Injuries intertwined for Tiger Woods

In a moment of déjà vu from 2010, Tiger Woods made an early exit from the 2011 Players Championship because of an injury. This year, he arrived at the tournament with his health already in question. And this time, it was not Woods' neck but rather his long troublesome left leg that was acting up.

After admittedly not practicing between the Masters and The Players Championship, Woods still thought he had improved enough to compete. Clearly, that was not the case as he failed to last beyond nine holes on the first day of the tournament.

"The treatment's been good," Woods said Thursday. "It's been getting better. It just wasn't enough."

Woods didn't play at the Wells Fargo Championship earlier this month, an event where he normally tees it up, because of the injury he suffered in the Masters. For an athlete who is often guarded when it comes to how much he reveals about his health, Woods offered the following concise but definitive statement regarding his injury on his personal website.

"Woods suffered a Grade 1 mild medial collateral ligament sprain to his left knee and a mild strain to his left Achilles tendon while hitting a difficult and awkward second shot from the pine straw under the Eisenhower tree left of the fairway at No. 17 during the third round of the Masters."

So why was this dual injury -- which by all accounts sounds relatively minor compared with his previous leg issues -- so problematic for Woods?

The injury on its own isn't particularly dire. The medial collateral ligament (MCL) is the ligament that reinforces the inner aspect of the knee joint, running from the femur (thighbone) to the tibia (shinbone).

A Grade 1, or mild, sprain indicates an overstretching of the ligament. Actual tissue damage is often in the form of microtearing, giving little visual evidence of deformity of the ligament upon imaging. Often, the most significant findings are tenderness directly over the injury site and minimal swelling.

The pain tends to worsen when the ligament is stretched. Bowing in of the knee (the "knock-kneed" position, also called valgus) will place strain on the MCL, resulting in discomfort. Depending which fibers within the ligament are affected, pain also can occur at extremes of motion when the knee is fully straight or fully flexed.

The Achilles tendon strain, also described as mild, suggests the same level of minor injury as Woods' MCL diagnosis. The Achilles tendon is a broad, flat tendon that serves as the bridge anchoring the calf muscles to the heel bone (calcaneus).

A sore Achilles tendon will be aggravated when the calf muscle contracts, transferring load through the tendon to the heel to advance the foot when walking. The tendon also can be sensitive to extreme stretch, such as when the toes are pulled toward the shin. One reason a walking boot (such as the one Woods was wearing after the Masters) can be helpful is that it elevates the heel from the ground and helps shift the weight forward, decreasing the effort the calf muscle has to exert and consequently decreasing the load on the tendon.

Although neither injury is particularly alarming on its own, any performance-altering ailment in an otherwise finely tuned athlete can render the athlete, at the very least, ineffective. At worst, it can cause him to be incapable of performing. On Thursday, Woods' performance deteriorated rapidly along that spectrum.

Although it's impossible to know precisely what symptoms Woods was experiencing at which moment, there are several biomechanical considerations. The position of Woods' left knee at the top of his backswing is the knock-kneed position, and the bulk of his weight is over his right leg. During the downswing action, he has to rapidly transfer his weight toward his front foot to drive the ball.

The extreme backswing position and subsequent transition phase certainly could bother his MCL, perhaps enough to prevent adequate weight transfer. Failure to transfer body weight properly can manifest as a loss of power through the remainder of the swing, resulting in decreased accuracy. The ball might not travel as far as it should and might end up being misdirected.

Then there's the matter of walking the course. Every step means work for the Achilles, and if there is an incline, as there often is at TPC Sawgrass, the work increases.

Woods said he did not play golf between tournaments, meaning he also didn't take an extended walk on any courses. After consecutive nine-hole practice rounds on Tuesday and Wednesday, his Achilles might have been fatigued heading into Thursday's round. Any soreness or fatigue in the Achilles will make it more difficult to walk with a normal gait. Combine an aggravated knee with a less-than-healthy Achilles, and it starts to get messy for the entire extremity.

As Woods noted, "The knee acted up and then the Achilles followed after that and then the calf started cramping up. Everything started getting tight, so it's just a whole chain reaction."

The analysis is simple, but accurate. And in the face of his body's failure to cooperate, Woods bowed out.

Stephania Bell is the injury expert for ESPN.com fantasy.