Impact of K-Line (-) in the Neck-Flexion Position on Patient-reported Outcomes After Cervical Laminoplasty For Patients With Ossification of the Posterior Longitudinal Ligament

Effect of K-line (-) or (+) on surgical outcomes in cervical ossification of the posterior longitudinal ligament: A systematic and meta-analysis

BACKGROUND

To conduct a systematic review and meta-analysis assessing the influence of K-line status on postoperative clinical outcomes in patients with cervical posterior longitudinal ligament ossification (OPLL).

METHODS

We searched PubMed, Embase, OVID, Cochrane Library, and Web of Science databases for English-language literature related to K-line and OPLL up to June 7, 2024. The study underwent rigorous selection, quality assessment, and data extraction, followed by meta-analysis using Review Manager 5.3 and Stata 17.0 software. This study has been registered with the international PROSPERO registry (registration number: CRD42024558578).

RESULTS

Seventeen articles encompassing 1247 patients were included. The meta-analysis revealed that patients with a positive K-line (K-line (+)) exhibited significantly enhanced Japanese Orthopaedic Association score recovery rate (mean differences [MD] = 19.28, 95% confidence interval [CI]: 12.28-26.28, P < .00001), Japanese Orthopaedic Association score (MD = 1.51, 95% CI: 0.64-2.37, P = .0007), C2-C7 Cobb angle (MD = 6.45, 95% CI: 3.73-9.17, P < .00001), alongside reduced occupation ratio (MD = -7.67, 95% CI: -10.86 to -4.49, P < .00001), C2-C7 sagittal vertical axis (MD = -6.18, 95% CI: -8.36 to -3.99, P < .00001), and neck disability index (MD = -1.85, 95% CI: -3.18 to -0.52, P = .006) at final follow-up compared to those with a negative K-line (K-line (-)). No significant differences were observed in postoperative complication rates (odds ratio = 1.15, 95% CI: 0.41-3.20, P = .79), final follow-up visual analog scale scores (MD = -0.10, 95% CI: -0.80 to 0.59, P = .77), or T1 slope (MD = 2.66, 95% CI: -0.20 to 5.52, P = .07) between the 2 groups.

CONCLUSION

A positive preoperative K-line (K-line (+)) is a better predictor of prognosis and is associated with improved clinical outcomes in patients with multi-segmental cervical OPLL compared to a negative K-line (K-line (-)).

An Algorithmic Roadmap for the Surgical Management of Degenerative Cervical Myelopathy: A Narrative Review

Degenerative cervical myelopathy (DCM) is a leading cause of disability, and its surgical management is crucial for improving patient neurological outcomes. Given the varied presentations and severities of DCM, treatment options are diverse. Surgeons often face challenges in selecting the most appropriate surgical approach because there is no universally correct answer. This narrative review aimed to aid the decision-making process in treating DCM by presenting a structured treatment algorithm. The authors categorized surgical scenarios based on an algorithm, outlining suitable treatment methods for each case. Four primary scenarios were identified based on the number of levels requiring surgery and K-line status: (1) K-line (+) and ≤3 levels, (2) K-line (+) and ≥3 levels, (3) K-line (-) and ≤3 levels, and (4) K-line (-) and ≥3 levels. This categorization aids in determining the appropriateness of anterior or posterior approaches and the necessity for fusion, considering the surgical level and K-line status. The complexity of surgical situations and diversity of treatment methods for DCM can be effectively managed using an algorithmic approach. Furthermore, surgical techniques that minimize the stages and address challenging conditions could enhance treatment outcomes in DCM.

Effect of K‑line on posterior cervical surgery versus anterior cervical surgery in patients with multi-level ossification of posterior longitudinal ligament

PURPOSE

To evaluate the influence of K-line on the outcome of open-door laminoplasty versus anterior cervical corpectomy decompression and fusion (ACCF) for patients with more than two levels of ossification of the posterior longitudinal ligament (OPLL).

METHODS

60 patients undergoing open-door laminoplasty and 62 patients undergoing ACCF from January 2013 to January 2020 with more than 2 years of follow-up were included. Eighty-four cases with the ossification mass not beyond the K-line were grouped as K-line (+), while thirty-eight cases were grouped as K-line (-). The operation time, intraoperative blood loss, hospital stay, preoperative, postoperative, and last follow-up JOA scores, and postoperative complications were investigated.

RESULTS

The improvement rate of JOA scores after posterior approaches in cases of group K-line (+) and K-line (-) was 72.4% and 53.1%, respectively, which showed a significant difference (P < 0.01). In group K-line (+), the improvement of JOA scores for open-door laminoplasty was 73.4% and 71.8% for ACCF, which showed no significant difference (P > 0.05). In group K-line (-), the improvement of JOA scores for ACCF was 52.1% and 42.9% for open-door laminoplasty, which showed a significant difference (P < 0.05). The incidence of C5 palsy was significantly lower in cases with ACCF than in cases with open-door laminoplasty (P < 0.05).

CONCLUSION

For patients with more than two levels of OPLL, preoperative K-line (+) predicates a better outcome than K-line (-). For cases with K-line (-), ACCF provides better neurologic function recovery. For patients with K-line (+), open-door laminoplasty provides the same neurologic function recovery of ACCF.

Are clinical outcomes affected by laminoplasty method and K-line in patients with cervical ossification of posterior longitudinal ligament? A multicenter study

BACKGROUND

Open-door laminoplasty (ODL) and French-door laminoplasty (FDL) are the main laminoplasty techniques used to treat cervical ossification of the posterior longitudinal ligament (C-OPLL). However, few studies have compared the outcomes of ODL and modified FDL (mFDL) for C-OPLL. We explored the differences in outcomes between ODL and mFDL for C-OPLL and analyzed the technical efficacy of each procedure in patients with K-line (+) or (-) C-OPLL.

METHODS

From January 2010 to December 2015, 202 patients with K-line (+) or (-) C-OPLL were retrospectively recruited from 4 institutions. Clinical outcomes were evaluated using the Japanese Orthopaedic Association (JOA) score, JOA score recovery rate, operative time, blood loss, and complications. Univariate analysis and binary logistic regression models were adjusted for confounding factors.

RESULTS

Two hundred patients (mFDL, n = 69; ODL, n = 131) with a median follow-up of 42 months (range 36-54 months) were included. The postoperative JOA score significantly improved in both groups (P < 0.05). After adjusting for confounding factors, there was a statistically significant difference in blood loss (≥ 300 mL) between the two groups (P = 0.005), but there was no significant difference in the postoperative JOA score (≥ 14) (P = 0.062), JOA score recovery rate (≥ 0.82) (P = 0.187), or operative time (≥ 90 min) (P = 0.925). C5 palsy tended to occur more often in the mFDL group, although the difference was not significant (P > 0.05). The stratified analysis of the K-line status showed more blood loss in K-line (+) patients who underwent mFDL, but there was no significant difference in the postoperative JOA score, JOA score recovery rate, or operative time between the ODL and mFDL groups. Additionally, there was no significant difference in blood loss, postoperative JOA score, JOA score recovery rate, or operative time among all patients with K-line (+) or (-) C-OPLL in both groups.

CONCLUSIONS

Both ODL and mFDL are effective for patients with C-OPLL. However, more blood loss tends to occur during mFDL. This study showed no significant difference in the operative time or incidence of complications between the two techniques. The efficacy of ODL and mFDL was not affected by the K-line status (+ or -) in patients with C-OPLL.

The effect of K-line classification in different cervical dynamic position on surgical outcomes in patients with ossification of the posterior longitudinal ligament after anterior controllable antedisplacement and fusion

Purpose

To investigate whether the K-line classification in different cervical dynamic position of patients with Ossification of the Posterior Longitudinal Ligament (OPLL) affects clinical outcome after Anterior Controllable Antedisplacement and Fusion (ACAF) surgery.

Methods

A total of 93 patients who suffered from cervical spondylosis caused by OPLL underwent ACAF surgery between June 2015 and December 2017 in a single institution. Neutral, neck-flexed and neck-extended cervical radiographs were obtained from every patient. Subsequently they were classified into K-line (+) and K-line (−) with reference to the K-line classification criteria. Clinical outcomes were assessed by the JOA score, improvement rate (IR) and visual analogue scale (VAS). Radiological assessment included Cobb angle and occupation ratio (OR) of OPLL. Correlations between the long-term surgical outcomes and classification of K-line in different dynamic position were analyzed by one-way analysis of variance.

Results

Significant improvements were shown in all postoperative clinical and radiographic assessments (P < 0.05). There were no differences in IR, Cobb angle and VAS among flexion K-line (−), flexion K-line (+), extension K-line (−) and extension K-line (+) at the 2-year follow-up (P > 0.05). However, the OR of extension K-line (−) (16.13% ± 11.58%) was higher than that of extension K-line (+) (9.00% ± 10.27%) and flexion K-line (+) subgroup (9.47% ± 9.97%) (P < 0.05).

Conclusion

The ACAF procedure has shown satisfactory surgical outcomes in various K-line classifications in different dynamic position.

Factors contributing to neck pain in patients with degenerative cervical myelopathy: A prospective multicenter study

PURPOSE

Although the understanding of the mechanisms of low back pain due to spinopelvic sagittal imbalance has strengthened, the understanding of the mechanisms of neck pain remains insufficient. Thus, this study aimed to identify the factors associated with preoperative and postoperative neck pain in patients with degenerative cervical myelopathy who underwent laminoplasty.

METHODS

In this prospective multicenter study, we prospectively enrolled patients who were scheduled for laminoplasty for degenerative cervical myelopathy. The associations between different variables and the Numerical Pain Rating Scale (NRS) scores for neck pain were investigated using univariate and multiple linear regression models.

RESULTS

In total, 92 patients were included in the current study. The univariate analysis showed that age, sex, cervical lordosis in neutral and extension, and thoracic kyphosis were significantly associated with the preoperative NRS score for neck pain; moreover, preoperative cervical lordosis in extension and range of motion and postoperative cervical lordosis in neutral, flexion, and extension were significantly associated with the postoperative NRS Scale score for neck pain. Stepwise multiple regression analysis showed that the independent factors contributing to preoperative neck pain were preoperative cervical lordosis in extension, sex, and age. The independent preoperative predictor and contributor to postoperative neck pain were preoperative cervical lordosis in extension and postoperative cervical lordosis in extension, respectively.

CONCLUSIONS

Cervical lordosis in extension showed significant association with neck pain in patients with degenerative cervical myelopathy. Therefore, when performing laminoplasty for patients with a low cervical lordosis in extension, attention should be paid to residual postoperative neck pain.

The Kappa Line as a Regional Modification of the K-line: A Predictor of Neurological Outcome and Indicator of the Adequate Level of Decompression in Selective Laminoplasty

STUDY DESIGN

This is a retrospective cohort study.

OBJECTIVE

The aim was to introduce Kappa line (modification of K-line) for the prediction of postoperative neurological recovery after selective cervical laminoplasty (LMP) and use in determining the decompression level.

SUMMARY OF BACKGROUND DATA

The K-line is a radiographic marker that can predict prognosis and aid in surgical planning for patients undergoing LMP through C3 to C7. However, its efficacy in LMP involving limited segments is unclear. Furthermore, no specific radiographic marker to predict the prognosis of selective LMP has been reported.

MATERIALS AND METHODS

Fifty-one consecutive patients with a minimum 2-year follow-up after selective LMP for cervical myelopathy caused by ossification of posterior longitudinal ligament were retrospectively reviewed. The Kappa line was defined as a straight line connecting the midpoints of the spinal canal made by remaining bony structure after decompression procedures on a plain lateral radiograph in the neutral position. Patients were classified as K-line (+) or (-) and Kappa line (+) or (-) based on whether the ossified mass crossed the indicator line.

RESULTS

The Kappa line (+) group demonstrated significantly higher Japanese Orthopaedic Association (JOA) recovery rate (P=0.01), final JOA score (P<0.01), and dural sac diameter (P<0.01) postoperatively than the Kappa line (-) group. Cord compression grade was significantly lesser in the Kappa line (+) group. However, the K-line-based classification did not demonstrate significant difference in JOA recovery rate, final JOA score, and cord compression grade between the (+) and (-) groups; the dural sac diameter was significantly higher in the K-line (+) group (P<0.01).

CONCLUSIONS

The Kappa line showed better correlation with ossification of posterior longitudinal ligament size and cervical alignment, providing better prediction of neurological recovery and remaining cord compression following selective LMP. Therefore, the Kappa line can aid in determining the level of decompression in selective LMP.

Factors Negatively Influencing Postoperative Improvement After Laminoplasty in Degenerative Cervical Myelopathy

STUDY DESIGN

This was a retrospective study of prospectively collected data.

OBJECTIVE

In this study, we aimed to characterize a population of patients with degenerative cervical myelopathy (DCM) and a history of poor postoperative neurological recovery and to identify risk factors associated with poor neurological recovery after laminoplasty.

SUMMARY OF BACKGROUND DATA

Kyphotic cervical alignment has been considered a relative contraindication to laminoplasty in recent years; hence, laminoplasty has been decreasingly performed for the treatment of DCM in patients with cervical kyphosis. However, the effect of global spinal alignment on postoperative outcomes has not been extensively investigated.

MATERIALS AND METHODS

We prospectively enrolled patients who were scheduled for laminoplasty for DCM. Outcome (at enrollment and 1 y after surgery) and risk factor analyses were performed by comparing the good recovery and poor recovery groups. The Spearman correlation coefficient was used to evaluate the relationships between the recovery rate and the preoperative radiographic factors.

RESULTS

In total, 101 patients completed the 1-year follow-up. Regarding clinical outcomes, the Japanese Orthopedic Association score for the assessment of cervical myelopathy, European Quality of Life-5 Dimensions, and Neck Disability Index scores improved postoperatively. The recovery rate was significantly correlated with the preoperative sagittal vertical axis (SVA). The patients in the poor recovery group were older than those in the good recovery group. Univariate analyses showed that the SVA and T1 pelvic angle were significantly higher in the poor recovery group. Lastly, stepwise logistic regression analysis showed that a higher SVA was an independent predictor of poor recovery after laminoplasty.

CONCLUSIONS

The SVA and T1 pelvic angle were significantly higher in the poor recovery group. A high preoperative SVA is an independent predictor for poor recovery after laminoplasty. Therefore, indications for laminoplasty in elderly DCM patients with a high preoperative SVA should be carefully considered.

LEVEL OF EVIDENCE

Level III.

Modified K-Line in Neck Extension Is a Prognostic Indicator of the Surgical Outcome at 5 Years After Cervical Laminoplasty for Cervical Spondylotic Myelopathy

STUDY DESIGN

A retrospective comparison of the surgical outcome after cervical laminoplasty for cervical spondylotic myelopathy (CSM) using a modified K-line based on lordosis in neck extension as a predictor: in K-line Back CSM (KB group), the K-line crosses the ventral edge of any of the spinous processes, whereas in K-line Front CSM (KF group), the K-line does not.

OBJECTIVE

To investigate the neurological and radiological outcomes 5 years after surgery and the contact between the spinal cord and posterior elements after laminoplasty for CSM using the modified K-line.

SUMMARY OF BACKGROUND DATA

No indicators on a lateral radiograph can predict the neurological outcome after laminoplasty for CSM.

METHODS

Patients with CSM were divided into KB (n = 20) and KF groups (n = 13). We compared the postoperative Japanese Orthopedic Association (JOA) score, recovery rate, grip-and-release and foot-tapping test results, alignment, and contact between the spinal cord and posterior elements between the two groups.

RESULTS

The postoperative JOA score and its recovery rate were significantly lower in the KB group (12.4 points and 34.1%, respectively) than in the KF group (14.1 points and 59.0%, respectively) at final follow-up (P = 0.0415 and 0.0458). The grip-and-release and foot-tapping test results improved significantly in the KF group but not in the KB group. In the KB group, a larger lordotic angle in extension at 1 year postoperatively continued until final follow-up. The rate of recovery of the JOA score in patients with contacts at both C4/5 and C5/6 and any contact in the KB group (-1.5% and 31.9%, respectively) were lower (P = 0.0013 and 0.0534, respectively) than those in the KF group (58.6% and 60.7%, respectively).

CONCLUSION

The K-line Back predicts a poor neurological outcome after laminoplasty for CSM. Decompression with fusion may be recommended for these patients.Level of Evidence: 4.

Flexional distance index: A new prognostic indicator of neurological outcomes at 4 years after cervical laminoplasty for K-line (+) ossification of the posterior longitudinal ligament

OBJECTIVE

We aimed to investigate whether K-line in the neck flexion (FK-line), flexion angle (FA), or flexion distance index (FDI) could predict the recovery rate of the Japanese Orthopedic Association score (RR-JOA) at 4 years after cervical laminoplasty (LP) for ossification of the posterior longitudinal ligament (OPLL).

METHODS

A new index, i.e., the FDI, which is based on the degree of neck flexion and the OPLL size on a lateral radiograph. "Flexional distance" is the distance from C2 to C7 in neck flexion, and "distance to OPLL" is the maximal distance from the line of the flexional distance to OPLL. FDI was defined as follows: FDI = flexional distance/distance to OPLL. Twenty-three patients with K-line (+) OPLL were evaluated at 4 years after LP (follow-up rate, 92%). We investigated the relationships between preoperative radiological factors, including FK-line, FA, and FDI, and RR-JOA at 4 years postoperatively.

RESULTS

Preoperative FK-line and FA were significantly related with the RR-JOA at 1 year postoperatively, but not at 4 years postoperatively. Preoperative FDI was significantly positively correlated with the RR-JOA at 1 year and 4 years postoperatively (P = 0.0132, r = 0.504 and P = 0.0183, r = 0.484, respectively). Preoperative FDI < 2.5 was associated with worsening of the RR-JOA at 4 years postoperatively, with a probability of 80% DISCUSSIONS: FDI could predict the RR-JOA at 4 years after LP for OPLL. Decompression with fusion may be recommended for patients with preoperative FDI < 2.5.

LEVEL OF EVIDENCE

4.

Exceptional Conditions for Favorable Neurological Recovery After Laminoplasty in Cases with Cervical Myelopathy Caused by K-line (-) Ossification of Posterior Longitudinal Ligament

STUDY DESIGN

A retrospective observational study.

OBJECTIVE

To clarify the exceptional conditions for a favorable neurological recovery after laminoplasty (LMP) for cervical myelopathy caused by K-line (-) ossification of the posterior longitudinal ligament (OPLL).

SUMMARY OF BACKGROUND DATA

The K-line-based classification of cervical OPLL was developed to predict insufficient neurological recovery after LMP. For patients with K-line (-) OPLL, LMP generally yields the least improvement because of inadequate decompression of the spinal cord; however, there are some exceptional cases wherein LMP promotes favorable neurological recoveries.

METHODS

We retrospectively reviewed the medical records of 106 consecutive patients who underwent LMP for cervical OPLL to determine the demographic data, radiographic findings, and neurological recoveries of the patients as assessed preoperatively and 2 years postoperatively by their Japanese Orthopedic Association (JOA) scores. The factors associated with favorable outcomes after LMP in patients with K-line (-) were then investigated.

RESULTS

Of 106 total patients, 31 were classified as K-line (-), of whom 21 achieved the least neurological recovery after LMP (JOA recovery rate <50%), while the remaining 10 patients achieved favorable outcomes (JOA recovery rate ≥50%). Among the K-line (-) group patients, those with ext-K-line (+), which changed to K-line (+) in the neck-extended position, and the patients with up-K-line (-), in whom the lesion responsible for myelopathy in the upper cervical spine (C3 or above), showed favorable neurological recoveries after LMP.

CONCLUSION

Our data shows that, even for patients with K-line (-) OPLL, a favorable neurological recovery can be expected after LMP in cases in which the OPLL is in the upper cervical spine or the K-line changes to (+) in the neck-extended position. This means that K-line-based predictions of surgical outcomes after LMP should be indicated for patients with OPLL in the middle and lower cervical spine with limited extension mobility.Level of Evidence: 4.

Influence of K-line on intraoperative and hidden blood loss in patients with ossification of the posterior longitudinal ligament when undergoing unilateral open-door laminoplasty

Background

The K-line is a virtual straight line that connects the midpoints of the anteroposterior spinal canal diameter from C2 to C7 on a cervical lateral X-ray film. Patients with cervical ossification of the posterior longitudinal ligament (OPLL), in which the peak of the OPLL exceeds the K-line (K-line [-]), are less likely to experience sufficient decompression after laminoplasty compared with patients for whom the OPLL does not exceed the K-line (K-line [+]). This retrospective study investigated the influence of K-line position relative to the OPLL on intraoperative and hidden blood loss during unilateral open-door laminoplasty for OPLL.

Methods

Data were retrospectively analyzed of 108 patients with OPLL who underwent unilateral open-door laminoplasty between April 2015 and March 2018. Patient cases were categorized as K-line (+) or (-). The evaluated perioperative parameters were haematocrit, haemoglobin, intraoperative and hidden blood loss, surgical time, postoperative drainage, and complications. Radiological parameters included ossification occupancy ratio and C2-7 lordosis.

Results

The K-line (+) and K-line (-) groups were statistically comparable with regard to age, gender, body mass index, OPLL classification, medication history, C2-7 lordosis, postoperative haemoglobin and haematocrit, postoperative drainage, hidden blood loss, and complications. The occupying ratio of the K-line (-) group was significantly greater than that of the K-line (+) group (49.5 ± 15.3% cf. 42.3 ± 10.1%; P = 0.006), and the intraoperative blood loss was also significantly higher (286 ± 110.5 mL cf. 205.5 ± 98.3 L, P = 0.003). The hidden blood loss of the K-line (-) group was higher than that of the K-line (+), but not significantly (295.5 ± 112.6 mL cf. 265.6 ± 103.8 mL; P = 0.072).

Conclusion

Intraoperative and hidden blood loss associated with unilateral open-door laminoplasty can be predicted by the spatial relationship of the K-line and osteophyte. This relationship is a simple and practical index that may help surgeons determine the appropriate surgical strategy for patients with OPLL.

Vertebral Body Sliding Osteotomy for Cervical Myelopathy With Rigid Kyphosis

Cervical spondylotic myelopathy is surgically demanding when associated with rigid kyphosis. Posterior surgery cannot restore cervical lordosis, and adequate decompression is not possible with rigid kyphosis. Vertebral body sliding osteotomy (VBSO) is a safe and novel technique for anterior decompression in patients with multilevel cervical spondylotic myelopathy. It is safe in terms of dural tear, pseudarthrosis, and graft dislodgement, which are demonstrated at high rates in anterior cervical corpectomy and fusion. In addition, VBSO is a powerful method for restoring cervical lordosis through multilevel anterior cervical discectomy and fusion above and below the osteotomy level. It may be a feasible treatment option for patients with cervical spondylotic myelopathy and kyphotic deformity. This is a technical note and literature review that describes the procedures involved in VBSO.