As visible here, Madson throws a knuckle-y curveball that might have aggravated that finger. (Gary A. Vasquez/USA Today)

HOUSTON — Ryan Madson slipped away from the Nationals after their series in San Diego this past weekend and headed to Phoenix, where he saw a hand specialist who does work for the Arizona Diamondbacks and also saw Jay Schroeder, the trainer who Madson credits with saving his career. Madson was trying to discover what was wrong with the top knuckle of his right index finger. All he knew after his abrupt arrival on the disabled list last week was that something was not right, and his finger was hurting.

The diagnosis the Nationals received is this: The sheath around the tendon that runs up through that knuckle is inflamed. Madson must calm that inflammation so that it won’t flare again when he throws, then he will be able to return. He received treatment in Phoenix from Schroeder, whose electric therapy system has helped Madson eliminate daily inflammation and bigger aches and pains. According to Nationals General Manager Mike Rizzo, the Nationals expect Madson to be ready in plenty of time for the postseason.

As for how he suffered the strange injury, one person familiar with the situation proposed this theory: Madson throws a knuckle-y type curveball, one in which he drives his index finger into the ball at the top knuckle. Many pitchers do this. It doesn’t cause them trouble.

But Madson never used to throw that curveball much at all — 3.3 percent of the time in his decade-long career. This season, he has thrown it 17.6 percent of the time, a massive jump that could cause an overuse injury. If that theory is correct, Madson might have to reconsider his pitch selection. Or perhaps something else caused the injury. Regardless, that curveball has been a key element of what seemed to be a devastating arsenal during his Nationals tenure and seems certain to be a part of that arsenal down the stretch.

Whatever the cause of his injury, Madson’s importance to the bullpen became even more apparent Thursday night, when Manager Dusty Baker’s experiment with Brandon Kintzler in the ninth and Sean Doolittle in the eighth did not work, and the Nationals blew their first save since acquiring that trio. While Madson might not have changed the outcome, he simply changes the game. As good as Kintzler is, Baker would have had another right-handed option to bail out Doolittle, or perhaps to throw the ninth if he needed Kintzler to get a groundball in the eighth. Or perhaps, Baker would not have experimented at all. Kintzler to Madson to Doolittle certainly seems like a formidable trio, though Baker did not rule out the possibility of playing the matchup game again some day.

“I’m very open to it. You go with matchups. There’s no absolutes on anything in baseball,” Baker said. “You can have the numbers. You can have this or that. But sometimes things go against the numbers. Like I said, it just didn’t work.”

Regardless, that Madson’s injury does not seem to be so structurally disruptive as to threaten his season should stand as a major relief for Baker as he plots out postseason plans. While he might be without the veteran right-hander for the near future, the expectation remains that he will have him in October, restoring the three-headed monster that pulled his bullpen out of frustrating oblivion over the past month.

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