Satoshi Inami

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.

Immunohistochemical demonstration of nerve fibers in the synovial fold of the human cervical facel joint

The role of the intra‐articular synovial fold as a source of facet joint pain is unclear, because the nature of nociceptive innervation in lumbar synovial folds is controversial, and there have been no such studies in cervical synovial folds. The present study aimed to demonstrate the presence of nerve fibers including nociceptive fibers in synovial folds of human cervical facet joints using immunohistochemistry. Synovial folds of cervical facet joints removed from patients undergoing cervical spine laminoplasty were analyzed immunohistochemically using antibodies to protein gene product 9.5, β III‐tubulin, substance P and calcitonin gene‐related peptide. Many nerve fibers immunoreactive for protein gene product 9.5 and β III‐tubulin were demonstrated both around blood vessels and as free fibers in the stroma of the synovial fold. Also, immunostaining showed the presence of free nerve fibers immunoreactive for substance P and calcitonin gene‐related peptide in the stroma. The presence of putative nociceptive fibers in cervical synovial folds supports a possible role for these structures as a source of cervical facet joint pain.

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.

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.

A comparison of volunteer, BioRID P3 and Hybrid III performance in rear impacts

The most important tool for testing seat-systems in rear impacts is a crash test dummy. However, investigators have noted limitations of the most commonly used dummy, the Hybrid III. The BioRID I is a step closer to a biofidelic crash test dummy, but it is not user-friendly and the straightening of the thoracic spine kyphosis is smaller than that 220of humans. To reduce these problems, a new BioRID prototype was developed, the P3. It has new neck muscle substitutes, a softer thoracic spine and a softer rubber torso than does the BioRID I. The BioRID P3 was compared with volunteer test data in a rigid and a standard seal without head restraints. The dummy kinematic performance, pressure distribution between subject and seatback, neck loads and accelerations were compared with those of ten volunteers and a Hybrid III. The BioRID P3 provided repeatable test results and its response was very similar to that of the average volunteer in rear impacts at Δv = 9 km/h.

Clinical outcomes of combined anterior and posterior spinal fusion for dystrophic thoracolumbar spinal deformities of neurofibromatosis-1: fate of nonvascularized anterior fibular strut grafts.

Study Design. Retrospective study. Objective. To analyze the clinical outcomes of anterior and posterior spinal fusion (APSF) using a fibular strut autograft (FSAG) and to investigate the morphological changes in the reconstructed spinal column of dystrophic deformities in neurofibromatosis (NF)-1. Summary of Background Data. APSF is desirable for dystrophic deformities in NF-1 with more than 50° of dystrophic kyphosis. There are few reports regarding the clinical outcomes of APSF in which the morphological changes over time of the anterior strut graft have been investigated. Methods. The clinical and radiographic outcomes of APSF with FSAG were investigated in 10 consecutive patients with dystrophic deformity in NF-1. For qualitative and quantitative analyses, the chronological changes in the FSAG configuration, length, and diameter were evaluated. Results. The mean follow-up period was 9 years, 9 months (range, 1–30 years). Graft bone erosion and postoperative curve progression were not observed in any patient. In quantitative analyses of the anterior strut, the mean ratio of the latest and immediately postoperative FSAG lengths was 0.98 (0.93–1.09). The mean central/peripheral ratios of the FSAG diameter (central portion/[upper end + lower end]/2) were 1.02 (0.92–1.10) immediately after surgery, and 1.01 (0.92–1.07) at the latest follow-up, with no significant change between these 2 time points (P = 0.937). The mean preoperative cross-sectional area of the apical vertebral body and its mean virtual cross-sectional area at the final follow-up were 3.80 (1.83–5.43) and 4.87 (2.46–7.00) cm2, respectively, with a significant difference between these 2 parameters (P = 0.0078). The mean final/preoperative ratio was 1.31 (1.10–1.43). Conclusion. APSF with FSAG for dystrophic deformity in NF-1 successfully reconstructed a reliable spinal column with a rich bone stock. The FSAG and surrounding vertebral bodies were free from postoperative erosion due to dystrophic changes and maintained their stability for a long time.

Influence of Human Spinal Deformation on Minor Neck Injuries for Low Speed Rear Impacts

The aim of the current study is to verify the influence of the change of the spine configuration on human cervical vertebral motion and head/neck/torso kinematics under low speed rear-end impacts. During the experiment, the change of the spine configuration, measured by a newly developed flexible spine deformation sensor on the skin, and the interface load-pressure distribution between seat and subject were recorded. The localized straightening of the lumbar spine starts at around 20 ms with the rigid seat, and the localized straightening of the thoracic spine reaches the maximum at around 80 ms. On the other hand, the pelvis starts to sink into the seat back and cushion at around 50 ms with softer seat. The load-pressure on the torso region for the softer seat is widely distributed. The results of this study can help clarify the relationship between the localized straightening of the spine and cervical vertebrae with respect to the difference in seat stiffness.