Anterior cervical discectomy, corpectomy followed by fusion (ACDCF) is primarily for the treatment of cervical spondylotic myelopathy, a disease in which the cervical spinal cord is compressed by overgrown bone and soft tissues, usually as a result of degenerative arthritis. The surgical approach for this disease from the back of the neck is presented in Cervical Laminectomy. Corpectomy may also be used for the treatment of metastatic cancer to the body of a cervical vertebra.

Anatomy

• The normal cervical spine is composed of seven building blocks called vertebrae (labeled C1 through C7) that sit on the thoracic (chest) spine (Figure 1). At the upper end of the cervical spine sits the head

Figure 1 - Seven cervical vertebrae as seen from the front.

• The cervical spine allows bending of the head forward (flex) and backward (extend) and tilt and twist the head to the left and right
• Each vertebra is constructed of a body, lamina, and pedicles, which surround an opening, the spinal canal (Figure 2). On each side of a cervical vertebra lie the facets, the portion of the vertebra that forms the joints between two vertebrae (Figure 3)

Figure 2 - Cervical vertebra and disk seen from below.	Figure 3 - Cervical vertebrae seen from the side.

• Through the spinal canal passes the spinal cord. Nerve roots are present at each level and exit the spine through holes (foramina) formed by two adjacent vertebrae
• The nerve roots eventually form into nerves that go to the arms. The spinal cord and roots float in fluid (cerebrospinal fluid) and are contained within a fibrous sac called the dura
• Separating any two vertebral bodies is a soft elastic material called a disk. The disk is composed of two parts, a soft center called the nucleus and a tough outer band called the annulus. Lining the surface of the disk space of the two vertebrae on top and bottom are thin plates of cartilage. There are seven cervical disks beginning below C2 and extending below C7. There is no disk between C1 and C2
• Strong ligaments run along the anterior (front) and posterior (back) aspect of the vertebrae. These are the anterior and posterior longitudinal ligaments
• The spinal cord is made up of many nerve tracts that run the length of the cord and carry electrical impulses from the brain to the nerve roots at every level and from the nerve roots to the brain. The major tracts that control movement are in the front (anterior) part of the cord. The major tracts that carry sensation to the brain are in the back (posterior) part of the cord

Pathology

• Some individuals have a congenital narrowing of the spinal canal (spinal stenosis) that causes spinal cord compression when young. With advancing age, injury or surgical removal of a disk, several changes occur in the bone, disk, joints and ligaments of the cervical spine that can produce neck and arm pain as a result of a nerve root being compressed or weakness and loss of feeling in the arm and legs because the spinal cord is compressed
• Bones. With aging, bones tend to lose water and become less dense, a condition called spondylolsis. These degenerative changes near the disk may cause an overgrowth of bone producing bony spurs (osteophytes) that can compress the spinal cord. (Figure 4)

Figure 4 - Sagittal (midline) section through the cervical spine showing the degenerative changes of cervical spondylosis. Note the narrowing of the disk space with posterior spurs compressing the spinal cord. © S. Brett

• Disk. The disks also lose water and shrink thus narrowing the disk space. As the disk becomes thinner the space between the vertebrae likewise narrows which narrows the foramina causing nerve root compression and pain. As the disk space narrows, the annulus tends to bulge and mushroom out causing pressure on the spinal cord
• Joints. Along with the other degenerative changes, there can develop a degenerative arthritis of the facet joints that causes the joints to enlarge. Sometimes the lining of the joint (synovium) enlarges or becomes like a cyst. This combination of events results in narrowing of the spinal canal and increasing stiffness of the spine. If the joints degenerate such that one vertebra slips over the one below (called spondylolesthesis) the spine may become unstable resulting in pain and the spinal cord may be compressed
• Ligaments: With advancing age the ligaments tend to stretch and thicken. This may cause instability between vertebrae, as well as result in pressure on the spinal cord and nerve roots. In some patients the posterior longitudinal ligament becomes thickened and calcified (deposited with calcium). This thickened, hardened ligament may act to compress the spinal cord
• Spinal cord. Myelopathy (malfunction of the spinal cord) occurs due to compression of the spinal cord. Motion of the spine rubbing on the cord may also contribute to the myelopathy. Furthermore compression of the spinal cord may lead to a compromise of the blood vessels feeding the spinal cord, which further aggravates the myelopathy. This myelopathy caused by overgrowth of bone and supporting tissues in the neck is called 'cervical spondylotic myelopathy'
• The spine is one of the most common sites for metastases (cancer going from the tumor to another place in the body) to bone. This occurs in about 5% of cancer patients
  1. The cervical spine is involved in about one-fourth of the spine metastases of which about 20% actually develop symptoms
  2. The most common cancers that metastasize to the cervical spine are breast, lung, kidney, prostate and thyroid

History and Examination

Because of the variety of ways the degenerative process in the cervical spine may cause compression of the cord, the neurologic syndrome (the presentation of brain, spinal cord or nerve damage) that a patient with cervical spondylotic myelopathy presents to the physician may vary in degree and position of pain, numbness, paresthesias (tingly sensations), weakness, loss coordination in the arms and weakness or unsteadiness in walking

• When all the nerve tracts are involved, the patient presents with weakness in the arms and legs and inability to normally feel pain and touch
• The patient may present only with weakness. Sometimes this may occur only in the legs or only in the arms
• There may be pain in the arms similar to that presented by a person with a ruptured cervical disk (Cervical Discectomy for ruptured disc) combined with weakness in the legs
• The patient may present with weakness on one side of the body and numbness on the other side (Brown-Sequard syndrome)
• Weakness in the hands and forearms

Testing

Various tests may be necessary to help your doctor decide whether you need surgery, and to determine the exact location of the cervical spinal stenosis or cancer. Some of these tests are:

• X-ray of the cervical spine. The x-ray may show narrowing of the disk space, bony overgrowth of bone, evidence of instability of the spine or destruction of the bone caused by cancer
• An electromyogram (EMG), which measures nerve function. This is accomplished by placing small needles in the muscles and recording the result on a special machine
• A CT (computerized tomography) scan or MRI (magnetic resonance imaging). These scans produce detailed computer generated images of the bony spine (CT) and spinal cord and surrounding tissues (MRI). These tests may also rule out other causes of pain and weakness. (Figure 5A)

Figure 5a - MRI of the cervical spine showing compression of the spinal cord.

• A myelogram followed by a CT scan. A myelogram is an invasive test. Though invasive, a myelogram is probably the most accurate test for determining the degree of spinal stenosis (narrowing). An iodine containing dye, which shows-up on x-rays, is injected into the cerebrospinal fluid in the lumbar spine. The dye is then positioned in the cervical spine and X-rays followed by a CT scan are taken. (Figure 5B) Leakage of cerebrospinal fluid following the procedure may cause subsequent headaches which usually does not last more that a couple of days

Figure 5b - CT myelogram showing spurs compressing the spinal cord.

• Bone scan is a test in which a radioisotope (radioactive material) is injected into a vein. The isotope collects in the bone metastases and is detected by a scanner that produces a picture of the skeleton with the areas of cancer. This is a very sensitive test for metastases to bone and may be the first imaging test to show the tumor

Non-operative Treatment

• Non-operative treatment for cervical spondylosis is recommended for those individuals who have
  1. Only mild or moderate complaints and are not disabled
  2. Advanced cervical spondylotic myelopathy with nerve deficits that cannot be changed with surgery
  3. Advanced age or medical conditions that pose a considerable risk for surgery
  4. Non-operative treatment includes
  • The use of a firm collar
  • Cervical traction - this usually can be done at home 2-3 times a day
  • Anti-inflammatory medication such as motrin
  • Physical therapy
  • Epidural steroid injection (injection into the cervical spine between the covering of the spinal cord and the bone) to control symptoms in those individuals who are poor surgical risks in order to control complaints
• Non-operative treatment for metastatic tumor to the cervical spine is recommended for
  1. Patients with a life expectancy less than 3 months
  2. Patients with neck pain but with no evidence of instability of the spine or neurologic abnormality
  3. Non-operative treatment includes
  • Radiation therapy is an effective treatment for metastatic cancer to the cervical spine, particularly for breast, prostate, melanoma (cancer of the skin) and lymphoma (cancer of the lymph nodes)
  • Chemotherapy may be used and the drugs used are determined by the sensitivity of the original cancer
  • Corticosteroids (cortisone) is beneficial for those patients who may have spinal cord compression. It is particularly effective for lymphoma since corticosteroids also kills the tumor. When used with surgery, there are higher rates of infection, wound breakdown and fusion failure

Indications and Contraindications for Surgery

• The most common reason is cervical spondylotic myelopathy particularly when there is
  1. Acute or progressive muscle weakness
  2. Disabling loss of sensation
  3. Difficulty in walking
• ACDCF is preferred to cervical laminectomy when there is kyphosis (curved forward) of the cervical spine instead of the normal cervical lordosis (curved backward)
• ACDCF is also used for trauma to the cervical spine in which the body of the vertebra compresses the spinal cord
• ACDCF is usually not used
  1. When there is disease at three or more spinal levels
  2. When carrying out the surgery from in front is difficult because of
  • Failure of prior surgery
  • Obesity, particularly with a short, stout neck
  3. In older patients who tolerate cervical laminectomy better than surgery from in front
  4. When better exposure of the nerve roots is necessary
  5. When there is need to fuse the spine from behind
  6. In the presence of a tracheostomy (opening into the windpipe) or other obstruction to an approach from in front

Relative contraindications

• Elderly patient particularly combined with osteoporosis
• Severe lung disease
• Severe heart disease

Operative Procedure

• The patient is positioned on the operating table with the head and neck in a neutral position since undue flexion or extension of the neck may cause pressure on the spinal cord · Because placing a tube in the airway (endotracheal tube) may result in excessive extension of the neck, the tube is frequently inserted with the patient awake
• Steroid medication may be given to help in protecting the spinal cord
• In some instances the surgeon may monitor the ability of the spinal cord to transmit impulses (somatosensory evoked potentials)
• The patient is placed supine (face up) on the operating table with the head rotated to the side opposite the incision. The incision may be placed on either side
• After the skin is cleaned and disinfected and sterilely draped, an incision is made in the skin opposite the vertebrae to be operated upon. Depending on the number of vertebrae to be fused, the incision may be made horizontally (from the midline out to one side) or vertically (a more up and down incision) (Figure 6)

Figure 6 - Incisions for ACDCF. © S. Brett

• The tissues between the skin and the front of the vertebrae are dissected apart and the front of the involved vertebrae is reached (Figure 7)

Figure 7 - The anterior aspect of the bodies of the involved vertebrae is exposed. © S. Brett

• The anterior longitudinal ligament and annulus are cut and the soft nucleus is removed from the disc above and blow the involved vertebra(e). This is carried out under the operating microscope or with special magnifying lenses called loupes (Figure 8)

Figure 8 - The discs are removed between each of the involved vertebrae. © S. Brett

• A vertical channel approximately 16-20 mm (3/4 inch) is cut through the body of the vertebra(e) using an air powered bur and small rongeurs (fine cutting instruments). The cut is taken all the way back to the posterior longitudinal ligament. The ligament is removed to expose the dura over the spinal cord (Figure 9A,B)

Figure 9a - Central channel is cut through the body of the involved vertebrae through to the dura. © S. Brett	Figure 9b - © S. Brett

• Care is taken to remove the spurs that project back towards the spinal dura
• The plates of cartilage that line the interspaces are removed otherwise the fusion will not occur and the surface of the bone reshaped (Figure 10)

Figure 10 - The cartilage is removed and the surfaces of the adjacent vertebrae are shaped with curette and bur to receive the bone graft. © S. Brett

• A piece of bone (bone graft) is taken from the patient's iliac crest (hip bone). Cadaver bone is usually not used for the fusion. The bone graft is shaped and placed in the channel with each end against the vertebral body above and below. (Figure 11) The fusion between the vertebrae takes a minimum of 4-6 months to complete

Figure 11 - The bone graft is inserted and a titanium plate placed across the fusion site © S. Brett.

• A titanium plate is frequently placed between the vertebra above and below to aid the fusion and stabilize the vertebrae. The plate is attached to the two vertebrae using titanium screws. Another screw through the center of the plate is frequently placed into the bone graft (Figure 12, 13)

Figure 12 - CT scan sagittal reconstruction obtained after surgery showing the bone graft and titanium plate.	Figure 13 - CT scan showing the bone graft, titanium plate and the area of bone removed to decompress the spinal cord.

• All bleeding is controlled during the procedure. After the graft is placed the wound is sutured
• For metastatic tumor
  1. It is necessary to remove the bone involved with the tumor
  2. With patients who have a longer life expectancy, bone taken from the patient is preferable though cadaver bone graft may be used in those patients with good bone quality
  3. Methylmethacrylate (a plastic) may be used particularly is those individuals who have a life expectancy less than one year. It has the advantage of giving the spine immediate stability but has the disadvantage of loosening over time

Complications

• No surgery is absolutely safe and free of complications. Some of the possible complications of cervical disk surgery are:
• Negative effects of anesthesia
• Bleeding or hemorrhage with the possible need for blood transfusions
• Worsening of the neurologic condition such as increased paralysis or loss of sensation including injury to nerve roots
• Infection
• Tear in the covering of the nerves with leaking of cerebrospinal fluid
• Injury to blood vessels
• Vocal cord paralysis
• Injury to the various structures in the neck such as the carotid artery, jugular vein, trachea and esophagus, etc
• Failure of the bone graft to stay in place
• Postoperative instability of the spine
• Failure of the fusion to take place
• Deep venous thrombosis (clots in the legs) with embolus to the lung
• The possibility of unforeseen complications

Postoperative Care

• Most patients are discharged from hospital on the first to third post-operative day. Elderly patients and patients with cancer may require additional hospital stay
• Following surgery, the patient may wear a collar for several months
• If there is weakness or paralysis the patient may go to a rehabilitation unit
• Pain medication is given as necessary
• After discharge, the patient is seen in the surgeon's office in one to three weeks
• Follow up X-rays, CTs or MRIs may be obtained as required by the surgeon