Review ArticleFive major controversial issues about fusion level selection in corrective surgery for adolescent idiopathic scoliosis: a narrative review
Introduction
Two major advances in the management of idiopathic scoliosis over the past 30 years include the development of modern instrumentation techniques and the enhanced understanding of the nature of curvature. After several trials and errors, strong and secure instrumentation systems have been developed, which have led to marked improvements in postoperative patient care and in the amount of correction. However, adverse effects of modern instrumentation, such as coronal decompensation [1], [2] or adding-on phenomenon [3], have also been observed. These unexpected complications primarily result from the incorrect determination of the fusion level.
To standardize the fusion level, several curve classification systems have been proposed by previous reports. The two most widely used classifications are those by King et al. and Lenke et al. [4], [5]. Although the King classification is easy to use, it considers only the thoracic curve and coronal plane deformity. In contrast, the Lenke classification includes the lumbar curve and sagittal plane profile, and exhibits good interobserver and intraobserver reliability; however, the limitations include its complexity and the lack of consideration of rotational deformity [6].
With the advent of modern instrumentation systems involving segmental pedicle screw insertion, the fusion level to be selected now differs from that used in the traditional Harrington era. Nevertheless, the principles of fusion established by Moe remain valid [7]. A maximal amount of curve correction should be achieved to obtain a stable and balanced spine. Similarly, efforts should be made to save mobile segments, particularly in the lumbar spine. The prevention of postoperative shoulder imbalance is another controversial issue. In fact, there are many debatable issues related to fusion level selection. Among these, we selected five major issues and have reviewed the problems with appropriate examples and literature.
Section snippets
Selective thoracic fusion
Selective thoracic fusion (STF) remains the most debatable issue during the selection of fusion level. The STF concept was introduced for the correction of main thoracic (MT) curves and minor lumbar curves, including King type 2 or Lenke type 1B, 1C, or 3B (Fig. 1) [8], [9].
In thoracic and lumbar double curves, the level of correction and fusion could involve either both the curves or only the thoracic curve. If both curves are included for fusion, a larger amount of correction is achieved,
Selective thoracolumbar or lumbar fusion
Correction and fusion can be limited to the thoracolumbar or lumbar (TL-L) curves in Lenke 5C or 6C curves. In fact, a satisfactory result was predicted in cases with a TL-L-to-T Cobb ratio of ≥1.25, in cases where the thoracic curve was bent to ≤20°, or in cases with closure of triradiate cartilages [25]. This suggests that selective thoracolumbar or lumbar fusion should be applied only when the thoracic curve is flexible and the patient is close to the end of maturity. Otherwise, the thoracic
How to prevent adding-on phenomenon?
Although correction appears to be easy in single thoracic curves (King type 3 or Lenke type 1A) and double thoracic curves (King type 4 or Lenke type 2A), there is a major complication: the “adding-on phenomenon” [3]. This is characterized by a progressive loss of correction by either vertebral deviation of the lumbar spine or disc angulation below the LIV. The manner in which adding-on phenomenon develops has been illustrated in Fig. 3. If unsatisfactory outcomes are derived as a result of the
Distal fusion level selection in major lumbar-thoracolumbar curves, L3 or L4?
In large lumbar curves and thoracic curves such as King type 1 or Lenke type 3C, 4C, 5C, or 6C, the selection of the distal fusion level is a debatable issue. The pain intensity is reportedly increased in patients with fusion to L4 as compared with those with fusion to L2 or L3 [43]. However, no clinical difference was observed according to the distal fusion level (L3 vs. L4) in another study [44]. As intradiscal pressure increases in the disc subjacent to the LIV [45], the preservation of one
Proximal fusion level selection and shoulder imbalance
If the proximal thoracic curve (PT curve) is structural (King type 5 or Lenke type 2 or 4), two major issues need to be carefully considered. The first issue is whether the PT curve should be included in correction and fusion, and the second issue is the level up to which fusion should be performed proximally. Inappropriate proximal fusion level selection could result in poor outcomes such as shoulder imbalance or coronal imbalance.
In 1993, it was proposed that both the PT and the MT curves
Limitations
Our study has a few limitations. As this study is not a systematic review, the evidence of brief suggestions or opinions about each debatable issue is inherently insufficient. However, this study will provide the current concept about fusion level selection in AIS. In addition, specific guidelines could not be suggested because of the paucity of highly qualified, relevant studies.
Conclusion
Although many difficult problems in the diagnosis and treatment of AIS have been resolved by understanding its mechanism and via technical advancement, definite guidelines for fusion level selection have still not been established. Selective thoracic fusion and selective TL-L fusion can help reduce the number of fusion segments. Nevertheless, the careful selection of patients and the fusion level is critical to avoid complications such as coronal decompensation or progression of residual
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Prediction of long-term postoperative results of disc wedge and vertebral tilt with intraoperative prone radiograph in posterior correction of thoracolumbar/lumbar curve in adolescent idiopathic scoliosis: a minimum 5-year follow-up
2022, Spine JournalCitation Excerpt :An increased DWA angle is also reported as a risk factor for early disc degeneration or the adding-on phenomenon [1,3,9,13]. Therefore, choosing the LIV and appropriate surgical technique to minimize DWA below LIV or LIV+1 tilt should also be considered to achieve optimal deformity correction [2–4,9]. DWA below the LIV and LIV+1 tilt could be assessed intraoperatively using prone radiographs [11].
Spontaneous Improvement of Postoperative Coronal Imbalance Following Selective Thoracolumbar-Lumbar Fusion in Lenke 5C Adolescent Idiopathic Scoliosis
2021, World NeurosurgeryCitation Excerpt :The goal of SLF for patients with Lenke 5C is correction of the main TL/L curve and subsequent correction of the compensatory thoracic curve. An advantage of SLF is that it preserves mobile segments, but coronal imbalance (CIB) and decompensation are predictable complications.5-10 Trunk imbalance is reportedly associated with the magnitude of the curve in AIS, but not with back pain and function.11
FDA device/drug status: Not applicable.
Author disclosures: CSL: Nothing to disclose. CJH: Nothing to disclose. D-HL: Nothing to disclose. JHC: Nothing to disclose.
This study did not receive any funding.