Maintenance of Thoracic Kyphosis in the 3D Correction of Thoracic Adolescent Idiopathic Scoliosis Using Direct Vertebral Derotation

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1 Spine Deformity 1 (2013) 46e50 Maintenance of Thoracic Kyphosis in the 3D Correction of Thoracic Adolescent Idiopathic Scoliosis Using Direct Vertebral Derotation Satoru Demura, MD a,c, Burt Yaszay, MD a, Joseph H. Carreau, MD b, Vidyadhar V. Upasani, MD b, Tracey P. Bastrom, MA a, Carrie E. Bartley, MA a, Peter O. Newton, MD a, * a Department of Orthopedics, Rady Children s Hospital, 3030 Children s Way, San Diego, CA 92123, USA b Department of Orthopedic Surgery, University of California San Diego, 200 West Arbor Drive, San Diego, CA 92103, USA c Department of Orthopedic Surgery, Kanazawa University, 13-1 Takaramachi, Kanazawa, , Japan Received 10 March 2012; revised 21 June 2012; accepted 25 June 2012 Abstract Objectives: Through a review of prospectively collected data, we sought to analyze the outcomes related to 3-dimensional correction of adolescent idiopathic scoliosis (AIS) after posterior spinal fusion (PSF) and instrumentation using an aggressive combination of correction strategies. Background Summary: New techniques have been used to address sagittal plane deformity while maximizing coronal and axial correction, including Ponte osteotomy, differential rod over-contouring, and direct vertebral rotation with uniplanar screws. Methods: This is a consecutive single-center series of AIS patients with thoracic curves (Lenke 1 and 2) with 2-year follow-up who underwent PSF and instrumentation with the use of the following correction strategies: segmental uniplanar screws, ultra high-strength 5.5 mm steel rods, aggressive differential rod contouring, periapical Ponte osteotomies, and segmental direct vertebral derotation. Scoliosis Research Society (SRS)-22, radiographic and clinical parameters were evaluated at preoperative and 2-year time points. Results: Twenty-six patients were included (mean age years). Preoperative thoracic Cobb measured 52 9, which improved to 17 4 at 2-year follow-up, resulting in 68 9% correction. The average thoracic kyphosis from T5-T12 did not significantly change (21 10 to 22 5 at 2 years); however, in patients with kyphosis less than 20 preoperatively (avg ) kyphosis increased significantly at 2-year follow-up (avg. 20 4,p!.05). Preoperatively, axial rotation was more than 13 in 21 of 26 cases. At 2-year follow-up, axial rotation remained more than 13 in4of26cases(p!.01). Rib hump prominence was 17 5 preoperatively, which improved significantly to 10 4 at 2-year follow-up (p!.05). Postoperative SRS domain scores significantly improved in pain (4.3 to 4.7), self-image (3.7 to 4.3), and satisfaction (3.3 to 4.6) (p!.05). Conclusion: A high degree of coronal correction can be achieved in association with vertebral derotation without sacrificing sagittal plane alignment. High-strength rods aggressively bent to create kyphosis allow both restoration of kyphosis and axial plane derotation in thoracic idiopathic scoliosis. Ó 2013 Scoliosis Research Society. Keywords: Adolescent idiopathic scoliosis; Sagittal alignment; Uniplanar screw; Ponte osteotomy Author disclosures: DS (none); BY (consulting for K2M, Synthes, Ellipse; research support to institution from KCI, DePuy, K2M, Ellipse; speaking fees from DePuy; royalties from Orthopediatrics); JHC (none); VVU (none); TPB (none); CEB (none); PON (consulting for DePuy and Stanford University; expert testimony; research support to instituion from NIH, OREF, POSNA, SRS, Harms Study Group Foundation, DePuy, Axial Biotech, and Biospace Med/EOS Imaging; speaking frees from DePuy; patents with DePuy; royalties from DePuy and Thieme Publishing; development of educational presentations from DePuy; stock from Nuvasive). This work is supported in part by a grant from JJKK Medical Company, a Division of DePuy Spine, Japan and in part by a grant to the Harms Study Group Foundation from Depuy Spine. *Corresponding author. Department of Orthopedics, Rady Children s Hospital, 3030 Children s Way, Suite 410, San Diego, CA 92123, USA. Tel.: (858) ; fax: (858) address: pnewton@rchsd.org (P.O. Newton) X/$ - see front matter Ó 2013 Scoliosis Research Society.

2 S. Demura et al. / Spine Deformity 1 (2013) 46e50 47 Introduction In the past several years, excellent coronal correction has been reported using segmental pedicle screw fixation in the treatment of adolescent idiopathic scoliosis (AIS) [1-9]. However, many of these same studies have demonstrated an associated loss of thoracic kyphosis. One of the goals of AIS treatment is to maximize coronal and axial plane correction while restoring thoracic kyphosis. Recently, uniplanar screws were developed to provide the benefits seen with polyaxial screws in the sagittal plane in maintaining thoracic kyphosis, while maintaining the advantages of a fixed angle screw in the coronal and axial planes. The purpose of this study was to analyze the 3-dimensional correction after posterior instrumentation and fusion with the combined use of uniplanar screws, Ponte osteotomy, differential rod contour, and direct vertebral rotation. Materials and Methods A retrospective review of prospectively collected data of a single center from a larger multi-center study was conducted. Patients with AIS, Lenke type 1 or type 2 curves who underwent posterior spinal fusion and instrumentation at a single institution from 2006 to 2008 by a single surgeon were included. Uniplanar screws, ultra highstrength 5.5 mm steel rods, Ponte osteotomies, differential rod contouring, and direct vertebral rotation were used in all cases. Patients who underwent an anterior release were excluded. All cases followed the same procedure. After exposure of the posterior elements, soft tissue release and Ponte osteotomies were performed, and then followed by the insertion of segmental uniplanar screws. To avoid violation of the facet joint and to minimize the incision, down-going transverse process hooks were used at the most proximal instrumented vertebra. Deformity correction was done first by placement of a hyperkyphotic ultra high-strength contoured rod on the concave side, followed by cantilever reduction of the thoracic hump with an under-contoured convex rod. The coronal and sagittal corrections were fine tuned with compression and distraction. Segmental direct vertebral rotation was done to maximize axial correction. Ultra-strength (200 KSI) stainless steel rods (5.5 mm) were used in all cases (Fig. 1). Radiographic evaluations were performed at preoperative, 1-year, and 2-year postoperative time periods. Coronal measurements included Cobb angle of the proximal thoracic curve, major thoracic curve, thoracolumbar/lumbar curve, and coronal balance (from C7 to the central sacral vertical line). Sagittal measurements included thoracic kyphosis (T2eT12, T5eT12), lumbar lordosis (T12eS1), thoracolumbar junction (T10eL2), distal junctional kyphosis, proximal junctional kyphosis, and sagittal balance (from C7eS1). Axial radiographic evaluation was performed by measurement of vertebral rotation described by Perdriolle [10] preoperatively and grading of apical vertebral rotation by Upasani et al. [11] postoperatively. Angle of trunk rotation (rib hump, lumbar prominence), trunk shift, and shoulder height difference were also assessed. Patient-reported Scoliosis Research Society (SRS) 22 data were collected and analyzed at preoperative and 2-year follow-up. Statistical data were analyzed using SPSS (SPSS Inc., Chicago, IL). For comparison of paired values, repeatedmeasures analysis of variance was used followed by the Scheffe post-hoc test. A p value less than.05 was considered significant. Results There were 26 patients (23 female, 3 male) with a mean age at the time of surgery of years (11-17 years). There were 16 Lenke type 1 curves and 10 type 2 curves. The lumbar modifier was type A in 11 patients, type B in 6, and type C in 9. Preoperatively, 21 out of 26 patients had Fig. 1. A 14-year-old female pre-operatively with a 48 right thoracic curve and a sagittal profile from T5-T12 of 5 (left), and postoperatively with a 14 curve and 24 of kyphosis from T5-T12.

3 48 S. Demura et al. / Spine Deformity 1 (2013) 46e50 Table 1 Coronal radiographic parameters. The values represent mean SD with ranges in parentheses. Preop. (N526) 1-year (N525) 2-year (N526) Difference between Pre and 1 yr, 2 yr Proximal thoracic curve (15-51) (1-19) (2-22) p!.01, p!.01 % correction (14-93) (24-89) Main thoracic curve (40-70) (8-25) (10-25) p!.01, p!.01 % correction (47-88) (44-82) Thoracolumbar-lumbar curve (12-53) (3-32) (2-32) p!.01, p!.01 % correction (29-94) (33-93) Coronal balance (cm) ( ) (0-4.0) (0-3.0) p5.274, p5.061 (C7 translation from CSVL, absolute value) Abbreviation: CSVL, central sacral vertical line. a sagittal profile in the normal range (T5eT ), 5 patients were hypokyphotic (T5eT12!10 ), and none were hyperkyphotic (T5eT12 O40 ), according to the Lenke Classification system. The mean operative time was min (range min) with a mean blood loss of cc ( cc). The number of levels fused was 102 vertebrae on average (range 7-15). The upper instrumented vertebra ranged from T2eT5, and lower instrumented vertebra ranged from T11eL4. In this series, Ponte osteotomies were done at 51 interspaces at the region of the thoracic apical hypokyphosis or lordosis (range 3-9 osteotomies). The mean anchor density was anchors per level. The coronal radiographic parameters and correction rates are described in Table 1. The proximal thoracic, main thoracic, and lumbar curves all showed significant improvement from preoperative to 1- and 2-year postoperative (p!.001). The change in coronal balance trended toward significant correction (p5.06), with patients more balanced postoperatively. The sagittal parameters are shown in Table 2. The average thoracic kyphosis (both T5eT12 and T2eT12) was similar from preoperative to postoperative (po.05). However, when patients were divided into groups based on the magnitude of their preoperative kyphosis, a significant difference was found in kyphosis correction from preoperative to postoperative (Fig. 2, Table 3). Patients with kyphosis less than or equal to 20 preoperatively had a significant increase in T5eT12 kyphosis from 13 5 (range, 6-20 ) preoperative to 20 4 (range, ) at 2 years (p!.01). In those patients with kyphosis greater than 20 preoperatively, T5eT12 kyphosis decreased from 30 7 (range )to24 5 (range, ) at 2 years (p!.05). The change in lumbar lordosis, thoracolumbar junction, proximal junctional kyphosis, and distal junctional kyphosis were not significantly different. Preoperatively, axial rotation greater than 13 by Perdriolle was observed in 21 out of 26 cases. At 2 years, axial rotation greater than 13 was found in only 4 of the 26 cases (p!.01), (Table 4). Rib hump prominence was 17 5 (range ) preoperatively, which improved significantly to 10 4 (range, 3-16 ) at 2-year follow-up (p!.01). Lumbar prominence was 7 5 (range, 0-18 ) preoperatively, which improved significantly to 2 3 (range, 0-8 ) at 2-year follow-up (p!.01). Postoperative SRS domain scores significantly improved in pain ( ), self-image ( ), satisfaction ( ), and total score ( ) (p!.05). No significant differences were found in SRS domains of function and mental health (po.05). The mean improvement for the pain domain was 0.3 and 0.6 for appearance (self-image), which for self-image is below the minimally clinically important difference for this domain [12]. Discussion The achievement and maintenance of high degrees of coronal correction in the surgical treatment of AIS using segmental pedicle screw fixation is well documented in the literature, dating back to the work of Suk et al. in 1995, Table 2 Sagittal radiographic parameters. The values represent mean SD with ranges in parentheses. Preop. (N526) 1-year (N525) 2-year (N526) Difference Between (Pre and 1 yr, 2 yr) Thoracic kyphosis (T2eT12) (8-50) (19-43) (15-43) p5.210, p5.537 Thoracic kyphosis (T5e12) (6-40) (12-36) (13-32) p5.246, p5.674 Thoracolumbar junction (T10eL2) ( 17-14) ( 25-31) ( 22-28) p5.715, p5.893 Lumbar lordosis (T12eS1) (32-81) (38-78) (37-82) p5.518, p5.493 Proximal junctional kyphosis ( 3-10) ( 5-14) ( 2-12) p5.731, p5.456 Distal junctional kyphosis ( 18-8) ( 14-20) ( 17-22) p5.192, p5.335 Sagittal balance (cm) (C7 translation from S1) ( ) ( ) ( ) p5.078, p5.018

4 S. Demura et al. / Spine Deformity 1 (2013) 46e50 49 Table 4 Axial radiographic parameters. Perdriolle s method Pre-op (N) Upasani s grade Grade 0 (0-8 ) Grade 1 (9-12 ) 2-year (N) Grade 2 (>13 ) Fig. 2. Distribution of T5-T12 kyphosis pre-operatively and at 2-years postoperatively. which described the efficacy of pedicle screw fixation compared with all hook constructs [1]. Since that time, numerous studies have reported on the effectiveness of pedicle screws in achieving coronal correction [1-8]. Lehman et al., for example, reported a coronal major curve correction of 72.1% with the use of segmental pedicle screws [5]. Lonner et al. compared major curve correction with the use of monoaxial screws (69%) to polyaxial screws (68%), and found there was not a significant difference between the two groups [6]. Similarly, Kim et al. reported on the superiority of all screw constructs [9]. In the current study, the use of uniplanar screws resulted in similar correction in the coronal plane compared with the literature. Although some studies have shown maintenance of thoracic kyphosis [2,3], most recent studies have demonstrated a trend of hypokyphosis of the thoracic spine after correction with all pedicle screw constructs. Lowenstein reported hypokyphotic tendencies with thoracic pedicle screw constructs compared with hybrid instrumentation [4]. Lehman et al. also described a decrease in thoracic kyphosis with the use of monoaxial screws [5]. Furthermore, Lonner et al. compared the results using hybrid instrumentation, polyaxial, and monoaxial segmental screw fixation and found that the polyaxial constructs were able to best maintain thoracic kyphosis [6]. The authors speculated that various factors affect postoperative thoracic kyphosis, such as implant density, derotation maneuver through the convex monoaxial screws, and rod diameter. Our results showed that the use of uniplanar screws in combination with ultra high-strength 5.5 mm steel rods maintained thoracic kyphosis similar to that which has been reported with polyaxial screws. One possible reason for this might be the ability of uniplanar screws to angulate in the sagittal direction similar to polyaxial screws. In this series, Ponte osteotomies, which is a procedure commonly used in the treatment of Scheuermann s kyphosis, were performed in all cases [13,14]. However, in this series, the osteotomies were done to gain and/or maintain kyphosis in most cases, rather than to reduce kyphosis as in Scheuermann s. To preserve thoracic kyphosis in the treatment of AIS, it has been suggested that one must attempt to lengthen the posterior column [15]. By removing the facets and soft tissues of posterior elements including the supraspinous ligaments, interspinous ligaments, ligamentum flavum, and facet joint capsule, we have effectively detethered the posterior elements allowing the posterior column to lengthen. In this series, we placed greater kyphosis in the rods, especially the corrective concave rod. It is challenging to estimate the unique effect of each of the techniques or strategies on the sagittal profile, as they were used in combination. In the current study, there was a 3 gain in thoracic kyphosis in the entire series and approximately 7 gain in patients with kyphosis less than 20 preoperatively. This significant increase in T5eT12 kyphosis was not seen in previous studies on all pedicle screw constructs. To evaluate radiographic spinal deformity in the axial plane, Kuklo et al. reported on apical rib hump prominence, apical vertebral body-rib ratio, and apical rib spread Table 3 Sagittal parameters by kyphosis group. The values represent mean SD with ranges in parentheses. Preop. 1-year 2-year Difference Between Pre and 1 yr, 2 yr Under 20 group T2eT12 kyphosis (8-31) (19-34) (15-43) p!.01, p!.01 T5eT12 kyphosis (6-20) (12-30) (13-25) p!.01, p!.01 Over 20 group T2eT12 kyphosis (28-50) (27-43) (26-41) p5.600, p5.025 T5eT12 kyphosis (22-40) (19-36) (17-32) p5.136, p5.013

5 50 S. Demura et al. / Spine Deformity 1 (2013) 46e50 difference [3]. This study used a more direct measurement of axial deformity based on direct vertebral measures [11]. In this series, 22 out of 26 cases had less than 13 of rotation (Upasani grade 0 or 1), which was similar to the results of 210 cases that compared vertebral rotation between uniplanar and polyaxial screws [16]. A recent report by Lonner et al. showed that improvement of angle of trunk rotation (ATR) was around 50% after surgery utilizing pedicle screws [6]. However, their preoperative thoracic ATR was 13.0 to 14.8 on average, which was a relatively modest rib prominence compared with the current study (17 5 ). We believe there is residual rib deformity (altered rib shape) that is not corrected completely despite axial vertebral correction, and that the current results indicate excellent correction of axial deformity without thoracoplasty. Several strategies were consistently used in this fairly typical series of patients with thoracic idiopathic scoliosis with the goals of achieving high degrees of 3-dimensional balance and spinal deformity correction. These methods largely allowed the goals to be achieved, particularly with regard to the sagittal plane, which has been most problematic, particularly when surgeons have focused on coronal and axial correction. Unfortunately, this series offers little in determining if all the techniques are important, and if so, what each contributes to the 3D correction. Restoring the relative length of the posterior column of the thoracic spine appears to be an important feature of ideal AIS correction. Shortening the anterior column or lengthening the posterior column (or both) are the options. In larger, stiffer deformities, both may be required; however, in the magnitude of scoliosis treated in this series of patients, the posterior lengthening approach was effective. Ultrastrength steel rods with aggressive rod contouring also allowed greater force application to the spine; however, the limit of the bone-screw interface strength must also be recognized when attempting to maximize correction forces. Conclusion This study shows that excellent coronal and axial correction can be achieved without sacrificing thoracic kyphosis. Several strategies were employed: multi-level Ponte osteotomies, differential rod over-contouring, uniplanar screws and ultra-strength 5.5 mm steel rods. This combination offers a solution to the commonly seen problem of induced hypokyphosis associated with pedicle screw constructs and direct vertebral rotation used in the correction of thoracic AIS. References [1] Suk SI, Lee SM, Kim WJ, et al. Segmental pedicle screw fixation in the treatment of thoracic idiopathic scoliosis. Spine (Phila Pa 1976) 1995;20:1399e405. [2] Suk SI, Lee SM, Chung ER, et al. Selective thoracic fusion with segmental pedicle screw fixation in the treatment of thoracic idiopathic scoliosis: more than 5-year follow-up. Spine (Phila Pa 1976) 2005;30:1602e9. [3] Kuklo TR, Potter BK, Polly Jr DW, et al. Monaxial versus multiaxial thoracic pedicle screws in the correction of adolescent idiopathic scoliosis. Spine (Phila Pa 1976) 2005;30:2113e20. [4] Lowenstein JE, Matsumoto H, Vitale MG, et al. Coronal and sagittal plane correction in adolescent idiopathic scoliosis: a comparison between all pedicle screw versus hybrid thoracic hook lumbar screw constructs. Spine (Phila Pa 1976) 2007;32:448e52. [5] Lehman Jr RA, Lenke LG, Keeler KA, et al. Operative treatment of adolescent idiopathic scoliosis with posterior pedicle screw-only constructs: minimum three-year follow-up of one hundred fourteen cases. Spine (Phila Pa 1976) 2008;33:1598e604. [6] Lonner BS, Auerbach JD, Boachie-Adjei O, et al. Treatment of thoracic scoliosis: are monoaxial thoracic pedicle screws the best form of fixation for correction? Spine (Phila Pa 1976) 2009;34:845e51. [7] Quan GM, Gibson MJ. Correction of main thoracic adolescent idiopathic scoliosis using pedicle screw instrumentation: does higher implant density improve correction? Spine (Phila Pa 1976) 2010;35:562e7. [8] Fu G, Kawakami N, Goto M, et al. Comparison of vertebral rotation corrected by different techniques and anchors in surgical treatment of adolescent thoracic idiopathic scoliosis. J Spinal Disord Tech 2009;22:182e9. [9] Kim YJ, Lenke LG, Cho SK, et al. Comparative analysis of pedicle screw versus hook instrumentation in posterior spinal fusion of adolescent idiopathic scoliosis. Spine (Phila Pa 1976) 2004;29:2040e8. [10] Perdriolle R, Vidal J. Thoracic idiopathic scoliosis curve evolution and prognosis. Spine (Phila Pa 1976) 1985;10:785e91. [11] Upasani VV, Chambers RC, Dalal AH, et al. Grading apical vertebral rotation without a computed tomography scan: a clinically relevant system based on the radiographic appearance of bilateral pedicle screws. Spine (Phila Pa 1976) 2009;34:1855e62. [12] Carreon LY, Sanders JO, Diab M, et al. The minimum clinically important difference in Scoliosis Research Society-22 appearance, activity, and pain domains after surgical correction of adolescent idiopathic scoliosis. Spine (Phila Pa 1976) 2010;35:2079e83. [13] Geck MJ, Macagno A, Ponte A, et al. The Ponte procedure: posterior only treatment of Scheuermann s kyphosis using segmental posterior shortening and pedicle screw instrumentation. J Spinal Disord Tech 2007;20:586e93. [14] Lonner BS, Newton P, Betz R, et al. Operative management of Scheuermann s kyphosis in 78 patients: radiographic outcomes, complications, and technique. Spine (Phila Pa 1976) 2007;32: 2644e52. [15] Newton PO, Yaszay B, Upasani VV, et al. Preservation of thoracic kyphosis is critical to maintain lumbar lordosis in the surgical treatment of adolescent idiopathic scoliosis. Spine (Phila Pa 1976) 2010;35:1365e70. [16] Dalal A, Upasani VV, Bastrom TP, et al. Apical vertebral rotation in adolescent idiopathic scoliosis: comparison of uniplanar and polyaxial pedicle screws. J Spinal Disord Tech 2011;24:251e7.