Koshiro Ono

Motion analysis of cervical vertebrae during whiplash loading

STUDY DESIGN The motion of each cervical vertebra during simulated rear-end car collisions was analyzed. OBJECTIVES To clarify the mechanism of zygapophysial joint injury during whiplash loading. SUMMARY OF BACKGROUND DATA The zygapophysial joint is the suspected origin of neck pain after rear-end car collision. However, no studies have been conducted on the mechanisms of zygapophysial joint injuries. METHODS Ten healthy male volunteers participated in this study. Subjects sat on a sled that glided backward on inclined rails and crashed into a damper at 4 km/kr. The motion of the cervical spine was recorded using cineradiography. Each vertebras rotational angle and the instantaneous axes of rotation of the C5-C6 motion segments were quantified. These measurements implemented the template method. RESULTS There were three distinct patterns of cervical spine motion after impact. In the flexion-extension group, C6 rotated backward before the upper vertebrae in the early phase; thus, the cervical spine showed a flexion position (initial flexion). After C6 reached its maximum rotational angle, C5 was induced to extend. As upper motion segments went into flexion, and the lower segments into extension, the cervical spine took an S-shaped position. In this position, the C5-C6 motion segments showed an open-book motion with an upward-shifted instantaneous axis of rotation. CONCLUSIONS The cervical spine is forced to move from the lower vertebrae during rear-end collisions. This motion completely differs from normal extension motion and is probably related to the injury mechanism.

CERVICAL INJURY MECHANISM BASED ON THE ANALYSIS OF HUMAN CERVICAL VERTEBRAL MOTION AND HEAD-NECK-TORSO KINEMATICS DURING LOW SPEED REAR IMPACTS

Twelve male volunteers participated in this study. They sat on a seat mounted on a newly developed sled that simulated actual car impact acceleration. Impact speeds (4, 6 and 8 km/h), seat stiffness, neck muscle tension, and cervical spine alignment were selected for the parameter study of the head-neck-torso kinematics and cervical spine responses. The motion patterns of cervical vertebrae in the crash motion and in the normal motion were compared. Subjects muscles in the relaxed state did not affect the head-neck-torso kinematics upon rear-end impact. The ramping-up motion of the subjects torso was observed due to the seatback inclination. An axial compression force occurred when this motion was applied to the cervical spine, which in turn developed the initial flexion, with the lower cervical vertebral segments extended and rotated prior to the motions of the upper segments. Those motions were beyond the normal physiological cervical motion, which should be attributed to the facet joint injury mechanism. The difference in alignment of the cervical spine affected the impact responses of head and neck markedly. Based on the differences in the alignment of the cervical spine between male and female occupants, it is pointed out that the neck injury incidence tends to become higher for women than for men.(A) For the covering abstract of the conference see IRRD E201172.

INFLUENCES OF THE PHYSICAL PARAMETERS ON THE RISK TO NECK INJURIES IN LOW IMPACT SPEED REAR-END COLLISIONS

The current state of neck injuries sustained in car-to-car rear-end collisions were investigated according to recent automobile accident statistical data in Japan. To clarify the neck injury mechanisms for low impact speed car collisions, the newly developed impact sled experiment which simulates actual car impact acceleration was performed using human subjects. In order to measure and analyze the physical parameters such as human head rotational acceleration, neck bending moment, shearing and axial forces, the component measurement method with six-degrees of freedom was applied and demonstrated. Furthermore, relationships among the physical parameters, impact speeds, sitting positions, headrest heights and neck muscle tones applied on the subjects head and neck system were analyzed. These analyses would enable us to comprehend the conditions of the neck muscle tone and the effects of the sitting postures including headrest height, factors which are of vital importance to the understanding of neck injury mechanisms.

Motion analysis of human cervical vertebrae during low-speed rear impacts by the simulated sled

In an attempt to better understand the mechanism of motion of human cervical vertebrae during low speed impacts, the motion of the cervical vertebrae was analyzed using conditions such as the sitting position and the seat performance characteristics. A new impact sled was developed which simulated actual car impact acceleration. Ten volunteers participated in the experiment. Test speeds of 2, 4, and 6 km/h (.8, 1.6 and 3.2 mi/h) were selected. Two types of seat performance were used; a conventional car seat and a rigid wooden seat. Cineradiography recorded the motion of the cervical vertebrae at impact. The test results showed that a downward and rearward extension motion of C3 compared to C6 occurred and the cervical spine was compressed in an early stage of impact. Moreover, it was found that when the seat was rigid and speeds were increased, the ramping up motion of the body of the subject and neck compression were more typical. The vertebrae motion was analyzed and then compared with the differences between crash motion and normal motion. Based on this study, it is concluded that compressive vertical motion plays an important role in minor neck injuries.

Influence of seat characteristics on occupant motion in low-speed rear impacts

To analyze the effect of the seat characteristics on dummy motions and human volunteer motions, sled tests simulating low-speed rear impacts were conducted with some seats which had different characteristics. Volunteers cervical vertebral motions were photographed with an X-ray cineradiographic system at a speed of 90 frames/s as well as the visible motions of dummys and volunteers were recorded. Although the tests were conducted under limited conditions, the results indicated the relationship between the occupants visible motions, which are assumed to be closely related to the whiplash injury mechanism, and seat characteristics. It should be noted that the volunteer sled tests were discussed and approved by the Tsukuba University Ethics Committee and the volunteer submitted his informed consent in writing in line with the Helsinki Declaration.

SIMULATION OF CAR IMPACT TO PEDESTRIAN LOWER EXTREMITY: INFLUENCE OF DIFFERENT CAR-FRONT SHAPES AND DUMMY PARAMETERS ON TEST RESULTS

Sled impact tests on mechanical substitutes for a pedestrian were conducted as a preliminary study for the purpose of developing a subsystem test procedure for the assessment of car-front aggressiveness to pedestrian legs. Four mechanical substitutes for a pedestrian were used in the test: the leg of a rotationally symmetrical pedestrian dummy (RSPD) as the representation of a subsystem, a HYBRID-II pedestrian dummy, a modified HYBRID-II pedestrian dummy equipped with a steel bar serving as knee joint, and a RSPD - HYBRID-IIP combined dummy in which the lower part of the RSPD and the upper part of the HYBRID-IIP were connected by a joint in such a way that the movements of the upper part were similar to those in cadaver tests. In the tests the following were evaluated: (i) the influence of vehicle shape on knee response and on vehicle impact force; (ii) the influence of the upper body mass on knee response and on vehicle impact forces; (iii) the influence of the bumper system on knee response, the kinematics of pedestrian mechanical substitute, and on vehicle impact forces; (iv) the influence of pedestrian mechanical substitute characteristics on its kinematics and knee response, and on vehicle impact forces. This paper describes a primary concept when subsystem test methods for the assessment of car-front aggressiveness to pedestrian legs in a car-pedestrian collision are considered.

Analysis and comparison of reflex times and electromyogram of cervical muscles under impact loading using surface and fine-wire electrodes

Myoelectric signals [electromyograms (EMGs)] can be collected using either surface or fine-wire electrodes. Application of the latter results in higher-frequency contents of EMG. In the field of impact biomechanics, surface electrodes are more often utilized than fine-wire ones. However, the removal of motion artefacts from EMG recorded under transient loads requires application of high-pass filters with relatively high cutoff frequencies, which may eliminate a significant part of the surface EMG power spectra. Therefore, in the current study, both surface and fine-wire electrodes were utilized to record the EMG of cervical muscles under conditions simulating a rear-end car collision at low speed. The results indicated that application of high-pass filtering at 50 Hz can be necessary to remove motion artefacts from the EMG collected under such conditions. Such filtering resulted in a higher decrease in amplitude of the surface EMG than that of the fine-wire one. However, the reflex times obtained here were not significantly affected by the type of the electrodes utilized to collect EMG.

Neck Injury Mechanisms During Direct Face Impact

Study Design. Digitized measurements of the intervertebral motions using cervical cineradiographs of 10 volunteers during direct impacts applied to their faces. Objectives. To clarify the cervical spine motion during direct face impact and postulate some mechanisms of neck injuries. Summary of Background Data. Neck injury occurs mostly in traffic or falling accidents. Hyperextension of the neck is considered the most common mechanism of the injury because most victims have lacerations or contusions on their faces. Methods. A low-level backward impact load was applied to 10 healthy male volunteers’ faces at the forehead and maxilla via a strap using a free-falling small mass. Cervical vertebral motion was recorded by radiograph cineradiography during the impact. Results. The upper cervical spine showed a flexion motion for both conditions. Consequently, the cervical spine had an S-shaped curvature similar to that in cervical retraction. Intervertebral motions of the cervical spine were evaluated using an radiograph frame taken at the maximum cervical retraction. For the forehead load, intervertebral motion at C1–C2 was flexion, and motions of the lower cervical spine were extension. For the maxilla load, intervertebral motions from occiput-C1 through C4–C5 were flexion. The inflection point of the curvature was influenced by the impact location. Conclusion. We detected a flexion motion of the upper or middle cervical spine during direct face impact. In an actual accident, if the cervical spine is forced into similar motion, we speculate that neck injury would occur in this retraction-like curvature of the cervical spine.

Cervical Vertebral Motions and Biomechanical Responses to Direct Loading of Human Head

There is little known data characterizing the biomechanical responses of the human head and neck under direct head loading conditions. However, the evaluation of the appropriateness of current crash test dummy head-neck systems is easily accomplished. Such an effort, using experimental means, generates and provides characterizations of human head-neck response to several direct head loading conditions. Low-level impact loads were applied to the head and face of volunteers and dummies. The resultant forces and moments at the occipital condyle were calculated. For the volunteers, activation of the neck musculature was determined using electromyography (EMG). In addition, cervical vertebral motions of the volunteers have been taken by means of X-ray cineradiography. The Ethics Committee of Tsukuba University approved the protocol of the experiments in advance. External force of about 210 N was applied to the head and face of five volunteers with an average age of 25 for the duration of 100 msec or so, via a strap at one of four locations in various directions: (1) an upward load applied to the chin, (2) a rearward load applied to the chin without facial mask, (3) a rearward load applied to the chin with the facial mask, and (4) a rearward load applied to the forehead. The same impact force as those for the human volunteers was also applied to HY-III, THOR, and BioRID. We found that cervical vertebral motions differ markedly according to the difference in impact loading condition. Some particular characteristics are also found, such as the flexion or extension of the upper cervical vertebrae (C0, C1, and C2) or middle cervical vertebrae (C3-C4), showing that the modes of cervical vertebral motions are markedly different among the different loading conditions. We also found that the biofidelity of dummies to neck response characteristics of the volunteers at the low-level impact loads is in the order of BioRID, THOR, and HY-III. It is relevant in this regard that the BioRID dummy was designed for a low-severity impact environment, whereas THOR and HY-III were optimized for higher-severity impacts.

A Simulation Analysis of Human Cervical Spine Motion During Low Speed Rear-End Impacts

The non-physiological motions of human cervical vertebrae were analyzed in volunteer tests for rear-end impacts and were considered to be an important parameter for neck injuries. The objectives of this study are to improve the Marko de Jager neck model using volunteer test data and to analyze the influence of horizontal and vertical accelerations on cervical vertebral motion. In the beginning of this study, a neck model was positioned based on X-ray cineradiography of a volunteer. Motions of each vertebra were compared with those of volunteer test data for low speed rear-end impacts (4, 6, 8km/h). In these comparisons, the differences of vertebrae motions between the neck model and the volunteer tests were found. To improve the validity of the neck model, the connection properties and the bending properties of the upper and lower vertebrae of the model were modified to increase rigidity. Using the modified neck model, simulation analysis was performed by changing horizontal and vertical accelerations to analyze the influence of seat property on vertebrae motion. The forces caused by contact with each adjacent facet of the vertebrae, vertebra angles and vertebra rotation center relative to adjacent vertebra were calculated to evaluate the severity for the vertebrae and to analyze the motions of the vertebrae just before facet contact. It was found that the facet force and the height of rotation center were influenced not only by horizontal acceleration but also by vertical acceleration. (A) For the covering abstract see ITRD E106349.