I’ve had this mechanism of injury described about once a year for my entire career.
“I was just washing the dishes, and I dropped a knife while I was drying it. When I went to pick it up, I lost my balance and tripped over the rug in front of my sink. Then I fell down on the knife, and there you have it”.
What does it really mean?
First, think about physics. Most knives do not land standing straight up. They don’t even land on their side with the blade side up. They land flat with the sharp side perpendicular to anything that might fall on top of it.
Then think about Occam’s razor. You remember, Sir William of Occam back in the 1300’s. He popularized the principle of parsimony in problem solving. What does this mean? If you have more than one possible explanation (or hypothesis) for an event, the simplest one should be selected. Well, the falling down “hypothesis” is way too complicated.
What does it really mean? Your patient either stabbed themself (most common reason), or they are trying to protect the person who really did it (significant other). What to do? Interrogate them, asking the same thing over and over. Ask for exact details. Ask until the story changes. Have other people ask. Sooner or later, you’ll get the answer you were expecting. Then get the appropriate professionals involved to help with the problem (psych, law enforcement, etc).