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DOS Kongressen 2017 ·
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A rod construct with differentiated rigidity im-
proves the restoration of thoracic kyphosis in sur-
gical treatment of adolescent idiopathic scoliosis
Søren Ohrt-Nissen, Casper Dragsted, Benny Dahl, John Ferguson, Martin Geh-
rchen
Orthopaedic Surgery, Rigshospitalet; Orthopaedic Surgery, Rigshospitalet; De-
partment of Orthopedics and Scoliosis Surgery, Texas Children¡¯s Hospital; ,
Starship Children’s Hospital; Orthopaedic Surgery, Rigshospitalet
Background:
All-pedicle screw instrumentation has been shown to induce hy-
pokyphosis in adolescent idiopathic scoliosis (AIS).
Purpose / Aim of Study:
Compare postoperative sagittal alignment between
three rod constructs with different rigidity profiles.
Materials and Methods:
A dual-center retrospective cohort study was con-
ducted involving two consecutive cohorts operated with all- pedicle screw
instrumentation for AIS. Three different rod constructs were used: A hybrid
construct (HC) consisting of a normal circular rod on the convex side and a
beam-like rod (BR) on the concave side, a standard construct (SC) using bilat-
eral BRs in the full length of the fusion and a modified construct (MC) where the
rod transitions from a beam-like shape to a circular shape at the cranial fusion
levels. Radiographs were analyzed preoperatively and at the first postoperative
follow-up.
Findings / Results:
The HC, SC and MC groups included 23, 70 and 46 pa-
tients, respectively. The groups did not differ significantly in preoperative radio-
graphic parameters, mean preoperative main curve or mean curve correction.
The mean postoperative TK was 23.1±6.3º, 19.6±7.6º and 23.4±6.9º in the
HC, SC and MC groups, respectively (p=0.013) and the mean change in TK
was -3.5±11.3º, -7.1±11.6º and 0.1±10.9º, respectively (p=0.005). The MC
group had significantly higher postoperative TK and less loss of TK compared to
the SC group (p≤0.018). A postoperative TK ≤ 10º was found in 12 patients
(17%) in the SC group, one patient (5%) in the HC group and one patient (2%)
in the MC group (p=0.021).
Conclusions:
We found significantly better restoration of kyphosis with the use
of bilateral modified rods compared to bilateral standard rods. In the modified-
and hybrid construct group the rate of severe postoperative hypokyphosis was
significantly lower than in the standard group.
Conflict of interest:
Benny Dahl: institutional grants from K2M and Medtronic
Martin Gehrchen: institutional grants from K2M and Medtronic
143.