Abstract
Study design
A retrospective study.
Objectives
This study aims to investigate the relationship between the resection of ossification of the nuchal ligament (ONL), its morphological features, and cervical stability following modified laminoplasty.
Methods
We retrospectively reviewed the data of patients diagnosed as degenerative cervical myelopathy (DCM) who underwent modified laminoplasty with muscle-ligament complex (MLC) reconstruction in our hospital between July 2018 and October 2022. Demographic information (e.g., age, gender), cervical sagittal parameters, cervical angular displacement (AD), cervical horizontal displacement (HD), range of motion and patient-reported outcomes were compared between patients with and without ONL.
Results
The cervical AD at C4-C5, C5-C6 and cervical HD at C5-6 were significantly higher in ONL (+) group than ONL (-) group before surgery and at the 24-month follow-up time (p < 0.05, all). The AD and HD at C4-C5 and C5-C6 were higher in ONL (+) segments before surgery and at the 24-month follow-up (p < 0.05, all). But the values of AD or HD were lower in ONL (+) segments at 3- or 6-month follow-up (p < 0.05, all). ONL (+) group with two or more consecutive segments demonstrate significantly increased cervical AD and HD at the C4-C5 level after a 24-month follow-up period (p < 0.01, both).
Conclusion
Resection of the ONL, particularly involving ≥ 2 cervical segments, is moderately associated with an increased likelihood of cervical instability and abnormal sagittal alignment in long-term follow-up after laminoplasty. Reconstruction of the MLC during laminoplasty may enhance cervical stability in the early follow-up period. For DCM patients with long segmental ONL, more attention should be paid to protecting the MLC structure during posterior cervical surgery.
Clinical trial number
Not applicable.
Supplementary Information
The online version contains supplementary material available at 10.1186/s12891-025-08729-2.
Keywords: Ossification of the nuchal ligament (ONL), Degenerative cervical myelopathy (DCM), Laminoplasty, Cervical stability, Muscle-ligament complex (MLC)
Introduction
The nuchal ligament is centrally located between the dorsal musculature and the cervical spine, extending from the external occipital protuberance to the spinous process of C7. The fascial septum consisted of dense connective tissue and ran ventrally from the midline raphe to become continuous with the interspinous ligaments and atlantoaxial and atlantooccipital membranes [1].
Ossification of the nuchal ligament (ONL) has the highest prevalence in Asia compared with other regions, which can occur secondary to the ossification of other spinal ligaments, it is typically related to chronic stress, trauma, age, hormonal and genetic factors [2]. Numerous studies have investigated the function of the nuchal ligament and the impact of the ONL before cervical surgery, however, the influence of ONL in cervical instability after laminoplasty remains underestimated [3].
Nuchal ligament is critical for prevention of excessive cervical flexion [4]. Patients with larger cross-sectional areas ONL had severer cervical radiculopathy, decreased flexion-extension motion and more degenerative change of spine [5]. Cervical laminoplasty is a classic posterior procedure for degenerative cervical myelopathy (DCM) patients, and the dorsal complex of cervical spine is located at the mandatory site for this procedure [6]. Avoiding damage to the nuchal ligament during cervical laminoplasty is commonly overlooked, and this tissue has sometimes been regarded as less significant. While its impairment may elevate the risk of cervical spine instability and malalignment [4]. Repair of the nuchal ligament is clinically important for preventing postoperative axial symptoms and maintaining cervical alignment and range of motion (ROM) after posterior cervical spine surgery [7].
The C2 and C7 muscle-ligament attachment points were respectively sutured back to the C2 and C7 spinous processes to maintain the strength of the muscle-ligament complex (MLC) in the back of the neck in this study, which was different from the traditional laminoplasty [8].
To the best of our knowledge, this is the first study to explore the association between the morphological characteristics of the ONL and clinical outcomes in patients who have undergone a modified laminoplasty. The objective of the present study was to investigate the relationship between the resection of ONL, its morphological features, and cervical stability following the modified laminoplasty during long-term follow-up.
Methods
Study design and participants
We conducted a retrospective review of patients diagnosed with DCM who were admitted to our hospital between July 2018 and October 2022. Diagnostic criteria were the same as previous study [9]. The study protocol was approved by Ethics Review Committee of Guangdong Provincial People’s Hospital. Ethics Review Committee of Guangdong Provincial People’s Hospital provided waiver for informed consent due to the retrospective nature of this study (No. KY2024-613-01), Study was conducted in accordance with the Declaration of Helsinki. Using G-Power software (Version: 3.1.9.2, effect size: 0.5, statistical power: 0.8) to estimate the expected need for 64 people in two groups, respectively. In accordance with other studies, patients with ONL exhibit statistically significant differences in age, sex ratio, and BMI values when compared with those without ONL [2, 5, 10]. After propensity score matching (SPSS software, matching ratio 1:1, variables: Age, Sex, BMI), a total of 146 patients were included in this study. Among these, 77 patients were combined with ONL, while 69 patients without ONL were selected for matching in further analysis. All these patients received modified laminoplasty with reconstruction of the MLC, which were performed by the same senior surgeon from our center, with a minimum of two-years follow-up. The details of inclusion and exclusion criteria data were shown in Fig. 1.
Fig. 1.
The inclusion and exclusion criteria were presented. DCM, degenerative cervical myelopathy; ONL, ossification of the nuchal ligament
Cervical sagittal alignment and instability definition
All lateral radiographs were obtained using the standard radiographic technique and shown in Fig. 2(A). The following cervical sagittal parameters were measured: C0-C2 Cobb, C2-C7 Cobb, T1 slope, T1 slope minus cervical lordosis (TS-CL), C2-C7 sagittal vertical axis (C2-C7 SVA) and Pavlov’s ratio at C4. Clinical symptoms exhibit a strong correlation with radiological alterations. Among Chinese populations, degenerative cervical instability was defined as angular displacement (AD) more than 10° or horizontal displacement (HD) more than 3.0 mm at the lesion level during flexion-extension, appear to be more appropriate [10]. The range of ROM of the cervical spine was calculated as the C2-C7 Cobb during extension minus that during flexion.
Fig. 2.
The measurement of radiological parameters, classification of ONL and reconstruction of the MLC. (A) Cervical sagittal-alignment parameters on lateral radiographs. (B) Measurement of the features of ONL. The morphological features of ONL (length, thickness and width) were measured as the longest axis of the ossified area on 3D- or 2D- CT reconstruction. (C) Illustrations of the modified laminoplasty which are combined with reconstruction of the muscle and ligament complex. Lateral and posterior view of the reconstruction of the muscle and ligament complex of the C2 and C7 spinous process. (D) A 56-year-old male DCM patient with the continuous ONL type underwent modified laminoplasty. After two-year follow-up, cervical instability could find that increased AD and HD in C4-C5 and C5-C6 segments. Two intermittent small blue circles indicate the resection area of ONL, and two large blue circles indicate the anchor points at C2 and C7 when reconstructing ONL. (E) A 55-year-old male DCM patient without ONL who underwent modified laminoplasty with two-year follow-up and maintained good cervical spine stability. ONL, ossification of the nuchal ligament; 3D-CT, three-dimensional computed tomography; 2D-CT, two-dimensional computed tomography. Two large blue circles indicate the anchor points at C2 and C7 when reconstructing MLC. MLC, muscle-ligament complex; ONL, ossification of the nuchal ligament; DCM, degenerative cervical myelopathy
Classification and measurement of ONL
The type and location of ONL were evaluated on lateral plain radiographs and Computed Tomography in the sagittal plane, by using the measurement methods proposed by Wang et al [11]. ONL was classified into 5 types according to its appearance on lateral radiographs of the cervical spine (supplementary Fig. 1(A)). Intra-observer variability for the classification of ONL assessment in Supplementary Fig. 1B demonstrated almost perfect agreement (Cohen’s Kappa, median = 0.827). The length, width and thickness of ONL were measured as Fig. 2(B) illustrated.
Surgical procedures
All surgical procedures were conducted in a standardized manner by one senior spine surgeon. After the induction of general anesthesia, the nuchal fascia was longitudinally divided in line with the midline skin incision, and the ossified nuchal ligament was resected in the ONL (+) group. The posterior surfaces of the laminae between C2 and C7 as well as the medial border of the facet joints were exposed. C3 laminectomy and C2, C7 dome decompression were performed. From C4 to C6, the right lamina was selected as the hinge side, and the left lamina served as the conventional open-door side. The posterior MLC was reconstructed by using simple interrupted suture with NO.2 ETHIBOND EXCEL Polyester Suture (Ethicon LLC, Puerto Rico, USA). The C2 and C7 muscle-ligament attachment points were the fixation points, which were sutured back to the C2 and C7 spinous processes, respectively, to complete the reconstruction of the MLC (Fig. 2(C)). Two representative cases are illustrated in Figs. 2(D) and 2(E).
Follow-up and clinical results
All patients wore a cervical collar for 1 month postoperatively. Follow-up visits were scheduled at 3-, 6-, 12-, and 24 months after surgery. X-ray examinations were conducted at each follow-up visit. All preoperative radiological parameters were assessed by two senior spine surgeons from our institution. One other senior spine surgeon reviewed the radiological parameters and measurements. All three aforementioned senior spine surgeons were blinded to the group assignments of the patients in order to eliminate potential bias. Clinical patient report outcomes including the neck pain Visual Analogue Scale (VAS-neck), the Japanese Orthopaedic Association (JOA) scores and the Neck Disability Index (NDI). Complications such as C5 palsy and axial pain were recorded.
Statistical analysis
The independent-samples t-test, chi-square test, or Fisher exact test was used to evaluate the differences in basic information and radiographic outcome between the two groups, as appropriate. A one-way ANOVA method was used to compare the differences in radiological parameters at different time periods. Multiple comparisons were accounted appropriately for statistically to avoid type I error. Likewise, the chi-square test was used to compare differences in gender, the prevalence of diabetes, and the number of unstable cervical segments between the ONL (+) group and ONL (-) group. The correlation of the morphological characteristics of ONL with cervical AD and HD at C4-C5 and C5-6 at the 24-month follow up was analyzed using Spearman correlation. Using SPSS version 26.0 and the software GraphPad Prism 8, graphs were generated and statistical analyses were performed, and the result was deemed statistically significant at p < 0.05.
Results
Demographic characteristics and distribution of ONL
After propensity score matching (matching ratio 1:1, variables: Age, Sex, BMI), there were not significant differences in age, gender, duration of symptoms and body mass index between the two groups (p = 0.378, p = 0.632, p = 0.199 and 0.244, respectively) (Table 1). The most common types of ONL were local (31.17%) and continuous (29.87%) (Supplementary Fig. 1(B)), and the most affected segments were C5/6 (67.53%) and C4/5 (61.04%) (Supplementary Fig. 1(C)).
Table 1.
Demographic information for the 146 matched patients after propensity score matching
| Variable | ONL (+) group (n = 77) | ONL (-) group (n = 69) | p-value |
|---|---|---|---|
| Age (years) | 59.28 ± 8.86 | 57.01 ± 4.55 | 0.378 |
| Male/Female (n) | 41/36 | 34/35 | 0.632 |
| Duration of disease (months) | 34.39 ± 23.63 | 37.32 ± 21.69 | 0.199 |
| Body mass index (kg/m²) | 23.09 ± 1.82 | 22.77 ± 1.36 | 0.244 |
Values are presented mean ± standard deviation
ONL, ossification of the nuchal ligament
Complications and clinical results
In the present study, 2 patients developed C5 palsy in ONL (+) group within 1 day after surgery and 2 patients developed C5 palsy in ONL (-) group within 1 day after surgery. Patients with C5 palsy in ONL (+) group both recovered after 2 months of rehabilitation exercises, and patients with C5 palsy in ONL (-) group recovered at 1 month and 2 months respectively after rehabilitation exercises. In the ONL (+) and ONL (-) groups, 29 and 20 patients, respectively, experienced mild axial pain during the short-term follow-up period. All 49 patients’ symptoms were in remission at the 6-month follow-up. Prior to surgery and at the 12- and 24-month follow-up intervals, the Vas-neck and NDI scores were significantly higher in the ONL (+) patients compared to the ONL (-) groups (p = 0.009, p < 0.001, p < 0.001, p < 0.001, p = 0.002 and p < 0.001, respectively). Conversely, the ROM was significantly reduced in the ONL (+) group relative to the ONL (-) group before operation and at 12- and 24-month follow-up. (p < 0.001, all). (Fig. 3)
Fig. 3.
Comparisons of ROM, JOA scores, VAS-neck and NDI between ONL (+) group and ONL (-) group at different follow-up periods. (A) ROM, (B) JOA scores, (C) VAS-neck scores, (D) NDI. Values are presented mean ± standard deviation. ONL, ossification of the nuchal ligament; Pre-op, the time before operation; ROM, range of motion; JOA, Japanese Orthopaedic Association; VAS-neck, neck pain Visual Analogue Scale; NDI, Neck Disability Index. * p < 0.05
Comparison of cervical alignment and cervical instability
The T1 slope, TS-CL and C2-C7 SVA were higher in ONL (+) group than in ONL (-) group before surgery (p = 0.038, p = 0.018 and p = 0.018, respectively) and at the 24-month follow-up (p = 0.007, p = 0.013 and p = 0.008, respectively). The cervical AD at C4-C5 and C5-C6 and HD at C5-6 were significantly higher in ONL (+) group than in ONL (-) group before surgery and at the 24-month follow-up time (p = 0.010, p = 0.041, p = 0.038, p = 0.022, p = 0.038 and p = 0.005). No significant differences related to the C0-C2 Cobb, C2-C7 Cobb and Pavlov’s ratio of C4 between two groups before surgery (p = 0.303, p = 0.243 and p = 0.710, respectively). The proportion of unstable cervical segments was larger in the ONL (+) group than in the ONL (-) group both before the operation (p = 0.016) and at the 24-month follow-up (p = 0.039). (Table 2)
Table 2.
Comparison of cervical vertebra parameters between the ONL (+) group (n = 77) and ONL (-) group (n = 69) before surgery and the 24-month follow-up period
| Variable | Before surgery | 24-month follow-up | |||||
|---|---|---|---|---|---|---|---|
| ONL (+) | ONL (-) | p-value | ONL (+) | ONL (-) | p-value | ||
| C0-C2 Cobb (°) | 24.51 ± 2.15 | 23.75 ± 2.97 | 0.303 | 26.23 ± 1.72 | 26.11 ± 2.12 | 0.710 | |
| C2-C7 Cobb (°) | 14.25 ± 1.51 | 14.49 ± 1.29 | 0.243 | 13.18 ± 1.38 | 13.20 ± 1.20 | 0.740 | |
| T1 slope (°) | 24.87 ± 3.06 | 23.81 ± 3.07 | 0.038 | 25.51 ± 2.77 | 24.33 ± 2.39 | 0.007 | |
| TS-CL (°) | 10.62 ± 3.41 | 9.32 ± 3.12 | 0.018 | 12.34 ± 3.37 | 11.13 ± 2.37 | 0.013 | |
| C2-C7 SVA (mm) | 21.10 ± 3.85 | 19.65 ± 3.42 | 0.018 | 22.07 ± 3.00 | 20.79 ± 2.64 | 0.008 | |
| Pavlov’s ratio of C4 (%) | 67.83 ± 3.60 | 67.61 ± 3.59 | 0.710 | 97.61 ± 5.01 | 96.61 ± 4.29 | 0.199 | |
| AD (°) | |||||||
| C2-C3 | 3.65 ± 1.09 | 3.61 ± 0.94 | 0.815 | 3.55 ± 0.97 | 3.51 ± 0.91 | 0.840 | |
| C3-C4 | 5.75 ± 1.92 | 5.63 ± 1.93 | 0.769 | 5.68 ± 1.64 | 5.57 ± 1.70 | 0.704 | |
| C4-C5 | 8.14 ± 3.39 | 6.81 ± 2.76 | 0.010 | 7.35 ± 2.57 | 6.45 ± 2.25 | 0.041 | |
| C5-C6 | 8.87 ± 2.37 | 7.97 ± 2.77 | 0.038 | 8.55 ± 1.93 | 7.56 ± 2.63 | 0.022 | |
| C6-C7 | 7.01 ± 3.12 | 6.34 ± 2.72 | 0.206 | 6.74 ± 2.66 | 6.33 ± 2.35 | 0.393 | |
| HD (mm) | |||||||
| C2-C3 | 1.14 ± 0.39 | 1.17 ± 0.29 | 0.589 | 1.09 ± 0.34 | 1.07 ± 0.29 | 0.553 | |
| C3-C4 | 1.62 ± 0.55 | 1.57 ± 0.56 | 0.558 | 1.60 ± 0.57 | 1.59 ± 0.50 | 0.761 | |
| C4-C5 | 2.28 ± 0.74 | 2.02 ± 0.74 | 0.056 | 2.06 ± 0.74 | 1.88 ± 0.60 | 0.186 | |
| C5-C6 | 2.55 ± 0.73 | 2.38 ± 0.69 | 0.038 | 2.32 ± 0.66 | 1.98 ± 0.72 | 0.005 | |
| C6-C7 | 1.92 ± 0.83 | 1.99 ± 0.68 | 0.570 | 1.88 ± 0.75 | 1.96 ± 0.68 | 0.311 | |
| Stability | |||||||
| Instable segments (n) | 110(28.57%) | 72(20.87%) | 0.016 | 77(20.00%) | 49(14.20%) | 0.039 | |
| Stable Segments (n) | 275(71.43%) | 273(79.13%) | 308(80.00%) | 296(85.80%) | |||
Values are presented mean ± standard deviation
ONL, ossification of the nuchal ligament; TS-CL, T1 slope minus cervical lordosis; C2-C7 SVA, C2–C7 sagittal vertical axis; AD, angular displacement; HD, horizontal displacement
Cervical instability changes at different follow-up
In the ONL (+) group, the ONL were detected at the C2-C3 (n = 4), C3-C4 (n = 24), C4-C5 (n = 47), C5-C6 (n = 52), and C6-C7 (n = 17) segments. In the ONL (-) group, all segment numbers were 69.
The AD and HD at C2-C3 were not compared because the number of patients with ONL in this segment was too small. The preoperative AD at C4-C5 significantly higher than that at the 3- and 6-month follow-up (p < 0.001 and p = 0.022) (Fig. 4(A)). The AD at C4-C5 at 3-month follow-up was significantly lower than that at the 12- and 24-month follow-up (p = 0.020 and p = 0.005) (Fig. 4(A)). The AD at C4-C5 at 6-month follow-up was significantly lower than that at the 24-month follow-up (p = 0.046) (Fig. 4(A)). The preoperative AD at C5-C6 was significantly differed from that at the 3-, 6-, and 12-month follow-up (p < 0.001, p < 0.001 and p = 0.015, respectively) (Fig. 4(A)). The AD at C5-C6 at the 3-month follow-up was significantly lower than that at the 12- and 24-month follow-up (p < 0.001, both) (Fig. 4(A)). The AD at C5-C6 at the 6-month follow-up was significantly lower than that at the 12- and 24-month follow-up (p < 0.001, both) (Fig. 4(A)). The preoperative HD at C4-C5 was significantly higher than that at the 3- and 6-month follow-up (Both p < 0.001) (Fig. 4(B)). In addition, the HD at C4-C5 at the 24-month follow-up was significantly higher than that at the 3- and 6-month follow-up (p = 0.008 and p = 0.022) (Fig. 4(B)). The preoperative HD at C5-C6 was significantly higher than that at the 3-, 6-, 12- and 24-month follow-up, respectively (All p < 0.001) (Fig. 4(B)). The HD at C5-C6 at the 3-month and 6-month follow-up were significantly lower than that at the 12-month and 24-month follow-up (p = 0.001, p < 0.001, p < 0.001 and p < 0.001) (Fig. 4(B)). The AD and HD at C3-C4 and C6-C7 did not differ among various time points (Fig. 4(A, B)).
Fig. 4.
Comparison of AD and HD in cervical segments with or without ossification at different follow-up periods. (A, B) AD and HD in the ONL (+) group for segments C3-C4 (n = 24), C4-C5 (n = 47), C5-C6 (n = 52), and C6-C7 (n = 17). (C, D) AD and HD in the ONL (-) group for segments C3-C4, C4-C5, C5-C6, and C6-C7 (each n = 69). Values are presented mean ± standard deviation. * indicates that there is a statistically significant difference compared with the preoperative values; # indicates that there is a statistically significant difference in interpolation between the two time points indicated in the parentheses. AD, angular displacement; HD, horizontal displacement; Pre-op, the time before operation; 3 m, 6 m, 12 m, and 24 m refer to follow-ups at 3, 6, 12, and 24 months, respectively
In the ONL (-) group (n = 69), the AD at different segments were no significant difference at various periods (Fig. 4(C)). The preoperative HD at C5-C6 was significantly higher than that at the 3-, 6-, 12- and 24-month follow-up (p < 0.001, p < 0.001, p < 0.001 and p = 0.011, respectively) (Fig. 4(D)).
Comparison of cervical instability between ossified and non-ossified segments
Before surgery and at the 24-month follow-up, the AD at C4-C5 was higher in the ONL (+) group compared to the ONL (-) group (p = 0.016 and p = 0.030), but it was lower in the ONL (+) group than in the ONL (-) group (p = 0.044) (Fig. 5(B)). Similarly, the AD at C5-C6 in the ONL (+) group was higher than in the ONL (-) group before surgery and at the 24-month follow-up (p = 0.028 and p = 0.025), but lower at the 3-month follow-up (p = 0.044) (Fig. 5(C)). The HD at C4-C5 between ONL (+) and ONL (-) group are different before surgery and at the 24-month follow-up, respectively (p = 0.017 and p = 0.036) (Fig. 5(B)). The HD at C5-C6 in ONL (+) group were higher than ONL (-) group before surgery and at the 24-month follow-up (p = 0.012 and p = 0.025) (Fig. 5(C)). The HD at C5-C6 in ONL (+) group were lower than ONL (-) group at the 6-month follow-up (p = 0.029) (Fig. 5(C)). The AD and HD at C3-C4 and C6-C7 between ONL (+) group and ONL (-) group did not exhibit statistically significant differences across various time points (Fig. 5(A, D)).
Fig. 5.
Comparison of cervical AD and HD between ONL (+) and ONL (-) groups at different follow-up times. (A) AD and HD in C3-C4 segment, ONL (+) (n = 24) vs. ONL (-) (n = 69), (B) AD and HD in C4-C5 segment, ONL (+) (n = 47) vs. ONL (-) (n = 69), (C) AD and HD in C5-C6 segment, ONL (+) (n = 52) vs. ONL (-) (n = 69), (D) AD and HD in C6-C7 segment, ONL (+) (n = 17) vs. ONL (-) (n = 69). * p < 0.05. Values are presented mean ± standard deviation. AD, angular displacement; HD, HD, horizontal displacement; ONL, ossification of the nuchal ligament; Pre-op, the time before operation; 3 m, 6 m, 12 m, 24 m means 3-month, 6-month, 12-month and 24-month follow-up, respectively
Association of ONL characteristics with cervical instability
The length of ONL were correlated with the value of segmental cervical AD and HD at C4-C5 and C5-C6 at the 24-month follow-up, with correlation coefficients of 0.51, 0.50, 0.33 and 0.26 respectively (p < 0.001, p < 0.001, p = 0.003 and p = 0.024) (Fig. 6). And we further found that DCM patients contain ≥ 2 consecutive cervical segments of ONL have higher AD and HD at C4-C5 at 24-month follow-up time (p = 0.001 and p < 0.001, respectively) (Table 3).
Fig. 6.
Spearman correlation analysis (Correlation coefficients: rs) of dimensional characteristics of ONL, AD and HD (C4-C5 and C5-C6) at 24-month follow up (n = 77). 0.4 < rs < 0.7, moderately related; 0.2 < rs < 0.4, mildly related; ONL, ossification of the nuchal ligament; AD, angular displacement; HD, horizontal displacement
Table 3.
Comparison of the AD and HD at different cervical segments between the patients in long-segment ONL and short-segment ONL groups at 24-month follow-up period
| Variable | Short-segment ONL (n = 37) | 2 cervical segments (n = 26) | 3 cervical segments (n = 12) |
|---|---|---|---|
| AD (°) | |||
| C2-C3 | 3.50 ± 0.89 | 3.67 ± 1.04 | 3.61 ± 1.02 |
| C3-C4 | 5.59 ± 1.71 | 5.80 ± 1.71 | 5.48 ± 1.27 |
| C4-C5 | 6.37 ± 2.31 | 8.87 ± 2.27* | 7.37 ± 2.60 |
| C5-C6 | 8.39 ± 2.09 | 8.72 ± 1.74 | 8.83 ± 1.62 |
| C6-C7 | 6.51 ± 2.90 | 7.09 ± 2.32 | 6.75 ± 2.66 |
| HD (mm) | |||
| C2-C3 | 1.03 ± 0.32 | 1.17 ± 0.34 | 1.10 ± 0.38 |
| C3-C4 | 1.52 ± 0.50 | 1.69 ± 0.67 | 1.56 ± 0.49 |
| C4-C5 | 1.74 ± 0.68 | 2.47 ± 0.62* | 2.24 ± 0.71 |
| C5-C6 | 2.33 ± 0.72 | 2.38 ± 0.57 | 2.18 ± 0.70 |
| C6-C7 | 1.81 ± 0.75 | 1.90 ± 0.65 | 1.97 ± 0.88 |
Values are presented mean ± standard deviation. Data analysis was performed using Bonferroni correction. Data of Patients with 4 cervical segmental ONL was not presented because there were only 2 cases
*, P < 0.001 between patients with ONL of one cervical segment and patients with ONL of 2 cervical segments. ONL, ossification of the nuchal ligament; AD, angular displacement; HD, horizontal displacement; Long-segment ONL, ONL ≥ 2 cervical segments; Short-segment ONL, ONL < 2 cervical segments
Discussion
Many studies have focused on epidemic characteristics and the changes in cervical radiological sagittal parameters of patients with ONL before operation [10, 11, 12]. To the best of our knowledge, this is the first study to investigate the changes in clinical outcomes after resection of the ONL during laminoplasty. ONL was often caused by chronic high-load injury, especially at C5-C6 and C4-C5 [2, 13]. The most common distribution of ONL based on classification were local and continuous [11]. In this research, we also found that the most common types of ONL were local and continuous, and the most commonly involved segments were also at C5-C6 and C4-C5. We propose that, for DCM patients with ONL, protecting the posterior cervical tension structure during posterior single-door laminoplasty is crucial. Posterior laminectomy and fusion also should be considered if cervical instability is present.
Ying et al, [10] reported that the AD and HD, the segmental instability indicators, in the dynamic lateral plane were significantly greater in patients with ONL than in those without ONL before surgery. Nuchal ligament is a critical anatomical structure that contributes to the stability of the cervical spine, which exerts biomechanical influence by limiting cervical flexion and modulating muscular activity in the neck region [1, 4, 7]. The injured ligament exhibits fibrous scarring, a condition that subsequently precipitates ligamentous thickening. Furthermore, upon exposure to recurrent episodes of overloading or injury, the thickened ligament is rendered more susceptible to additional pathological transformations, including fibrosis and calcification. These progressive alterations substantially compromise the ligament’s capacity to restore its original structural and functional integrity [14]. The presence of ONL elevate the risk of degenerative disk diseases, diminished cervical ROM, progressive cervical spine instability and malalignment in DCM patients [5, 15]. In our cohort, cervical stability in ONL (+) group were worse than in ONL (-) group before surgery and at long-term follow-up time. Besides, as previous studies, T1 slope, TS-CL and C2-C7 SVA play an important role in cervical sagittal alignment [16]. Ying et al. [10] found that C2-C7 SVA, TS-CL and T1 slope were higher in patients with ONL before surgery. In this study, at the 24-month follow-up period, the T1 slope, TS-CL and C2-C7 SVA in ONL (+) group were significantly higher than these in ONL (-) group which indicated that ONL might be related to abnormal cervical sagittal balance at the long-term follow-up time.
The maintenance of cervical spine stability is critically dependent on the ligaments, facet joints, and intervertebral disc nucleus, which are particularly important for enabling sagittal plane rotational movement and facilitating the redistribution of mechanical loads. Additionally, degeneration of the cervical facet joints and paraspinal muscles has been recognized as a significant factor contributing to the development of DCM [17, 18]. Muscular dysfunction exerts a more substantial impact on spinal stability compared to disc degeneration [19]. The superior and interspinous ligaments of the cervical spine play a crucial role in maintaining the cervical strength and stability [20]. As the severity of surgical invasion to the posterior MLC increased during laminoplasty, the loss of cervical sagittal balance also increased [21]. Preserving posterior MLC is an effective approach to maintain the cervical curvature and ROM, which might also accelerate the recovery of neck movement and reduce the risk of the cervical kyphosis and axial pain [8, 22]. As mentioned above, during the modified laminoplasty, we used non-absorbable No.2 tendon sutures to reconstruct the MLC. Non-absorbable No.2 tendon surgical sutures play a crucial role in repairing integrity and healing [23]. The cervical stability at C4-C5 and C5-C6 increased at the early follow-up periods in the two groups, which might be attributable to the reconstruction of MLC during laminoplasty. Puttlitz et al. [24] also found that intervertebral motion decreased significantly at 6 months after laminoplasty because of the absence of the early physical therapy. We excised ONL and performed fusiform reconstruction of the MLC, which might contribute more to maintaining the posterior cervical tension and cervical stability in ONL (+) group and the cervical stability in ONL (+) group better than ONL (-) group at the early follow-up periods.
DCM patients with ONL had severer preoperative chronic injury to posterior cervical ligament and were more likely to suffer from cervical spine muscle dysfunction [4, 11, 12, 25]. In addition, Cheng et al. [19] indicated that muscle dysfunction had significant negative effect on cervical stability. At the 24-month follow-up period, patients in the ONL (+) group had worse cervical spine stability than those in the ONL (-) group. On the one hand, there was a significant correlation between ONL and cervical sagittal malalignment and disc degeneration and laminoplasty could increase disc stress which can lead to instability [10, 26]. On the other hand, Yang et al. [27] supposed that fibrous tissue could gradually form scar-like tendon tissue. Even though we reconstructed the MLC with NO.2 tenson surgical sutures, the effect of the reconstruction seems to gradually diminish with time passed. Paraspinal muscular atrophy is associated with mechanical injury, ischemia, disuse, and denervation. These factors have been implicated in poor outcomes following spine surgery, contributing to pain, instability [28]. Fujimura et al. [29] observed significant atrophy of bilateral posterior cervical muscles at an average of 53 months following laminoplasty which was particularly pronounced in the multifidus muscles, cervical semispinalis, and capitis semispinalis. In a related study, Wen et al. [30] demonstrated that during the muscle healing process, the interface between muscle and bone often fails to heal effectively, resulting in steatosis. This condition subsequently leads to a reduction in muscle elasticity and tension [31]. In our study, patients with ONL might have worse posterior cervical muscle, which also suffered from more severe injury of MLC compared with patients without ONL during laminoplasty. At the long-term follow-up in the ONL (+) group, we claim that it is easier to return to the preoperative unstable state or even more severe, but further biomechanical studies are needed.
We found that the length of ONL were correlated with the number of unstable cervical segments at the 24-month follow-up period. In this study, the correlation between length of ONL and AD/HD (C4-5 segment) indicate moderate associations (rs = 0.50–0.51) at the 24-month follow-up time. DCM patients with long segmental ONL (≥ 2 cervical segments) were more likely to occur cervical instability at long-term follow-up time after laminoplasty, which could be explained by previous finding that there was a significant correlation between the size of ONL and the severity of cervical sagittal malalignment and segmental instability at the corresponding levels [10]. However, given the limited number of existing related studies and the potential presence of unconsidered confounding or bias factors, the correlation coefficient obtained in this study has not yet reached a level of high correlation. Moving forward, we aim to enrich the dataset and integrate additional relevant literature to further enhance the clinical significance of our findings.
Some studies described that segmental cervical instability was a potential risk factor for kyphosis after laminoplasty, but the posterior laminectomy and fusion might be recommended for such patients [32, 33, 34]. However, Obo et al. [35] found that segmental cervical instability was not the specific driver for loss of cervical lordosis in DCM patients after laminoplasty and was not a contraindication in it. Both laminoplasty and posterior decompression and fusion are the effective treatment of DCM, but posterior laminectomy and fusion has a higher incidence of adverse outcomes [36]. In our study, we only reviewed the cohort of DCM patients who underwent laminoplasty in our institution to discuss the changes in cervical segmental stability after modified laminoplasty which with reconstruction of MLC. Zhou et al. [37] reported that laminoplasty with lateral mass screw fixation has the advantage of extensive application scope, safety and steadiness. Meanwhile laminectomy with fusion shows favorable long-term results compared with laminoplasty. And laminectomy with fusion should be the preferred choice when treating multilevel DCM patients with preoperative axial pain and segmental instability [38]. Laminoplasty has been proven to exhibit a lower risk of complications, lower costs and shorter hospital stays compared with laminectomy combined with fusion. However, for patients with unstable spines or insufficient cervical lordosis reserve, laminectomy combined with fusion may be more beneficial [39]. For patients with long-segment (≥ 2 cervical segments) ONL, as shown in this study, it is worth weighing which surgical procedure is the most appropriate choice in the future.
Additionally, we recorded and compared patient-reported outcomes to investigate potential differences between the ONL (+) and ONL (-) groups. It has also been demonstrated that patients with ONL may exhibit reduced cervical ROM. Hyun et al. [40] found that loss of cervical ROM after laminoplasty is time-dependent and Kim et al. [41] proposed that weaker preoperative extension capacity and greater T1 slope might lead to greater decrease in lordosis. These results supposed that DCM patients with ONL were more likely to have greater decreased ROM at 12- and 24-month follow-up time. The NDI showed a strong correlation with VAS [42]. Fujibayashi et al. [43] found that neck muscle strength and axial symptoms were strongly correlated. Patients with ONL withstand chronic overload damage, which might be associated with neck muscle disability [4, 11, 12, 25]. We supposed that DCM patients combined with ONL are prone to experiencing neck pain and neck disability both prior to surgery and during long-term follow-up.
The present study has some limitations. First, the sample size in our study was relatively small. To further verify the conclusions, a randomized controlled trial study with a larger sample size is needed in the future. Second, the underlying mechanisms of enhanced cervical stability at the early follow-up period by resection the ONL and reconstruction the MLC in cervical laminoplasty remain to be elucidated. A further study of its biomechanics would be helpful to develop strategies to prevent unfavorable outcomes. At the same time, some potential biases such as surgeon experience, neck exercises and other rehabilitation protocols also could affect surgical outcomes. Finally, the retrospective study design is inherently susceptible to biases, which necessitate a thorough discussion within the limitations section. This includes, but is not limited to, potential selection bias and the confounding factors.
Conclusion
Resection of the ONL, particularly involving ≥ 2 cervical segments, is associated with an increased likelihood of cervical instability and abnormal sagittal alignment in long-term follow-up after modified laminoplasty. Reconstruction of the MLC during laminoplasty could enhance cervical stability at the early follow-up period. For DCM patients with long segmental ONL, more attention should be paid to protecting the MLC structure during posterior cervical surgery.
Electronic supplementary material
Below is the link to the electronic supplementary material.
Acknowledgements
Not applicable.
Author contributions
CC, YC and XQZ conceived the study; WY and TY drafted the study; XC, LW and XCZ recruited the participants and collected demographic data; CC and XQZ collected radiological data; YC reviewed the radiological parameters; WY, XL and OY were in charge of the statistics analysis, tables and figures. WY and TY carried out the writing-original draft preparation. CC and WY carried out the writing, review and editing. CC, YC, XQZ have primary responsibility for the final content. All authors reviewed the manuscript.
Funding
This work was supported by National Natural Science Foundation of China (No. 82102636 and No. 82472533 to CC, No. 82201360 to XC), Guangzhou Municipal Science and Technology Project (No. 2024A04J10010 to CC), Basic and Applied Basic Research Foundation of Guangdong Province (No. 2023B1515120078 to YC) and Guangdong Provincial People’s Hospital Full-time High-level Talent Introduction Foundation (No. KY0120231008 to XC).
Data availability
All data used during the current study are available from the corresponding author on reasonable request.
Declarations
Ethical approval and consent to participate
The study protocol was approved by Ethics Review Committee of Guangdong Provincial People’s Hospital. Ethics Review Committee of Guangdong Provincial People’s Hospital provided waiver for informed consent due to the retrospective nature of this study (No. KY2024-613-01), Study was conducted in accordance with the Declaration of Helsinki.
Consent for publication
Informed consent was obtained from all relevant individuals, and any identifying details have been removed to ensure confidentiality.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Chong Chen, Wenlin Ye and Tao Yu contributed equally to this work.
Contributor Information
Yunbing Chang, Email: changyunbing@gdph.org.cn.
Xiaoqing Zheng, Email: zhengxiaoqing@gdph.org.cn.
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Associated Data
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Supplementary Materials
Data Availability Statement
All data used during the current study are available from the corresponding author on reasonable request.