22.1 Introduction

Surgical correction of neuromuscular spinal deformity has historically been associated with higher rates of perioperative and postoperative complications than correction of idiopathic spinal deformity. A number of factors contribute to this disparity, including such host factors as nutritional status, continence, and bone quality, as well as structural factors related to the severity and flexibility of the curve. This combination of fragile hosts with more severe deformities demands careful preoperative planning and medical optimization to ensure the success of any surgical intervention. With a comprehensive multidisciplinary approach to perioperative care, rates of complications continue to improve over time, but additional efforts will be required in order to approach the more predictable outcomes following idiopathic deformity correction or degenerative spinal procedures.

Early reports of rates of complications associated with surgery for neuromuscular scoliosis have been as high as 63% overall ¹ (Table 22‑1). While more recent series have demonstrated substantial improvements, certain high-risk groups have been identified. Banit et al reported a persistent 48% overall complication rate in 50 patients with myelomeningocele. ² In a series of 110 consecutive neuromuscular deformity corrections, Duckworth et al reported a 38.5% rate in the 26 patients with muscular dystrophy. ³ Master et al in their series of 131 patients (75 with cerebral palsy [CP]) identified nonambulatory status and curve magnitude greater than 60 degrees as significant risk factors for major complications, which occurred in 28% of patients. ⁴ These rates are in contrast to the 16.7% overall rate for the overall Duckworth et al cohort. This latter rate is largely consistent with the 17.9% rate of overall complications observed by Reames et al in their analysis of 4,657 neuromuscular procedures in the Scoliosis Research Society’s morbidity and mortality database. ⁵

Perioperative complications in neuromuscular deformity correction may contribute to the relatively high in-hospital mortality rate in this patient population. An analysis of the U.S. national inpatient sample by Barsdorf et al also revealed an in-hospital mortality rate of 1.2% for 437 pediatric patients undergoing correction of neuromuscular spinal deformity as compared to 0.2% in pediatric patients with non-neuromuscular deformity. ⁶ A similar perioperative mortality rate of 1.0% was reported by Tsirikos et al in their series of 287 patients with CP undergoing both all-posterior and combined anteroposterior spinal deformity corrections. ⁷ It is important that providers, patients, and their families be aware of the rare but nontrivial risk of mortality surrounding neuromuscular deformity correction and that this information be included in the informed consent process for surgery.

We have subclassified complications by timing at presentation into (1) intraoperative, occurring during surgery, and (2) postoperative, occurring after surgery or as a consequence of decisions made during surgery. Admittedly, this classification is an oversimplification and is not meant to imply causality. For example, surgical site infection is multifactorial and may have components in both categories, but this has been included in the postoperative category due to its typically postoperative presentation. It is likely that many complications, both intraoperative and postoperative, may be mitigated by comprehensive preoperative medical optimization to the extent that this is feasible on a case-by-case basis.

22.2 Intraoperative Complications

Complications commonly encountered intraoperatively during neuromuscular spinal deformity correction include (1) poor bone quality or instrumentation failure, (2) incidental durotomy, (3) malfunction of intrathecal medication pumps or cerebrospinal fluid shunts, when present, (4) large intraoperative blood loss (defined here as >50% of a patient’s estimated blood volume), and (5) new neurologic deficits.

A number of factors contribute to the high prevalence of osteopenia encountered in neuromuscular diseases, including nutritional deficiencies, medication side effects, and low activity level or nonambulatory status. ^{8 ,​ 9} In particular, increasing use of corticosteroid therapy in the treatment of Duchenne’s muscular dystrophy, despite reducing the severity of spinal deformity and prolonging time to loss of ambulation, may result in worsening vertebral osteoporosis. ^{10 ,​ 11 ,​ 12} The potential gains in pulmonary function, time to loss of ambulatory capacity, and severity of spinal deformity must be weighed carefully against the risk of vertebral osteopenia that may increase the complexity of surgical correction. Despite the challenges inherent to instrumentation of the osteopenic spine, overall rates of reported implant-related complications with modern instrumentation remain relatively low. Sharma et al in their meta-analysis of complications in neuromuscular spinal deformity surgery found a combined rate of intraoperative and postoperative implant-related complications of 12.5%, with rates of malplacement and cutout/pullout/migration of 4.8 and 2.8%, respectively. ¹³ While there is little literature specifically reporting intraoperative rates of screw malposition, pedicle fracture, or cutout during deformity correction, such reports are likely to underestimate the true incidence as corrective measures may be taken when these occurrences are recognized intraoperatively.

While uncommon, incidental durotomy remains an undesirable complication in this group of patients at high risk for infection and often with preexisting disturbances in cerebrospinal fluid circulation. In their analysis of the Scoliosis Research Society morbidity and mortality database, Williams et al reported 5,191 neuromuscular deformity cases with a 1% rate of incidental durotomy. ¹⁴ This compares favorably to the 1.6% overall rate and the 2.2% rate seen in degenerative spinal deformity correction. While the overall incidence is relatively low, there are a number of patient-specific factors that may increase the risk of incidental durotomy in patients with neuromuscular scoliosis. Preoperative imaging must be carefully reviewed for the presence of dural ectasia that may contribute to the risk of inadvertent dural injury. Patients with myelomeningocele present additional challenges as disturbances in cerebrospinal fluid flow and even neurologic deterioration have been reported in the setting of deformity correction. ¹⁵ Untethering of the cord has been advocated prior to deformity correction to minimize these risks, though one recent series suggests that this may not be required in otherwise asymptomatic patients. ¹⁶ In addition, the presence of laminotomies for intrathecal pump placement may increase the potential for inadvertent canal penetration, and dislodgement of the pump catheter itself may also result in persistent cerebrospinal fluid leakage. ¹⁷

Many patients with spastic CP have intrathecal catheters in place. The local delivery of intrathecal baclofen reduces the dose required to decrease spasticity compared to oral baclofen, thus decreasing undesirable side effects. ¹⁸ Gerszten et al reported on the effect of baclofen in reducing the occurrence and postoperative recurrence of lower extremity contractures. ¹⁹ However, these catheters are frequently associated with scar tissue formation and are at risk of being damaged or dislodged during surgery. Caird et al reported a matched series of patients with spastic CP with and without baclofen pumps. ¹⁷ Nine of 20 patients (45%) experienced complications related to their pumps, including 3 patients who had their catheters inadvertently damaged or pulled out intraoperatively. More recently, Yaszay et al have reported equivalent surgical time, blood loss, curve correction, and rates of wound complications in groups with and without baclofen pumps in place preoperatively. ²⁰ It is possible that greater awareness and familiarity with the perioperative management of such pumps over time may reduce the complications associated with their use.

Neuromuscular spinal deformity correction has been associated with greater overall estimated blood loss than idiopathic deformity correction. While not necessarily a complication when accompanied by appropriate resuscitation, increasing blood loss may increase the likelihood of developing life-threatening coagulopathy. ⁴ Edler et al performed a retrospective comparison of 18 patients with neuromuscular spinal deformity to 145 patients with non-neuromuscular (congenital or idiopathic) deformity. ²¹ The authors found that over 65% of the neuromuscular patients experienced a total blood loss of greater than 50% of their estimated blood volume (EBV). After statistically adjusting for total number of levels fused, neuromuscular patients had an almost seven times higher risk (adjusted odds ratio of 6.9; p < 0.05) of losing greater than 50% of their EBV when compared to patients with non-neuromuscular scoliosis. Modi et al, in their series of 27 patients undergoing all-posterior corrections of flaccid myopathic spinal deformities, reported a mean estimated blood loss of 123% of the EBV, with 85% of patients experiencing blood loss of greater than 50% of their EBV. ²² Several factors may contribute to the predisposition toward increased blood loss seen in the neuromuscular population, including nutritional status, smaller body habitus, ²³ and disease-specific factors such as inherent clotting dysfunction observed in CP. ²⁴ In addition, certain antiseizure medications, especially valproic acid, have been associated with increased blood loss despite otherwise normal coagulation testing. ²⁵ Consideration should be given to bridging with alternative antiepileptic medications perioperatively, whenever feasible per the patient’s neurologist.

Neurologic injury is a potentially devastating complication in an already impaired host. Loss of bladder control and protective sensation can compound the risk of decubiti in nonambulatory patients. Fortunately, neurologic injury is relatively rare and is becoming even more rare with the development of better neuromonitoring techniques and the trend away from implants that occupy the spinal canal such as sublaminar wires and laminar hooks. Tsirikos et al reported only one possible neurologic injury in their series of 287 patients with CP. ⁷ In their analysis of the Scoliosis Research Society’s morbidity and mortality database, Hamilton et al found a 1.03% rate of new neurologic deficit following 5,147 cases of neuromuscular deformity correction in adult and pediatric patients. ²⁶ These rates are similar to the 1.0% overall rate for all reported spinal procedures, and compare favorably to the 2.49% rate seen with adult degenerative deformity correction. With the exception of patients with complete spinal cord injuries, intraoperative neurophysiologic monitoring is often feasible. Ashkenaze et al reported that they were able to obtain somatosensory evoked potential (SSEP) signals reliably in 72% of their neuromuscular patients. ²⁷ Subsequent series have confirmed the feasibility and utility of SSEP monitoring in the neuromuscular population. ^{28 ,​ 29} Some surgeons consider motor evoked potential (MEP) monitoring to be contraindicated in patients with shunts and/or a history of seizures. However, Schwartz et al reported no difficulties or complications in a series of 30 patients with neuromuscular scoliosis undergoing fusion who had a seizure history and intraoperative MEP monitoring. ³⁰

Cerebrospinal fluid shunts are common in patients with CP and myelomeningocele. As these shunts are often gravity dependent, prolonged periods of time intraoperatively and postoperatively in a prone or supine position may lead to shunt malfunction. Preoperative evaluation by the patient’s neurosurgeon is advised. In rare cases, it may be necessary to perform intraoperative intracranial pressure monitoring and periodic intraoperative decompression via removal of cerebrospinal fluid through the cranial shunt portal. While rates of shunt failure have not been examined in large series, this complication has been reported in the literature and requires vigilance on the part of the surgical and anesthesia teams. ³¹