## Facts

- Linda D. Polston was severely injured when her vehicle collided with another car.
- Polston sued, among others, the vehicle’s manufacturer (General Motors Corporation) and a dealer, alleging the vehicle’s defective design was not reasonably crashworthy and increased (“enhanced”) her injuries beyond those caused by the initial impact.
- At trial, Polston offered expert testimony from Murray Burnstine, a mechanical engineer experienced in accident reconstruction and injury mechanics.
- The district court allowed Burnstine to testify about crashworthiness defects but barred him from opining that those defects enhanced Polston’s injuries because he lacked medical credentials to express causation “to a reasonable degree of medical certainty.”
- The district court concluded Polston failed to prove the existence and extent of enhanced injuries and granted the manufacturer a directed verdict.

## Issues

1. Whether the evidence, viewed favorably to Polston, was sufficient to permit a jury to find that a design defect was a substantial factor in causing enhanced injuries, making a directed verdict improper.
2. Whether the district court improperly restricted the engineering expert’s causation testimony on enhanced injuries based solely on the absence of a medical degree.
3. Under Georgia law, whether a crashworthiness plaintiff must precisely apportion damages between the initial collision and the alleged enhancement, or whether apportionment burdens may shift in part to defendants once substantial-factor causation is shown.

## Decision

- The Eleventh Circuit held the directed verdict for the manufacturer was erroneous insofar as it rested on an asserted failure to prove the existence of enhanced injuries.
- Relying on the Georgia Supreme Court’s answer to a certified question, the court held Georgia law does not require a plaintiff to precisely apportion damages between the initial impact and enhanced injuries to reach the jury.
- The court recognized that engineering expertise may be relevant to causation in crashworthiness cases because injury mechanisms can turn on forces, deformation, and occupant movement, not only medical diagnosis.
- The directed verdict was reversed, and the case was remanded for further proceedings consistent with the clarified burden-allocation rule.

## Legal Principles

- In a crashworthiness/enhanced-injury claim governed by Georgia law, the plaintiff must prove that a design defect was a substantial factor in causing some enhanced injury.
- Precise, mathematical apportionment of damages between the initial collision and the enhancement is not a prerequisite to submission to the jury; once substantial-factor causation is shown, responsibility for separating damages may shift in part to defendants.
- On a directed-verdict motion, courts must view evidence and reasonable inferences in the nonmovant’s favor and may not weigh credibility or choose among competing inferences.
- In crashworthiness litigation, qualified engineering experts may testify about the causal relationship between vehicle design, crash dynamics, and injury patterns when those matters fall within engineering and biomechanics.

## Conclusion

The Eleventh Circuit reversed the directed verdict because Polston presented sufficient evidence for a reasonable jury to find that an alleged design defect substantially contributed to injuries beyond those caused by the initial collision, and Georgia law did not require her to precisely apportion enhanced damages before the case could go to the jury.


Polston v. Boomershine Pontiac-GMC Truck, Inc., 952 F.2d 1304 (11th Cir. 1992)