Preoperative and Surgical Planning for Avoiding Complications

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Chapter 26 Preoperative and Surgical Planning for Avoiding Complications

Technical complications in spine surgery usually arise from the overaggressive handling of soft tissue or from hardware “failure” (when hardware “fails,” the cause of the “failure” usually rests squarely on the shoulders of the surgeon). Other reasons for complications include poor patient selection, incorrect diagnosis, ill-chosen approach, inadequate operation (e.g., incomplete decompression of a compressive lesion), and injury to normal anatomic structures.

The surgeon should have clearly established a diagnosis and a clear, three-dimensional understanding of the pathologic anatomy, as demonstrated by imaging studies. Finally, an astute surgeon should use common sense by measuring twice, cutting once, and paying meticulous attention to detail.

General Precautions

Antibiotics

The role of preoperative and perioperative antibiotics in spine surgery remains controversial. The average infection rate for spine operations is relatively low. Evidence suggests that the incidence of infections may be decreased further if antibiotics are administered before the operation.14 Indeed, a review of the literature provides support for the use of perioperative antibiotics.2 Because the most frequently detected organism is a Staphylococcus species, a first-generation cephalosporin is usually satisfactory, unless an allergic propensity is recognized.5

Steroids

The role of perioperative steroids in spine surgery is also controversial. The administration of steroids before spinal cord injury confers greater benefit than administration after injury.5,6 Although the literature is inconclusive, some surgeons choose to administer 4 to 8 mg of dexamethasone (or an equivalent dosage of methylprednisolone) preoperatively and to continue steroid administration for 24 hours postoperatively in high-risk cases. Because the short-term use of steroids is effective in experimental studies6,7 and long-term administration is associated with an increased risk of complications, its use for more than 24 hours seems unnecessary (and possibly harmful).

Positioning

Numerous complications are associated with improper positioning, including air embolism, quadriplegia, peripheral nerve palsies, pyriformis syndrome, posterior compartment syndrome, and excessive bleeding.

Elastic bandages or sequential compression devices should be placed on the lower extremities before the induction of anesthesia. The legs must not be lower than the hips in the sitting position. Great care should be taken in moving the patient to the prone position. Three-point skull fixation in the prone position may be used, although it can be associated with a variety of complications (generally minor).

Extreme rotation, extension, or flexion of the head may cause cervical spinal cord damage. Older patients with cervical spondylotic bars are more prone to this complication. Awake positioning, awake intubation, and evoked-potential monitoring may be helpful. Loss of somatosensory evoked potentials, with neck flexion and recovery with repositioning, has been reported.8 In patients with severe spinal canal narrowing, the neutral or near-neutral position is preferred.

A stretch injury of the brachial plexus may occur in both the prone and supine positions by abducting the arm greater than 90 degrees. An axillary roll should be used to prevent injury, with the lateral decubitus position when the dependent arm is compressed. The ulnar nerve could be injured because of its superficial position at the elbow. A pad under an extended elbow helps prevent this injury. Elbow extension minimizes exposure of the ulnar nerve to compression. The radial nerve may be injured if the arm hangs over the operating table edge. Padding under the arm may prevent compression injury. Common peroneal nerve injury with resulting footdrop may occur in the supine, the sitting, and the lateral decubitus positions. The superficial location of the nerve at the head of the fibula may increase the risk of compression. The superficial femoral nerve may be compressed in the prone position and cause a postoperative transient meralgia paresthetica.

Compression and stretch injury of any nerve is possible during positioning. A general rule of thumb is to use a position without excessive compression of the extremities and to place appropriate pads beneath potentially exposed nerves. If the patient appears comfortable, nerve injury is less likely. Injury to the lateral femoral cutaneous nerve has been reported to be as high as 20%.9 External pressure at the anterior superior iliac spine during prone position is the main reason for the injury of the nerve. The nerve can also be injured at the retroperitoneum by hematoma or traction, as well as during bone graft harvesting at the ventral iliac crest.

Compression of the eyes, with resulting blindness, has been reported with the use of the horseshoe headrest.1012 The head should be positioned to prevent it from slipping on the horseshoe headrest. Three-point skull fixation is a viable alternative to the horseshoe and should significantly reduce the incidence of this complication.

Air Embolism

Air embolism is one of the most serious complications encountered. It is predominantly related to operations performed above the level of the heart.13 Two precautions to avoid air embolism are suggested: (1) if possible, avoid the sitting position; and (2) monitor the patient at risk meticulously with Doppler ultrasound and end-tidal Pco2. In such patients a central venous catheter should be used so that if an air embolism is detected, air can be emergently evacuated from the right atrium. The central venous pressure should be maintained at greater than 10 cm, so that the pressure in epidural veins does not decline.

One should not administer nitrous oxide when using the sitting position. The incidence and clinical importance of air embolism is greater in the sitting position than in other positions.14 Its incidence has been reported to be as high as 50%.13 If air embolism occurs, a central venous catheter may be used to withdraw air from the left atrium. At the same time, the surgeon should flood the wound with Ringer solution and inspect and control any open veins with bipolar coagulation. Bleeding bone surfaces should be treated with wax, and the wound should be precisely packed with wet gauze. If signs of air embolism persist, the patient should quickly be placed in a side-lying position, with the right side facing up, to aid the removal of air via the central venous catheter from the right atrium.

Incidental Durotomy, Cerebrospinal Fluid Fistula, and Pseudomeningocele

Unintended tear of the dura mater is a common complication of spine surgery. Its incidence has been reported between 3.1% and 14% in different series.1618 Immediately after surgery, a tear causes headaches, wound infection, and cerebrospinal fluid (CSF) fistulae. In the long-term, persistent CSF leakage, pseudomeningocele, neurologic deficit, and arachnoiditis are common problems associated with durotomy.16 The tear should be better recognized and treated appropriately.

CSF leakage may cause wound dehiscence and subsequent infection. If the fistula is substantial, fluctuations in conscious state may be observed.19 In fact, an intracranial hemorrhage may develop.20 After ventral cervical spine surgery, the fistula may even cause airway obstruction,21 and after ventral or dorsolateral surgery of the thoracic spine, it may even cause a subarachnoid-pleural fistula.22,23

Fibrin sealants may be used to prevent leakage. They are biologically derived substances consisting of fibrinogen solution and thrombin, with a calcium cofactor.24 They are used as adhesives to augment other layers of closure. A retrospective review of fibrin sealants noted that the incidence of postoperative CSF leaks and tension pneumocranium was reduced, while also reducing overall management costs.24 Nakamura et al.25 have found that autologous fibrin tissue adhesive was superior to that of commercial fibrin tissue adhesive in terms of cost.

CSF cutaneous fistula and pseudomeningocele are end-stage complications of an improperly treated dural tear. Because these complications may lead to increased morbidity, increased cost, increased pain, and increased neurologic deficit, they must be treated properly and aggressively.26 The first priority is to implement CSF diversion (i.e., external lumbar drainage). A percutaneous blood patch may also be used. A revision surgery to repair the dural defect may also be indicated. If a pseudomeningocele is noted and the leakage of CSF persists, it may become necessary to perform dural and myofascial closure via an open reoperation surgical procedure. In difficult cases, a shunt (possibly lumboperitoneal shunt) may also be necessary.

Thromboembolism

Venous thromboembolic disease, including deep vein thrombosis and pulmonary embolism, is a serious and potentially life-threatening complication in spine surgery. In a recent meta-analysis, the prevalence of deep vein thrombosis was 1.09%, and the prevalence of pulmonary embolism was 0.06% following elective spine surgery.28 The use of pharmacologic prophylaxis significantly reduced the prevalence of deep vein thrombosis relative to no prophylaxis (P < 0.01).

In a recent retrospective study conducted by the Scoliosis Research Society,29 the complication rate in 9692 lumbar microdiscectomies was 3.6%. In anterior cervical discectomy and fusion, the complication rate was 2.4%, and with 10,329 lumbar stenosis decompressions, it was 7%. Overall rates of pulmonary embolism were 1.38%, death due to pulmonary embolism 0.34%, and deep vein thrombosis 1.18%.29

Upper Cervical Spine: Complication Avoidance

The reducibility of a subluxation is a critically important consideration for upper cervical spine pathologic processes. If the lesion is reducible, only a dorsal fixation and fusion procedure may be indicated. If the lesion is not reducible, the optimal operation depends on the localization of the compression. For an extradural lesion located between the midclivus and the C3 vertebral body, a transoral approach may provide the trajectory and exposure of choice. If the lesion is intradural, a dorsal or lateral transcondylar approach may be more appropriate. Complex pathologic lesions with lateral extension that are located between the C1 and midcervical levels may involve a transmandibular, transglossal approach. For more limited pathologic lesions located between the lower clivus and the C2 vertebral body, a ventrolateral or ventromedial retropharyngeal approach may be appropriate. In general, if stabilization is required, a dorsal or lateral transcondylar approach with instrumentation should be considered.

Transoral Approach

Subaxial Cervical Spine: Complication Avoidance

Surgical intervention in a patient with a complete traumatic spinal cord lesion and overt instability may be necessary to reestablish spinal stability. Systemic complications of trauma such as hypotension, respiratory difficulties, and metabolic derangements should be well controlled before embarking on a stabilization procedure.

For cervical spondylotic pathologies, the shape of the cervical curvature should be considered in deciding on the operative approach. In general, cervical kyphosis is a specific indication for a ventral approach, to avoid postoperative instability31 and to provide adequate ventral decompression.32

Often, intradural tumors are optimally approached dorsally, whereas vertebral body tumors are best approached ventrally. A burst or wedge fracture with spinal canal compromise is best approached ventrally. However, severe three-column instability may require both a ventral and a dorsal approach. The indications for the ventrolateral approach are laterally situated tumors, nerve root decompression,33,34 and the rarely observed symptomatic vertebral artery compression.