Anterior Cervical Hybrid Decompression and Fusion Surgery to Treat Multilevel Cervical Spondylotic Myelopathy

This paper describes a hybrid surgical technique that combines anterior cervical discectomy and fusion with anterior cervical corpectomy and fusion to treat patients with multilevel cervical spondylotic myelopathy.

Cervical spondylotic myelopathy (CSM) is a common disease resulting from intervertebral disc herniation, ossification of the posterior longitudinal ligament, and other pathological changes that cause spinal cord compression. CSM progresses insidiously with mild upper-limb numbness, which patients tend to ignore. As the condition worsens, the patients may experience a limp, limited fine motor activity, and eventually, a loss of daily activity. Conservative treatments, such as physical therapy and medication, are frequently ineffective for CSM. Once surgery is deemed to be required, decompression surgery is the best option. So far, both anterior cervical discectomy and fusion (ACDF) and anterior cervical corpectomy and fusion (ACCF) have been commonly used to treat CSM. In addition, a type of hybrid procedure that combines ACDF with ACCF has been used to treat some CSM cases and achieved satisfying results. Thus, this study aims to introduce this hybrid surgical technique and advocate for it based on its patient success.

Cervical spondylotic myelopathy (CSM) is a common cause of cervical nerve dysfunction. It is characterized by acquired stenosis of the cervical spinal canal, osteoarthritic degeneration, or spinal column ligamentous aberrations¹. Due to the pathological characteristics of the disease, conservative treatments are ineffective in removing the increasing compression, and prompt surgical intervention is required. In clinical practice, anterior cervical discectomy and fusion (ACDF) surgery is usually the first option for single-level CSM². Despite the variety of procedures available, the best procedure for multilevel cervical spondylotic myelopathy (MCSM) remains debatable.

In MCSM cases, the typical compression of the spinal cord comes from the ventral side, and this compression causes central and peripheral nerve injury symptoms. Cervical surgeries are usually needed to treat MCSM. There are two common surgical approaches: anterior and posterior surgeries. The anterior approach includes ACDF, anterior cervical corpectomy and fusion (ACCF), and anterior cervical hybrid decompression and fusion surgery (ACHDF, the combination of ACDF and ACCF). These anterior surgeries are suitable for MCSM with ventral compression to the spinal cord. The benefits of ACHDF as a hybrid surgical technique include maintaining the anterior and middle columns of the cervical spine while ensuring as much decompression as possible and allowing the surgeons to customize their surgical strategy. In this study, we aim to introduce the ACHDF technique combining ACDF and ACCF for treating MCSM.

Case presentation
A 50-year-old female patient who complained of neck pain for 1.5 years and numbness in her left limbs for 7 months was admitted to the spine surgery department of the Third Hospital of Hebei Medical University. Consent from the patient was obtained to use her medical history in this study. This patient's main symptoms were aggravated by daily activities and relieved by rest and unrelated to temperature changes. The patient had undergone conservative treatments in a local clinic, including transfusion therapy and acupuncture, but without any successful relief of her symptoms. Physical examination revealed decreased strength in the left biceps and triceps (grade 3) and muscle groups of the left lower extremity (grade 4), as well as diminished biceps and triceps tendon reflexes. The Hoffmann's sign and Babinski's sign were both negative.

Diagnosis, assessment, and plan
The patient underwent cervical X-rays, CT scans, MRIs, and laboratory tests in preparation for surgery. The radiological examinations revealed a straightening of the physiological curvature of the cervical spine, herniated intervertebral discs, and spinal cord compression. The patient's visual analog scale (VAS) was 5, and her cervical Japanese Orthopaedic Association Score (JOA) was 7. Cervical spondylotic myelopathy was diagnosed according to the symptoms of decreased muscle strength, decreased tendon reflexes, and limb numbness. As the patient showed no signs of peripheral nerve compression, cervical spondylotic radiculopathy was ruled out. In addition, pain caused by muscle strain and rheumatic diseases was ruled out because there was no obvious correlation between the pain symptoms and temperature changes in the patient^3,4.

As conservative treatment was ineffective, surgical treatment was recommended to the patient. ACHDF surgery was selected to treat the disease because an osteophyte could be observed in the patient's X-ray and CT in segment C6/7 (Figure 1A,B, yellow arrow). Meanwhile, a low-signal shadow protruding posteriorly and pressing on the dural sac could be observed on MRI in C6/7 (Figure 1C, yellow arrow). Sagittal CT imaging revealed osteophytes protruding from the posterior margin of the vertebral body by ~5.7 mm, which compressed the spinal cord not only at the disc levels but also behind the cervical vertebral body in C6 and C7. A herniated disc could be observed in C5/6, while C4/5 suffered a relatively mild disc herniation. In line with the recommendations of the WFNS Spine Committee⁵, C6 corpectomy and C4/5 discectomy were performed to treat the disease. The patient's neck pain and numbness improved after surgery, and although physical examination revealed no significant recovery of muscle strength, the patient reported improvement in her own perception of her muscle strength. There were no major postoperative complications observed.

The protocol was approved and followed the guidelines of the Ethics Committee of the Third Hospital of Hebei Medical University. Informed consent was obtained from patients for including them and the data generated as a part of this study.

1. Preoperative preparation

1. Apply the following inclusion criteria.
   1. Ensure that the radiological examination shows three or more diseased levels.
   2. Ensure that the symptoms are caused by pathological changes of the cervical vertebrae with the exclusion of other systemic diseases.
   3. Look for hypertonia, hyperreflexia, positive pathological signs, or symptoms of upper motor neuron injury.
2. Apply the following exclusion criteria.
   1. Exclude those diagnosed with cervical spondylotic radiculopathy.
   2. Exclude patients who have undergone cervical surgery or have a history of cervical injury.
   3. Exclude patients with a cervical tumor or inflammation.
   4. Exclude patients with serious ossification of the posterior longitudinal ligament.
3. After general anesthesia and tracheal intubation are performed, place the patient in the supine position on the operating table.
4. Place a cylindrical pillow on the back of the patient's neck to maintain the cervical spine in a hyperextension position.
5. Disinfect the surgical area with iodine and alcohol, and then lay the sterile sheets over the patient.

2. Lesion exposure

1. Make a right transverse or longitudinal incision (depending on the surgeon's preference) centered on the fusion segments (localization according to body surface markers).
2. Use a scalpel to cut the skin, and use an electrocoagulation electrotome to isolate the subcutaneous tissue and cut through the platysma myoides (cut the omohyoid muscle if the scope of surgery is large and there is no need to suture the muscle).
3. Determine the carotid pulse and carotid sheath location with a finger. Perform blunt dissection of the muscle medial to the carotid sheath up to the prevertebral fascia.
4. Use a periosteal detacher to separate the muscle along the attachment points. Use a goiter retractor to pull the thyroid and tracheoesophageal structures to the patient's left side.
5. Use an electrocoagulation electrotome to cut the prevertebral fascia and expose the vertebral body; then, use a cervical spreader to widen the intervertebral space.

3. Decompression

1. ACDF surgery
   1. Use a scalpel to cut the required amount of the annulus fibrosus. Then, use a curette and a nucleus pulposus clamp to remove the nucleus pulposus until the dura is exposed. Use a laminectomy rongeur to remove the endplates and hyperplastic bone.
   2. Use a nerve dissector to search for potential compression, and use to remove part of the posterior vertebral body edge to make a decompression.
   3. Insert a properly sized interbody fusion cage filled with autologous bone into the intervertebral space.
2. ACCF surgery
   1. Use rongeur forceps to remove the vertebral body located between two diseased discs. Use a curette and a nucleus pulposus clamp to remove the two adjusted discs and endplates, similar to step 3.1.1.
   2. After the dura is exposed, use the nerve dissector to search for potential compression. Use gelatin sponges or fluid gelatin accompanied by brain cotton pieces to stop bleeding.
   3. Insert a properly sized titanium mesh cage filled with autologous bone into the space between the two vertebrae.

4. Titanium plate fixation

1. Choose a titanium plate of an appropriate length to cover the surgical segment. Implant six screws into the vertebrae to fix the titanium plate.

5. Closing the incision

1. Use saline to flush the surgical area, and elicit hemostasis with bipolar electrocoagulation. Fill the void by using gelatin sponges, and insert a drainage tube.
2. Use an interrupted suture to close the superficial fascia and skin (size 2-0 suture material).

NOTE: The suturing method can be chosen according to the operator's preference or patient's request.

6. Postoperative care

1. Measure the blood loss through the drainage bottle each day. When the daily blood loss is less than 50 mL, the drainage tube can be removed.
2. Allow the patient to walk with a separated collar support the day after surgery. Advise the patient to keep wearing the support for 1.5 months.

The CT and MRI scans revealed disc herniation in the cervical segments C3-C7 and ossification in C6-C7 (Figure 1). Although C3-C4 had pathological changes, spinal cord compression was not observed. As a result, C4-C7 was chosen as the surgical segment. The postoperative VAS score decreased from 5 before the operation to 3 at 3 months and 1 at 20 months. The JOA score increased from 7 before the operation to 8 at 3 months and 12 at 20 months. The neck pain only occurred if the patient bowed their head for a long time; the numbness and loss of muscle strength in the limbs still existed but were better compared to the pre-operation levels in the last follow-up. A postoperative X-ray revealed no significant implant-related complications (Figure 1)⁶.

In a previous study, we compared clinical outcomes between multilevel ACDF and ACHDF⁶. The results showed that ACHDF was comparable to ACDF surgery in terms of intraoperative trauma, as assessed by hospitalization, operation time, and intraoperative blood loss, as well as imaging parameters, including the Cobb angle and anterior column height. With the exception of the long-term maintenance of the anterior column height at the fusion level, multilevel ACDF surgery had better outcomes in terms of keeping the anterior column height stable compared to ACHDF surgery, although this difference did not affect the patients' VAS or JOA scores (Table 1 and Table 2)⁶.

Figure 1: Pre- and postoperative imaging. The patient's (A) pre-operative X-ray, (B) CT, and (C) MRI and postoperative X-ray images at (D) 3 months and (E) 20 months. This figure has been modified from Tian et al.⁶. Please click here to view a larger version of this figure.

Table 1: The comparison of the length of hospitalization (days), operation time (min), blood loss (mL), VAS score, JOA score, and improvement rate (%) of the two groups with ACDF versus ACHDF. This table has been modified from Tian et al.⁶. * Significant difference between pre-operation and the last follow-up in the same group. Abbreviations: ACDF = anterior cervical discectomy and fusion surgery; ACHDF = anterior cervical hybrid decompression and fusion surgery (the combination of ACDF and ACCF); VAS = visual analog scale; JOA = Japanese Orthopaedic Association; IQR = interquartile ranges.

Table 2: Comparison of Cobb angle (degree) and anterior column height (mm) of the two groups with ACDF versus ACHDF. This table has been modified from Tian et al.⁶ * Significant difference between pre-operation and the last follow-up in the same group; ∫ significant difference between pre-operation and the 3 month follow-up in the same group; ∫∫ significant difference between the 3 month follow-up and the last follow-up in the same group. Abbreviations: ACDF = anterior cervical discectomy and fusion surgery; ACHDF = anterior cervical hybrid decompression and fusion surgery (the combination of ACDF and ACCF).

Multilevel cervical spondylotic myelopathy is a disease that affects multiple intervertebral discs. This increases the severity of the disorder, makes it more challenging to obtain a good prognosis, and makes determining the responsible segment more difficult than for single-level CSM. Clinically, the mJOA score is commonly used to grade CSM. An mJOA score ≤ 11 is generally regarded as severe, 12-14 is moderate, and 15-17 is mild; moderate and severe CSM require prompt surgical treatment, while patients graded as mild can use non-operative treatment¹. Clinicians should also think about the connection between imaging and signs and symptoms. If only spinal cord compression is observed on imaging but no symptoms are present, surgical intervention should be performed with caution. The most common anterior approaches for MSCM are ACDF, ACCF, and ACHDF.

Multilevel ACDF is preferred when the patients have minimal retrovertebral disease; however, when significant retrovertebral disease is observed, ACCF and ACHDF are recommended⁷. Although ACCF can improve surgical vision and provide more complete decompression, studies have shown that multilevel ACCF has no advantage in treating MCSM^8,9,10 due to the extensive damage to the cervical spine structure. The other two techniques show similar efficacy⁸. ACHDF is a technique that combines ACDF and ACCF. ACDF is used to treat minor lesions that only involve the intervertebral disc, whereas ACCF is used to treat lesions that involve the posterior edge of the vertebral body, resulting in more widespread decompression. The advantage of ACHDF is the combination of minor trauma from ACDF and complete decompression from ACCF, which allows for patient-specific treatment.

According to a prior study, poor local kyphosis correction, advanced age, a longer duration of symptoms, and a bigger T1 slope angle are associated with poor prognosis¹¹. When dorsal compression to the spinal cord is prominent or there is generalized spinal stenosis in MCSM, such as ossification of the posterior longitudinal ligament, decompression from the ventral side is risky. This can cause complications such as iatrogenic nerve damage and cerebrospinal fluid leakage. In these cases, laminoplasty and laminotomy¹² - the two prominent posterior approach surgeries that use the bowstring effect to widen the spinal canal - are safer choices. Neurologic, vascular, or esophageal injury could occur if the surgeons do not have a thorough understanding of the surgical anatomy, and implant-related complications such as implant displacement and fusion failure may also occur based on an inappropriate choice of implants. Therefore, surgeons should be aware of the mechanical properties of the implants and choose appropriately sized titanium plates and screws to avoid complications⁵.

The steps involved in removing the disc in this surgery must be performed with care. When approaching the posterior longitudinal ligament, extra precautions must be taken to avoid injuring the dura. Capillary hemorrhage may occur during the removal of the posterior longitudinal ligament, and the use of bipolar coagulation forceps should be avoided due to the risk of nerve damage. Compression with gelatin sponges and brain cotton pieces is a good way to stop or treat cerebrospinal fluid leakage. Another critical factor is focusing on cervical curvature recovery, which is an important indicator of postoperative efficacy^13,14. Mild cervical spine convexity cushions the spinal cord and is also a protective factor against axial symptoms¹⁵. It is critical to consider the pre-operative position, the extent of intervertebral space distraction, and the selection of an appropriate size interbody fusion cage and titanium cage. When formulating these strategies, surgeons should also consider that some people have physiologically straight spines or kyphotic spines^16,17, depending on gender, age, region, and other factors.

The hybrid operation has some limitations when compared to ACDF. ACDF has better long-term outcomes in terms of the restoration of the anterior column height⁶. Due to the differences in span and hardness between the titanium cage and the interbody fusion cage, cancellous bone is subjected to more pressure in ACCF than in ACDF. A comparison study investigated the differences between titanium and polyetheretherketone (PEEK) interbody fusion and discovered that titanium and PEEK cages had similar fusion rates, but titanium had a higher rate of subsidence¹⁸. A finite element study compared the biomechanical characteristics of ACDF, ACCF, and ACHDF in MCSM and found that the ACCF group had the highest stress on the intervertebral disc. In contrast, ACDF without titanium plate fixation had the lowest stress¹⁹. To resolve this concern, researchers have focused on adapting the material and shape of the titanium cage^20,21,22,23, with positive results. Due to the sensitivity of the spinal cord, not all patients are candidates for anterior approaches.

Posterior approaches such as laminoplasty and laminotomy can increase the spinal canal volume primarily through indirect decompression and help avoid spinal cord injury from lesion removal to achieve similar prognoses²⁴. Thus, for patients with posterior longitudinal ligaments, posterior approaches may achieve better outcomes²⁵. Most patients can have good outcomes with the anterior or posterior approach alone, but a few patients can have residual symptoms, which may be due to incomplete intraoperative decompression. Therefore, in patients with complex MCSM, a combined anterior and posterior approach can provide extensive decompression and can compensate for the inadequacy of using either the anterior or posterior approach alone. Combined anterior and posterior approaches should be considered when spinal cord cervical spondylosis is combined with severe or fixed kyphosis or with severe osteoporosis or when the stability is affected by multi-segmental involvement²⁶. For patients with severe cervical ossification of the posterior longitudinal ligament, anterior controllable antedisplacement and fusion surgery provide unique advantages²⁷ compared to laminoplasty. This study demonstrates a hybrid surgical technique that combines ACDF and ACCF to treat MCSM. This hybrid technique possesses the advantages of both the ACDF and ACCF procedures and, thus, can be used effectively to treat MCSM and produce satisfactory results.

The authors have no conflicts of interest to disclose.

None.