Defining the "Three-Dimensional Sagittal Plane" in Thoracic Adolescent Idiopathic Scoliosis.
BACKGROUND
Obtaining accurate measurements of scoliosis from two-dimensional (2-D) radiographs can be challenging because of the three-dimensional (3-D) nature of the deformity. Previous studies have shown that the sagittal plane, in particular, is misrepresented on 2-D radiographs because of the influence of axial plane rotation. The purpose of the current study was to define a methodology for measuring the 3-D segmental sagittal alignment of the spine in patients with adolescent idiopathic scoliosis (AIS) and to assess the effect of axial plane rotation on differences between 3-D and 2-D measures of deformity.


METHODS
Preoperative and postoperative EOS images of 120 consecutive patients with AIS (primary thoracic curves) treated with segmental thoracic pedicle-screw instrumentation were analyzed in the "3-D sagittal plane." The technique measured 3-D kyphosis or lordosis in the specific plane of sagittal motion for each spinal motion segment. The kyphosis (+) and lordosis (-) values of the segments from T5 to T12 were summed to give the 3-D measurement of T5-T12 kyphosis. These values were compared with the standard 2-D measurements of T5-T12 kyphosis on lateral radiographs, and a correlation analysis with regard to axial plane rotation of the apex was performed.


RESULTS
The average age (and standard deviation) of the patients was 14 ± 2 years. The mean preoperative Cobb angle on the standard 2-D view was 55° ± 10° and on the 3-D view was 52° ± 9° (p ≤ 0.001). On the 3-D view, the mean preoperative T5-T12 kyphosis was 6° ± 14°, and the kyphosis significantly increased to 26° ± 6° postoperatively (p < 0.001). The T5-T12 kyphosis on the standard 2-D view measured 18° ± 13° preoperatively and 27° ± 6° postoperatively (p < 0.001). The difference between the 2-D and 3-D measurements of T5-T12 kyphosis strongly correlated with apical vertebral rotation (r = 0.85; p < 0.01).


CONCLUSIONS
Routine 2-D measurements of thoracic kyphosis erroneously underestimate the preoperative loss of kyphosis in AIS because of errors associated with axial plane rotation, an inherent component of thoracic scoliosis.
Department of Orthopedic Surgery, Rady Children's Hospital, 3030 Children's Way, Suite 410, San Diego, CA 92123. E-mail address for P.O. Newton: pnewton@rchsd.org.
Peter O
PO
Newton
Department of Orthopedic Surgery, Sumitomo Hospital, 5-3-20 Nakanoshima, Kita Ward, Osaka, Osaka Prefecture 530-0005, Japan.
Takahito
T
Fujimori
Department of Orthopedic Surgery, Rady Children's Hospital, 3030 Children's Way, Suite 410, San Diego, CA 92123. E-mail address for P.O. Newton: pnewton@rchsd.org.
Joshua
J
Doan
Department of Orthopedic Surgery, Rady Children's Hospital, 3030 Children's Way, Suite 410, San Diego, CA 92123. E-mail address for P.O. Newton: pnewton@rchsd.org.
Fredrick G
FG
Reighard
Department of Orthopedic Surgery, Rady Children's Hospital, 3030 Children's Way, Suite 410, San Diego, CA 92123. E-mail address for P.O. Newton: pnewton@rchsd.org.
Tracey P
TP
Bastrom
Department of Orthopaedic Surgery, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093.
Amirhossein
A
Misaghi
D000293:Adolescent; D002648:Child; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D010027:Osteotomy; D011859:Radiography; D012189:Retrospective Studies; D012600:Scoliosis / Q000000981:diagnostic imaging* / Q000601:surgery; D013123:Spinal Fusion; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging* / Q000601:surgery; D016896:Treatment Outcome