K-line tilt as a novel radiographic parameter in cervical sagittal alignment

Current Concepts of Cervical Spine Alignment, Sagittal Deformity, and Cervical Spine Surgery

There are not many reports on cervical spine alignment, and only a few analyze ideal surgical approaches and optimal amounts of correction needed for the various types of deformity. We comprehensively reviewed the present literature on cervical spinal deformities (with or without myelopathy) and their surgical management to provide a framework for surgical planning. A general assessment of the parameters actually in use and correlations between cervical and thoracolumbar spine alignment are provided. We also analyzed posterior, anterior, and combined cervical surgical approaches and indications for the associated techniques of laminoplasty, laminectomy and fusion, and anterior cervical discectomy and fusion. Finally, on the basis of the NDI, SF-36, VAS, and mJOA questionnaires, we fully evaluated the outcomes and measures of postoperative health-related quality of life. We found the need for additional prospective studies to further enhance our understanding of the importance of cervical alignment when assessing and treating cervical deformities with or without myelopathy. Future studies need to focus on correlations between cervical alignment parameters, disability scores, and myelopathy outcomes. Through this comprehensive literature review, we offer guidance on practical and important points of surgical technique, cervical alignment, and goals surgeons can meet to improve symptoms in all patients.

Risk Factors for Postoperative Loss of Lordosis, Cervical Kyphosis, and Sagittal Imbalance After Cervical Laminoplasty

OBJECTIVE

A retrospective cohort study was undertaken to elucidate the risk factors of loss of cervical lordosis (LCL), kyphotic deformity, and sagittal imbalance after cervical laminoplasty.

METHODS

A total of 108 patients who underwent laminoplasty to treat cervical myelopathy and were followed for ≥2 years were included. Logistic regression analysis and multiple regression analysis were performed to identify preoperative risk factors of LCL, kyphotic deformity (cervical lordosis <0°), and sagittal imbalance (sagittal vertical axis >40 mm) at postoperative 2 years.

RESULTS

Within multivariate multiple regression analysis, C2-C7 lordosis (P = 0.002), and C2-C7 extension capacity (P<0.001) showed significant association with LCL. Furthermore, age (P = 0.043) and C2-C7 lordosis (P = 0.038) were significantly associated with postoperative kyphosis. Receiver operating characteristic curve analysis for postoperative kyphosis showed that preoperative C2-C7 lordosis of 10.5° had a sensitivity and specificity of 81.3% and 82.4%, respectively. Preoperative K-line tilt (P = 0.034) showed a significant association with postoperative cervical sagittal imbalance at postoperative 2 years. Receiver operating characteristic curve analysis showed that a K-line tilt cutoff value of 12.5° had a sensitivity and specificity of 78.6% and 77.7%, respectively, for predicting postoperative sagittal imbalance.

CONCLUSIONS

Higher preoperative C2-C7 lordosis and less preoperative cervical extension capacity were risk factors of LCL. Small preoperative C2-C7 lordosis <10.5° and younger age were risk factors of postoperative kyphosis. Furthermore, a greater K-line tilt would increase the risk of postoperative sagittal imbalance, with a cutoff value of 12.5°.

Comparative study of preoperative sagittal alignment between patients with multisegment cervical ossification of the posterior longitudinal ligament and cervical spondylotic myelopathy

BACKGROUND CONTEXT

Preoperative sagittal alignment is of great significance in the development of spinal deformities, degenerative diseases, preoperative planning, postoperative clinical evaluation, and functional recovery. However, few reports have focused on the difference in preoperative sagittal alignment between patients with ossification of the posterior longitudinal ligament (OPLL) and patients with cervical spondylotic myelopathy (CSM).

PURPOSE

To compare preoperative sagittal alignment between patients with multisegment cervical OPLL and multilevel CSM.

STUDY DESIGN

Retrospective study.

PATIENT SAMPLE

A total of 243 patients were included in this study.

OUTCOME MEASURES

The outcome measures were the Japanese Orthopaedic Association (JOA) score, visual analog scale (VAS) score, number of hand actions in 10 seconds, hand-grip strength, C2 to C7 Cobb angle, C2 to C5 Cobb angle, C5 to C7 Cobb angle, C2 to C7 sagittal vertical axis, C7 slope, T1 slope, K-line, K-line tilt, and range of motion (ROM).

METHODS

The outcome measures were calculated in the OPLL group and CSM group and the data were analyzed using the unpaired t-test, χ² test, and one-way analysis of variance.

RESULTS

A total of 243 patients (136 men, 107 women; mean age, 59.1±10.6 years) underwent surgical treatment from September 2013 to December 2021. In total, 123 patients were diagnosed with multisegment cervical OPLL, including continuous type (n=39), segmental type (n=38), and mixed type (n=46). The remaining 120 patients had multisegment CSM. The disease course in the OPLL group was significantly shorter than that in the CSM group (p<.05). Among the above preoperative measurements, the JOA score, number of hand actions in 10 seconds, hand-grip strength, and VAS score were not significantly different between the two groups (p>.05). The C2 to C7 Cobb angle was significantly larger in the OPLL than CSM group (17.7°±9.2° and 14.9°±9.3°, respectively; p< .05), as was the C5 to C7 Cobb angle (10.0°±6.3° and 7.5°±6.1°, respectively; p<.05). The ROM was significantly smaller in the OPLL than CSM group (33.1°±8.1° and 40.1°±10.9°, respectively; p<.001). Within the OPLL group, the ROM was significantly smaller in the continuous type than in the segmental type (p<.05).

CONCLUSION

Patients with multisegment cervical OPLL have greater lordotic preoperative sagittal alignment and smaller preoperative ROM than patients with CSM.

K-line tilt as a novel potential risk factor for cervical Modic change: a retrospective study

BACKGROUND

Cervical sagittal parameters are important parameters that reflect the mechanical stress in the sagittal plane of the cervical spine and are an important basis for predicting the clinical status and prognosis of patients. Although it has been confirmed that there is a significant correlation between cervical Modic changes and some sagittal parameters. However, as a newly discovered sagittal parameter, there is no report on the relationship between the K-line tilt and the Modic changes of cervical spine.

METHODS

A retrospective analysis was performed for 240 patients who underwent cervical magnetic resonance imaging scan for neck and shoulder pain. Among them, 120 patients with Modic changes, namely the MC(+) group, were evenly divided into three subgroups of 40 patients in each group according to different subtypes, namely MCI subgroup, MCII subgroup and MCIII subgroup. One hundred twenty patients without Modic changes were included in MC(-) group. We measured and compared the sagittal parameters of cervical spine among different groups, including K-line tilt, C2-C7 sagittal axial vertical distance (C2-C7 SVA), T1 slope and C2-7 lordosis. Logistic regression was used to analyse the risk factors of cervical Modic changes.

RESULTS

The K-line tilt and C2-7 lordosis were significantly different between MC(+) group and MC(-) group (P < 0.05). The K-line tilt greater than 6.72° is a risk factor for Modic changes in cervical spine (P < 0.05). At the same time, the receiver operating characteristic curve showed that this change had moderate diagnostic value when the area under the curve was 0.77.

CONCLUSION

This study shows that the K-line tilt greater than 6.72° is a potential risk factor for Modic changes in cervical spine. When the K-line tilt is greater than 6.72°, we should be alert to the occurrence of Modic changes.

TRIAL REGISTRATION NUMBER

2022ER023-1.

Correlation and reliability of cervical sagittal alignment parameters between plain radiographs and multipositional MRI images

STUDY DESIGN

A retrospective study.

OBJECTIVES

To assess the validity and reliability of cervical sagittal alignment parameters from multipositional magnetic resonance imaging (MRI) and dynamic cervical radiography.

SETTING

Hospital in Suzhou, China.

METHODS

Patients who underwent both multipositional MRI and dynamic plain radiography of the cervical spine within a 2-week interval between January 2013 and October 2021 were retrospectively enrolled in this study. The C2-7 angle, C2-7 cervical sagittal vertical axis (C2-7 SVA), T1 slope (T1S), cervical tilt, cranial tilt, and K-line tilt were measured in three different positions (neutral, flexion, and extension) with multipositional MRI and dynamic radiography. Inter- and intraobserver reliabilities were assessed by intraclass correlation coefficients (ICCs). Pearson correlation coefficients were used for statistical analyses.

RESULTS

A total of 65 (30 males and 35 females) patients with a mean age of 53.4 years (range 23-69 years) were retrospectively enrolled in this study. Significant positive correlations were noted regarding all parameters between the plain radiographs and multipositional MRI images. Inter- and intraobserver reliabilities were excellent for all cervical sagittal alignment parameters measured in the two imaging modalities. All cervical sagittal parameters had significant positive correlations with those from multipositional MRI in all three positions (p < 0.05). Pearson correlation coefficients demonstrated moderate and strong correlations between the two examinations.

CONCLUSIONS

Cervical sagittal alignment parameters measured on multipositional MRI could reliably substitute for those measured on plain radiographs. Multipositional MRI is a valuable, radiation-free alternative for diagnostic evaluation in degenerative cervical diseases.

Analysis between preoperative cervical radiographic parameters represented by the K-line tilt and the short-term prognosis of laminoplasty for posterior longitudinal ligament ossification: A retrospective study

Objectives

To investigate the relationship between preoperative radiographic parameters and the short-term prognosis of patients with cervical ossification of the posterior longitudinal ligament (OPLL) who underwent laminoplasty (LAMP).

Methods

A retrospective analysis of Cervical OPLL 50 patients with K-line (+) OPLL with no cervical kyphosis who received LAMP was performed. Based on preoperative neutral position x-ray, the K-line tilt, C2–C7 SVA (sagittal vertical axis), CL (cervical lordosis), T1 slope, and T1 slope-CL were recorded. The JOA (Japanese orthopaedic association scores) score and the cervical kyphosis change were recorded 1 year after surgery. Patients were divided into good and poor prognosis groups according to the median (12.5) of the postoperative JOA score.

Results

There were differences between the two groups in K-line tilt, C2–C7 SVA, and T1 slope (all ps &lt; 0.05). There was a strong linear correlation between the three, K-Line tilt, JOA score, and C2–C7 SVA. The degree of influence of K-line tilt, C2–C7 SVA, T1 slope on postoperative JOA score was analyzed using multiple linear regression, and the absolute value of the standardized coefficient Beta were 0.550, 0.319, 0.185, respectively. There was no cervical kyphosis change 1 year after surgery.

Conclusion

As preoperative cervical parameters, the influence of K-line tilt, C2–C7 SVA, and T1 slope on postoperative JOA score decreases in order. There was a linear relationship between preoperative K-line tilt and postoperative JOA score, implying that patients with cervical OPLL with high K-line tilt were not eligible for LAMP. K-line tilt was not predictive of cervical kyphosis change after LAMP in patients with OPLL at short-term follow-up.

K-Line Tilt is a Predictor of Postoperative Kyphotic Deformity After Laminoplasty for Cervical Myelopathy Caused by Ossification of the Posterior Longitudinal Ligament

STUDY DESIGN

Retrospective single-center study.

OBJECTIVES

K-line is a decision-making tool to determine the appropriate surgical procedures for patients with cervical ossification of the posterior longitudinal ligament (C-OPLL). Laminoplasty (LAMP) is one of the standard surgical procedures indicated on the basis of K-line measurements (+: OPLL does not cross the K-line). We investigated the impact of K-line tilt, a radiographic parameter of cervical sagittal balance measured using the K-line, on surgical outcomes after LAMP.

METHODS

The study included 62 consecutive patients with K-line (+) C-OPLL who underwent LAMP. The following preoperative and postoperative radiographic measurements were evaluated: (1) the K-line, (2) K-line tilt (an angle between the K-line and vertical line), (3) center of gravity of the head -C7 sagittal vertical axis, (4) C2-C7 lordotic angle, (5) C7 slope, and (6) C2-C7 range of motion. Clinical results were evaluated using the Japanese Orthopedic Association scoring system for cervical myelopathy (C-JOA score).

RESULTS

All the patients had non-kyphotic cervical alignment (CL ≥ 0°) preoperatively; however, kyphotic deformity (CL < 0°) was observed in 6 patients (9.7%) postoperatively. The recovery rate of the C-JOA scores was poor in the kyphotic deformity (+) group (7.8%) than in the kyphotic deformity (-) group (47.5%). The K-line tilt was identified to be a preoperative risk factor in the multivariate analysis, and the cutoff K-line tilt for predicting the postoperative kyphotic deformity was 20°.

CONCLUSIONS

LAMP is not suitable for K-line (+) C-OPLL patients with K-line tilts >20°.

Clinical Effects of Preoperative K-Line Tilt on Patient Outcomes After Laminoplasty for Cervical Ossification of the Posterior Longitudinal Ligament

OBJECTIVE

We sought to clarify the effects of the preoperative K-line tilt on cervical sagittal balance and patient outcomes after laminoplasty for cervical ossification of the posterior longitudinal ligament (OPLL).

METHODS

A retrospective analysis of 45 patients with OPLL treated by laminoplasty from January 2013 to December 2018 was performed. The radiological parameters included the K-line tilt, C2-C7 sagittal vertical axis, C2-C7 lordosis, T1 slope, and T1 slope minus C2-C7 lordosis. The patient quality of life outcomes were assessed using the neck disability index, Japanese Orthopaedic Association disability scale, and visual analog scale. The patients were classified into 2 groups according to the median preoperative K-line tilt angle (14.1°): the high K-line tilt group (n = 23) and the low K-line tilt group (n = 22). The postoperative cervical alignment changes and patient outcomes were compared and analyzed.

RESULTS

The clinical outcomes demonstrated overall improvement at the final follow-up. The C2-C7 lordosis had significantly decreased from 13.5° ± 9.5° preoperatively to 10.2° ± 9.7°. The C2-C7 lordosis was less in the high K-line tilt group than that in the low K-line tilt group. In addition, the high K-line tilt group revealed significantly greater kyphotic changes and a greater loss of cervical lordosis compared with the low K-line tilt group. Finally, the quality of life outcomes and postoperative visual analog scale scores were higher in the high K-line tilt group.

CONCLUSIONS

The results of the present study have shown that the parameter K-line tilt is an ideal radiological parameter for predicting the outcomes and determining the need for laminoplasty for cervical ossification of the OPLL. Patients with a higher K-line tilt preoperatively experienced more kyphotic alignment changes and neck pain after laminoplasty.

Mid-term Surgical Outcome of Posterior Decompression With Instrumented Fusion in Patients With K-line (-) Type Cervical Ossification of the Posterior Longitudinal Ligament With a 5-Year Minimum Follow-up

STUDY DESIGN

A retrospective case-control study.

OBJECTIVE

The objective of this study was to assess mid-term surgical outcomes after posterior decompression with instrumented fusion (PDF) in patients with K-line (-) type cervical ossification of the posterior longitudinal ligament (OPLL).

SUMMARY OF BACKGROUND DATA

The poor surgical outcome for K-line (-) type cervical OPLL can result from posterior decompression alone.

MATERIALS AND METHODS

We reviewed cases of K-line (-) type cervical OPLL in 24 patients who underwent PDF in our institute from 2002 to 2014. As a control, we used K-line (-) type cervical OPLL in 9 patients who underwent laminoplasty before 2002 (LMP group). The neurological status and radiographic findings were evaluated retrospectively.

RESULTS

The preoperative Japanese Orthopedic Association score was 7.9±2.4 points in the PDF group and 7.4±2.3 points in the LMP group (P=0.584). The postoperative Japanese Orthopedic Association score was 11.7±2.6 points in the PDF group and 9.2±2.0 points in the LMP group at a 5-year follow-up (P=0.008). The recovery rate on average was 39.0% in the PDF group and 14.9% in the LMP group at a 5-year follow-up (P=0.037). The range of motion postoperatively at the maximal spinal cord compression level decreased significantly in the PDF group. The C2-C7 angle was 2.7 degrees of kyphosis in the PDF group, whereas 5.5 degrees of kyphosis was found in the LMP group at a 5-year follow-up (P=0.303). The center of gravity of the head-C7 sagittal vertical axis was 40 mm in the PDF group and 43 mm in the LMP group (P=0.936).

CONCLUSIONS

The relatively good surgical outcome could be obtained by PDF for patients with K-line (-)-type cervical OPLL. The addition of posterior instrumented fusion eliminated the dynamic factor at the level of maximal spinal cord compression.

LEVEL OF EVIDENCE

Level IV.

Cervical Sagittal Alignment: Literature Review and Future Directions

Cervical alignment as a concept has come to the forefront for spine deformity research in the last decade. Studies on cervical sagittal alignment started from normative data, and expanded into correlation with global sagittal balance, prognosis of various conditions, outcomes of surgery, definition and classification of cervical deformity, and prediction of targets for ideal cervical reconstruction. Despite the recent robust research efforts, the definition of normal cervical sagittal alignment and cervical spine deformity continues to elude us. Further, many studies continue to view cervical alignment as a continuation of thoracolumbar deformity and do not take into account biomechanical features unique to the cervical spine that may influence cervical alignment, such as the importance of musculature connecting cranium-cervical-thoracic spine and upper extremities. In this article, we aim to summarize the relevant literature on cervical sagittal alignment, discuss key results, and list potential future direction for research using the '5W1H' framework; "WHO" are related?, "WHY" important?, "WHAT" to evaluate and "WHAT" is normal?, "HOW" to evaluate?, "WHEN" to apply sagittal balance?, and "WHERE" to go in the future?

Analysis of a radiographic parameter K-line tilt following adjacent two-level anterior cervical discectomy and fusion: a retrospective study

BACKGROUND

T1s, C2-7 lordosis, and C2-7 sagittal vertical axis (SVA) are the three most important sagittal parameters in the cervical spine. This study was conducted to investigate the relationships between classical sagittal alignment parameters and a new parameter, K-line tilt, and to study the impact of K-line tilt.

MATERIAL AND METHODS

A total of 72 patients who underwent adjacent two-level anterior cervical discectomy and fusion (ACDF) were retrospectively analyzed. Radiographic measurements included T1 slope (T1s), C2-7 lordosis, segment angle (SA), C2-7 SVA, and K-line tilt. The Neck Disability Index (NDI) scores were used to evaluate the clinical prognosis. Pearson correlation coefficients were calculated between radiographic measures. Linear regression analysis was used to analyze the relationship between follow-up K-line tilt and NDI.

RESULTS

ΔNDI was positively correlated with ΔT1s (r = 0.620, p < 0.05), ΔC2-7 SVA (r = 0.645, p < 0.05), and ΔK-line tilt (r = 0.702, p < 0.01); ΔK-line tilt was positively correlated with ΔT1s (r = 0.650, p < 0.05), ΔSA (r = 0.269, p < 0.05), and ΔC2-7 SVA (r = 0.293, p < 0.05); ΔT1s was positively correlated with ΔC2-7 lordosis (r = 0.428, p < 0.05), ΔSA (r = 0.631, p < 0.01), and ΔC2-7 SVA (r = 0.235, p < 0.05); ΔC2-7 lordosis was positively correlated with ΔSA (r = 0.666, p < 0.05) and negatively correlated with ΔC2-7 SVA (r = - 0.467, p < 0.01). The preoperative and postoperative K-line tilt values were statistically significant (p < 0.01), increasing from (7.50 ± 6.48)° to (9.95 ± 5.09)°. Preoperative NDI was positively correlated with preoperative C2-7 SVA (r = 0.639, p = 0.011) and K-line tilt (r = 0.516, p = 0.026); follow-up NDI was positively correlated with follow-up T1s (r = 0.664, p = 0.038), C2-7 SVA (r = 0.756, p = 0.004), and K-line tilt (r = 0.832, p = 0.006). The linear regression model showed that when the follow-up K-lint tilt was > 23.75°, NDI scores were > 25 (R² = 0.737, p = 0.000).

CONCLUSION

This study showed that the K-line tilt was strongly correlated with the C2-C7 SVA, indicating that the K-line tilt can be used as another cervical parameter to evaluate cervical alignment in adjacent two-level ACDF. K-line tilt is an important parameter similar to the classical parameter C2-C7 SVA. In particular, a K-line tilt greater than 23.75 corresponded to a worse clinical prognosis, which was defined as an NDI score greater than 25.

Cervical kyphosis in asymptomatic populations: incidence, risk factors, and its relationship with health-related quality of life

Background

Cervical kyphosis has been pointed out in asymptomatic populations. The purposes of this study were (1) to investigate the incidence of cervical kyphosis in asymptomatic populations, (2) to identify risk factors related to cervical kyphosis, and (3) to assess the relationship between cervical kyphosis and health-related quality of life (HRQOL).

Methods

A cohort of 235 asymptomatic volunteers’ records was retrospectively analyzed. Radiographic parameters of the coronal and sagittal planes were measured in the full-length spine x-ray. All patients were classified into two groups based on the cervical lordosis angle: cervical lordosis (CL) and cervical kyphosis (CK). HRQOL was evaluated by EQ-5D and SF-36 (PCS and MCS) questionnaires.

Results

CK was observed in 90 of 235 (38.3%) participants. There was a significant difference with regard to age between volunteers with CK and CL (32.23 ± 8.12 vs. 42.12 ± 6.14, p < 0.05). Several parameters had a significant relationship with CK, including TK, T1 slope, TIA, SVA, and CT. Logistic regression analysis identified age, TK, T1 slope, and SVA as independent risk factors of CK. In addition, there was a negative correlation between CK and the parameters of HRQOL (EQ-5D, − 0.63; PCS, − 0.68; MCS, − 0.59).

Conclusions

The incidence of CK in normal populations is 38.3%. Some spinal parameters are related to CK. CK is associated with the HRQOL.

Cervical Cord Compression and Whole-Spine Sagittal Balance: Retrospective Study Using Whole-Spine Magnetic Resonance Imaging and Cervical Cord Compression Index

OBJECTIVE

We sought to investigate the relationship between cervical cord compression and factors related to whole-spine sagittal balance.

METHODS

This retrospective single-center study included patients who visited our clinic for the evaluation of lumbar pathology including trauma and degeneration. Patients aged 60-89 years who underwent whole-spine sagittal T2 scout magnetic resonance imaging and whole-spine radiograph between 2014 and 2018 were included in our study. We consecutively enrolled 100 patients for our study without any prejudice. We collected data on patient characteristics, diagnosis, cervical cord compression index (CCI), sagittal vertical axis (C7-S1, C2-7), and other parameters related to sagittal balance such as pelvic incidence minus lumbar lordosis. Pearson correlation coefficients were calculated to compare CCI with each whole-spine sagittal balance parameter.

RESULTS

Of the 100 patients, 44 were men. The mean age was 74.21 years. On the basis of Pearson correlation coefficients, CCI showed the strongest positive linear correlation with C7-S1 sagittal vertical axis (r = 0.688; P < 0.01), followed by the C2-7 sagittal vertical axis (r = 0.563; P < 0.01).

CONCLUSIONS

Cervical cord compression is more likely to develop in patients with sagittal imbalance. It is important to use whole-spine radiograph and whole-spine T2 scout magnetic resonance imaging to analyze CCI in these patients.