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Patient-specific rods for thoracic kyphosis correction in adolescent idiopathic scoliosis surgery: Preliminary results
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Original article
Patient-specific rods for thoracic kyphosis correction in adolescent idiopathic scoliosis surgery: Preliminary results Federico Solla a,∗ , Jean-Luc Clément a , Vincent Cunin b , Carlo M. Bertoncelli a , Vincent Fière c , Virginie Rampal a a
Orthopédie Pédiatrique, hôpital Pédiatrique de Nice CHU-Lenval, 57, avenue Californie, 06200 Nice, France Orthopédie Pédiatrique, CHU de Lyon, 69800 Bron, France c Chirurgie du rachis, centre orthopédique Santy et HPJM Lyon GDS Ramsay, Lyon, France b
a r t i c l e
i n f o
Article history: Received 30 October 2018 Accepted 22 July 2019 Available online xxx Keywords: Adolescent idiopathic scoliosis Posterior fusion Patient-specific rods. Contouring Thoracic kyphosis
a b s t r a c t Introduction: Restoring a degree of kyphosis consistent with good sagittal alignment of the spine is a key concern when performing surgery to correct adolescent idiopathic scoliosis (AIS). The objective of this study was to assess the preliminary outcomes of posterior fusion for AIS using patient-specific rods that were pre-contoured based on pelvic incidence. The primary evaluation criterion was thoracic kyphosis at last follow-up. Hypothesis: The use of pre-bent patient-specific rods has a favourable effect on thoracic kyphosis at last follow-up. Material and methods: A total of 37 patients with AIS, including 17 with hypokyphosis, managed with patient-specific rods were included in a prospective study. The rod contouring angles were based on predefined pelvic incidence criteria (25◦ to 40◦ for the rod on the convex side and the same value plus 10◦ for the rod on the concave side). Thoracic kyphosis was assessed before surgery and at last follow-up, after 12–36 months (mean, 19 months). Student’s t test was applied to compare means. Multivariate linear regression analysis was performed. Results: At last follow-up, the mean increase in kyphosis was 14◦ and was comparable to the planned increase (mean difference = 0, p = 0.85). Factors associated with kyphosis at last follow-up were the concave rod contouring angle and the pre-operative kyphotic angle of the thoracic segment to be instrumented (p < 0.05). Mean differences between kyphosis of the instrumented thoracic segment at last follow-up and target kyphosis were −5◦ in the subgroup with hypokyphosis (< 20◦ ) before surgery and +4◦ in the subgroup with normal kyphosis before surgery. Conclusion: With patient-specific rods, kyphosis at last follow-up was close to the target value. Predictors of kyphosis at last follow-up were the concave rod contouring angle and pre-operative kyphotic angle of the thoracic segment to be instrumented. Over-contouring of the concave rod seems necessary in patients with preoperative hypokyphosis but not in patients with normal kyphosis. Level of evidence: III, prospective non-comparative study. © 2019 Elsevier Masson SAS. All rights reserved.
1. Introduction The curves that characterise adolescent idiopathic scoliosis (AIS) develop in all three planes. In the sagittal plane, thoracic hypokyphosis and lumbar hypolordosis are common [1–3]. Postoperative hypokyphosis is associated with trunk imbalance that results in osteoarthritis in adulthood [4,5]. Whereas posterior vertebral instrumentation now ensures nearly complete curve
∗ Corresponding author. E-mail address: [email protected] (F. Solla).
correction in the coronal plane, outcomes in terms of sagittal alignment have varied widely across studies [1,2,6–10]. The accepted range of normal overall thoracic kyphosis (TK) is 10◦ to 55◦ [1,2,11–14]. However, few data are available on the optimal amount of TK for each individual. Nonetheless, geometric associations exist between pelvic incidence and lumbar lordosis, as well as between TK and pelvic parameters [1–3,11]. When performing surgery to correct AIS, an important goal is to restore a degree of TK consistent with optimal sagittal alignment. Most surgeons use their personal experience to contour the rods during surgery, without first determining the desired amount of kyphosis or measuring the angle created in the rod. The use of
https://doi.org/10.1016/j.otsr.2019.07.027 1877-0568/© 2019 Elsevier Masson SAS. All rights reserved.
Please cite this article in press as: Solla F, et al. Patient-specific rods for thoracic kyphosis correction in adolescent idiopathic scoliosis surgery: Preliminary results. Orthop Traumatol Surg Res (2019), https://doi.org/10.1016/j.otsr.2019.07.027
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2 Table 1 Main patient features.
Males/Females, n Age, years, mean (range) Follow-up, months, mean (range) Risser stage 0/1/2/3/4/5, n Lenke type, 1/2/3/4/5/6, n Proximal end vertebra, T2/T3/T4, n Distal end vertebra, T11/T12/L1/L2/L3/L4, n Implant density, %, mean (range) SRS-22 before surgery, mean SRS-22 at last follow-up, mean SRS-22 difference from pre-operative to last follow-up, p value
2.4. Surgical planning 3/34 14 (12–19) 19 (12–36) 0/1/15/13/6/2 21/13/0/1/0/2 10/6/21 4/1/13/11/5/3 82% (71%–92%) 3.61 4.08 0.008
rods that are industrially pre-bent according to patient-specific data has been found effective in correcting spinal deformities in adults [15]. We suggest using patient-specific rods for AIS surgery, with the goal of obtaining a kyphotic angle similar to the planned value, thereby optimising post-operative sagittal alignment. Other expected advantages are a decrease in operative time and better mechanical properties of machine-contoured rods [15]. The objective of this study was to assess the preliminary outcomes of posterior fusion for AIS using patient-specific rods that were pre-contoured based on pelvic incidence. The primary evaluation criterion was the kyphotic angle of the instrumented thoracic segment at last follow-up (postopKA-ITS). Associations linking TK at last follow-up to other angle values and quality of life were also evaluated. The working hypothesis was that the use of patientspecific rods has a favourable effect on postopKA-ITS and, therefore, on overall TK at last follow-up. 2. Material and methods 2.1. Ethics All procedures performed for the study complied with the ethical requirements set forth in the 1964 Declaration of Helsinki and its subsequent amendments. The study was approved by the appropriate ethics committee (#14.009). Written informed consent was obtained from all patients and parents. 2.2. Patients Between 2015 and 2017, two surgeons (JLC and FS) prospectively included patients scheduled for AIS surgery who met the following criteria: instrumentation including at least the T4-T11 segment, use of machine-bent patient-specific rods, availability of a comprehensive radiographic workup including standing full-spine antero-posterior and lateral views and bending views, reduction by simultaneous translation on two rods with a high anchor density [10,16,17] and hybrid constructs (pedicle screws, claw hooks and, in some cases, sublaminar bands), and follow-up of at least 1 year. Patients with anterior release or halo traction before posterior fusion were excluded. We also excluded patients with Lenke 5 AIS, who were managed by selective fusion excluding mid-thoracic spine [18]. 2.3. Patient subgroups The pre-operative kyphotic angle of the instrumented thoracic segment (preopKA-ITS), between the proximal and distal thoracic vertebras included in the instrumentation, was measured (Fig. 1). Thus, the patients were divided into two groups based on whether preopKA-ITS was normal or decreased. A value ≤ 20◦ was taken to define hypokyphosis and a value > 20◦ normal kyphosis [1] (Table 1).
When determining the limits of the instrumentation, Lenke’s criteria were applied to determine which curves required instrumentation and Groupe d’Étude de la Scoliose (French Scoliosis Study Group) criteria to select the end vertebrae [12,19]. Overall TK was defined as the greatest value of the kyphotic curve between the cranial transition vertebra (at the junction of the TK and cervical lordosis) and the caudal transition vertebra (between the TK and the lumbar lordosis) (Fig. 1). Overall target TK was determined during planning for each patient using pre-operative calibrated radiographs (Figs. 2 and 3), based on pelvic incidence [20]. Target TK increased with pelvic incidence and ranged from 27◦ to 44◦ (Table 2). The pre-operative value of the kyphotic curve was not considered when determining the target TK. The instrumented thoracic segment did not necessarily include the entire kyphotic curve (which usually extends from T2 to T11). For instance, if the instrumentation extended from T4 to T11, only about 8/10th of the kyphotic region were instrumented. This fraction of the entire TK served to determine the fraction of the target TK related to the spine segment to be instrumented which was therefore used as the rod contouring angle on the convex side (cvRCA). Thus, the rod contouring angle (RCA) was formed by the proximal end of the construct and either the distal end of the rod, if this last was applied to T11, or the transition point between the anteriorly concave curve and the anteriorly convex curve i.e., the theoretical position of the T12 implant (Figs. 1 and 2). We elected to increase this angle by 10◦ for the concave rod to compensate for any flattening it might experience during the corrective manoeuvres; thus, the concave RCA (ccRCA) was equal to cvRCA + 10◦ (Figs. 3 and 4) [21]. The target lumbar lordosis value was computed as the pelvic incidence plus 10◦ . Two-thirds of this value were attributed to the L4-S1 segment and the remaining third to the L1-L4 segment. Lumbar lordosis was then distributed according to the levels to be instrumented. Lumbar lordosis results were not assessed in this study due to the considerable variation in the distal end of the instrumentation, which ranged from T11 to L4. Rod length was measured on the antero-posterior radiograph (Fig. 2). Cobalt-chromium rods measuring 6 mm in diameter (Medicrea, Rillieux-la Pape, France) were ordered 10–20 days before the scheduled date of the procedure, delivered to the operating room, and implanted with no change in contouring (Fig. 3). 2.5. Evaluation criteria All the radiographic parameters were measured before surgery and at last follow-up by an independent observer (VC) using Keops Analyzer® software (SMAIO, Lyon, France) [22]. PreopKAITS is defined above; for instance, for T3-L2 instrumentation, preopKA-ITS was measured between T3 and T12. The cvRCA was defined as the anteriorly concave angle of the rod on the convex side. For example, when planning T3-L2 instrumentation, the cvRCA was measured between the proximal end of the construct (i.e., the T3 implant) and the theoretical position of the T12 implant. Postoperative kyphosis of the instrumented thoracic segment (postopKA-ITS) was defined as the kyphotic angle measured at last follow-up between the proximal and distal instrumented thoracic vertebrae (Figs. 1 and 4). We were able to compare these three angles (preopKA-ITS, cvRCA, and postopKA-ITS) since they were measured on the same segments in each patient. The expected gain was defined as the difference between the cvRCA and the preopKA-ITS. The actual gain was defined as the
Please cite this article in press as: Solla F, et al. Patient-specific rods for thoracic kyphosis correction in adolescent idiopathic scoliosis surgery: Preliminary results. Orthop Traumatol Surg Res (2019), https://doi.org/10.1016/j.otsr.2019.07.027
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Fig. 1. Patient #1, measurement of the kyphotic angles on the lateral radiographs taken before surgery (1a) and 1 year after surgery (1b). The black lines and numbers indicate overall kyphosis measured pre-operatively between T2 and T11 and post-operatively between T3 and T12. The white lines and numbers indicate the pre-operative degree of kyphosis of the thoracic segment planned for instrumentation (preopKA-ITS in the text) and the post-operative degree of kyphosis of the thoracic segment that was actually instrumented (postopKA-ITS in the text).
Fig. 2. Patient #2, pre-operative radiograph and planning for T4-L2 fusion. a: coronal view with identification of the spinal levels to be instrumented. b: lateral view showing 7◦ of overall (T2-T12) pre-operative kyphosis. c: the planned alignment involves 35◦ of overall T2-T12 kyphosis and 30◦ of T4-T12 kyphosis; the virtual rod is shown in blue.
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Fig. 3. Pre-bent rods prepared for patient 2. a: pre-bent convex rod with a T4-T12 angle of 30◦ and a T12-L2 angle of 15◦ ; b: pre-bent concave rod with a T4-T12 angle of 40◦ and a T12-L2 angle of 15◦ . Table 2 Measured angles in the overall cohort and in the subgroups with pre-operative hypokyphosis (H) and normal kyphosis (N); the data are mean (range). Parameters
Overall cohort n = 37
H group n = 17
N group n = 20
p value (H vs. N)
preopKA-ITS cvRCA postopKA-ITS p value, postopKA-ITS vs. preopKA-ITS Expected gaina Measured gainb Gain difference: expected gain – measured gain Distribution by gain differencec , n T4-T12 kyphosis before surgery T4-T12 kyphosis at last follow-up P value (T4-T12 kyphosis before surgery vs. at last follow-up) Overall kyphosis before surgery Planned overall kyphosis Overall kyphosis at last follow-up p value (overall kyphosis before surgery vs. at last follow-up) Coronal Cobb angle before surgery Coronal Cobb angle at last follow-up Coronal correction at last follow-up, %
21 (1 to 39) 34 (25 to 40) 34 (24 to 49) 0.001 14 (−14 to 36) 14 (−1 to 39) 0 (–16 to 18) 13–12–12 16 (0 to 36) 31 (22 to 46) Eto5 20 (1 to 46) 37 (27 to 44) 35 (25 to 56) E–4 53 (39 to 64) 13 (1 to 32) 74 (51 to 98)
9 (1 to 18) 34 (25 to 40) 29 (24 to 39) Eto9 25 (11 to 36) 20 (10 to 39) –5 (–16 to 10) 2–5–10 7 (0 to 14) 29 (22 to 36) Eto7 11 (1 to 19) 37 (28 to 44) 32 (25 to 39) E–7 55 (39 to 64) 16 (2 to 32) 70 (53 to 98)
29 (20 to 39) 34 (25 to 40) 38 (27 to 49) Eto6 5 (−14 to 17) 9 (−1 to 21) 4 (18 to−8) 11–7–2 24 (18 to 36) 34 (26 to 46) Eto5 30 (20 to 46) 37 (27 to 43) 38 (27 to 56) 0.002 51 (40 to 62) 11 (1 to 21) 77 (51 to 98)
Eto10 0.66 Eto5 E–8 E–5 0.001 0.002 Eto9 Eto4 Eto10 0.51 0.001 0.09 0.03 0.09
The p values < 0.05 are in bold type. H: subgroup with hypokyphosis before surgery; N: subgroup with normal kyphosis before surgery; preopKA-ITS, pre-operative kyphotic angle of the thoracic segment to be instrumented (before surgery); cvRCA, convex side rod contouring angle (equal to the amount of kyphosis planned for the thoracic segment to be instrumented); postopKA-ITS, post-operative kyphotic angle of the instrumented thoracic segment (at last follow-up) a Expected gain: cvRCA minus preopKA-ITS. b Measured gain: postopKA-ITS minus preopKA-ITS. c Outcome distribution: overcorrection (difference ≥ 5◦ ); optimal correction (difference between –5◦ and +5◦ ), and undercorrection (difference < −5◦ ).
difference between the preopKA-ITS and the postopKA-ITS. The difference between the expected and actual gains was computed and used to define three outcome categories: optimal outcome, difference ± 5◦ ; undercorrection, difference < –5◦ ; and overcorrection, difference > + 5◦ .
2.6. Secondary evaluation criteria T4-T12 TK, overall TK, and the coronal Cobb angle of the main curve were measured before surgery and at last follow-up. Proximal junctional kyphosis (PJK) was sought [8]. Finally, the patients
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Fig. 4. Patient #2, antero-posterior and lateral radiographs 2 years after surgery (hybrid construct). T4-T12 thoracic kyphosis is 29◦ and L1-S1 lumbar lordosis is 50◦ .
completed the SRS-22 quality-of-life questionnaire before surgery and at last follow-up. 2.7. Statistical analysis The statistical analyses were performed using XLStat (Addinsoft, Paris, France). Mean values were compared using the Wilcoxon test, Student’s test, or analysis of variance. Fisher’s exact test was applied to compare rates. Pearson’s test was used to assess correlations. Multivariate linear regression analyses were performed. Regression coefficients are reported with their 95% confidence intervals (95%CIs) [23]. Values of p smaller than 0.05 were considered significant. 3. Results 3.1. Patients and procedures Of 38 patients with AIS whose instrumentation included T4-T11, 1 was lost to follow-up and the remaining 37 were included in the study. Outcomes were analysed after at least 1 year of follow-up (Table 1). Of the 37 patients, 20 had normal TK and 17 hypokyphosis before surgery. Among anchors used in the study population, 85% were polyaxial pedicle screws, 11% were double hook claws, and 4% were sublaminar bands (Figs. 1 and 4). 3.2. Thoracic kyphosis (TK) In the overall cohort, the mean actual gain (difference between postopKA-ITS and preopKA-ITS) was 14◦ and was equal to the mean
expected gain. Mean postopKA-ITS was comparable to the mean cvRCA (mean difference = 0, p = 0.85, Cohen’s d = 0.047) (Table 2). However, 12 patients had an optimal outcome, 12 were undercorrected, and 13 were overcorrected (Table 2). In the subgroup with pre-operative hypokyphosis, the mean actual gain was 20◦ for an expected gain of 25◦ . Of the 17 patients in this subgroup, 10 were undercorrected. In the subgroup with normal pre-operative kyphosis, the mean actual gain was 8◦ for an expected gain of 4◦ . In this subgroup, 11 were overcorrected. Factors associated with postopKA-ITS by multivariate analysis were the preopKA-ITS (regression coefficient, 0.72; 95%CI: 0.497–0,937; p = E–5) and ccRCA (regression coefficient, 0.27; 95%CI: 0.005–0.540; p = 0.04). The difference between the postopKA-ITS and the cvRCA correlated closely with the expected gain (correlation coefficient, 0.74; p = E–7). Factors associated with this difference by multivariate linear regression were the preopKAITS (correlation coefficient = 0.41, p = 0.002) and expected gain (correlation coefficient = 0.62, p = E–5).
3.3. Other results Mean coronal correction was 74% (Table 1). None of the coronal parameters (Cobb angles, flexibility, correction) correlated with the TK parameters (all correlation coefficients < 0.10). No patient developed PJK. The coronal and sagittal angles measured at last follow-up showed no differences according to the Lenke classification (p > 0.1). Finally, the SRS-22 score increase showed weak correlations with actual gain, postopKA-ITS, and coronal correction (correlation coefficients < 0.20).
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4. Discussion This study assessed outcomes of patients with AIS managed using patient-specific rods that were pre-contoured according to a protocol based on pelvic incidence. The results confirm the working hypothesis that postopKA-ITS was favourably influenced by patient-specific pre-contouring of the rods, notably the concave rod, and was also associated with pre-operative TK. Overall TK at last follow-up was normal in all patients. Mean postopKA-ITS was not very different from the cvRCA. At last followup, postopKA-ITS was within the planned range in one-third of patients, overcorrected in another third, and undercorrected in the last third. The cvRCA value was the same in the subgroups with normokyphosis and hypokyphosis because it was determined based on pelvic incidence and not on pre-operative TK, which is a component of the scoliotic deformity [20]. The expected gain was therefore greater in the subgroup with hypokyphosis than in the subgroup with normal TK. The clinical and radiological outcomes of this strategy require evaluation in the longer term. In the hypokyphotic subgroup, the large TK increase of 20◦ on average is consistent with earlier studies of the same correction technique [2,10,17]. Nevertheless, the postopKA-ITS values indicated mean undercorrection of 5◦ compared to cvRCA and 15◦ compared to the ccRCA. These results indicate ‘loss’ of sagittal correction related to rod flattening during correction due to the stiffness of the spine. Clear evidence of concave rod flattening during translation manoeuvres has been reported elsewhere [21]. In the subgroup with normal pre-opKA-ITS, the postopKA-ITS indicated 4◦ of mean overcorrection compared to cvRCA. These findings suggest that the practice of overbending the concave rod by 10◦ (or more) should be continued for patients with hypokyphosis but not for patients with normal TK. Overbending tailored to the individual patient may also deserve consideration; for instance, overbending by 5◦ might be helpful in patients with moderate hypokyphosis. Our decision to measure the degree of TK of the instrumented vertebral segment (preop and postopKA-ITS) allowed us to assess the effect of the pre-contoured rods (RCA) on the instrumented spine. PreopKA-ITS is not necessarily equal to overall TK or to TK between T4 (orT5) and T12, which is the value often reported in the literature [7–9,12]. When planning the RCA, an important consideration is that the instrumented thoracic spine includes only a fraction of the overall TK, whose size varies with the number of instrumented thoracic levels. The coronal parameters and quality-of-life data were in accordance with earlier reports [6,9,19] and showed no correlations with the sagittal parameters. The trend toward less coronal correction in the hypokyphotic subgroup suggests that 3D correction may be more challenging to achieve in patients with hypokyphosis. The limitations of this study include the short follow-up, small sample size, and absence of a comparison group. Our preliminary results pertain only to simultaneous translation on two 6-mm cobalt-chrome rods. They cannot be directly extrapolated to other techniques and materials. Strong points of this study are the original design, prospective recruitment, uniform surgical technique, low patient attrition rate, and standardised evaluation of the radiographs by an independent observer.
5. Conclusion The use of patient-specific rods provided postopKA-ITS values that were similar to the cvRCA values. Predictors of postopKA-ITS at last follow-up were not only the amount of concave rod precontouring but also the degree of pre-operative KA-ITS. In patients with pre-operative hypokyphosis, kyphosis at last follow-up indicated undercorrection, which was partially offset
by 10◦ of concave rod overbending. In contrast, in the patients with pre-operative normokyphosis, overcorrection of the kyphosis occurred, probably as a result of the overbending of the concave rod. Therefore, concave rod overbending would seem unnecessary when TK is normal before surgery. Disclosure of interest F.S. has received funding for symposia from Medicrea International. V.C. has received funding for symposia from Medicrea International and Synthes. J.L.C. is a consultant for Medicrea International. V.F. is a consultant for Medicrea International and Clariance. C.M.B. and V.R. declare that they have no competing interest. Funding None. Contributions of each author F.S. conceived the study, performed the statistical analyses, drafted the manuscript, and created the tables. J.L.C. operated the patients, contributed to conceive the study, and revised the manuscript. V.C. measured the radiographic parameters, contributed to conceive the study, and revised the manuscript. V.F. created the patient-specific rod concept, contributed to conceive the study, and revised the manuscript. VR contributed to conceive the study, and revised the manuscript. C.M.B. contributed to collect and analyse the data, contributed to patient monitoring, and revised the final manuscript. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.otsr.2019.07.027. References [1] Clement JL, Geoffray A, Yagoubi F, et al. Relationship between thoracic hypokyphosis, lumbar lordosis and sagittal pelvic parameters in adolescent idiopathic scoliosis. Eur Spine J 2013;22:2414–20. [2] Clement JL, Pelletier Y, Solla F, Rampal V. Surgical increase of thoracic kyphosis increases unfused lumbar lordosis in selective fusion for thoracic adolescent idiopathic scoliosis. Eur Spine J 2019;28:581–9. [3] Abelin-Genevois K, Sassi D, Verdun S, Roussouly P. Sagittal classification in adolescent idiopathic scoliosis: original description and therapeutic implications. Eur Spine J 2018;27:2192–202. [4] Glassman SD, Berven S, Bridwell K, et al. Correlation of radiographic parameters and clinical symptoms in adult scoliosis. Spine 2005;30:682. [5] Bernstein P, Hentschel S, Platzek I, et al. Thoracal flat back is a risk factor for lumbar disc degeneration after scoliosis surgery. Spine J 2014;14:925–32. [6] Angelliaume A, Ferrero E, Mazda K, et al. Titanium vs cobalt chromium: what is the best rod material to enhance adolescent idiopathic scoliosis correction with sublaminar bands? Eur Spine J 2017;26:1732–8. [7] Suk SI, Lee CK, Min HJ, et al. Comparison of Cotrel-Dubousset pedicle screws and hooks in the treatment of idiopathic scoliosis. Int Orthop 1994;18:341–6. [8] Kim YJ, Lenke LG, Bridwell KH, et al. Proximal junctional kyphosis in adolescent idiopathic scoliosis after 3 different types of posterior segmental spinal instrumentation and fusions: incidence and risk factor analysis of 410 cases. Spine 2007;32:2731–8. [9] Suk SI, Kim WJ, Kim JH, et al. Restoration of thoracic kyphosis in the hypokyphotic spine: a comparison between multiple-hook and segmental pedicle screw fixation in adolescent idiopathic scoliosis. J Spinal Disord 1999;12:489–95. [10] Clement JL, Chau E, Kimkpe C, et al. Restoration of thoracic kyphosis by posterior instrumentation in adolescent idiopathic scoliosis: comparative radiographic analysis of two methods of reduction. Spine (Phila Pa 1976) 2008;33:1579–87. [11] Vialle R, Levassor N, Rillardon L, et al. Radiographic analysis of the sagittal alignment and balance of the spine in asymptomatic subjects. J Bone Joint Surg Am 2005;87:260–7.
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G Model OTSR-2459; No. of Pages 7
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[12] Lenke LG, Edwards CC, Bridwell KH. The Lenke classification of adolescent idiopathic scoliosis: how it organizes curve patterns as a template to perform selective fusions of the spine. Spine 2003;28:S199–207. [13] Winter RB, Lonstein JE, Denis F. Sagittal spinal alignment: the true measurement, norms, and description of correction for thoracic kyphosis. J Spinal Disord Tech 2009;22:311–4. [14] Mac-Thiong JM, Labelle H, Roussouly P. Pediatric sagittal alignment. Eur Spine J 2011;20(Suppl 5):586–90. [15] Solla F, Barrey C, Burger E, Kleck C, Fiere V. Patient specific rods for surgical correction of sagittal imbalance in adults: technical aspects and preliminary results. Clin Spine Surg 2019;32:80–6. [16] Solla F, Clément JL, Doria C, et al. Adolescent Idiopathic Scoliosis exceeding 70◦ : a single center surgical experience. Minerva Ortopedica 2018;69:69–77. [17] Allia J, Clément JL, Rampal V, et al. Influence of derotation connectors on 3D surgical correction of adolescent idiopathic scoliosis. Clin Spine Surg 2018;31:E209–15.
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[18] Solla F, Gallo M, Doria C, et al. Prognostic role of rib hump in overlying thoracic curve correction above selective fusion for Lenke 5 idiopathic adolescent scoliosis. Clin Spine Surg 2018;31:E140–5. [19] Clément JL, Solla F, Tran A, et al. Five-year outcomes of the First Distal Uninstrumented Vertebra after posterior fusion for Adolescent Idiopathic Scoliosis Lenke 1 or 2. Orthop Traumatol Surg Res 2017;103:727–31. [20] Legaye J, Duval-Beaupère G. Sagittal plane alignment of the spine and gravity: a radiological and clinical evaluation. Acta Orthop Belg 2005;71:213–20. [21] Le Naveaux F, Aubin CE, Parent S, et al. 3D rod shape changes in adolescent idiopathic scoliosis instrumentation: how much does it impact correction? Eur Spine J 2017;26:1676–83. [22] Maillot C, Ferrero E, Fort D, et al. Reproducibility and repeatability of a new computerized software for sagittal spinopelvic and scoliosis curvature radiologic measurements: Keops(® ). Eur Spine J 2015;24:1574–81. [23] Solla F, Tran A, Bertoncelli D, et al. Why a p-value is not enough. Clin Spine Surg 2018;31:385–8.
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Original article
Patient-specific rods for thoracic kyphosis correction in adolescent idiopathic scoliosis surgery: Preliminary results Federico Solla a,∗ , Jean-Luc Clément a , Vincent Cunin b , Carlo M. Bertoncelli a , Vincent Fière c , Virginie Rampal a a
Orthopédie Pédiatrique, hôpital Pédiatrique de Nice CHU-Lenval, 57, avenue Californie, 06200 Nice, France Orthopédie Pédiatrique, CHU de Lyon, 69800 Bron, France c Chirurgie du rachis, centre orthopédique Santy et HPJM Lyon GDS Ramsay, Lyon, France b
a r t i c l e
i n f o
Article history: Received 30 October 2018 Accepted 22 July 2019 Available online xxx Keywords: Adolescent idiopathic scoliosis Posterior fusion Patient-specific rods. Contouring Thoracic kyphosis
a b s t r a c t Introduction: Restoring a degree of kyphosis consistent with good sagittal alignment of the spine is a key concern when performing surgery to correct adolescent idiopathic scoliosis (AIS). The objective of this study was to assess the preliminary outcomes of posterior fusion for AIS using patient-specific rods that were pre-contoured based on pelvic incidence. The primary evaluation criterion was thoracic kyphosis at last follow-up. Hypothesis: The use of pre-bent patient-specific rods has a favourable effect on thoracic kyphosis at last follow-up. Material and methods: A total of 37 patients with AIS, including 17 with hypokyphosis, managed with patient-specific rods were included in a prospective study. The rod contouring angles were based on predefined pelvic incidence criteria (25◦ to 40◦ for the rod on the convex side and the same value plus 10◦ for the rod on the concave side). Thoracic kyphosis was assessed before surgery and at last follow-up, after 12–36 months (mean, 19 months). Student’s t test was applied to compare means. Multivariate linear regression analysis was performed. Results: At last follow-up, the mean increase in kyphosis was 14◦ and was comparable to the planned increase (mean difference = 0, p = 0.85). Factors associated with kyphosis at last follow-up were the concave rod contouring angle and the pre-operative kyphotic angle of the thoracic segment to be instrumented (p < 0.05). Mean differences between kyphosis of the instrumented thoracic segment at last follow-up and target kyphosis were −5◦ in the subgroup with hypokyphosis (< 20◦ ) before surgery and +4◦ in the subgroup with normal kyphosis before surgery. Conclusion: With patient-specific rods, kyphosis at last follow-up was close to the target value. Predictors of kyphosis at last follow-up were the concave rod contouring angle and pre-operative kyphotic angle of the thoracic segment to be instrumented. Over-contouring of the concave rod seems necessary in patients with preoperative hypokyphosis but not in patients with normal kyphosis. Level of evidence: III, prospective non-comparative study. © 2019 Elsevier Masson SAS. All rights reserved.
1. Introduction The curves that characterise adolescent idiopathic scoliosis (AIS) develop in all three planes. In the sagittal plane, thoracic hypokyphosis and lumbar hypolordosis are common [1–3]. Postoperative hypokyphosis is associated with trunk imbalance that results in osteoarthritis in adulthood [4,5]. Whereas posterior vertebral instrumentation now ensures nearly complete curve
∗ Corresponding author. E-mail address: [email protected] (F. Solla).
correction in the coronal plane, outcomes in terms of sagittal alignment have varied widely across studies [1,2,6–10]. The accepted range of normal overall thoracic kyphosis (TK) is 10◦ to 55◦ [1,2,11–14]. However, few data are available on the optimal amount of TK for each individual. Nonetheless, geometric associations exist between pelvic incidence and lumbar lordosis, as well as between TK and pelvic parameters [1–3,11]. When performing surgery to correct AIS, an important goal is to restore a degree of TK consistent with optimal sagittal alignment. Most surgeons use their personal experience to contour the rods during surgery, without first determining the desired amount of kyphosis or measuring the angle created in the rod. The use of
https://doi.org/10.1016/j.otsr.2019.07.027 1877-0568/© 2019 Elsevier Masson SAS. All rights reserved.
Please cite this article in press as: Solla F, et al. Patient-specific rods for thoracic kyphosis correction in adolescent idiopathic scoliosis surgery: Preliminary results. Orthop Traumatol Surg Res (2019), https://doi.org/10.1016/j.otsr.2019.07.027
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2 Table 1 Main patient features.
Males/Females, n Age, years, mean (range) Follow-up, months, mean (range) Risser stage 0/1/2/3/4/5, n Lenke type, 1/2/3/4/5/6, n Proximal end vertebra, T2/T3/T4, n Distal end vertebra, T11/T12/L1/L2/L3/L4, n Implant density, %, mean (range) SRS-22 before surgery, mean SRS-22 at last follow-up, mean SRS-22 difference from pre-operative to last follow-up, p value
2.4. Surgical planning 3/34 14 (12–19) 19 (12–36) 0/1/15/13/6/2 21/13/0/1/0/2 10/6/21 4/1/13/11/5/3 82% (71%–92%) 3.61 4.08 0.008
rods that are industrially pre-bent according to patient-specific data has been found effective in correcting spinal deformities in adults [15]. We suggest using patient-specific rods for AIS surgery, with the goal of obtaining a kyphotic angle similar to the planned value, thereby optimising post-operative sagittal alignment. Other expected advantages are a decrease in operative time and better mechanical properties of machine-contoured rods [15]. The objective of this study was to assess the preliminary outcomes of posterior fusion for AIS using patient-specific rods that were pre-contoured based on pelvic incidence. The primary evaluation criterion was the kyphotic angle of the instrumented thoracic segment at last follow-up (postopKA-ITS). Associations linking TK at last follow-up to other angle values and quality of life were also evaluated. The working hypothesis was that the use of patientspecific rods has a favourable effect on postopKA-ITS and, therefore, on overall TK at last follow-up. 2. Material and methods 2.1. Ethics All procedures performed for the study complied with the ethical requirements set forth in the 1964 Declaration of Helsinki and its subsequent amendments. The study was approved by the appropriate ethics committee (#14.009). Written informed consent was obtained from all patients and parents. 2.2. Patients Between 2015 and 2017, two surgeons (JLC and FS) prospectively included patients scheduled for AIS surgery who met the following criteria: instrumentation including at least the T4-T11 segment, use of machine-bent patient-specific rods, availability of a comprehensive radiographic workup including standing full-spine antero-posterior and lateral views and bending views, reduction by simultaneous translation on two rods with a high anchor density [10,16,17] and hybrid constructs (pedicle screws, claw hooks and, in some cases, sublaminar bands), and follow-up of at least 1 year. Patients with anterior release or halo traction before posterior fusion were excluded. We also excluded patients with Lenke 5 AIS, who were managed by selective fusion excluding mid-thoracic spine [18]. 2.3. Patient subgroups The pre-operative kyphotic angle of the instrumented thoracic segment (preopKA-ITS), between the proximal and distal thoracic vertebras included in the instrumentation, was measured (Fig. 1). Thus, the patients were divided into two groups based on whether preopKA-ITS was normal or decreased. A value ≤ 20◦ was taken to define hypokyphosis and a value > 20◦ normal kyphosis [1] (Table 1).
When determining the limits of the instrumentation, Lenke’s criteria were applied to determine which curves required instrumentation and Groupe d’Étude de la Scoliose (French Scoliosis Study Group) criteria to select the end vertebrae [12,19]. Overall TK was defined as the greatest value of the kyphotic curve between the cranial transition vertebra (at the junction of the TK and cervical lordosis) and the caudal transition vertebra (between the TK and the lumbar lordosis) (Fig. 1). Overall target TK was determined during planning for each patient using pre-operative calibrated radiographs (Figs. 2 and 3), based on pelvic incidence [20]. Target TK increased with pelvic incidence and ranged from 27◦ to 44◦ (Table 2). The pre-operative value of the kyphotic curve was not considered when determining the target TK. The instrumented thoracic segment did not necessarily include the entire kyphotic curve (which usually extends from T2 to T11). For instance, if the instrumentation extended from T4 to T11, only about 8/10th of the kyphotic region were instrumented. This fraction of the entire TK served to determine the fraction of the target TK related to the spine segment to be instrumented which was therefore used as the rod contouring angle on the convex side (cvRCA). Thus, the rod contouring angle (RCA) was formed by the proximal end of the construct and either the distal end of the rod, if this last was applied to T11, or the transition point between the anteriorly concave curve and the anteriorly convex curve i.e., the theoretical position of the T12 implant (Figs. 1 and 2). We elected to increase this angle by 10◦ for the concave rod to compensate for any flattening it might experience during the corrective manoeuvres; thus, the concave RCA (ccRCA) was equal to cvRCA + 10◦ (Figs. 3 and 4) [21]. The target lumbar lordosis value was computed as the pelvic incidence plus 10◦ . Two-thirds of this value were attributed to the L4-S1 segment and the remaining third to the L1-L4 segment. Lumbar lordosis was then distributed according to the levels to be instrumented. Lumbar lordosis results were not assessed in this study due to the considerable variation in the distal end of the instrumentation, which ranged from T11 to L4. Rod length was measured on the antero-posterior radiograph (Fig. 2). Cobalt-chromium rods measuring 6 mm in diameter (Medicrea, Rillieux-la Pape, France) were ordered 10–20 days before the scheduled date of the procedure, delivered to the operating room, and implanted with no change in contouring (Fig. 3). 2.5. Evaluation criteria All the radiographic parameters were measured before surgery and at last follow-up by an independent observer (VC) using Keops Analyzer® software (SMAIO, Lyon, France) [22]. PreopKAITS is defined above; for instance, for T3-L2 instrumentation, preopKA-ITS was measured between T3 and T12. The cvRCA was defined as the anteriorly concave angle of the rod on the convex side. For example, when planning T3-L2 instrumentation, the cvRCA was measured between the proximal end of the construct (i.e., the T3 implant) and the theoretical position of the T12 implant. Postoperative kyphosis of the instrumented thoracic segment (postopKA-ITS) was defined as the kyphotic angle measured at last follow-up between the proximal and distal instrumented thoracic vertebrae (Figs. 1 and 4). We were able to compare these three angles (preopKA-ITS, cvRCA, and postopKA-ITS) since they were measured on the same segments in each patient. The expected gain was defined as the difference between the cvRCA and the preopKA-ITS. The actual gain was defined as the
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Fig. 1. Patient #1, measurement of the kyphotic angles on the lateral radiographs taken before surgery (1a) and 1 year after surgery (1b). The black lines and numbers indicate overall kyphosis measured pre-operatively between T2 and T11 and post-operatively between T3 and T12. The white lines and numbers indicate the pre-operative degree of kyphosis of the thoracic segment planned for instrumentation (preopKA-ITS in the text) and the post-operative degree of kyphosis of the thoracic segment that was actually instrumented (postopKA-ITS in the text).
Fig. 2. Patient #2, pre-operative radiograph and planning for T4-L2 fusion. a: coronal view with identification of the spinal levels to be instrumented. b: lateral view showing 7◦ of overall (T2-T12) pre-operative kyphosis. c: the planned alignment involves 35◦ of overall T2-T12 kyphosis and 30◦ of T4-T12 kyphosis; the virtual rod is shown in blue.
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Fig. 3. Pre-bent rods prepared for patient 2. a: pre-bent convex rod with a T4-T12 angle of 30◦ and a T12-L2 angle of 15◦ ; b: pre-bent concave rod with a T4-T12 angle of 40◦ and a T12-L2 angle of 15◦ . Table 2 Measured angles in the overall cohort and in the subgroups with pre-operative hypokyphosis (H) and normal kyphosis (N); the data are mean (range). Parameters
Overall cohort n = 37
H group n = 17
N group n = 20
p value (H vs. N)
preopKA-ITS cvRCA postopKA-ITS p value, postopKA-ITS vs. preopKA-ITS Expected gaina Measured gainb Gain difference: expected gain – measured gain Distribution by gain differencec , n T4-T12 kyphosis before surgery T4-T12 kyphosis at last follow-up P value (T4-T12 kyphosis before surgery vs. at last follow-up) Overall kyphosis before surgery Planned overall kyphosis Overall kyphosis at last follow-up p value (overall kyphosis before surgery vs. at last follow-up) Coronal Cobb angle before surgery Coronal Cobb angle at last follow-up Coronal correction at last follow-up, %
21 (1 to 39) 34 (25 to 40) 34 (24 to 49) 0.001 14 (−14 to 36) 14 (−1 to 39) 0 (–16 to 18) 13–12–12 16 (0 to 36) 31 (22 to 46) Eto5 20 (1 to 46) 37 (27 to 44) 35 (25 to 56) E–4 53 (39 to 64) 13 (1 to 32) 74 (51 to 98)
9 (1 to 18) 34 (25 to 40) 29 (24 to 39) Eto9 25 (11 to 36) 20 (10 to 39) –5 (–16 to 10) 2–5–10 7 (0 to 14) 29 (22 to 36) Eto7 11 (1 to 19) 37 (28 to 44) 32 (25 to 39) E–7 55 (39 to 64) 16 (2 to 32) 70 (53 to 98)
29 (20 to 39) 34 (25 to 40) 38 (27 to 49) Eto6 5 (−14 to 17) 9 (−1 to 21) 4 (18 to−8) 11–7–2 24 (18 to 36) 34 (26 to 46) Eto5 30 (20 to 46) 37 (27 to 43) 38 (27 to 56) 0.002 51 (40 to 62) 11 (1 to 21) 77 (51 to 98)
Eto10 0.66 Eto5 E–8 E–5 0.001 0.002 Eto9 Eto4 Eto10 0.51 0.001 0.09 0.03 0.09
The p values < 0.05 are in bold type. H: subgroup with hypokyphosis before surgery; N: subgroup with normal kyphosis before surgery; preopKA-ITS, pre-operative kyphotic angle of the thoracic segment to be instrumented (before surgery); cvRCA, convex side rod contouring angle (equal to the amount of kyphosis planned for the thoracic segment to be instrumented); postopKA-ITS, post-operative kyphotic angle of the instrumented thoracic segment (at last follow-up) a Expected gain: cvRCA minus preopKA-ITS. b Measured gain: postopKA-ITS minus preopKA-ITS. c Outcome distribution: overcorrection (difference ≥ 5◦ ); optimal correction (difference between –5◦ and +5◦ ), and undercorrection (difference < −5◦ ).
difference between the preopKA-ITS and the postopKA-ITS. The difference between the expected and actual gains was computed and used to define three outcome categories: optimal outcome, difference ± 5◦ ; undercorrection, difference < –5◦ ; and overcorrection, difference > + 5◦ .
2.6. Secondary evaluation criteria T4-T12 TK, overall TK, and the coronal Cobb angle of the main curve were measured before surgery and at last follow-up. Proximal junctional kyphosis (PJK) was sought [8]. Finally, the patients
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Fig. 4. Patient #2, antero-posterior and lateral radiographs 2 years after surgery (hybrid construct). T4-T12 thoracic kyphosis is 29◦ and L1-S1 lumbar lordosis is 50◦ .
completed the SRS-22 quality-of-life questionnaire before surgery and at last follow-up. 2.7. Statistical analysis The statistical analyses were performed using XLStat (Addinsoft, Paris, France). Mean values were compared using the Wilcoxon test, Student’s test, or analysis of variance. Fisher’s exact test was applied to compare rates. Pearson’s test was used to assess correlations. Multivariate linear regression analyses were performed. Regression coefficients are reported with their 95% confidence intervals (95%CIs) [23]. Values of p smaller than 0.05 were considered significant. 3. Results 3.1. Patients and procedures Of 38 patients with AIS whose instrumentation included T4-T11, 1 was lost to follow-up and the remaining 37 were included in the study. Outcomes were analysed after at least 1 year of follow-up (Table 1). Of the 37 patients, 20 had normal TK and 17 hypokyphosis before surgery. Among anchors used in the study population, 85% were polyaxial pedicle screws, 11% were double hook claws, and 4% were sublaminar bands (Figs. 1 and 4). 3.2. Thoracic kyphosis (TK) In the overall cohort, the mean actual gain (difference between postopKA-ITS and preopKA-ITS) was 14◦ and was equal to the mean
expected gain. Mean postopKA-ITS was comparable to the mean cvRCA (mean difference = 0, p = 0.85, Cohen’s d = 0.047) (Table 2). However, 12 patients had an optimal outcome, 12 were undercorrected, and 13 were overcorrected (Table 2). In the subgroup with pre-operative hypokyphosis, the mean actual gain was 20◦ for an expected gain of 25◦ . Of the 17 patients in this subgroup, 10 were undercorrected. In the subgroup with normal pre-operative kyphosis, the mean actual gain was 8◦ for an expected gain of 4◦ . In this subgroup, 11 were overcorrected. Factors associated with postopKA-ITS by multivariate analysis were the preopKA-ITS (regression coefficient, 0.72; 95%CI: 0.497–0,937; p = E–5) and ccRCA (regression coefficient, 0.27; 95%CI: 0.005–0.540; p = 0.04). The difference between the postopKA-ITS and the cvRCA correlated closely with the expected gain (correlation coefficient, 0.74; p = E–7). Factors associated with this difference by multivariate linear regression were the preopKAITS (correlation coefficient = 0.41, p = 0.002) and expected gain (correlation coefficient = 0.62, p = E–5).
3.3. Other results Mean coronal correction was 74% (Table 1). None of the coronal parameters (Cobb angles, flexibility, correction) correlated with the TK parameters (all correlation coefficients < 0.10). No patient developed PJK. The coronal and sagittal angles measured at last follow-up showed no differences according to the Lenke classification (p > 0.1). Finally, the SRS-22 score increase showed weak correlations with actual gain, postopKA-ITS, and coronal correction (correlation coefficients < 0.20).
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4. Discussion This study assessed outcomes of patients with AIS managed using patient-specific rods that were pre-contoured according to a protocol based on pelvic incidence. The results confirm the working hypothesis that postopKA-ITS was favourably influenced by patient-specific pre-contouring of the rods, notably the concave rod, and was also associated with pre-operative TK. Overall TK at last follow-up was normal in all patients. Mean postopKA-ITS was not very different from the cvRCA. At last followup, postopKA-ITS was within the planned range in one-third of patients, overcorrected in another third, and undercorrected in the last third. The cvRCA value was the same in the subgroups with normokyphosis and hypokyphosis because it was determined based on pelvic incidence and not on pre-operative TK, which is a component of the scoliotic deformity [20]. The expected gain was therefore greater in the subgroup with hypokyphosis than in the subgroup with normal TK. The clinical and radiological outcomes of this strategy require evaluation in the longer term. In the hypokyphotic subgroup, the large TK increase of 20◦ on average is consistent with earlier studies of the same correction technique [2,10,17]. Nevertheless, the postopKA-ITS values indicated mean undercorrection of 5◦ compared to cvRCA and 15◦ compared to the ccRCA. These results indicate ‘loss’ of sagittal correction related to rod flattening during correction due to the stiffness of the spine. Clear evidence of concave rod flattening during translation manoeuvres has been reported elsewhere [21]. In the subgroup with normal pre-opKA-ITS, the postopKA-ITS indicated 4◦ of mean overcorrection compared to cvRCA. These findings suggest that the practice of overbending the concave rod by 10◦ (or more) should be continued for patients with hypokyphosis but not for patients with normal TK. Overbending tailored to the individual patient may also deserve consideration; for instance, overbending by 5◦ might be helpful in patients with moderate hypokyphosis. Our decision to measure the degree of TK of the instrumented vertebral segment (preop and postopKA-ITS) allowed us to assess the effect of the pre-contoured rods (RCA) on the instrumented spine. PreopKA-ITS is not necessarily equal to overall TK or to TK between T4 (orT5) and T12, which is the value often reported in the literature [7–9,12]. When planning the RCA, an important consideration is that the instrumented thoracic spine includes only a fraction of the overall TK, whose size varies with the number of instrumented thoracic levels. The coronal parameters and quality-of-life data were in accordance with earlier reports [6,9,19] and showed no correlations with the sagittal parameters. The trend toward less coronal correction in the hypokyphotic subgroup suggests that 3D correction may be more challenging to achieve in patients with hypokyphosis. The limitations of this study include the short follow-up, small sample size, and absence of a comparison group. Our preliminary results pertain only to simultaneous translation on two 6-mm cobalt-chrome rods. They cannot be directly extrapolated to other techniques and materials. Strong points of this study are the original design, prospective recruitment, uniform surgical technique, low patient attrition rate, and standardised evaluation of the radiographs by an independent observer.
5. Conclusion The use of patient-specific rods provided postopKA-ITS values that were similar to the cvRCA values. Predictors of postopKA-ITS at last follow-up were not only the amount of concave rod precontouring but also the degree of pre-operative KA-ITS. In patients with pre-operative hypokyphosis, kyphosis at last follow-up indicated undercorrection, which was partially offset
by 10◦ of concave rod overbending. In contrast, in the patients with pre-operative normokyphosis, overcorrection of the kyphosis occurred, probably as a result of the overbending of the concave rod. Therefore, concave rod overbending would seem unnecessary when TK is normal before surgery. Disclosure of interest F.S. has received funding for symposia from Medicrea International. V.C. has received funding for symposia from Medicrea International and Synthes. J.L.C. is a consultant for Medicrea International. V.F. is a consultant for Medicrea International and Clariance. C.M.B. and V.R. declare that they have no competing interest. Funding None. Contributions of each author F.S. conceived the study, performed the statistical analyses, drafted the manuscript, and created the tables. J.L.C. operated the patients, contributed to conceive the study, and revised the manuscript. V.C. measured the radiographic parameters, contributed to conceive the study, and revised the manuscript. V.F. created the patient-specific rod concept, contributed to conceive the study, and revised the manuscript. VR contributed to conceive the study, and revised the manuscript. C.M.B. contributed to collect and analyse the data, contributed to patient monitoring, and revised the final manuscript. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.otsr.2019.07.027. References [1] Clement JL, Geoffray A, Yagoubi F, et al. Relationship between thoracic hypokyphosis, lumbar lordosis and sagittal pelvic parameters in adolescent idiopathic scoliosis. Eur Spine J 2013;22:2414–20. [2] Clement JL, Pelletier Y, Solla F, Rampal V. Surgical increase of thoracic kyphosis increases unfused lumbar lordosis in selective fusion for thoracic adolescent idiopathic scoliosis. Eur Spine J 2019;28:581–9. [3] Abelin-Genevois K, Sassi D, Verdun S, Roussouly P. Sagittal classification in adolescent idiopathic scoliosis: original description and therapeutic implications. Eur Spine J 2018;27:2192–202. [4] Glassman SD, Berven S, Bridwell K, et al. Correlation of radiographic parameters and clinical symptoms in adult scoliosis. Spine 2005;30:682. [5] Bernstein P, Hentschel S, Platzek I, et al. Thoracal flat back is a risk factor for lumbar disc degeneration after scoliosis surgery. Spine J 2014;14:925–32. [6] Angelliaume A, Ferrero E, Mazda K, et al. Titanium vs cobalt chromium: what is the best rod material to enhance adolescent idiopathic scoliosis correction with sublaminar bands? Eur Spine J 2017;26:1732–8. [7] Suk SI, Lee CK, Min HJ, et al. Comparison of Cotrel-Dubousset pedicle screws and hooks in the treatment of idiopathic scoliosis. Int Orthop 1994;18:341–6. [8] Kim YJ, Lenke LG, Bridwell KH, et al. Proximal junctional kyphosis in adolescent idiopathic scoliosis after 3 different types of posterior segmental spinal instrumentation and fusions: incidence and risk factor analysis of 410 cases. Spine 2007;32:2731–8. [9] Suk SI, Kim WJ, Kim JH, et al. Restoration of thoracic kyphosis in the hypokyphotic spine: a comparison between multiple-hook and segmental pedicle screw fixation in adolescent idiopathic scoliosis. J Spinal Disord 1999;12:489–95. [10] Clement JL, Chau E, Kimkpe C, et al. Restoration of thoracic kyphosis by posterior instrumentation in adolescent idiopathic scoliosis: comparative radiographic analysis of two methods of reduction. Spine (Phila Pa 1976) 2008;33:1579–87. [11] Vialle R, Levassor N, Rillardon L, et al. Radiographic analysis of the sagittal alignment and balance of the spine in asymptomatic subjects. J Bone Joint Surg Am 2005;87:260–7.
Please cite this article in press as: Solla F, et al. Patient-specific rods for thoracic kyphosis correction in adolescent idiopathic scoliosis surgery: Preliminary results. Orthop Traumatol Surg Res (2019), https://doi.org/10.1016/j.otsr.2019.07.027
G Model OTSR-2459; No. of Pages 7
ARTICLE IN PRESS F. Solla et al. / Orthopaedics & Traumatology: Surgery & Research xxx (2019) xxx–xxx
[12] Lenke LG, Edwards CC, Bridwell KH. The Lenke classification of adolescent idiopathic scoliosis: how it organizes curve patterns as a template to perform selective fusions of the spine. Spine 2003;28:S199–207. [13] Winter RB, Lonstein JE, Denis F. Sagittal spinal alignment: the true measurement, norms, and description of correction for thoracic kyphosis. J Spinal Disord Tech 2009;22:311–4. [14] Mac-Thiong JM, Labelle H, Roussouly P. Pediatric sagittal alignment. Eur Spine J 2011;20(Suppl 5):586–90. [15] Solla F, Barrey C, Burger E, Kleck C, Fiere V. Patient specific rods for surgical correction of sagittal imbalance in adults: technical aspects and preliminary results. Clin Spine Surg 2019;32:80–6. [16] Solla F, Clément JL, Doria C, et al. Adolescent Idiopathic Scoliosis exceeding 70◦ : a single center surgical experience. Minerva Ortopedica 2018;69:69–77. [17] Allia J, Clément JL, Rampal V, et al. Influence of derotation connectors on 3D surgical correction of adolescent idiopathic scoliosis. Clin Spine Surg 2018;31:E209–15.
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[18] Solla F, Gallo M, Doria C, et al. Prognostic role of rib hump in overlying thoracic curve correction above selective fusion for Lenke 5 idiopathic adolescent scoliosis. Clin Spine Surg 2018;31:E140–5. [19] Clément JL, Solla F, Tran A, et al. Five-year outcomes of the First Distal Uninstrumented Vertebra after posterior fusion for Adolescent Idiopathic Scoliosis Lenke 1 or 2. Orthop Traumatol Surg Res 2017;103:727–31. [20] Legaye J, Duval-Beaupère G. Sagittal plane alignment of the spine and gravity: a radiological and clinical evaluation. Acta Orthop Belg 2005;71:213–20. [21] Le Naveaux F, Aubin CE, Parent S, et al. 3D rod shape changes in adolescent idiopathic scoliosis instrumentation: how much does it impact correction? Eur Spine J 2017;26:1676–83. [22] Maillot C, Ferrero E, Fort D, et al. Reproducibility and repeatability of a new computerized software for sagittal spinopelvic and scoliosis curvature radiologic measurements: Keops(® ). Eur Spine J 2015;24:1574–81. [23] Solla F, Tran A, Bertoncelli D, et al. Why a p-value is not enough. Clin Spine Surg 2018;31:385–8.
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