Medial Location Shifting of the Gutter on the Open Side in Expansive Open-Door Laminoplasty Might Minimize the Incidence of C5 Palsy

Abstract

Study Design

Retrospective cohort study.

Objectives

To investigate whether shifting the medial location of the gutter on the open side during posterior cervical expansive open-door laminoplasty affects postoperative C5 palsy (C5P) incidence.

Methods

Patients were divided into two groups based on the opening-side location: the conventional laminar transitional zone (conventional group, dural sac decompression) and a position 1 mm medial to the laminar transitional zone (modified group, spinal cord decompression). The incidence of C5P, radiological parameters, and neurological outcomes were compared.

Results

A total of 258 consecutive patients with degenerative cervical myelopathy (DCM) who underwent laminoplasty in the spine surgery unit of our institution between May 2024 and October 2024 were included. C5P occurred in 5/128 (3.9%) in the conventional group and 0/130 in the modified group (P = 0.029). At the final follow-up, the mean JOA improvement rates were 55.8% ± 18.9% and 54.6% ± 16.9% in the conventional and modified groups, respectively (P = 0.599). The modified group showed a significantly smaller width between the bilateral gutters (median, 18.7 vs 20.3 mm; P < 0.001) and less posterior spinal cord shift (median, 2.0 vs 3.0 mm; P < 0.001) than the conventional group, with a significant correlation between the two parameters.

Conclusions

Positioning the gutter on the open side 1 mm medial to the junction of the laminae and facet joints during cervical expansive open-door laminoplasty may reduce the incidence of C5P without affecting neurological recovery, potentially by limiting posterior spinal cord shift.

Keywords

degenerative cervical myelopathy laminoplasty C5 palsy open-side gutter’s position posterior spinal cord shift

Introduction

Postoperative C5 palsy (C5P) is a common delayed complication of expansive open-door laminoplasty (LAMP) for degenerative cervical myelopathy (DCM). Classic C5P presents as new or worsening postoperative shoulder abduction weakness, with or without elbow flexion weakness, and may be accompanied by sensory deficits in the C5 dermatome.¹ Reported incidence ranges from 0% to 30%. A meta-analysis of 11 481 patients found a cumulative incidence of 6.3%, with higher rates in posterior approaches.² Most C5P cases show favorable neurological recovery, with approximately 70% of patients achieving functional restoration within the first 6 months post-onset. While conservative management, including physical therapy and pharmacological intervention, typically leads to gradual improvement over weeks to months, 19.0% of patients experience residual pain or deficits at the final follow-up, compromising their quality of life.³

Several mechanisms have been proposed to cause C5P, including intraoperative ischemic injury to anterior horn cells, mechanical compression of the C5 nerve root, and distraction of the C5 nerve root due to shifting of the spinal cord after decompressive spine surgery.⁴ Reducing the distance of the spinal cord shift to relieve nerve root traction while achieving sufficient decompression may help minimize the incidence of C5P without affecting surgical outcomes.^5,6

In this study, we retrospectively compared the incidence of C5P in patients who underwent classic LAMP with those who underwent LAMP with a modified gutter position shifted 1 mm medially (targeting spinal cord decompression instead of dural sac decompression; Figure 1). We hypothesized that medially shifting the gutter location on the open side during expansive open-door laminoplasty by 1 mm would reduce the incidence of C5P without impairing neurological recovery.

Figure 1.

Conventional and modified cervical expansive open-door laminoplasty (LAMP). (A): The conventional LAMP had the gutter on the open side positioned at the junction of the laminae and facet joints (the outer margin of the dural sac). (B): The modified LAMP had the gutter on the open side positioned 1 mm medial to the junction of the laminae and facet joints (between the outer margin of the dural sac and the lateral side of the spinal cord). (C): The high-speed burr should be placed about 1 mm medial to the junction

Materials and Methods

Study Cohort

A retrospective analysis was conducted on 258 consecutive patients with DCM without ossification of the posterior longitudinal ligament (OPLL) who underwent LAMP in the spine surgery unit of our institution between May 2024 and October 2024, all of whom completed at least 1 year of follow-up (Figure 2). Patients were divided into a conventional group (n = 128) and a modified group (n = 130) according to the opening side gutter location during laminoplasty. Group allocation was determined by the operating surgeon’s preference, without predefined selection criteria or patient-specific indications.

Figure 2.

Flowchart of patient inclusion and exclusion

Inclusion criteria: (1) DCM diagnosed with relevant clinical and imaging findings; (2) Multilevel cervical spinal canal stenosis (involving ≥3 segments); (3) Age ≥18 years. Exclusion criteria: Segmental kyphosis or instability requiring anterior surgery, posterior fusion with fixation, postoperative epidural hematoma causing cord injury, previous history of spinal fractures, tumors, infections, deformities, metabolic bone diseases, and prior spine surgery.

Surgical Procedure

LAMP was performed as described by Hirabayashi and Satomi.⁷ Under general anesthesia, the patient was placed prone with the head fixed in a Mayfield head clamp. For the C3-7 procedure, a midline posterior cervical incision was made, and subperiosteal dissection was performed to expose the posterior elements of the cervical spine to the lateral margins of the facet joints.

On the hinge side, the inner cortex of the lamina was preserved, whereas the lamina on the open side was completely cut through. In the conventional group, the gutter on the open side was made at the junction of the lamina and the spinous processes. In the modified group, the gutter on the open side was shifted 1 mm medially during laminoplasty (Figures 1 and 3). After the decompression, a titanium plate with screws was used to maintain the expanded lamina. All procedures were performed by experienced spine surgeons using a standardized institutional laminoplasty technique. Prophylactic C4–C5 foraminotomy was not performed in any patient, and excessive laminar opening (>60°) was intentionally avoided.

Figure 3.

Intraoperative Photo of the modified group

Outcome Measures

The primary outcome was C5P, defined as a ≥1-grade decrease in deltoid strength on Manual Muscle Testing (MMT) scale, with or without radiating pain or sensory loss in the C5 dermatome. Neurological recovery was assessed using the Japanese Orthopaedic Association (JOA) scoring system (17-point scale). Improvement rate was calculated as: Improvement rate (%) = (Postoperative score – Preoperative score)/(17 – Preoperative score) × 100%.⁸

Radiological Assessment

Preoperative cervical spine radiographs, computed tomography (CT), and magnetic resonance imaging (MRI) scans were obtained for each patient. Postoperative radiography, CT, and MRI were performed at least 3 months postoperatively. The sagittal C2‒C7 Cobb angle, measured between the C2 superior and C7 inferior endplates on neutral lateral radiograph, was assessed.⁹ Postoperative posterior spinal cord shift (PSS) was obtained using the following formula: PSS at the C4/5 level = postoperative distance–preoperative distance. The width between the bilateral medial margins of the bony gutters was measured as described by Nori et al¹⁰ (Figure 4). Radiological data were assessed by two independent spine surgeons. In cases of discrepancy, a third senior reviewer was consulted, and consensus measurements were used for analysis.

Figure 4.

Radiological assessment. Representative MRI and postoperative CT (A-C, the conventional group; D-F, the modified group). (A and D) For posterior spinal cord shift measurement, the distances between the cephalocaudal midpoint of the posterior margin of the C4/5 vertebral disc and the nearest point of the anterior margin of the spinal cord were measured on postoperative T2-weighted mid-sagittal MRI. (B and E) Axial MRIs at the C4 laminae of the patients. (C and F) The width between the bilateral medial margins of the bony gutters was measured at the cephalocaudal midpoint of the decompression laminae in the axial plane on postoperative CT

Statistical Analysis

Data were analyzed using SPSS 26.0 (IBM Corp., Armonk, NY, USA). Normality was assessed for all continuous variables. Depending on distribution, data were expressed as mean ± standard deviation or median (interquartile range), and compared using the independent-samples t test or the Mann–Whitney U test, as appropriate. Categorical variables were analyzed using chi-square or Fisher’s exact tests, as appropriate. Spearman’s rank correlation analysis was performed because the normality assumptions were not met to assess linear associations between continuous variables, with reported correlation coefficients (ρ) and two-tailed P-values. Statistical significance was set at P < 0.05.

Results

Participant Characteristics

A total of 258 patients with DCM were included in the analysis. The conventional group (dural sac decompression) consisted of 128 patients, including 89 males and 39 females (mean age, 59.6 ± 9.8 years). The modified group (spinal cord decompression) comprised 130 patients, including 94 males and 36 females (mean age, 57.4 ± 10.2 years). The follow-up period ranged from 13 to 23 months. The median follow-up duration was 14 months (interquartile range [IQR], 13-23) in the conventional group and 17 months (IQR, 14-21.25) in the modified group. There were no statistically significant differences between the two groups in terms of age, sex, surgical level, operative time, or length of hospital stay (Table 1).

Table 1.

The Baseline Clinical Data Comparison Between the Conventional and Modified Group

	Conventional Group (n = 128)	Modified Group (n = 130)	P
Age (mean ± SD) (yrs)	59.6 ± 9.8	57.4 ± 10.2	0.113
Sex (n, male/female)	89/39	94/36	0.681
Operated laminea (n)
C3-6	39	39	0.757
C4-7	11	13
C4-6	4	6
C2-7	12	7
C3-7	62	65
Operation time (mean ± SD) (mins)	87.6 ± 12.0	84.6 ± 16.8	0.072
Length of stay (days), median (IQR)	5 (4-5)	4 (4-5)	0.137
Follow-up time (months), median (IQR)	14 (13-23)	17 (14-21.25)	0.259

IQR: interquartile range, n: number of patients, SD: standard deviation.

Incidence of C5 Palsy

The incidence of C5 palsy was 3.9% (5/128) in the conventional group and 0% (0/130) in the modified group, corresponding to an absolute risk reduction of 3.9%. Fisher’s exact test showed a significant difference between groups (two-sided P = 0.029). Five patients in the conventional group developed C5P, including three males and two females. All patients with C5P showed unilateral symptoms from postoperative day 1 to day 10 (Table 2). All five patients experienced difficulty with arm elevation, and deltoid muscle strength on the affected side decreased to Grade II. Three patients also had biceps weakness (Grades II–III), and one had concomitant triceps weakness (Grade III).

Table 2.

Characteristics of Patients With Postoperative C5 Palsy

No.	Sex	Age (years)	Symptoms	Day of onset	MMT			Recovery status at final follow-up	Recovery time (months)
No.	Sex	Age (years)	Symptoms	Day of onset	Muscle	Preoperative	Follow-up	Recovery status at final follow-up	Recovery time (months)
1	Male	59	Numbness, weakness	Post-op day 2	Deltoid	II	III	80% recovery	12
					Biceps	II	III
					Triceps	III	III
2	Female	67	Pain, weakness	Post-op day 4	Deltoid	II	V	Full recovery	1
					Biceps	V	III
					Triceps	V	V
3	Male	66	Weakness	Post-op day 10	Deltoid	II	III	80% recovery	12
					Biceps	III	III
					Triceps	V	V
4	Female	60	Weakness	Post-op day 2	Deltoid	II	IV	Full recovery	10
					Biceps	V	V
					Triceps	V	V
5	Male	65	Numbness, weakness	Post-op day 1	Deltoid	II	V	Full recovery	3
					Biceps	III	V
					Triceps	V	V

Clinical Outcomes

At the final follow-up, the average JOA score improved from 13.0 ± 2.2 to 15.2 ± 1.3 in the conventional group, with a recovery rate of 55.8 ± 18.9%. In the modified group, JOA scores improved from 12.6 ± 2.2 to 15.0 ± 1.2, with a recovery rate of 54.6 ± 16.9%. No statistically significant difference in JOA recovery rates was observed between groups (P = 0.599, Table 3).

Table 3.

Comparison of Clinical Outcomes Between Groups

	Conventional Group(n = 128)	Modified Group(n = 130)	P
Preoperative JOA score (mean ± SD)	13.0 ± 2.2	12.6 ± 2.2	0.131
Postoperative JOA score (mean ± SD)	15.2 ± 1.3	15.0 ± 1.2	0.304
JOA recovery rate (mean ± SD) (%)	55.8 ± 18.9	54.6 ± 16.9	0.599
C5 palsy (n/total (%))	5 (3.9%)	0	0.029^a
CSF leak (n/total (%))	3 (2.3%)	1 (0.8%)	0.368

^aSignificant. SD: standard deviation, JOA: Japanese orthopaedic association, CSF: cerebrospinal fluid.

Postoperative complications included cerebrospinal fluid (CSF) leakage in 3 patients in the conventional group and 1 patient in the modified group. No severe complications‒such as spinal cord injury, hinge collapse, screw loosening, or surgical site infection‒were reported.

Radiological Findings

Preoperative C2-7 Cobb angles were comparable between the two groups (11.3 ± 7.5° in the conventional group vs 11.3 ± 7.8° in the modified group, P = 0.128). At the final follow-up, no significant difference in C2-7 Cobb angle was observed (11.3 ± 7.8° in the conventional group vs 11.8 ± 7.5° in the modified group, P = 0.594, Table 4). The width between the bilateral gutters, measured between the opening and hinge sides, was significantly larger in the conventional group (median, 20.3 mm; interquartile range [IQR], 19.1-21.7 mm) than in the modified group (median, 18.7 mm; IQR, 17.0-19.8 mm; P < 0.001). The posterior spinal cord shift distance was greater in the conventional group (median, 3.0 mm; IQR, 2.5-3.8 mm) compared with the modified group (median, 2.0 mm; IQR, 1.2-2.5 mm; P < 0.001). Spearman’s rank correlation analysis showed a positive correlation between gutter width and posterior spinal cord shift distance (ρ = 0.294, P < 0.001).

Table 4.

Comparison of Radiological Data Between Groups

	Conventional group (n = 128)	Modified group (n = 130)	P
Preoperative C2-7 cobb angle (mean ± SD) (°)	11.3 ± 7.5	12.8 ± 7.7	0.128
Preoperative C2-7 cobb angle (mean ± SD) (°)	11.3 ± 7.8	11.8 ± 7.5	0.594
Width between the bilateral gutters (mm) median (IQR)	20.3 (19.1-21.7)	18.7 (17.0-19.8)	<0.001^a
Posterior spinal cord shift distance* (mm) median (IQR)	3.0 (2.5-3.8)	2.0 (1.2-2.5)	<0.001^a

^aSignificant. SD: standard deviation, IQR: interquartile range.

Discussion

C5P is a well-documented but poorly understood complication of laminoplasty (LAMP) for DCM. A meta-analysis reported a cumulative incidence of 6.3%, with higher rates observed in posterior approaches.² In our cohort, the overall incidence of C5P was 1.9% (5/258) and 3.9% in the conventional LAMP group (5/128), both at the lower end of the reported ranges. Anatomical studies have shown that the C5 nerve root is particularly vulnerable because it has the shortest distance from the dura mater to the neural foramen, making it prone to traction or impingement during postoperative cord shift.^11,12 Consequently, strategies that limit the width of lamina resection and open angle to prevent excessive posterior spinal cord shift may reduce C5P risk.^10,13,14 In this study, shifting the open-sided gutter medially by 1 mm lowered the postoperative C5P level in the modified group, which had no C5P cases (n = 130), compared with 5 cases in the conventional group (n = 128; P = 0.029), without compromising JOA recovery.

Previous studies have similarly demonstrated that wider gutter width and larger open angles increase posterior spinal cord shift and C5P incidence. Radcliff et al.¹⁵ and Nori et al¹⁰ reported that a wider laminectomy trough increased posterior shift, while Zhang et al¹³ and Tsuji et al¹⁴ found that greater open angles were associated with increased posterior spinal cord shift and incidence of C5P. In our study, the width between the bilateral gutters and posterior spinal cord shift distance decreased in the modified group. Correlation analysis revealed that the width between the bilateral gutters was associated with the posterior spinal cord shift distance.

We propose shifting the open-side gutter 1 mm medially from the junction of the lamina and the spinous process, between the outer margin of the dural sac and the lateral side of the spinal cord (Figure 1). Nakajima et al⁶ reported that the position of the bony gutter at the open side may have a central role in the pathomechanism of C5P. They suggested that the best starting point for drilling is about half a ball tip inward from the medial line of the facet joint using a high-speed burr, to avoid making an excessively bony gutter beyond the most medial part of the C5 facet joint and to prevent kinking of the C5 nerve root at the intervertebral foramen. We further modified the approach by shifting the open-side gutter more medially to achieve a limited-width decompression (spinal cord decompression). Nakajima et al⁶ reported that the posterior shift of the spinal cord (PSS) was higher in the C5P group, without a significant difference (4.3 mm vs 4.2 mm, N = 10, 40 respectively). Our results showed a greater decrease in PSS (3.2 mm vs 2.1 mm), which may be due to the smaller decompression width. This aligns with evidence that limited-width decompression can reduce the posterior spinal cord shift distance, thereby lowering the risk of C5P.^13-15

Limited-width decompression may cause insufficient decompression. Zhang et al¹⁶ reported that door shaft position significantly increased the spinal cord area. Patients in the wide-opening group showed a greater increase in spinal cord area, which may have influenced patient recovery. However, there was no significant difference in the JOA recovery rate at follow-up in the present study. This modification may help prevent C5 palsy while maintaining adequate decompression and comparable clinical outcomes.

This study had some limitations. First, its retrospective design may have introduced recall bias, especially in cases where information was supplied by patient proxies. Second, because postoperative C5 palsy was a rare event in this cohort, the observed association may be susceptible to type I error, highlighting the need for validation in larger, multicenter studies. Third, the study did not include high-risk subgroups, such as patients with ossification of the posterior longitudinal ligament (OPLL), who demonstrate higher C5P incidence. In addition, formal inter- or intra-observer reliability testing for radiological measurements was not performed, which may affect measurement reproducibility. Although several potential sources of bias inherent to retrospective observational studies cannot be fully eliminated, we attempted to mitigate these biases through consecutive patient inclusion, standardized surgical techniques, and independent radiological assessment. Future prospective multicenter studies with standardized protocols and longer follow-up are needed to validate these findings.

Conclusion

During expansive open-door laminoplasty, positioning the open-side gutter 1 mm medially from the junction of the lamina and facet joint (spinal cord decompression) may reduce the incidence of C5P without affecting neurological recovery, potentially by limiting posterior spinal cord shift.

Footnotes

Acknowledgments

We thank Dr Shilin Xue for his help with the sketch drawings.

ORCID iDs

Yang Gao

Zexiang Liu

Ethical Considerations

The study protocol was approved by the institutional research ethics committee (IRB00006761-M2023296), according to the principles of the Declaration of Helsinki. The institutional review board granted a waiver of informed consent because of the retrospective nature of the study.

Author contributions

Yang Gao and Zexiang Liu were responsible for data acquisition, data analysis, and drafting and revising the manuscript. Liang Jiang, as the corresponding author, was responsible for the study conception and design, supervision of the research process, critical revision of the manuscript, and overall quality assurance. All authors have read and approved the final version of the manuscript.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was funded by Peking University Third Hospital (JT-0019).

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Data Availability Statement

Research data supporting this publication are available from the Peking University Third Hospital, but restrictions apply to the availability of these data, which were used under license for the current study, and so are not publicly.*

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