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The Effect of Time and Fusion Length on Motion of the Unfused Lumbar Segments in Adolescent Idiopathic Scoliosis
Spine Deformity 3 (2015) 549e553 www.spine-deformity.org
The Effect of Time and Fusion Length on Motion of the Unfused Lumbar Segments in Adolescent Idiopathic Scoliosis Michelle C. Marks, PT, MAa,*, Tracey P. Bastrom, MAb, Maty Petcharaporn, BSa, Suken A. Shah, MDd, Randal R. Betz, MDe, Amer Samdani, MDe, Baron Lonner, MDf, Firoz Miyanji, MDg, Peter O. Newton, MDa,b,c a Setting Scoliosis Straight Foundation, San Diego, CA, USA Department of Orthopedics, Rady Children’s Hospital, San Diego, CA, USA c Department of Orthopedic Surgery, University of California San Diego, La Jolla, CA, USA d Department of Orthopedics, Nemours/Alfred I. DuPont Hospital for Children, Wilmington, DE, USA e Department of Orthopedics, Shriners Hospital for Children, Philadelphia, PA, USA f Scoliosis Associates, New York, NY, USA g Department of Orthopedics, BC Children’s Hospital, Vancouver, BC, Canada Received 10 June 2014; revised 16 March 2015; accepted 19 March 2015 b
Abstract Objective: The purpose of this study was to assess L4eS1 inter-vertebral coronal motion of the unfused distal segments of the spine in patients with adolescent idiopathic scoliosis (AIS) after instrumented fusion with regards to postoperative time and fusion length, independently. Methods: Coronal motion was assessed by standardized radiographs acquired in maximum right and left bending positions. The intervertebral angles were measured via digital radiographic measuring software and the motion from the levels of L4eS1 was summed. The entire cohort was included to evaluate the effect of follow-up time on residual motion. Patients were grouped into early (!5 years), midterm (5e10 years), and long-term (O10 years) follow-up groups. A subset of patients (n 5 35) with a primary thoracic curve and a nonstructural modifier type ‘‘C’’ lumbar curve were grouped as either selective fusion (lowest instrumented vertebra [LIV] of L1 and above) or longer fusion (LIV of L2 and below) and effect on motion was evaluated. Results: The data for 259 patients are included. The distal residual unfused motion (from L4 to S1) remained unchanged across early, midterm, to long-term follow-up. In the selective fusion subset of patients, a significant increase in motion from L4 to S1 was seen in the patients who were fused long versus the selectively fused patients, irrespective of length of follow-up time. Conclusion: Motion in the unfused distal lumbar segments did not vary within the O10-year follow-up period. However, in patients with a primary thoracic curve and a nonstructural lumbar curve, the choice to fuse longer versus shorter may have significant consequences. The summed motion from L4 to S1 is 50% greater in patients fused longer compared with those patients with a selective fusion, in which postoperative motion is shared by more unfused segments. The implications of this focal increased motion are unknown, and further research is warranted but can be surmised. Ó 2015 Scoliosis Research Society. Keywords: Adolescent Idiopathic Scoliosis; Post-operative; Spinal flexibility; Long-term follow-up
Introduction The well-established goal of the surgical management of adolescent idiopathic scoliosis (AIS) is to maximize deformity correction, achieve coronal and sagittal balance, and retain spinal flexibility [1,2]. If the deformity *Corresponding author. Setting Scoliosis Straight Foundation, 2535 Camino Del Rio South, Suite 325, San Diego, CA 92108. Tel.: (520) 529 2546; fax: (520) 577 4539. E-mail address: [email protected] (M.C. Marks). 2212-134X/$ - see front matter Ó 2015 Scoliosis Research Society. http://dx.doi.org/10.1016/j.jspd.2015.03.007
correction can be achieved with minimal levels of fusion, the retention of spinal flexibility is maximized. However, notwithstanding the unfused status of the distal segments of the spine, the mobility/flexibility is altered from the proximal fusion that has occurred. As the spine functions as a unit [3], alterations to segments above or below can disturb the delicate balance that exists in the mobility of the spinal column. These motion alterations are poorly understood, and the short- and long-term effects of disrupted mechanics are also poorly understood.
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Previous research has demonstrated that extending fusion levels distally have an impact on spinal mobility [4,5]. In particular, coronal bending is significantly more concentrated and increased below the fusion, with more distal lowest instrumented vertebra (LIV) at an average of 3 years’ follow-up [5]. Yet two very common clinical questions remain unanswered with regards to motion in the unfused lumbar segments before fusion for AIS: What will happen in the long term and what effect will the fusion length have? The purpose of this study was to assess the L4eS1 intervertebral coronal motion of the unfused distal segments of the spine in patients with AIS after instrumented fusion with regards to postoperative time and fusion length, as both independent and interactive factors. Materials and Methods Patients with AIS who had undergone spinal fusion for correction of their deformity were prospectively offered inclusion into this IRB approved cross-sectional study at their routine 2e16-year postoperative visits at one of five participating centers. All curve types (Lenke classification types) were included, and fusion with either posterior or anterior instrumentation was accepted. Motion was assessed by standardized radiographs acquired in maximum right and left bending positions (Fig. 1A and B). Radiographic acquisition
was standardized at all sites with the following instructions: the right and left bend film were performed in the standing position, with the patient laterally bending to each side with maximum effort and allowing the neck to also bend in the same direction, and rotation in the transverse plane minimized. The intervertebral angles were measured via digital radiographic measuring software (SpineView 2.4, Surgiview, Paris, France) at each level from T12 to S1. All measurements were made by one individual. The intrarater reliability of the individual measurer was tested (on the first 57 patients) and confirmed to be ‘‘very good,’’ with an intraclass correlation coefficient of 0.86 and standard error of measurement of 2 degrees. Static angles in the coronal plane at each intervertebral angle between T12 and S1 were measured with the following conventions: (þ) intervertebral angle opens to the right and (e) intervertebral angle opens to the left. The range of motion in the coronal plane was measured by the summation of the static angle on the left bend with the static angle on the right bend to equal the total motion at the respective segment (eg, at the L1eL2 disc space: angle measured on left bend of þ6 and angle measured on the right bend of e4 summed to equal a total motion of 10 degrees of motion) (Fig. 2). This method of angular measurement has been previously reported and as stated by these authors, ‘‘although the radiographic measurements were made in static positions, the term ‘dynamic’ motion is a calculated quantity and refers to
Fig. 1. (A) Left and (B) right coronal bend films.
M.C. Marks et al. / Spine Deformity 3 (2015) 549e553
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Fig. 2. Digital radiograph measuring methodology of coronal plane motion.
the relative movement between two vertebrae that occurred in the time interval between the two static radiographs’’ [6]. The intervertebral motion for each segment from L4 to S1 was summed for each patient and is reported as ‘‘summed L4eS1 coronal motion.’’ All patients in this study were grouped by their postoperative follow-up time point: into early (!5 years), midterm (5e10 years), and long-term (O10 years) followup groups. A subset of patients (n 5 35) with a primary thoracic curve and a nonstructural modifier type C lumbar curve were grouped as either selective fusion (LIV of L1 and above) or longer fusion (LIV of L2 and below) and its effect on L4eS1 motion was evaluated. This subgroup was selected as a primary thoracic curve and a nonstructural modifier type C lumbar curve is a curve type in which a selective thoracic fusion is a treatment option but variability in this approach exists. This allowed for a comparison of shorter versus longer fusions in a curve presentation that is often treated by either approach. The effects of follow-up time and the differences in selective versus nonselective fusion were evaluated with an analysis of variance. Data were analyzed using the Statistical Package for the Social Sciences (SPSS, Inc. v.12, Chicago, IL). The alpha level was set at p !.05 to declare significance.
met the inclusion criteria at each of the 5 sites was approached for enrollment. The average age at surgery was 14 2 years (range 10e24). Curve types included 134 Lenke 1 curves, 51 Lenke 2 curves, 9 Lenke 3 curves, 10 Lenke 4 curve, 40 Lenke 5 curves, and 15 Lenke 6 curve type. Preoperative primary curve magnitude was 55 12 degrees (range 36e103), which corrected to 21 8 degrees postoperatively (range 1e44). There were 228 (88%) females and 31 (12%) males. All 259 patients were grouped by their postoperative follow-up time point: into early (!5 years), midterm (5-10 years), and long-term (O10 years) follow-up groups. There were 176 patients in the early (!5 years) follow-up
Results The data for 259 patients are included were collected in total for this study. Patients were contributed from 5 sites with the following distribution: Site A (115), Site B (38), Site C (23), Site D (32), and Site E (51). Each patient that
Fig. 3. Percentage distribution of the lowest instrumented vertebrae for the early (!5 years), midterm (5e10 years), and long-term (O10 years) follow-up groups.
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compared with nine degrees of motion in the selective fusion group (p ! .001) (Fig. 5). Discussion
Fig. 4. Coronal L4eS1 summed motion at each of the postoperative time periods. LIV, lowest instrumented vertebra.
group, 51 in the midterm (5-10 years) follow-up group, and 32 in the long-term (O10 years) follow-up group. The surgical approaches included 180 posterior only, 64 anterior only, and 15 combined anterior and posterior surgery. The LIV percentage for each follow-up group showed varied distribution (Fig. 3). The interaction term of time of followup and LIV was not significant (p 5 .789). The distal residual unfused coronal motion (from L4 to S1) was not significantly different across early, midterm, to long-term follow-up (p 5 .526) (Fig. 4). In the subset of patients (n 5 35) with a primary thoracic curve and a nonstructural modifier type C lumbar curve in which a selective thoracic fusion is a treatment option, patients were grouped as either selective fusion (LIV of L1 and above) or longer fusion (LIV of L2 and below). There were 26 patients in the selective group (25 patients fused to T12 or above and 1 fused to L1) and 9 patients in the longer fusion group (3 fused to L2, 4 fused to L3, and 2 fused to L2). The surgical approaches for the 26 patients treated selectively included 15 posterior only, and 11 anterior only approaches. All nine patients in the longer fusion group were treated via posterior only approaches. There was a statistically significant difference in the residual unfused coronal motion, with the longer fusion group showing a mean of 18 degrees of motion
Fig. 5. Coronal L4eS1 summed motion in the longer versus selective fusions.
Prior studies have demonstrated the impact of distal fusion level on both spinal mobility and pain experience [4,5,7]. Many of these studies report on the increased pain and decreased mobility associated with distal fusion levels utilizing Harrington instrumentation [7-9]. Recent work on more modern instrumentation systems has corroborated the negative impact on overall mobility with more distal fusions [10]. Although the overall mobility is decreased, the remaining mobility is concentrated at the remaining motion segments in these distal fusions [5]. Understanding the impact of fusion level choice on future mobility, pain, and disc health is critical. In an effort to begin to understand the changes in mobility below the fusion over time (as the likelihood of developing symptoms of degenerative disc disease increases with age [11]) this study compared motion below the fusion in patients at their early (!5 years) postoperative follow-up time point to patients at a midterm (5e10 years) operative follow-up time point to patients with longer (O10 years) follow-up. An effect of time was not identified within this data set, as the magnitude of distal motion observed in patients from early to longer follow-up after surgery is similar. A limitation in our evaluation is the lack of standardized preoperative bending films, to provide an understanding in the ‘‘change’’ in motion for each patient. In addition, preoperative characteristics in bending motion are not accounted for in this investigation. Although an interaction of time of follow-up and LIV was not found in this series, this potential effect should be examined further with a larger patient population. An initial understanding of the impact of performing a longer fusion was elucidated with our comparison of a subgroup of patients with a primary thoracic curve and a nonstructural modifier type C lumbar curve. According to the Lenke Classification algorithm for treatment, a 1C curve type should be selectively fused. But as shown with earlier work evaluating adherence to the classification treatment algorithm, there are other aspects of the clinical and radiographic deformity that suggest deviation from the recommendations of the classification system [12]. However, whatever the factors associated with deciding to fuse longer, consequences may exist. The summed motion at L4eS1 in the patients that are fused longer (LIV of L2 and below) was significantly greater than motion in the patients that were selectively fused (LIVof L1 and above). With less mobile segments to share motion, the impact on the remaining unfused distal portions is detrimental. The potential for ‘‘remote’’ versus ‘‘adjacent’’ segment disease has previously been described [5,13] and this provides further evidence of alterations in distal motion that may potentially lead to disc degeneration. The implication of the
M.C. Marks et al. / Spine Deformity 3 (2015) 549e553
concentrated increased motion on future disc health is not completely understood. Studies have identified increased indices of degenerative disc disease below the distal fusion level [13-18]; however, there has not been a causal link established between motion below the fusion and degenerative disc disease. A limitation of this study is the small sample size of patients in the long fusion group, and additional study with larger patient groups is warranted. Further research with long-term follow-up (10 years postoperatively) is currently underway utilizing magnetic resonance imaging and radiographic evaluations. This investigation will assist in the understanding of the relationship of increased segmental motion and disc health in AIS. The sample of magnetic resonance imaging data in this patient population will also provide ‘‘gold standard’’ comparison for the potential of radiographic parameter assessment of intervertebral disc degeneration. Conclusion In this comparison of motion in the unfused distal lumbar segments in patients with varying amounts of follow-up, there were no differences in motion in patients at the early, mid-, and long-term follow-up periods. When considering fusion length in patients with a primary thoracic curve and a nonstructural lumbar curve, the choice to fuse longer versus shorter may have deleterious consequences. The summed motion from L4 to S1 is 50% greater in patients fused longer compared with those with a selective fusion, in which postoperative motion is shared by more unfused segments. The implications of this focal increased motion are unknown and further research on motion alterations and disc health is warranted.
Acknowledgment This study was supported by research grants from DePuy Synthes Spine and the Scoliosis Research Society to Setting Scoliosis Straight Foundation for Harms Study Group research efforts. References [1] Bridwell K. Surgical treatment of idiopathic adolescent scoliosis. Spine 1999;24:2607e16. [2] Majdouline YA, Robitaille M, Sarwark JF, Labelle H. Scoliosis correction objectives in adolescent idiopathic scoliosis. J Pediatric Orthop 2007;27:775e81.
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[3] Stokes IA. Spinal biomechanics. In: Weinstein S, editor. The Pediatric Spine Principles and Practice. 2nd ed. Philadelphia: PA Lippincott Williams & Wilkins; 2001. p. 57e71. [4] Hayes MA, Tomkins SF, Herndon WA, Gruel CR, Kopta JA, Howard TC. Clinical and radiological evaluation of lumbosacral motion below fusion levels in idiopathic scoliosis. Spine 1988;13: 1161e7. [5] Marks M, Newton PO, Petcharaporn M, et al. Postoperative segmental motion of the unfused spine distal to the fusion in 100 patients with adolescent idiopathic scoliosis. Spine 2012;37: 826e32. [6] Boden SD, Wiesel SW. Lumbosacral segmental motion in normal individualsdhave we been measuring instability properly? Spine 1990;15:571e9. [7] Aaro S, Ohlen G. The effect of Harrington instrumentation on the sagittal configuration and mobility of the spine in scoliosis. Spine 1983;8:570e5. [8] Bartie BJ, Lonstein JE, Winter RB. Long-term follow-up of adolescent idiopathic scoliosis patients who had Harrington instrumentation and fusion to the lower lumbar vertebrae: is low back pain a problem? Spine (Phila Pa 1976) 2009;34:E873e8. [9] Cochran T, Irstam L, Nachemson A. Long-term anatomic and functional changes in patients with adolescent idiopathic scoliosis treated by Harrington rod fusion. Spine (Phila Pa 1976) 1983;8: 576e84. [10] Newton PO, Marks MC, Bastrom T, et al. Harms Study Group. Post operative trunk flexibility loss is modest but incremental as the fusion progresses distally. Paper presented at: Scoliosis Research Society Annual Meeting; September 10e13, 2008; Salt Lake City, Utah. [11] Siemionow K, An H, Masuda K, Andersson G, Cs-Szabo G. The effects of age, sex, ethnicity, and spinal level on the rate of intervertebral disc degeneration: a review of 1712 intervertebral discs. Spine 2011;36:1333e9. [12] Clements DH, Marks M, Newton PO, Betz RR, Lenke L, Shufflebarger H. Harms Study Group. Did the Lenke classification change scoliosis treatment? Spine 2011;36:1142e5. [13] Green DW, Lawhorne 3rd TW, Widmann RF, et al. Long-term magnetic resonance imaging follow-up demonstrates minimal transitional level lumbar disc degeneration after posterior spine fusion for adolescent idiopathic scoliosis. Spine 2011;36:1948e54. [14] Violas P, Estivalezes E, Briot J, et al. Quantification of intervertebral disc volume properties below spine fusion, using magnetic resonance imaging, in adolescent idiopathic scoliosis surgery. Spine 2007;32: E405e12. [15] Balderston RA, Albert TJ, McIntosh T, et al. Magnetic resonance imaging analysis of lumbar disc changes below scoliosis fusions. A prospective study. Spine 1998;23:54e8. [16] Edwards II CC, Bridwell KH, Patel A, et al. Thoracolumbar deformity arthrodesis to L5 in adults: the fate of the L5-S1 disc. Spine (Phila Pa 1976) 2003;28:2122e31. [17] Kuhns CA, Bridwell KH, Lenke LG, et al. Thoracolumbar deformity arthrodesis stopping at L5. Spine 2007;32:2771e6. [18] Kepler CK, Meredith DS, Green DW, Widmann RF. Long-term outcomes after posterior spine fusion for adolescent idiopathic scoliosis. Curr Opin Pediatr 2012;24:68e75.
The Effect of Time and Fusion Length on Motion of the Unfused Lumbar Segments in Adolescent Idiopathic Scoliosis Michelle C. Marks, PT, MAa,*, Tracey P. Bastrom, MAb, Maty Petcharaporn, BSa, Suken A. Shah, MDd, Randal R. Betz, MDe, Amer Samdani, MDe, Baron Lonner, MDf, Firoz Miyanji, MDg, Peter O. Newton, MDa,b,c a Setting Scoliosis Straight Foundation, San Diego, CA, USA Department of Orthopedics, Rady Children’s Hospital, San Diego, CA, USA c Department of Orthopedic Surgery, University of California San Diego, La Jolla, CA, USA d Department of Orthopedics, Nemours/Alfred I. DuPont Hospital for Children, Wilmington, DE, USA e Department of Orthopedics, Shriners Hospital for Children, Philadelphia, PA, USA f Scoliosis Associates, New York, NY, USA g Department of Orthopedics, BC Children’s Hospital, Vancouver, BC, Canada Received 10 June 2014; revised 16 March 2015; accepted 19 March 2015 b
Abstract Objective: The purpose of this study was to assess L4eS1 inter-vertebral coronal motion of the unfused distal segments of the spine in patients with adolescent idiopathic scoliosis (AIS) after instrumented fusion with regards to postoperative time and fusion length, independently. Methods: Coronal motion was assessed by standardized radiographs acquired in maximum right and left bending positions. The intervertebral angles were measured via digital radiographic measuring software and the motion from the levels of L4eS1 was summed. The entire cohort was included to evaluate the effect of follow-up time on residual motion. Patients were grouped into early (!5 years), midterm (5e10 years), and long-term (O10 years) follow-up groups. A subset of patients (n 5 35) with a primary thoracic curve and a nonstructural modifier type ‘‘C’’ lumbar curve were grouped as either selective fusion (lowest instrumented vertebra [LIV] of L1 and above) or longer fusion (LIV of L2 and below) and effect on motion was evaluated. Results: The data for 259 patients are included. The distal residual unfused motion (from L4 to S1) remained unchanged across early, midterm, to long-term follow-up. In the selective fusion subset of patients, a significant increase in motion from L4 to S1 was seen in the patients who were fused long versus the selectively fused patients, irrespective of length of follow-up time. Conclusion: Motion in the unfused distal lumbar segments did not vary within the O10-year follow-up period. However, in patients with a primary thoracic curve and a nonstructural lumbar curve, the choice to fuse longer versus shorter may have significant consequences. The summed motion from L4 to S1 is 50% greater in patients fused longer compared with those patients with a selective fusion, in which postoperative motion is shared by more unfused segments. The implications of this focal increased motion are unknown, and further research is warranted but can be surmised. Ó 2015 Scoliosis Research Society. Keywords: Adolescent Idiopathic Scoliosis; Post-operative; Spinal flexibility; Long-term follow-up
Introduction The well-established goal of the surgical management of adolescent idiopathic scoliosis (AIS) is to maximize deformity correction, achieve coronal and sagittal balance, and retain spinal flexibility [1,2]. If the deformity *Corresponding author. Setting Scoliosis Straight Foundation, 2535 Camino Del Rio South, Suite 325, San Diego, CA 92108. Tel.: (520) 529 2546; fax: (520) 577 4539. E-mail address: [email protected] (M.C. Marks). 2212-134X/$ - see front matter Ó 2015 Scoliosis Research Society. http://dx.doi.org/10.1016/j.jspd.2015.03.007
correction can be achieved with minimal levels of fusion, the retention of spinal flexibility is maximized. However, notwithstanding the unfused status of the distal segments of the spine, the mobility/flexibility is altered from the proximal fusion that has occurred. As the spine functions as a unit [3], alterations to segments above or below can disturb the delicate balance that exists in the mobility of the spinal column. These motion alterations are poorly understood, and the short- and long-term effects of disrupted mechanics are also poorly understood.
550
M.C. Marks et al. / Spine Deformity 3 (2015) 549e553
Previous research has demonstrated that extending fusion levels distally have an impact on spinal mobility [4,5]. In particular, coronal bending is significantly more concentrated and increased below the fusion, with more distal lowest instrumented vertebra (LIV) at an average of 3 years’ follow-up [5]. Yet two very common clinical questions remain unanswered with regards to motion in the unfused lumbar segments before fusion for AIS: What will happen in the long term and what effect will the fusion length have? The purpose of this study was to assess the L4eS1 intervertebral coronal motion of the unfused distal segments of the spine in patients with AIS after instrumented fusion with regards to postoperative time and fusion length, as both independent and interactive factors. Materials and Methods Patients with AIS who had undergone spinal fusion for correction of their deformity were prospectively offered inclusion into this IRB approved cross-sectional study at their routine 2e16-year postoperative visits at one of five participating centers. All curve types (Lenke classification types) were included, and fusion with either posterior or anterior instrumentation was accepted. Motion was assessed by standardized radiographs acquired in maximum right and left bending positions (Fig. 1A and B). Radiographic acquisition
was standardized at all sites with the following instructions: the right and left bend film were performed in the standing position, with the patient laterally bending to each side with maximum effort and allowing the neck to also bend in the same direction, and rotation in the transverse plane minimized. The intervertebral angles were measured via digital radiographic measuring software (SpineView 2.4, Surgiview, Paris, France) at each level from T12 to S1. All measurements were made by one individual. The intrarater reliability of the individual measurer was tested (on the first 57 patients) and confirmed to be ‘‘very good,’’ with an intraclass correlation coefficient of 0.86 and standard error of measurement of 2 degrees. Static angles in the coronal plane at each intervertebral angle between T12 and S1 were measured with the following conventions: (þ) intervertebral angle opens to the right and (e) intervertebral angle opens to the left. The range of motion in the coronal plane was measured by the summation of the static angle on the left bend with the static angle on the right bend to equal the total motion at the respective segment (eg, at the L1eL2 disc space: angle measured on left bend of þ6 and angle measured on the right bend of e4 summed to equal a total motion of 10 degrees of motion) (Fig. 2). This method of angular measurement has been previously reported and as stated by these authors, ‘‘although the radiographic measurements were made in static positions, the term ‘dynamic’ motion is a calculated quantity and refers to
Fig. 1. (A) Left and (B) right coronal bend films.
M.C. Marks et al. / Spine Deformity 3 (2015) 549e553
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Fig. 2. Digital radiograph measuring methodology of coronal plane motion.
the relative movement between two vertebrae that occurred in the time interval between the two static radiographs’’ [6]. The intervertebral motion for each segment from L4 to S1 was summed for each patient and is reported as ‘‘summed L4eS1 coronal motion.’’ All patients in this study were grouped by their postoperative follow-up time point: into early (!5 years), midterm (5e10 years), and long-term (O10 years) followup groups. A subset of patients (n 5 35) with a primary thoracic curve and a nonstructural modifier type C lumbar curve were grouped as either selective fusion (LIV of L1 and above) or longer fusion (LIV of L2 and below) and its effect on L4eS1 motion was evaluated. This subgroup was selected as a primary thoracic curve and a nonstructural modifier type C lumbar curve is a curve type in which a selective thoracic fusion is a treatment option but variability in this approach exists. This allowed for a comparison of shorter versus longer fusions in a curve presentation that is often treated by either approach. The effects of follow-up time and the differences in selective versus nonselective fusion were evaluated with an analysis of variance. Data were analyzed using the Statistical Package for the Social Sciences (SPSS, Inc. v.12, Chicago, IL). The alpha level was set at p !.05 to declare significance.
met the inclusion criteria at each of the 5 sites was approached for enrollment. The average age at surgery was 14 2 years (range 10e24). Curve types included 134 Lenke 1 curves, 51 Lenke 2 curves, 9 Lenke 3 curves, 10 Lenke 4 curve, 40 Lenke 5 curves, and 15 Lenke 6 curve type. Preoperative primary curve magnitude was 55 12 degrees (range 36e103), which corrected to 21 8 degrees postoperatively (range 1e44). There were 228 (88%) females and 31 (12%) males. All 259 patients were grouped by their postoperative follow-up time point: into early (!5 years), midterm (5-10 years), and long-term (O10 years) follow-up groups. There were 176 patients in the early (!5 years) follow-up
Results The data for 259 patients are included were collected in total for this study. Patients were contributed from 5 sites with the following distribution: Site A (115), Site B (38), Site C (23), Site D (32), and Site E (51). Each patient that
Fig. 3. Percentage distribution of the lowest instrumented vertebrae for the early (!5 years), midterm (5e10 years), and long-term (O10 years) follow-up groups.
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compared with nine degrees of motion in the selective fusion group (p ! .001) (Fig. 5). Discussion
Fig. 4. Coronal L4eS1 summed motion at each of the postoperative time periods. LIV, lowest instrumented vertebra.
group, 51 in the midterm (5-10 years) follow-up group, and 32 in the long-term (O10 years) follow-up group. The surgical approaches included 180 posterior only, 64 anterior only, and 15 combined anterior and posterior surgery. The LIV percentage for each follow-up group showed varied distribution (Fig. 3). The interaction term of time of followup and LIV was not significant (p 5 .789). The distal residual unfused coronal motion (from L4 to S1) was not significantly different across early, midterm, to long-term follow-up (p 5 .526) (Fig. 4). In the subset of patients (n 5 35) with a primary thoracic curve and a nonstructural modifier type C lumbar curve in which a selective thoracic fusion is a treatment option, patients were grouped as either selective fusion (LIV of L1 and above) or longer fusion (LIV of L2 and below). There were 26 patients in the selective group (25 patients fused to T12 or above and 1 fused to L1) and 9 patients in the longer fusion group (3 fused to L2, 4 fused to L3, and 2 fused to L2). The surgical approaches for the 26 patients treated selectively included 15 posterior only, and 11 anterior only approaches. All nine patients in the longer fusion group were treated via posterior only approaches. There was a statistically significant difference in the residual unfused coronal motion, with the longer fusion group showing a mean of 18 degrees of motion
Fig. 5. Coronal L4eS1 summed motion in the longer versus selective fusions.
Prior studies have demonstrated the impact of distal fusion level on both spinal mobility and pain experience [4,5,7]. Many of these studies report on the increased pain and decreased mobility associated with distal fusion levels utilizing Harrington instrumentation [7-9]. Recent work on more modern instrumentation systems has corroborated the negative impact on overall mobility with more distal fusions [10]. Although the overall mobility is decreased, the remaining mobility is concentrated at the remaining motion segments in these distal fusions [5]. Understanding the impact of fusion level choice on future mobility, pain, and disc health is critical. In an effort to begin to understand the changes in mobility below the fusion over time (as the likelihood of developing symptoms of degenerative disc disease increases with age [11]) this study compared motion below the fusion in patients at their early (!5 years) postoperative follow-up time point to patients at a midterm (5e10 years) operative follow-up time point to patients with longer (O10 years) follow-up. An effect of time was not identified within this data set, as the magnitude of distal motion observed in patients from early to longer follow-up after surgery is similar. A limitation in our evaluation is the lack of standardized preoperative bending films, to provide an understanding in the ‘‘change’’ in motion for each patient. In addition, preoperative characteristics in bending motion are not accounted for in this investigation. Although an interaction of time of follow-up and LIV was not found in this series, this potential effect should be examined further with a larger patient population. An initial understanding of the impact of performing a longer fusion was elucidated with our comparison of a subgroup of patients with a primary thoracic curve and a nonstructural modifier type C lumbar curve. According to the Lenke Classification algorithm for treatment, a 1C curve type should be selectively fused. But as shown with earlier work evaluating adherence to the classification treatment algorithm, there are other aspects of the clinical and radiographic deformity that suggest deviation from the recommendations of the classification system [12]. However, whatever the factors associated with deciding to fuse longer, consequences may exist. The summed motion at L4eS1 in the patients that are fused longer (LIV of L2 and below) was significantly greater than motion in the patients that were selectively fused (LIVof L1 and above). With less mobile segments to share motion, the impact on the remaining unfused distal portions is detrimental. The potential for ‘‘remote’’ versus ‘‘adjacent’’ segment disease has previously been described [5,13] and this provides further evidence of alterations in distal motion that may potentially lead to disc degeneration. The implication of the
M.C. Marks et al. / Spine Deformity 3 (2015) 549e553
concentrated increased motion on future disc health is not completely understood. Studies have identified increased indices of degenerative disc disease below the distal fusion level [13-18]; however, there has not been a causal link established between motion below the fusion and degenerative disc disease. A limitation of this study is the small sample size of patients in the long fusion group, and additional study with larger patient groups is warranted. Further research with long-term follow-up (10 years postoperatively) is currently underway utilizing magnetic resonance imaging and radiographic evaluations. This investigation will assist in the understanding of the relationship of increased segmental motion and disc health in AIS. The sample of magnetic resonance imaging data in this patient population will also provide ‘‘gold standard’’ comparison for the potential of radiographic parameter assessment of intervertebral disc degeneration. Conclusion In this comparison of motion in the unfused distal lumbar segments in patients with varying amounts of follow-up, there were no differences in motion in patients at the early, mid-, and long-term follow-up periods. When considering fusion length in patients with a primary thoracic curve and a nonstructural lumbar curve, the choice to fuse longer versus shorter may have deleterious consequences. The summed motion from L4 to S1 is 50% greater in patients fused longer compared with those with a selective fusion, in which postoperative motion is shared by more unfused segments. The implications of this focal increased motion are unknown and further research on motion alterations and disc health is warranted.
Acknowledgment This study was supported by research grants from DePuy Synthes Spine and the Scoliosis Research Society to Setting Scoliosis Straight Foundation for Harms Study Group research efforts. References [1] Bridwell K. Surgical treatment of idiopathic adolescent scoliosis. Spine 1999;24:2607e16. [2] Majdouline YA, Robitaille M, Sarwark JF, Labelle H. Scoliosis correction objectives in adolescent idiopathic scoliosis. J Pediatric Orthop 2007;27:775e81.
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[3] Stokes IA. Spinal biomechanics. In: Weinstein S, editor. The Pediatric Spine Principles and Practice. 2nd ed. Philadelphia: PA Lippincott Williams & Wilkins; 2001. p. 57e71. [4] Hayes MA, Tomkins SF, Herndon WA, Gruel CR, Kopta JA, Howard TC. Clinical and radiological evaluation of lumbosacral motion below fusion levels in idiopathic scoliosis. Spine 1988;13: 1161e7. [5] Marks M, Newton PO, Petcharaporn M, et al. Postoperative segmental motion of the unfused spine distal to the fusion in 100 patients with adolescent idiopathic scoliosis. Spine 2012;37: 826e32. [6] Boden SD, Wiesel SW. Lumbosacral segmental motion in normal individualsdhave we been measuring instability properly? Spine 1990;15:571e9. [7] Aaro S, Ohlen G. The effect of Harrington instrumentation on the sagittal configuration and mobility of the spine in scoliosis. Spine 1983;8:570e5. [8] Bartie BJ, Lonstein JE, Winter RB. Long-term follow-up of adolescent idiopathic scoliosis patients who had Harrington instrumentation and fusion to the lower lumbar vertebrae: is low back pain a problem? Spine (Phila Pa 1976) 2009;34:E873e8. [9] Cochran T, Irstam L, Nachemson A. Long-term anatomic and functional changes in patients with adolescent idiopathic scoliosis treated by Harrington rod fusion. Spine (Phila Pa 1976) 1983;8: 576e84. [10] Newton PO, Marks MC, Bastrom T, et al. Harms Study Group. Post operative trunk flexibility loss is modest but incremental as the fusion progresses distally. Paper presented at: Scoliosis Research Society Annual Meeting; September 10e13, 2008; Salt Lake City, Utah. [11] Siemionow K, An H, Masuda K, Andersson G, Cs-Szabo G. The effects of age, sex, ethnicity, and spinal level on the rate of intervertebral disc degeneration: a review of 1712 intervertebral discs. Spine 2011;36:1333e9. [12] Clements DH, Marks M, Newton PO, Betz RR, Lenke L, Shufflebarger H. Harms Study Group. Did the Lenke classification change scoliosis treatment? Spine 2011;36:1142e5. [13] Green DW, Lawhorne 3rd TW, Widmann RF, et al. Long-term magnetic resonance imaging follow-up demonstrates minimal transitional level lumbar disc degeneration after posterior spine fusion for adolescent idiopathic scoliosis. Spine 2011;36:1948e54. [14] Violas P, Estivalezes E, Briot J, et al. Quantification of intervertebral disc volume properties below spine fusion, using magnetic resonance imaging, in adolescent idiopathic scoliosis surgery. Spine 2007;32: E405e12. [15] Balderston RA, Albert TJ, McIntosh T, et al. Magnetic resonance imaging analysis of lumbar disc changes below scoliosis fusions. A prospective study. Spine 1998;23:54e8. [16] Edwards II CC, Bridwell KH, Patel A, et al. Thoracolumbar deformity arthrodesis to L5 in adults: the fate of the L5-S1 disc. Spine (Phila Pa 1976) 2003;28:2122e31. [17] Kuhns CA, Bridwell KH, Lenke LG, et al. Thoracolumbar deformity arthrodesis stopping at L5. Spine 2007;32:2771e6. [18] Kepler CK, Meredith DS, Green DW, Widmann RF. Long-term outcomes after posterior spine fusion for adolescent idiopathic scoliosis. Curr Opin Pediatr 2012;24:68e75.