The hearts of Green Bay Packers fans broke this week when they learned receiver Jordy Nelson, a favorite target of MVP quarterback Aaron Rodgers, will be sidelined for the year with a “significant right knee injury.”

The 30-year-old suffered the season-ending injury on Sunday during a preseason match against Pittsburgh, where the Pack lost 24-19. While missing an offensive weapon who put up more than 1,500 receiving yards last year will no doubt hurt Green Bay, it gets one wondering about what kinds of injuries NFL players suffer most often.

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Recently, there’s been a lot of talk about concussions in football. But from what we can gather, head injuries aren’t the most common type of injury in the rough and physically demanding sport.

However, the kind of injury Nelson suffered is.

The Most Common Football Injuries

1. Knee.

According to the physical therapy site SimpleTherapy.com, knee injuries were the most common type of injury suffered by NFL players last year, accounting for more than 20 percent of all injuries.

Knee injuries are common at all levels of football, as there are many moving parts in the knee that can be torn or strained when a player is tackled while running. Common injuries are tears to the meniscus, PCL, MCL and ACL.

An ACL tear, like what happened to Vikings running back Adrian Peterson, often has a life-changing effect on a player. Not many bounce back like Peterson did, as surgery and considerable physical therapy are required for healing.

2. Ankle

The second-most common injury on the SimpleTherapy.com list is ankle injuries, which totaled about 15 percent of all injuries in the league last year. Unlike knee injuries, which can easily end a player’s career, ankle injuries have a much broader range of severity.

Players can suffer a minor pull and be back on the gridiron in no time. However, some sprains – such as the high ankle sprain – can sideline a player for a season.

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3. Upper Leg

The next most-common injury on the list is also below the waist. SimpleTherapy.com says upper leg injuries accounted for almost 12 percent of injuries last year.

Of those injuries, hamstrings were by far the most common, with about 100 of those documented. Hamstring tears can occur when a player isn’t properly warmed up and tries to push his legs to run as fast as possible.

The next most common upper leg injuries are wounds to the thigh and quadriceps.

4. Shoulder

Now we’re moving above the waist. Shoulder injuries added up to be about 9 percent of injuries suffered by NFL players last year.

Common injuries are AC joint injuries and dislocated shoulders. These can range in severity and aren’t often seen as season-ending.

5. Head

Injuries to the noggin totaled about 7 percent of injuries suffered last year. Even though players wear all sorts of protective gear around their heads, injures to the head are quite common.

The NFL said that during the 2014 regular season, players suffered 111 concussions. While that number is down when compared with stats from previous years, it’s still concerning.

The concern stems, in part, because concussions occur at all levels of the contact sport. Moreover, concussions – or brain trauma – can sometimes take weeks to recover from, and the effects of the injury are lasting, affecting memory, brain function and even mood/personality.

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With pro players taking 900-1,500 blows to the head every year, it’s little wonder some young NFL players are retiring early and others are asking the league to do more to prevent concussions.