Assessment of spinal flexibility in adolescent idiopathic scoliosis: suspension versus side-bending radiography.
METHODS
Prospective evaluation of a new suspension test to determine curve flexibility in adolescent idiopathic scoliosis (AIS) in comparison with erect side-bending.


OBJECTIVE
To verify whether the suspension is a better method than side-bending to estimate curve reducibility and to assess spine flexibility.


BACKGROUND
Spinal flexibility is a decisive biomechanical parameter for the planning of AIS surgery. Side-bending is often referred as the gold standard, but it has a low reproducibility and there is no agreement amongst surgeons about the most advantageous method to use. Even more, every technique evaluates reducibility instead of flexibility since the forces involved in the change in shape of the spine are not considered.


METHODS
Eighteen patients scheduled for AIS surgery were studied. Preoperative radiological evaluation consisted of 4 radiographs: standing posteroanterior, left and right erect side-bending, and suspension. The side-bending and the suspension tests were compared on the basis of the apical vertebrae derotation and the scoliosis curve reduction. Frontal and axial flexibility indices, expressed as the ratio between the moment induced by the body weight and the reduction, were calculated from the suspension data.


RESULTS
The average scoliosis curve reduction and apical vertebra derotation were 21 degrees (37%) and 3 degrees (12%), respectively for erect side-bending and 26 degrees (39%) and 7 degrees (28%), respectively for suspension. The erect side-bending test generated a larger curve reduction (P = 0.05) when considering the moderate curves only and the suspension test (P = 0.02) when considering the severe curves. The suspension test produced a larger axial derotation (P = 0.007) when considering all the curves. The average traction force during suspension was 306 N (187 N-377 N). The average estimation for the frontal flexibility index was 1.64 degrees/Nm (0.84-2.82) and 0.51 degrees/Nm (0.01-1.39) for the axial flexibility index.


CONCLUSIONS
Results of this study demonstrate the feasibility to really evaluate the spine flexibility with the suspension test. The estimated flexibility values are realistic and similar to those reported in vitro. Suspension should be used in the future for spine flexibility assessment.
Lamarre
Marie-Eve
ME
Sainte-Justine University Hospital Center, Montreal, Quebec, Canada.
Parent
Stefan
S
Labelle
Hubert
H
Aubin
Carl-Eric
CE
Joncas
Julie
J
Cabral
Anne
A
Petit
Yvan
Y
D000293:Adolescent; D001175:Arthrography / Q000379:methods* / Q000592:standards*; D001696:Biomechanical Phenomena; D002648:Child; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D008297:Male; D008954:Models, Biological; D009479:Neuropeptides; D011300:Preoperative Care / Q000379:methods / Q000592:standards; D016059:Range of Motion, Articular / Q000502:physiology; D015203:Reproducibility of Results; D012600:Scoliosis / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery; D014143:Traction / Q000379:methods
D009479:Neuropeptides; C057855:postural asymmetry factor