Case SeriesOptimal Lowest Instrumented Vertebra for Thoracic Adolescent Idiopathic Scoliosis
Introduction
The surgical management of thoracic adolescent idiopathic scoliosis (AIS) has progressed through many different surgical concepts over the last century. The goals remain the same: (1) halt curve progression; (2) maintain coronal and sagittal balance including the shoulders; (3) preserve motion segments; (4) correct the deformity, including the ribs; and (5) avoid complications such as adding-on (AO), distal junctional kyphosis (DJK), proximal junctional kyphosis (PJK), and crankshaft phenomenon [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18]. Choosing “the most proximal and stable” lowest instrumented vertebra (LIV) without increasing the risk of adding-on (AO) or distal junctional kyphosis (DJK) for patients with AIS has been a challenging process, with many theories starting from end-to-end vertebrae without rotation by Hibbs, neutral vertebra by Goldstein, stable zone by Harrington, stable vertebra by Moe, selective fusion concept, side-bender flexibility, and push-prone radiography [2], [3], [4], [6], [8], [9], [10], [19]. To our knowledge, no study has analyzed the optimal LIV based on the stable vertebra, center sacral vertical line (CSVL), and neutral vertebra simultaneously. The purpose of this study was to determine “the most proximal and stable” LIV without AO or DJK at ultimate follow-up after posterior segmental spinal instrumented fusion (PSSIF) for Lenke 1 and 2 AIS cases according to the preoperative CSVL and vertebral rotation.
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Materials and Methods
After obtaining approval by the institutional review board at the respective institutions involved, all AIS patients who underwent PSSIF for thoracic AIS between 1990 and 2008 at four institutions were analyzed. Inclusion criteria were age at surgery ≤25 years, AIS with Lenke type 1 or 2 curve, PSSIF with LIV at L2 or above, and minimum 2 years' follow-up with a complete set of radiographs. Of the 604 patients with Lenke type 1 or 2 curve, 60 patients were lost to follow-up, did not have a
Demographic data
Five hundred forty-four patients were identified with minimum 2-year follow-up. The average age at surgery was 14.7 ± 2.2 years (range 10.1-22.9) (Table 1). The average follow-up was 4.1 ± 3.3 years (range 2-16.7). There were 425 female and 119 male patients. According to the AIS classification by Lenke et al. [21], the breakdown of curves was 399 Type 1 (main thoracic, 73%) and 145 Type 2 (double thoracic, 27%). Lumbar modifiers were as follows: A (n = 269), B (n = 146), and C (n = 129).
Discussion
A more proximal LIV preserves more motion segments below the fusion, but is associated with a higher prevalence of adding-on or distal junctional kyphosis. Prior to the instrumentation era, end to end vertebra with neutral rotation was recommended as the ideal upper and LIV for thoracic AIS to prevent an adding-on phenomenon [1], [2], [3], [4], [5], [7], [8], [15]. The stable vertebra by CSVL defined by King et al. [10] was the ideal LIV for thoracic AIS during the Harrington rod era. Since the
Conclusions
The prevalence of PX at ultimate follow-up after posterior segmental spinal fixation for AIS with the LIV at L2 or above is 13.6%. CSVL that does not touch the selected LIV, LIV 3 or more vertebrae proximal to the NV, open TRC, lumbar C modifier, and Risser 0 were all identified as risk factors for poor radiographic outcome. To prevent adding-on or distal junctional kyphosis, selection of the LIV that is touched by the CSVL and within 2 vertebra proximal to the NV in patients after TRC closure
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Author disclosures: none.