Introduction: During thoracic curve correction, the tightening of the sublaminar wires through concavity creates a medial and a dorsal translation of the spine. However, little is known about the effect of the sublaminar wires on the axial plane.
Methods: This is prospective case series analysis of 30 consecutive surgical patients with main thoracic adolescent idiopathic scoliosis. All of the patients were fused with hybrid instrumentation (apical concavity-sublaminar wires) and differential rod contouring (over-kyphosis concavity/under-kyphosis convexity). The degrees of the rib hump were measured with a scoliometer placed at the apex of the deformity at five different times: (1) preoperatively through the Adam's test, and during surgery (sterilised scoliometer), (2) with the patient lying prone, (3) after the Ponte osteotomies, (4) after the apical sublaminar tightening, and (5) after convexity apical derotation and compression manoeuvres.
Results: (1) Preoperatively, the Adam's test was 16.3° ± 4.6. (2) Lying prone and under general anaesthesia, it decreased to 11.4° ± 3.9. (3) After exposure and Ponte osteotomies, it was 7.1° ± 4. (4) After the wire tightening, it was 10.8° ± 4.7. (5) After the convexity manoeuvres, it was 4.8° ± 3.7. The degrees of the rib hump final correction were 11.6° ± 4 (70 % correction). The tightening of the sublaminar wires increased the rib hump by 3.5°.
Conclusions: The sublaminar wire tightening towards the concave rod seemed to create an effect opposite of the desired effect, increasing the apical rotation and the thoracic rib hump deformity. Convexity manoeuvres (apical screw derotation and compression) are necessary and must be coupled with an under-bending of the convex rod to neutralise this effect.
Keywords: Adolescent idiopathic scoliosis; Correction manoeuvres; Rib hump correction; Rib hump deformity; Scoliometer; Scoliosis correction; Scoliosis translation; Sublaminar wires scoliosis derotation; Thoracic curves; Transverse plane and wires.