Open posterior lumbar fusion is performed for a variety of indications, including preoperative instability, iatrogenic instability as the result of decompression, correction of scoliosis deformity, and certain manifestations of back pain.

As with other spinal procedures, complications can arise during and after surgery. During the Federation of Spine Associations Specialty Day program, North American Spine Society member S. Babak Kalantar, MD, of Georgetown University Hospital, addressed the following complications that might occur in patients undergoing an open posterior procedure:

• hardware malposition
• cerebrospinal fluid (CSF) leakage
• neural injury
• bony injury to the facet
• vascular injury
• wrong-level surgery
• patient positioning issues
• ophthalmic complications

Hardware malposition may involve placement of pedicle screws, hooks, wires, and interbody cages and may cause neurologic, vascular, or visceral injury. “Malposition at the cranial level could injure the adjacent facet, possibly accelerating junctional disease,” Dr. Kalantar said. However, he noted, not all hardware malposition is clinically relevant.

Malpositioning issues most commonly involve pedicle screws. The nerve root is vulnerable to injury with inferomedial pedicle breaches. CSF leakage may result from dural puncture from an implant or the tools used to place that implant.

These problems can be avoided by “meticulous preoperative planning and intraoperative assessment,” Dr. Kalantar said. Intraoperative assessment may utilize fluoroscopy with a free hand technique, intraoperative CT scanning, or computer navigation. Verification of screw position can also be done with electromyography. A threshold reading of 15 mA provides a confidence level for good positioning of 98 percent, while a reading of 10 mA to15 mA yields an 87 percent confidence level.

If identified intraoperatively, malpositioned hardware should be removed and repositioned if possible.

Postoperative CT scans can effectively reveal malpositioning; if malpositioning is detected, it should be correlated to clinical symptoms before revision is considered, Dr. Kalantar said.

CSF leak and other complications
Although CSF leakage occurs more often in open surgery than in minimally invasive procedures, “it is also easier to address in open surgery rather than through a small portal,” Dr. Kalantar said. The risk of leakage is higher in revision surgery, and surgeon skill does correlate with the rate of injury.

Dural tears should be repaired immediately to prevent long-term sequelae. “If the CSF continues to leak during the procedure, significant bleeding from the epidural veins might occur,” Dr. Kalantar said.

“Anterior tears can be difficult, but typically don’t require repair as they tend to tamponade against the posterior vertebral body. If they don’t, opening the posterior dura and retracting the caudal equina provides access for direct repair,” he continued.

If undue tension is present, a patch graft is recommended. Fat, muscle or thoracodorsal fascia, or a synthetic graft, secured with suture, can be used, and the repair may be augmented with fibrin glue or collagen matrix.

After a good repair, “postoperative precautions and bed rest are not required; however if there is any leaking, bed rest for 48 to 72 hours may be considered,” he said.

The neural elements are vulnerable during open surgery. Most frequently, nerve roots are injured by a high-speed burr or Kerrison rongeur. “Use caution with the rongeur in a stenotic patient as it may create more compression,” Dr. Kalantar said.

Injury to the facet or pars may occur in dissection, decompression, or hardware placement. “An obvious injury may require extending the fusion, taking care not to violate the facet capsule,” he advised.

To avoid vascular injury to the aorta, vena cava, and iliac vessels, their location in relation to the L4 and L5 disks and bodies should be noted on preoperative imaging. “The injury can occur with overaggressive use of a pituitary ronquer or curette that violates the anterior annulus,” Dr. Kalantar said.

Wrong-level surgery is rare, but surgeons should be meticulous about using radiographs to confirm the level and conducting a time-out to verify the patient and procedure.

Patient positioning can be an issue in both open and minimally invasive surgery. Positioning is a special concern for minimally invasive procedures due to the longer surgical time and steep learning curve.

“Be cognizant of pressure points and how the arms are positioned,” Dr. Kalantar said. Elbows should be flexed to 90 degrees and knees bent to relieve the sciatic nerve. The abdomen should hang free on a Jackson table to allow normal diaphragm excursions and venous return.

A rare but devastating complication is postoperative vision loss from ischemic optic neuropathy (ION). Prevention involves avoiding pressure on the eyes. Comorbidities that contribute to ION include hypertension, obesity, vascular disease, and diabetes. Surgical factors include intraoperative prone position, use of a Mayfield pin head holder, anesthetic duration greater than 6 hours, and blood loss greater than 1 liter.

Postoperative complications
Complications that may occur after surgery include pseudarthrosis, neurologic decline, CSF leakage, epidural hematoma, acute or delayed/chronic infection, and bone graft problems.

from 1.6 percent to 18 percent and are lower with instrumented fusions. The condition may not be clinically relevant in the setting of a stable fibrous nonunion.

On radiographs, a halo formation around screws is a likely indicator of nonunion (Fig. 1), Dr. Kalantar said. He suggested that a solid fusion can be assumed if no halo is seen during the first 5 years, with no implant failure or fatigue.

Risk factors for nonunion include smoking and nicotine use, use of nonsteroidal anti-inflammatory drugs and steroids, postoperative deep infection, postoperative anemia, inadequate fixation points, poor fusion bed preparation, and quality and quantity of bone graft.

Implant fatigue usually occurs late—1 to 5 years after surgery—and generally is indicative of pseudarthrosis. Implant pullout during the first year is more likely the result of implant stress relating to kyphotic deformity, revision, infection, osteoporosis, and loss of interior column support.

After surgery, surgeons should have a high suspicion for new neurologic dysfunction and should evaluate patients carefully. A CT scan may be used to evaluate hardware, check for misplaced screws, and examine bony anatomy. Postoperative MRI is used to identify fluid collection indicating a hematoma or abscess. Reoperation should be considered if screw malposition or fluid collection is seen and correlated with progressive weakness.

When CSF leakage after surgery occurs, the cause may be a dural tear that was not identified at the time of surgery. It is indicated by clear fluid drainage from the incision and a fluctuating mass that changes with position. Signs and symptoms include postural spinal headache, nausea, vomiting, photophobia, tinnitus, blurred vision, and dizziness. An MRI may be obtained to identify the pseudomeningocele. Treatment may consist of simple bed rest or rest along with placement of a subarachnoid drain. Persistent leakage may require a second surgery to correct.

Epidural hematoma is a rare but potentially devastating complication; however, most are small and clinically insignificant. Large hematomas can cause rapid onset of pain as well as neurologic deficit. Early diagnosis and rapid surgical decompression are critical.

In the event of an acute infection (typically within 1 month of surgery), instrumentation may be retained with the aggressive use of antibiotics and débridement. Dr. Kalantar noted that elevated erythrocyte sedimentation rate (ESR) and white blood cell (WBC) count may occur normally after surgery, so a C-reactive protein test may be more useful in detecting infection.

Delayed infection, occurring 1 to 3 years after surgery, may be accompanied by fever, malaise, drainage, and elevated ESR and WBC. Because it is generally caused by a low-virulence bacteria on the hardware, implants need to be removed, surgical débridement performed, and intravenous antibiotics administered. If pseudarthrosis occurs, subsequent fusion surgery and reinstrumention may be necessary.

Posterior iliac bone graft harvest in open surgery should not be viewed as a completely benign procedure, Dr. Kalantar said. Problems are rare, but they include injury to the superior gluteal artery and the cluneal nerves, fracture of the iliac wing, hematoma, infection, and ureteral injury.

Summarizing, Dr. Kalantar said, “A multitude of complications exist, and surgeons are likely to experience some or all during their practice lifetimes. You have to recognize them early and treat them appropriately and, if necessary, aggressively.”

Dr. Kalantar reported potential conflicts of interest; details of his disclosure as submitted to the Orthopaedic Disclosure Program may be accessed electronically at www.aaos.org/disclosure

Terry Stanton is a senior science writer for AAOS Now. He can be reached at tstanton@aaos.org

Bottom Line

• Complications that may occur during and after open lumbar fusion surgery include hardware malposition, cerebrospinal fluid (CSF) leakage, neural injury, injury to the facet, vascular injury, wrong-level surgery, patient positioning issues, and ophthalmic complications.
• Proper hardware positioning should be confirmed during and after surgery. Options include imaging technology and electromyography.
• CSF leakage is a common intraoperative complication, and dural tears should be repaired immediately.
• Acute infection after surgery may be resolved with débridement and antibiotics, but delayed infection occurring 1 to 3 years after surgery generally requires implant removal.