work should concentrate on correlation of cervical alignment parameters to disability scores and myelopathy outcomes.

Summary Statements.

Statement 1: Cervical sagittal alignment (cervical SVA and kyphosis) is related to thoracolumbar spinal pelvic alignment and to T1 slope.

Statement 2: When significant deformity is clinically or radiographically suspected, regional cervical and relative global spinal alignment should be evaluated preoperatively via standing 3-foot scoliosis X-rays for appropriate operative planning.

Statement 3: Cervical sagittal alignment (C2-C7 SVA) is correlated to regional disability, general health scores and to myelopathy severity.

Statement 4: When performing decompressive surgery for CSM, consideration should be given to correction of cervical kyphosis and cervical sagittal imbalance (C2-C7 SVA) when present.

Cervical deformity is disruption of normal cervical alignment. This review focuses on normal cervical alignment, methods for quantifying alignment, and how alignment is associated with cervical deformity, myelopathy. Included are discussions of health-related-quality of life, surgical considerations, and the future direction of cervical alignment assessment.

*Department of Neurological Surgery, University of California, San Francisco, San Francisco, CA

Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York, NY

Université Aix-Marseille, Marseille, France

§University of California, San Diego, School of Medicine, La Jolla, CA

Spine Unit 2, Bordeaux University Hospital, Bordeaux, France

Division of Neurosurgery, University of Toronto, Toronto, Ontario Canada

**Department of Orthopaedic Surgery, Loyola University, Chicago, IL

††Department of Neurosurgery, Rush University, Chicago, IL

‡‡Department of Orthopaedic Surgery, Hospital for Special Surgery, New York, NY; and

§§Department of Neurosurgery, University of Virginia Health System, Charlottesville, VA.

Address correspondence and reprint requests to Christopher P. Ames, MD, Department of Neurosurgery, University of California, San Francisco, Medical Center, 400 Parnassus Ave, A850, San Francisco, CA; E-mail: amesc@neurosurg.ucsf.edu

Acknowledgment date: March 7, 2013. First revision date: June 8, 2013. Second revision date: July 15, 2013. Acceptance date: July 25, 2013.

The manuscript submitted does not contain information about medical device(s)/drug(s).

Supported by AOSpine North America, Inc. Analytic support for this work was provided by Spectrum Research, Inc., with funding from the AOSpine North America.

Relevant financial activities outside the submitted work: board membership, payment for lectures, consultancy, grants/grants pending, patents, royalties, support for travel, provision of writing assistance, medicines, equipment, or administrative support, expert testimony, grant, consulting fee or honorarium, travel/accommodations/meeting expenses, and stock/stock options.

The cervical spine is very complex as it allows the widest range of motion relative to the rest of the spine and also supports the mass of the head. This complex nature of the cervical region lends it self-susceptible to a variety of disorders and complications, many of which begin with, and inevitably lead to, alignment pathology that may warrant surgical consideration. Abnormalities of the cervical spine are usually very debilitating and induce adverse effects on the overall functioning and health-related quality of life (HRQOL) of the patient.

Currently, indications for surgery to correct cervical alignment are not well-defined, and there is no set standard to address the amount of correction to be achieved. In addition, classifications of cervical deformity have yet to be fully established and treatment options defined and clarified. Furthermore, cervical myelopathy and its relationship to cervical alignment is a relatively new concept and currently being investigated. Cervical myelopathy has historically been viewed as a result of multilevel spondylosis, however recent studies suggest cervical alignment contributing to pathogenesis of cervical myelopathy. It has been shown in cadaver and animal models that an increase in sagittal malalignment leads to greater cord tension, flattening, and an increase in intramedullary pressure resulting in neurological compromise.1–7 Shimizu et al5 found a significant correlation between the degree of kyphosis and the amount of cord flattening leading to decreased vascular supply and ultimately demyelination with neuronal loss in small animals. Farley et al7 found an increase in intramedullary pressure with kyphosis greater than 51° in cadavers. The effect of cervical alignment on myelopathy has also been demonstrated radiographically with flexion-extension magnetic resonance imaging (MRI) studies.8–12 These studies show changes in T2 intensity and morphological changes of the cord consistent with myelopathy when the spine is in flexion or extension. Sagittal malalignment is a significant factor in contributing to cervical myelopathy, but with few reports investigating this subject.

Therefore, the purpose of this article is to provide a comprehensive narrative review of cervical alignment parameters, the methods for quantifying cervical alignment, normal cervical alignment values, and how alignment is associated with cervical deformity and myelopathy with discussions of HRQOL.

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CERVICAL SPINE ALIGNMENT PARAMETERS AND METHODS

The 3 primary methods to assess cervical lordosis (CL) include Cobb angles, the Harrison posterior tangent method, and Jackson physiological stress lines.13 The Cobb angle method measures the lordosis from either C1–C7 or C2–C7 and includes drawing 4 lines. The first line is drawn either parallel to the inferior endplate of C2 or extending from the anterior tubercle of C1 to the posterior margin of the spinous process and the second line drawn parallel to the inferior endplate of C7. Perpendicular lines are then drawn from each of the 2 lines noted in the earlier text, and the angle subtended between the crossing of the perpendicular lines is the cervical curvature angle (Figure 1B).13 The Harrison posterior tangent method involves drawing parallel lines to the posterior surfaces of all cervical vertebral bodies from C2–C7 and then sums the segmental angles for an overall cervical curvature angle.13 It has been suggested that the Cobb C1–C7 angle overestimates the CL, that the Cobb C2–C7 underestimates the CL, and that the Harrison method may provide the best estimate of lordosis.13 Despite this finding, the Cobb method remains the clinical mainstay of CL measurement due to its ease of use, as well as its good intra- and inter-rater reliability.14,15 Lastly, the Jackson physiological stress lines method requires drawing a parallel lines to the posterior surface of the C7 and C2 vertebral bodies and measuring the angle between them.16

Figure 1

Figure 1

Sagittal plane translation of the cervical spine is measured through the cervical sagittal vertical axis (SVA), for which there are a few different methods of measurements. Both C2 SVA and C7 SVA have been used to define global sagittal alignment by measuring the distance between the C2 and C7 plumb line, respectively, from the posterior superior corner of the sacrum. Cervical SVA (C2 SVA) can also be defined regionally using the distance between a plumb line dropped from the centroid of C2 (or odontoid) and the posterior superior aspect of C7 (C2–C7 SVA; Figure 1A, Figure 2). Another option that has been proposed for global SVA, in addition to the C7 SVA, is the gravity line. This is measured in the same way as the C7 SVA, however, the plumb line is drawn from the center of gravity (COG) of the head (COG SVA; Figure 1A, Figure 2).17–23 On lateral radiographs, the COG of the head can be approximated by using the anterior portion of the external auditory canal as the initial point for the plumb line.24 This method may also be applied regionally to C2 SVA instead of the C2 SVA (COG-C7 SVA) (Figure 1A). However, the C2 plumb line is especially clinically relevant as it has been directly correlated with HRQOL (specifically, Neck Disability Index and SF-36 PCS) in which larger C2 SVA relates to poorer HRQOL.25

Figure 2

Figure 2

When managing severe rigid cervical kyphotic deformities, measurement of horizontal gaze is especially useful as the loss of horizontal gaze has a significant impact on activities of daily living and quality of life.26 The chin-brow vertical angle (CBVA) is the current method used when measuring horizontal gaze and is defined as the angle subtended between a line drawn from the patients chin to brow and a vertical line (Figure 1B).26 The angle is measured on clinical photographs of the patient standing with hips and knees extended, while their neck is in a neutral or fixed position.26 This parameter is gaining popularity, and deformity correction that has considered CBVA has been shown to be associated with positive postoperative outcomes, such as improved gaze, ambulation, and activities of daily living.26–31

Recent studies have investigated novel cervical parameters that have been found to be related to cervical alignment.32 Lee et al32 introduced the concepts of neck tilt and thoracic inlet angle (TIA). Neck tilt was defined as an angle between 2 lines both originating from the upper end of the sternum with one being a vertical line and the other connecting to the center of the T1 endplate. The TIA has been defined as the angle between a line originating from the center of the T1 endplate and perpendicular to the T1 endplate and a line from the center of the T1 endplate and the upper end of the sternum. A relationship exists such that TIA = T1 slope (angle between horizontal plane and T1 endplate [Figure 1B]) + NT. This is similar to the equation in the lumbar spine where pelvic incidence (PI) equals the sacral slope (SS) plus the pelvic tilt (PT) (PI = SS + PT; Figure 1C).

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NORMAL CERVICAL ALIGNMENT

The cervical spine is the most mobile part of the spinal column, thus, a wide range of normal alignment has been described (Tables 1–4).33–35 In asymptomatic normal volunteers, the mean total CL is approximately −40°, with, on average, the occiput-C1 segment being kyphotic.35 Furthermore, the largest percentage of cervical standing lordosis (approximately, 75%–80%) is localized to C1–C2,35,36 and relatively little lordosis exists in the lower cervical levels. Only 6° (15%) of lordosis occurs at the lowest 3 cervical levels (C4–C7).35 The loss of subaxial lordosis has been reported in occiput-C2 fusions in which excessive hyperlordosis is created at occiput-C2.37,38 This type of unfavorable reciprocal change is also seen in lumbar and thoracic osteotomy and has been reported by Lafage et al.39 The majority of CL being localized to C1–C2 may be explained by the findings by Beier et al24 that the COG of the head sits almost directly above the centers of the C1 and C2 vertebral bodies. Moreover, there is no difference between asymptomatic males and females in total CL, and there is a positive correlation with CL and increasing age.34,35 Normal CBVA has not been characterized, but postoperative values of +10° to −10° have been well tolerated in patients.26–31 The average odontoid-C7 plumb line distance ranges from 15 to 17 ± 11.2 mm.35

TABLE 1

TABLE 1

TABLE 2

TABLE 2

TABLE 3

TABLE 3

TABLE 4

TABLE 4

Cervical sagittal alignment may be dependent on the anatomy of the cervicothoracic junction. This is due to the shape and orientation of the thoracic inlet to maintain a balanced, upright posture and horizontal gaze, similar to the relationship between the PI and lumbar lordosis (LL; Figure 1C, Figure 3).32 Lee et al32 found significant correlations between the TIA and both the cranial offset and craniocervical alignment (Figure 4). The authors also found that a small TIA creates a small T1 slope and small CL angle to maintain the physiological neck tilting, and vice versa. The TIA and T1 slope may be used as parameters to evaluate sagittal balance, predict physiological alignment, and guide deformity correction of the cervical spine.32 The T1 slope will determine the amount of subaxial lordosis required to maintain the COG of the head in a balanced position, and it will vary depending on global spinal alignment as measured by SVA and by inherent upper thoracic kyphosis (TK). In patients with scoliosis, the T1 slope has been shown to correlate directly with SVA measured from the C2 odontoid plumb line to provide a measure of overall sagittal alignment40 (Figure 1A).

Figure 3

Figure 3

Figure 4

Figure 4

The authors of this review performed a retrospective radiographical analysis of all spinal parameters in an asymptomatic volunteer population of New York City (n = 55) with a mean age of 45 (range, 20–77) and without a history of chronic low back pain or prior spine surgery (normative values are presented in Table 4). The spinal regions (pelvis, lumbar, thoracic, and cervical) are not independent of one another, and multiple significant correlations were found between them. After an extensive analysis, the authors found that PI correlates with LL, LL correlates with TK, and TK correlates with CL (Figure 5). Thus, an increase in PI correlates with an increase in LL, which correlates with an increase in TK, which then correlates with an increase in CL. However, there was a lack of correlation found between PI and TK making the chain of correlation from the pelvis to the cervical spine more complicated. The current view is that LL is proportional to PI and TK because PI is a fixed parameter and TK has little flexibility. Subjects with a small PI or small TK had smaller LL than subjects with small PI and large TK. This demonstrates that TK is not a result of LL, but rather LL is a result of TK and PI. As mentioned in the earlier text, CL was correlated with TK showing that as TK increases, CL also increases. However, this change in CL is not large enough to maintain the head over the pelvis, but it does provide adequate maintenance of horizontal gaze. In addition to the correlations between CL and TK, CL was also found to correlate with SVA, PT (Figure 6), and T1 slope. Subjects that had a positive SVA demonstrated an increase in CL, regardless of whether their SVA was within the normal range of values. This is a compensatory mechanism in which the cervical adaptation to the sagittal global alignment occurs to maintain a horizontal gaze as mentioned in the earlier text. Therefore, CL can be considered as an adaptive spinal segment to global alignment, similar to TK and LL. When TK and LL adapt to the patient's PI, the amount of CL will be proportional to the other curves. However, when the patient has an anterior malalignment of the spine (from a reduction in LL and/or an increase in TK), an increase in CL is a compensatory mechanism. Conversely, if a primary cervical deformity exists, changes in the lumbar spine and pelvis will attempt to compensate.

Figure 5

Figure 5

Figure 6

Figure 6

The cervical alignment parameters discussed in the earlier text are critical during the evaluation and surgical planning for cervical deformity correction. Therefore, CBVA, T1 slope, C2 SVA and regional CL should all be considered in preoperative planning strategies, and consideration should be given to obtaining preoperative 3-ft standing radiographs that provide visualization from the external auditory canal (approximation of the center of mass of the head) to the femoral heads.

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CERVICAL ALIGNMENT, DEFORMITY, AND HRQOL

Cervical kyphosis is the most prevalent cervical spinal deformity and may develop secondary to multilevel laminectomies, advanced degenerative disease, systemic arthritides, trauma, and neoplastic etiologies.41–46 However, cervical sagittal alignment (e.g., C2 SVA) is closely related to the cervical sagittal Cobb angle (e.g., C2–C7 Cobb angle) as described in the earlier text; however, cervical sagittal alignment also takes into account the alignment of subjacent segments, including the thoracolumbar spine and pelvis (Figure 7A–C). Cervical spine deformities affect, and are affected by, other parameters of the spine in preserving global sagittal alignment. Sagittal alignment factors into maintenance of posture, and patients with poor sagittal alignment often develop potentially painful compensatory mechanisms that affect the cervical spine, including hyperlordosis of subaxial segments.47–51

Figure 7

Figure 7

The current literature reports changes in radiographical parameters of lordosis and kyphosis after surgical correction,52–56 but there lacks a clear indication of an optimal amount postoperative CL to be achieved. It has become an accepted general rule to correct cervical kyphosis to be as close to neutral as possible.43 Current research is adopting a trend toward defining cervical sagittal alignment parameters similar to the accepted C7 SVA (Figure 2)57 traditionally used to measure sagittal alignment of the thoracolumbar spine. Specifically, as noted in the earlier text, the C2 plumb line and CBVA are increasingly being used.25,26,35,58,59 To evaluate the effect of cervical alignment properly in relation to the overall sagittal alignment of the spine, standing 3-ft spine radiographs are needed.

Few studies, report the relationship between radiographical parameters in the cervical spine and HRQOL.25 The effects of the cervical radiographical measurements on outcome scores are not nearly as well-defined as global and pelvic parameters are in thoracolumbar deformity.60–63 The majority of the literature focuses on regional measurements of kyphosis. A common finding throughout the studies is the increase in neck pain in patients with greater kyphosis, whether after cervical spine trauma64 or operative procedures such as anterior cervical spine fusion65 or single-level anterior cervical discectomy and fusion.66 Naderi et al67 concluded that the presence of abnormal cervical curvature predicts less postoperative neurological improvement.

More recent studies of cervical alignment parameters, mostly lordosis between C2 and C7, in relation to postoperative clinical outcomes are weak in suggesting significant correlations. A double-blind, randomized controlled trial evaluating the relationship between lordotic alignment, both cervical and segmental, and clinical outcomes using normal and lordotically-shaped allografts for anterior cervical discectomy and fusion was conducted by Villavicencio et al.68 They found that improved cervical Cobb angle alignment did not correlate significantly with clinical outcomes, but that maintaining or improving segmental sagittal alignment had significant implications for a higher degree of improvement in outcome scores. Guerin et al69 also noted that only segmental sagittal alignment correlated with clinical outcomes after cervical disc arthroplasty, whereas overall cervical lordotic alignment did not. Jagannathan et al70 found no significant relationship between the change in segmental kyphosis and postoperative functional status. CBVA is recognized to be the most objective measure of horizontal gaze; however, it had no significant correlation to overall clinical outcome (Modified Arthritis Impact Measurement Scale) in cervical kyphosis in patients with ankylosing spondylitis.26 Despite this result, it has proven to be a very reliable and useful tool in assessing pre- and postoperative horizontal gaze, and correction of the CBVA does lead to positive postoperative outcomes regarding patient's satisfaction of horizontal gaze improvement.26–31

These studies have primarily focused on lordosis between C2 and C7 and not the aforementioned SVA parameters, with the exception of one study.25 When assessing thoracolumbar deformity, SVA values are standard measurements. It is well known that both Glassman et al71 and Mac-Thiong et al21 concluded that positive sagittal malalignment, defined as a C7 plumb line greater than 50 mm anterior to the posterior-superior aspect of the sacrum, is associated with a deterioration of quality of life in patients with adult spinal deformity. Mac-Thiong et al21 even extended this association to involve the global balance as defined by the gravity line. Currently, only one study has broadened these observations between SVA measurements and HRQOL scores (Neck Disability Index and SF-36 PCS) to include the cervical spine.25 It suggests that increasing C2 SVA is a cause for clinical concern of cervical malalignment indicated by poor HRQOL scores and C2 SVA more than 40 mm is correlated to worse outcomes assessed by the NDI.25 In addition, the authors found significant correlations between T1 slope and C2–C7 lordosis, T1 slope and C2–C7 SVA, as well as C2–C7 SVA and the difference between T1 slope and C2–C7 lordosis (T1 slope − C2–C7 lordosis); Table 5.

TABLE 5

TABLE 5

The T1 slope, as mentioned in the earlier text, has only been studied in a few select reports32,40,72 and is being found to play an important role in cervical and global alignment. Knott et al40 investigated multiple sagittal and coronal alignment parameters in an attempt to identify the ones that may influence global sagittal alignment. The T1 slope was the greatest predictor of C2–C7 SVA, and they recommended full standing radiographs when T slope is less than 13° or more than 25°.40 They also recommended the use of C2 global SVA instead of the standard C7 SVA because the C2 SVA was found to be larger than the C7 SVA, and it takes into account the position of the head.40 The most recent study involving T1 slope was by Kim et al72 in which they investigated the relationship between preoperative T1 slope and postoperative cervical sagittal alignment in patients undergoing laminoplasty for cervical myelopathy. The patients were divided into 2 groups: high and low preoperative T1 slope based on the 50th percentile. They found that patients with high preoperative T1 slope were more likely to have postoperative kyphotic changes at 2-year follow-up.72 This further highlights the importance of the T1 slope in cervical sagittal alignment and surgical planning.

Despite the progressive findings linking radiographical parameters and clinical outcomes, study limitations still exist because most are retrospective analyses. Furthermore, the contribution of the overall improvement in postoperative status that may be attributed to spinal cord decompression in many of these procedures is especially overlooked in many of these studies. There is a clear need for future prospective studies to further isolate the effect of cervical alignment on outcome measures and eliminate confounding variables. Analysis of the cervical regional alignment with respect to overall spinal pelvic alignment will be critical as well as evaluation of inter- and intrarater reliability for the cervical parameters.

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CERVICAL ALIGNMENT AND MYELOPATHY

Cervical spondylotic myelopathy (CSM) has been reported as the most common cause of spinal cord dysfunction in patients older than 55 years.73 Traditionally, the etiology of CSM has been described as a result of multilevel spondylosis in which osteophyte formation occurs as a result of degenerative changes in the discs.74,75 However, less attention has been made to the fact that progressive cervical kyphosis has also been associated with myelopathy. The mechanism behind the development of the myelopathy is a result of the kyphosis forcing the spinal cord against the vertebral bodies inducing anterior cord pathology as well as increasing the longitudinal cord tension due to the cord being tethered by the dentate ligaments and cervical nerve roots41,44 (Figure 8A–C). Over time, as the curve becomes more pronounced, the anterior and posterior margins of the cord compress and the lateral margins expand.5 Cord tethering has been shown to cause an increase in intramedullary pressure leading to neuronal loss and demyelination.1–3,5 Furthermore, the small feeder blood vessels on the cord become flattened, leading to reduced blood supply.5 As the curve magnitude increases these pathological changes become more pronounced, especially on the anterior side that is directly exposed to the mechanical compression.5 It has been shown in animal models that greater cord tension increases intramedullary cord pressure1–4 and leads to neuronal apoptosis.5 Shimizu et al5 quantitatively analyzed that the severity of demyelination and neuronal loss in histological sections of spinal cords after induction of cervical kyphosis was small game fowls. They found a significant correlation between the degree of kyphosis and the amount of cord flattening.5 Analysis with angiography demonstrated that the vascular supply to the anterior portion of the cords was decreased.5 Furthermore, neuronal loss and atrophy of the anterior horn as well as demyelination of the anterior fasciculus was observed with the extent of demyelination progressing as the kyphosis became greater.5 The pattern of demyelination began with the anterior fasciculus, but then progressed to the lateral and posterior fasciculi.5 Thus, sagittal alignment of the cervical spine may play a large role in the development of cervical myelopathy.

Figure 8

Figure 8

Dynamic radiographical studies have found cervical cord changes upon flexion-extension, which may contribute to possible mechanisms of cervical myelopathy. Muhle et al76 measured the sagittal cord diameter in 40 healthy subjects and found that, upon flexion, the cord diameter significantly reduces compared with the neutral position. Yanase et al77 measured the cervical cord volume in healthy patients and found that the cord volume varies with sex, age, height, and body weight.77 However, when calculating a volume ratio (foramen magnum to inferior C2 volume to foramen magnum to inferior C7), there were no variations noted.77 When radiographically measuring cervical cord volumes in patients with cervical myelopathy as a result of cord atrophy, they recommend using the ratio, given it's free of individual variation. Yu et al11 investigated the relationship of high intensity lesions on T2-weighted MR images and dynamic changes in the cervical spine for patients with CSM. On a T2-weighted MR image, they found that segmental hyperextension and range of motion were risk factors for high intensity lesions.11 These results are similar to the results derived by Zhang et al,12 in which they also investigated flexion-extension MRI in patients with spondylotic CSM. They showed that the cervical cord is significantly longer in flexion than in the neutral or extension positions.12 The cord available space was found to be the greatest in the neutral position with it being the least in extension.12 Furthermore, patients were more likely to have cord impingement on extension than flexion.12 In patients with spondylotic cervical myelopathy, flexion may be a larger contributor to the etiology as cord impingement is exacerbated. However, in patients with primary cervical malalignment, in which flexion/kyphosis is the predominant position of the spine, the myelopathy may be due to cord lengthening, flattening, and vascular compromise. Further flexion-extension MRI studies in patients with primary cervical deformity are required to expand on this potential difference in etiology.

There exist a great deal of controversy surrounding the optimal surgical approach to correct cervical myelopathy.73 Surgical considerations and options for cervical myelopathy must take into account the sagittal alignment of the cervical spine as it affects the approach as well as myelopathy etiology and progression. Decompression alone, even ventral decompression, which does not decrease cord tension induced by kyphosis may therefore not result in optimal outcomes.5 Cervical myelopathy correction without sagittal malalignment may develop postlaminectomy kyphosis, the most common etiology of cervical spinal deformity,41,44,78 and should be considered preoperatively. The posterior neural arch is responsible for the majority of the load transmission through the cervical spine as the natural biomechanics of the spine rely on a lordotic curve to distribute most of the load posteriorly. Removal of it causes a significant loss of stability. However, the spine may not become destabilized initially. Over time, the added instability with losing the posterior arch-facet complex tends to cause a shift in load bearing from the posterior column to the anterior column. This shift leads to cervical kyphosis as the discs and vertebral bodies become wedged with greater sagittal malalignment during the course of months to years. Cervical myelopathy may develop from the change in sagittal alignment to a kyphotic predominance and draping of the cord as discussed in the earlier text. In the end, the postlaminectomy kyphosis created a worsened myelopathy from a surgical treatment that was intended to treat myelopathy. With the recent work of Kim et al72 specifically investigating postlaminoplasty, the preoperative T1 slope should be measured as the likelihood of developing kyphotic changes at 2 years increases with a higher preoperative T1 slope.

Posterior approaches alone may not be sufficient to correct cervical lordotic alignment in the subaxial spine above C7. Reconstruction using lordotic interbody spacers through an anterior approach may be needed to restore the natural lordotic curve of the cervical spine. If posterior decompression alone is undertaken or the cervical spine is fused in a kyphotic position, future myelopathy may develop because of the reasons discussed in the earlier text. Studies have shown that patients who underwent 1- or 2-level corpectomies for CSM had maintenance of CL and positive long-term HRQOL (modified Japanese Orthopaedic Association myelopathy scale) outcomes.79

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CONCLUSION

The future direction of cervical deformity correction should take on a comprehensive approach in assessing global cervical-pelvic relationships. As discussed, because the T1 slope and the TIA relate to CL, they are important parameters to consider in optimizing cervical deformity correction as well as the potential to develop postlaminectomy kyphosis.63,72 However, because these are regional relationships, they do not characterize the global relationships in the spine, and a thorough approach to describing cervical deformities entails understanding the relationship of the cervical spine to the pelvis. It is very important to remember that the spinal regions are not independent of one another, and CL depends on both TK and LL. CL can be considered an adaptive spinal segment in which it changes relative to the other spinal segments to attempt to maintain the head over the pelvis and maintain horizontal gaze. In a patient with global sagittal malalignment, CL increases as a compensatory mechanism. There are limitations to the normative data presented by the authors, which is because of the retrospective design and limited number of subjects included. Furthermore, the lack of inclusion of C1–C2 mobility is a limitation because it may also be an important source of cervical adaptation. However, the reported normative data on cervical alignment and correlations between key parameters related to standing posture offer key reference values as well as a foundation for the analysis and treatment of spinal malalignment conditions. Cervical myelopathy is a serious manifestation of cervical spine disease and may be initiated or exacerbated in a patient with cervical sagittal malalignment. Therefore, preoperative T1 slope and postoperative sagittal alignment must be considered when correcting cervical deformities to prevent the onset or exacerbation of the cervical myelopathy symptoms. This is especially true when performing multilevel laminectomies in which the spine may not initially be destabilized. Other important parameters that account for the cervical-pelvic relationship are surveyed in detail, and it is recognized that all such parameters need to be validated in studies that correlate HRQOL outcomes after cervical deformity correction. Future work should also include inter- and intrarater reliability testing of the cervical parameters among large patient populations. In addition, thresholds for decision making on alignment and deformity correction need to be established as well as what factors may have the largest impact on HRQOL.

Summary Statements.

Statement 1: Cervical sagittal alignment (C2 SVA and kyphosis) is related to thoracolumbar spinal pelvic alignment and to T1 slope.

Statement 2: When significant deformity is clinically or radiographically suspected, regional cervical and relative global spinal alignment should be evaluated preoperatively via standing 3-ft scoliosis radiographs for appropriate operative planning.

Statement 3: Cervical sagittal alignment (C2–C7 SVA) is correlated to regional disability, general health scores, and myelopathy severity.

Statement 4: When performing decompressive surgery for CSM, consideration should be given to correction of cervical kyphosis and cervical sagittal imbalance (C2–C7 SVA) when present.

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Key Points

  • Recent cadaveric and animal studies suggest cervical alignment may be important in assessment and treatment of cervical myelopathy.
  • The radiographical parameters that effect HRQOL scores are not well-defined in comparison with global/pelvic parameters in thoracolumbar deformity.
  • CBVA, C2 SVA, and regional CL should be considered in preoperative planning strategies involving standing 3-ft radiographs, in which the external auditory canal (approximation of head center of mass) to femoral heads are visible.
  • The T1 inclination will determine the amount of subaxial lordosis required to maintain the COG of the head in a balanced position and will vary depending on global spinal alignment as measured by the SVA and by inherent upper TK.
  • The future direction of cervical deformity correction with regard to potential spinal cord tension issues in kyphosis should take on a comprehensive approach in assessing global cervical and spinal pelvic alignment.
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References

1. Jarzem PF, Quance DR, Doyle DJ, et al. Spinal cord tissue pressure during spinal cord distraction in dogs. Spine (Phila Pa 1976) 1992;17:S227–34.
2. Tachibana S, Kitahara Y, Iida H, et al. Spinal cord intramedullary pressure. A possible factor in syrinx growth. Spine (Phila Pa 1976) 1994;19:2174–8; discussion 8–9.
3. Iida H, Tachibana S. Spinal cord intramedullary pressure: direct cord traction test. Neurol Med Chir (Tokyo) 1995;35:75–7.
4. Kitahara Y, Iida H, Tachibana S. Effect of spinal cord stretching due to head flexion on intramedullary pressure. Neurol Med Chir (Tokyo) 1995;35:285–8.
5. Shimizu K, Nakamura M, Nishikawa Y, et al. Spinal kyphosis causes demyelination and neuronal loss in the spinal cord: a new model of kyphotic deformity using juvenile Japanese small game fowls. Spine (Phila Pa 1976) 2005;30:2388–92.
6. Chavanne A, Pettigrew DB, Holtz JR, et al. Spinal cord intramedullary pressure in cervical kyphotic deformity: a cadaveric study. Spine (Phila Pa 1976) 2011;36:1619–26.
7. Farley CW, Curt BA, Pettigrew DB, et al. Spinal cord intramedullary pressure in thoracic kyphotic deformity: a cadaveric study. Spine (Phila Pa 1976) 2012;37:E224–30.
8. Kato Y, Imajo Y, Kanchiku T, et al. Dynamic electrophysiological examination of cervical flexion myelopathy. J Neurosurg Spine 2008;9:180–5.
9. Miura J, Doita M, Miyata K, et al. Dynamic evaluation of the spinal cord in patients with cervical spondylotic myelopathy using a kinematic magnetic resonance imaging technique. J Spinal Disord Tech 2009;22:8–13.
10. Rosen CL, Orphanos JR, Nugent RG, et al. The use of MR-myelography combining flexion and extension imaging in the diagnosis of cervical myelopathy: a case report. W V Med J 2009;105:10–4.
11. Yu L, Zhang Z, Ding Q, et al. Relationship between signal changes on T2-weighted magnetic resonance images and cervical dynamics in cervical spondylotic myelopathy. J Spinal Disord Tech 2013.
12. Zhang L, Zeitoun D, Rangel A, et al. Preoperative evaluation of the cervical spondylotic myelopathy with flexion-extension magnetic resonance imaging: about a prospective study of fifty patients. Spine (Phila Pa 1976) 2011;36:E1134–9.
13. Harrison DE, Harrison DD, Cailliet R, et al. Cobb method or Harrison posterior tangent method: which to choose for lateral cervical radiographic analysis. Spine (Phila Pa 1976) 2000;25:2072–8.
14. Polly DW Jr, Kilkelly FX, McHale KA, et al. Measurement of lumbar lordosis. Evaluation of intraobserver, interobserver, and technique variability. Spine (Phila Pa 1976) 1996;21:1530–5; discussion 5–6.
15. Singer KP, Jones TJ, Breidahl PD. A comparison of radiographic and computer-assisted measurements of thoracic and thoracolumbar sagittal curvature. Skeletal Radiol 1990;19:21–6.
16. Jackson R. The Cervical Syndrome. 2nd ed. Springfield, IL: Thomas; 1958.
17. El Fegoun AB, Schwab FJ, Gamez L, et al. Center of gravity and radiographic posture analysis: a preliminary review of adult volunteers and adult patients affected by scoliosis. Spine (Phila Pa 1976) 2005;30:1535–40.
18. Gangnet N, Pomero V, Dumas R, et al. Variability of the spine and pelvis location with respect to the gravity line: a three-dimensional stereoradiographic study using a force platform. Surg Radiol Anat 2003;25:424–33.
19. Lafage V, Schwab FJ, Skalli W, et al. Standing balance and sagittal plane spinal deformity: analysis of spinopelvic and gravity line parameters. Spine (Phila Pa 1976) 2008;33:1572–8.
20. Legaye J, Duval-Beaupere G. Gravitational forces and sagittal shape of the spine. Clinical estimation of their relations. Int Orthop 2008;32:809–16.
21. Mac-Thiong JM, Transfeldt EE, Mehbod AA, et al. Can C7 plumb line and gravity line predict health related quality of life in adult scoliosis? Spine (Phila Pa 1976) 2009;34:E519–27.
22. Schwab FJ, Lafage V, Boyce R, et al. Gravity line analysis in adult volunteers: age-related correlation with spinal parameters, pelvic parameters, and foot position. Spine (Phila Pa 1976) 2006;31:E959–67.
23. Zheng X, Chaudhari R, Wu C, et al. Repeatability test of C7 plumb line and gravity line on asymptomatic volunteers using an optical measurement technique. Spine (Phila Pa 1976) 2010;35:E889–94.
24. Beier G, Schuck M, Schuller E, et al. Determination of Physical Data of the Head I. Center of Gravity and Moments of Inertia of Human Heads: Office of Naval Research; 1979:44.
25. Tang JA, Scheer JK, Smith JS, et al. The impact of standing regional cervical sagittal alignment on outcomes in posterior cervical fusion surgery. Neurosurgery 2012;71:662–9; discussion 9.
26. Suk KS, Kim KT, Lee SH, et al. Significance of chin-brow vertical angle in correction of kyphotic deformity of ankylosing spondylitis patients. Spine (Phila Pa 1976) 2003;28:2001–5.
27. Deviren V, Scheer JK, Ames CP. Technique of cervicothoracic junction pedicle subtraction osteotomy for cervical sagittal imbalance: report of 11 cases. J Neurosurg Spine 2011;15:174–81.
28. Kim KT, Lee SH, Son ES, et al. Surgical treatment of “Chin-on-Pubis” deformity in an ankylosing spondylitis patient: a case report of consecutive cervical, thoracic and lumbar corrective osteotomies. Spine (Phila Pa 1976) 2012;37:E1017–21.
29. Kim KT, Suk KS, Cho YJ, et al. Clinical outcome results of pedicle subtraction osteotomy in ankylosing spondylitis with kyphotic deformity. Spine (Phila Pa 1976) 2002;27:612–8.
30. Pigge RR, Scheerder FJ, Smit TH, et al. Effectiveness of preoperative planning in the restoration of balance and view in ankylosing spondylitis. Neurosurg Focus 2008;24:E7.
31. Wang Y, Zhang Y, Mao K, et al. Transpedicular bivertebrae wedge osteotomy and discectomy in lumbar spine for severe ankylosing spondylitis. J Spinal Disord Tech 2010;23:186–91.
32. Lee SH, Kim KT, Seo EM, et al. The influence of thoracic inlet alignment on the craniocervical sagittal balance in asymptomatic adults. J Spinal Disord Tech 2012;25:E41–7.
33. Gore DR. Roentgenographic findings in the cervical spine in asymptomatic persons: a ten-year follow-up. Spine (Phila Pa 1976) 2001;26:2463–6.
34. Gore DR, Sepic SB, Gardner GM. Roentgenographic findings of the cervical spine in asymptomatic people. Spine (Phila Pa 1976) 1986;11:521–4.
35. Hardacker JW, Shuford RF, Capicotto PN, et al. Radiographic standing cervical segmental alignment in adult volunteers without neck symptoms. Spine (Phila Pa 1976) 1997;22:1472–80; discussion 80.
36. Jackson RP, McManus AC. Radiographic analysis of sagittal plane alignment and balance in standing volunteers and patients with low back pain matched for age, sex, and size. A prospective controlled clinical study. Spine (Phila Pa 1976) 1994;19:1611–8.
37. Yoshida G, Kamiya M, Yoshihara H, et al. Subaxial sagittal alignment and adjacent-segment degeneration after atlantoaxial fixation performed using C-1 lateral mass and C-2 pedicle screws or transarticular screws. J Neurosurg Spine 2010;13:443–50.
38. Yoshimoto H, Ito M, Abumi K, et al. A retrospective radiographic analysis of subaxial sagittal alignment after posterior C1-C2 fusion. Spine (Phila Pa 1976) 2004;29:175–81.
39. Lafage V, Ames CP, Schwab FJ, et al. Changes in thoracic kyphosis negatively impact sagittal alignment after lumbar pedicle subtraction osteotomy: a comprehensive radiographic analysis. Spine (Phila Pa 1976) 2012;37:E180–7.
40. Knott PT, Mardjetko SM, Techy F. The use of the T1 sagittal angle in predicting overall sagittal balance of the spine. Spine J 2010;10:994–8.
41. Albert TJ, Vacarro A. Postlaminectomy kyphosis. Spine (Phila Pa 1976) 1998;23:2738–45.
42. Kaptain GJ, Simmons NE, Replogle RE, et al. Incidence and outcome of kyphotic deformity following laminectomy for cervical spondylotic myelopathy. J Neurosurg 2000;93:199–204.
43. Steinmetz MP, Stewart TJ, Kager CD, et al. Cervical deformity correction. Neurosurgery 2007;60:S90–7.
44. Deutsch H, Haid RW, Rodts GE, et al. Postlaminectomy cervical deformity. Neurosurg Focus 2003;15:E5.
45. Butler JC, Whitecloud TS, 3rd. Postlaminectomy kyphosis. Causes and surgical management. Orthop Clin North Am 1992;23:505–11.
46. O'Shaughnessy BA, Liu JC, Hsieh PC, et al. Surgical treatment of fixed cervical kyphosis with myelopathy. Spine (Phila Pa 1976) 2008;33:771–8.
47. Booth KC, Bridwell KH, Lenke LG, et al. Complications and predictive factors for the successful treatment of flatback deformity (fixed sagittal imbalance). Spine (Phila Pa 1976) 1999;24:1712–20.
48. Boachie-Adjei O. Role and technique of eggshell osteotomies and vertebral column resections in the treatment of fixed sagittal imbalance. Instr Course Lect 2006;55:583–9.
49. Kim YJ, Bridwell KH, Lenke LG, et al. Results of lumbar pedicle subtraction osteotomies for fixed sagittal imbalance: a minimum 5-year follow-up study. Spine (Phila Pa 1976) 2007;32:2189–97.
50. Lu DC, Chou D. Flatback syndrome. Neurosurg Clin N Am 2007;18:289–94.
51. Smith JS, Shaffrey CI, Lafage V, et al. Correction of global sagittal balance following lumbar pedicle subtraction osteotomy results in spontaneous improvement of cervical alignment. [published online ahead of print August 3, 1012] J Neurosurg Spine 2012;17:300–7.
52. Nottmeier EW, Deen HG, Patel N, et al. Cervical kyphotic deformity correction using 360-degree reconstruction. J Spinal Disord Tech 2009;22:385–91.
53. Zdeblick TA, Bohlman HH. Cervical kyphosis and myelopathy. Treatment by anterior corpectomy and strut-grafting. J Bone Joint Surg Am 1989;71:170–82.
54. Abumi K, Shono Y, Taneichi H, et al. Correction of cervical kyphosis using pedicle screw fixation systems. Spine (Phila Pa 1976) 1999;24:2389–96.
55. Belanger TA, Milam RAt, Roh JS, et al. Cervicothoracic extension osteotomy for chin-on-chest deformity in ankylosing spondylitis. J Bone Joint Surg Am 2005;87:1732–8.
56. Mummaneni PV, Dhall SS, Rodts GE, et al. Circumferential fusion for cervical kyphotic deformity. J Neurosurg Spine 2008;9:515–21.
57. Van Royen BJ, Toussaint HM, Kingma I, et al. Accuracy of the sagittal vertical axis in a standing lateral radiograph as a measurement of balance in spinal deformities. Eur Spine J 1998;7:408–12.
58. Hwang SW, Samdani AF, Tantorski M, et al. Cervical sagittal plane decompensation after surgery for adolescent idiopathic scoliosis: an effect imparted by postoperative thoracic hypokyphosis. J Neurosurg Spine 2011;15:491–6.
59. Langeloo DD, Journee HL, Pavlov PW, et al. Cervical osteotomy in ankylosing spondylitis: evaluation of new developments. Eur Spine J 2006;15:493–500.
60. Bridwell KH, Baldus C, Berven S, et al. Changes in radiographic and clinical outcomes with primary treatment adult spinal deformity surgeries from two years to three- to five-years follow-up. Spine (Phila Pa 1976) 2010;35:1849–54.
61. Glassman SD, Bridwell K, Dimar JR, et al. The impact of positive sagittal balance in adult spinal deformity. Spine (Phila Pa 1976) 2005;30:2024–9.
62. Schwab FJ, Farcy JP, Bridwell K, et al. A clinical impact classification of scoliosis in the adult. Spine (Phila Pa 1976) 2006;31:2109–14.
63. Schwab FJ, Smith VA, Biserni M, et al. Adult scoliosis: a quantitative radiographic and clinical analysis. Spine (Phila Pa 1976) 2002;27:387–92.
64. Jenkins LA, Capen DA, Zigler JE, et al. Cervical spine fusions for trauma. A long-term radiographic and clinical evaluation. Orthop Rev 1994(suppl):13–9.
65. Kawakami M, Tamaki T, Yoshida M, et al. Axial symptoms and cervical alignments after cervical anterior spinal fusion for patients with cervical myelopathy. J Spinal Disord 1999;12:50–6.
66. Kwon B, Kim DH, Marvin A, et al. Outcomes following anterior cervical discectomy and fusion: the role of interbody disc height, angulation, and spinous process distance. J Spinal Disord Tech 2005;18:304–8.
67. Naderi S, Ozgen S, Pamir MN, et al. Cervical spondylotic myelopathy: surgical results and factors affecting prognosis. Neurosurgery 1998;43:43–9; discussion 9–50.
68. Villavicencio AT, Babuska JM, Ashton A, et al. Prospective, randomized, double-blind clinical study evaluating the correlation of clinical outcomes and cervical sagittal alignment. Neurosurgery 2011;68:1309–16; discussion 16.
69. Guerin P, Obeid I, Gille O, et al. Sagittal alignment after single cervical disc arthroplasty. J Spinal Disord Tech 2012;25:10–6.
70. Jagannathan J, Shaffrey CI, Oskouian RJ, et al. Radiographic and clinical outcomes following single-level anterior cervical discectomy and allograft fusion without plate placement or cervical collar. J Neurosurg Spine 2008;8:420–8.
71. Glassman SD, Berven S, Bridwell K, et al. Correlation of radiographic parameters and clinical symptoms in adult scoliosis. Spine (Phila Pa 1976) 2005;30:682–8.
72. Kim TH, Lee SY, Kim YC, et al. T1 slope as a predictor of kyphotic alignment change after laminoplasty in cervical myelopathy patients. Spine (Phila Pa 1976) 2013;38:E992–7.
73. Klineberg E. Cervical spondylotic myelopathy: a review of the evidence. Orthop Clin North Am 2010;41:193–202.
74. Matz PG, Anderson PA, Holly LT, et al. The natural history of cervical spondylotic myelopathy. J Neurosurg Spine 2009;11:104–11.
75. Tracy JA, Bartleson JD. Cervical spondylotic myelopathy. Neurologist 2010;16:176–87.
76. Muhle C, Wiskirchen J, Weinert D, et al. Biomechanical aspects of the subarachnoid space and cervical cord in healthy individuals examined with kinematic magnetic resonance imaging. Spine (Phila Pa 1976) 1998;23:556–67.
77. Yanase M, Matsuyama Y, Hirose K, et al. Measurement of the cervical spinal cord volume on MRI. J Spinal Disord Tech 2006;19:125–9.
78. Uchida K, Nakajima H, Sato R, et al. Cervical spondylotic myelopathy associated with kyphosis or sagittal sigmoid alignment: outcome after anterior or posterior decompression. J Neurosurg Spine 2009;11:521–8.
79. Andaluz N, Zuccarello M, Kuntz C. Long-term follow-up of cervical radiographic sagittal spinal alignment after 1- and 2-level cervical corpectomy for the treatment of spondylosis of the subaxial cervical spine causing radiculomyelopathy or myelopathy: a retrospective study. J Neurosurg Spine 2012;16:2–7.
Keywords:

cervical spine alignment; cervical deformity; cervical myelopathy; T1 slope; cervical lordosis; cervical SVA; thoracic inlet angle; cervical HRQOL; chin-brow vertical angle

© 2013 by Lippincott Williams & Wilkins
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