Fixed lumbar apical vertebral rotation predicts spinal decompensation in lenke type 3c adolescent idiopathic scoliosis after selective posterior thoracic correction and fusion

Retrospective radiographic review of surgically treated double major curves (Lenke type 3C) in adolescent idiopathic scoliosis. To evaluate the role of selective posterior thoracic correction and fusion in double major curves with third generation instrumentation and to identify preoperative radiographic parameters that predict postoperative coronal spinal decompensation. Traditionally the surgical treatment of double major curves consists of fusion of both the thoracic and the lumbar curve. Few attempt to perform selective thoracic fusion in this curve pattern because of the potential to create spinal imbalance. Thirty-six patients with Lenke type 3C curves underwent a selective posterior thoracic correction and fusion with either Cotrel–Dubousset instrumentation or the Universal Spine System. Radiographs were evaluated to assess coronal and sagittal balance, curve flexibility, and curve correction at a minimum follow up of 2 years. Postoperative coronal spinal decompensation was investigated with respect to preoperative radiographic parameters on standing anteroposterior (AP), standing lateral radiographs, thoracic and lumbar supine side-bending radiographs. Coronal spinal decompensation was defined as plumbline deviation of C7 of more than 2 cm with respect to the centre sacral vertical line (CSVL) within 2 years of surgery. Twenty-six patients (72%) showed satisfactory frontal plane alignment patients (28%) showed coronal spinal decompensation. Significant group differences, however, were identified for lumbar apical vertebral rotation, measured according to Perdriolle (La scoliose. Son êtude tridimensionnelle. Maloine, Paris, pp 179, 1979) (A 16°, B 22°, P = 0.02), percentage correction (derotation) of lumbar apical vertebrae in lumbar supine side-bending films in comparison to standing AP radiographs (A 49%, B 27%, P = 0.002) and thoracic curve flexibility (A 43%, B 25%, P = 0.03). High correlation was noted between postoperative decompensation and derotation of lumbar apical vertebrae in pre-operative lumbar supine side-bending films with a critical value of 40% (Pearson correlation coefficient; P = 0.62, P < 0.001). Ten of 36 patients (28%) with Lenke type 3C adolescent idiopathic scoliosis showed coronal spinal decompensation of more than 2 cm after selective posterior thoracic correction and fusion. Lumbar apical vertebral derotation of less than 40% provided the radiographic prediction of postoperative coronal spinal imbalance. We advise close scrutiny of the transverse plane in the lumbar supine bending film when planning surgical strategy

Variability of spinal instrumentation configurations in adolescent idiopathic scoliosis

Surgical instrumentation for the correction of adolescent idiopathic scoliosis (AIS) is a complex procedure involving many difficult decisions (i.e. spinal segment to instrument, type/location/number of hooks or screws, rod diameter/length/shape, implant attachment order, amount of rod rotation, etc.). Recent advances in instrumentation technology have brought a large increase in the number of options. Despite numerous clinical publications, there is still no consensus on the optimal surgical plan for each curve type. The objective of this study was to document and analyse instrumentation configuration and strategy variability. Five females (12–19 years) with AIS and an indication for posterior surgical instrumentation and fusion were selected. Curve patterns were as follows: two right thoracic (Cobb: 34°, 52°), two right thoracic and left lumbar (Cobb T/L: 57°/45°, 72°/70°) and 1 left thoraco-lumbar (Cobb: 64°). The pre-operative standing postero-anterior and lateral radiographs, supine side bending radiographs, a three-dimensional (3D) reconstruction of the spine, pertinent 3D measurements as well as clinical information such as age and gender of each patient were submitted to six experienced independent spinal deformity surgeons, who were asked to provide their preferred surgical planning using a posterior spinal approach. The following data were recorded using the graphical user interface of a spine surgery simulator (6×5 cases): implant types, vertebral level, position and 3D orientation of implants, anterior release levels, rod diameter and shape, attachment sequence, rod rotation (angle, direction), adjustments (screw rotation, contraction/distraction), etc. Overall, the number of implants used ranged from 11 to 26 per patient (average 16; SD ±4). Of these, 45% were mono-axial screws, 31% multi-axial screws and 24% hooks. At one extremity of the spectrum, one surgeon used only mono-axial screws, while at the other, another surgeon used 81% hooks. The selected superior- and inferior-instrumented vertebrae varied up to six and five levels, respectively (STD 1.2 and 1.5). A top-to-bottom attachment sequence was selected in 61% of the cases, a bottom-up in 29% and an alternate order in 11%. The rod rotation maneuver of the first rod varied from 0° (no rotation) to 140°, with a median at 90°. In conclusion, a large variability of instrumentation strategy in AIS was documented within a small experienced group of spinal deformity surgeons. The exact cause of this large variability is unclear but warrants further investigation with multicenter outcome studies as well as experimental and computer simulation studies. We hypothesize that this variability may be attributed to different objectives for correction, to surgeon’s personal preferences based on their previous experience, to the known inter-observer variability of current classification systems and to the current lack of clearly defined strategies or rational rules based on the validated biomechanical studies with modern multi-segmental instrumentation systems