Let's talk about...oh, why not, microfracture surgery. It's a subject of some importance, since both Chad Tracy and Doug Slaten underwent the procedure during the off-season, and their status for Opening Day this year remains uncertain, even though it's now little more than a month away. So, what is it? Why is it done? And, most importantly, what are the likely long-term effects?

The procedure was pioneered by Dr. Richard Steadman of the Steadman-Hawkins clinic in Vail, Colorado, at the end of the 1980's, though it didn't become popular among athletes until the late nineties, with basketball's John Stockton the "patient zero". The main purpose of microfracture surgery is to help repair damaged knee cartilage, which helps cushion the joint. It can also be used to treat arthritis or trauma-induced damaged to the cartilage, though there's no indication these are involved in the cases of Tracy or Slaten, who both basically seem to have ground down the cartilage through normal wear and tear [or as "normal" as professional sports gets]. The procedure itself is relatively quick: 30 minutes or so, and requires only a quarter-inch incision on the knee. An arthroscope is then used to work directly on the joint itself, where the surgeon uses an awl to drill tiny holes in the bone, about one-eighth of an inch deep, near the target area. Bone marrow seeps out of the holes, releasing cartilage-building cells as part of the clotting process.

It should be noted that the fibrocartilage produced by the procedure is not identical to what it's replacing, lacking the Type II collage present in the original. As a result, it is less durable than the original, and will break down, albeit over a period of years. It's generally agreed that a strict program of careful rehabilitation is key to its success. After the operation, patients are required to be on crutches, generally for six to eight weeks. They can also spend up to six hours a day with a machine that moves the knee in a continuous passive motion, "For reasons we don't know, passive motion, which rocks your knee like a cradle, promotes healthy growth cells and promotes a more durable tissue," said Dr. Nicholas DiNubile, an orthopedic consultant for the Philadelphia 76ers and the Pennsylvania Ballet. Which is one hell of a diverse client base, if you ask me.

Part of the problem with assessing the chances of recovery for Tracy and Slaten, is that the procedure has hardly-ever been used on baseball players, so there's not much of a track-record. It is much more common in other sports, with the NBA being in the fore-front of things. The Suns' Amare Stoudemire, for example, underwent the procedure in October 2005, and returned to action barely five months later. However, he missed the rest of the 2006 season thereafter, but has make a successful return to play for the Suns since. A full list of NBA microfracturees reveals the rehab time varies widely, anywhere from two to 16.5 months - and the results are similarly mixed. For every success like Stoudemire, there are those such as Allan Houston, Jamal Mashburn and Penny Hardaway. The trend does seem to be towards better results: this comparison shows that some players, like Jason Kidd, can return to almost exactly their pre-op level of performance.

Obviously, playing in the NBA will put a great deal more weight on the knee, both because of the jumping which is a crucial part of the game and because the players are usually significantly taller and heavier. Stoudemire, for example, is 6'10" and 249 lbs, whereas Tracy is listed at diamondbacks.com at 6'2", 200 lbs, the same weight as Slaten, who is three inches taller. Even for a pitcher, it seems unlikely the stresses on the knee will quite reach the levels of those seen in the NBA. Moving over, in the NFL, a 2003 study of 25 players treated with microfracture documented that 19 of them returned to play the season after surgery and continued to play for an average of 4.6 additional seasons. That's pretty good, considering the average length of an NFL career is only about 3.5 seasons, according to the NFL Player's Association. [This compared to 5.6 years for baseball]

Again, however, this is not perhaps the best comparison: gridiron is a contact sport and we are once more dealing with bigger men. We might have to go across the pond to find the closest parallels, as several cricketers have been treated by Steadman. England captain Michael Vaughan was operated on in July 2006, and returned to the international fray in January the following year, without apparent ill effects. Vaughan is an 'all-rounder' - a cricketer who, in baseball terms, can both hit and pitch, somewhat like Micah Owings - so his recovery from the same kind of surgery bodes well for both Slaten and Tracy. A number of soccer stars, including Ronaldo, and Michael Owen are also on Steadman's client list. Owen, indeed, had two such ops: in July 2006, Steadman fixed lateral cartilage damage, then in September operated on the striker's cruciate ligament. Owen still returned to play for Newcastle United in April the following year.

But for baseball players? Almost nothing in the way of precedent. Tony Gwynn underwent the procedure in June 2000, and did come back at the start of the next season - he missed two months, but that was with a hamstring problem - though that was his last hurrah. However, Gwynn was significantly older, being aged forty at the time of the operation. Mariners reliever Mark Lowe had the technique done on his elbow at the end of 2006, and hasn't really returned yet [2.2 innings for Seattle last year]. This off-season saw Brian Giles of the Padres and Brewers minor-league pitcher Mark DiFelice undergo the procedure on their knees, so it's not just being used in Arizona. I asked Baseball Prospectus injury guru Will Carroll for his take on the topic, and what he thought of the recovery chances of our pair:

Sunday saw Tracy take a step - literally - forward in his rehab, safely negotiating a series of agility drills down in Tucson. He said, "Today was the day that I feel like you get over the hump and you start back on the good side. I know now that I'll be ramping up the intensity every time out... The goal is opening day. I also realize that this injury is not something you can rush, and it can easily be set back. For me, the bottom line is no setbacks. You try to get out there sooner and you end up coming back a lot later." However, he has not yet been cleared to run fully, and there is no current expectation for when we might see him in a game. Slaten was last seen throwing off a mound for the first time on Thursday. His comment afterwards: "It was very encouraging," he said. "It was more mental, trying to get through the hesitation at first, and that was gone really quick." We'll monitor both men as we head towards Opening Day; fingers crossed, and we wish them the best.