Legal Definitions - sudden-onset rule

The sudden-onset rule is a legal principle that applies when an injury's symptoms are so clear and appear so immediately after a specific traumatic event that expert medical testimony isn't necessarily required to prove the event caused those obvious symptoms. In essence, if the connection between an incident and an injury is straightforward and easily understood by a layperson, a court might not demand a doctor's explanation of causation.

Here are some examples to illustrate this rule:

• Example 1: Car Accident Whiplash

  Imagine a driver who is rear-ended at a stoplight. Immediately after the impact, they experience a sharp, burning pain in their neck and upper back, along with stiffness that wasn't present before the collision. Their doctor later diagnoses whiplash.

  This scenario demonstrates the sudden-onset rule because the obvious symptoms of neck pain and stiffness immediately followed a known traumatic incident (the car accident). A jury, relying on common knowledge, could reasonably conclude that the accident caused the whiplash symptoms without needing a medical expert to testify that car collisions can lead to such injuries.

• Example 2: Slip and Fall Injury

  Consider a shopper who slips on a wet, unmarked floor in a supermarket, falling hard onto their outstretched hand. They immediately feel intense pain in their wrist, which quickly swells and becomes discolored. An X-ray later confirms a fractured wrist.

  The sudden-onset rule would apply here because the severe wrist pain, swelling, and discoloration (obvious symptoms) appeared instantly after the traumatic incident (the fall). The direct and immediate link between the fall and the visible, painful injury makes it unnecessary to require medical experts to explain that falling on a hard surface can cause a fracture.

• Example 3: Workplace Incident

  A construction worker is operating a jackhammer when it unexpectedly kicks back, striking them forcefully in the leg. The worker immediately collapses, clutching their leg in agony, and a large, visible bruise quickly forms where the jackhammer hit. They are later diagnosed with a deep tissue contusion.

  This situation illustrates the sudden-onset rule because the immediate, severe pain and the rapidly appearing bruise on the leg are obvious symptoms that directly and instantly followed the known traumatic incident (being struck by the jackhammer). A court would likely consider the causal link between the impact and the leg injury to be self-evident, not requiring specialized medical testimony to establish causation.