A guide to the most common NFL injuries, from Achilles tendon tears to concussions

Injuries can play as big a role in an NFL team’s successes or failures as the best game plans. Depth is crucial during a rigorous 17-game regular season that’s preceded by a month of training camp practices in hot conditions and three preseason games as players try to make their team’s 53-man active rosters. So being able to navigate injuries and ailments to key players could make all the difference between a team seeing its season sink or making the playoffs.

Here’s a look at some of the most common injuries suffered by NFL players throughout the season: Achilles tendon tears The Achilles is the longest and strongest tendon in the body and stretches from the heel to the calf. It’s a springy band located behind the ankle and just above the heel that helps players push off their feet, jump and accelerate. Due to overuse or excessive force placed on the tendon, it can tear or rupture.

Surgery is typically necessary to reconnect the ends, sidelining a player for several months because of the extensive rehabilitation needed. ACL/PCL/MCL/LCL tears The anterior cruciate, posterior cruciate, medial collateral and lateral collateral ligaments are all located in the knee and serve different purposes. The ACL connects the thigh bone to the shin bone in the front of the knee.

While a sprain could sideline a player for a few weeks, a tear can end a season. The PCL is located behind the ACL, crisscrossing it to form an “X” in the center of the knee. The MCL connects the thigh bone to the shin bone on the inner side of the knee, while the LCL connects the thigh bone to the top of the lower leg, or fibula, and is located on the outer side of the knee.

Concussions A concussion is a brain injury caused by a hit to the head or a sudden movement that makes the head and brain shake violently. Symptoms may include headaches, neck pain, nausea, dizziness and sluggishness. The NFL has been regularly testing and upgrading helmets for players to help reduce the risk of concussions, with position-specific helmets for quarterbacks and offensive and defensive linemen approved by the NFL and the NFL Players Association.

Several players also have worn Guardian Caps, which are soft, protective helmet covers. Chronic traumatic encephalopathy, or CTE, is a degenerative brain disease that has been linked to concussions and can only be diagnosed posthumously.