Management of sagittal balance in adult spinal deformity with minimally invasive anterolateral lumbar interbody fusion: a preliminary radiographic study

Clinical article

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Object

Minimally invasive (MI) fusion and instrumentation techniques are playing a new role in the treatment of adult spinal deformity. The open pedicle subtraction osteotomy (PSO) and Smith-Petersen osteotomy (SPO) are proven segmental methods for improving regional lordosis and global sagittal parameters. Recently the MI anterior column release (ACR) was introduced as a segmental method for treating sagittal imbalance. There is a paucity of data in the literature evaluating the alternatives to PSO and SPO for sagittal balance correction.

Thus, the authors conducted a preliminary retrospective radiographic review of prospectively collected data from 2009 to 2012 at a single institution. The objectives of this study were to: 1) investigate the radiographic effect of MI-ACR on spinopelvic parameters, 2) compare the radiographic effect of MI-ACR with PSO and SPO for treatment of adult spinal deformity, and 3) investigate the radiographic effect of percutaneous posterior spinal instrumentation on spinopelvic parameters when combined with MI transpsoas lateral interbody fusion (LIF) for adult spinal deformity.

Methods:

Patient demographics and radiographic data were collected for 36 patients (9 patients who underwent MI-ACR and 27 patients who did not undergo MI-ACR). Patients included in the study were those who had undergone at least a 2-level MI-LIF procedure; adequate preoperative and postoperative 36-inch radiographs of the scoliotic curvature; a separate second-stage procedure for the placement of posterior spinal instrumentation; and a diagnosis of degenerative scoliosis (coronal Cobb angle > 10° and/or sagittal vertebral axis > 5 cm). Statistical analysis was performed for normality and significance testing.

Results

Percutaneous transpedicular spinal instrumentation did not significantly alter any of the spinopelvic parameters in either the ACR group or the non-ACR group. Lateral MI-LIF alone significantly improved coronal Cobb angle by 16°, and the fractional curve significantly improved in a subgroup treated with L5–S1 transforaminal lumbar interbody fusion. Fifteen ACRs were performed in 9 patients and resulted in significant coronal Cobb angle correction, lumbar lordosis correction of 16.5°, and sagittal vertebral axis correction of 4.8 cm per patient. Segmental analysis revealed a 12° gain in segmental lumbar lordosis and a 3.1-cm correction of the sagittal vertebral axis per ACR level treated.

Conclusions

The lateral MI-LIF with ACR has the ability to powerfully restore lumbar lordosis and correct sagittal imbalance. This segmental MI surgical technique boasts equivalence to SPO correction of these global radiographic parameters while simultaneously creating additional disc height and correcting coronal imbalance. Addition of posterior percutaneous instrumentation without in situ manipulation or overcorrection does not alter radiographic parameters when combined with the lateral MI-LIF.

Abbreviations used in this paper:ACR = anterior column release; ALIF = anterior lumbar interbody fusion; CSVL = central sacral vertebral line; LIF = lumbar interbody fusion; MI = minimally invasive; PSO = pedicle subtraction osteotomy; SPO = Smith-Petersen osteotomy; TLIF = transforaminal LIF.

Object

Minimally invasive (MI) fusion and instrumentation techniques are playing a new role in the treatment of adult spinal deformity. The open pedicle subtraction osteotomy (PSO) and Smith-Petersen osteotomy (SPO) are proven segmental methods for improving regional lordosis and global sagittal parameters. Recently the MI anterior column release (ACR) was introduced as a segmental method for treating sagittal imbalance. There is a paucity of data in the literature evaluating the alternatives to PSO and SPO for sagittal balance correction.

Thus, the authors conducted a preliminary retrospective radiographic review of prospectively collected data from 2009 to 2012 at a single institution. The objectives of this study were to: 1) investigate the radiographic effect of MI-ACR on spinopelvic parameters, 2) compare the radiographic effect of MI-ACR with PSO and SPO for treatment of adult spinal deformity, and 3) investigate the radiographic effect of percutaneous posterior spinal instrumentation on spinopelvic parameters when combined with MI transpsoas lateral interbody fusion (LIF) for adult spinal deformity.

Methods:

Patient demographics and radiographic data were collected for 36 patients (9 patients who underwent MI-ACR and 27 patients who did not undergo MI-ACR). Patients included in the study were those who had undergone at least a 2-level MI-LIF procedure; adequate preoperative and postoperative 36-inch radiographs of the scoliotic curvature; a separate second-stage procedure for the placement of posterior spinal instrumentation; and a diagnosis of degenerative scoliosis (coronal Cobb angle > 10° and/or sagittal vertebral axis > 5 cm). Statistical analysis was performed for normality and significance testing.

Results

Percutaneous transpedicular spinal instrumentation did not significantly alter any of the spinopelvic parameters in either the ACR group or the non-ACR group. Lateral MI-LIF alone significantly improved coronal Cobb angle by 16°, and the fractional curve significantly improved in a subgroup treated with L5–S1 transforaminal lumbar interbody fusion. Fifteen ACRs were performed in 9 patients and resulted in significant coronal Cobb angle correction, lumbar lordosis correction of 16.5°, and sagittal vertebral axis correction of 4.8 cm per patient. Segmental analysis revealed a 12° gain in segmental lumbar lordosis and a 3.1-cm correction of the sagittal vertebral axis per ACR level treated.

Conclusions

The lateral MI-LIF with ACR has the ability to powerfully restore lumbar lordosis and correct sagittal imbalance. This segmental MI surgical technique boasts equivalence to SPO correction of these global radiographic parameters while simultaneously creating additional disc height and correcting coronal imbalance. Addition of posterior percutaneous instrumentation without in situ manipulation or overcorrection does not alter radiographic parameters when combined with the lateral MI-LIF.

Minimally invasive (MI) fusion and instrumentation techniques are playing a larger role in the treatment of adult spinal deformity. Traditional open approaches have been the mainstay treatment for adult spinal deformity, though MI techniques are becoming increasingly popular.2,3,11,21,22,31,33 The MI lateral retroperitoneal transpsoas approach to spinal fusion has been heavily investigated in the past several years and has been used by multiple groups to augment their management strategies for adult spinal deformity and degenerative scoliosis.2,3,13,31,33 This technique has demonstrated improvement in coronal Cobb angle, segmental lumbar lordosis, and restoration of disc height.1,20 The MI lateral transpsoas technique alone has failed, however, to show a significant improvement in lumbar lordosis and sagittal vertebral axis.1 Dakwar found that in one-third of patients sagittal plane correction was not adequate after they had undergone lateral interbody fusion for adult degenerative scoliosis.13 Even though the use of lateral MI lumbar interbody fusion (LIF) for adult spinal deformity can improve some spinal parameters, more data are needed to determine its effect on sagittal balance, the radiographic measure critically linked to quality of life, function, and health status outcomes.16,25

Traditionally, the primary methods for correcting sagittal imbalance have been the pedicle subtraction osteotomy (PSO) and Smith-Petersen osteotomy (SPO).6–9,12 Recently, Deukmedjian et al. reported on the anatomical considerations in and several cases of MI anterior column release (ACR) as a means of correcting sagittal imbalance via a lateral MI-LIF approach.5,14 Open and endoscopic ACR is well established in the pediatric literature to augment sagittal deformity correction.4,24,28,29 However, the role of MI-ACR in adult spinal deformity and its influence on spinopelvic parameters warrant further investigation. The MI placement of posterior instrumentation is necessary when an ACR is performed and can be used to obtain further correction. However, the literature is unclear regarding the additive value of percutaneous posterior transpedicular instrumentation on spinopelvic parameters when combined with LIF.

In the present study our goals were as follows: 1) to describe the radiographic effect of ACR on spinopelvic parameters, 2) to compare the radiographic effect of ACR to PSO and SPO for treatment of adult spinal deformity, and 3) to describe the radiographic effect of posterior percutaneous transpedicular spinal instrumentation on spinopelvic parameters when combined with the transpsoas MI-LIF for adult spinal deformity.

Methods

Patient Population and Radiographic Measurements

We performed a retrospective review of collected data from 2009 to 2012 at a single institution. Patient demographics and radiographic characteristics are summarized in Table 1. A total of 36 patients were identified (9 patients who underwent ACR and 27 patients who did not undergo ACR) based on the following inclusion criteria: 1) diagnosis of degenerative scoliosis (coronal Cobb angle > 10° or sagittal vertebral axis > 5 cm), 2) treatment of adult degenerative scoliosis with at least a 2-level lateral MI-LIF procedure, 3) delayed second-stage procedure with percutaneous posterior spinal instrumentation, and 4) availability of preoperative and postoperative 36-inch radiographs of the scoliotic curvature. Only patients with adequate radiographs obtained preoperatively (P0), after the Stage 1 procedure (P1), and after the Stage 2 procedure (P2) were included in this study. Furthermore, patients with hybrid constructs involving open posterior osteotomies were also excluded. Spinopelvic parameters were measured at each pre- and postoperative (P0, P1, P2) interval by a single experienced observer. The coronal Cobb angle, central sacral vertebral line (CSVL), fractional curve, segmental lumbar lordosis, lumbar lordosis, sagittal vertebral axis, pelvic incidence, and sacral slope were determined and compared.

TABLE 1:

Demographic and operative data

VariableValue (%)*
demographics
 age in yrs
  mean64.3
  range32–80
 total no. of patients36
  male13 (36)
  female23 (64)
operative summary
 procedure
  w/o ACR27
  w/ ACR9
 no. of levels fused141
  w/o ACR126
  w/ ACR15
 L5–S1 fused15
  ALIF4
  TLIF11
non-ACR subgroup
 no. of patients27
 no. of fused levels110
 mean no. of levels fused/patient4.2
ACR subgroup
 no. of patients9
 no. of fused levels31
 mean no. of levels fused/patient3.4
 mean no. of ACRs/patient1.7

Values represent the number (%) of patients unless otherwise specified.

Operative Data

The surgical details for each operated level are listed in Table 1. All MI-LIF levels were performed using the XLIF system (NuVasive, Inc.). In all routine lateral LIF levels, a 10° lordotic, 18- to 22-mm wide × 8- to 10-mm high × 50- to 60-mm long cage was used (CoRoent XL or XLW, NuVasive, Inc.). The ACR was performed based on the anatomical and technical considerations published by Deukmedjian et al.,14 and readers may refer to that paper for detailed technical and diagrammatic descriptions of the procedure. For ACR levels, a 30° lordotic, 22-mm wide × 8- to 22-mm high × 50- to 60-mm long cage was used at each level (CoRoent XLH, NuVasive, Inc.). All procedures in both the ACR and non-ACR groups were performed using Osteocel Plus allograft with cadaveric cancellous bone with mesenchymal cells (NuVasive, Inc.) packed into the cage. Bone morphogenetic protein was not used in any of the 36 patients. Each patient underwent surgeries in 2 stages. The first stage consisted of the LIF with or without ACR. The delayed second stage consisted of the placement of percutaneous transpedicular posterior spinal instrumentation (Longitude, Medtronic, Inc., or Precept, NuVasive, Inc.). If a fractional curve existed, an MI L5–S1 anterior LIF (ALIF) was performed during Stage 1 (Pillar, Orthofix, Inc.) or an MI L5–S1 transforaminal LIF (TLIF) was performed during Stage 2 (CoRoent Large/Narrow, NuVasive, Inc.). Parameters for the TLIF cage are as follows: 0°, 8–14 mm high, 9 mm wide, and 25–30 mm long.

Statistical Analysis

Data were collected and analyzed using Excel (Microsoft) and SPSS 20.0 (IBM) software. The Shapiro-Wilk test was used to test for normality of all data sets. Significance testing was performed with the paired t-test for parametric data and the Wilcoxon signed-ranked test for nonparametric data. Comparison of spinopelvic parameters was performed for each operative interval (P0, P1, and P2). Subgroup analysis was also performed, using data collected in patients who underwent L5–S1 interbody fusion for fractional curve correction in the non-ACR group.

Results

Thirty-six patients (13 male, 23 female) whose mean age was 64.3 years (range 32–80 years) were identified. Degenerative scoliosis was the primary diagnosis for all patients. The mean clinical follow-up was 22.9 months (range 6–37.1 months) for the non-ACR group and 11.3 months for the ACR group (range 4.2–16.7 months). A total of 141 levels were treated with interbody grafts; 126 by lateral LIF technique, 11 by TLIF technique at L5–S1, and 4 by ALIF at L5–S1 (all among the ACR group). Patients who did not undergo ACR had interbody grafts placed at a mean of 4.2 levels (range 1–6). Patients treated with ACR had interbody grafts placed on average at 3.4 levels (range 1–6). In the ACR group, 15 ACRs were performed in 9 patients (mean 1.7 ACRs/patient).

Non-ACR Group

Spinopelvic parameters with significant change (preoperative vs second staged procedure) were the coronal Cobb angle (p < 0.0001) and fractional curve (p < 0.002) (Fig. 1, Table 2). The addition of posterior instrumentation (Stage 1 to Stage 2) only significantly affected the CSVL (p < 0.038). All other parameters were associated with insignificant change in the non-ACR group. Graft subsidence was found at the 1-year follow-up at 14 treated levels, yielding a total subsidence rate of 12.5%.

Fig. 1.
Fig. 1.

Comparison of preoperative, post–Stage 1 (MI-LIF with or without ACR), and post–Stage 2 (percutaneous pedicle instrumentation) radiographic parameters. Significance is denoted with p values. CCA = coronal Cobb angle; FC = fractional curve; LL = lumbar lordosis; PI = pelvic incidence; PT = pelvic tilt; SLL = segmental LL; SS = sacral slope; SVA = sagittal vertebral axis.

TABLE 2:

Radiographic data for preoperative, post–Stage 1, and post–Stage 2 spinopelvic parameters*

Group & MeasurementMean Valuep Value (no.)Mean Valuep Value (no.)
P0P2P1P2
non-ACR group
 CCA (°)28.912.9<0.0001 (21)16.912.4NS (15)
 CSVL (cm)21.6NS (16)2.544.6<0.038 (9)
 SVA (cm)2.33.8NS (13)2.93.8NS (9)
 PI (°)66.865.8NS (16)64.967.7NS (15)
 PT (°)24.928.6NS (16)27.227.7NS (11)
 SS (°)37.936.1NS (19)38.140.5NS (7)
 LL (°)43.745.9NS (21)45.53.8NS (14)
 FC (°)8.24.2<0.002 (16)9.53.7NS (5)
L5–S1 TLIF subgroup
 CCA (°)28.812.8<0.0001 (12)16.312.8NS (10)
 CSVL (cm)17.715.7NS (9)23.76.0<0.006 (7)
 SVA (cm)3.14.5NS (8)3.84.6NS (8)
 PI (°)57.156.8NS (8)57.657.6NS (9)
 PT (°)22.426.2NS (8)27.827.5NS (9)
 SS (°)35.132.9NS (11)26.130.4NS (5)
 LL (°)39.536.7NS (11)37.435.0NS (9)
 FC (°)9.24.1<0.009 (9)8.33.5NS (3)
ACR group
 CCA (°)24.89.7<0.014 (7)15.39.0NS (6)
 CSVL (cm)4.22NS (6)5.33.7NS (5)
 SVA (cm)8.33.5<0.017 (6)33.7NS (3)
 PI (°)62.663.1NS (6)57.959.9NS (4)
 PT (°)25.719.1NS (6)7.119.7NS (4)
 SS (°)34.842.3NS (6)40.849.6NS (6)
 LL (°)36.553.4<0.004 (9)49.653.4NS (6)
 SLL (°)2.414.4<0.0001 (15)13.414.4NS (6)
 FC (°)6.34.5NS (7)NANANA

Significant p values are denoted by boldface. The parenthetical values in the table body (no.) indicate the number of measurements made and represent the number of patients for each measurement such that each counted value is derived from a distinct patient. CCA = coronal Cobb angle; FC = fractional curve; LL = lumbar lordosis; NA = not applicable; NS = not significant; PI = pelvic incidence; PT = pelvic tilt; SLL = segmental LL; SS = sacral slope; SVA = sagittal vertebral axis.

Subgroup Analysis

Data from the cohort that underwent an L5–S1 TLIF for the presence of a fractional curve were separately analyzed. Similar to the non-ACR group, the coronal Cobb angle (p < 0.0001) and fractional curve (p < 0.009) showed significant improvement (preoperative vs the second staged procedure). The addition of posterior instrumentation significantly affected the CSVL only (p < 0.006). Conversely, the remaining cohort not requiring an L5-S1 TLIF had a fractional curve change that approached significance (p < 0.051) and a significant improvement in the coronal Cobb angle (p < 0.0001). The addition of posterior instrumentation did not significantly alter any of the other spinopelvic parameters in these subgroups.

ACR Group

Spinopelvic parameters with significant change (preoperative vs second staged procedure) were coronal Cobb angle (p < 0.014), sagittal vertebral axis (p < 0.017), lumbar lordosis (p < 0.004), and segmental lumbar lordosis (p < 0.0001) (Fig. 1, Table 2). The addition of posterior instrumentation (Stage 1 to Stage 2) did not significantly alter spinopelvic parameters. Based on lateral spine radiographs, subsidence was found at the 1-year follow-up at 7 treated levels in the ACR group. Two cases of subsidence were found at the levels where no anterior longitudinal ligament release was performed. These preliminary data indicate a subsidence rate of 33% at ACR levels and 22.5% overall in ACR constructs.

Discussion

The role for MI lateral transpsoas interbody fusion in the treatment of adult spinal deformity and its effect on regional/global alignment correction are a matter of debate. The addition of posterior instrumentation implanted with MI techniques can augment MI deformity correction. This preliminary study outlines the role of percutaneous instrumentation placed using MI technique as an adjunct to MI-LIF and, more importantly, addresses the effect of MI-ACR on lumbar lordosis and sagittal vertebral axis.

Posterior Spinal Instrumentation

To our knowledge, the effect of percutaneous transpedicular posterior instrumentation on spinopelvic parameters, used as a supplement to interbody techniques, has not been reported. Our preliminary data provide a unique opportunity to address this question because of the 2-stage approach that we used for scoliosis repair. The analysis of data obtained between Stages 1 and 2 addresses the effect of percutaneous posterior spinal instrumentation as well as changes from the MI-TLIF. In the non-ACR group, posterior instrumentation does not significantly change any of the spinopelvic or general radiographic spine parameters except the CSVL and fractional curve. The CSVL can be explained in that the fractional curve was not addressed in Stage 1, but the coronal Cobb angle was (which was reduced significantly), leading to an increase in distance from the coronal midline (“leaning tower of Pisa” effect). When the fractional curve was addressed in Stage 2 with the TLIF, the post–Stage 1 CSVL corrected toward the midline to a statistically significant degree, but not in comparison with the preoperative value. In regard to the fractional curve, subset analysis revealed that its significance is most likely due to the Stage 2 TLIF treatment of L5–S1.

In the ACR group, no radiographic parameter achieved statistical significance from P1 to P2 including the CSVL. This finding is in contrast to the result from the non-ACR group, but this is most likely due to inadequate statistical power. From these data, we can say that percutaneous posterior instrumentation does not affect radiographic parameters in patients treated with the lateral MI-LIF with or without ACR, excluding CSVL. This may be due to the surgeon's attempt to contour the posterior rod to mimic the already existing curve from Stage 1. In situ rod bending, however, may have a greater effect on radiographic parameters.

Segmental Spine Parameters

The lateral MI-LIF has been proven to increase disc height, foraminal size, segmental coronal Cobb angle, and segmental lumbar lordosis.1,20 We did not evaluate disc height, foraminal size, or segmental coronal Cobb angle in this study. We did evaluate segmental lumbar lordosis in the ACR group. As reported, the segmental lumbar lordosis significantly improved by 12.0° per ACR level. The lateral MI-LIF provides a very powerful segmental technique that significantly improved regional and global parameters. Segmental spine disease is a frequent cause of radiculopathy, neurological deficit, and focal pain in patients with scoliosis. Addressing the symptom requires inclusion of the segmental level in the treatment plan. Regional and global symptoms—for example, nonfocal back pain—are unlikely to be adequately addressed by a segmental intervention. At this time, it appears the only segmental techniques capable of creating significant change in the global sagittal parameter include the PSO, SPO, vertebral column resection, and ACR.

Regional Spine Parameters

Correction of regional spine abnormalities is vital for global parameter correction. Our data indicate the ability of the lateral MI-LIF, with or without ACR, to significantly change the regional coronal Cobb angle. We also see that the lateral MI-LIF without ACR did not significantly change regional lumbar lordosis in our series, which agrees with already published data regarding the regional effect of the lateral MI-LIF in nonscoliotic patients.1,20 In contrast, the lateral MI-LIF with ACR significantly changed lumbar lordosis by 16.5°. Therefore, patients with a lumbar lordosis abnormality that contributes to spinopelvic disharmony should be treated with an ACR if the lateral MI-LIF approach is to be used. In the non-ACR group, lateral MI-LIF did not produce a significant change in sacral slope or pelvic tilt. In contrast, sacral slope did significantly improve in the ACR group by 7.5°. This again supports the statistically significant effect of the ACR on regional radiographic parameters.

Global Spine Parameters

The importance of addressing global spine parameters cannot be overstated in adult spinal deformity. Our data suggest that the lateral transpsoas MI-LIF can significantly improve the segmental and regional coronal Cobb angle, but does not achieve significant correction of the global coronal parameter, CSVL. Recently Acosta et al. showed that lateral MI-LIF was associated with a significant improvement in CSVL, from 1.9 cm to 1.25 cm. Given these conflicting results, patient selection may need to be tailored to the case—that is, lateral MI-LIF without ACR is best adapted to the symptomatic mild adult spinal deformity patient with coronal Cobb angle abnormality and without significant global coronal abnormality (CSVL). Subgroup analysis did show, however, that if a global coronal abnormality exists in the setting of a fractional curve, the addition of an MI-TLIF or an ALIF at L5–S1 can significantly improve global coronal balance.

In the ACR group, the average correction of sagittal balance was a 4.8-cm decrease in sagittal vertebral axis. This correction was accompanied by a significant change in regional lumbar lordosis of 16.5° and increase in sacral slope by 7.5°. Although not significant, a decrease in pelvic tilt by 5.2° is congruent with improvement of global spinopelvic balance. Coronal parameter correction has already been established for the lateral MI-LIF and clearly shows improvement in the coronal Cobb angle. When evaluated for global power, the MI-ACR boasts a 3.1-cm sagittal vertebral axis correction per level.

Traditional Approach Versus MI-LIF With ACR

The SPO was first described for correction of ankylosing spondylitis–related kyphosis in 1945.27 Alberto Ponte23 described a similar osteotomy for use in the flexible thoracic curve of patients with Scheuermann's kyphosis in 1984. In 1985, a more aggressive osteotomy, PSO, was reported by Thomasen for fixed spinal deformity with ankylosing spondylitis.30 Subsequently, these techniques have been adapted to treat fixed sagittal imbalance with excellent results.6–8,15 These publications have elucidated the power of the PSO and SPO to affect regional and global parameters and have provided valuable guidance in operative planning.6,15 The anticipated rate of lumbar lordosis and sagittal vertebral axis correction for the PSO is 30°–40° and 5.5–13.5 cm per level, respectively.9,18,26 The expected lumbar lordosis correction for the SPO is approximately 10° per level.6,9,10,12,15 An SPO is preferred in cases of smooth kyphotic curves of the lumbar spine so long as the required sagittal vertebral axis correction is 10 cm or less. If a sharp angular kyphosis exists, or if sagittal vertebral axis correction exceeding 10 cm is required, a PSO is preferred, according to recently proposed management paradigms.6 Currently the MI-ACR has not been factored into sagittal correction in scoliosis treatment paradigms.

From our preliminary data, it is clear that the ACR approach is equivalent to the SPO in terms of radiographic outcomes for segmental lumbar lordosis correction (12.0° vs 10°, respectively, at 1 year). It also provides an average of 3.1 cm of sagittal vertebral axis correction per level through an MI technique. Three SPOs have been reported as being as powerful as a single PSO, and our data indicate that this rule of thumb may also apply to the lateral MI-ACR. Based on our data, we know that multilevel MI-ACR is feasible: 1 patient had a 3-level ACR, and 4 patients had a 2-level ACR. Whether these multilevel MI-ACR procedures are durable or result in delayed complications is unknown at this time. This combination of MI approach and powerful sagittal balance correction may be of significant benefit in cases of de novo degenerative scoliosis in which sagittal imbalance is mild and moderately severe—that is, sagittal vertebral axis less than 10 cm. We acknowledge that its use may be of limited value in the setting of previous posterior instrumentation, whose supplementation would require redo posterior dissection regardless. When correction of sagittal balance through an MI surgical technique is desired, the lateral MI-LIF with ACR is a feasible option.

Another surgical option for sagittal balance correction is the “less invasive” OptiMesh TLIF (Spineology, Inc.) combined with posterior percutaneous instrumentation, as recently reported by Wang.32 He shows lumbar lordosis correction of 17.8° and sagittal vertebral axis correction of 3.2 cm over long regional spine constructs. Although statistically significant, these results reveal the inferior segmental power of the TLIF to correct sagittal vertebral axis compared with the single-level lateral MI-LIF with ACR.

Durability

The durability of scoliosis correction has been demonstrated in the literature, although all forms of treatment show decremental results over time. This is the case for posterior osteotomy and instrumentation as well as for interbody fusion.8,17 The MI-LIF procedure and its modifications may produce similar results over time because of cage subsidence.19 It is clear from our data that cage subsidence does occur at an expected rate at non-ACR fusion levels.19 Subsidence trended toward a higher rate at the ACR levels, but power levels were inadequate for formal evaluation. Several factors, however, favor the durability of the lateral MI-LIF with or without ACR: 1) an interbody cage construct with posterior instrumentation provides more evenly distributed biomechanical support in all 3 spinal columns, 2) an interbody cage takes advantage of the apophysial ring bone of the vertebral endplate, the strongest area of the endplate, and 3) an interbody cage with greater surface area than traditional cages allows for placement of more fusion-promoting product. Fusion rates have not been calculated for either cohort because we do not routinely acquire postoperative CT scans to evaluate for fusion and because of incomplete postoperative flexion/extension radiographs at 1 year to assess for bridging bone or movement.

Spinopelvic Harmony: Is ACR Necessary?

The lateral MI-LIF has the ability to correct coronal curve and segmental lordosis, as well as relieve scoliosis-associated back pain and radiculopathy in patients with mild to moderate disease severity (sagittal vertebral axis < 5 cm). There is some question as to whether the lateral MI-LIF technique without ACR can provide regional lumbar lordosis correction. Because of this limitation, we feel the lateral MI-LIF is an appropriate stand-alone technique or in combination with percutaneous pedicle screw instrumentation for adult spinal deformity so long as the patient exhibits sagittal spinopelvic harmony. If achieving coronal balance and symptom relief is the goal, careful attention must be paid to correcting the fractional curve, as the CSVL can worsen if the fractional curve is not addressed using an L5–S1 MI-TLIF or ALIF. If an MI surgical technique is desired and sagittal vertebral axis correction is required (sagittal vertebral axis > 5 cm) to bring a spine into balance or to prevent a borderline condition from slipping out of sagittal balance, an ACR should be strongly considered.

Limitations

There are several limitations to this preliminary radiographic study. First, we do not address clinical outcomes because of the radiographic focus of this paper. Clearly, the clinician must consider these results to reflect a preliminary description of a novel MI surgical technique that can correct sagittal balance. Clinical outcomes data will be forthcoming as increasing numbers of cases are performed and follow-up time accumulates. Second, this study is inadequately powered to compare short- and long-term follow-up for durability of scoliosis correction. Likewise, subsidence and fusion rates are not yet available given the short-term follow-up duration of 1 year. The results should be cautiously interpreted in the context of currently known subsidence and fusion rates for the MI-LIF until more data are available. Third, selection bias may have affected the results in that we selected only those patients who had adequate imaging per inclusion criteria. As a means of limiting this potential bias, patients were selected based on having undergone imaging prior to our knowing the results of the individual radiographic measurements. Fourth, inadequate power may have led to Type 2 error in the ACR group.

Conclusions

As technology advances, different tools for the treatment of adult spinal deformity are becoming available. The most recent interbody fusion technique, the lateral MI-LIF, shows great promise for treating mild and moderate severity adult spinal deformity. The lateral MI-LIF combined with ACR has the ability to correct sagittal balance (sagittal vertebral axis) by 3.1 cm and lumbar lordosis by 12.0° at each treated level. This MI surgical technique shows equivalent power to the SPO for these parameters while simultaneously creating additional disc height and correcting coronal imbalance. Addition of percutaneous transpedicular posterior instrumentation without in situ manipulation or overcorrection does not alter radiographic parameters. The limits of sagittal vertebral axis correction over multiple segments need further evaluation for safety and durability to determine the role of the procedure in the treatment of adult spinal deformity of different severities.

Disclosure

Dr. Uribe maintains a consulting relationship with NuVasive, Inc. No funding was provided for any portion of this research product. All other authors report no conflict of interest concerning the materials and methods used in this study or findings specified in this paper.

Author contributions to the study and manuscript preparation include the following. Conception and design: Manwaring, Bach, Uribe. Acquisition of data: Manwaring, Bach. Analysis and interpretation of data: Manwaring, Ahmadian. Drafting the article: Manwaring, Ahmadian. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Manwaring. Statistical analysis: Manwaring, Ahmadian. Study supervision: Uribe.

This article contains some figures that are displayed in color online but in black-and-white in the print edition.

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    Bridwell KHLewis SJLenke LGBaldus CBlanke K: Pedicle subtraction osteotomy for the treatment of fixed sagittal imbalance. J Bone Joint Surg Am 85-A:4544632003

  • 9

    Bridwell KHLewis SJRinella ALenke LGBaldus CBlanke K: Pedicle subtraction osteotomy for the treatment of fixed sagittal imbalance. Surgical technique. J Bone Joint Surg Am 86-A:Suppl 144502004

  • 10

    Buchowski JMBridwell KHLenke LGKuhns CALehman RA JrKim YJ: Neurologic complications of lumbar pedicle subtraction osteotomy: a 10-year assessment. Spine (Phila Pa 1976) 32:224522522007

  • 11

    Carreon LYPuno RMDimar JR IIGlassman SDJohnson JR: Perioperative complications of posterior lumbar decompression and arthrodesis in older adults. J Bone Joint Surg Am 85-A:208920922003

  • 12

    Cho KJBridwell KHLenke LGBerra ABaldus C: Comparison of Smith-Petersen versus pedicle subtraction osteotomy for the correction of fixed sagittal imbalance. Spine (Phila Pa 1976) 30:203020382005

  • 13

    Dakwar ECardona RFSmith DAUribe JS: Early outcomes and safety of the minimally invasive, lateral retroperitoneal transpsoas approach for adult degenerative scoliosis. Neurosurg Focus 28:3E82010

  • 14

    Deukmedjian ALe TVBaaj AADakwar ESmith DAUribe JS: Anterior longitudinal ligament release using the minimally invasive lateral retroperitoneal transpsoas approach: a cadaveric feasibility study and report of 4 clinical cases. Laboratory investigation. J Neurosurg Spine 17:5305392012

  • 15

    Gill JBLevin ABurd TLongley M: Corrective osteotomies in spine surgery. J Bone Joint Surg Am 90:250925202008

  • 16

    Glassman SDBerven SBridwell KHorton WDimar JR: Correlation of radiographic parameters and clinical symptoms in adult scoliosis. Spine (Phila Pa 1976) 30:6826882005

  • 17

    Jagannathan JSansur CAOskouian RJ JrFu KMShaffrey CI: Radiographic restoration of lumbar alignment after transforaminal lumbar interbody fusion. Neurosurgery 64:9559642009

  • 18

    Lafage VSchwab FVira SHart RBurton DSmith JS: Does vertebral level of pedicle subtraction osteotomy correlate with degree of spinopelvic parameter correction? Clinical article. J Neurosurg Spine 14:1841912011

  • 19

    Le TVBaaj AADakwar EBurkett CJMurray GSmith DA: Subsidence of polyetheretherketone intervertebral cages in minimally invasive lateral retroperitoneal transpsoas lumbar interbody fusion. Spine (Phila Pa 1976) 37:126812732012

  • 20

    Le TVVivas ACDakwar EBaaj AAUribe JS: The effect of the retroperitoneal transpsoas minimally invasive lateral interbody fusion on segmental and regional lumbar lordosis. ScientificWorldJournal 2012:5167062012

  • 21

    Okuda SMiyauchi AOda THaku TYamamoto TIwasaki M: Surgical complications of posterior lumbar interbody fusion with total facetectomy in 251 patients. J Neurosurg Spine 4:3043092006

  • 22

    Park YHa JW: Comparison of one-level posterior lumbar interbody fusion performed with a minimally invasive approach or a traditional open approach. Spine (Phila Pa 1976) 32:5375432007

  • 23

    Ponte AVero BSiccardi GLSurgical treatment of Scheuermann's hyperkyphosis. Winter RB: Progress in Spinal Pathology: Kyphosis BolognaAulo Gaggi1984. 7580

  • 24

    Potaczek TJasiewicz BTesiorowski MZarzycki DSzcześniak A: Treatment of idiopathic scoliosis exceeding 100 degrees–comparison of different surgical techniques. Ortop Traumatol Rehabil 11:4854942009

  • 25

    Schwab FPatel AUngar BFarcy JPLafage V: Adult spinal deformity-postoperative standing imbalance: how much can you tolerate? An overview of key parameters in assessing alignment and planning corrective surgery. Spine (Phila Pa 1976) 35:222422312010

  • 26

    Schwab FJPatel AShaffrey CISmith JSFarcy JPBoachie-Adjei O: Sagittal realignment failures following pedicle subtraction osteotomy surgery: are we doing enough? Clinical article. J Neurosurg Spine 16:5395462012

  • 27

    Smith-Petersen MNLarson CBAufranc OE: Osteotomy of the spine for correction of flexion deformity in rheumatoid arthritis. Clin Orthop Relat Res 66:691969

  • 28

    Sucato DJElerson E: A comparison between the prone and lateral position for performing a thoracoscopic anterior release and fusion for pediatric spinal deformity. Spine (Phila Pa 1976) 28:217621802003

  • 29

    Sucato DJErken YHDavis SGist TMcClung ARathjen KE: Prone thoracoscopic release does not adversely affect pulmonary function when added to a posterior spinal fusion for severe spine deformity. Spine (Phila Pa 1976) 34:7717782009

  • 30

    Thomasen E: Vertebral osteotomy for correction of kyphosis in ankylosing spondylitis. Clin Orthop Relat Res 1941421521985

  • 31

    Tormenti MJMaserati MBBonfield CMOkonkwo DOKanter AS: Complications and radiographic correction in adult scoliosis following combined transpsoas extreme lateral interbody fusion and posterior pedicle screw instrumentation. Neurosurg Focus 28:3E72010

  • 32

    Wang MY: Improvement of sagittal balance and lumbar lordosis following less invasive adult spinal deformity surgery with expandable cages and percutaneous instrumentation. Clinical article. J Neurosurg Spine 18:4122013

  • 33

    Wang MYMummaneni PV: Minimally invasive surgery for thoracolumbar spinal deformity: initial clinical experience with clinical and radiographic outcomes. Neurosurg Focus 28:3E92010

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Article Information

Address correspondence to: Jotham Manwaring, M.D., Department of Neurosurgery and Brain Repair, University of South Florida Morsani College of Medicine, 2 Tampa General Circle, Tampa, FL 33606. email: jmanwari@health.usf.edu.

Please include this information when citing this paper: published online March 14, 2014; DOI: 10.3171/2014.2.SPINE1347.

© AANS, except where prohibited by US copyright law.

Headings

Figures

  • View in gallery

    Comparison of preoperative, post–Stage 1 (MI-LIF with or without ACR), and post–Stage 2 (percutaneous pedicle instrumentation) radiographic parameters. Significance is denoted with p values. CCA = coronal Cobb angle; FC = fractional curve; LL = lumbar lordosis; PI = pelvic incidence; PT = pelvic tilt; SLL = segmental LL; SS = sacral slope; SVA = sagittal vertebral axis.

References

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    Anand NBaron EMThaiyananthan GKhalsa KGoldstein TB: Minimally invasive multilevel percutaneous correction and fusion for adult lumbar degenerative scoliosis: a technique and feasibility study. J Spinal Disord Tech 21:4594672008

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    Anand NRosemann RKhalsa BBaron EM: Mid-term to long-term clinical and functional outcomes of minimally invasive correction and fusion for adults with scolios. Neurosurg Focus 28:3E62010

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    Auerbach JDSpiegel DAZgonis MHReddy SCDrummond DSDormans JP: The correction of pelvic obliquity in patients with cerebral palsy and neuromuscular scoliosis: is there a benefit of anterior release prior to posterior spinal arthrodesis?. Spine (Phila Pa 1976) 34:E766E7742009

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    Berjano PLamartina C: Far lateral approaches (XLIF) in adult scoliosis. Eur Spine J 22:Suppl 2S242S2532013

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    Bridwell KH: Decision making regarding Smith-Petersen vs. pedicle subtraction osteotomy vs vertebral column resection for spinal deformity. Spine (Phila Pa 1976) 31:19 SupplS171S1782006

  • 7

    Bridwell KHLewis SJEdwards CLenke LGIffrig TMBerra A: Complications and outcomes of pedicle subtraction osteotomies for fixed sagittal imbalance. Spine (Phila Pa 1976) 28:209321012003

  • 8

    Bridwell KHLewis SJLenke LGBaldus CBlanke K: Pedicle subtraction osteotomy for the treatment of fixed sagittal imbalance. J Bone Joint Surg Am 85-A:4544632003

  • 9

    Bridwell KHLewis SJRinella ALenke LGBaldus CBlanke K: Pedicle subtraction osteotomy for the treatment of fixed sagittal imbalance. Surgical technique. J Bone Joint Surg Am 86-A:Suppl 144502004

  • 10

    Buchowski JMBridwell KHLenke LGKuhns CALehman RA JrKim YJ: Neurologic complications of lumbar pedicle subtraction osteotomy: a 10-year assessment. Spine (Phila Pa 1976) 32:224522522007

  • 11

    Carreon LYPuno RMDimar JR IIGlassman SDJohnson JR: Perioperative complications of posterior lumbar decompression and arthrodesis in older adults. J Bone Joint Surg Am 85-A:208920922003

  • 12

    Cho KJBridwell KHLenke LGBerra ABaldus C: Comparison of Smith-Petersen versus pedicle subtraction osteotomy for the correction of fixed sagittal imbalance. Spine (Phila Pa 1976) 30:203020382005

  • 13

    Dakwar ECardona RFSmith DAUribe JS: Early outcomes and safety of the minimally invasive, lateral retroperitoneal transpsoas approach for adult degenerative scoliosis. Neurosurg Focus 28:3E82010

  • 14

    Deukmedjian ALe TVBaaj AADakwar ESmith DAUribe JS: Anterior longitudinal ligament release using the minimally invasive lateral retroperitoneal transpsoas approach: a cadaveric feasibility study and report of 4 clinical cases. Laboratory investigation. J Neurosurg Spine 17:5305392012

  • 15

    Gill JBLevin ABurd TLongley M: Corrective osteotomies in spine surgery. J Bone Joint Surg Am 90:250925202008

  • 16

    Glassman SDBerven SBridwell KHorton WDimar JR: Correlation of radiographic parameters and clinical symptoms in adult scoliosis. Spine (Phila Pa 1976) 30:6826882005

  • 17

    Jagannathan JSansur CAOskouian RJ JrFu KMShaffrey CI: Radiographic restoration of lumbar alignment after transforaminal lumbar interbody fusion. Neurosurgery 64:9559642009

  • 18

    Lafage VSchwab FVira SHart RBurton DSmith JS: Does vertebral level of pedicle subtraction osteotomy correlate with degree of spinopelvic parameter correction? Clinical article. J Neurosurg Spine 14:1841912011

  • 19

    Le TVBaaj AADakwar EBurkett CJMurray GSmith DA: Subsidence of polyetheretherketone intervertebral cages in minimally invasive lateral retroperitoneal transpsoas lumbar interbody fusion. Spine (Phila Pa 1976) 37:126812732012

  • 20

    Le TVVivas ACDakwar EBaaj AAUribe JS: The effect of the retroperitoneal transpsoas minimally invasive lateral interbody fusion on segmental and regional lumbar lordosis. ScientificWorldJournal 2012:5167062012

  • 21

    Okuda SMiyauchi AOda THaku TYamamoto TIwasaki M: Surgical complications of posterior lumbar interbody fusion with total facetectomy in 251 patients. J Neurosurg Spine 4:3043092006

  • 22

    Park YHa JW: Comparison of one-level posterior lumbar interbody fusion performed with a minimally invasive approach or a traditional open approach. Spine (Phila Pa 1976) 32:5375432007

  • 23

    Ponte AVero BSiccardi GLSurgical treatment of Scheuermann's hyperkyphosis. Winter RB: Progress in Spinal Pathology: Kyphosis BolognaAulo Gaggi1984. 7580

  • 24

    Potaczek TJasiewicz BTesiorowski MZarzycki DSzcześniak A: Treatment of idiopathic scoliosis exceeding 100 degrees–comparison of different surgical techniques. Ortop Traumatol Rehabil 11:4854942009

  • 25

    Schwab FPatel AUngar BFarcy JPLafage V: Adult spinal deformity-postoperative standing imbalance: how much can you tolerate? An overview of key parameters in assessing alignment and planning corrective surgery. Spine (Phila Pa 1976) 35:222422312010

  • 26

    Schwab FJPatel AShaffrey CISmith JSFarcy JPBoachie-Adjei O: Sagittal realignment failures following pedicle subtraction osteotomy surgery: are we doing enough? Clinical article. J Neurosurg Spine 16:5395462012

  • 27

    Smith-Petersen MNLarson CBAufranc OE: Osteotomy of the spine for correction of flexion deformity in rheumatoid arthritis. Clin Orthop Relat Res 66:691969

  • 28

    Sucato DJElerson E: A comparison between the prone and lateral position for performing a thoracoscopic anterior release and fusion for pediatric spinal deformity. Spine (Phila Pa 1976) 28:217621802003

  • 29

    Sucato DJErken YHDavis SGist TMcClung ARathjen KE: Prone thoracoscopic release does not adversely affect pulmonary function when added to a posterior spinal fusion for severe spine deformity. Spine (Phila Pa 1976) 34:7717782009

  • 30

    Thomasen E: Vertebral osteotomy for correction of kyphosis in ankylosing spondylitis. Clin Orthop Relat Res 1941421521985

  • 31

    Tormenti MJMaserati MBBonfield CMOkonkwo DOKanter AS: Complications and radiographic correction in adult scoliosis following combined transpsoas extreme lateral interbody fusion and posterior pedicle screw instrumentation. Neurosurg Focus 28:3E72010

  • 32

    Wang MY: Improvement of sagittal balance and lumbar lordosis following less invasive adult spinal deformity surgery with expandable cages and percutaneous instrumentation. Clinical article. J Neurosurg Spine 18:4122013

  • 33

    Wang MYMummaneni PV: Minimally invasive surgery for thoracolumbar spinal deformity: initial clinical experience with clinical and radiographic outcomes. Neurosurg Focus 28:3E92010

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