Effects of Cervical Extension on Deformation of Intervertebral Disk and Migration of Nucleus Pulposus.
BACKGROUND
We theorized that active cervical extension should influence the position of the nucleus pulposus (NP) within the intervertebral disk (IVD) in the sagittal plane. Although several studies on the lumbar IVD have been conducted, there are no quantitative data for in vivo positional changes of the NP in the cervical IVD.


OBJECTIVE
To evaluate the influence and mechanism of cervical extension on the deformation and migration of IVD and NP in the sagittal plane and understand underlying mechanisms of the extension maneuver.


METHODS
Asymptomatic subjects underwent magnetic resonance imaging while supine with their cervical spines in neutral and extended positions.


METHODS
Academic medical center.


METHODS
Ten young, healthy male participants (age range 19-30 years; mean 22.4 ± 1.64 years).


METHODS
T2-weighted sagittal images from C3-C4 to C6-C7 of subjects in both neutral and extension positions were analyzed.


METHODS
Deformation of IVD and positional change of NP were quantified and compared between neutral and extension positions. Intersegmental angles between vertebrae, horizontal positions of anterior and posterior IVD and NP margins, IVD outer and inner heights, and sagittal morphology of NP were quantified and compared between the neutral and extension positions. Correlations between the measured parameters and segmental extension angle were also investigated.


RESULTS
Anterior and posterior IVD margins moved posteriorly with respect to the vertebral body in extension. Both NP margins remained unchanged relative to the vertebral body but moved anteriorly with respect to the IVD. IVD outer and inner heights in the anterior region increased in extension, and morphological changes of the NP were less noticeable when compared with its relative migration within the IVD. Most of the intradiskal changes were linearly correlated with the segmental extension angle.


CONCLUSIONS
Cervical extension induces anterior migration of the NP away from the posterior disk margin and may have a clinical effect on diskogenic neck pain resulting from internal disk disruption.


METHODS
Not applicable.
Harvard-MIT Health Sciences and Technology, and Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA(∗).
Yoon-Ho
YH
Kim
College of Medicine, Seoul National University, Seoul, South Korea(†).
Sung-In
SI
Kim
Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA(‡).
Seongjun
S
Park
Department of Radiology and Institute of Radiation Medicine, Seoul National University College of Medicine, Seoul, South Korea(§).
Sung Hwan
SH
Hong
Department of Rehabilitation Medicine, Seoul National University College of Medicine & Hospital, 101 Daehak-ro, Jongno-gu, Seoul 110-744, South Korea; Rheumatism Research Institute, Medical Research Center, Seoul National University, Seoul, South Korea; and Institute of Aging, Seoul National University, Seoul, South Korea(¶). Electronic address: suncg@snu.ac.kr.
Sun G
SG
Chung
D000046:Academic Medical Centers; D000328:Adult; D002574:Cervical Vertebrae / Q000033:anatomy & histology / Q000502:physiology*; D064368:Healthy Volunteers; D006801:Humans; D007403:Intervertebral Disc / Q000000981:diagnostic imaging* / Q000502:physiology; D055959:Intervertebral Disc Degeneration / Q000503:physiopathology*; D007405:Intervertebral Disc Displacement / Q000503:physiopathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D000070614:Nucleus Pulposus / Q000033:anatomy & histology / Q000502:physiology; D056910:Republic of Korea; D012494:Sampling Studies; D016683:Supine Position; D014143:Traction / Q000379:methods; D055815:Young Adult