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September 30, 2008
Microfracture Under the Microscope
Tracking Players Post-Surgery

by Kevin Pelton

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As NBA teams across the country open training camps this week, one of the biggest stories will be both a debut and a comeback. Last September, less than three months after the Portland Trail Blazers made him the No. 1 overall pick of last year's NBA Draft, Greg Oden underwent microfracture knee surgery, sidelining him for the entire 2007-08 season. Now, after a lengthy rehab process, Oden is back and ready to get his NBA career underway.

Two years ago, I tried to throw some facts into the murky discussion of the microfracture procedure, compiling a list of every NBA player known to have had the surgery and looking at how it affected their performance. Last year, I extended that research to a different sport, penning a guest column for sister site Football Outsiders on microfracture in the NFL. With Oden's return pushing microfracture surgery back into our collective consciousness, now seemed like a good time to revisit the data and look for some conclusions about Oden's comeback.

The first step was updating that complete list, which you can find here. I've found 30 NBA players who have undergone a total of 33 microfracture procedures, dating all the way back to Kevin Johnson having it at some unknown point in the early 1990s. (Penny Hardaway, Matt Harpring and Kenyon Martin are the three players who have had a pair of microfracture surgeries.) There are reliable timetables and before and after numbers available for 19 cases, and this is the group I've used.

This time, I decided to explore the numbers first by finding how much per-minute performance (as measured by Win %, the per-minute incarnation of my WARP rating system) the players lost (or, in the rare cases of Kerry Kittles and Harpring's second procedure, gained) when they came back, and graphing this against three key factors--how recently the surgery was performed, the player's age and how long they rehabbed before coming back.

Somewhat surprisingly, the first two factors, which I once believed to be critical, came up as essentially meaningless in this analysis. More recent microfracture procedures do not appear to have been any more successful than those performed as far back as the 1990s on average, and old players lose no more productivity than young players. This mirrors what I found (or more accurately did not find) in my NFL research.

Now, this does not necessarily mean that age does not matter at all. Players in their thirties are much more likely to see microfracture end up a career-ending procedure, often because it is a last resort following long-running knee problems. Meanwhile, the only player in his twenties who has been unable to come back so far has been Darius Miles, who is attempting to do just that in training camp with the Boston Celtics this month. However, when older players have been able to return, they have done so just as successfully as their younger counterparts have.

As for the recency factor, I previously speculated that the microfracture technique had improved over the years. This may not in fact be the case. The pioneer of microfracture treatment, Dr. Richard Steadman, introduced the procedure on the skiers he treated in Vail, Colo. in the 1980s. We have record of (frequently successful) microfractures performed on NFL players dating back to the late '80s. By the time it came to the NBA, then, the actual procedure itself may have already been sound.

What clearly has improved is teams' and players' understanding of microfracture. When the first players had microfracture surgeries, they were treated like traditional arthroscopic knee surgeries that also seek to treat cartilage problems in a less aggressive fashion, procedures which needed only a couple of months of rehabilitation. We now know that time is crucial for the development of the pseudo-cartilage microfracture hopes to promote (see here for more on how microfracture works) and that anything less than about six months of recovery is dangerous.

Graphing the time between when the procedure was performed and when the player first returns to an NBA game shows a clear and positive relationship. While the correlation is far from perfect, the trendline shows that on average players lose about 1% less of their pre-microfracture productivity for every extra month spent rehabbing.

This is great news for Oden and the Blazers, who were very conservative following his surgery and immediately ruled him out for the entire 2007-08 season instead of trying to rush him back late in the year. On opening night, Oden will be 13-and-a-half months removed from his microfracture procedure, marking the second-longest rehab on record (Kittles, one of those two players to improve coming back, sat out 16.5 months, making him the top right dot on the chart).

Additionally, that Oden will be able to ease his way back in training camp should be a positive. The way I'm calculating rehab length tends to overstate how long players who come back in camp are actually sidelined because they are testing the knee a full month before the date I use, when they play their first regular-season game. Even with this caveat, players who return in camp still tend to do better than those who return midseason.

Accounting for their lengthier rehabs, the players who come back in camp would be expected to return at 90.1 percent of their pre-microfracture productivity. In fact, they've performed at a 93.0 percent level. Meanwhile, those who have returned midseason have underperformed their expected 85.7 percent of pre-surgery productivity, reaching just 83.7 percent.

Based solely on the length of his rehab, Oden would be expected to lose 4.7 of his per-minute productivity following the surgery. Add in the training-camp factor and that gets as low as a negligible 1.8 percent. Of course, as the first player to undergo the procedure prior to his rookie season, Oden does not have an established level of performance, but his college numbers project very nicely indeed. Using the translation system I introduced before this year's draft, Oden rates as the second-best prospect to enter the NBA dating back through 2000.

The data also offer interesting insights into how microfracture affects players when they return. Here's the before and after comparison for several major stats:

          GP%      MPG    P40   R40   A40   S40   B40  TO40    TS%   Win%
Before   88.5%    32.6   18.4   7.2   3.7   1.4   0.6   2.3   .543   .541
After    82.5%    28.0   16.3   6.9   3.6   1.4   0.7   2.3   .505   .476

Change   -6.8%  -14.1% -11.4% -4.6% -2.8%    -  +6.8% -1.1%  -6.9%  -12.0%

What is somewhat surprising here is that the players tended not to see much drop-off in what would be considered markers of athleticism--rebounding, steals and blocks, the latter of which actually went up. Now, it is true that in many cases we're making a comparison to when the player was limited by the knee injury that was ultimately repaired by microfracture, but that is still pretty remarkable.

Where players have tended to be limited is in terms of stamina and scoring. Their availability (as measured by number of potential games played) goes down, while their minutes take a sizeable hit. Both of those changes make sense. I'm somewhat more at a loss to explain why players see their True Shooting Percentage take a dive. It would be interesting to compare to other players who miss extensive time due to injury and see whether this can be explained by rust or something along those lines.

The good news is that many players have seen their scoring rebound after the initial hit. Amaré Stoudemire is a good example; his scoring rate dropped by nearly four points per 40 minutes in his first year back before improving beyond the pre-microfracture mark in 2007-08. Rashad McCants saw his True Shooting Percentage fall from 53.9 percent to 45.4 percent, then jump back to 55.0 percent.

Along with Oden's college profile, this suggests that he might need some time to develop into a consistent scorer in the post. However, he should be able to come in and be an elite defender in the middle fairly quickly. In the short term, his recovery from microfracture surgery should be considered a speed bump on his way to superstardom.

Oden is not the only player coming back from a microfracture this fall. Miles is the most interesting case. A return after missing two full seasons would be entirely unprecedented and it remains an open question what, if anything, Miles has left. Charlotte's Sean May, who had surgery last October, is in a similar position to Oden with one caveat--he's experienced trouble with his right knee for some time, and previously had traditional arthroscopic surgery that failed to rectify his cartilage problems. Lastly, Oklahoma City's Mouhamed Sene has had the shortest recovery timeline after having microfracture in April. Expect the Thunder to be cautious with Sene in training camp if he participates at all. Given he is not a key part of the team's rotation, there is no major rush to get Sene back in the lineup.

Kevin Pelton is an author of Basketball Prospectus. You can contact Kevin by clicking here or click here to see Kevin's other articles.

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