Continuous cervical spine kinematics during in vivo dynamic flexion-extension

Abstract

BACKGROUND CONTEXT A precise and comprehensive definition of “normal” in vivo cervical kinematics does not exist due to high inter-subject variability and the absence of mid-range kinematic data. In vitro test protocols and finite element models that are validated using only end range of motion data may not accurately reproduce continuous in vivo motion. PURPOSE The primary objective of this study was to precisely quantify cervical spine intervertebral kinematics during continuous, functional flexion-extension in asymptomatic subjects. The advantages of assessing continuous intervertebral kinematics were demonstrated by comparing asymptomatic controls with single-level anterior arthrodesis patients. STUDY DESIGN Cervical spine kinematics were determined during continuous in vivo flexion-extension in a clinically relevant age group of asymptomatic controls and a group of C5/C6 arthrodesis patients. PATIENT SAMPLE 6 single-level (C5/C6) anterior arthrodesis patients (average age: 48.8 ± 6.9 yrs; 1 M, 5 F; 7.6±1.2 mo. post-surgery) and 18 asymptomatic control subjects of similar age (average age: 45.6 ± 5.8 yrs; 5 M, 13 F). OUTCOME MEASURES The physiologic measure of continuous kinematic motion paths at each cervical motion segment (C2 to C7) during flexion-extension. METHODS Participants performed flexion-extension while biplane radiographs were collected at 30 images per second. A previously validated tracking process determined three-dimensional vertebral positions with sub-millimeter accuracy. Continuous flexion-extension rotation and anterior-posterior translation motion paths were adjusted for disc height and static orientation of each corresponding motion segment. This study was funded by NIH/NIAMS Grant #1R03AR056265 and The Cervical Spine Research Society 21st Century Development Grant. The authors have no potential financial conflict of interest biases related to this study. RESULTS Inter-subject variability in flexion-extension angle was decreased 15% to 46% and inter-subject variability in anterior-posterior translation was reduced 14% to 33% after adjusting for disc height and static orientation angle. Average inter-subject variability in continuous motion paths was 1.9° in flexion-extension and 0.6 mm in translation. Third-order polynomial equations were determined to precisely describe the continuous flexion-extension and anterior-posterior translation motion path at each motion segment (all R2 > .99). CONCLUSIONS A significant portion of the inter-subject variability in cervical kinematics can be explained by the disc height and the static orientation of each motion segment. Clinically relevant information may be gained by assessing intervertebral kinematics during continuous functional movement rather than at static, end range of motion positions. The fidelity of in vitro cervical spine mechanical testing protocols may be evaluated by comparing in vitro kinematics to the continuous motion paths presented.

Endotracheal intubation in elective cervical surgery

“…A shift beyond this limit would cause cervical spine instability and potentially lead to iatrogenic cervical SCI. [ 21 ] GS laryngoscopy was associated with a significantly greater change in the whole-length cervical spine curvature compared with the CTrach LMA and SOS laryngoscopy. Moreover, changes in the C0–1 and C1–2 Cobb angles for the GS group, as well as the C1–2 Cobb angle for the LMA and SOS groups, were above the physiological upper limit and potentially subject to secondary SCI.…”

Ranges of Cervical Intervertebral Disc Deformation During an In Vivo Dynamic Flexion–Extension of the Neck

“…Various in vitro and in vivo studies [31][32][33][34][35][42][43][44] have investigated the cervical spine kinematics under various external loading conditions, but few data have been reported on the physiological cervical disc deformation during dynamic neck motion. Most of the studies on disc biomechanics used finite element modeling methods and few reported the data of disc deformation [21,45].…”

“…Three-dimensional (3D) finite element modeling methods have been used to study cervical disc deformation under various simulated loading conditions [21][22][23][24][25][26]. Cervical interverterbral kinemeatics has also been investigated by using in vitro human cadaveric models [27][28][29][30] and in vivo human subjects [15,[31][32][33][34][35].…”

Differences between C3–4 and other subaxial levels of cervical disc arthroplasty: more heterotopic ossification at the 5-year follow-up

“…There are also built-in differences in the biomechanics between each level of the cervical spine, including the segmental contribution to the global ROM and instant center of rotation. [1][2][3]19,24,27,38 Miller et al reported that the correlation between neutral cervical posture and flexion or extension ROM was only strong at the C-4 and C-5 levels. 19 Wu et al demonstrated that neck flexion relied more on the middle cervical segments and less on the lower ones, and vice versa during extension.…”