Introduction

The cervical spine plays a critical role in the normal physiological function and positioning of the head, neck, and spine. Not only does the cervical spine carry the weight of the head, but it also functions as the region of the spine with the largest range of motion [1,2,3]. The cervical spine serves as the critical link between the head and the body and is often associated with major disability and neurologic compromise [4, 5]. Due to the flexible nature of the cervical spine, it is susceptible to a wide range of both acute and degenerative conditions [6,7,8]. Advancements in surgical techniques, correction of malalignment and better recognition of symptoms now allow for improved interventions and management to increase patients’ quality of life [9].

The relatively increased flexibility of the cervical spine is due to its distinctive biomechanical structure. In particular, the atlanto-occipital joint heavily influences flexion and extension with the atlantoaxial joint playing a pivotal role in the rotational component of cervical movement [10,11,12,13]. The freedom of motion, however, comes at a cost, as it makes the cervical spine particularly vulnerable to significant acute injury. Additionally, the cervical spine compensates for changes in the caudal spine to maintain horizontal gaze. Likewise, as a consequence, chronic reciprocal changes may occur leading to cervical deformities [12, 14, 15]. As demonstrated, cervical deformity is a broad term encompassing many structural changes that can become symptomatic. These changes include scoliosis, kyphosis, hyper-lordosis, spondylolisthesis, and retrolisthesis. In particular, this work will focus on the cervical deformities that present with sagittal alignment, lordotic, kyphotic, and hyper-lordotic changes.

Due to its complexity and the relative infancy of the field, our understanding of cervical spine deformities (CSD) is far from complete. New research is published with ever-increasing frequency, adding to our knowledge and driving rapidly developing and evolving surgical techniques. This review will give healthcare providers a general reference regarding the care of cervical deformity patients and propose typical surgical strategies. Beginning by defining the normal cervical spine with standard measurement parameters, we will address what constitutes a CSD and its common etiologies. To assist in standardizing diagnosis and management, multiple groups have proposed classification systems for both the cervical and thoracolumbar spine deformity, and we will summarize those systems and comment on their validity. Lastly, there will be an overview of the most current surgical management options, as well as identification of common complications to address areas of safety improvement.

Normal cervical alignment

Establishing normal values of cervical spinal alignment has revealed a wide variance of normal. However, the accepted thought throughout the field has remained that the cervical spine normally presents with a lordotic alignment (Fig. 1). Previous work suggests an average normal value for cervical (occiput to C7) lordosis (CL) of approximately − 35° to − 40° in a North American population cohorts and − 16.2° in a Japanese cohort [3, 16, 17]. However, other studies have shown that a non-lordotic cervical spinal alignment is present in up to one-third of people and the presence of a non-lordotic cervical spine is not definitively linked to an increased incidence of pathology or symptomatology [18,19,20,21]. Normal C2-7 sagittal cervical alignment, measured by the cervical sagittal vertical axis (cSVA), has been estimated at + 21.2 ± 12.1 mm and does not change significantly with aging [3, 18, 22, 23]. Similarly, the difference between T1 slope and C2-7 cervical lordosis (TS-CL) has been proposed as a way to monitor cervical alignment in a manner similar to the pelvic incidence-lumbar lordosis (PI-LL) mismatch of the lumbar spine and pelvis [23]. The T1 slope (T1S) correlates with thoracic kyphosis and is an important factor in the sagittal alignment of the spine [19,20,21]. Ultimately, the T1S is the critical link between the cervical spine and distal spine parameters, including the thoracic, lumbar and spinopelvic regions [24, 25]. Normal TS-CL has been found to be approximately below 20° and, similar to C2-7 SVA, does not increase with age in normal controls [18].

Fig. 1
figure 1

Illustration depicting the parameters used for cervical and global spinal alignment: C2-C7 sagittal cervical alignment (cSVA), chin-brow vertical angle (CBVA), C2-C7 lordosis (C2-7 CL), thoracic kyphosis (TK), lumbar lordosis (LL), sagittal vertical axis (SVA), pelvic tilt (PT), pelvic incidence (PI)

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Changes to the normal alignment of the cervical spine is what ultimately can lead to a CSD and its accompanying pathologies. Increasing C2-7 SVA has shown to correlate with increased disability on Health-related Quality of Life (HRQOL) metrics and current literature shows that a C2-7 SVA > 40–50 mm correlates to severe disability on the Neck Disability Index (NDI) [26,27,28,29]. Hyun et al. found that a TS-CL mismatch of 26.1° correlated to a C2-7 SVA of > 50 mm and severe disability [29]. Follow-up work has reiterated that a TS-CL mismatch value in the range of 20°–25° corresponds to moderate and severe disability respectively, on the NDI score [30]. It was also found that T1 slope < 20° and C7 sagittal vertical alignment (SVA) < 10 mm are predictive of abnormal C2-7 kyphosis [24]. Despite some overlap amongst normal variants and the radiographic elements of CSD classification, it has been definitively demonstrated that symptomatic CSD patients present with structural changes that fall outside of normal measurement parameters [31]. Based upon these findings, our group defines a CSD as TS-CL difference of more than 20°, C2–C7 SVA more than 40 mm, or C2–C7 kyphosis more than 10° [25].

It is important to note that the cervical spine is influenced by the remainder of spinal global alignment. Ames et al. examined the interplay of spinal parameters in 55 subjects with a mean age of 45. They found a correlation between CL and the thoracic spine alignment, as well as the global sagittal alignment. Specifically, CL increases as the thoracic kyphosis and T1 slope increase, and increasing C7 SVA is correlated to increasing cervical lordosis [32]. Bao et al. examined the full-length standing radiographs of 171 patients consulted to spine surgeons for thoracolumbar pathology, and split them into two groups based on presence of cervical spine disability on NDI, Visual Analog Scale (VAS) neck, and VAS arm. The C2-7 SVA and thoracic kyphosis were significantly different between the neck symptomatic group and the non-symptomatic group [26]. However, cervical lordosis was not significantly different between the two groups. Hey et al. examined cervical parameters in three different physiological positions: standing, erect sitting, natural sitting. Increased cervical lordosis was observed more during sitting than standing, and even further lordosis was observed during natural sitting as compared to erect sitting. This is an consideration when planning corrective CSD surgery, especially as it relates to the patients mobility status [24].

Etiology

As surgeons have developed a greater understanding about the normal function and alignment of the cervical spine, information regarding the etiology of the loss of normal cervical lordosis and the development of kyphotic cervical deformities has emerged in the literature. Previous works show that 40–50% of adult spinal deformity (ASD) patients currently have or will subsequently develop a cervical deformity [33,34,35]. It is estimated that there are currently 27.5 million adult patients with a spinal deformity, and that number is predicted to rise to 60 million by 2050 [36]. This increasing prevalence may be the result of changes over the last 10 years in how physicians have evaluated the cervical spine. In the past, cervical lordosis was traditionally the only parameter assessed. Today, with current ongoing research, several other measures have been identified, such as C2-C7 SVA, T1 slope, and horizontal gaze (as measured by CBVA), with demonstrated clinical relevance. The heterogeneous etiologies of CSD and its significant impact on quality of life has led to investigation of its pathogenesis, classification and treatment, and attributing to the expansion of spinal alignment knowledge and surgical advancement seen today.

As interest has grown, physicians and researchers have focused their attention on describing the underlying disease and associated detrimental structural impact contributing to the development of cervical spine deformity. In particular, work has focused on elucidating the roles of inflammatory arthritides, dropped head syndrome (camptocephalia), advanced degenerative changes and secondary iatrogenic consequences due to corrective surgery performed in other regions of the spine. While kyphosis and cervical malalignment has thought to be the result of degenerative changes, recent work has demonstrated that cervical lordosis may also increase as patients get older [37]. Therefore, this has led researchers and surgeons alike to believe the frailty status of patients, rather than just the age, is much more important when considering the risk of postoperative complications and poor restoration of quality of life [38, 39]. With the incorporation of comorbidities like osteoporosis, demographics like age and gender, and patient-reported functionality assessment, frailty is a better overall indicator of a patient’s physical and functional age. Additionally, there may be unresearched and unappreciated psychosocial elements also playing a role in the development of cervical deformities. By being cognizant and recognizing the interplay of medical, psychological, and structural influencers of cervical deformity, physicians can more optimally treat their patients. This next section will focus on providing the most up to date understanding of each of these etiologies.

Degenerative changes

There are estimates that upwards of 60% of the population will experience radiographic degenerative cervical change in their lifetime [40]. The vast majority displaying symptoms will have spontaneous resolution. Of those that do not resolve, most involve intervertebral disc herniation, disc desiccation, and degenerative wear of the vertebrae presenting as osteophytic growths or narrowing of the cervical spinal canal [40,41,42]. The prevalence of severe cases has been estimated at 83/100,000 of the general population [40]. With severe degenerative change, the head begins to translate anteriorly and/or tilt caudally. This causes a loss in lordosis and over time will present as a kyphotic CSD. Narrowing of the foramina and compression of the exiting nerve roots secondary to the kyphosis leaves patients with a severe, shooting pain pattern radiating through the neck, shoulder and upper arm [40,41,42]. It has also been postulated that the kyphotic deformity pushes the spinal cord against the vertebral bodies [32, 42]. If the kyphosis is not corrected, patients may develop cervical myelopathy (CM) [43,44,45]. This will manifest itself as progressive loss of sensation, dexterity and muscle strength not only in the affected area, but also distally to the torso and lower extremities [42, 43, 46]. However, the incidence of CM is even more rare than radiculopathy, with an estimated prevalence of 4/100,000 in the general population [42].

In addition to the symptomatic presentation of CM, physicians have traditionally used radiographic techniques to provide measurements of the spinal canal and assess patients’ risk of developing CM [47]. An anterior to posterior diameter of less than 13 mm is defined as stenotic with high likelihood of CM [48, 49].   MRI techniques, rather than other soft tissue modalities, allow for more precise measurements and demonstrate that spinal cord canal cross-sectional areas less than 50 mm2 put patients at highest risk for myelopathic symptoms [50, 51]. Subsequent compression of the spinal cord from a greater than 30% loss of cross-sectional area has been correlated to the exhibition of neurological symptoms [46, 50].

Cervical myelopathy (CM) has been associated with multi-level spondylosis and cervical malalignment. Previous research in cadaver and animal models has shown an increase in sagittal malalignment leads to greater cord tension, flattening, and intramedullary pressure, ultimately resulting in neurological compromise [52,53,54,55,56]. Specifically, cervical sagittal alignment (C2–C7 SVA) is correlated with regional disability and myelopathy severity, and, therefore, should be assessed prior to performing decompression surgery for CM [57,58,59,60,61,62].

Effectively treating CM patients remains a case-to-case bases. Generally, surgical intervention is reserved for patients with significant symptoms and/or disease progression for an extended period of time. Figure 2 displays a 71-year old female patient who was diagnosed with cervical spinal stenosis, cervicalgia and cervical myelopathy due to degenerative changes. This patient underwent an anterior discectomy and fusion of C3–C7, with a corpectomy at C4–C5, and posterior laminectomy of C3–C7 with posterior fusion from C2–T2. At baseline (Fig. 2A) the patient had a T1S of 24°, TS–CL of 15°, CL of − 8°, and a cSVA of 28 mm. Figure 2B shows the alignment changes by 1-year post-operation: T1S of 25.6°, TS-CL of 2.1°, CL of 23.5°, and a cSVA of 18.1 mm with resolution of both the myelopathy and axial pain. This case demonstrates the clinical benefit of cervical deformity corrective surgery in restoring cervical sagittal alignment and lordosis due to degenerative changes. Cervical parameters show reciprocal changes following corrective surgery, correcting for both the physical malalignment of the cervical spine and patient reported symptoms of myelopathy and pain due to compression.

Fig. 2
figure 2

Radiographs of a 71-year old female cervical deformity patient with myelopathy (A: Baseline, B: 1-year post-operative follow up)

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In conjunction with the radiographic presentation of myelopathy, patient-reported questionnaires are vital in establishing an accurate picture of patient symptomology and developing a personalized care strategy. Previous work on CM determined that two clinical questionnaires, modified Japanese Orthopedic Association (mJOA) and American Spinal Injury Association (ASIA), especially when used in combination, are the most useful in providing surgeons with patient-outlook on myelopathy severity [46, 63]. With the additional patient input through these questionnaires, surgeons can better tailor management to the patient’s symptomatology.

Inflammatory arthritides

Inflammatory arthritides, such as rheumatoid arthritis (RA) and ankylosing spondylitis (AS), play prominent roles in the formation of cervical spinal deformities. While immunotherapy (which has its own inherent risks) has led to the reduction of subsequent development of deformity, both diseases still are quite prevalent amongst spine patients [64].

RA is estimated to occur in 1–2% of the general population and, within those patients, as high as 80% will present with cervical spine involvement [65, 66]. RA can quickly attack the cervical spine with destructive consequences [65, 66]. The pathogenesis of RA involves erosion of the bony structures of the spine thus leading to an increase in the laxity of the spinal ligaments that give structural integrity to the spine [67]. The inflammatory changes can ultimately reverse the normal cervical alignment, leading to instability and the development of a listhetic and/or kyphotic deformity [65, 67, 68]. In particular, atlanto-axial dislocations (AAD) and the swan-neck deformity are major concerns when RA presents in the cervical spine [69, 70].

Non-surgical treatment of RA patients is the use of disease-modifying antirheumatic drugs (DMARDs). DMARDs work as an immunosuppressive agent to interfere with the inflammatory processes of RA and act to prevent the incidence of cervical spine involvement. However, once RA involvement of the cervical spine begins to cause symptoms, surgical intervention is typically recommended to stabilize the spine and prevent progression [65].

The manifestations of the inflammatory processes of AS may also involve the cervical spine [71, 72]. The chronic inflammatory state induced by AS reduces bone density, increases vascularization and causes progressive deformity, which can often result in an ‘auto-fusion’ of vertebral bodies [73, 74]. This disease carries an increased fracture potential and develops into profound kyphotic cervical deformities [72]. Ultimately, patients with AS may require surgical intervention [71, 75]. Figure 3 displays a 38-year-old male with AS, progressive cervicothoracic kyphosis, dropped head syndrome, as well as cervical myelopathy and radiculopathy. This patient underwent corrective surgery via a posterior spinal fusion from C2–T10 with facet osteotomies from C2–T10, C7–T6 laminectomy, partial corpectomies at T2 and T4, and a complete corpectomy at T3. At baseline (Fig. 3A) the patient had a PT of 33°, PI–LL of 30°, T4–T12 of 46°, TS–CL of 63°, and a cSVA of 70 mm. Figure 3B shows the alignment changes by 2-years post-operation: PT of 32.7°, PI–LL of 28.9°, T4–T12 of 34.7°, TS–CL of 8.9°, and a cSVA of 40.6 mm. These parameters show a decrease in thoracic kyphosis and increase in cervical lordosis, exhibiting correction of the patient’s cervical deformity. Due to the patient’s residual AS in the lumbar spine, the PT and PI–LL parameters remain unchanged as reciprocal changes are less often seen because of the rigidity present. As explained by Tan et al. [76] the process of surgical evaluation for this patient was mostly dependent on his fixed deformity, resultant from his AS, indicating the need for more aggressive posterior osteotomies and instrumentation [77].

Fig. 3
figure 3

Radiographs of a 38-year old male cervical deformity patient with ankylosing spondylitis (A: Baseline, B: 2-year post-operative follow up)

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Dropped head syndrome (camptocephalia)

Dropped head syndrome (DHS), also known as dropped head deformity or camptocephalia, can be caused by a variety of conditions leading to the physical presentation of the chin dropping to the chest. While DHS is often the result of neuromuscular diseases, in rare cases it may present secondary to cervical kyphosis or as a sequela of corrective surgery [78, 79]. Interestingly, these two categories of DHS can have different presenting symptomatology. Neuromuscular causes of DHS are typically attributed to disease processes such as Amyotrophic Lateral Sclerosis (ALS), myasthenia gravis, Parkinson disease, multiple system atrophy, cervical dystonia, or cervical myelopathy [80]. DHS in the case of neuromuscular causes occurs as a result of weakness of neck extensor and/or flexor muscles. In DHS due to cervical kyphosis, the deformity is rigid with severe flexor muscle tension and/or extensor muscle atrophy, accompanied by changes to the bony architecture associated with inflammatory diseases [81, 82]. The current, most preferred surgical intervention for DHS is multi-level instrumented fixation and fusion, typically from C2 and extending caudally to at least T3, with decompressive laminectomies at sites of cord compression [83].

The alternative to rigid DHS is a flexible posturing presentation. Flexible DHS is correctible via passive neck extension, and may or may not present with structural changes. Continued weakness of neck extensor muscles can contribute to future cervical sagittal instability and degeneration. While this is less common, its development may have been the result of a laminectomy to correct cervical myelopathy [84]. The exact cause of flexible DHS is unknown, but it is believed to be the result of a combination of architectural changes from chronic disease, along with damage and/or changes to the supporting musculature in the extensor compartment and compensatory positional changes due to cervical pain [85]. Treatment typically requires a 360° fusion with extension through the cervicothoracic transition zone to correct for cervical alignment [84].

Since these structural drivers of DHS are slow to develop, the presentations are relatively rare [78, 79, 85]. However, the severity of the deformity present in these cases makes it worthwhile to explore. Early cases may be treated conservatively through nonoperative methods, but surgical intervention is typically required to prevent progression of cervical myelopathy and other neurological deficits. Surgical treatment of DHS depends on a variety of factors, such as the need for anterior muscle release, approach of fusion (anterior, posterior or circumferential), and the levels indicated for decompression and instrumented fusion [83]. Patients with dropped head syndrome show a rigid kyphotic deformity within the cervicothoracic spine, typically requiring anterior release and posterior fusion, depending on stability [76, 77]. Fig. 4 displays a 62-year-old female that presented with dropped head syndrome. The patient also had thoracic and cervical scoliosis, degenerative disc disease of the thoracic spine, cervical spinal stenosis and radiculitis. For the patient’s initial operation, she had an anterior cervical decompression and fusion of C3–C7 with a posterior cervical fusion of C2–T4. One year later, the patient underwent a revision posterior spinal fusion from C1-pelvis, followed by another revision posterior spinal fusion from C1–T10 due to recurrent pain. At baseline (Fig. 4A) the patient had a PT of 40.1°, PI–LL of 31.1°, T4–T12 of 28.4°, TS–CL of 48.9°, and a cSVA of 63.2 mm. Figure 4B shows the alignment changes by 2-year post-initial operation: PT of 10°, PI–LL of 8°, T4–T12 of 63°, TS–CL of 42°, and a cSVA of 57 mm. These changes show remarkable improvement in both her thoracolumbar and pelvic parameters, as well as cervical realignment.

Fig. 4
figure 4

Radiographs of a 62-year old female cervical deformity patient with dropped head syndrome (A: Baseline, B: 2-year post-operative follow up)

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CSD secondary to adult spinal deformity

The prevalence of ASD has been rapidly growing, due to better clinical detection by physicians and radiographic means, with an increase of 158% over the last decade [36]. An increase in patients presenting with concomitant thoracolumbar ASD and CSD has also been reported, along with those developing symptomatic CSD following corrective ASD surgery [33, 86,87,88,89,90,91,92]. Kyphosis and other sagittal malalignments are commonly seen as the cervical spine seeks to maintain horizontal gaze in the presence of thoracolumbar changes [32,33,34, 93].

The concurrent prevalence of CSD and ASD has gained researchers attention to the potential relationship between the cervical spine and neighboring thoracolumbar alignment. Using the Scoliosis Research Society (SRS)—Schwab classification system for thoracolumbar diagnosis, the International Spine Study Group (ISSG) examined the relationship between coronal curves; thoracic only, lumbar only, or double curve, and CSD. The results of this work demonstrated that patients with thoracic scoliosis more often presented with CK, defined as a C2–C7 sagittal Cobb angle more than 0°. Patients with sagittal spinopelvic malalignment more often presented with cervical positive sagittal malalignment, defined as C–C7 SVA more than 4 cm [33, 34]. Development of CSD in ASD patients is commonly seen, with rates as high as 53% [34, 89, 94, 95]. Fig. 5 displays a 62-year-old female that presented with a CSD secondary to her ASD. Initially to correct the patient’s ASD, she received a posterior spinal fusion from T2 to the pelvis, and a transforaminal lumbar interbody fusion (TLIF) from L4–S1. After 1 year, the patient underwent correction for her CSD via extension of the posterior spinal fusion from C2 to the pelvis. At baseline (Fig. 5A) the patient had a PT of 24°, PI–LL of 14°, T4–T12 of − 58°, SVA of 119 mm, TS–CL of 26°, and a cSVA of 62.7 mm. Figure 5B shows the alignment changes 1 year after the initial ASD corrective surgery, before her cervical spinal surgery. One year after her cervical corrective surgery, as shown in Fig. 5C, the patient’s radiographic parameters are as given: PT of 21°, PI–LL of 11°, T4–T12 of − 59°, SVA of 93 mm, TS–CL of 15°, and a cSVA of 38 mm. In comparison to baseline, correction of her CD one-year later showed great improvement in her TS–CL and cSVA parameters, indicating proper sagittal realignment of the cervical spine to normal. Although the patient already had adolescent idiopathic cervical scoliosis, her ASD corrective surgery caused resulting chin-on-chest deformity and cervicalgia, which required further surgical intervention and extension of her fusion. As described by Tan et al. [76], the patient’s history of scoliosis and spondylosis of the cervical spine, as well as prior spinal corrective surgery, were all components which led to severe fixed cervical deformity, requiring posterior fusion for correction.

Fig. 5
figure 5

Radiographs of a 62-year female patient that had adult spinal deformity secondary to their cervical deformity (A: Baseline, B: 1-year post-operative follow up, C: 1-year post-cervical corrective surgery follow up, 2-years after the initial spinal corrective surgery)

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Proximal junctional kyphosis (PJK) is a common complication following ASD correction [89, 90]. Research shows that PJK can be seen in almost 50% of ASD surgery patients [91]. PJK is defined as a greater than a 10° increase in the proximal junctional angle, measured from the upper-instrumented vertebra (UIV) to the vertebra two levels above (UIV + 2) [96]. The development of PJK is highly relevant to the field of CSD because, although it is not a primary ASD, PJK can also induce structural changes in the cervical spine [96]. In fact, 15–29% of patients developing PJK in the upper thoracic region following surgical correction eventually develop a concomitant CSD [91, 96]. While there is still limited work exploring the relationship between PJK and CSD, these preliminary findings indicate that surgeons need to properly examine the cervical spine prior to performing corrective ASD surgeries.

Classifications

There has been interest in establishing a uniform and reliable system for classifying CSD. However, the variable nature of deformities and the interplay between the cervical and thoracolumbar spine makes it quite difficult to understand which parameters and aspects of alignment to incorporate. In recent years, two classifications for spinal deformities, the SRS-Schwab, focusing on the thoracic and lumbar spine, and the Ames-ISSG CSD classification, have been developed. These systems combine radiographic and clinical findings to focus on the complex pathophysiological presentations of ASD (SRS-Schwab) and CSD (Ames-ISSG) [32, 97, 98]. In particular, the Ames-ISSG system intended to characterize the deformity, as well as capture the deformity-dependent disability and dysfunctionality [99].

The Ames-ISSG model uses a deformity driver descriptor and five possible modifiers of cervical deformity (Chart 1) [32, 98, 100]. These modifiers in particular help to illuminate the extent of cervical kyphosis, as well as global sagittal alignment of spine. As previously discussed, TS-CL values > 20° and cSVA > 40 mm are associated with more severe disability, as measured by NDI [26,27,28,29]. Work examining the inter- and intra-reliability could not confirm the efficacy of the system in relation to patient-reported preoperative disability [98, 99]. The authors did acknowledge that there is opportunity to improve the system and maintain that it provides a proven framework to classify CSD [98]. Additionally, there has also been discussion as to whether the system is too complex for clinicians to use due to the numerous categories [77, 101, 102].

Chart 1
figure 6

Description of Ames-ISSG classification system for the cervical spine. PI pelvic incidence, LL lumbar lordosis, PT pelvic tilt

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In comparison to Ames-ISSG, the SRS-Schwab thoracic and lumbar classification system is based upon a descriptive curve-type (thoracic only, lumbar only, double curve or no coronal deformity), with three possible spinopelvic sagittal modifiers [sagittal vertical axis (SVA), pelvic tilt (PT), and mismatch between pelvic incidence and lumbar lordosis (PI–LL)]. Using angular measurements for SVA, PT or PI–LL, SRS-Schwab classifies ASD as 0 (non-pathological), + (moderately deformed), and +  + (markedly deformed) [51]. Multiple studies have been conducted that examined the relationship between the SRS-Schwab radiographic parameters and HRQOL scores [103,104,105]. But, other studies have found that age can greatly affect the normal values for sagittal alignment and related HRQOL scores, and thus, Lafage et al. developed ideal age-adjusted parameters to help better account for these [106, 107]. Lafage et al. also found that when overcorrected according to these age-adjusted alignment goals, there was a higher rate of PJK development, especially for more elderly patients [106]. Due to the complexity of other surgical and patient factors that affect patient outcomes following corrective surgery cases, other cases have found that even though age-adjusted targets and GAP score alignment targets help to minimize mechanical complication rates and optimize HRQOL, they cannot predict mechanical complication rates, indicating the need for more patient-specific alignment targets for the preoperative planning process [108].

As mentioned previously, there is a significant body of work describing the relationship between the cervical and thoracolumbar spine. The compensatory nature of the cervical spine makes it difficult to differentiate a primary CSD or a cervical deformity due to a thoracolumbar malalignment [33, 88, 109]. The absence of a universally accepted classification system for cervical spine deformities highlights the complexity of the cervical region and the more recent evolution of CSD concerns. While the Ames-ISSG and SRS-Schwab systems have provided an excellent foundation, Lafage et al. published work consolidating cervical deformities into three morphotypes; lack of compensation (flat neck), focal deformity, and cervical-thoracic deformity [109]. They identified and correlated these morphotypes with four common clinical complaints: “dysphagia/impaired swallowing, neck pain, fatigue/sleep and myelopathy” [110]. Connecting patient’s clinical presentation and radiographic findings (flat neck with neck pain, focal deformity with fatigue, neck pain and difficulty swallowing, and cervicothoracic deformity with dysphagia/difficulty swallowing) may provide the basis for a new and improved classification system [109, 110].

Additional studies have utilized the Ames-ISSG cervical classification system to better correlate radiographic alignment parameters and HRQL outcome [61, 62, 111, 112]. Specifically, new research has focused on establishing new cervical parameter thresholds, correlated with patient frailty, through the C2–T3 angle, CL, C2 slope, McGregor slope, and T1–CL to improve patient-reported outcomes, including myelopathy [61, 62]. Correcting cervical sagittal alignment can be considered invasive, depending on the severity of deformity, age, comorbidities, or frailty status. Utilizing these parameters in cervical deformity cases has helped to minimize post-operative complications like pseudoarthrosis, distal junctional kyphosis (DJK), distal junctional failure (DJF) and development of secondary ASD [38, 113,114,115,116,117].

Research by Yilgor et al. in ASD corrective surgery has also helped to develop the Global Alignment and Proportion score (GAP score), which is used to predict mechanical complications based on pelvic incidence-based parameters [118]. Recent literature by Passias et al. has worked to construct a similar scoring profile, called the Regional Alignment and Proportion score (RAP score), specific to cervical deformity cases, to help optimize cervical surgical outcomes [119]. The RAP score utilizes relative cervical lordosis, cervical lordosis distribution index, relative McGregor’s slope, and relative pelvic version with a frailty component, to view cervical spinal alignment in the context of thoracic and global alignment. Patients who were proportioned in their RAP score showed to have diminished mechanical and radiographic complication rates and superior HRQL improvement. Through a better understanding of the patient characteristics and radiographic alignment parameters that define cervical deformity severity, surgeons have been able to use these measurements to optimize patient outcomes, preventing further post-operative complications and improving patient-reported outcomes.

More recently, Lafage et al. developed a composite alignment score, The Cervical Score, that predicts mechanical failures in CD surgery [120]. Previously, Passias et al. had worked to establish age-adjusted alignment targets for the prevention of DJK in CD surgery [121]. They found that larger preoperative malalignment of cSVA and poor post-operative sagittal alignment of C2-T3 SVA and C2 slope were associated with mechanical failure. The association of these variables with the development of DJK may be attributed to the increased shear stress on the distal end of the fusion, as it was found that greater anterior inclination of the distal construct, for patients with an LIV in the upper-thoracic spine, increased rates of DJK. Utilizing these findings and age-adjusted cervical parameters in the correction of cervical deformity can help to decrease mechanical complications and optimize patient outcomes.

Surgical correction

Surgical planning

Surgical correction of cervical deformity should be approached in a stepwise fashion. Initial planning should focus on evaluating the global spinal alignment, the primary driver of the cervical deformity, and the neurological status. Tan et al. proposed seven factors to be considered for CSD surgical planning: [76]

  1. I.

    Presence of neurological compression.

  2. II.

    Flexibility of the deformity.

  3. III.

    Presence of ankylosis.

  4. IV.

    Location of the deformity.

  5. V.

    Prior surgery.

  6. VI.

    Presence of degenerative change at proximal/distal vertebral levels.

  7. VII.

    General medical status.

Evaluation involves a detailed history and physical exam with a focus on neurological compromise, neck pain, swallowing difficulty, and quality of life. Neurological examination revealing myelopathy or radiculopathy guides the type of decompressive intervention. Flexibility of the deformity is assessed with flexion–extension x-rays of C2–C7 (extension minus flexion), but in cases of dropped head may require supine recumbent films to account for the weakness of the posterior paraspinal musculature. Computed tomography (CT) scans allow for further localization of the ankylosis limiting flexibility in rigid deformities and can guide osteotomy level requirements. Moreover, CTA (angiography) can assess for aberrant vertebral and carotid anatomy when considering invasive anterior cervical approaches. Full length standing films should be obtained to assess the location of the deformity, overall spinal balance, and contribution of possible thoracolumbar alignment. Since spinal alignment is maintained through compensatory mechanisms identified in the spine, pelvis, and lower extremities, it is imperative to capture the patient’s whole body to appropriately consider and achieve ideal alignment [122]. MRI is also necessary to assess neurologic compression and to help determine proximal and distal construct extent.

Flexibility and magnitude of correction play important roles in operative planning. Fixed rigid deformities can be sub-divided by non-ankylosed or ankylosed, to determine method of correction [77, 123]. For ankylosed patients, depending on whether the anterior column, posterior column, or both are fused, the patient may require either an anterior osteotomy with posterior instrumentation, posterior osteotomy with anterior release and posterior instrumentation, or a pedicle subtraction osteotomy, respectively. For patients who are non-ankylosed, they may only require an anterior release with or without posterior fusion, depending on stability.

Alternatively, flexible deformities can often be adequately corrected by a single anterior or posterior surgical approach. Potential for anterior column compromise warrants consideration of a combined anterior–posterior approach [77]. Controversy exists as to what degree of anterior column compromise can be overcome by posterior alone instrumentation, with some authors considering six fixations points above and below the deformity adequate for a posterior alone correction strategy [124]. Attempts at unifying algorithms have been proposed along with cervical osteotomy classifications, yet no consensus has been obtained [77, 125, 126]. Osteotomies range from facet joint resection (grade 1/2), corpectomy (grade 3), complete uncovertebral joint resection (grade 4), opening and closing wedge osteotomies (grade 5/6), and complete vertebral column resection (grade 7) [127]. Indications for more aggressive osteotomies typically involve severe fixed sagittal deformity or multiaxial instability. Operative adjuncts such as intraoperative neuromonitoring are critical in CSD surgery and should be included in the treatment armamentarium.

Surgical technique

Operative treatment also varies according to procedural approach and surgical techniques. An anterior approach has been regarded as safe and effective for symptomatic cervical disc disease patients with a stenotic cervical canal of less than four levels. Since its description in 1955, anterior cervical surgery has been considered a less invasive alternative to the traditional posterior technique as it yields satisfactory results with less morbidity, minimal interference of the spinal canal, and superior fusion rate. This approach also allows for lateral decompression without the need to destabilize the posterior elements of the cervical spine. An anterior surgical approach with a discectomy and fusion (ACDF) has also provided clinical post-operative benefits when compared to patients who were not treated with fusion, while also decreasing the likelihood of postoperative kyphosis and decreased cervical pain [128,129,130]. ACDF is commonly used for correcting sagittal cervical malalignment due to degenerative conditions, such as degenerative disc disease, but requires mobility through the disc space and facet joint. ACDF surgeries typically target vertebral levels of significant neural compression or at the apex of kyphosis [131]. ACCF is typically used to treat a fixed kyphotic deformity or pathologic fracture, and corpectomies that exceed three or more levels are generally associated with high instrumentation failure, especially without additional posterior fixation. Hybrid constructs of an ACCF with an adjacent ACDF can help to provide an additional fixation point to decrease the risk of pseudoarthrosis and instrumentation failure [131]. However, when performing a multi-level ACDF or ACCF, the surgery becomes technically demanding due to the increased usage of bone grafts, instrumentation, and development of surgery-related complications like adjacent segment disease [132, 133].

Another technically demanding area of the spine to treat is the cervicothoracic junction. Performing an anterior reconstruction and instrumentation of this junction offers a distinct advantage of stabilizing anteriorly while preserving the posterior osseo-ligamentous tension band. Moreover, the modified anterior approach (J-type manubriotomy) provides the same exposure of the cervicothoracic junction without a full median sternotomy and avoids injury to subclavian vessels during resection of the clavicle or sternoclavicular junction. There are previous studies supporting the use of an anterior approach with the manubriotomy to effectively treat the CTJ (Cervicothoracic Junction) with minimal complications [134, 135].

Figure 6 displays a 74-year-old female that presented with degenerative disc disease, cervical segmental kyphosis, and hand numbness. The patient had prior history of pulmonary disease, osteoporosis, and depression. The patient received an anterior fusion from C3–C6. Figure 6A displays baseline radiographs of the patient: cSVA of 41.7 mm, C2–C7 of − 8.1°, and TS–CL of 22.5°. Figure 6B displays 2 year follow up radiographic alignment: cSVA of 34.5 mm, C2–C7 of 5.4°, and TS–CL of 16.3°. By 2-year follow-up, the patient did not have any post-operative complications, and the cervical kyphosis has been corrected and stabilized.

Fig. 6
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Radiographs of a 74-year old female patient that presented with an anterior only correction of her degenerative disc disease and segmental kyphosis of her cervical spine (Fig. 5A: Baseline, Fig. 5B: 2-year post-operative follow up)

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On the other hand, posterior approaches are increasingly utilized in patients with exaggerated cervical lordosis, with better stabilization of the disc space and avoidance of nearby vascular structures [136]. Posterior-based cervical osteotomies are also favored in cases of rigid cervical deformity. Two major types of posterior-based osteotomies are the Smith-Peterson osteotomy (SPO) and the pedicle subtraction osteotomy (PSO) [137]. The SPO involves resecting the spinous process, lamina, ligamentum flavum and bilateral facet joints, as well as bilateral foraminotomies, to restore cervical lordosis and relieve compression of exiting nerve roots. The cervical PSO removes similar posterior vertebral elements as an SPO, as well as the pedicles, and involves taking a wedge of the vertebral body and posterolateral vertebral walls to allow for more angular correction [137].

Despite the many advantages identified with this approach, patients undergoing a posterior laminectomy or laminoplasty are more prone to develop residual myelopathy or C5 root palsy [138, 139]. In patients with cervical ossification of posterior longitudinal ligament (OPLL), the K-line, which is the straight line connecting the midpoints of the spinal canal at C2 and C7 on a neutral cervical lateral radiograph, has proven an effective alignment parameter. Patients being K + (OPLL did not exceed the K-line and stayed within the ventral area) had sufficient decompression and sufficient neurologic improvement. However, these benefits are not seen in K- patients (OPLL exceeded the K-line) which is why Takayuki et al. recommended anterior decompression surgery as the first choice for these patients [140]. Fig. 7 displays a 68-year-old female with cervical disc herniation and spondylolisthesis. To correct this deformity, the patient underwent posterior-only cervical fusion from C2–T10 with a C2–T4 laminectomy. Figure 7A displays baseline radiographs: cSVA of 32 mm, CL of 27°, and TS-CL of 38°. Figure 7B shows post-op radiographs at her 1-year follow up: cSVA of 30.7 mm, CL of 11°, and TS–CL of 21.2°. These results indicate an increase in cervical lordosis and correction of her cervicothoracic mismatch was adequately achieved via a posterior-only surgical approach.

Fig. 7
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Radiographs of a 68-year-old female patient that presented with a posterior only correction of her (Fig. 5A: Baseline, Fig. 5B: 1-year post-operative follow up)

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Determining whether to treat cervical deformity cases via an anterior or posterior surgical approach depends on the degree of deformity, etiology and status of deformity, required levels fused, and patient demographics. An anterior approach can directly remove compressive lesions of the spinal cord. However, those with greater cervical kyphosis, rigid deformities, and those who require more than three levels fused may be better indicated for a posterior or combined approach [141]. If anterior ankylosing is visualized via CT and the facet joints are not fused, anterior correction is preferred. But, if the facets are fused, a posterior osteotomy followed by an anterior correction, and posterior instrumentation may be more suitable to meet the needs of the patient. Focal kyphosis of the cervical spine is generally corrected via anterior corpectomy, but severe focal deformities at the cervicothoracic junction typically require a C7 or T1 PSO [142]. Depending on the type of cervical deformity, surgical planning can be based on a systematic approach, as proposed by Hann et al. [142].

In many cases, only conducting an anterior or posterior approach is insufficient to treat the spinal issue. This is especially the case in patients with severe fracture displacements, as they are at an increased risk for plate and screw loosening and are often times accompanied by osteoporosis or other pathological changes, which impact the rate of fusion [143]. For such cases, researchers have suggested using combined anterior–posterior surgery instead of just anterior approach [144]. However, there has not been a consensus on which approach should be done first. Some researchers have suggested that preoperative reduction of fractures by skull traction is an indication for anterior first, whereas posterior should be performed initially if there is the possible presence of articular process interlocking [145]. A study performed by Yang et al. identified that anterior-then-posterior surgeries should be done as it allows for convenient surgical positioning and decreases risk of further damage to the spinal cord [145]. For patients with severe flexion deformity, it is suggested that a short plate fixation via the anterior approach be performed followed by posterior. Potential drawbacks of combined surgeries are inherent to increased operative time, such as increased blood loss leading to an increased risk for lengthened hospital stay and perioperative complications [145]. Fig. 8 displays a 43-year-old male who underwent a cervical fusion using a combined anterior–posterior surgical approach. The patient presented with baseline hand numbness, myelopathy, degenerative kyphosis, and cervical arthritis. Figure 8A displays baseline radiographs: cSVA of 80.5 mm, CL of 21.5°, and TS-CL of 27.7°. This patient underwent a posterior fusion form C3–C7 and an anterior fusion from C5–C7. Figure 8B displays post-op radiographs (2 years): cSVA of 9.4 mm, CL of 10.5°, and TS–CL of 30.1°. At 2 years post-op, the patient did not have any radiographic or mechanical complications, and did not undergo reoperation.

Fig. 8
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Radiographs of a 43-year old male patient that underwent a combined anterior and posterior approach to the surgical correction of her cervical spine (Fig. 5A: Baseline, Fig. 5B: 2-year post-operative follow up)

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Wide variance exists amongst expert deformity surgeons on approach and levels fused in surgical management of CSD cases [146]. Despite this, there are some general principles which can be discussed. Operative goals should aim for decompression of symptomatic neurological compression, restoration of alignment within the parameters previously discussed, and each case should be considered independently. Current literature suggests a close relationship between the global spine balance parameters and quality of life of patients, but factors such as age, gender, BMI and baseline posture all have a large effect on cervical alignment that may present as normal, without symptomatology, for some patients [113]. Conservative management can be utilized for patients with mild cervical deformity and minimal to no neurologic compromise, but early surgical intervention is suggested for better patient outcomes once there are symptoms present [147]. Previously, malalignment-only deformities were typically not treated, and there is still no general consensus or support on whether surgical intervention is beneficial in the absence of deformity-related symptoms, given the possibility of post-operative complications [131].

Surgical intervention in CSD is a technically challenging endeavor, but has potential for achieving significant clinical improvement in appropriately selected patients. The strategies to best treat cervical deformities through surgery are still in their infancy. In particular, compensatory CSD that result secondary to changes in distal spinal alignment need further investigation in order to better identify patients eligible for surgical correction. Radiographic findings alone should not be the primary driver of surgical candidacy. When planning surgical treatment, consideration must be given to the global spinal alignment. Focusing solely on the presenting region of pain and disability may ultimately have unintentional consequences on the alignment, symptomatology, and may necessitate further surgical intervention.

An important concept to consider with surgical intervention for CSD, is invasiveness. As studied before in ASD cases, invasiveness indices measure procedure-related and alignment parameters to compare levels of surgical invasiveness to one another. These scores have been based on levels of decompression, extent of graft material, and area of instrumentation, as proposed by Mirza et al. and Neuman et al. for ASD patients [148, 149]. Recently, Passias et al. developed a surgical invasiveness score for CD patients, using surgical factors and radiographic parameters. It was found that extended length of stay, operative time, and high blood loss were highly predictive of the invasiveness index for CD corrective surgery [150]. Parameters included in the CD invasiveness index, that were different from that of the ASD, was removal of interbody fusions and fusion to the iliac spine or S2 from the index while being replaced by corpectomy, ACDF, and fusion to the upper cervical spine. An analysis of surgical invasiveness is important for preoperative risk assessment and surgical planning, to optimize patient outcomes and experiences.

HRQOLs in CSD surgery

To quantify the influence CSD has on the health-related quality of life (HRQOL) of patients, there are many validated self-reporting tools given to patients preoperatively and at postoperative follow-up. These multi-dimensional questionnaires provide the patient an opportunity to detail the impact their pain or disability has on day-to-day life. These include, but are not limited to, the Neck Disability Index (NDI), modified Japanese Orthopedic Association (mJOA), Short Form 36 (SF-36) and the Scoliosis Research Society (SRS)-22 item. Additionally, the EuroQol 5 dimensional (EQ-5D) questionnaire, a general survey of patient health, has been used to compare the HRQOL of CSD patients to those of other debilitating diseases [31]. Adults suffering from spinal deformities had markedly worse HRQOL scores based off of the SF-36 questionnaire compared to both self-reported healthy individuals and those with other chronic diseases [151]. Symptomatic CSD patients have EQ-5D scores on par with the bottom 25th percentile of disease states, such as blindness/low vision, emphysema, renal failure, and stroke [31]. Surgical correction of cervical deformity can result in significant improvement of patient-reported outcomes and function. Ailon et al. found 1 year follow-up of 55 CSD patients had significantly improved HRQOL metrics, as well as the EQ-5D sub-scores of mobility, return to usual activities, and pain/discomfort [152]. Other studies by Passias et al. have examined CD-specific MCID thresholds for NDI (5.42–7.48) and mJOA (1.80), which have been useful in evaluating the success of cervical corrective surgery [153]. More recent studies by Passias et al. have also investigated 2-year outcomes for patients undergoing surgical correction of CD, showing that improvement of the mJOA modifier correlated with patients also meeting the MCID for NDI [154]. Advancements in surgical technique and research, surrounding CD corrective surgery has improved surgical corrective outcomes, but tailoring correction and technique to patient frailty and deformity are key to improving associated surgical complications and post-operative outcomes.

It is also important to consider the psychological health of patients presenting with CSD. Patients that present concurrently with CSD and depression not only have worse baseline anxiety scores, but also higher levels of pre-operative pain and worse EQ-5D scores, demonstrating current tools may not be the most accurate assessment of cervical-related pain and disability [155, 156]. These measures of HRQOLs are not without limitation. The JOA, for example, uses “ability to use chopsticks” as a measure of disease impact and, therefore, the mJOA was developed [157]. While standard questionnaires do allow patients more opportunity to report individualized symptoms and health impacts, they are still limited in their ability to fully capture unique presentations. Recently, using adaptive technology and machine learning, the Patient Reported Outcomes Measurement Information System (PROMIS) has been introduced to provide more personalized measurements of pre and post-operative HRQOL impacts of CSD [156, 158, 159]. With the advancements in physicians’ ability to more fully capture individual HRQOL impact of each CSD patient, plan of care can be more specifically tailored to patients and better overall patient outcomes achieved.

Complications and safety in CSD surgery

The advancements in identifying, diagnosing and treating CSD patients over the last decade have helped to substantially improve the health and quality of life of countless patients. As the demographics change, with more patients presenting to their physicians with complaints related to the cervical spine and becoming eligible candidates for surgical intervention, it is vital that the field continues to innovate and improve patient care [99]. In particular, the rates of complications and surgical revisions are still relatively high following cervical deformity correction. Rates of complications vary depending on the surgical approach, as high as 43.6% [36, 160, 161]. The extent of these complications ranges from transient hospital-acquired conditions (HACs) to longer term radiographic and mechanical complications, often necessitating revision. Some of the most common reasons for surgical revision are infection, disease of segments adjacent to site of operation, postoperative kyphosis, incomplete fixation of the deformity and the development of either junctional pathologies, mechanical failure, or pseudoarthrosis [162]. With severe deformities, primary surgical correction may not fully resolve the structural malalignment, and symptoms may recur following a period of relief [162].

Data following cervical deformity surgeries is more limited compared to the long-term follow-up studies on the thoracolumbar spine, with a much more limited population. This may be due to the field’s relative infancy of investigation compared to thoracic and lumbar deformity care. Examination of the available data on cervical spine surgeries shows the revision rate is 12.4% by one-year follow-up, but longer term studies show rates greater than 20% [162, 163]. A significant driver necessitating reoperations is distal junction kyphosis (DJK) leading to radiographic failure (DJF), a serious complication secondary to corrective cervical spine surgery. DJK is the radiographic finding of a loss of alignment between the lowest-instrumented vertebra (LIV) and the LIV + 2, with a distal junctional angle less than − 10°, and a pre- to post-operative change in the angle of less than − 10° [161]. Unlike PJK, DJK has not been as extensively examined as it is a relatively new concept. However, two recent studies report the development of DJK in approximately 24% of cervical deformity surgery patients [161, 164]. Preliminary research in the field have elucidated important risk factors for the development of DJK, including pre-operative cSVA > 56.3 mm, TS-CL > 36.4°, and a thoracic kyphosis > 50.6° [161]. Patients presenting with radiographic measurements exceeding these cut-offs were found to be five to six times more likely to develop DJK, due to the increase in shear stress at the distal construct. More recent literature has looked at the correlation between the development of neurological comorbidities and DJK, with symptomatic DJK being defined as an angle greater than or equal to 20°. Surgical variables that predicted symptomatic occurrence were identified as using a combined approach, having a UIV of C3-4, and receiving > 7 levels fused [165]. More recently, a composite score has been developed to help evaluate the risk of the development of DJK using post-operative sagittal alignment measurements of the spine [120].

Although not as well defined, the more clinically relevant form of DJK, is the development of distal junctional failure (DJF). Some studies have found that correcting the T1S below the severe threshold of 45.5°, and further below the optimal threshold of 26° greatly reduces the risk of DJK and subsequent, DJF. Additionally, optimal alignment of C2S has also been found to minimize post-operative complications and the development of DJK and DJF [166]. Other studies have also examined how frailty and surgical parameters, such as fusions ending at L5, instead of the sacrum, also contribute to the development of DJF [167]. Not only does the development of DJK and DJF pose risk for further structural and neurologic impairment, but failure requires further surgical revision.

The high rate of revisions and complications seen in corrective cervical deformity surgeries not only have consequences for patient health but also create the possibility for inflated total cost of care. Recent studies have looked at how revision patients have significantly greater neck pain and worse myelopathy symptoms at their 1-year post-operative follow up, when compared to patients undergoing their primary procedure [168]. By 2 years, it was found that both groups had comparable outcomes. Theories surrounding these worsened outcomes are due to reduced vascular supply related to surgical damage, and scar tissue accumulation which extends operating times. Other studies have analyzed how frailty affects the cost of initial surgeries, showing comparative cost effectiveness between the two groups based on cost per QALY at 2 years ($36,731.03 vs $37,356.75) [169]. But, for older and frail patients, there is also a higher economic healthcare burden for risk of perioperative adverse events, longer hospital stays and risk of a non-home discharge destination [170].

Patients that undergo cervical spine surgery tend to show improved clinical recovery by 1 year post-operatively, however, the cost-utility of correction may be lost if the patient requires additional corrective surgery [9, 171]. Patients who undergo secondary surgery to correct DJK, incur an average additional $44,310 in costs [162]. Beyond that, the cost of treating other complications from cervical spine surgery increase the expense by tens of thousands of dollars [163, 172, 173]. To combat the economic burden of cervical spine surgery, recent work has elucidated predictive factors like body mass index and discharge destination that influence the total cost of care [174,175,176]. However, still more work examining follow-up at later time points and factors that influence rates of complications and cost is needed.

Conclusion

This literature-based state-of-the-art review highlights the current understanding of the field of cervical spine deformities. Deformities in the cervical spine cause a significant burden of disease for patients. Additionally, the management of cervical deformities is complex due to the interplay between the mechanics of the distal and proximal cervical spine, and the multiple etiologies of disease. Proposed classification systems may help in quantifying and managing cervical deformities, but these early attempts need to be refined. Surgical management of disease has made great strides in recent years in helping to alleviate patients’ symptoms however, more needs to be done to limit complications and reduce the need for reoperation. Unfortunately, at present, data relating to the field of cervical spine deformity is limited, and more research is still needed. As a result, our knowledge of cervical spine deformities in comparison with thoracic or lumbar deformities are still in its infancy.

Key points

  • When surgical correction is utilized as the mode of correction, a stepwise approach that includes global alignment, primary driver, and neurological dysfunction should be applied.

  • The advancements in diagnosis, treatment and care of CSD patients over the last decade have helped to substantially improve the health and quality of life of countless patients.

  • To combat the economic burden of cervical spine surgery, recent work has elucidated predictive factors like body mass index and discharge destination that influence the total cost of care.