Is Cobb angle progression a good indicator in adolescent idiopathic scoliosis?
METHODS
A retrospective follow-up study of spine geometry after posterior instrumentation and fusion for adolescent idiopathic scoliosis (AIS).


OBJECTIVE
To evaluate 1) if Cobb angle progression is a reliable indicator of the crankshaft phenomenon; 2) if significant growth of the spine can occur after surgery without the development of a crankshaft phenomenon?


BACKGROUND
Anterior fusion of the spine is often recommended for skeletally immature scoliotic patients to avoid the risk of a crankshaft phenomenon, a long-term loss of curve correction caused by residual growth of the spine combined with the constraints of a posterior fusion. The crankshaft phenomenon is usually assessed indirectly by documenting progression of the Cobb angle on frontal radiographs. Thus far, no study has directly measured the three-dimensional growth of the spine after surgery in AIS.


METHODS
Cobb angle, spine length and spine height were obtained from three-dimensional radiographic reconstructions of the spine in 48 adolescent scoliotic patients undergoing posterior instrumentation and fusion. Measurements were done before surgery, after surgery and at skeletal maturity. A significant growth of the spine was defined as a > or = 10 mm increase in spine length, while a significant curve progression was defined as a > or = 10 degrees increase in Cobb angle at skeletal maturity.


RESULTS
In the majority of patients (56%), there was no significant change in spinal length or in Cobb angle measurements at an average 2.4 years post surgery. A crankshaft phenomenon was detected in 6 patients (12%) for which significant increases both in spinal length and Cobb angle measurement were found. Significant curve progression without any change in spine length was noted in 9 patients (19%) while an increase in spine length with no evidence of curve progression was present in 6 patients at last follow-up.


CONCLUSIONS
Spinal growth as indicated by an increase in spinal length can be measured in a significant proportion of adolescents with idiopathic scoliosis after posterior instrumentation and fusion. Some of these study participants will develop a crankshaft phenomenon but Cobb angle progression is not a reliable indicator of this complication, since it may occur without any detectable growth of the spine.
Delorme
Sébastien
S
Research Centre, Sainte-Justine Hospital, Montréal, Québec, Canada.
Labelle
Hubert
H
Aubin
Carl-Eric
CE
D000293:Adolescent; D002648:Child; D015331:Cohort Studies; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007738:Kyphosis / Q000175:diagnosis / Q000601:surgery; D008141:Lordosis / Q000175:diagnosis / Q000601:surgery; D008297:Male; D011183:Postoperative Complications / Q000175:diagnosis* / Q000209:etiology; D011237:Predictive Value of Tests; D011859:Radiography; D012189:Retrospective Studies; D012307:Risk Factors; D012600:Scoliosis / Q000175:diagnosis* / Q000601:surgery; D013123:Spinal Fusion / Q000009:adverse effects; D013131:Spine / Q000000981:diagnostic imaging* / Q000254:growth & development* / Q000601:surgery; D016896:Treatment Outcome