Adding Thoracic Fusion Levels in Lenke 5 Curves: Risks and Benefits
Lark, Robert K. MD*; Yaszay, Burt MD†; Bastrom, Tracey P. MA†; Newton, Peter O. MD†; Harms Study Group
*Department of Orthopaedic Surgery, Duke University Medical Center, Durham, NC; and
†Rady Children's Hospital and Health Center, San Diego, CA.
Address correspondence and reprint requests to Burt Yaszay, MD, 3030 Children's Way, Suite 410, San Diego, CA 92123; E-mail: email@example.com
Acknowledgment date: November 19, 2011. First revision date: May 30, 2012. Acceptance date: June 5, 2012.
The manuscript submitted does not contain information about medical device(s)/drug(s).
Harms Study Group from DePuy Spine Inc. and Children's Specialists Foundation Orthopedic Research and Education Fund grants were received to support this work.
One or more of the author(s) has/have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this manuscript: for example, honoraria, gifts, consultancies, royalties, stocks, stock options, decision-making position.
Study Design. Multicenter; review of prospectively collected data.
Objective. To determine the risks and potential benefits of nonselective versus selective fusion in a matched set of patients with Lenke 5 curves.
Summary of Background Data. The Lenke classification suggests a limited thoracolumbar/lumbar fusion for type 5 curves, although many experienced adolescent idiopathic scoliosis surgeons, at times, include a fusion of the thoracic curve.
Methods. Prospectively collected cases from a multicenter database were analyzed. Patients with Lenke type 5 scoliosis curves were divided into 2 groups: 109 selective or short (only thoracolumbar/lumbar curve fused), and 41 nonselective or long (both thoracolumbar/lumbar and thoracic curves fused). Patients were then matched on the basis of the preoperative radiographical and clinical measures. Two-year postoperative radiographical and clinical outcomes were compared, using analysis of variance, with Bonferroni correction (P < 0.008).
Results. Twenty-nine matched pairs (58 patients) with Lenke 5 curves were identified. There were no preoperative differences between groups in age, thoracic or lumbar Cobb angle, curve flexibility, thoracic kyphosis, clinical trunk flexibility, or Scoliosis Research Society outcomes questionnaire scores. Postoperatively, patients in the nonselective group exhibited greater coronal correction for thoracic (residual Cobb; 22° vs. 12°) and lumbar curves (residual Cobb; 19° vs. 13°). However, the longer fusions had significantly less thoracic kyphosis (27° vs. 18°), truncal side bending (14 vs. 10 cm), and rotational flexibility (53° vs. 42°). There was no difference in clinical balance or Scoliosis Research Society questionnaire, version 22, scores.
Conclusion. Adolescent idiopathic scoliosis surgeons attempt to achieve balanced correction with the fewest motion segments fused. Our data suggest that fusion of the thoracic curve in primary thoracolumbar scoliosis may improve coronal correction, but at the cost of decreased thoracic kyphosis and clinical flexibility 2 years postoperatively.
Multiple classification schemes have been proposed over the years in an effort to better understand curve types and fusion levels in adolescent idiopathic scoliosis.1–3 Generally, it is recommended to treat the primary or structural curve and leave flexible compensatory curves unfused. Significant attention has been given to the King Moe type II or Lenke type 1C curves with regard to fusion levels to preserve motion segments in the lumbar spine.4–12 This may not always be the case with regard to the thoracolumbar/lumbar (TL/L) curve. Some surgeons may be less concerned about fusing the compensatory thoracic curve above the structural thoracolumbar curve.
The relatively small amount of motion in the thoracic spine may not be as critical to maintain, compared with the lumbar spine. Unfortunately, little is known about the consequences of losing motion segments in the thoracic spine. The purpose of the present study was to determine the effects of fusing the thoracic and lumbar spine (long fusion) when compared with fusing just the TL/L curve (short fusion) in patients with primary TL/L scoliosis (Lenke type 5).
After institutional review board approval, a retrospective review of a multicenter prospectively collected adolescent idiopathic scoliosis database was conducted to select all patients with a Lenke type 5 curve. The curve pattern defines a major TL/L curve with nonstructural thoracic and upper thoracic region curves (Cobb angle <25° on best bend films; and <20° kyphosis at T2–T5 and T10–L2). Only patients with a minimum of 2 years of postoperative follow-up were included.
Patients were divided into 2 groups: those who underwent a short (selective) fusion of just the TL/L curve (n = 109) and those who underwent a long (nonselective) fusion inclusive of the thoracic curve (n = 41) (Figure 1). A matched pair design was created. A patient who underwent a long fusion was matched to a patient with a short fusion based on a preoperative thoracic Cobb angle within 2°, followed by a lumbar Cobb angle within 2°. Flexibility measures were then matched within 5° on bending thoracic Cobb and 15% when expressed as a percentage of preoperative Cobb angle.
Preoperative and 2-year postoperative coronal and sagittal radiographical measures were compared. Clinical assessment of trunk motion was measured in the coronal, sagittal, and axial (rotation) planes by a trained research coordinator (Figure 2). The Scoliosis Research Society (version 22) questionnaire was administered preoperatively and 2 or more years postoperatively.
Statistical Package for Social Sciences (SPSS, Chicago, IL) was used for all analyses in this study. The data were checked for normality and equal variances. Multivariate analysis of variance was used to compare radiographical measures, trunk motion data, and Scoliosis Research Society questionnaire scores between the short and long fusion groups. A P value of less than 0.05 was selected as statistically significant, and adjusted by using Bonferroni correction for multiple statistical tests to P < 0.008.
A total of 150 patients with Lenke 5 curves were identified. One hundred and nine (73%) of those patients underwent short fusion, whereas 41 patients (27%) had a long fusion. Preoperatively, the groups were significantly different in thoracic Cobb angle magnitude and thoracic translation (apex to C7 plumb) (P ≤ 0.001) (Table 1).
The 29 matched pairs were similar in all preoperative variables measured (Table 2). The average age at the time of surgery was 15 ± 2 years in both groups (P > 0.05). The thoracic Cobb angle magnitude was 34 ± 8° in both fusion groups (P > 0.05) and thoracic flexibility was similar (54 ± 19% in the long fusion group; 60 ± 18% in the short fusion group; P > 0.05). The number of levels fused was significantly different, with more levels fused in the long fusion group (12 ± 1) compared with the short fusion group (4 ± 1; P < 0.001). Operative time trended toward being greater in the long fusion group and estimated blood loss was significantly greater in the long fusion group (Table 3).
Postoperative radiographs revealed a significant coronal correction of the lumbar curve in both groups with a significantly smaller residual Cobb angle in those who underwent a long fusion (13 ± 6° vs. 19 ± 6°; P = 0.001) (Figure 3). The thoracic curve also improved significantly in both groups with less postoperative deformity in the long fusion group (11 ± 6° vs. 22 ± 8°; P = 0.000) (Figure 4). In the sagittal plane, there was significantly less postoperative thoracic kyphosis (T5–T12) after the long fusion compared with the short (18 ± 6° vs. 27 ± 12°; P = 0.002) (Table 4).
Measures of trunk motion were also found to be significantly different between the 2 groups. Patients who underwent a long fusion were significantly less flexible in forward flexion, lateral flexion, and axial rotation (Table 5). Other clinical measures including thoracic rib hump and lumbar angle of trunk rotation as measured by scoliometer were no different between the groups, postoperatively.
There were no statistically significant differences in cosmesis measures such as trunk shape and coronal decompensation, pre- or postoperatively between the groups (Table 6). Scoliosis Research Society questionnaire domains, including pain, self-image, general function, and activity also demonstrated no difference (Table 7).
The typically recommended treatment for Lenke 5 curves is fusion only of the primary TL/L curve.3,13 However, nearly 27% of fusions for these curves were treated nonselectively by experienced adolescent idiopathic scoliosis surgeons. This is in contrast with 17% of patients with primary thoracic scoliosis undergoing nonselective fusion by surgeons with similar experience as reported by Newton et al.11 This suggests that protecting thoracic motion segments may not be approached with the same vigilance as preserving lumbar motion, or that the Lenke classification criteria for a structural minor curve are interpreted differently for the thoracic and lumbar regions.
One of the primary purposes in performing a selective thoracic fusion is to minimize the loss of lumbar motion and theoretically the risk of lumbar degeneration or pain. Multiple studies have demonstrated the negative long-term risks of extending a scoliosis spinal fusion into the lower lumbar spine.14–19 Reducing the number of fused levels maximizes spinal flexibility and distributes stress across more distal lumbar motion segments.20 Theoretically, this may diminish the long-term risk of disc degeneration at adjacent distal levels. Therefore, it is clear why many studies have focused on the topic of selective thoracic fusion.4–12
Some attention has been given to the concept of selective TL/L fusion. In their multicenter study, Sanders et al 21 attempted to determine when the associated thoracic curve could be left unfused in a major TL/L curve. They determined that patients who had a TL/L to thoracic Cobb angle magnitude ratio of 1.25 or greater, a flexible thoracic curve (bending to 20° or less), and closed triradiate cartilage had good results and did not require further surgery. Another study retrospectively evaluated whether the Lenke classification could predict a successful selective TL/L fusion based on the criteria for a Lenke 5 curve.13 In their patients, the radiographical and clinical outcomes supported the suggestions for a selective fusion of a Lenke 5 curve. The authors, however, did report on 1 patient (of 21) who required a revision operation for a progressive thoracic curve.
The concept of minimizing fusion levels in TL/L curves is not novel in the literature. Many of the proponents for anterior fusion have suggested that an anterior approach can save fusion levels compared with a posterior approach.22–24 On average, the number of saved levels range from 1 to 1.6. The majority of these studies have focused on the caudal extent of the fusion. Other authors have suggested that the combination of wide posterior releases combined with segmental instrumentation can result in similar or improved results, without some of the problems associated with an anterior approach.25
The present study is the first to evaluate the effects of extending the fusion into the thoracic spine in a matched set of patients. Those fused into the thoracic spine had significantly better postoperative thoracic Cobb angle measurements. This allowed for greater lumbar curve correction in the long fusion group. In both groups, the resulting thoracic and lumbar curve corrections had a similar effect on the coronal alignment.
In the sagittal plane, fusion of the thoracic spine caused a decrease in thoracic kyphosis compared with a gain in kyphosis in the short fusion group. Overall, there was a significant difference in the thoracic kyphosis between the 2 groups. A great deal of attention has been given to sagittal profile after fusion of a main thoracic curve, especially with the use of modern segmental instrumentation. Multiple studies have demonstrated the influence of surgical approach and instrumentation type.26–31 The specific concerns discussed are the risk of junctional kyphosis and reduced lumbar lordosis associated with postoperative thoracic hypokyphosis.32,33 It is unclear what the relative effects of decreasing thoracic kyphosis are, when fusing into the lumbar spine in patients with long fusion.
Clinically, the most significant finding was the relative decrease in flexibility associated with the long fusion. Patients who underwent a short fusion were relatively more flexible than those who had their fusion extended into the thoracic spine. As already discussed, decreased lumbar mobility associated with a lumbar fusion may increase the risk of degenerative changes and low back pain.14–19 It is unclear if the increased immobility of a longer thoracic and lumbar fusion will also increase the risk of degeneration or low back pain compared with a patient with a short lumbar fusion. Long-term studies will be needed to address this question. In the more immediate future, the importance of flexibility in the patient's postoperative activity (sport, dance, etc.) should be considered when selecting fusion levels for a Lenke 5 curve.
One of the limitations of this study is the number of anterior and posterior approaches used to treat the patients. Our intent was to obtain a very close match of patients with similar preoperative values. As such, we did mix anterior and posterior approaches to obtain the closest match possible. Some may consider that an anterior-only approach may result in better flexibility, because there is no dissection through the posterior paraspinous musculature. We did analyze the anterior versus posterior selective fusions separately, but were underpowered to report the results (n = 6, posterior selective fusions). The data did suggest, however, that the flexibility measures were influenced most by the long fusion as opposed to the surgical approach.
It is unclear why 27% of the patients in our cohort had their thoracic spine included in the fusion. Although the patients matched similarly, specific clinical factors or patient concerns (skeletal maturity, shoulder balance, rib prominence, etc.) may have influenced the specific treatment plan. Interestingly, at short-term follow-up, whether the patient had a short or long fusion did not influence patient outcome as measured by the Scoliosis Research Society questionnaire. Overall, the relative importance of minor differences in coronal and sagittal correction as well as truncal flexibility need to be balanced with individual surgeon and patient criteria that determine fusion levels for Lenke 5 curves. Only long-term follow-up will help us to understand the risk and benefit of preserving thoracic motion segments in primary TL/L curves.
Fusion of the thoracic curve in a Lenke type 5 curve improves coronal correction.
Fusion of the thoracic curve in a Lenke type 5 curve reduces thoracic kyphosis and clinical flexibility.
At 2 years postoperatively, Scoliosis Research Society questionnaire scores and clinical balance are not significantly different between a matched set of patients that had either a selective or nonselective fusion of their Lenke 5 curve.
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adolescent idiopathic scoliosis; thoracolumbar/lumbar curve; selective fusion
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