Vol 9, No 2, March/April 2001 137 Neurologic complications after lum- bar spine surgery may be broadly classified by the mechanism of injury and by the time period dur- ing which they occur. The causes of injury are generally either indirect or direct, with the latter including laceration, compression, traction, and avulsion injuries to the neural elements. Such direct causes are most commonly the result of a tech- nical mishap by the surgeon. In- direct injuries are due to the disrup- tion of the blood supply to the spinal cord and nerve roots or to the gradual compression of the neural elements, as by correction of defor- mity or by a postoperative hema- toma. This type of injury is usually the result of ischemia or the disrup- tion of axoplasmic flow, which pro- vides neural nutrition. Its causes are more difficult to define and are often inexplicable. Neurologic injuries categorized by the time period during which the insult occurs may be intraoper- ative, early postoperative (1 to 14 days), or delayed postoperative (after 14 days) events. Intraopera- tive events are generally related to complications arising from anes- thesia, patient positioning, surgical technique, or procedure-specific risks. Early in the postoperative period and up to 2 weeks after sur- gery, neurologic injuries are most commonly secondary to direct compression of the neural ele- ments. This is often caused by the mass effect of postoperative hema- toma, pseudomeningoceles, and epidural abscesses. After partial diskectomy, retained fragments or recurrent herniations may also cause neurologic symptoms in this time period. After 14 days from surgery, recurrent disk herniation should be considered more likely, although this may occur earlier as well. To both minimize and prevent potential neurologic complications that may occur in association with lumbar spine surgery, the surgeon must thoroughly understand the relevant anatomy and must do meticulous preoperative planning. Additionally, a thorough under- standing of the etiology of the com- plications can decrease their inci- dence. When complications do occur, rapid recognition and appro- priate treatment can minimize their effect. Anatomy Knowledge of the relevant anatomy is essential to minimizing direct neural injuries. The spinal cord ter- minates as the conus medullaris at the level of the inferior border of L1 and the superior border of L2. Spinal cord tissue is much less tol- erant of traction and compression than the nerve roots are. Even minimal manipulation of the cord may cause profound neurologic consequences. Focal injury to the conus medullaris can cause injury to the function of the lower sacral roots and result in disturbances in bowel, bladder, or sexual function with or without other obvious neu- rologic deficits in the lower extrem- ities. Dr. Antonacci is Assistant Professor of Orthopaedic Surgery and Director, Spine Diagnostic and Treatment Center, MCP Hahnemann University School of Medicine, Philadelphia, Pa. Dr. Eismont is Professor of Orthopaedic Surgery, University of Miami School of Medicine, Miami, Fla. Reprint requests: Dr. Antonacci, Spine Diagnostic and Treatment Center, Graduate Hospital, 1800 Lombard Street, Philadelphia, PA 19103. Copyright 2001 by the American Academy of Orthopaedic Surgeons. Abstract With the increasing complexity and number of lumbar spine operations being performed, the potential number of patients who will sustain perioperative com- plications, including those that involve neural structures, has also increased. Neurologic complications after lumbar spine surgery can be categorized by the perioperative time period during which they occur and by their mechanism of injury. Although the overall incidence of neurologic complications after lumbar surgery is low, the severity of these injuries mandates careful preoperative plan- ning, awareness of risk, and meticulous attention to perioperative details. J Am Acad Orthop Surg 2001;9:137-145 Neurologic Complications After Lumbar Spine Surgery M. Darryl Antonacci, MD, and Frank J. Eismont, MD The spinal nerve roots, while more tolerant of mechanical defor- mation than the spinal cord, are less tolerant than the peripheral nerves. The intradural nerve rootlets are covered by only a thin membra- nous root sheath, which is perme- able to cerebral spinal fluid for nu- trition. 1 In contrast, peripheral nerves are protected by an epineu- rium and a perineurium. This, in addition to a more developed con- nective tissue layer, makes periph- eral nerves much less susceptible to injury than the intrathecal nerve rootlets. The results of experimental stud- ies in dogs suggest that when the thecal sac is compressed acutely to 45% of its normal area (i.e., to ap- proximately 75 of the normal 170 mm 2 ), significant nerve-root com- pression occurs, with measurable changes in both motor and sensory function. 2 The motor nerve roots recover more quickly than the sen- sory roots after the pressure is re- leased; thus, transient compression is more likely to affect the sensory roots. The critical value of 75 mm 2 can be used for the radiologic diag- nosis of central spinal stenosis. Re- ducing the cross-sectional area of the thecal sac to approximately 65 mm 2 generates a pressure level of about 50 mm Hg in the cauda equina. Measurable changes in spinal nerve- root conduction generally occur between 50 and 75 mm Hg. 3 The effects of compression are related not only to the duration of compres- sion and the pressure itself but also to the rate of onset. 4 In the acute injury setting, rapid application of compression to the nerve roots causes more pronounced tissue changes than slow application. The application of pressure over multi- ple spinal levels and the combina- tion of compression with systemic hypotension can lower these thresh- old injury levels. The pedicle is a constant anatomic landmark that can be used to locate the exiting nerve root and thus min- imize the likelihood of inadvertent injury to it. If the anatomy is aber- rant, the one constant is the relation- ship of the pedicle to the nerve root, which lies along the inferomedial edge of the pedicle. In cases with poor visualization of the nerve root, resection of bone until the pedicle is visible will aid in the identification of the exiting nerve root. During anterior lumbar surgery, the hypogastric nerve plexus and sympathetic chain are at risk of injury. The aorta, the vena cava, and collateral vessels are preverte- bral and in close proximity to the hypogastric nerve plexus. This nerve plexus is approximately 6 to 8 cm in length along the surface of the aorta and extends from the cephalad aspect of L4 (as the supe- rior hypogastric plexus) to the first sacral vertebra. As the plexus en- ters the pelvis, it divides into right and left divisions, which course dis- tally and join the inferior hypogas- tric plexus. These fibers innervate the seminal vesicles and vas deferens in the male; injury to these struc- tures can lead to retrograde ejacu- lation. Injury to the hypogastric plexus in approaches to the L5-S1 disk space is minimized by blunt dissection directly on the anterior surface of the disk. Sweeping the prevertebral tissues and hypogas- tric nerve plexus laterally, rather than dissecting through these struc- tures, decreases the risk of injury to the nerve fibers. The use of bipolar cautery and limited exposure also helps to minimize the risk of injury. The exposure of upper lumbar seg- ments is not associated with as high a risk for retrograde ejacula- tion as the exposure of L5-S1, be- cause the sympathetic fibers in- volved lie on the anterior aortic wall. Injury to the sympathetic chain, which lies along the anterior border of the psoas muscle, can manifest as patient complaints of contralateral foot coldness. In fact, vasodilatation secondary to this in- jury causes increased warmth in the ipsilateral foot. Preoperative Planning Failure to recognize variations in normal anatomy on preoperative studies may predispose to injury (e.g., asymptomatic spina bifida). Such a finding may necessitate a particularly careful dissection or alteration in surgical approach. Similar caution is necessary after prior laminectomies or with wid- ened interlaminar spaces. It is good practice to review all preop- erative radiographs just prior to surgery, with special attention to the variant anatomy in each indi- vidual case. In other situations, such as in patients with high-grade lumbar or cervical stenosis, preoperative con- sideration of patient positioning may help avoid unexpected injury. For example, patients with cervical stenosis should be carefully trans- ferred to the prone position with their heads in a neutral or slightly flexed position, or awake position- ing should be used. In severe cases, consideration should also be given to fiberoptic intubation. In patients with high-grade lumbar spinal stenosis, use of large Kerrison ron- geurs should be avoided in favor of the motorized diamond burr. Un- der these conditions, placement of cottonoid pledgets within a tightly narrowed epidural space should be avoided. Prior to surgery, patients should be instructed to discontinue the use of anti-inflammatory medications (for 2 to 3 days) and aspirin (for 2 to 10 days) to minimize intraoperative and postoperative blood loss. Pa- tients should also be questioned about complementary or alternative medications, such as gingko and cayenne, which can have effects on clotting. Neurologic Complications After Lumbar Spine Surgery Journal of the American Academy of Orthopaedic Surgeons 138 Complications Related to Induction of Anesthesia and Patient Positioning The risk of intraoperative neuro- logic injuries begins with the in- duction of anesthesia and position- ing of the patient for surgery. The incidence of significant neurologic injury, including complete paraly- sis, secondary to spinal or epidural anesthesia has been reported to be approximately 0.02%. 5 Injuries re- lated to these types of anesthesia are usually secondary to direct mecha- nisms. These include laceration by inadvertent needle placement and compression of the neural elements secondary to postinjection hema- toma. Paralysis can occur in patients with low-lying spinal cords who undergo routine epidural or intra- thecal injections of anesthetic agents. Peripheral nerve injury secondary to the placement of intravenous and arterial lines, although uncom- mon, can also occur. Peripheral nerve injuries after lumbar spine surgery more typically occur secondary to malpositioning or improper padding of the patient. In posterior lumbar surgery, the patient is usually placed in a prone position on rolls or on a four-poster padded frame (e.g., Relton frame) or Andrews-type table. After posi- tioning, it is important to ensure that the abdomen hangs free, so as to minimize intraoperative blood loss. Regardless of the type of frame used, well-padded support is neces- sary, with care taken to avoid exces- sive pressure on the chest wall and pelvis. Extra foam padding of the posts aids in distributing pressure uniformly to the patient’s skin and helps to avoid skin blisters and burns. Every patient should be positioned and padded as would be appropriate for a much longer duration of surgery than projected. Direct compressive or traction inju- ries of upper- and lower-extremity nerves can occur. In particular, ex- cessive pressure or stretch at the brachial plexus or femoral nerve can lead to upper- and lower-extremity nerve palsies, respectively. In the upper extremity, the ulnar and an- terior interosseous nerves are par- ticularly susceptible to external pressure, as are the peroneal and lateral femoral cutaneous nerves of the lower limbs. In patients with coexistent cervi- cal and lumbar stenosis, careful positioning of the head in neutral or slight flexion is mandatory to avoid cervical myelopathy or spinal cord injury, either while transferring the patient prone or during final posi- tioning. A Mayfield three-point head holder provides very reliable positioning for long-duration sur- gical procedures and for high-risk patients. This avoids pressure on the face and in particular on the eyes. Ophthalmic injuries have been reported secondary to excessive pressure on the eyes, resulting in permanent blindness in rare in- stances. 6 Direct and Indirect Surgical Injuries Direct and indirect injuries related to surgical technique make up the ma- jority of intraoperative neurologic complications. Three factors appear to predispose to iatrogenic injuries: the relative inexperience of the sur- geon, failure to follow meticulous surgical technique, and a history of prior surgical procedures on the patient. In patients with undis- turbed anatomy, the frequency of injury should be very rare. If inju- ries are occurring relatively more frequently, it is mandatory that the surgeon reevaluate the surgical techniques employed (Table 1). Most neurologic injuries from direct trauma are related to either trauma by surgical instruments or placement of pedicle screws or hooks. Several principles should be observed to minimize risks. Appro- priately sized rongeurs down to 1 mm with a small foot-plate should be available. When removing bone or soft tissue, one must always check to see that the dura has been dissected free (especially in patients with rheumatoid arthritis) and that adequate space is available for the Kerrison foot-plate. If scarring or adhesions are present, careful dis- section with angled curettes or dural elevators is required. If the area is too narrow, bone must be removed from above with either motorized burrs or osteotomes before rongeurs can be safely used. Protection of the dura with cot- tonoid pledgets should be avoided in these conditions. Use of magnifi- cation, such as with loupes or an op- erating microscope, can be helpful in difficult situations. In general, Kerrison rongeurs should be directed parallel to the exiting nerve root to avoid transection. Motorized burrs are passed from medial to lateral to avoid dural damage. Diamond- tipped burrs with copious saline irri- gation can be used safely close to the dura with a lower risk of laceration. During diskectomy, the exiting nerve root must be mobilized me- dially to expose the herniation. In large herniations, it may not be pos- sible to completely mobilize the root without excessive traction. If that is the case, the disk should be removed before complete mobilization. Be- fore incising the disk anulus, one should always make sure that the exiting root has been mobilized and protected. Meticulous hemostasis is important to avoid mistaking a nerve root for a disk fragment. The smallest pituitary rongeurs should be used to remove the disk, and they should be opened only after they have been inserted in the disk space. Occasionally, the suction tip can become nicked by another instru- ment, such as the burr. The sharp edge created can cause a dural or nerve root laceration. For this rea- M. Darryl Antonacci, MD, and Frank J. Eismont, MD Vol 9, No 2, March/April 2001 139 son, the suction tip should be checked and discarded if damaged. Other laceration injuries may occur with the use of osteotomes during medial facetectomies and during aggressive bone removal with the rongeur. Tearing or rip- ping of the ligamentum flavum should be avoided. Particular care is needed when removing the bone fragments of the medial facet, because the capsule of the facet is often adherent to the ligamentum flavum or the dura itself. Any movement of the dura while bone is being removed, either during facetectomy or when a Kerrison rongeur is being used, should alert the surgeon that such an attach- ment may be present. Use of a Penfield or Woodson probe can help loosen any attachments to the dura. Performing bone removal while leaving the ligamentum flavum intact may also serve as an added measure of protection to the thecal sac. Compression or contusion of the nerve roots or cauda equina is another potential type of neurologic injury related to surgical technique. Excessive thecal sac retraction, especially prior to adequate decom- pression of the spinal canal in pa- tients with lumbar stenosis, can cause ischemic injuries. As noted previously, compression of the the- cal sac to less than 45% of its cross- sectional area can cause changes in motor and sensory root conduction. Poorly visualized nerve roots are often subject to such unrecognized compression. Bertrand described the “battered-root” syndrome, in which new-onset numbness after laminectomy or laminotomy strongly suggests intraoperative root injury. 5 Excessive compression with cot- tonoid pledgets, gel foam, or mal- positioned fat grafts has also been reported as a source of intraopera- tive neurologic compromise. 7 The incidence of nerve-root avul- sion injuries has been reported to be approximately 0.4%. 5 Forceful retraction of a nerve root, especially within a stenotic foramen, can be an inadvertent cause of a nerve-root avulsion. This can also occur during aggressive bone removal. The inci- dence of conjoined nerve roots in the lumbar spine has been reported to be between 2% and 14%, 5 and probably is more common than is generally acknowledged. Failure to recognize a conjoined nerve root can result in excessive compression, laceration, or avulsion. Adequately visualizing the nerve-root sleeve and working laterally relative to the nerve root will help to minimize the incidence of this complication. In many instances, when the nerve root cannot be identified or mobi- lized, it is better to remove more bone until the pedicle is exposed than to place undue traction on the neural elements. The frequency of dural tears as a complication of lumbar surgery can be reduced through meticulous technique. Although identification of a dural tear is typically made after the sudden leak of spinal fluid, identification of dural tears that have not yet disrupted the arachnoid layer is also important. Most tears can be repaired primarily with 5-0 or 6-0 suture with a run- ning stitch. Care must be taken to avoid incorporating any neural ele- ments into the closure. After clo- sure, a Valsalva maneuver aids in the identification of a persistent or residual leak. In these cases, rein- forcement of the repair is possible Neurologic Complications After Lumbar Spine Surgery Journal of the American Academy of Orthopaedic Surgeons 140 Table 1 Basic Spine Surgery Technique 1. Ensure adequate exposure and lighting 2. Do not pass instruments over the open wound 3. Avoid overaggressive bone removal 4. Use the Kerrison rongeur with foot-plate oriented parallel to thecal sac 5. Use Kerrison rongeur without upward or downward pressure 6. Leave ligamentum flavum intact to protect thecal sac 7. Do not pull or tear ligamentum flavum 8. Release all tissue attachments to dura 9. Use disposable and undamaged suction tips around thecal sac 10. Be aware of conjoined nerve roots 11. Use knife to incise anulus only vertically 12. Open mouth of pituitary rongeur within disk space 13. Avoid use of electrocautery near the dura 14. Use cottonoid pledgets cautiously 15. Use burr in medial-to-lateral direction under direct visualization 16. Never manipulate thecal sac above L2 17. Never retract thecal sac more than 50% 18. Consider neurologic monitoring 19. Do not leave spikes of bone after decompression 20. Control bleeding with bone wax, hemostatic agents, and cautery prior to closure 21. Use drains when appropriate 22. Have anesthesiologist do Valsalva maneuver before closure with muscle or fat grafts sutured over the repair to the dura. The use of fibrin glue, which is derived from equal volumes of thrombin and cryoprecipitate, may add to the reinforcement of tenuous repairs. Larger defects in the dura may re- quire patch grafting with a seg- ment of fascia from the paraverte- bral muscles. Once the repair has been made, a watertight closure without wound drains is required for the overlying fascia, subcuta- neous tissue, and skin. Postopera- tively, patients are typically kept supine for several days to reduce the hydrostatic pressure on the dural repair. Persistent or residual dural leaks at the time of initial repair may be treated by the percutaneous place- ment of a subarachnoid drain im- mediately after the procedure. The placement of a subarachnoid drain above the dural tear allows diver- sion of spinal fluid and a decrease in hydrostatic pressure at the repair site. Patients should be kept supine after surgery for as long as 5 days, and prophylactic antibiotic coverage should be maintained. Continuous drainage at a rate of 10 to 15 mL/hr is recommended. In addition, close monitoring of spinal fluid levels of protein, glucose, and cell count is important until the drain is discon- tinued. Daily Gram stains and cul- tures of the collected spinal fluid should also be obtained. Complications Due to Changes in Spinal Alignment Neurologic complications some- times occur without an obvious intraoperative cause. These indirect injuries are usually the result of dis- ruption of the vascular perfusion of the spinal cord or nerve roots. More commonly associated with scoliosis surgery, cord ischemia can occur secondary to application of exces- sive distraction forces to a relatively rigid spinal deformity. It can also occur secondary to excessive hypo- tension. Any change in neurologic monitoring signals during these maneuvers should alert the surgeon to possible neurologic injury. The degree of correction of the spinal deformity should be lessened or completely released, and a return to baseline of the evoked potentials should occur before further reduc- tion is attempted. In some instances, the removal of the posterior instru- mentation is indicated. Ischemic events involving the spinal cord and neural elements are estimated to occur in approximately 1 of every 3,000 surgical procedures for sco- liosis. 5 Another procedure with high risk for neural deficit is reduction of spondylolisthesis. Decompression of the neural foramina (especially at L5) before instrumentation and avoidance of nerve-root compres- sion from manual downward pres- sure during the process of drilling, tapping, and insertion of pedicle screws or the placement of rods reduces the risk of neurologic in- jury. However, root injury is prob- ably secondary to effective length- ening of the root associated with deformity reduction or to release of reduction or resection of the sacral dome (sacral shortening). Injuries Due to Instrumentation The risk of neural injury secondary to aberrant pedicle-screw place- ment has been reported. 5 A num- ber of principles should be adhered to in order to minimize that risk. The proper starting point should be identified by using osseous land- marks or, in cases of severe de- formity, by directly palpating the pedicle through a laminotomy. Once the pedicle has been probed, it should be checked for inadvertent perforations. After tapping, the hole should be checked again for perforations. Radiography or fluo- roscopy should be used to evaluate the placement of screws and the overall alignment after insertion of hardware. Intraoperative pedicle- screw stimulation with electromyog- raphy is commonly used to ensure proper pedicle-screw placement. 8 Stimulation of the pedicle screw that results in nerve-root conductivity below a certain threshold stimula- tion can be indicative of screw breakout or pedicle fracture. Re- orientation or redrilling of the screw hole is warranted. Fractures of the pedicle secondary to screw mis- placement can also cause direct nerve-root impingement by the frag- ment of bone. Patients noted to have postoper- ative neurologic deficits or leg pain after the placement of instrumenta- tion should be evaluated with com- puted tomography (CT). This is preferable to magnetic resonance (MR) imaging because it accurately demonstrates screw placement. Questionable screw placement in the clinical setting of new-onset leg pain or neurologic deficit is best managed by reoperation to remove or replace the device and to ensure adequate neural foraminal decom- pression (Fig. 1). Posterior interbody grafts, or cages, used during posterior-lumbar interbody fusions potentially can dislodge and impinge on the nerve roots or cauda equina, causing seri- ous neurologic sequelae. The inci- dence of this complication is in the range of 0.3% to 2.4%. 9 Another problem with such procedures is the wide exposure required for graft insertion, with resultant traction injury or development of instability. Anterior interbody devices carry similar risks with regard to incor- rect placement and dislodgment. With the placement of anterior in- terbody fusion devices, injury to the hypogastric plexus secondary to the M. Darryl Antonacci, MD, and Frank J. Eismont, MD Vol 9, No 2, March/April 2001 141 traumatic exposure can result in retrograde ejaculation in men. The incidence of injury to the plexus has been reported to be in the range of 1% to 5% with the use of these de- vices, especially when utilizing a laparoscopic approach. 10 The risk of such an injury after open anterior lumbar fusion surgery has been reported to be 0.42%. 11 Additionally, malplacement of anterior interbody devices themselves or expulsion of disk material posteriorly into the spinal canal can cause neurologic compromise, with an incidence of 2% to 4%. 10 Bone Graft–Related Neurologic Injury The site from which bone graft is harvested is often the origin of post- operative pain. Kurz et al 12 noted a 15% incidence of pain in the first 3 postoperative months. Frymoyer et al 13 noted this problem in up to 37% of patients as long as 14 years after surgery. In many instances, the postoperative pain was part of a general pain syndrome. Persistent pain was more common in patients in whom the grafts had been taken from the same side as their preoper- ative sciatica. Donor-site pain can also be spe- cifically related to peripheral nerve injury. This may be secondary to involvement of the lateral femoral cutaneous nerve (meralgia pares- thetica) during harvesting of ante- rior iliac crest bone. Nerve symp- toms may result from entrapment secondary to scar formation, hema- toma, or laceration. The variant anatomy of this nerve as it crosses the anterior ilium mandates careful dissection. The incidence of this complication is reportedly between 1% and 14%. 14 Beginning the inci- sion at a point 3 cm posterior to the anterior superior iliac spine lessens the chance of this complication. When taking a bone graft from the posterior iliac crest, one should be aware of the location of the su- perior cluneal nerves and the sciatic nerve. 12 The risks associated with bone-graft harvesting from this area can be significant. The incision should be parallel to the midline, as the incidence of superior cluneal nerve injuries increases with exten- sion of the incision more than 8 cm lateral to the posterior superior iliac spine. The superior cluneal nerves are cutaneous branches of the proxi- mal three lumbar nerves and sup- ply sensation to a large portion of the buttock after piercing the lum- bodorsal fascia. Although there is a large degree of cross-innervation, numbness or painful neuromas may develop after laceration. Pal- pation of the sciatic notch may aid the surgeon in establishing land- marks for taking the graft and avoiding injury to the sciatic nerve or superior gluteal artery. The direction of use of the osteotome or gouge should always be cephalad and tangential to the notch. Complications in the Early Postoperative Period A careful neurologic assessment when the patient awakens from surgery provides an index exami- nation to distinguish a deficit that may have occurred intraoperatively from one that occurs in the early postoperative period. Anatomic correlation of the neurologic deficit noted on examination with intraop- erative events often facilitates early diagnosis. This is often more valu- able than attempts at postoperative imaging with CT, MR imaging, or plain radiography. Evaluation of perineal sensation and sphincter tone is also essential, particularly after high lumbar surgery when the possibility of spinal cord injury exists. The development of neuro- logic symptoms in a patient who awakened from lumbar surgery neurologically intact should alert the surgeon to the possibility of the development of new neural ele- ment compression. The importance of an early accurate baseline exami- nation cannot be overemphasized, as diagnostic imaging of the neural elements with MR imaging or CT Neurologic Complications After Lumbar Spine Surgery Journal of the American Academy of Orthopaedic Surgeons 142 A B Figure 1 Lateral (A) and anteroposterior (AP) (B) radiographs of a 46-year-old man who underwent anterior diskectomy with bone grafting and posterior fusion with pedicle screws 4 years previously. The patient awakened from surgery with severe left leg pain extending to the dorsum of his foot and was subsequently seen by several physicians. Radiographs demonstrate misplacement of three of the four pedicle screws. can be difficult to interpret in the early postoperative period. Neurologic deficits that develop in the early postoperative period (1 to 14 days) usually occur secondary to retained disk fragments after diskectomy, postoperative hema- toma, pseudomeningocele, hernia- tion of a fat graft, or (rarely) an epidural abscess. Acute spondy- lolisthesis secondary to iatrogenic instability may also present with a new neurologic deficit. This is more likely to occur in the late postopera- tive period; when it does occur in the early postoperative period, it is more likely to occur after aggressive lateral decompressions with viola- tion of the pars or facet joints. Plain radiography and CT may be helpful in the evaluation of this problem. Recurrent Disk Herniation After diskectomy for disk hernia- tion, the incidence of neural com- pression by a retained or missed fragment of disk is approximately 0.2%. 15 The patient typically awak- ens from surgery and reports unre- lieved symptoms of radiculopathy. Because early postoperative imag- ing is difficult to interpret, reexplo- ration based on the clinical exami- nation findings and symptoms may be indicated to ensure the removal of any remaining disk fragment. Of course, more than one fragment may be causing residual compres- sion. At the time of the index proce- dure, suspicion that a fragment of disk may have been missed should be raised by the presence of friable disk material or multiple fragments. Epidural Hematoma The development of a postoperative epidural hematoma may be associ- ated with excessive or poorly con- trolled intraoperative bleeding. Pa- tients often have few complaints initially, but significant increasing back pain subsequently develops. This may progress to unremitting leg pain or even cauda equina syn- drome in severe cases. Patients with increasing back or leg pain require careful monitoring. A complete neurologic assessment is mandatory, including a rectal examination and a check for perianal pin-prick sensa- tion. If neurologic deterioration oc- curs, a spinal imaging study, such as CT-myelography or MR imaging, should be performed. In obvious cases, the patient can be immediately taken to the operating room for evacuation without imaging. The presence of an epidural hematoma is a surgical emergency, requiring decompression. Epidural Abscess In the 2- to 4-week period after sur- gery, epidural abscess (Fig. 2) be- comes a potential cause of new- onset neurologic deficits, although this is a rare complication. Epidural abscesses, like hematomas, require urgent decompression. Pseudomeningocele Dural tears that occur during sur- gery and that are not recognized and repaired or are inadequately repaired can result in the formation of a pseudomeningocele 5 (Fig. 3). With the increased number of oper- ations for stenosis being performed, this complication may be more fre- quent than previously suspected. The incidence of pseudomeningo- cele formation is estimated to be between 0.07% and 2%. 8 The prev- alence of incidental durotomy is higher, at approximately 4%. 8 In- cidental durotomy is the second most common cause of lawsuits after lumbar spine surgery and the most common complication of re- peat laminectomy. 8 The formation of pseudomenin- goceles is more common after lum- bar spine surgery than after cervi- cal spine surgery. Although small dural tears can close spontaneously, many continue to leak and form pseudomeningoceles. The use of agents such as Adcon-L may pre- cipitate continued leakage of unrec- ognized dural lacerations. 16 These can be noted as a slowly expanding fluid mass or soft-tissue bulging on physical examination. Patients usu- ally present with a progressively worsening headache. Both the mass and the headache may in- crease in magnitude on standing. Diagnosis is readily made early by using myelography followed by CT. Magnetic resonance imaging may also be helpful in the diagno- sis, but it may be difficult to differ- M. Darryl Antonacci, MD, and Frank J. Eismont, MD Vol 9, No 2, March/April 2001 143 Figure 2 T2-weighted MR image of a 50- year-old man who underwent posterior laminectomy. Approximately 3 to 4 weeks after surgery, severe, unremitting back pain developed. The image demonstrates enhanced signal in the disk space with enhancement anterior to the thecal sac extending cephalad, consistent with an epidural abscess. Treatment included irri- gation and debridement and intravenous antibiotic therapy. entiate a pseudomeningocele from a postoperative hematoma with this modality. The onset of neuro- logic symptoms may present either insidiously or acutely with pain, headache, and sudden neurologic deficit. A neurologic deficit may occur when one or more nerve roots herniate out of the dural tear and become trapped within the pseudomeningocele. Treatment of pseudomeningoceles includes surgical exploration and repair. Careful dissection is required. Excision of the cyst is not necessary, but opening of the cyst to avoid in- jury to the trapped roots is usually required before closure and repair. Summary Neurologic complications after lumbar spine surgery are neither common nor necessarily foresee- able. With the increasing number of lumbar spine operations being performed, the number of patients who will sustain neurologic injury can be expected to increase. Be- cause of the often irreversible and dramatic nature of these injuries, as well as the lack of definitive treat- ments once they have occurred, it is obviously best to prevent these in- juries through use of meticulous op- erative technique, awareness of risk, and close attention to perioperative details. Neurologic Complications After Lumbar Spine Surgery Journal of the American Academy of Orthopaedic Surgeons 144 Figure 3 Lateral (A) and axial (B) MR images of a 55-year-old man approximately 4 to 5 weeks after lumbar laminectomy. He reported a sudden sharp pain with coughing, and a fluctuant mass was noted in his low back. The images demonstrate a large pseudomeningocele. A B References 1. Rydevik B, Holm S, Brown MD, Lundborg G: Diffusion from the cere- brospinal fluid as a nutritional path- way for spinal nerve roots. Acta Physiol Scand 1990;138:247-248. 2. Delamarter RB, Bohlman HH, Dodge LD, Biro C: Experimental lumbar spinal stenosis: Analysis of the cortical evoked potentials, microvasculature, and histopathology. J Bone Joint Surg Am 1990;72:110-120. 3. Olmarker K, Rydevik B: Single- versus double-level nerve root compression: An experimental study on the porcine cauda equina with analyses of nerve impulse conduction properties. Clin Orthop 1992;279:35-39. 4. Olmarker K, Rydevik B, Holm S: Edema formation in spinal nerve roots induced by experimental, graded com- pression: An experimental study on the pig cauda equina with special ref- erence to differences in effects between rapid and slow onset of compression. Spine 1989;14:569-573. 5. Stambough JL, Simeone FA: Neuro- logic complications in spine surgery, in Herkowitz HN, Eismont FJ, Garfin SR, Bell GR, Balderston RA, Wiesel SW (eds): Rothman-Simeone: The Spine, 4th ed. Philadelphia: WB Saunders, 1999, vol 2, pp 1724-1733. 6. Stevens WR, Glazer PA, Kelley SD, Lietman TM, Bradford DS: Ophthal- mic complications after spinal surgery. Spine 1997;22:1319-1324. 7. Hoyland JA, Freemont AJ, Denton J, Thomas AM, McMillan JJ, Jayson MI: Retained surgical swab debris in post- laminectomy arachnoiditis and peri- dural fibrosis. J Bone Joint Surg Br 1988;70:659-662. M. Darryl Antonacci, MD, and Frank J. Eismont, MD Vol 9, No 2, March/April 2001 145 8. Calancie B, Madsen P, Lebwohl N: Stimulus-evoked EMG monitoring during transpedicular lumbosacral spine instrumentation: Initial clinical results. Spine 1994;19:2780-2786. 9. Lin PM: Posterior lumbar interbody fusion technique: Complications and pitfalls. Clin Orthop 1985;193:90-102. 10. Kitchell SH: Complications of ante- rior cage interbody fusion tech- niques. Semin Spine Surg 1998;10: 256-262. 11. Flynn JC, Price CT: Sexual complica- tions of anterior fusion of the lumbar spine. Spine 1984;9:489-492. 12. Kurz LT, Garfin SR, Booth RE Jr: Harvesting autogenous iliac bone grafts: A review of complications and techniques. Spine 1989;14:1324-1331. 13. Frymoyer JW, Matteri RE, Hanley EN, Kuhlmann D, Howe J: Failed lumbar disc surgery requiring second opera- tion: A long-term follow-up study. Spine 1978;3:7-11. 14. Mirovsky Y, Neuwirth M: Injuries to the lateral femoral cutaneous nerve during spine surgery. Spine 2000;25: 1266-1269. 15. Zeidman SM, Long DM: Failed back surgery syndrome, in Menezes AH, Sonntag VKH (eds): Principles of Spinal Surgery. New York: McGraw-Hill, 1996, vol 1, pp 657-679. 16. Le AX, Rogers DE, Dawson EG, Kropf MA, De Grange DA, Delamarter RB: Unrecognized durotomy after lumbar discectomy: A report of four cases associated with the use of ADCON-L. Spine 2001;26:115-118. . Garfin SR, Bell GR, Balderston RA, Wiesel SW (eds): Rothman-Simeone: The Spine, 4th ed. Philadelphia: WB Saunders, 1999, vol 2, pp 1724-1733. 6. Stevens WR, Glazer PA, Kelley SD, Lietman TM, Bradford DS: