According to Ian Rapoport, coach Jim Harbaugh described the injury as a complete tear—one that requires surgical repair almost without exception. Crabtree underwent that surgery on Wednesday according to Chris Mortensen of ESPN, with Adam Schefter reporting doctors project a six-month recovery time.
While six months of rehab may seem extensive, it pales in comparison to what an Achilles rupture used to mean for an athlete. As Bleacher Report's Will Carroll writes, such an injury used to end seasons—and even careers. An examination of the underlying anatomy makes it clear why that is.
Also known as the calcaneal tendon, the Achilles tendon connects two large, bulky calf muscles—the gastrocnemius and soleus—to the calcaneus, or heel bone.
When the gastrocnemius and soleus contract, they pull on the Achilles tendon. In turn, the tendon pulls on the back of the heel, resulting in pointing of the toes—a movement known as "plantarflexion."
Plantarflexion is important in just about every practical movement of the lower body—from walking all the way up to sprinting and cutting. During the normal walking and running gaits, while one foot is about halfway through its forward swing, the other foot begins to plantarflex in order to push off the ground. Effective vertical leaps also require strong plantarflexion to propel upward.
Complete Achilles ruptures disconnect the gastrocnemius and soleus from the back of the heel, making plantarflexion nearly impossible. Though other muscles are also involved in plantarflexion, they cannot make up the difference.
Likely owing to its importance in the biomechanics of so many crucial human movements, the Achilles tendon evolved as the largest and strongest tendon in the human body. Unfortunately, that does not mean it is immune to injury.
Muscle and tendon injuries usually occur when an outside force counteracts a contracting muscle. For instance, if a hit forcefully straightens an athlete's biceps while he is flexing it, a biceps tendon tear can result.
According to Janie McCauley of the Associated Press, it appears Crabtree's injury occurred via a similar mechanism.
McCauley also reported the injury involves Crabtree's right leg.
By putting together the information available within the report, one can clearly envision what probably happened.
It appears likely that Crabtree started in motion to his right before the snap. When the play started, he presumptively planted on the toes of his right foot in order to stop his rightward-moving momentum, turn to his left and start upfield.
When he planted his toes, the ground forced his plantarflexed right foot to bend back upward, stretching—and eventually tearing—his contracted Achilles tendon.
Of course, Achilles tendons do not rupture every time an athlete plants his or her foot. It is likely that Achilles tendinitis, offseason deconditioning or some other previous, possibly unknown injury weakened the tendon prior to Crabtree suffering the complete tear.
Regardless of why Crabtree sustained the injury, surgery is necessary for proper repair.
Conceptually, the operation is simple. Though precise details are unavailable to the public, Crabtree's surgeons likely made incisions around the tear, exposed the two torn ends of the tendon, trimmed down damaged tissue and stitched the remaining ends back together. Doctors probably also used relatively thick sutures due to the toughness of the tissue in question.
However, while the procedure is simple, it is not easy. About.com's Dr. Jonathan Cluett writes:
While the concepts of surgery are straightforward, the execution is more complex. Care must be taken to ensure the tendon is repaired with the proper tension -- not too tight or too loose. . .Nerves are located just adjacent to the tendon, and must be protected to prevent nerve injury.
Following surgery, Crabtree will start rehab. Physical therapists will slowly guide him through a progressive sequence of exercises. Each protocol differs, but he will likely begin with simple range of motion and gait exercises, move on to strength training and finish with real-game agility drills.
During therapy, therapists will only advance Crabtree to each next step when he proves his Achilles tendon and calf muscles are up to the task. Doing so prevents overexerting the tendon too soon and before the body cements it into place. It also keeps the strengths of the muscle bodies and muscle tendon in proper balance.
If all goes well, modern-day rehab could very well allow Crabtree to return this season. The ability of therapists to individualize treatment protocols is invaluable and largely responsible for shortened recovery times compared to historical records.
What's more, Crabtree could elect to use platelet-rich plasma (PRP)—one of the many new medical techniques changing the NFL—in an attempt to speed his recovery, though the evidence for its efficacy is controversial.
Dr. Mark Niedfeldt—team physician for MLB's Milwaukee Brewers and associate clinical professor for Family and Community Medicine at the Medical College of Wisconsin—weighed in on PRP in January.
PRP has been studied in augmentation of ACL grafts, Achilles tendon repairs and rotator cuffs. Results have been mixed. . .A study of PRP augmentation of Achilles repair suggested earlier restoration of function.
Nevertheless, no treatment is as important as time—time the 49ers do not have.
After losing wide receiver Mario Manningham to a serious knee injury last December and tight end Delanie Walker to free agency in March, the 49ers receiving core looks quite different than last year's Super Bowl team.
The Anquan Boldin trade will help stem the tide, but as Bleacher Report's Matt Miller and Aaron Nagler discuss, losing Crabtree—who developed an impressive rapport with quarterback Colin Kaepernick in the last half of the 2012 season—represents a serious blow to the San Francisco offense.
That said, should the 49ers make the playoffs, Crabtree could return late in the season for another Super Bowl run.
Dave Siebert is a medical writer for Bleacher Report who will join the University of Washington as a resident physician in June. Medical information is based on his own knowledge except where otherwise cited, and all quotes were obtained firsthand unless otherwise noted.
Follow Dave on Twitter for more sports, medicine and sports medicine.