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A Prospective, Nonrandomized, Multicenter Evaluation of Extreme Lateral Interbody Fusion for the Treatment of Adult Degenerative Scoliosis: Perioperative Outcomes and Complications

Isaacs, Robert E., MD*; Hyde, Jonathan, MD; Goodrich, J. Allan, MD; Rodgers, William Blake, MD§; Phillips, Frank M., MD

Author Information
doi: 10.1097/BRS.0b013e3182022e04
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Surgical treatment of adult scoliosis refractory to nonoperative treatments represents a challenge to surgeons. Several surgical options are available depending on the patient's symptoms, degree, and type of deformity encountered. Decompression alone may be indicated for patients with mild scoliosis and minimal segmental instability; however, this approach can result in iatrogenic instability1 and deformity progression.2 Decompression and instrumented arthrodesis are usually required when treating more advanced spinal deformity often with coronal and sagittal plane imbalance.2–5 In addition to posterior segmental instrumentation, the use of interbody fusion via either an anterior or posterior approach may facilitate deformity correction and enhance fusion rates.6–8 These instrumented arthrodesis procedures for the treatment of degenerative scoliosis have traditionally been associated with significant risk of complications, long operative times, high blood loss, and extended hospitalizations.9–10 Overall major complication rates for these procedures, including neurologic deficit, infection, thromboembolism, and death, can exceed 30%.9,11,12

In recent years, a minimally disruptive lateral transpsoas retroperitoneal technique to accomplish interbody fusion has been developed as an alternative approach to avoid the potential morbidities of traditional open surgery.13 The extreme lateral interbody fusion (XLIF) technique minimizes blood loss and allows for early patient mobilization,14–16 benefits which are particularly advantageous when addressing the older age group affected by degenerative scoliosis. To date, no multicenter large series using a minimally invasive approach in the treatment of adult scoliotic deformity has been published.

The current study was designed to prospectively evaluate perioperative complications of a minimally invasive lateral approach to treat adult degenerative scoliosis in a multicenter cohort. This report discusses initial perioperative findings, specifically the rate and type of complications encountered in a large group of patients undergoing a minimally disruptive lateral approach to interbody fusion (XLIF) in the treatment of adult deformity.

Methods

A multicenter prospective nonrandomized observational study was undertaken. Each of 14 participating study sites received institutional review board approval before patient enrollment. All patients who met inclusion criteria were consented to participate in the study and underwent an XLIF procedure as described by Pimenta and coworkers13,15 at one or more levels using dynamic real-time neural monitoring. Surgeon–investigators were not restricted by the protocol in the number of levels treated, side of approach, method or extent of supplemental internal fixation, bone graft material, or adjunctive procedures performed (e.g., inclusion of L5–S1, additional direct posterior decompression). Although an XLIF was required in the treatment of these cases, the addition of supplemental instrumentation (anterior, lateral, or posterior), the use of direct decompression, the addition of a posterior approach (using either open or minimally invasive techniques), and the inclusion of L5–S1 was left to the choice of the surgeon. Figures 1 to 3 show some characteristic examples of procedures performed in this study.

Figure 1
Figure 1:
Example of a stand-alone procedure: T11–L5 XLIF without instrumentation. The patient is 65-year-old woman with a severe stenosis at L3–L4 and L4–L5, neurogenic claudication, and back pain. Preoperative AP plain films (A) reveal degenerative scoliosis, lateral listhesis at L3–L4 and L2–L3, and a low grade anterolisthesis is seen at L2–L3 and L4–L5 on the lateral views. Note that the top of L5 is horizontal on the plain films and above the iliac crest allowing for easy access to the L4–L5 disc space from either side. Intraoperative AP imaging (B) shows radiographic segmental correction of the rotational deformity before proceeding with a lateral minimally invasive approach to the spine (done by rotating the bed rather than the imaging source). We also chose to approach the spine from the concavity of the curve (left lateral decubitus position), as is our norm. Image (C) shows the marking of the posterior aspect of the incision at the disc space of L3–L4, displaying a perfectly flat end plate view, again accomplished through patient positioning. We generally use one incision per 3 lumbar levels (or 2 thoracic) centered at the middle disc space. AP images (D) taken at 1 year postoperative visit showing the final construct.
Figure 2
Figure 2:
Example of a staged MIS anterior/open posterior case: Staged multilevel XLIF (L2–L3, L3–L4, L4–L5) followed by open posterior instrumentation and fusion T10-ilium. The Patient is a 65-year-old woman with a known history of osteoporosis and progressive neurological deterioration with bilateral L4–S1 distribution lower extremity weakness and severe lumbar canal stenosis. Preoperative AP and lateral plain films (A, B) reveal a degenerative scoliosis slightly decompensated to the left with adequate sagittal balance. Note that the asymmetric collapse at L4–L5 influences the approach side of the XLIF, as both the L3–L4 and L4–L5 disc spaces would not be able to be approached from the left-hand side without risking the integrity of the endplates. Plain films taken between stages (C, D) show height restoration in the lumbar disc spaces and a slight improvement of the spondylolisthesis at L4–L5. Images taken at her 1-year postoperative visit (E, F) show the final construct after her open posterior decompression and fusion.
Figure 3
Figure 3:
Example of a staged all MIS anterior/posterior case: Staged multilevel XLIF (L2–L3, L3–L4, L4–L5) followed by MIS posterior instrumentation and fusion L2–S1, with an MIS-TLIF performed at L5–S1. The patient is a 65-year-old woman with an L5 radiculopathy with motor weakness on the left hand side. Preoperative AP and lateral plain films (A, B) reveal a degenerative scoliosis with a lateral and anterolisthesis at L4–L5, as well as severe asymmetric collapse causing foraminal stenosis at L5–S1 on the left. Adequate decompression of the L5 nerve root necessitated addressing both potential causes of her radiculopathy. Plain films taken 1 year postoperatively (C, D) show the construct spanning the symptomatic region of her deformity. Computed tomography images from the same time point (E, F) show a solid interbody fusion at all instrumented levels.

Subjects

A total of 107 patients were enrolled. The included patients met the following criteria: at least 45 years of age, diagnosed with adult thoracolumbar scoliosis including any number of intervertebral levels between T8 and S1, unresponsive to conservative treatment for at least 6 months, and had a preoperative coronal Cobb angle of at least 10° and preoperative ODI score of at least 30%. Patients with prior lumbar fusion surgery or spondylolisthesis greater than Grade II were excluded.

Procedures

Pretreatment data collection included patient demographic information, symptoms, health history, physical examination including neurologic assessment, and baseline patient-reported outcomes as recorded on health-related quality of life questionnaires. Intraoperative data collection included operative time, estimated blood loss (EBL), level(s) treated, type and extent of fixation instrumentation, any adjunctive procedures performed, and surgical complications. In the perioperative period, postoperative complications, length of hospital stay, and postoperative neurologic status were recorded. Longitudinally, late-occurring complications, patient-reported clinical outcomes scores, and patient satisfaction were collected. Plain-film, dynamic, and long-standing radiographs were taken at preoperative, postoperative, and all follow-up visits. This report focuses on perioperative complications reported through the 6-week postsurgical follow-up clinic appointment.

Complications were reported by site research personnel as they occurred, and were summarized and reviewed by an independent physician unrelated to the study. Defined as events that required treatment or intervention, complications were classified as medical or surgical and major or minor, and further categorized by system. In addition, new postoperative motor and sensory deficits identified by physical examination were also evaluated as complications. Transient proximal weakness in the lower extremity after multiple passes through the psoas muscle should be expected to occur in many patients undergoing this procedure, which, for the most part, represents direct muscle trauma to the iliopsoas. In the majority of cases, this is muscular in etiology. When the weakness was limited (both in time and significance), it was judged as muscular; if more protracted (any weakness not fully resolved by the 6 month examination) or more significant (decreased by more than 2 motor grades at any point in time), it was judged as a major surgical complication regardless of the assumed etiology. Similarly, significant or long-lasting sensory deficits were included as minor surgical complications.

Statistical Analysis

Multivariate logistic regression analysis was performed to test whether demographic or surgical parameters were interdependently associated with the incidence of complications. χ2 tests, t tests, and analysis of variance were used where appropriate to assess differences between those with complications and those without. All analyses were performed using Analyze-It software (Analyze-It, Ltd, Leeds, England) with a significance level of 0.05.

Results

Demographics

Average age at the time of surgery was 68.4 years (range, 45–87); 72.9% of the patients were female. Average body mass index was 28.4 (range, 16.1–42.4). The average preoperative coronal Cobb angle was 24.3°. All patients were symptomatic with 15.4% reporting solely back pain, 1.9% reporting isolated radicular pain, and 82.7% reporting combined back and leg pain. The majority of patients (60.7%) also complained of neurologic deficits with 23.1% reporting sensory deficits, 9.2% reporting motor deficits, and 67.7% reporting combined motor and sensory deficits. The vast majority of patients (78%) reported having symptoms for greater than 2 years. A substantial portion of the patient population (28.3%) presented with at least one comorbidity before surgery. The average Charlson et al17 comorbidity score was 1.7. Of all enrolled patients, 21.5% were diagnosed with osteoporosis and 10.6% reported being smokers.

Procedural Data

A total of 451 levels were treated, including combinations of both interbody (344 levels: 322 XLIF, 22 other approaches at L5–S1) and/or supplemental internal fixation procedures (363 levels). An average of 4.4 levels were treated per patient (range, 1–9) (Figure 4). The most frequent levels treated with XLIF were L3–L4 (28.8% of all levels; 92.5% of all patients), L4–L5 (25.9%; 83.2%), and L2–L3 (25.6%; 82.2%). Figure 5 illustrates the frequency at which each interbody level was treated. The 20.5% of cases (22/107) that included L5–S1 were all done using interbody techniques, either from a direct anterior approach (9), AxiLIF (4), or a posterior interbody approach (9). Most cases included supplemental fixation: 75.7% used posterior pedicle screws (64.2% placed using minimal access surgical techniques; 35.8% using standard open techniques), 5.6% used lateral fixation in combination with the XLIF approach, and 18.7% were completed standalone. Whereas the majority of patients underwent only 1 procedure or a same day combined procedure, XLIF and posterior fusion procedures were staged in 16.5% of the patients. Additionally, 32.7% of procedures included direct posterior decompression.

Figure 4
Figure 4:
Frequency of number of levels treated with XLIF per case.
Figure 5
Figure 5:
Percentage of cases that included each level. Note that while L3–L4 was the most commonly treated level, most procedures included L2–L3, L3–L4, and L4–L5. None of the cases at L5–S1 was an XLIF.

Mean operative time was 177.9 minutes (range, 43–458 minutes) per surgery and 57.9 minutes per interbody fusion level. Almost two-thirds (62.5%) of patients had a recorded EBL of <100 mL, and only 9 patients (8.4%) had >300 mL EBL (Figure 6). Mean length of hospital stay was 2.9 days for unstaged procedures (median, 2), 8.1 day for staged procedures (median, 8), and 3.8 days overall.

Figure 6
Figure 6:
Frequency of levels of estimated blood loss (mL) per case.

Complications

Overall, 5 patients (4.7%) received a transfusion, 1 (0.9%) required in-patient rehabilitation services, and 3 (2.8%) required an intensive care unit (ICU) stay. The ICU stays were associated with 1 episode of atrial fibrillation accompanied by pulmonary hypertension, 1 kidney laceration, and 1 case of sepsis secondary to urinary tract infection. There were 3 early reoperations (2.8%), all for deep wound infections associated with open posterior instrumentation procedures. Further, 1 patient required a stent placement following a myocardial infarction during the perioperative period.

Rates of complication, categorized by major and minor, as well as medical and surgical are summarized in Table 1. Of the 107 patient cohort, 13 (12.1%) individuals experienced 14 major complications; 2 (1.9%) of the complications were major medical, 12 (11.2%) were major surgical. In total, there were 21 surgical complications in 16 patients, 12 of which were major. There were 16 medical complications in 11 patients, 2 of which were major. Specifics of each type of complication are listed in Table 2. There was 1 reported myocardial infarction, 1 reported deep vein thrombosis, and 1 case of pneumonia that required antibiotics. There were no reports of stroke or pulmonary embolism. There were no deaths.

Table 1
Table 1:
Rates and Categorization of Complications
Table 2
Table 2:
Complications in 107 Patients

Of the 36 patients (33.6%) with some evidence of weakness after surgery, 29 (80.6% of those with weakness) had isolated proximal lower extremity (hip) weakness felt to be related to passage of retractors through the psoas muscle to access the spine. In the majority of these patients (86.2%), as expected, this weakness was transient. This was statistically correlated only to length of surgery (P = 0.03) but not any other factor, including inclusion of any particular level (L4–L5, P = 0.70) or number of levels treated (P = 0.21). Of all patients with weakness at any time after surgery, 77.8% (28/36; 26% of all 107 patients in this series) were graded as a single motor grade decrease, 2 grades in 16.7% (6/36) (5.6% of patients), and >2 grades in 5.6% (2/36) (1.9% of patients). In total, 6.5% (7/107) had weakness that either did not resolve by the 6-month visit or was decreased by more than 2 grades at any point, and were therefore included as major surgical complications. All of those with 2 grades of weakness resolved fully (83% by the 3-month examination). By the 6-week, 3-month, and 6-month examinations, 32.1%, 60.7%, and 82.1%, respectively, of those with 1 grade of weakness initially had fully resolved. Only 1 patient had a major (1/5) weakness of the proximal muscles of the lower extremity that could be attributable to a lumbar plexus injury (0.9% of cases, or 0.3% of levels approached) and this improved to 4/5 by the 6-month visit. There was no statistical correlation for the 7 cases of protracted or severe weakness to any factor evaluated, including operative time (P = 0.10), number of levels treated (P = 0.25), type of fixation (open or MIS) (P = 0.49), use of lateral plating (P = 0.32), addition of a primary decompression (P = 0.41), or XLIF at the level of L4–L5 (P = 0.19). Included in these results, 2 patients had new onset of distal lower extremity weakness noted only after a staged posterior fusion procedure. Details of these neurologic outcomes are listed in Table 3.

Table 3
Table 3:
Detailed Description of Change in Postoperative Motor Exam for all Patients With any Documented Weakness (Muscular or Neural) During the Perioperative Period

The presence of at least 1 comorbidity affects the incidence of major complications (P = 0.0291). Of procedures involving only minimally invasive techniques (XLIF stand-alone or with lateral or percutaneous posterior instrumentation), 19.2% (15/78) experienced one or more complications; 9.0% (7/78) were major. In patients who underwent XLIF with open posterior instrumentation, 37.9% (11/29) experienced one or more complications; 20.7% (6/29) were major. Between those with entirely minimally invasive procedures and those with open posterior instrumentation, the incidence of having any complication (19.2% vs. 37.9%) was significantly different (P = 0.0450).

The incidence of having any complication was significantly higher in those with open posterior fixation (27.9%) than those with percutaneous posterior fixation (15.4%) (P = 0.0217). Similarly, the incidence of major complications specifically was higher in those with open posterior fixation (20.7% vs. 5.8%, P = 0.0405). All reoperations and deep wound infections were associated with open posterior instrumentation procedures.

The strongest independent predictor of complications was the total number of levels operated per patient (P = 0.0004). Logistic regression showed neither demographic parameters (age, gender, body mass index, preexisting comorbidities, and severity of preoperative deformity) nor other surgical factors (inclusion of specific levels, additional posterior decompression, type of fixation) were statistically significant when evaluated alongside number of operative levels. Logistic regression suggests that for each additional level treated there is approximately a 59% increase in complication rate (odds ratio, 1.59; P = 0.0105).

Discussion

With the aging of the population, the frequency of spine surgery in the elderly population is increasing.18 However, the incidence of medical comorbidities increases with age, as does prevalence of spinal deformity.18,19 Although the clinical results of surgery to address spinal deformity in the elderly patients are laudable,9,20 perioperative complication rates are high,9,10,21,22 and there is a small but definite risk of mortality.23 These factors have provided impetus to the desire to address spinal deformity in the elderly patient using minimally disruptive techniques.

In a large series of patients >65 years of age undergoing spinal fusion,24 of 98 patients 2 (2%) died in the initial perioperative period. In Daub's series of 46 patients >60 years of age undergoing adult deformity surgery,9 1 patient (2.2%) died because of complications related to perioperative paraplegia. Deyo et al25 noted that in the entire Medicare population undergoing surgery for stenosis, mortality was directly related to age, with more than 1% incidence of mortality in patients aged >70 years. In the current 107 patient series, 88 (82.2%) of whom were >60 years of age and 49 of whom (45.8%) were >70, it should be noted that no patient died in the perioperative period.

It would seem intuitive that patients undergoing surgery for spinal deformity in this age group are predisposed to having higher complication rates, because of both age and medical comorbidities. Surprisingly, there are conflicting data as to whether incidence of complications in spinal arthrodesis in the elderly patients is increased with presence of preoperative medical comorbidities.9,19,24,25 Increasing age has been shown to correlate with surgical complications,9,19 as has the surgical approach chosen.21–23 In the current study, the extent of surgery (number of levels operated) was a strong predictor of complications, independent of age, or incidence of comorbidities. Furthermore, patients undergoing a strictly minimally disruptive approach had fewer major complications in the perioperative period than those undergoing supplemental open posterior fusion (9.0% vs. 20.7%).

XLIF implies an anterior interbody arthrodesis, albeit performed via lateral access to the spine. The traditional direct anterior approach to the spine is associated with a higher incidence of vascular injury because of mobilization of thoracoabdominal vasculature. In Daub's series of patients undergoing an anterior interbody arthrodesis as part of the surgical treatment of degenerative scoliosis, a 10.9% incidence of major vascular complications (iliac vein tears) was reported.9 The XLIF technique circumvents the need to manipulate the great vessels and consequently minimizes the risk of vascular injuries, as demonstrated by the 0% vascular complication rate in the current series.

Further, incidence of symptomatic pulmonary embolus (PE) appears lower in this series than has been reported. In the study of Pateder et al, a series of patients undergoing fusions for adult deformity reported an overall incidence of 2.4%, with almost all (90%) of their PEs seen in patients undergoing an anterior approach.23 The frequency of PE differed in their series based on approach, with anterior alone (4.5%), same day anterior-posterior (AP) (2.4%), or staged AP (5.8%) all exceeding the posterior-alone group. Crandall and Revella reported an incidence of nonfatal PE of 5% (2/40) in a comparative series of anterior lumbar interbody fusion and transforaminal lumbar interbody fusion (TLIF) procedures for adult scoliosis.26 Again one should note that with the XLIF procedure, thoracoabdominal vasculature is not mobilized, which may very well account for the absence of PE in the current series and only 1 documented deep venous thrombosis, despite all patients having an anterior interbody arthrodesis.

Incidence of major neurologic injury after deformity surgery in Pateder's series of >400 surgical procedures (a combination of anterior, posterior, and anterior/posterior approaches) averaged 2.9% and was related to the number of levels addressed, primary versus revision surgery, and surgical approach.21 Incidence of nerve root palsy for same day AP and staged AP surgery was higher than posterior-only surgery, averaging 3%, 7.2%, and 1.3%, respectively. Crandall and Revella reported a 2.5% incidence of transient foot drop.26 In the current study, apart from the mild transient hip flexion weakness related to the transpsoas approach, significant transient lower limb motor weakness or weakness which persisted more than a few months was seen in 6.5% of cases and, as Pateder and Kostuik21 found, was much more common in AP surgeries. We believe that it is important to counsel patients before undergoing XLIF that it is not uncommon to experience mild, transient weakness in the upper thigh; however, significant and/or persistent weakness is uncommon. In this cohort, only 1 patient was affected with more profound weakness of lumbar plexus origin and the strength improved to 4/5 by the 6-month follow-up visit. This makes the rate of lumbar plexus injury rare in these procedures (0.3% per level approached). It is important to note that the XLIF procedure involves the use of integrated neural monitoring with all instruments that traverse the psoas muscle providing real-time neural feedback. The neurologic results from the current study should therefore not be generalized to lateral approach interbody fusion without the use of such neural monitoring.

Reoperation because of surgical complications tends to increase in frequency as more complex surgical procedures are required. In the Carreon series, reoperation rate was 5% in the initial 30 days after the initial surgery (4 for irrigation and debridement, 1 for instrumentation repositioning).24 Deep wound infections were reported at a rate of 7.5% by Crandall and Revella.26 It should be noted that 2.7% of all patients in the current study required reoperation to treat a posterior wound infection, and all of these patients had initial open approaches.

Although a majority of patients in this series presented with both neurogenic claudication and scoliosis, no patients treated with fusion-only procedures required subsequent unplanned direct posterior neural decompression. This would suggest that indirect neural decompression may be achieved on select patients by lateral interbody fusion with disc space distraction and stabilization of the involved motion segment.

The results of the current study show that in an older patient population with significant comorbidities, the minimally invasive XLIF procedure with or without posterior instrumentation to address degenerative scoliosis results in a complication profile that is substantially less than that reported in the literature in similar patients undergoing standard open surgery. This is consistent with other reports in the literature of a lower incidence of complications in patients undergoing minimally invasive procedures, including posterior procedures27–30 as well as anterior procedures.31–33 Blood loss and need for transfusion, which has been correlated to overall complication rate of spine surgery,24 is frequently radically different between the standard open approaches and the minimally invasive alternatives.27,28,34 In the current study, less than 200 mL of blood loss was encountered in >80% of patients, and the need for transfusions in 4.7% of cases is vastly different than what is typically reported with multilevel fusion surgery in the literature.35

Several minimally invasive studies have found a lower rate of infection in patients undergoing decompression and arthrodesis as compared to historic rates with open procedures.29,30,36 Rovner et al reported a 0% infection rate in 196 consecutive minimally invasive fusions compared with a 3.6% rate in 251 concomitant open surgical approaches.37 In the current series, a low infection rate was observed despite AP surgeries being performed in a majority of patients. Of note is that no infections were observed when XLIF was performed alone or combined with minimally invasive posterior instrumentation.

Many other complications are less likely when minimally invasive techniques are applied to spinal surgery; mortality appears to be lower, the length of time required in the ICU appears to lessen, hospitalization is shorter, and other approach-specific morbidities are reduced.27–33,36 In the current series, major medical complications were seen in only 2 patients (1.9%), only 3 patients required any type of ICU stay (2.8%), and only 1 patient required discharge to a rehabilitation facility (0.9%). The data from the current study represent one of the largest prospective studies of degenerative scoliosis and the largest multicenter study of minimally invasive techniques applied to this disorder. In that vein, the major complication rate seen in this study (12.1%) compares very favorably to that seen in other studies of degenerative deformity, which ranges from 20% to 66%,9,10 as well as fusion for degenerative disease in the elderly overall (21%).24

Conclusion

Perioperative morbidity of adult deformity surgery can be minimized through the use of less invasive techniques, as demonstrated by the minimal blood loss, short hospitalization, low rates of ICU usage, infection, transfusion, reoperation, and major complication rates found in this multicenter study of XLIF in adult scoliosis. Further reports on the long-term clinical and radiographic effectiveness are forthcoming; however, this report demonstrates the initial safety of the minimally disruptive lateral approach for deformity surgery.

Key Points

  • This report demonstrates the initial safety of the minimally disruptive lateral approach (XLIF) for the treatment of adult scoliosis in a large patient cohort.
  • The XLIF approach to anterior column reconstruction results in less blood loss, shorter hospital stays, fewer infections, transfusions, early reoperations, and perioperative complications than reported for traditional open procedures in the treatment of adult scoliosis.
  • Morbidity and complication rate increased with the number of levels treated and with the use of open posterior instrumentation.

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Keywords:

XLIF; minimially disruptive; degenerative scoliosis; de novo scoliosis; complications

© 2010 Lippincott Williams & Wilkins, Inc.