• Kenny Yat Hong Kwan, Cheuk Pang Wong, Hui Yu Koh, and Cheung Kenneth Man Chee KMC Department of Orthopaedics and Traumatology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong..
• Department of Orthopaedics and Traumatology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong.
• Spine. 2019 Dec 15; 44 (24): E1419-E1427.

Study DesignRetrospective study with prospective radiographic data collection.ObjectiveTo compare fusion level determination criteria using the fulcrum bending radiograph (FBR) and the last substantially touched vertebra (STV) as the lowest instrumented vertebra (LIV) in the radiographic outcomes of correction surgery for Lenke 1A and 2A scoliosis patients with a minimum of 2-year follow-up.Summary Of Background DataThe STV has been proposed as the LIV in Lenke 1A and 2A curves to avoid postoperative distal adding-on. However, the influence of the inherent flexibility of the curves on selecting the LIV in relation to the STV is not known.MethodsA total of 65 consecutive Lenke 1A and 2A patients who underwent posterior selective thoracic fusion were included in this study with a minimum of 2-year follow-up. LIV determination was compared with the FBR and STV methods. The curve correction, trunk shift, radiographic shoulder height, list, and the incidence of distal adding-on were documented.ResultsMean preoperative, postoperative, and final follow-up standing coronal Cobb angles of primary curves were 59.37°, 15.58°, and 16.62° respectively. Using the FBR to determine the LIV, STV was selected in 16 patients (25%), STV-1 in 34 (52%), STV-2 in 11 (17%), and STV-3 in three (5%). Fusion level difference between using FBR and STV method was statistically significantly larger (P = 0.019) in patients with more than 70% fulcrum flexibility (mean: 1.18 levels, range: 0-3 levels) than those with less than or equal to 70% flexibility (mean: 0.70 level, range: -1 to 3 levels). Mean fulcrum flexibility was 73.9% in patients who achieved a shorter fusion by FBR method and 66.3% in patients who did not achieve a shorter fusion. Adding-on was observed in three patients (4.6%).ConclusionBy considering the curve flexibility, LIV determination using FBR method achieved a shorter fusion than STV method in over 70% of Lenke 1A and 2A patients, while being safe and effective at 2-year follow-up.Level Of Evidence3.

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