24.1 Introduction

Adolescent idiopathic scoliosis (AIS) is the most common form of pediatric scoliosis, accounting for 80 to 90% of pediatric spine deformity. ¹ For children with progressively worsening curvatures unresponsive to conservative therapy, instrumented spinal arthrodesis is the gold standard surgical therapy. Over the last three decades, advances in surgical techniques, spinal instrumentation, and intraoperative neurophysiologic monitoring (IONM) have combined to allow safer surgical correction of progressive spinal deformities. However, surgical corrections are not without risk and can be devastating.

The incidence of complications after AIS surgery has ranged from 0 to 89% in various retrospective reviews. ² More recent prospectively collected data from high-volume pediatric centers for spinal deformity revealed an overall complication rate of 5.7%, with only 2 deaths occurring in 6,334 patients. ³ Although these outcomes may not be generalizable to low-volume centers, in general, families and providers should expect relatively low rates of complication as compared to other subtypes of deformity (such as neuromuscular spine deformity, congenital spine deformity, and early-onset scoliosis). ⁴

Within this chapter, we will examine intraoperative, perioperative, and late postoperative complications that occur during AIS deformity surgery. Additionally, we will review best practice guidelines for optimizing surgical outcomes.

24.2 Intraoperative Complications

General: The complication profile and the likelihood of an adverse event after surgery for AIS is related to the planned surgical procedure and magnitude of deformity to be corrected. Historically, anterior and combined anteroposterior surgeries incurred much higher rates of morbidity and mortality than posterior alone surgeries, with some authors reporting up to 50% morbidity associated with anterior approaches due to pulmonary complications. ⁵ A report from the Scoliosis Research Society (SRS) Morbidity and Mortality Committee found the complication rate of posterior surgery alone to be 5.1%, anterior surgery alone 5.2%, and combined anterior and posterior surgery nearly twice that (10.2%). Several potential complications such as pneumothorax, bowel injury, sympathetic chain injury, injury to the superior and inferior hypogastric plexus, injury to the lymphatic vessels, and major vascular injury occur primarily after anterior approaches. Over the last 20 years, however, the rate of anterior and combined anterior and posterior surgeries has dropped to now represent less than 5% of the overall surgical approaches for AIS. ^{6 , 7}

In addition to procedural risk factors, patient-specific risk factors may influence the rate of complications and postoperative morbidity and mortality. In general, patients with AIS are relatively healthy and do not have significant medical comorbidities. The presence of medical comorbidities in general has portended an increased likelihood of adverse events after surgery for AIS. ⁸ Pulmonary complications are common postoperatively irrespective of anterior or posterior approach, and patients with preexisting respiratory diseases are at an increased risk of postoperative pulmonary complications. ⁹ Patient-specific risk factors will be discussed individually with respect to each specific potential complication.

The prevalence of non-neurologic complications, including respiratory issues, excessive bleeding, wound infections, wound issues other than hematoma, and required reoperation, was defined by Carreon et al. ¹⁰ In a retrospective review of prospectively collected data from multiple high-volume centers, they found an overall non-neurologic complication incidence of 15.4%. Most of these issues occurred in the perioperative period (from the time of induction until the transfer of the patient to the ward; 6.13%) and the early postoperative period (within the first 24 hours after surgery; 6.27%). The incidence of non-neurologic complications is closely related to the time of spinal surgery, duration of general anesthesia, and blood loss. ¹⁰ The most common complications include pulmonary complications, excess blood loss, and wound-related issues (including infection). Published complications from the SRS database are self-reported and may underestimate the true incidence. Table 24‑1 summarizes complications reported from the Harms Study Group, a prospectively collected registry with a minimum 2-year follow-up.

Blood loss: Due to the number of vertebral levels that are exposed and the need for osteotomies, a moderate amount of blood loss is expected during spine deformity correction. Loss of blood (and need for intraoperative blood transfusion) may subject patients to the potential for blood-borne diseases, increased incidence of wound infections, transfusion reactions, pulmonary complications, and other autoimmune phenomena. Estimated blood loss for posterior spinal surgery in idiopathic scoliosis ranges from 600 to 1,500 mL. ^{11 , 12} The expected blood loss has been correlated to several variables including the number of expected fusion levels, curve magnitude and stiffness (both are indirect indicators of the need for higher-grade osteotomies), patient age and body mass index (BMI), skeletal maturity, and surgical technique chosen (anterior vs. posterior vs. combined) as well as the number of high-grade osteotomies. ^{13 , 14 , 15} As mentioned earlier, increasing blood loss is directly correlated with an increasing rate of postoperative complications.

Although uncommon in AIS, prior to surgery patients should stop any blood thinning or antiplatelet agents. In patients who are underweight or malnourished, preoperative nutrition optimization may be useful to correct electrolyte imbalances and coagulopathies that may result in higher amounts of intraoperative blood loss. Hemoglobin and hematocrit values should be at the very least normal prior to embarking on large-scale deformity corrections. Particularly in postmenarchal female patients who may have chronic anemia, surgeons should consider routine preoperative lab work.

Preoperative planning should be nuanced and include a discussion of techniques to minimize blood loss. The use of tranexamic acid has been demonstrated in multiple prospective and retrospective studies to reduce expected blood loss after spinal surgery. ^{12 , 16 , 17} Intraoperative blood salvage appliances (e.g., Cell Saver) may be useful to avoid the need for allogenic blood transfusion.

Several general operative techniques are useful to mitigate blood loss during surgery. To reduce intra-abdominal pressure and venous stasis, patients should be positioned with the abdomen hanging freely, avoiding pressure on the spleen and liver. The patient should be checked periodically throughout the case to ensure that he or she has not slipped off the bolsters. Pre-incision infiltration of local anesthetic with epinephrine diminishes bleeding from the skin incision and dermis. Muscle paralysis and relative hypotension (mean arterial pressure between 65 and 70 mm Hg) during the exposure minimizes soft-tissue trauma and bleeding. Once the exposure is completed, nonactive areas should be packed off with sponges to diminish bleeding. Bleeding during exposure can be minimized with excellent technique and attention to hemostasis. Meticulous hemostasis should be obtained before embarking on osteotomies and pedicle cannulation.

During cannulation of pedicles, blood loss is expected as the cancellous vertebral body is accessed. Mechanical plugging over the cortical bony opening or a small amount of passively applied injectable hemostatic matrix may stay blood loss long enough to allow tapping, pedicle sounding, and subsequent screw insertion. Bleeding can be profuse but will often show some fatty particles within the blood, informing the surgeon that the origin of the bleeding is the vertebral body. If the bleeding is profuse and there is any breach in the pedicle, the origin may be epidural bleeding. In these instances, screw insertion at this level should be aborted and the entry point can be sealed with bone wax or other available agents such as hemostatic absorbable putty (Hemasorb, Abyrx, Irvington, New York, United States), collagen soaked in thrombin, etc. During three-column osteotomies, a large amount of blood loss is expected from the epidural veins and during the decancellation of the vertebral body. Generous use of bipolar coagulation, hemostatic agents, and packing is critical to mitigate blood loss. However, definitive closure of the osteotomy may be most effective at controlling blood loss.

A large amount of blood loss with or without an associated decrease in systemic blood pressure may indicate a major vascular injury. This may occur during pedicle cannulation (particularly on the concavity of the curve, as lateral and deep breaches may be in closer proximity to the great vessels), during diskectomy if the rongeurs or disk prep devices breach the anterior longitudinal ligament, or during exposure of the vertebral body in preparation for high-grade osteotomies. If there is suspicion for a major vascular injury, one should pack off the area as able with gelfoam and sponges, apply compression, and observe. If bleeding is controlled and the patient is hemodynamically stable, surgeons may decide to either continue the surgery or abort and further interrogate the vascular structures postoperatively. In instances of overt hemodynamic instability, the packing should be left in place and the wound closed over with plans for emergent anterior to stop the bleeding. Emergent consultation with a general surgery or vascular surgeon is recommended.

Ultimately, surgeons must be willing to abort surgical corrections once the estimated blood loss has reached critical levels. If the definitive surgical correction is to be abandoned, surgeons should leave whatever instrumentation has already been inserted and close the wound. During instances in which destabilizing osteotomies have been performed (Schwab 3 or higher), it may be prudent to place (or leave) a temporary rod across the unstable segment. After a period of convalescence, the instrumentation and correction can usually be resumed without long-term sequelae. During that recovery period, total parenteral nutrition (TPN) and transfusion of blood, platelets, or coagulation factors may be necessary.

Certain risk factors including male sex and increased thoracic lordosis (i.e., hypokyphosis) are correlated to increased blood loss within the idiopathic population. ¹⁸ In general, male patients tend to have stiffer curves, longer surgical time, and more blood loss, with a correlative higher complication rate as compared to females. ^{19 , 20} Overall, many techniques to minimize blood loss lack sufficient evidence to ascertain their utility but are employed nonetheless. The Harms Study Group developed a consensus recommendation using the Delphi method addressing techniques to minimize blood loss (Table 24‑2).

Durotomy: Unintended durotomy (i.e., incidental durotomy) and spinal fluid leak occur rarely during pediatric spine surgery. Overall, the incidence has been noted to be less than 2% in index surgeries, although the occurrence is much more common in revision cases. ²¹ Dural injury may occur during decompression of the neural elements, osteotomy for deformity correction, or pedicle cannulation. Intraoperative management of spinal fluid leak is dependent on the degree of dural violation.

The primary treatment of durotomy at the time of surgery includes primary repair of the dura with nonabsorbable 4–0, 5–0, or 6–0 suture. The closure may be augmented with muscle or fat plugs and dural fibrin sealants as needed. In the rare instance of a large durotomy, the use of dural substitutes (autograft, allograft, or synthetic products) for patch grafting may be indicated. It is critical to ensure that the neural elements (i.e., nerve rootlets) are within the thecal sack prior to primary closure. Spinal fluid leak due to medial breach during pedicle cannulation can often be managed with bone wax (an alternate point of fixation should be used at this site). Valsalva maneuver prior to closure is useful to determine whether there is persistent cerebrospinal fluid (CSF) leakage.

Postoperatively, a period of bed rest with or without recumbency may help prevent the formation of a fistula. The use of subfascial drains is controversial due to the potential for CSF overdrainage, intracranial hypotension, and subsequent meningitis; however, their use has been described. ²² In patients with persistent CSF leak through the surgical incision, CSF diversion via subarachnoid lumbar drain may allow epithelialization and closure of the CSF track. Return to the operating room (OR) for revision related to spinal fluid leakage is exceptional in the AIS population.

Neuromonitoring Changes and Neurologic Injury: The most feared postoperative complication after AIS surgery is neurologic injury. Fortunately, the incidence of spinal cord injury is low in the AIS population and is less than 1% at high-volume institutions. ^{23 , 24} In the United States, IONM has emerged as the standard of care during routine and complex deformity correction surgeries, largely replacing the Stagnara wake-up test. ²⁵

Certain causes of IONM change may be apparent and readily reversible. The surgical causes of neuromonitoring alert include thoracic pedicle screw placement (25%), osteotomy (20%), cage placement (3%), wiring (2%), resection (17%), and correction (34%). ²⁵ Neurologic injury can often be avoided by reversing the immediate cause of the IONM change. A recent prospective study by Yang et al ²⁶ demonstrated that raising the mean arterial pressure alone restores 20% of IONM losses. The appropriate management and response to IONM changes are discussed in further depth in another chapter. An IONM checklist provides a useful algorithmic approach to managing these complex situations (see Chapter 28).

Spinal cord infarction due to injury or ligation of the artery of Adamkiewicz or other large segmental vessels is a rare complication that has been described. The vascular supply and drainage to the spinal cord is inconsistent, however, and predicting risk from segmental vessel ligation can be a challenge. Koshino et al ²⁷ described the vascular supply of the spinal cord on cadaveric dissection and found significant variability in the number of arteries of Adamkiewicz, side of origin, and the level of origin. The artery was found to originate between T8 and L1 in 90% of patients. Because the sacrifice of this vessel may lead to devastating infarction of the cord, several authors have proposed temporary ligation of prominent segmental vessels to prevent neurologic injury. This may be particularly helpful in severely angulated kyphosis or kyphoscoliosis, where the spinal cord already has a tenuous blood supply. Despite the theoretical risk, most surgeons agree that the risk of spinal cord infract after segmental vessel ligation is extraordinarily low. ²⁸ In the rare instance of a delayed neurologic deficit due to spinal cord infarction, long-term recovery with medical management has been described. ²⁹

Less common causes of neurologic injury include stroke due to vertebral artery injury (a consideration in constructs that extend into the cervical spine) and root avulsion or injury. These are exceptional occurrences.

Instrument-related intraoperative failures: Failure of instrumentation intraoperatively occurs most frequently during attempted correction in the setting of either more rigid deformities or patients in whom adequate bony anchors cannot be obtained. In such cases, deformity maneuvers may result in pedicle fracture, hook pullout, and, in rare instances, neurologic injury. Malposition of instrumentation, which is not noted on intraoperative fluoroscopy, CT, or neuromonitoring, may also be a source of instrumentation-related morbidity.

In rare instances, systemic complications can occur due to implanted metals. The use of dissimilar metals within a construct can result in the formation of a galvanic cathode–anode coupling and subsequent erosion or dissolution of alloy components. ³⁰ Within the spine, this is most relevant in chromium alloy–stainless steel couplings. Cobalt chromium alloy and titanium alloy coupling is relatively stable and is commonly employed. ³¹ Serum metal concentrations have also been noted to increase after instrumented spinal arthrodesis with titanium constructs, though the clinical significance of elevated serum titanium levels is unclear. ³²

Rare Intraoperative Complications/Complications Related to Anterior Procedures: As mentioned earlier, anterior and anteroposterior approaches for AIS have decreased in frequency over the last two decades. There are a fair number of complications that are restricted to the anterior approach, which are obviated in this era of posterior-only deformity surgery. The vast majority of injuries specific to anterior surgery occur during the approach to the spine and can be managed without postoperative sequelae by the approach surgeons. These include major vascular injury (aorta, vena cava, iliac artery and vein, segmental arteries, and iliolumbar/hypogastric veins), injury to the urologic system (ureteral injury during retroperitoneal surgery), and injury to the peritoneal contents (less common, as transperitoneal approaches are rarely used).

Injury to the lymphatic vessels can occur after transthoracic and retroperitoneal approaches. Although identification of chylous leakage during a retroperitoneal or transthoracic surgery is common, the incidence of clinically significant chylous-related issues is low. Chylothorax, chylous ascites, chylous pericardium, chylous urea, and chylous retroperitoneum have all been described. ^{33 , 34} If chyle leakage is noted intraoperatively, one can give milk or cream with methylene blue down the nasogastric (NG) tube, which in about 15 to 20 minutes will leak out if a perforation exists, and direct repair can be done at the time of surgery. However, most are identified later with milky chest tube drainage or pleural effusions noted on postoperative imaging. The typical treatment involves changes in diet and nutritional support. A low-fat diet of medium chain length triglycerides may be employed with spontaneous closure of the leakage. Persistent chylous lymphoceles or fistula may require sclerosing agents to induce closure of the injured lymph duct. Rarely, patients may be required to be nil per os (NPO) for a period of time, during which total parenteral nutrition may be necessary.

The sympathetic chain and parasympathetic plexus (superior and inferior hypogastric plexuses) lie in close proximity to the thoracic and lumbosacral spine, respectively. Injury to the superior hypogastric plexus during exposure of the lumbosacral spine may result in retrograde ejaculation. In a survey of surgeons worldwide, Flynn and Hoque ³⁵ found the incidence of sterility due to retrograde ejaculation in male patients to be about 0.42% (19/4,500), and the rate of impotence was 0.44% (20/4,500). This included surgeries within both the adult and pediatric populations. Injury to the sympathetic chain may occur during retroperitoneal or transthoracic approaches to the spine. These autonomic nerves may be challenging to mobilize. The consequences of disruption of these nerves typically include increased blood flow to the ipsilateral extremity, which may be perceived as increased warmth of that extremity or as coolness to the contralateral extremity. Most of these sympathetic and parasympathetic injuries are self-limited. Flynn and Price ³⁶ noted that 25% of patients had resolution of retrograde ejaculation and return of sexual function. Rajaraman et al ³⁷ meanwhile reported that five of six patients with sympathetic dysfunction had resolution of their symptomatology after 3 to 4 months. In approaches to the upper thoracic spine, rarely, injury to the stellate ganglion of the sympathetic chain can result in ipsilateral ptosis, anhidrosis, and myosis (Horner syndrome). ³⁸

24.3 Early Postoperative Complications

Infection: Early surgical site infection (SSI), defined as infection within the first 90 days after the index operation, occurs rarely after surgery for AIS. However, it is the most common reason for early readmission overall, accounting for 33% of early AIS readmissions. ³⁹ Recently, Marks et al ⁴⁰ defined the incidence of early SSI after AIS surgery, finding a rate of 1.6%. In this study, only patient weight was found to be a significant risk factor for SSI. Previous studies have reported the following to be a risk factor for early SSI: BMI over 30 kg/m²; nutritional deficiencies; pulmonary, gastrointestinal (GI), cardiac, and neurologic comorbidities; American Society of Anesthesiologists class of 3 or 4; and patients with developmental delay. ⁴¹

Overall, most early SSIs can be managed without implant removal. In the series by Marks et al, ⁴⁰ 92% of early SSIs were managed without implant removal or with immediate exchange with titanium instrumentation without postoperative sequelae. The management of these infections is variable, however, and may be related to whether there is frank wound dehiscence, underlying abscess, systemic signs of infection (i.e., sepsis), the causative organism, and the time in which the infection presents. For a more detailed discussion on the management of infection after AIS surgery, please see Chapter 23.

GI-Related Issues: The incidence of GI-related issues in the immediate perioperative period following AIS surgery is high. Recently, Villamor et al ⁴² prospectively examined the incidence of post-op GI complaints and found that constipation (68%), nausea (65%), emesis (63%), and abdominal pain (50%) were common after surgery. This was not indicative of a major complication; however, it may serve as a barrier to discharge. GI-related issues comprise the second most common reason for early readmission after AIS surgery, accounting for 30% of early readmissions. ³⁹ As such, patients should have soft abdomens, bowel sounds, and return of flatus prior to discharge. Traditionally, surgeons required patients to have a bowel movement prior to discharge, but increasing evidence from accelerated pathways supports earlier discharges without bowel movements. ⁴³ There may be diminished GI-related issues such as postoperative ileus with increased mobilization and earlier discontinuation of patient-controlled analgesia (PCA) pump, as has been noted in accelerated discharge pathway studies. ⁴⁴ Other authors have found chewing gum postoperatively ⁴⁵ and preoperative bowel prep ⁴⁶ to be useful in facilitating the early return of bowel function. The rate of ileus after anterior AIS surgery was estimated to be 3.5% by Grossfeld et al, ⁴⁷ whereas the rate after posterior surgery was 1.0%. Most often, uncomplicated ileus can be managed with bowel rest, intravenous hydration, and correction of electrolyte deficiencies.

Superior mesenteric artery (SMA) syndrome is a rare phenomenon that occurs when the duodenum becomes compressed between the SMA and the aorta after the correction of the deformity. ⁴⁸ An incidence of 0.5 to 1.5% has been reported in multiple series. ^{49 , 50 , 51} Clinical symptoms include prolonged ileus and bilious vomiting. Diagnosis is made on barium swallow evaluation. Symptoms are managed expectantly with NG decompression, alimentation via postduodenal feeding tubes, or intravenous hyperalimentation. Risk factors include short stature, low BMI, more lumbar lateralization, and a low percent correction of the thoracic curve on bending. ⁵² Pancreatitis should be considered in the differential.Fig. 24‑1

Early Instrumentation-Related Issues: Early issues are typically related to poor bony anchorage, suboptimal bone quality, and excessive mechanical loads on the instrumentation. Whereas poor bone quality is more often seen in patients with early onset, syndromic, or neuromuscular scoliosis, patients with AIS who are underweight or have poor preoperative nutrition may also have poor bone quality. In patients with suboptimal bony anchorage, surgeons may consider an increased implant density ratio. Likewise, such patients may benefit from additional osteotomies to loosen the spine and obtain correction. Poor fixation may be augmented with cables or Mersilene tape in addition to hook and screw fixation. Early instrumentation failure is typically managed by the return to the operating room for revision of instrumentation and supplemental fixation.

Pain: A moderate amount of pain is expected within the early postoperative period. Due to the extensive length of the surgical incision, the amount of muscle and soft-tissue dissection, periosteal stripping, and subsequent osteotomies/articular cartilage removal, there may be several neurophysiologic pathways of postoperative pain. The most extensive amount of pain is expected in the first 24 to 48 hours, with moderate amounts of pain lasting up to 1 to 2 weeks. Preoperative pain levels, anxiety sensitivity in children, and parental pain catastrophizing may all play a role in the pain response and recovery in children. ^{53 , 54} Unfortunately, the incidence of persistent pain in both the early and late postoperative periods is likely higher than what is reported in the literature. ⁵⁵ Successful postoperative analgesia involves a multimodal approach to pain including both opiate and nonopiate therapies. Gabapentin may be useful to address neuropathic postoperative pain if started preoperatively. PCA is a mainstay in postoperative pain management. Other modalities such as single-dose intrathecal narcotics, epidural analgesia, long-acting postoperative local anesthetic, nonsteroidal anti-inflammatory drugs, and ketamine are benificial that are less often utilized but may be options in select situations. Best practice pain pathways to reduce perioperative pain and accelerate discharge are discussed later in this chapter. Availability of a “pain service” with dedicated nurses and pain management providers may also greatly contribute to immediate postoperative pain management.

Neurologic Issues: Positioning-related neuropraxias can occur after long deformity surgeries. Lateral femoral cutaneous nerve compression may occur causing sensory dysesthesias in the thigh after prone positioning, particularly in patients with high BMI. Likewise, ulnar neuropathy and brachial plexopathy have been described due to inappropriate padding of the axilla and cubital tunnel. IONM may be useful in preventing motor neuropathy related to the positioning, and any decrement in upper extremity motor in typical AIS surgery is usually related to positioning issues. However, injury to sensory nerves (such as the lateral femoral cutaneous nerve) is more challenging to detect. Treatment is conservative, with the vast majority of positioning neuropraxias recovering over time. A short course of steroids may also be employed.

Very rarely, paralysis can occur in the early postoperative period despite uneventful spine surgery. ^{56 , 57} The exact rate of delayed neurologic deficit (24–48 hours after surgery, with a normal postoperative musculoskeletal examination) is unknown, but it is an exceptionally rare occurrence. Immediately reversible causes of myelopathy (such as spinal epidural hematoma) must be ruled out. In the event that no compressive lesion is identified and conservative measures to increase spinal cord perfusion (such as blood pressure augmentation and transfusion of blood products) do not reverse the myelopathy in the first 3 to 6 hours, a return to the operating room for release of correction to see if the neurologic function is restored should be considered.

Pulmonary Issues: Pulmonary issues, particularly in the immediate perioperative period, comprise a common medical complication after spine surgery. These range from pleural effusions with minor clinical significance to life-threatening conditions such as acute respiratory distress syndrome (ARDS). Whereas certain pathologies such as pneumothorax, hemothorax, and prolonged chest tube requirement are rare in this era of posterior-only surgery for AIS, atelectasis and pneumonia may still occur transthoracic procedures. Certain procedures such as osteotomies and thoracoplasty may predispose patients to postoperative pulmonary complications such as ARDS, whereas blood transfusions may result in transfusion-related lung injuries (Fig. 24‑2).

Vision Loss: Perioperative vision loss is a rare complication after spine surgery. ⁵⁸ In the pediatric population, the risk is lower and the pathophysiology different than in the adult population. Historically, prone positioning in which the face and eyes are below the level of the heart are theorized to increase intraocular pressure, posing a risk factor for postoperative vision loss as a result of decreased perfusion of the optic nerve. Risk factors for this complication include patients younger than 18 years, obesity, male gender, hypertension, peripheral vascular disease, intraoperative blood loss (and the need for blood transfusion), intraoperative hypotension, and deformity correction. ⁵⁸ In a recent retrospective review, De la Garza-Ramos et al ⁵⁹ found the incidence of perioperative vision loss to be 0.16% for pediatric patients undergoing corrective surgery for idiopathic scoliosis. Interestingly, all perioperative vision loss in their study was due to cortical blindness, as opposed to retinal vascular occlusion or ischemic optic neuropathy, which has been described in adult patients. In their study, younger age, male gender, iron deficiency anemia, Medicaid as the primary insurance source, and fusion of eight or more spinal levels were risk factors for perioperative vision loss.

24.4 Late Postoperative Complications

Instrumentation-Related Issues: Late instrumentation-related issues are more often related to trauma, infection, or pseudarthrosis. In contrary to early instrumentation, late failures of instrumentation are often managed nonoperatively if the patient is asymptomatic. In instances where there is progressive deformity, such as in cases of “adding on,” proximal or distal junctional kyphosis, or instability due to pseudarthrosis, patients may require a return to the operating room for revision of instrumentation. Chapter 26 will delve into late instrumentation failure in more detail.

Infection: The management of late presenting infections (defined as > 90 days after the index surgery) is often distinct from early infections. In contrast to early infections, which are typically managed without explantation of instrumentation, late infection often requires washout and exchange of instrumentation. Ahmed et al. ⁶⁰ recently examined the 5-year reoperation risk and causes for revision after AIS surgery and found the incidence of late infections to be 2.2%. In instances of recurrence and failure of medical and surgical management, a period free of instrumentation may be necessary. The nuances of both early and late SSIs are more thoroughly examined in Chapter 23.

Adding On: The goals of surgery for progressive AIS curves include arthrodesis of the main structural curves. In certain instances, surgeons may opt to exclude proximal and distal compensatory curves that are flexible and have minimal rotation and minimal disk space angulation. The topic of appropriate level selection is controversial and has been extensively debated ^{61 , 62 , 63 , 64} and is more fully addressed in other sections of this book. In certain instances, there can be progression or extension of the primary coronal curve angle after fusion below the lowest instrumented vertebra (LIV). This phenomenon, known as adding on, may ultimately lead to coronal decompensation, disk wedging, failure of instrumentation, and the need for revision surgery. Adding on can be defined by the following: (1) increased coronal curve angle angle of at least 5 degrees and destabilization of the end vertebra or (2) a change in disk angulation of ≥5 degrees below the LIV from the first erect scoliosis film to the 2-year follow-up radiograph. ^{65 , 66 , 67 , 68} The impact of adding on to patients’ health-related quality of life is unclear. ⁶⁹

The cause of adding on is also unclear. Significant risk factors include skeletal immaturity and selection of a LIV that is overly rotated or deviated from the central sacral vertical line (CSVL). The risk is heightened in selective thoracic fusions that attempt to maintain maximal motion segments. It is expected that compensatory curves distal to the main curve will spontaneously correct after selective thoracic fusions; however, if the instrumentation is too short distally to maintain spontaneous correction of the distal curve, there will be a tendency for the curve to decompensate. ⁶⁵ Certain curve types, such as the Lenke 1A-R curve type described by Miyanji et al, ⁷⁰ are more likely to experience adding on after shorter fusion constructs (Fig. 24‑2).

Proximal Junctional Kyphosis PJK/Distal Junctional Kyphosis: Proximal junctional kyphosis (PJK) and distal junctional kyphosis (DJK) are postoperative radiographic changes to the vertebrae cephalad and caudal to a long segment instrumented spinal segment. Various authors have provided different diagnostic criteria for PJK. ^{71 , 72 , 73} Whereas there is no consensus on the precise definition of PJK, the most frequently used definition is greater than 10 degrees of angulation between the lower endplate of the upper instrumented vertebra (UIV) and the upper endplate of the two supra-adjacent vertebrae. Despite the radiographic appearance, there does not appear to be a correlation between the radiographic development of PJK and clinical outcomes in the pediatric patient population. ⁷⁴

The surgical technique appears critical to minimizing PJK. As the posterior ligamentous complex acts to constrain flexion motions, loss of this tension band has been shown to lead to increased forward angulation. ⁷⁵ Naturally, several studies have identified the posterior approach as being a risk factor for the development of PJK. ⁷⁶ Combined anteroposterior surgery has also been found to be a high-risk factor for developing PJK. ⁷⁷ Because posterior approaches are now the preferred technique for addressing AIS, most patients undergoing deformity correction are at risk for this complication. As instrumentation has evolved from less stiff hook and wire constructs to more rigid constructs that incorporate a preponderance of pedicle screws, pelvic fixation, and stiff metals such as cobalt chrome, PJK has become more prevalent. Most surgeons advocate preserving the proximal soft-tissue structures including the interspinous ligament and the joint capsules at the vertebrae adjacent to the UIV. In some instances, surgeons have advocated placing the upper levels of instrumentation in a percutaneous fashion to avoid disrupting the soft-tissue tension band. The creation of less stiff constructs proximally may create a so-called soft landing, diminishing the transition from the flexible uninstrumented spine to the stiff instrumented portion. This has been achieved using different methods, including the use of transverse process hooks proximally instead of pedicle screws, ^{73 , 78} the use of transition rods proximally, ⁷⁹ prophylactic vertebral cement augmentation at the rostral adjacent vertebra, ⁸⁰ and the use of Mersilene tape, rib anchors, and sublaminar bands to create semi-rigid fixation at the proximal intervening levels adjacent to a rigid construct. ^{81 , 82}

In addition to these techniques to minimize PJK, surgeons must be aware of the global spinal parameters and tailor surgical correction of thoracic kyphosis and lumbar lordosis accordingly. Ensuring a match between the pelvic incidence, lumbar lordosis, and thoracic kyphosis may ensure physiologic biomechanical loading and stress throughout the spine, preventing compensatory mechanisms that advance the expected rate of spinal degeneration. Maintenance or induction of kyphosis in typically lordotic AIS curves appears to diminish PJK. ⁸³ Patient-specific risk factors including increasing BMI and poor bone quality may also contribute to PJK. Fig. 24‑3 ⁷²

Crankshaft: The crankshaft phenomenon was first described by Dubousset et al. ⁸⁴ This occurs when rigid posterior spinal fixation in a skeletally immature patient tethers the posterior column, while allowing continued growth of the anterior column. Subsequently, patients develop axial deformity and may go on to develop spinal imbalance through rotation and lateral deviation. This is defined radiographically by a coronal curve angle greater than 10 degrees, a rib vertebral angle difference (RVAD) of greater than 10 degrees, and an apical vertebral rotation (AVR) greater than 5 degrees. ⁸⁵ Crankshafting may occur in either the thoracic or the lumbar spine, though it may be more prevalent in the lumbar spine in boys due to continued growth throughout the late teenage years. ⁸⁶

Fortunately, crankshaft represents an uncommon complication within the AIS population. As this complication occurs most frequently in skeletally immature patients, it is seen more commonly in patients with early-onset scoliosis. Surgeons should be particularly wary of the crankshaft in AIS patients with open triradiate cartilages. ⁸⁷ It is unlikely to occur after the closure of the triradiate cartilages, which generally indicates that the peak height growth velocity has passed. ⁸⁸

The incidence of the crankshaft has decreased with the advent of three-column transpedicular fixation. ^{89 , 90} Though crankshafting occurs less frequently in all pedicle screw constructs, further measures to control the anterior column such as anterior epiphysiodesis or anteroposterior surgery may be indicated in patients who have significant growth potential. ⁸⁷ Subsequent surgical correction of patients with crankshaft may ultimately require a three-stage procedure with posterior osteotomies, an anterior release and interbody fusion, followed by a final posterior re-instrumentation and refusion. ⁸⁴ Adding on, PJK, DJK, and crankshafting are explored in more detail in Chapter 22.

Persistent Back Pain: There is a relative paucity of literature examining the long-term impact of AIS surgery on back pain. ⁹¹ Despite AIS being considered a “painless” deformity, the incidence of preoperative back pain in patients with AIS may be as high as 50%. ^{91 , 92 , 93} The presence of preoperative back pain is correlated with subsequent disability and morbidity postoperatively, as well as an increased rate of both early and late readmission after surgery for AIS. ⁹⁴ Preoperative pain may also be associated with increased BMI, increasing degree of deformity, and older age. ⁹⁵ A recent retrospective study by Chan et al ⁹⁶ showed that pain, not degree of correction, is the most pressing concern for patients and families prior to deformity correction in AIS.

Danielsson et al ⁹⁷ examined the long-term outcomes with regard to pain in patients with AIS who were treated between 1968 and 1977 who had at least 20-year follow-up after treatment. In a case-control study, they found no significant difference in pain or dysfunction 23 years after follow-up between patients undergoing fusion for AIS compared to control patients without scoliosis. Overall, they noted that reduced spinal mobility was correlated with higher pain intensity, a larger extension of lumbar back pain, and extension of pain all over the body. Yet they noted only weak correlations between back pain and either braced or surgically treated AIS. Significant changes in degenerative disk disease, disk height reduction, and endplate changes in the lowest unfused disk of patients with fusions for AIS have been noted compared to control groups in long-term radiographic studies, though the clinical significance of this is unclear. ⁹⁸