Effect of cervical kyphotic deformity type on the motion characteristics and dynamic spinal cord compression.
METHODS
Retrospective analysis of kinematic magnetic resonance images.


OBJECTIVE
To provide baseline data on the segmental angular and translational motion of the degenerated cervical spine by subtype of kyphotic cervical deformity and to elucidate the relationship between motion and degree of spinal cord compression.


BACKGROUND
Kyphotic deformities of the cervical spine are relatively common and are classified as either global or focal. Nevertheless, the effects of kyphotic subtype on cervical segmental motion and degree of spinal cord compression are unknown.


METHODS
A total of 1171 symptomatic patients (618 females, 553 males) underwent cervical kinematic magnetic resonance imaging in the neutral, flexion, and extension positions. Cervical spines demonstrating kyphosis were included and classified into 3 groups: (1) "global kyphotic deformity" (C-type) (n = 54); (2) "sigmoid deformity" (S-type) with kyphotic upper and lordotic lower cervical segments (n = 29); and (3) "reverse sigmoid deformity" (R-type) with lordotic upper and kyphotic lower cervical segments (n = 39). Translational motion, angular motion, and degree of spinal cord compression were evaluated for each cervical level along with the changes associated with flexion and extension.


RESULTS
In the C- and R-types, angular motion with extension was increased in the upper cervical spine, where there was kyphosis; when compared with the S-type, in which there was lordosis in the upper segments. The results were opposite for flexion angular motion. R-type displayed more translational motion at C3-C4 and C5-C6. Degree of static spinal cord compression of R-type was higher than the others at C3-C4. The dynamic spinal cord compression increased in extension more than flexion in all subtypes.


CONCLUSIONS
Cervical spine studies that aim to investigate kyphotic deformities should make efforts to discern the different subtypes of kyphotic deformities to more accurately characterize and study the effects that the sagittal alignment has on the kinematics of the spine and the degree of spinal cord compression.
*Department of Orthopaedic Surgery, University of California Los Angeles, Santa Monica, CA; and †Department of Orthopaedic Surgery, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand. Dr. Wang is now with the Department of Orthopaedic and Neurological Surgery, University of Southern California, Los Angeles, CA.
Monchai
M
Ruangchainikom
Michael D
MD
Daubs
Akinobu
A
Suzuki
Tetsuo
T
Hayashi
Gil
G
Weintraub
Christopher J
CJ
Lee
Hirokazu
H
Inoue
Haijun
H
Tian
Bayan
B
Aghdasi
Trevor P
TP
Scott
Kevin H
KH
Phan
Areesak
A
Chotivichit
Jeffrey C
JC
Wang
D000328:Adult; D001696:Biomechanical Phenomena; D002574:Cervical Vertebrae / Q000503:physiopathology*; D005260:Female; D006801:Humans; D055959:Intervertebral Disc Degeneration / Q000209:etiology; D007738:Kyphosis / Q000145:classification / Q000150:complications* / Q000503:physiopathology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009038:Motion; D011312:Pressure; D012189:Retrospective Studies; D012720:Severity of Illness Index; D013117:Spinal Cord Compression / Q000209:etiology* / Q000503:physiopathology; D055815:Young Adult