Longitudinal Spinous‐Splitting Laminoplasty with Coral Bone for the Treatment of Cervical Adjacent Segment Degenerative Disease: A 5‐Year Follow‐up Study

C3/4 is Prone to ASDis

After the first anterior cervical surgery, ASDis was significantly higher in C3/4 than in other gaps. Our results suggest that ASDis is more likely to develop at C3/4. Furthermore, among the 13 cases of first-time SLAC, ASDis developed at C3/4 in eight (61.5%) cases.

Yue et al.12 and Ishihara et al.13 found that ASDeg increased at a rate of 3%–8% per year after 10 years of follow-up after ACDF. Hashimoto et al.10 reported that after cervical fusion, the incidence of imaging ASDeg was 32.8%, and 1/4 to 1/3 of cases eventually developed into clinically symptomatic ASD. Hilibrand et al.14 showed that among patients undergoing ACDF, 25.6% develop ASDeg within 10 years after surgery. Hilibrand et al.11 reported a 2.9% rate of reoperation in patients with ASDis development and no symptomatic improvement after receiving conservative treatment; however, other scholars believe that the incidence of ASDis requiring reoperation is higher. Zigler et al.15 believe that the incidence of ASDeg after ACDF is as high as 54.7% and the rate of ASDis reoperation is as high as 11.6%. Buttermann et al.3 found that 29% of patients with ASDis needed secondary surgery after 10 years of follow-up after ACDF. Ahn et al.1 provided evidence that the anterior vertebral plate and ACDF increase the risk of ASDis and pointed out that this finding is consistent with the findings of randomized controlled trials conducted in the United States, in which the anterior vertebral plate fixation method and ACDF were used. In Europe and other countries, ACDF usually does not include the front side of the steel plate, and only the cages are involved. The original purpose of using a steel plate is to reduce the incidence of pseudarthrosis in the surgical segment, but a meta-analysis reported by Shriver et al.16 showed that the risk of pseudarthrosis was low. Ji et al.17 reported that there was evidence that the use of the anterior vertebral plate fixation method, together with ACDF of the two segments, increases the incidence of ASDis compared to the use of an ACDF without the anterior vertebral plate method. In another analysis, Park et al.18 reviewed the lateral radiographs of 118 patients with anterior cervical fusion and found that the probability of adjacent disc degeneration increased in patients with a distance between the edge of the anterior vertebral plate and the adjacent disc of <5 mm. In a biomechanics study, Eck et al.7 reported that the use of prevertebral plates may accelerate the motion of adjacent segments, leading to ASDis. Our study results showed that ASDis was mostly located in the C3/4 segment and not in the gap below the surgical segment.

Matsumoto et al.19 found through imaging studies that the C3/4 and C6/7 intervertebral space heights of the non-surgical segment in an anterior cervical fixation group indicated progressive spinal stenosis. Maiman et al.20 showed that the pressure of the C4/5 intervertebral disc after C5/6 internal fixation was significantly higher than that of C5/6 after C4/5 internal fixation; thus, it was considered that the pressure increase of the upper intervertebral disc of the fixed segment was more obvious than that of the lower disc. Chang et al.4 found the same result by studying cadaver specimens. The upper intervertebral space pressure was higher in the flexion/extension position. Chung et al.5 conducted a biomechanical study and reported that the upper articular surface pressure of the adjacent segment was higher than that of the normal non-surgical group, and the pressure increased by 31.5%.

Basis for Selecting SLAC as Secondary Surgery

ASDis was characterized by the presence of a screw and anterior plate in the vertebral body (Figs 1B,2B,3A,B). Even when the anterior plate and screw can be removed and reconstructed with ACDF, new screws still need to be inserted. As the bone of the lower vertebral body is destroyed by the last screw, the holding force of the new screws will be significantly reduced, and internal fixation will fail.

In a meta-analysis article, although the JOA score and clinical symptom relief after ACDF were significantly better than after laminoplasty, the surgical technique and the rate of complications, such as cerebrospinal fluid leakage, internal fixation displacement, hematoma, and esophageal perforation21-27 were higher with ACDF. Injury to the recurrent laryngeal nerve, postoperative dysphagia, and hoarseness were common2, 28. Eichholz and Ryken8 analyzed 30 cases of patients with cervical revision surgery, and the complication rate was 27%. Hannallah et al.29 performed a statistical analysis of 1994 patients who underwent cervical spine surgery and found the incidence of postoperative cerebrospinal fluid leakage was 1% and the incidence of cerebrospinal fluid leakage during the revision surgery was 2.77 times that of the first surgery. Eichholz and Ryken8 believe that some implantable barriers administered during surgery cannot prevent the formation of scar tissue.

Therefore, when there is a requirement for a second surgery for ASDis, although ACDF can be performed again, some cases may require a multi-segment ACDF, which makes the operation difficult because the anatomical level of scar tissue is unclear. Moreover, the technical skill level and operative experience of doctors in primary-level hospitals may be limited. Using SLAC with indirect decompression, the risk is relatively low, the operation is simple, and the learning curve is low. Thus, the attending physician can complete the surgery independently.

For 52 patients, SLAC was performed the secondary surgery at our hospital, and these patients' clinical results were satisfactory.

SLAC Requires Laminectomy and C2 Laminoplasty-dome

In the 13 SLAC cases treated at our hospital, although the C2/3 and C3/4 segments of the intervertebral disc did not present with degeneration, protrusion, or spinal stenosis on imaging before the first operation, ASDis developed in 33 months (21–59 months) postoperatively. There were four (30.8%) cases of ASDis at C2/3 and eight (61.5%) cases of ASDis at C3/4. Increased contact and pressure during treatment or adjacent levels of facet joints may lead to micro-damage of the facet joint and eventually accelerate the degradation of the adjacent segment facet joint30, 31.

Therefore, we recommend (especially for patients older than 70 years) that SLAC should include C3 laminectomy and C2 dome laminoplasty to avoid a second operation on C2/3 or C3/4 for ASDis, even if the intervertebral discs of the C2/3 and C3/4 segments do not show degeneration, protrusion, or spinal stenosis before the initial surgery and there are no corresponding symptoms. Because of the high risk and difficulty of reoperation, the following indications should be considered carefully: Residual or progressive compression confirmed on imaging, positive conservative treatment for 3 months (excluding myofascial pain) with no real improvement in the symptoms and signs, and detrimental effects on the work and life of the patients. There are two “threshold values” for selecting ACDF or SLAC. Fujimori et al.32, Denaro et al.6, and Kim et al.33 reported that when ossification of the posterior longitudinal ligament accounts for 50% of the cross-sectional area of the spinal canal, laminoplasty is less effective in relieving neurological symptoms than ACDF. Suda et al.34 and Uchida et al.35 reported that when cervical kyphosis is more than 10°, the effect of laminoplasty in relieving neurological symptoms is inferior to that of ACDF. Therefore, when the patient meets the two abovementioned criteria, posterior cervical SLAC can be considered for patients who are older, have other diseases, or are unable to undergo anterior reoperation. The social factors related to the patient, including mental status (presence of depression), age (presence of menopausal syndrome), marital emotional state, working status, economic status, and social identity must be considered. Patients often have high expectations and more negative emotions regarding revision surgery. Surgeons should communicate more with patients and their families, appropriately reduce the patient's expectations of the efficacy of the surgery, and consider social and legal issues, such as possible medical litigation and medical compensation.

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