If you have a pre-existing condition and get hurt at work, you may wonder whether you can still file a workers’ comp claim. The answer is not always straightforward, but having a prior injury or medical condition does not automatically end your claim. What matters most is what Missouri law requires you to prove.

What the prevailing factor standard means for your claim

Missouri law sets a higher bar than most states when it comes to workers’ comp. To qualify for benefits, you must prove that your job was the number one cause of your current condition and your inability to work. Showing that work contributed to your injury or made an existing problem flare up is not enough. The burden of proof is on you, and it can be a difficult standard to meet.

When a pre-existing condition can still qualify for benefits

Having a prior injury or diagnosis does not automatically end your claim. The issue is whether your job made your condition significantly worse. For example, if you had an old back injury but years of heavy lifting at work pushed it to the point where you can no longer do your job, that worsening may qualify for compensation.

Missouri courts have recognized this, but only when there is solid medical evidence showing that the work activity, not the pre-existing condition on its own, drove the decline.

How a prior condition can be used to deny your claim

When insurers learn of a prior injury or diagnosis, they often use it to argue that your current condition is not work-related. They may claim your disability stems from the pre-existing condition alone, or that work was merely a triggering factor rather than the primary cause.

This is one of the most common tactics used to deny or reduce workers’ comp claims, so the medical evidence you gather early in the process matters enormously.

Why medical evidence is the key to your claim

Winning a workers’ comp claim with a pre-existing condition comes down to medical documentation. You need a physician who can clearly connect your work activity to your current condition and disability, and who can articulate why work was the primary cause rather than a secondary one.

If your claim involves a pre-existing condition, the stakes are higher and the process is more complex. Speaking with a Missouri workers’ comp attorney before you file gives you a clearer picture of what you need to prove, how to document it and how to push back when the insurance company tries to use your medical history against you.