Oh. It has to be believable? Dammit.
I was going to say that he suffered the accident when the herd of llamas ran through the town yesterday. They were chasing people all through town, and into their cars, and homes. Businesses that weren’t llama proof had people being chase through the aisles. And the 911 dispatcher’s office was completely taken over by llama. Which refused to even try to answer the phones.
So your husband, after carefully placing the baby on the safety of the couch, since we all know that llama are allergic to couch foam, went out in traffic and starting using hand signals to direct the llamas and the people running from them. He forgot one important thing, though - his llama clove glove. (The scent of cloves make llamas calm down. didn’t you know that? So everyone who knows anything about the rampaging llamas keeps some cloves around the house.) So, while he was directing the llamas one bull llama kept trying to chase him. He’d spit on your husband, then chase, and your husband would twist, like a matador, and he’d run by. Your husband would heroically use the interval to direct a few more refuges and llamas to their separate corners. Then the bull would come back, and spit on him again, and charge, and with another matador twist, he’d spin aside, while the llama chased itself back to the edge of town.
The squirrels were so enthralled, they started throwing acorns at your husband, in a misguided attempt to reward his valor. And the bull llama still kept coming back and spitting on him and charging.
Finally, after about fifteen minutes of this, covered with llama spit, and surrounded by acorns, the llama control team finally showed up and started collecting the few remaining rampaging llamas. The llama control team gave your husband a voucher, in recognition of what he’d done to help protect people, good for one bag of clove-flavored peanuts from the Hudson Bay Company’s Edmonton store. Then when they said he could leave, the bull llama came back for one more screaming pass - it spit on your husband again, stole the voucher from his hand, and ate it, and then ran right into the llama control team’s van.
And while your husband was laughing at the llama control team’s efforts to get the bull llama out of their van, he stepped onto one of the spit slickened acorns, and fell, barely catching himself with his hands, but causing the break that they see his hand in a cast for, now.
ETA: Now that I know it has to be believable, I’d just say that he tripped on one of the cat’s sex toys.