Seahawks tight end Jimmy Graham was so close to recording his third touchdown of the season last Sunday when he fell awkwardly in the end zone, his right leg folding underneath him, rupturing his patellar tendon. He reached instinctively for his knee, as is often the case with this injury, perhaps anticipating the medical staff’s confirmation that his season had come to a premature close.

Season-ending knee injuries are nothing new in football; more commonly, ligament damage is the culprit, particularly involving the ACL. Patellar tendon injuries are less frequent, and in many ways, they are more challenging to overcome when it comes to returning to an elite level of play.

The postscript on an ACL injury is familiar. The athlete undergoes reconstructive surgery involving placement of a graft within the joint. The subsequent rehab is long and often dull for athletes accustomed to elite-level sports activities, but they are willing to endure it knowing that the success rate -- the chance of returning to their prior level of performance -- is relatively high.

However, there are never any guarantees following major injury. But there is a certain confidence level following ACL surgery based on the sheer number of players who have demonstrated their ability to return to form.

But what is the context for players who undergo surgery to repair a torn patellar tendon?

They certainly don’t have as many peers with whom they can compare notes. While ACL injuries happen at the rate of approximately 30-plus per year in the NFL (only counting those suffered while playing games), patellar tendon ruptures are in the single digits.

And then there’s the matter of returning to play. A study published in the American Journal of Sports Medicine in 2011 examined 22 NFL players who had suffered the injury across a decade. Approximately 79 percent of those players returned to play at least one NFL game. That number seems encouraging; however, the quality of return performance is not easily assessed.

Based on the post-injury history of several notable players, there is at least some cause for concern.

In 2008, Buccaneers running back Carnell “Cadillac” Williams returned to action following a patellar tendon repair on one knee, only to tear the patellar tendon in his opposite knee just a month later. He played three more seasons, the final two primarily in a backup role. Cardinals running back Ryan Williams, a second-round pick in the 2011 draft, suffered a patellar tendon rupture in his rookie training camp. Although he did play in a handful of games in 2012, he never truly got on track with his career (most recently, he was released by the Cowboys this past July). Safety Nate Allen, now with the Raiders, ruptured his patellar tendon as a rookie in 2010 and struggled to return to form until 2013, when he played all 16 games with the Eagles. This September, he suffered another knee injury, which was severe enough to send him to IR/designated for return until he was re-activated in Week 10. And Giants wide receiver Victor Cruz, who tore his patellar tendon last October, was unable to play this season after sustaining a calf injury.

Several variables likely contribute to the challenge of bouncing back from this particular injury. First, the tendon has to be able to withstand significant load to function properly. When the large muscle on the front of the thigh (the quadriceps) contracts, load is transferred through the patellar tendon to its bony attachment on the shin causing movement at the knee. When the foot is on the ground, the quadriceps helps control movement at the knee (for instance, the quad helps keep the knee from buckling when decelerating during running). A patellar tendon rupture occurs when the force placed on the tendon exceeds what it can handle. In order for the tendon to handle such loads after surgery, the repair has to be given adequate time to heal. The early days after surgery are critical to that healing process, and the athlete is required to keep the knee immobilized temporarily in a straight-leg position.

The lack of bending early on helps protect the repair but creates secondary challenges, most notably knee stiffness. The athlete then has to ultimately work through that stiffness to regain normal motion while trying to restore strength. In an effort to minimize stiffness, some surgeons advocate earlier motion. Dr. Lee Kaplan, Chief of Sports Medicine at the University of Miami, is a believer in moving the knee within 10 days of surgery to help counter some of the complications associated with stiffness.

“The inherent stiffness that comes with the repair combined with muscle atrophy can present a real problem for athletes who have to place significant load through their knee, whether it’s a receiver with deceleration and sharp cuts or a lineman who has to push against heavy loads,” Kaplan said. “So early motion combined with early muscle activation is critical.”

Strengthening has to be implemented gradually, however, so as not to overload and risk damaging the healing tendon. Even upon achieving a high level of function, the athlete is often left with some measure of residual weakness. While it may be subtle in appearance to the naked eye, it can show up in the form of diminished power, speed and explosiveness -- qualities highly dependent, in part, on the function of the quadriceps and consequently the patellar tendon.

It’s not only the quadriceps muscle that is affected with this injury; all of the lower-extremity muscles will suffer after an extended dormant period. Kaplan says he relies on early physical therapy for his athletes in order to begin activating all of the muscles potentially affected, even while the quadriceps is limited. Secondary compensation injuries can be a side product of a patellar tendon injury, often occurring on the opposite limb. Cruz, who tore his right patellar tendon, acknowledged as much when he injured his left calf during training camp this summer, according to the Star-Ledger.

“The reason I got the calf [injury originally] was from overcompensation from using the left leg for 10 months in a row. Things like that happen," Cruz said.

Beyond the challenges that accompany the injury and the subsequent repair and rehabilitation, there is also the matter of which underlying factors may have contributed to it. In some cases, the physics of the injury is such that a healthy tendon is subject to overwhelming forces and ruptures. In others, however, the health of the tendon may have been compromised leading up to the point of failure.

“If the underlying quality of the tendon is poor,” Kaplan said, “it may be not only more predisposed to rupturing, but also more problematic when it comes to post-surgical recovery.”

Soon, it will be Jimmy Graham’s story to tell. He underwent surgery Wednesday, according to Seahawks head coach Pete Carroll, who remains optimistic Graham will be ready by the start of the 2016 season. History would suggest that Graham has a good chance of returning to play; however, his performance level upon returning will be much harder to project.