Greg Childs injury: Vikings WR suffers "extremely rare" dual kneecap blowout [VIDEO]

Blowing out one knee is bad. Blowing out two? It'll be cause for celebration if Childs ever plays an NFL down.

Blowing out one knee is bad. Blowing out two? It'll be cause for celebration if Childs ever plays an NFL down.

SEE ALSO: Paul Allen's "No!" call the greatest of all time, says [VIDEO]

During a scrimmage on Saturday night, Vikings rookie receiver Greg Childs, the team's fourth-round pick in this year's draft, jumped to catch a pass that was thrown slightly behind him. The ball sailed over his head and Childs crashed to the ground. Though nothing looks particularly amiss during impact, he immediately began screaming and clutching his right knee -- the same one he seriously injured less than two years ago while playing at the University of Arkansas (footage is below the jump).

Childs was carted off the field, and fans assumed the worst -- a possible ACL tear in the right knee. But hours later, word began circulating that Childs's injury was even worse than that. Turns out, he had somehow suffered patella tendon (a.k.a., kneecap) tears in both knees.

[jump] How rare is that injury? A 2003 academic paper entitled "Spontaneous Bilateral Patellar Tendon Rupture In An Otherwise Healthy Patient" characterizes it as "extremely rare in a healthy individual, with fewer than 15 cases described." Other academic studies conclude full recovery from a single patella tear is impossible.

Vikings blog Daily Norseman discusses the one other known case of football-related dual kneecap blowout:

It's a bit of a rarity to see a player injure both of their knees, particularly if it happens on one play. Chicago Bears' receiver Wendell Davis had something similar happen back in 1993. He was attempting to catch a pass on the bad turf of Veterans Stadium in Philadelphia, and in the process of jumping for the pass managed to blow out both of his knees on the same play. I can't get a handle on exactly what Davis injured. . .his Wikipedia page says that he tore both his patellar tendons, but other sources say that he tore both ACLs.

That was the last game Davis played in the NFL. . .it happened five weeks into the 1993 season, and not only did Davis miss the rest of the 1993 season, he also missed the entire 1994 season as a result. He attempted a comeback with Indianapolis in 1995, but never played a game for the Colts.

The patella tendon.

The patella tendon.

Childs, unfortunately, has a history of knee injuries. ESPN Kevin's Seifert provides some details:
Another factor working against Childs is that he tore the patellar tendon in his right knee less than two years ago, an injury that essentially allowed the Vikings to get him where they did in the draft.

Childs was fast becoming one of the best college receivers in the country until he was hurt a little more than halfway through his junior season in 2010. He wasn't the same as a senior last year, limping noticeably during Arkansas' first preseason practice and struggling to hang onto the ball.

Childs finished with only 16 catches and 192 yards in 2011 while Jarius Wright, his friend since childhood who was also drafted this year by the Vikings, became the go-to Razorbacks receiver.

Childs had surgery yesterday. Coach Leslie Frazier told reporters Childs was "distraught" following his injury, but vowed to make it back on the field.

"Coach, I'll be back. I'm going to do it just like I did before. I'm going to work as hard as I can," Childs said, according to Frazier.

Without further ado, here's footage of Childs's injury: