ABSTRACT
Aims and Objectives:
Noncontiguous degenerative cervical disc disease (NCDDD) is characterized by cervical disc prolapse involving nonadjacent segments. This study aims to determine if skip discectomy and fusion technique compared to contiguous discectomy and fusion while preserving adjacent segment disease in uninvolved intermediate segments leads to equivalent or better clinical and radiological outcomes.
Methods:
Fifty-two patients who underwent management of NCDDD and two-level contigious disc disease (CDD) over 6 years from 2014 to 2020 were included in the study. There were 44 male and 8 female patients with a mean age of 46.75 years. These patients were divided into two groups: Those who underwent contiguous discectomy and those who underwent skip discectomy with either anterior cervical discectomy (ACD) alone, ACD and fusion (ACDF), or ACDF with plating based on individual pathology and surgeon preference. Outcomes were assessed using clinical parameters such as modified Japanese Orthopaedic Association Score (mJOAS) and Nurick grade and radiological parameters such as disc height improvement, spinal alignment change, and fusion rates.
Results:
The overall mean duration of follow-up was 15.23 ± 23.69 months, with a clinical follow-up period of 23.87 ± 21.51 months and a radiological follow-up period of 7.57 ± 5.91 months, with follow-up in Group 1 being 24.67 ± 23.17 months and in Group 2 being 20.03 ± 10.53 months. The mean blood loss in Group 1 was 200.47 mL; in Group 2, it was 172 mL. The preoperative mJOAS was 10.19 ± 3.16, and the postoperative mJOAS was 12.73 ± 2.92 (P = 0.001). Nurick grade showed improvement from a preoperative mean score of 4.23 ± 1.02–3.65 ± 0.88 postoperatively (P < 0.001). Statistically significant improvement in intervertebral height at superior and inferior levels was observed. Outcomes for Skip discectomy regarding mJOAS, Nurick grade, radiological parameters, fusion, and complication rates were noninferior to contiguous discectomy and fusion.
Conclusion:
Skip discectomy has a similar benefit and risk profile and is noninferior compared to contiguous discectomy in addition to the preservation of intermediate disc integrity.
Keywords: Anterior cervical discectomy, anterior cervical fusion, intermediate disc preservation, noncontiguous cervical degenerative disc disease, skip discectomy
INTRODUCTION
Noncontigous cervical degenerative disc disease (NCDDD) is characterized by cervical myelopathy or radiculopathy resulting from degeneration in two nonadjacent intervertebral discs, whereas an intermediate normal segment remains unaffected.[1,2] The accepted conventional approach for addressing degenerative cervical disc disease and relieving associated cervical myelopathy or radiculopathy is anterior cervical discectomy and fusion (ACDF).[3] Previous investigations have demonstrated the efficacy of ACDF, with more than 90% of patients experiencing improved reduced movement functions.[4]
In noncontiguous disc (NCD) disease, long segmental anterior fusion has conventionally been employed, encompassing the normal intermediate segments (ISs). This strategy aims to mitigate stress on the IS and prevent adjacent segment degeneration (ASD) in the unaffected segment.[5,6] However, long segmental anterior fusion is associated with a heightened risk of complications, including pseudarthrosis, persistent postoperative dysphagia, nonunion, and ASD.[7,8] Preservation of the IS has been proposed as a means to enhance postoperative outcomes.[6] Nevertheless, most studies advocating IS preservation utilize noncontinuous ACDF, introducing additional stress from the fused levels and potentially causing hypermobility in the IS, ultimately accelerating ASD.
In comparison, two-level contiguous discectomies are commonly performed, and the effect on adjacent segment disease is amplified as the number of fused segments increases. We have attempted to understand the impact of sparing the normal IS in NCDs and its effect on outcomes of cervical myelopathy. This study compares the outcomes of two-level contiguous and skip cervical discectomy to determine if preserving the IS offers equivalent postoperative results to fusing contiguous discs.
METHODS
Study design and population
This retrospective study was done at a tertiary care referral institution over 6 years from 2014 to 2020. We analyzed data from patients who underwent two-level cervical discectomy and fusion, divided into two groups: Those who received contiguous discectomy and those who underwent skip discectomy. The sample comprised 52 patients, 44 males and eight females, aged between 24 and 65 (mean age: 46.75 ± 10.43 years). The inclusion criteria were a diagnosis of cervical myelopathy or radiculopathy, two-level disc degeneration, and a follow-up period of at least 6 months.
Surgical procedures
The surgical procedures included ACD, ACDF, and ACDF with plating (ACDFP). The decision on the type of surgery and the approach (vertical or horizontal incision) was based on individual patient pathology and surgeon preference. Implants used included tricortical autografts, cages with granules, cage, and autografts, and cases without implants. Figures 1 and 2 showcase noncontiguous cervical Prolapsed intervertebral disc (PIVD) and postoperative imaging showing the fixation.
Figure 1.
(a) Preoperative T2 weighted magnetic resonance image lateral view of the cervical spine: C3–4 and C5–6 posttraumatic PIVD following fall from a height. Patient presented with neck pain with paresthesias involving C6 dermatome with no loss of motor power or sensation with bilateral plantars extensor. (b) Postoperative lateral X-ray of the cervical spine. C3–4 anterior cervical discectomy (ACD) and placement of stand-alone cage at C3–4 level and C5–6 ACD and instrumentation with titanium cage and plating
Figure 2.
(a) Preoperative T2 weighted magnetic resonance image lateral view of cervical spine with degenerative C3–4 and C5–6 PIVD. Patient presented with gradually progressive weakness of all 4 limbs with an MRC grade of 4/5, paresthesia of all 4 limbs, graded sensory loss below T2 dermatome and exaggerated deep tendon reflexes (b) Postoperative X-ray lateral cervical spine. Patient underwent noncontiguous anterior cervical discectomy at C3–4 and C5–6 levels and fixation with zero profile cage at both levels
Data collection
Data were collected on demographic variables, clinical presentation, surgical details, and postoperative outcomes. Clinical parameters assessed included the modified Japanese Orthopaedic Association Score (mJOAS) and Nurick grade, both preoperatively and postoperatively. Radiological parameters measured were intervertebral height (IVH) and the Ishihara index. Complications such as cage subsidence, ASD, implant failure, re-exploration, worsening of symptoms, and overall complication rates were recorded. Essential patient characteristics, clinical parameters, surgical outcomes, and complications are summarized in Table 1.
Tables 1.
Basic patient characteristics
| Variables | Frequency |
|---|---|
| Age (years) | 46.75±10.43 (24–65) |
| Sex | |
| Male | 44 |
| Female | 8 |
| Symptoms (months) | 15±23.69 (0.4–121.67) |
| Clinical follow up (months) | 23.87±21.51 (6.43–129.53) |
| Radiological follow up (months) | 7.57±5.91 (3.43–46.9) |
Statistical analysis
Statistical analyses were performed using independent samples t-test, Mann–Whitney U-test, paired sample t-test, and Chi-square test where appropriate. P <0.05 were considered statistically significant.
RESULTS
Demographic and clinical characteristics
The demographic and clinical characteristics of the study population are summarized in Tables 1 and 2. The mean age of the patients was 46.75 ± 10.43 years, with a male predominance (84.6%). The mean duration of symptoms before surgery was 15 ± 23.69 months, with a clinical follow-up period of 23.87 ± 21.51 months and a radiological follow-up period of 7.57 ± 5.91 months.
Table 2.
Clinical characteristics of patients in both groups
| Variables | Group 1 | Group 2 | P |
|---|---|---|---|
| Age | 45.86±11.18 | 51±3.43 | 0.181a |
| Sex | |||
| Male | 37 | 7 | 0.532a |
| Female | 6 | 2 | |
| Symptoms (months) | 13.67±23.66 | 21.34±24.16 | 0.282b |
| Clinical follow up (months) | 24.67±23.17 | 20.03±10.53 | 0.794b |
| Radiological follow up (months) | 7.59±6.41 | 7.48±2.6 | 0.536b |
| Blood loss (mL) | 200.47±187.03 | 172.22±83.33 | 0.905b |
| Surgical time (min) | 176.63±55.7 | 171.67±30.92 | 0.981b |
| Preoperative mJOAS | 10.35±3.04 | 9.44±3.78 | 0.440a |
| Postoperative mJOAS | 12.86±2.76 | 12.11±3.72 | 0.489a |
| Preoperative Nurick grade | 4.23±1 | 4.22±1.2 | 0.849b |
| Postoperative Nurick grade | 3.72±0.83 | 3.33±1.12 | 0.404b |
| Change in mJOAS | 2.51±1.78 | 2.67±1.12 | 0.812b |
| Change in Nurick grade | −0.49±0.63 | −0.89±0.6 | 0.101b |
aIndependent samples t-test; bMann–Whitney U-test. mJOAS - Modified Japanese Orthopedic Association Score; IVH - Intervertebral height
Surgical outcomes
Surgical details and outcomes are presented in Tables 3 and 4. The mean blood loss during surgery was 195.58 ± 173.24 mL, and the mean surgical time was 175.77 ± 52.04 min. Fusion was achieved in 90.38% of cases, with an average fusion duration of 164.6 ± 51.23 days.
Table 3.
Type of surgery, fusion status and complications in two groups
| Variables | Group-1 | Group-2 | P |
|---|---|---|---|
| Incision | |||
| Vertical | 2 | 7 | 0.001a |
| Horizontal | 41 | 2 | |
| Implants | |||
| No implants | 3 | 1 | 0.898a |
| Tricortical autograft | 16 | 4 | |
| Cage with granules | 23 | 4 | |
| Both cage and autograft | 1 | 0 | |
| Types of surgery | |||
| ACD | 4 | 2 | 0.538a |
| ACDF | 18 | 3 | |
| ACDFP | 21 | 4 | |
| Fusion status | |||
| Yes | 39 | 8 | 0.867a |
| No | 4 | 1 | |
| Complications | |||
| Cage subsidence | 2 | 0 | 0.282a |
| Adjacent segment disease | 1 | 0 | |
| Implant failure | 0 | 0 | |
| Re-exploration | 1 | 0 | |
| Worsening of symptoms | 2 | 0 | |
| Wound complication | 0 | 0 | |
| Overall complications | 6 | 0 |
aChi-square test. Worsening of symptoms: One patient had postoperative dysphagia, and another patient had postoperative increased paresthesia of limbs; one case required re-exploration due to disc cavity hematoma, two patients had cage subsidence and one patient had adjacent segment disease, both were managed conservatively. ACD - Anterior cervical discectomy; ACDF - Anterior cervical discectomy and fusion; ACDFP - Anterior cervical discectomy and fusion with plating
Table 4.
Clinical and radiological outcomes
| Variables | Preoperative | Postoperative | P |
|---|---|---|---|
| mJOAS | 10.19±3.16 | 12.73±2.92 | <0.001a |
| Nurick grade | 4.23±1.02 | 3.65±0.88 | <0.001b |
| Preoperative superior level IVH (mm) | 3.13±1.26 | 5.02±1.62 | <0.001b |
| Preoperative inferior level IVH (mm) | 3.11±1.26 | 5.29±1.94 | <0.001b |
aPaired sample t-test; bWilcoxon signed-rank test. mJOAS - Modified Japanese Orthopedic Association Score; IVH - Intervertebral height
Comparison between groups
Comparisons between the contiguous and skip discectomy groups are shown in Tables 2 and 3. No significant differences were found in demographic variables, preoperative and postoperative mJOAS, Nurick grades, or changes in radiological parameters. The only significant difference was the type of incision used, with a higher frequency of vertical incisions in the skip discectomy group (P = 0.001). Cases with NCDs sparing ISs improved similarly to contiguous disc cases.
Clinical and radiological outcomes
The mJOAS improved significantly from a preoperative mean of 10.19 ± 3.16 to a postoperative mean of 12.73 ± 2.92 (P < 0.001), and the Nurick grade improved from a mean of 4.23 ± 1.02 to 3.65 ± 0.88 (P < 0.001). Significant improvements were also observed in IVH at both superior and inferior levels (P < 0.001). Clinical and radiological outcomes are summarized in Table 4.
Complications
Complications were minimal, with a total complication rate of <4%. Specific complications included cage subsidence (3.85%), ASD (1.92%), re-exploration due to disc cavity hematoma (1.92%), and worsening of symptoms (3.85%). There were no significant differences in complication rates between the two groups. Complications are summarized in Table 1. Figure 3 shows a case of contiguous discectomy and fusion with subsidence on follow-up.
Figure 3.
(a) Preoperative T2 weighted magnetic resonance of lateral cervical spine showing C4–5 and C6–7 PIVD following fall. Patient presented with neck pain, with bilateral upper limb weakness and paraplegia with graded sensory loss below T4 level and bilateral plantars upgoing (b) Postoperative latertal computed tomography (CT) cervical spine: C4–5, C5–6 and C6–7 Anterior cervical discectomy and fixation with PEEK cage and Iliac crest graft with 3 level anterior cervical plating (c) Lateral CT cervical spine 3 months postoperatively showing implant subsidence
DISCUSSION
The results of this study highlight several essential aspects of the surgical management of two-level cervical disc degeneration, comparing contiguous and skip cervical discectomy. The significant improvements in both mJOAS and Nurick grades postoperatively across the entire cohort underscore the overall efficacy of surgical intervention for cervical disc degeneration, regardless of the approach.
Clinical outcomes
The clinical outcomes indicated by improvements in mJOAS and Nurick grades are pivotal. The average increase in mJOAS and decrease in Nurick grade demonstrate that both contiguous and skip discectomy effectively alleviate neurological symptoms and enhance functional capacity. These findings align with previous studies showing that ACDF effectively relieves cervical myelopathy and radiculopathy symptoms.
Notably, there was no significant difference in the improvement of mJOAS or Nurick grades between the contiguous and skip discectomy groups. This suggests preserving the IS in skip discectomy does not compromise the clinical outcome. These results are consistent with the notion that IS preservation might mitigate the stress on adjacent segments, potentially reducing the risk of ASD without sacrificing clinical benefit.[9] Park et al., in their cadaveric study using specimens of 5 cervical spines, simulated two-level ACDF with plating from C5 to C7, noted that there was a marked increase in intradiscal pressure in adjacent superior C4–5 level during physiological motion, thereby forming the basis for accelerated degenerative changes in vertebral level adjacent to anterior cervical fusion.[10]
Radiological outcomes
Radiological outcomes, such as changes in IVH and the Ishihara index, further reinforce the effectiveness of both surgical approaches. Significant improvements in IVH at both superior and inferior levels were observed postoperatively, indicating successful restoration of disc height and alignment. The lack of substantial differences between the groups suggests that both contiguous and skip discectomy are equally effective in achieving these radiological goals. The Ishihara index, which reflects the alignment and curvature of the cervical spine, showed significant improvement postoperatively, further supporting the efficacy of the surgical interventions. Again, no significant differences between the two groups were observed, indicating that skip discectomy, which preserves the IS, does not negatively impact spinal alignment and curvature. Wang et al. performed skip-level ACDF with a self-locking stand-alone PEEK cage; they also observed a reasonable fusion rate with preservation of spinal curvature and IVH.[11]
Complications and safety
The overall complication rate in this study was relatively low (11.53%), with specific complications including cage subsidence, ASD, re-exploration due to disc cavity hematoma, and worsening of symptoms. Significantly, the rates of these complications did not differ between the two groups. This finding suggests that skip discectomy, despite preserving the IS, does not introduce a higher risk of complications than contiguous discectomy. Interestingly, the type of incision used differed significantly between the two groups, with a higher frequency of vertical incisions in the skip discectomy group. This variation may reflect surgical preferences or anatomical considerations rather than a difference in surgical outcomes. The low complication rates observed in both groups indicate that both surgical approaches are safe and effective, with manageable complication profiles.
Fusion and intermediate segment preservation
Fusion rates were high in both groups, with no significant difference. This finding supports the feasibility of achieving successful fusion with both contiguous and skip discectomy approaches. The preservation of the IS in skip discectomy did not hinder the fusion process, indicating that it is a viable strategy for managing noncontiguous cervical disc degeneration. Preserving the IS has been proposed to enhance postoperative outcomes by reducing the stress on adjacent segments and potentially mitigating the risk of ASD.[12,13] The lack of significant differences in ASD rates between the two groups in this study suggests that IS preservation does not increase the risk of adjacent segment issues, supporting its use as a safe and effective surgical strategy.
Implications for surgical decision-making
The findings of this study have several implications for surgical decision-making in managing two-level cervical disc degeneration. Both contiguous and skip discectomy effectively improve clinical and radiological outcomes, with low complication rates and high fusion success. The choice between these approaches should be individualized based on patient-specific factors, including the extent and location of disc degeneration, anatomical considerations, and surgeon experience. For patients with NCD degeneration, preserving the IS through skip discectomy may reduce stress on adjacent segments without compromising clinical or radiological outcomes. This approach can be particularly advantageous in patients at higher risk for ASD or those with significant IS integrity.
The findings of this study align with and expand upon existing literature summarized in Table 5. Similar to Wang et al.[11] (2013) and Qizhi et al.[14] (2016), our results demonstrate significant postoperative improvements in clinical scores (mJOAS, Nurick grade) and radiological parameters, reinforcing the efficacy of skip discectomy in managing noncontiguous cervical disc disease. However, our observation of preserved intermediate disc height contrasts with Baram et al.[15] (2024), who reported a decline in intermediate disc height postoperatively, potentially due to differences in surgical techniques or follow-up duration. While cadaveric studies by Finn et al.[12] (2011) and Park et al.[10] (2007) highlighted biomechanical risks such as reduced IS mobility or elevated adjacent-level intradiscal pressure, our clinical data did not reveal increased rates of ASD in skip discectomy, diverging from Baumann et al.’s[16] (2024) systematic review that associated noncontiguous ACDF with higher ASD risk. These discrepancies may stem from variations in study design (e.g., retrospective vs. biomechanical), sample size limitations, or heterogeneity in fusion constructs. Notably, our low complication rates and equivalent fusion success between groups echo the outcomes of Wang et al.[11] (2013) and Qizhi et al.[14] (2016), further supporting skip discectomy as a viable alternative. Nevertheless, as Baumann et al.[16] (2024) emphasized, the current evidence remains limited by retrospective designs and small cohorts, underscoring the need for prospective randomized trials to validate these findings and clarify long-term implications for IS preservation.
Table 5.
Review of literature of studies comparing noncontiguous degenerative cervical disc disease and contiguous disc disease
| Author | Type of study | Method | Number of participants | Results |
|---|---|---|---|---|
| Wang et al.[11] | Retrospective study | Patients with noncontiguous CSM underwent skip level ACDF with self locking stand alone PEEK cage | 16 | At mean follow up of 43.6 months, JOA score, spinal alignment and IVH showed improvement as compared to that preoperatively (P<0.05) |
| Finn et al.[12] | Cadaveric study | Biomechanical response and motion data from cadaveric cervical spine before and after discectomy at C4–5 and C6–C7 level and fuseion with plates and interbody cage and also after 3 level fusion from C4 to C7 | 7 intact cadaveric cervical spines | In flexion/extension ROM decreased in intermediate segment (P=0.0003) with three level fixation although no difference at supra and infra-adjacent segments between the two plating systems |
| Qizhi et al.[14] | Prospective study | Patients with two level noncontiguous level of CSM underwent ACDF with zero profile device between December 2009 and August 2012 | 17 | At mean follow up of 48.59 months, JOA showed improvement (P<0.01) and NDI decreased (P<0.01), Cervical lordosis improved from 10.17 to 17.06. Fusion rate was 100% at 12 months |
| Park et al.[10] | Cadaveric study | Two level ACDF and plating from C5 to C7 level and recording intradiscal pressure at C4–5 level after loading C-3 to flexion, extension and lateral bending | 5 cadaveric cervical spine specimens | Significant increase in intradiscal pressure at superior adjacent C4–5 level from pre-ACDF 1275 mmHg to 2475 mmHg post-ACDF during physiological motion |
| Baram et al.[15] | Retrospective study | Retrospective evaluation of clinical and radiological outcomes and rate of adjacent segment disease for patients undergoing noncontiguous two level ACDF for patients with cervical myeloradiculopathy presenting between 2015 and 2021 | 32 | At mean follow-up of 43.3 months, mJOA score significantly improved from 14.57±2.3 to 16.5±2.1 (P<0.01) and the NDI score significantly decreased from 21.45±4.3 to 12.8±2.3 (P<0.01) postoperatively. Cervical lordosis increased after surgery (from 9.65±9.47 to 15.12±6.09); intermediate disc height decreased (5.68±0.57 mm–5.27±0.98 mm) |
| Baumann et al.[16] | Systematic review | Systematic review performed using PubMed, Cinahl, Medline, and Web of science from database inception till June 6, 2023. Patients undergoing noncontiguous ACDF, noncontiguous CDA, and/or noncontiguous hybrid cervical surgery were included | 388 | At a mean follow-up of 33±6 months, no clinically meaningful difference in neck disability index, JOA, and improvement in pain based on surgery type. However, the risk of adjacent segment disease was higher with noncontiguous ACDF (6.4%) as compared to contiguous HCS (1.7%) and noncontiguous CDA (0.0%) |
CSM - Cervical spondylotic myelopathy; ACDF - Anterior cervical discectomy and fusion; CDA - Cervical disc arthroplasty; JOA - Japanese Orthopaedic Association; ROM - Range of motion; IVH - Intervertebral height; PEEK - Polyetheretherketone; HCS - Hybrid cervical surgery
Limitations
There were certain limitations in the current study. The patients underwent intervention based on an individual evaluation and surgeon’s preference in the two groups. The fusion tools used for ACDF and ACDFP in both groups differ: Tricortical autografts, cages with granules, cage and autograft, and cases without implants. Different interventions affect the accuracy of the conclusion. Furthermore, the number of patients undergoing contiguous discectomy with or without fusion is more than that of patients undergoing skip discectomy, potentially introducing particular statistical bias. The sample size is small, with a short follow-up period of 6 months. Though the current study shows the noninferiority of skip discectomy over contiguous discectomy both with and without fusion, more conclusive evidence can be drawn by performing a randomized prospective study with more well-defined criteria for patient selection and selection of intervention.
CONCLUSION
The results drawn from the current study indicate that Skip discectomy with or without fusion in noninferior to contiguous discectomy provides similar clinical and radiological outcomes and similar complication profiles. Furthermore, skip discectomy has favorable outcomes for preserving intermediate disc integrity. Though available data from retrospective studies and biomechanical studies shows better results with skip discectomy than contiguous discectomy and fusion, skip discectomy is not commonly performed given the nonavailability of more reliable evidence from prospective randomized control studies to consider changing the current standard of care. Further research using high-quality evidence is required to assess the effects on clinical outcomes and to explore whether one cervical procedure is superior to another for noncontiguous cervical degenerative disc disease.
Conflicts of interest
There are no conflicts of interest.
Funding Statement
Nil.
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