Auto collision injury biomechanical analysis

Jun 23, 2007 by

GEI was assigned to perform a biomechanical analysis of the injury potential from an auto collision when the claimant’s Camaro was rear-ended by the insured’s pickup truck.   Based upon the vehicle damage, the accident reconstruction consultant calculated the impact speed to be in the range of 6 to 7 mph.

This caused a change in velocity (Delta V) of the Camaro in the range of 3 to 4 mph resulting in acceleration in the range of 1.3 to 1.8 g’s.   This minor, low-velocity impact was consistent with the cost of repairs done on the Camaro (parts $124, paint $230, and labor  $1,117).

Per deposition statements, the claimant was wearing a three-point seat belt and consequently was well restrained.   Her deposition statement claimed that her body moved “forward and back,” due to the impact. This was inconsistent with the laws of physics.

On impact, her head and thorax would tend to move backwards and her thorax would be pushed against the seat back.

There was no evidence that due to impact, any of her body segments struck any interior parts of the car.   She claimed that she “held the steering wheel tightly.”   In view of this, it was clear that she did not suffer injury due to direct-impact of body segments.

The g levels experienced by the claimant were in the range of 1.3 to 1.8 g’s.  These g levels fall well within the range of g levels experienced by people during the course of their daily lives.   It is noteworthy to compare the g levels experienced by the claimant to those measured by Szabo et al. (SAE 940532) in a study which subjected human volunteers (both male and female, ages 27 to 58 years old) with various degrees of cervical and lumbar spine degeneration, to impulsive loads. During the study, g levels in the range of 10 g’s at the head, between 5 and 7 g’s at the cervical spine and 3 to 5 g’s at the lumbar spine were experienced by these volunteers.  The impacts caused no injury to any of the volunteers and caused no objective changes in the condition of their cervical or lumbar spines, which already displayed various degrees of degeneration, as documented by pre- and post-test MRI scans.

A subsequent MRI of the claimant’s cervical spine found a spur in the anterior aspect of C-4 vertebral body and hypertrophy of the uncinate process of the vertebra.   In addition, despite a 1 mm bulge of the disc, no central canal stenosis was found.   The spur and hypertrophy (enlargement/growth) were manifestations of degenerative processes and were not attributable to the accident, both on account of the small magnitude of g forces, and the short duration of time between the accident and MRI date.

The claimant later complained of right hand numbness and a “hand swelling like a balloon.” The cause may have been arterial blockage, vein blockage, or nerve compression.
Blockages were ruled out, which left a mechanical compression of the nerve.

A neurosurgeon, consulted some nine months later, diagnosed a compressive neuropathy and opined that the condition was due to fibrosis of scaleneous muscle, which causes a squeezing effect on the brachial plexus.

Formation of fibrous tissue on scaleneous muscle requires a cause and requires time for the effect (fibrous tissue formation) to develop. The cause and effect could not be attributed to the accident since her hands were maintained steady on the steering wheel and did not impact any object on the interior of the car during the subject accident.

It was noted by later physical therapists that the claimant might be aggravating her symptoms by moderate to heavy household work at her home, and in the care of her young daughter, and her disabled parents.   Despite rehabilitation education to “pace herself,” there was evidence of increased arm use in unsupported positions, and prolonged forward head posture with increased cervical pain/sprain.

The claimant’s condition of heightened pain and discomfort was reasonable given her medical condition of steadily evolving degenerative joint disease, coupled with her history of prior motor vehicle accidents.  The subject rear-end accident, however, did not cause her symptoms or condition.

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