|
 
 |
| SYMPOSIUM: ADOLESCENT IDIOPATHIC SCOLIOSIS |
|
| Year : 2020 | Volume
: 3
| Issue : 2 | Page : 160-172 |
|
Current concepts in level selection for fusion in the adolescent idiopathic scoliosis patient
Paul Jaewook Park1, Andrew Sawires2, Lawrence G Lenke1
1 Department of Orthopedic Surgery, The Daniel and Jane Och Spine Hospital, NewYork-Presbyterian/Columbia University Medical Center, New York, USA
2 Department of Orthopedic Surgery, Lenox Hill Hospital, New York, USA
| Date of Submission | 20-Nov-2019 |
| Date of Decision | 03-Jan-2020 |
| Date of Acceptance | 23-Mar-2020 |
| Date of Web Publication | 13-Jul-2020 |
Correspondence Address:
Dr. Paul Jaewook Park
Department of Orthopedic Surgery, The Daniel and Jane Och Spine Hospital, NewYork-Presbyterian/Columbia University Medical Center, 5141 Broadway, 3 Field West-022, New York, NY.
USA
 Source of Support: None, Conflict of Interest: None
DOI: 10.4103/isj.isj_67_19
Over the past several decades, level selection for fusion in the patient with adolescent idiopathic scoliosis (AIS) has evolved alongside technique. Now, with the near ubiquitous use of pedicle screw fixation, selection criteria have changed to minimize the number of levels fused, especially distally in the lumbar spine. With each additional motion segment preserved, it has been suggested that postoperative function can be improved and the risk of degenerative disease down the line may be decreased. Currently, the Lenke classification for AIS is the most widely used system to describe AIS pathology. Understanding where the structural and nonstructural curves are may help determine the extent of fusion required distally. Proximally, shoulder balance is still considered a key consideration for upper instrumented vertebra (UIV) selection. In terms of the lowest instrumented vertebra (LIV), we focus on two key concepts to prevent serious complications such as distal junctional kyphosis (DJK) or adding-on phenomenon: the last touched vertebra (LTV) and the stable sagittal vertebra. In the AP radiograph, identifying the LTV as the LIV may allow the surgeon to save a fusion level without increasing risk of DJK or adding-on. However, one must also consider the sagittal plane; the authors identify the stable sagittal vertebra on the lateral radiograph to help determine the optimal LIV; of these two criteria, the more distal level will be selected to decrease the chance of adverse outcomes. Keywords: Adolescent idiopathic scoliosis, last touched vertebra, level selection, stable sagittal vertebra
How to cite this article:
Park PJ, Sawires A, Lenke LG. Current concepts in level selection for fusion in the adolescent idiopathic scoliosis patient. Indian Spine J 2020;3:160-72 |
How to cite this URL:
Park PJ, Sawires A, Lenke LG. Current concepts in level selection for fusion in the adolescent idiopathic scoliosis patient. Indian Spine J [serial online] 2020 [cited 2023 Mar 27];3:160-72. Available from: https://www.isjonline.com/text.asp?2020/3/2/160/289659 |
| Introduction | |  |
As the surgical treatment of adolescent idiopathic scoliosis (AIS) has evolved over the past several decades, now powerful three-dimensional correction is possible using posterior segmental pedicle screw fixation. The criteria for fusion level selection have also inevitably evolved. Level selection is critical and can have significant consequences in young adolescent patients over time, including worsening deformity or necessitating revision surgery. Preceded by the King–Moe classification, the Lenke classification for AIS developed in 2001 has helped provide a framework for level selection based on curve morphology[1] [Figure 1]. The Lenke classification continues to be widely used to this day; however, the associated guidelines for level selection for each curve type are being further explored as more longitudinal data becomes available and as surgical techniques advance. Now with the use of pedicle screw fixation, selective thoracic fusion has become feasible and goals of surgery have progressed as well, aiming for shorter fusion constructs while preserving more lumbar motion segments. Our objective was to review the most recent studies on both upper and lower instrumented vertebra selection in AIS, to address both the coronal and sagittal planes in preoperative planning, and to consolidate this information into several key principles. For each section of this review, a thorough PubMed search was performed. Keywords used for the upper instrumented vertebra (UIV) section included “UIV selection” for each Lenke type, “UIV selection + risk of PJK” and “UIV selection + kyphosis.” For the lowest instrumented vertebra (LIV), keywords included “LIV + AIS,” “last touched vertebra,” and “stable sagittal vertebra.” All studies included were retrospective analyses; no prospective data was available. Studies published in 2010 and thereafter were prioritized, with previous studies included for comparison and reference. | Figure 1: The Lenke Classification for adolescent idiopathic scoliosis[1]
Click here to view |
| UIV Selection | | |
Selection of the UIV in the patient with AIS has been shown to be important both for obtaining a stable and balanced fusion, as well as for controlling postoperative shoulder imbalance. Similar to selecting the LIV, UIV selection criteria have also evolved over time. In 1962, Harrington[2] first described fusing to one level above the measured curve. Over subsequent years, several authors recommended using rotation to determine the UIV by fusing to the first neutral vertebra (NV) above the curve.[3] Ultimately, the specific level in the proximal thoracic (PT) spine made little functional difference clinically, and attention was instead turned to obtaining appropriate shoulder balance while selecting the UIV. With the advent of the Lenke classification, several recommended treatment strategies based on curve type emerged.[4] Initial UIV selection strategy using curve type was based solely on the coronal plane; however, as the importance of sagittal balance became apparent in recent decades in all Lenke classification types, it became critical not to end the construct at a region of kyphosis to prevent complications such as proximal junctional kyphosis (PJK)[5] [Table 1] and [Table 2]. | Table 1: Selection of the upper instrumented vertebra based on Lenke classification curve type
Click here to view |
For Lenke type 1 curves, fusion should address the structural main thoracic curve. For UIV, the main consideration has been shoulder balance; briefly, T3 should be the UIV of choice for level shoulders, whereas T4 should be selected for right shoulder elevation;[6],[7] although less common, the T2 vertebra may be selected as a UIV if the left shoulder is higher preoperatively. This is possible in Lenke type 1 curves as spontaneous correction of PT curves has been observed, correlating with increased flexibility on preoperative side-bending radiographs.[8] A retrospective study of 64 patients with Lenke 1 AIS looked at radiographic outcome of shoulder balance after fusion using the aforementioned UIV selection criteria and found that radiological shoulder height difference (RSH) and clavicle angles (CA) were similar among these groups immediately after surgery and at average follow-up of 24 months, with improved Scoliosis Research Society (SRS)-22 scores at final follow-up for patients fused to T2 and T3.[9] In another series, 98.7% of patients with UIV selected as aforementioned had perceived cosmetic shoulder balance at the last follow-up appointment.[10]
For Lenke type 2 or 4 curves, the structural PT curve makes UIV selection, especially important to correct both the proximal curve and the shoulder imbalance.[11] Several studies have found that T2 or T3 should be the UIV of choice for a right main thoracic curve with level shoulders, whereas T3 or T4 would be selected in the rare circumstance when the right shoulder was higher to account for right shoulder depression postoperatively.[12],[13] T2 should be selected as the UIV of choice if the left shoulder is higher than the right.[14],[15] Although several studies found fusing to more cranial levels (T1, T2) improve postoperative radiographic balance measures such as RSH and proximal wedge angle (PWA),[16] other studies found that fusing to T2 can only effectively improve medial shoulder balance (T1 tilt and first rib angle) but has no effect on lateral shoulder balance.[17] Overall, the UIV selection in double thoracic curves is debatable, and postoperative shoulder balance is difficult to predict;[18] however, following the basic principle to fuse all structural curves minimizes the chances of inadequate control of the structural PT curve,[19] which often indicates a UIV of T2.
Type 3 double major (DM) curves require instrumentation and fusion of the main thoracic (MT) and thoracolumbar/lumbar (TL/L) regions. The UIV is similar to that of a type 1 curve as explained earlier. Type 6 TL/L-MT curves have a major curve in the TL/L region, with the MT region being a structural minor curve and both regions are treated similarly with fusion of the MT and TL/L regions.[20] Thus, type 3 and 6 curve patterns are both treated with the UIV selection criteria as aforementioned.[21]
The recommended treatment for Lenke type 5 curves is fusion of the entire TL/L curve (generally end vertebra to end vertebra).[22] Fusion can be extended to include the thoracic curve in primary TL scoliosis to improve coronal correction, but at the cost of decreased thoracic kyphosis and clinical flexibility 2 years postoperatively.[23] Of note, the rates of PJK were found to be higher in patients with fused cranial to the upper end vertebra (UEV), which is contrary to Lenke type I curves.[24],[25]
Besides shoulder balance, one must also consider the risk of PJK. The incidence of PJK ranges from 5% to 46%, and it has been reported that 66% of cases occur 3 months after surgery and approximately 80% occur within 18 months.[5],[26-28] Lonner et al.[24] found that the incidence of PJK after operative treatment of AIS varies based on Lenke type (Lenke 1, 6.35%; Lenke 2 and 4, 4.39%; Lenke 3 and 6, 11.64%; and Lenke 5, 8.49%). PJK is multifactorial in origin and likely results from variable risk factors, some of which are patient specific and not correctable preoperatively, such as preoperative hyperkyphotic thoracic alignment.[5],[29] There are several factors in the surgeon’s control, however, such as UIV selection. Of note, no correlation was found between cervical sagittal alignment (CSA) and UIV level chosen based on several studies.[30],[31]
| LIV Selection | | |
Selection of the LIV in the patient with AIS also has significant implications [Table 3]. The lumbar vertebrae are critical for flexibility and motion, with range of motion in the sagittal plane increasing in the native lumbar spine at each vertebral level caudally.[32] By saving levels, it has been shown that there is greater postoperative mobility as well as a greater distribution of motion across several discs with fewer segments fused;[33] there is some evidence correlating fewer segments fused with higher health-related quality of life SRS-22 scores and lower SRS-22 pain subscales as well.[34] This has implications in future disc degeneration as there are increased intradiscal pressures with each additional fused level on the adjacent caudal discs below the fusion.[35] Danielsson et al.[36] followed patients with AIS after fusion for 25 years radiographically. They found increased disc degeneration with fusion to L4 and above, relative to patients fused below L4. However, when L3 was chosen as the threshold, no significant changes were seen between patients fused to L3 and above and those patients fused below L3.[36] On the contrary, if too few levels are fused, it is possible that the patient may develop distal junctional kyphosis (DJK), in which progressive kyphosis occurs distal to the fusion construct, which may lead to pain, deformity, and may necessitate additional surgery. Distal adding-on may also occur, in which the coronal deformity progresses at the levels distal to the fusion construct. To strike this balance, one must consider not only the radiographic curve characteristics but patient characteristics as well, such as skeletal maturity. Several studies have shown that patients are at a greater risk of decompensating (either proximally or distally) if fused at a younger age, with open triradiate cartilage or at a lower Risser stage.[37],[38],[39]
In the early years of fusion surgery for scoliosis regarding level selection, Goldstein[3] described going “1 to 3 vertebrae below the primary curve” in 1964. Harrington[2] was more specific when he introduced the concept of the stable zone to select the LIV: this was the first caudal level to fall within the stable zone, defined as the area between the two lumbosacral facets. This concept was further defined by King et al.[40] as the stable vertebra, the vertebra most bisected by the central sacral vertical line (in the setting of Harrington rod instrumentation). Moe[41] emphasized the importance of vertebral rotation, in which the NV must be included distally; even in 1964, Moe described the concept of selective fusion, in which only the main thoracic curve would need to be included as the lumbar curve “often demonstrates a surprising degree of flexibility” on bending roentgenograms. Suk expanded on the concept of the NV in 2003 by establishing the relationship between the end vertebra and NV for the main thoracic curve, stating that the NV should be the LIV; if the NV is more than 1 level caudal to the end vertebra, then 1 level cranial to the NV would be sufficient, theorizing that de-rotation would most likely bring the cephalad vertebra into the stable zone[42],[43] [Figure 2]. | Figure 2: Timeline of concepts in selection of the lowest instrumented vertebra over the past 50 years
Click here to view |
Lenke et al.,[44] in 1999, showed that spontaneous lumbar curve correction occurs in patients with type 1 and 2 curves, allowing for selective fusion. Selecting the appropriate LIV is especially important in these cases as it is the transition between the rigid thoracic spine and the flexible lumbar spine.[45] With possible spontaneous correction, it may obviate the need to add more distal fusion segments; this is especially critical in curve types 1–4 where a selective thoracic fusion may be considered.
Last touched vertebra
As previously mentioned, creating shorter constructs while saving motion segments has become a goal of AIS treatment; all while avoiding significant complications associated with a shorter construct such as distal adding on. As such, new radiographic guidelines have been suggested to help guide level selection. Recently, two parameters have gained significant attention: the last substantially touched vertebra (LSTV) and the last touched vertebra (LTV). Cho et al.[46] described the LSTV as the cephalad most lumbar vertebra in which the central sacral vertical line (CSVL) intersected the pedicle outline or was medial to it, while the LTV was the most cephalad vertebra in which the CSVL intersected any portion of the vertebral body outline, including lateral to the pedicle. Ultimately, the LTV is often slightly less bisected by the CSVL, potentially saving a level compared to the LSTV. This study looked at 195 patients with Lenke 1A curves, of which 21% had adding-on distally. They looked specifically at type 1A curves and found that identifying whether the L4 vertebra tilted right (AR) or left (AL) helped predict how the 1A curve would behave following fusion; his recommendation for 1AR curves was to select an LIV approaching both the LSTV and NV, whereas for 1AL curves fusing to at least one level below the EV had better outcomes.[46] In a study of 112 patients with Lenke 1A curves, Matsumoto et al.[47] found residual apical translation of the main thoracic curve, and an LIV above the LTV had significant associations with adding on versus an LIV at or below the LTV. Cao et al.[48] looked at 116 Lenke 2A patients and found similarly that adding on was significantly more common with an LIV proximal to the LTV. Murphy et al.[49] looked at 160 patients with either a Lenke 1 or 2 curve pattern (with an AR modifier) and found that an LIV proximal to the LSTV had a significantly increased risk of adding on (differing from prior studies using the LTV). Regarding LTV versus LSTV as the LIV, Qin et al.[50] looked at 104 Lenke 1A patients and found that an LIV at the LTV (CSVL lateral to pedicle) was at a significantly higher risk of adding on relative to the LSTV (CSVL at least touching part of pedicle); they recommended an LIV at the LSTV or LSTV + 1. Similarly, Bai et al.,[51] in 2018, looked at 120 consecutive Lenke 1A and 2A patients undergoing posterior fusion and found that a greater LIV distance from the CSVL may lead to higher rates of distal adding on. A long-term study with minimum follow-up of 5 years of Lenke 1A and 2A curves showed that the LTV produced optimal LIV positioning; those fused short of the LTV showed increased LIV-CSVL distance at final follow-up.[52] Fujii et al.[53] looked at Lenke 1B and C type curves in 44 patients and similarly found that an LIV above the LTV was a risk factor for distal adding on as well. A multicenter study from 2017 looked at 182 patients with AIS with Lenke type 1 or 2 curves that focused on the first distal uninstrumented vertebra (FDUV) tilt, one of the criteria for adding-on phenomenon (>5°, 1 year after surgery). After an average follow-up of 5 years, the authors found that of the patients with an LIV proximal to the LTV, 84% had an FDUV >5°, indicating higher risk of DJK. Stopping instrumentation at NV-1 or NV-2 was also found to be a risk factor for FDUV tilt >5°. In cases where the LTV is caudal to the NV, the authors recommend fusing down to the LTV. If the LTV is cephalad to the NV and the NV is at L3-L4, stopping instrumentation at NV-1 is a reasonable alternative.[54]
For Lenke type 3 or 4 curves, where a structural TL/L curve is present, the decision to perform a selective fusion is controversial. One must understand the relationship of the MT and TL/L curve; Lenke et al.,[55] in 1992, initially described looking at three criteria. The apical vertebral translation (AVT) ratio looks at the distance of the thoracic AVT (distance from the thoracic apex to CSVL) and the TL/L AVT (distance from the TL/L apex to CSVL). The apical vertebral rotation (AVR) ratio compares thoracic apical rotation to TL/L apical rotation using the Nash–Moe classification.[56] Lastly, the thoracic Cobb angle is compared to the TL/L Cobb angle. A ratio of 1.2 or greater (greater translation, rotation, and Cobb angle of the thoracic curve) suggests that a selective thoracic fusion is feasible[55] [Figure 3]. There is a paucity of data regarding LIV for Lenke type 5 curves; LIV selection is critical for these curves, given the importance of each additional motion segment as one goes more distal [Figure 4].[33],[34],[35],[36] A study from 2017 reviewed 78 patients with Lenke type 5 curves that were divided into selective fusion (LIV at the stable and NV) versus hyperselective fusion (at maximum 2 levels above and below the apex of the curve).[57] There were no differences in outcome score or pain level at follow-up between groups though function was significantly better in hyperselective patients. The selective fusion group was fused to or below the LTV in 91% of patients, whereas only 16% of patients ended at or below the LTV for the hyperselective group. Of patients, 10% overall developed distal adding on, of which 75% were in the hyperselective group. Of patients, 62.5% with distal adding on had an LIV above the LTV.[57] | Figure 3: The use of apical vertebral translation, apical vertebral rotation, and Cobb angle in selective thoracic fusion.
Click here to view |
Stable sagittal vertebra
Considering the sagittal plane is arguably just as important as the coronal plane when selecting the LIV, with major implications in the development of DJK [Figure 5] and [Figure 6]. Much of the study in this area was initially performed in patients with Scheuermann kyphosis. Mainly, two different radiographic criteria have been described: the first lordotic vertebra (FLV) or the stable sagittal vertebra (SSV) is defined as the level most bisected by the SVA (a vertical line from the posterosuperior corner of the S1 endplate). Cho et al.[58] looked at 31 patients with a minimum of 2-year follow-up in patients with kyphosis and found that an LIV above the SSV had a 38% rate of DJK versus those at or below the SSV (8%) for distal junctional problems (such as DJK or implant-related failure). Lundine et al.[59] looked at 22 patients with kyphosis and found that fusion to the SSV had a lower rate of postoperative DJK versus fusion to the FLV (13% vs. 33%). Dikici et al.[60] also looked at 39 patients with Scheuermann kyphosis and found that DJK rates were lower in patients with an LIV at the SSV over either the FLV or lower end vertebra (LEV). Kim et al.[61] retrospectively looked at 44 posterior fusion patients with kyphosis and found that an LIV at or distal to the SSV had a significantly smaller lordotic disc angle than an LIV above the SSV. Yanik et al.,[62] however, looked at 54 patients with Scheuermann kyphosis and did not find a statistical difference between patients with an LIV at the FLV or SSV. Lowe et al.[63] then studied the SSV in the patient with AIS; 375 posterior fusion patients were significantly more likely to develop DJK if the curve was instrumented to less than 1 level distal to EV. Yang et al.[17] performed a retrospective study in 113 patients with AIS with an LIV at L2 or above and found that those with an LIV above the SSV had DJK rate of 17%, whereas those with an LIV caudal to the SSV had 0% rates of DJK, defined as ≥10° between the LIV and caudal endplate while standing. Fischer et al.[64] looked at 544 patients with AIS with major thoracic curves with a minimum follow-up of 2 years and found that an LIV 3 vertebrae proximal to either the stable or NV led to an increased risk of DJK. The coronal position of the LIV was also a risk factor, with greater translation correlating with increased risk of DJK.[64]
| Conclusion | | |
For the UIV in Lenke type 1, 3, and 6 curves, one should consider the preoperative shoulder imbalance and thoracic kyphosis. Fusing to T2 when the left shoulder is higher, T3 for when the shoulders are level, and T4 for when the right shoulder is higher has been associated with better postoperative shoulder balance and patient satisfaction. For Lenke type 2 and 4 curves, fusing to T2 is nearly always the appropriate UIV to control the PT curve as well as adjust for shoulder balance. Considering thoracic kyphosis is also important given the risk of PJK, those with higher preoperative thoracic kyphosis may necessitate extending the fusion cranially to T2 even in type 1 and 2 curves to control the PT kyphosis, regardless of shoulder balance. For Lenke type 5 curves, extending cephalad to the UEV may actually increase the risk of PJK. Critical intraoperative steps to prevent PJK include proper UIV selection and bending appropriate kyphosis into the proximal rod; one may consider using hook fixation proximally as well.
Regarding the LIV, selective thoracic fusion is possible in Lenke type 1–4 curves. We recommend fusing distally to the LTV on the AP radiograph to avoid DJK or distal adding on. Although there is evidence to support both the LSTV and LTV as the LIV, fusing to the LTV will often save one additional lumbar motion segment. In situations where the LTV may be questionable on the standing AP radiograph, the authors recommend using supine images to help assess for potential correction; the more proximal proposed LIV may ultimately appear more stable and neutral on the supine image, aiding in LIV selection. In patients with a structural TL/L curve, one should take into account the ratio of the MT to MT/L apical translation, rotation, and Cobb angle; a ratio of 1.2 (greater in the MT curve) is favorable for a selective fusion with spontaneous correction of the TL/L curve more likely. One must also pay careful attention to the rotation of the proposed LIV on the AP radiograph; in cases where the proposed LIV is rotated (Nash–Moe grade 2–4), we would recommend reassessing the LIV and going distally if necessary to a more NV to decrease chance of distal adding on and decompensation.
All these criteria in the coronal plane should also be considered in conjunction with the SSV on the lateral radiograph; the majority of studies reviewed indicate that fusing to the SSV has a lower risk of DJK relative to the FLV. In either case, fusing to the more distal segment (either the LTV or SSV) is likely the appropriate choice to decrease the risk of distal junctional problems. Not only is there minimal motion to be gained by preserving T12-L1 level, a study by Kim et al.[65] found no difference in the incidence of DJK whether the LIV was T12 or L1.
Lastly, one must consider the flexibility of the curve. Many different techniques have been proposed and compared such as traction, fulcrum bending, lateral bending, and supine bending radiographs among others.[66] Most studies, however, look only at the predictive value of these methods of curve flexibility compared to postoperative correction obtained. Although there are less data on whether determining LTV or SSV on these radiographs have different long-term outcomes in patients with AIS, the authors suggest using supine radiographs to assess for curve flexibility and potential curve correction as an additional piece of information to consider when determining the LIV. Less to no data are available on whether determining LTV or SSV on these radiographs have different long-term outcomes in patients with AIS. Decisions based on these imaging techniques to account for curve flexibility may result in additional levels spared safely and warrants further study.
Level selection in the patient with AIS is a complex and multifaceted decision. One must consider the patient as a whole—the patient’s goals, self-perception of shoulder balance, skeletal maturity, physical exam, and radiographic curve characteristics among other factors. Thorough preoperative planning accounting for the coronal and sagittal deformity while keeping the patient at the center of the discussion is crucial for level selection and for optimizing patient outcomes.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
| References | | |
| 1. | Lenke LG, Betz RR, Harms J, Bridwell KH, Clements DH, Lowe TG, et al. Adolescent idiopathic scoliosis: A new classification to determine extent of spinal arthrodesis. J Bone Joint Surg Am 2001;83:1169-81.  |
| 2. | Harrington PR. Treatment of scoliosis. Correction and internal fixation by spine instrumentation. J Bone Joint Surg Am 1962;44-A:591-610. |
| 3. | Goldstein LA. The surgical management of scoliosis. Clin Orthop Relat Res 1964;35:95-115. |
| 4. | Kim HJ, de Kleuver M, Luk K. Scoliosis—Diagnosis—AO Surgery Reference. Available from: https://www2.aofoundation.org/wps/portal/surgery?showPage= diagnosis&bone=Spine&segment=DeformityScoliosis&Language=en. [Last accessed on 2019 July 20]. |
| 5. | Kim DK, Kim JY, Kim DY, Rhim SC, Yoon SH. Risk factors of proximal junctional kyphosis after multilevel fusion surgery: More than 2 years follow-up data. J Korean Neurosurg Soc 2017;60:174-80. |
| 6. | Roussouly P, Labelle H, Rouissi J, Bodin A. Pre- and post-operative sagittal balance in idiopathic scoliosis: A comparison over the ages of two cohorts of 132 adolescents and 52 adults. Eur Spine J 2013;22:S203-15. |
| 7. | Suk SI, Lee SM, Chung ER, Kim JH, Kim SS. Selective thoracic fusion with segmental pedicle screw fixation in the treatment of thoracic idiopathic scoliosis: More than 5-year follow-up. Spine (Phila Pa 1976) 2005;30:1602-9. |
| 8. | Kuklo TR, Lenke LG, Won DS, Graham EJ, Sweet FA, Betz RR, et al. Spontaneous proximal thoracic curve correction after isolated fusion of the main thoracic curve in adolescent idiopathic scoliosis. Spine (Phila Pa 1976) 2001;26:1966-75. |
| 9. | Zhao J, Chen Z, Yang M, Li G, Zhao Y, Li M. Does spinal fusion to T2, T3, or T4 affects sagittal alignment of the cervical spine in Lenke 1 AIS patients: A retrospective study. Medicine (Baltimore) 2018;97:e9764. |
| 10. | Tang X, Luo X, Liu C, Fu J, Yao Z, Du J, et al. The spontaneous development of cosmetic shoulder balance and shorter segment fusion in adolescent idiopathic scoliosis with Lenke I curve: A consecutive study followed up for 2 to 5 years. Spine (Phila Pa 1976) 2016;41:1028-35. |
| 11. | Lee CS, Hwang CJ, Lee DH, Cho JH. Five major controversial issues about fusion level selection in corrective surgery for adolescent idiopathic scoliosis: A narrative review. Spine J 2017;17:1033-44. |
| 12. | Brooks JT, Bastrom TP, Bartley CE, Lonner BS, Shah SA, Miyanji F, et al; Harms Study Group. In search of the ever-elusive postoperative shoulder balance: Is the T2 UIV the key? Spine Deform 2018;6:707-11. |
| 13. | Lee CS, Hwang CJ, Lee DH, Cho JH. Does fusion to T2 compared with T3/T4 lead to improved shoulder balance in adolescent idiopathic scoliosis with a double thoracic curve? J Pediatr Orthop B 2019;28:32-9. |
| 14. | Suk SI, Kim WJ, Lee CS, Lee SM, Kim JH, Chung ER, et al. Indications of proximal thoracic curve fusion in thoracic adolescent idiopathic scoliosis: Recognition and treatment of double thoracic curve pattern in adolescent idiopathic scoliosis treated with segmental instrumentation. Spine (Phila Pa 1976) 2000;25:2342-9. |
| 15. | Namikawa T, Matsumura A, Kato M, Hayashi K, Nakamura H. Radiological assessment of shoulder balance following posterior spinal fusion for thoracic adolescent idiopathic scoliosis. Scoliosis 2015;10:S18. |
| 16. | Lee CS, Hwang CJ, Lim EJ, Lee DH, Cho JH. A retrospective study to reveal factors associated with postoperative shoulder imbalance in patients with adolescent idiopathic scoliosis with double thoracic curve in: J Neurosurg Pediatr 2016;18:655-758. |
| 17. | Yang H, Im GH, Hu B, Wang L, Zhou C, Liu L, et al. Shoulder balance in Lenke type 2 adolescent idiopathic scoliosis: Should we fuse to the second thoracic vertebra? Clin Neurol Neurosurg 2017;163:156-62. |
| 18. | Bjerke BT, Cheung ZB, Shifflett GD, Iyer S, Derman PB, Cunningham ME. Do current recommendations for upper instrumented vertebra predict shoulder imbalance? An attempted validation of level selection for adolescent idiopathic scoliosis. HSS J 2015;11:216-22. |
| 19. | Erken HY, Burc H, Saka G, Aydogan M. Disagreements in surgical planning still exist between spinal surgeons in adolescent idiopathic scoliosis: A multisurgeon assessment. Eur Spine J 2014;23:1258-62. |
| 20. | Puno RM, An KC, Puno RL, Jacob A, Chung SS. Treatment recommendations for idiopathic scoliosis: An assessment of the Lenke classification. Spine (Phila Pa 1976) 2003;28:2102-14; discussion 2114-5. |
| 21. | Lenke LG. The Lenke classification system of operative adolescent idiopathic scoliosis. Neurosurg Clin N Am 2007;18:199-206. |
| 22. | Shetty AP, Suresh S, Aiyer SN, Kanna R, Rajasekaran S. Radiological factors affecting post-operative global coronal balance in Lenke 5 C scoliosis. J Spine Surg 2017;3:541-7. |
| 23. | Lark RK, Yaszay B, Bastrom TP, Newton PO; Harms Study Group. Adding thoracic fusion levels in Lenke 5 curves: Risks and benefits. Spine (Phila Pa 1976) 2013;38:195-200. |
| 24. | Lonner BS, Toombs CS, Paul JC, Shah SA, Shufflebarger HL, Flynn JM, et al. Resource utilization in adolescent idiopathic scoliosis surgery: Is there opportunity for standardization? Spine Deform 2017;5:166-71. |
| 25. | Zhao J, Yang M, Yang Y, Chen Z, Li M. Proximal junctional kyphosis following correction surgery in the Lenke 5 adolescent idiopathic scoliosis patient. J Orthop Sci 2018;23:744-9. |
| 26. | Cho SK, Shin JI, Kim YJ. Proximal junctional kyphosis following adult spinal deformity surgery. Eur Spine J 2014;23:2726-36. |
| 27. | Wang J, Zhao Y, Shen B, Wang C, Li M. Risk factor analysis of proximal junctional kyphosis after posterior fusion in patients with idiopathic scoliosis. Injury 2010;41:415-20. |
| 28. | Lee J, Park Y-S. Proximal junctional kyphosis: Diagnosis, pathogenesis, and treatment. Asian Spine J 2016;10:593-600. |
| 29. | Hyun SJ, Lee BH, Park JH, Kim KJ, Jahng TA, Kim HJ. Proximal junctional kyphosis and proximal junctional failure following adult spinal deformity surgery. Korean J Spine 2017;14:126-32. |
| 30. | Hwang SW, Samdani AF, Tantorski M, Cahill P, Nydick J, Fine A, et al. Cervical sagittal plane decompensation after surgery for adolescent idiopathic scoliosis: An effect imparted by postoperative thoracic hypokyphosis. J Neurosurg Spine 2011;15:491-6. |
| 31. | Canavese F, Turcot K, De Rosa V, de Coulon G, Kaelin A. Cervical spine sagittal alignment variations following posterior spinal fusion and instrumentation for adolescent idiopathic scoliosis. Eur Spine J 2011;20:1141-8. |
| 32. | Cook DJ, Yeager MS, Thampi SS, Whiting DM, Cheng BC. Stability and load sharing characteristics of a posterior dynamic stabilization device. Int J Spine Surg 2015;9:9. |
| 33. | Marks M, Newton PO, Petcharaporn M, Bastrom TP, Shah S, Betz R, et al. Postoperative segmental motion of the unfused spine distal to the fusion in 100 patients with adolescent idiopathic scoliosis. Spine (Phila Pa 1976) 2012;37:826-32. |
| 34. | Sanchez-Raya J, Bago J, Pellise F, Cuxart A, Villanueva C. Does the lower instrumented vertebra have an effect on lumbar mobility, subjective perception of trunk flexibility, and quality of life in patients with idiopathic scoliosis treated by spinal fusion? J Spinal Disord Tech 2012;25:437-42. |
| 35. | Auerbach JD, Lenke LG, Bridwell KH, Sehn JK, Milby AH, Bumpass D, et al. Major complications and comparison between 3-column osteotomy techniques in 105 consecutive spinal deformity procedures. Spine (Phila Pa 1976) 2012;37:1198-210. |
| 36. | Danielsson AJ, Cederlund CG, Ekholm S, Nachemson AL. The prevalence of disc aging and back pain after fusion extending into the lower lumbar spine. A matched MR study twenty-five years after surgery for adolescent idiopathic scoliosis. Acta Radiol 2001;42:187-97. |
| 37. | Sponseller PD, Betz R, Newton PO, Lenke LG, Lowe T, Crawford A, et al; Harms Study Group. Differences in curve behavior after fusion in adolescent idiopathic scoliosis patients with open triradiate cartilages. Spine (Phila Pa 1976) 2009;34:827-31. |
| 38. | Schlechter J, Newton P, Upasani V, Yaszay B, Lenke LG, Betz R, et al. P130. Risk factors for distal adding-on identified: What to watch out For. Spine J 2008;8:164S. |
| 39. | Qin X, Xia C, Xu L, Sheng F, Yan H, Qiu Y, et al. Natural history of postoperative adding-on in adolescent idiopathic scoliosis: What are the risk factors for progressive adding-on? Biomed Res Int 2018;2018:3247010. |
| 40. | King HA, Moe JH, Bradford DS, Winter RB. The selection of fusion levels in thoracic idiopathic scoliosis. J Bone Joint Surg Am 1983;65:1302-13. |
| 41. | Moe JH. THE CLASSIC: A critical analysis of methods of fusion for scoliosis: An evaluation in two hundred and sixty-six patients. Clin Orthop 2007;460:21-8. |
| 42. | Suk SI, Kim JH, Lee SM, Chung ER, Lee JH. Anterior-posterior surgery versus posterior closing wedge osteotomy in posttraumatic kyphosis with neurologic compromised osteoporotic fracture. Spine (Phila Pa 1976) 2003;28:2170-5. |
| 43. | Suk SI. Pedicle screw instrumentation for adolescent idiopathic scoliosis: The insertion technique, the fusion levels and direct vertebral rotation. Clin Orthop Surg 2011;3:89-100. |
| 44. | Lenke LG, Betz RR, Bridwell KH, Harms J, Clements DH, Lowe TG. Spontaneous lumbar curve coronal correction after selective anterior or posterior thoracic fusion in adolescent idiopathic scoliosis. Spine (Phila Pa 1976) 1999;24:1663-71; discussion 1672. |
| 45. | Erickson MA, Baulesh DM. Lowest instrumented vertebra selection in AIS. J Pediatr Orthop 2011;31:S69-76. |
| 46. | Cho RH, Yaszay B, Bartley CE, Bastrom TP, Newton PO. Which Lenke 1A curves are at the greatest risk for adding-on. And why? Spine (Phila Pa 1976) 2012;37:1384-90. |
| 47. | Matsumoto M, Watanabe K, Hosogane N, Kawakami N, Tsuji T, Uno K, et al. Postoperative distal adding-on and related factors in Lenke type 1A curve. Spine (Phila Pa 1976) 2013;38:737-44. |
| 48. | Cao K, Watanabe K, Hosogane N, Toyama Y, Yonezawa I, Machida M, et al. Association of postoperative shoulder balance with adding-on in Lenke type II adolescent idiopathic scoliosis. Spine (Phila Pa 1976) 2014;39:E705-12. |
| 49. | Murphy JS, Upasani VV, Yaszay B, Bastrom TP, Bartley CE, Samdani A, et al. Predictors of distal adding-on in thoracic major curves with AR lumbar modifiers. Spine (Phila Pa 1976) 2017;42:E211-8. |
| 50. | Qin X, Sun W, Xu L, Qiu Y, Zhu Z. Effectiveness of selective thoracic fusion in the surgical treatment of syringomyelia-associated scoliosis: A case-control study with long-term follow-up. Spine (Phila Pa 1976) 2016;41:E887-92. |
| 51. | Bai J, Chen K, Wei Q, Chen Z, Chen Y, Ni H, et al. Selecting the LSTV as the lower instrumented vertebra in the treatment of Lenke types 1A and 2A adolescent idiopathic scoliosis: A minimal 3-year follow-up. Spine (Phila Pa 1976) 2018;43:E390-8. |
| 52. | Lenke LG, Newton P, Lehman RA, Kelly M, Clements D, Errico T, et al. Adolescent scoliosis 1A001: Radiographic results of selecting the touched vertebra as the lowest instrumented vertebra in Lenke type 1 (main thoracic) & type 2 (double thoracic) curves at a minimum 5-year follow-up. Glob Spine J 2017;7:2S-189S. |
| 53. | Fujii T, Daimon K, Fujita N, Yagi M, Michikawa T, Hosogane N, et al. Risk factors for postoperative distal adding-on in Lenke type 1B and 1C and its influence on residual lumbar curve. J Pediatr Orthop 2019;40:e77-83. |
| 54. | Clément JL, Solla F, Tran A, Morin C, Lakhal W, Sales de Gauzy J, 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. |
| 55. | Lenke LG, Bridwell KH, Baldus C, Blanke K, Schoenecker PL. Cotrel-Dubousset instrumentation for adolescent idiopathic scoliosis. J Bone Joint Surg Am 1992;74:1056-67. |
| 56. | Nash CL Jr, Moe JH. A study of vertebral rotation. J Bone Joint Surg Am 1969;51:223-9. |
| 57. | Ilharreborde B, Ferrero E, Angelliaume A, Lefèvre Y, Accadbled F, Simon AL, et al. Selective versus hyperselective posterior fusions in Lenke 5 adolescent idiopathic scoliosis: Comparison of radiological and clinical outcomes. Eur Spine J 2017;26:1739-47. |
| 58. | Cho KJ, Lenke LG, Bridwell KH, Kamiya M, Sides B. Selection of the optimal distal fusion level in posterior instrumentation and fusion for thoracic hyperkyphosis: The sagittal stable vertebra concept. Spine (Phila Pa 1976) 2009;34:765-70. |
| 59. | Lundine K, Turner P, Johnson M. Thoracic hyperkyphosis: Assessment of the distal fusion level. Global Spine J 2012;2: 65-70. |
| 60. | Dikici F, Akgul T, Sariyilmaz K, Korkmaz M, Ozkunt O, Sar C, et al. Selection of distal fusion level in terms of distal junctional kyphosis in Scheuermann kyphosis. A comparison of 3 methods. Acta Orthop Traumatol Turc 2018;52:7-11. |
| 61. | Kim HJ, Nemani V, Boachie-Adjei O, Cunningham ME, Iorio JA, O’Neill K, et al. Distal fusion level selection in Scheuermann’s kyphosis: A comparison of lordotic disc segment versus the sagittal stable vertebrae. Global Spine J 2017;7:254-9. |
| 62. | Yanik HS, Ketenci IE, Coskun T, Ulusoy A, Erdem S. Selection of distal fusion level in posterior instrumentation and fusion of Scheuermann kyphosis: Is fusion to sagittal stable vertebra necessary? Eur Spine J 2016;25:583-9. |
| 63. | Lowe TG, Lenke L, Betz R, Newton P, Clements D, Haher T, et al. Distal junctional kyphosis of adolescent idiopathic thoracic curves following anterior or posterior instrumented fusion: Incidence, risk factors, and prevention. Spine (Phila Pa 1976) 2006;31: 299-302. |
| 64. | Fischer CR, Lenke LG, Bridwell KH, Boachie-Adjei O, Gupta M, Kim YJ. Optimal lowest instrumented vertebra for thoracic adolescent idiopathic scoliosis. Spine Deform 2018;6:250-6. |
| 65. | Kim Y-J, Lenke L, Bridwell K, Kim J, Cho S. P23. Thoracolumbar junctional analysis in patients fixed to T12 vs L1 in adolescent idiopathic scoliosis: Is there any difference? Spine J 2004;4:S106. |
| 66. | He C, Wong MS. Spinal flexibility assessment on the patients with adolescent idiopathic scoliosis: A literature review. Spine (Phila Pa 1976) 2018;43:E250-8. |
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2], [Table 3]
|
Search Pubmed for