Comparison of different strategies on three-dimensional correction of AIS: which plane will suffer?

Abstract

Purpose There are distinct differences in strategy amongst experienced surgeons from different ‘scoliosis schools’ around the world. This study aims to test the hypothesis that, due to the 3-D nature of AIS, different strategies can lead to different coronal, axial and sagittal curve correction. Methods Consecutive patients who underwent posterior scoliosis surgery for primary thoracic AIS were compared between three major scoliosis centres (n = 193). Patients were treated according to the local surgical expertise: Two centres perform primarily an axial apical derotation manoeuvre (centre 1: high implant density, convex rod first, centre 2: low implant density, concave rod first), whereas centre 3 performs posteromedial apical translation without active derotation. Pre- and postoperative shape of the main thoracic curve was analyzed using coronal curve angle, apical rotation and sagittal alignment parameters (pelvic incidence and tilt, T1–T12, T4-T12 and T10-L2 regional kyphosis angles, C7 slope and the level of the inflection point). In addition, the proximal junctional angle at follow-up was compared. Results Pre-operative coronal curve magnitudes were similar between the 3 cohorts and improved 75%, 70% and 59%, from pre- to postoperative, respectively (P < 0.001). The strategy of centres 1 and 2 leads to significantly more apical derotation. Despite similar postoperative T4-T12 kyphosis, the strategy in centre 1 led to more thoracolumbar lordosis and in centre 2 to a higher inflection point as compared to centre 3. Proximal junctional angle was higher in centres 1 and 2 (P < 0.001) at final follow-up. Conclusion Curve correction by derotation may lead to thoracolumbar lordosis and therefore higher risk for proximal junctional kyphosis. Focus on sagittal plane by posteromedial translation, however, results in more residual coronal and axial deformity.

The use of statistical modelling to identify important parameters for the shape of the torso following surgery for adolescent idiopathic scoliosis

“…The ability to discuss the post‐operative torso shape following scoliosis surgery allows a more personalised expression of the end result. This is likely to be of more relevance than the current reported amount of ‘approximately 65% correction’ (Winter et al, 2007), particularly given the understanding that a greater correction in one plane leads to an under correction in another (Schlösser et al, 2021). This is especially true with the recent identification of different subtypes of the Lenke 1 curve when assessed using the parameters of scoliosis, kyphosis and skin angulation (Gardner, Berryman, & Pynsent, 2021; Gardner, Berryman, Sur, et al, 2021) where the clusters comprise varying amounts of the three parameters.…”

Assessment of the axial plane deformity in subjects with adolescent idiopathic scoliosis and its relationship to the frontal and sagittal planes

“…This finding may suggest that any surgery correcting both frontal and sagittal planes might not automatically fully correct the axial plane deformity. This was suggested by recent studies showing that surgical correction in two planes cannot fully correct the third plane [27,28].…”

Statistical modelling of how the sagittal alignment of the cervical spine is affected by adolescent idiopathic scoliosis and how scoliosis surgery changes that

“…Upright stance relies on a harmonic relationship between all components of the sagittal profile. With an alteration in sagittal profile, secondary to the reduction in thoracic kyphosis caused by AIS (Newton et al, 2019) and then changed by any subsequent surgery (Schlösser et al, 2021), the post-operative uninstrumented and still mobile spine will be recruited to maintain upright stance with an appropriate head position and horizontal gaze. Whilst statistical in nature, these models will allow a greater understanding of how the spine has the ability to compensate, even whilst performing a scoliosis correction, through the aspects of the spine that are directly modifiable by the surgeon.…”