It's kept Davi Millsaps out for a year...and counting. Ryan Villopoto is not racing in Motocross because of it. James Stewart almost bowed out of the final Supercross race in May because of it.

Knee injuries.

Motocross riders don't frighten easily but the thought of a knee injury, well, let's just say it's something they don't talk about. Motocross knee injuries can be mild allowing the rider to return to action or debilitating putting a question mark on their career and even the future health of that knee.

Dr. Paul Ruesch, an orthopedist with Eastside Orthopedics & Sports Medicine in Milwaukie, OR, said the most common injury a motocross rider faces to his or her knee would be a sprain or a bruise. This, he said, is a more simplistic type of injury but it obviously moves up the scale to ligament damage, fractures and knee dislocation.

"The bruise can be a result of bumping into another rider or a fall," he said. "I've seen tibia fractures and knee injuries occur when they go off a jump and their foot comes off the peg or putting a foot down in a turn."

It's rare for knee damage to occur when the rider remains on the bike. Typically, knee injuries result from some type of impact to the leg or knee with the ground. The more severe knee injuries in Motocross include ligament ruptures, bone fractures and blood vessel or nerve damage.

Millsaps tore his ACL while practicing prior to the 2014 Supercross season so did Marvin Musquin. Millsaps has not returned to action but Musquin is back racing in Motocross. Last year, Stewart tore his ACL which many feared he damaged again this year in Round 16 of Supercross when he jammed his left foot in the dirt trying to pass another rider.

Contact sports can be brutal to the knee which is made up of four ligaments all of which can suffer from a strain, tear or rupture:

  • ACL - Anterior Cruciate Ligament
  • PCL - Posterior Cruciate Ligament
  • MCL - Medial Collateral Ligament
  • LCL - Lateral Collateral Ligament

The ACL is one of two major ligaments in the knee along with the PCL. Both of these ligaments connect the femur or thigh bone to the tibia - the larger bone in the lower leg. The LCL connects the thigh bone to the fibula - the smaller bone in the lower leg - on the outer side of the knee and the MCL connects the thigh bone to the tibia (or shin bone) on the inner side of the knee.

Graphic: WebMD.com

Of the four, the ACL is the most common. According to WebMD.com, 95,000 people injure their ACL every year. Ruesch said an ACL rupture can be devastating but even worse a knee dislocation can tear multiple ligaments. Ligaments allow the knee to move in a proper and specific direction but when stretched into abnormal motions that leads to a rupture. Effects include, of course, immediate pain and later in life arthritis and instability of the knee.

In addition to pain, the other symptoms to a knee ligament injury include swelling, a feeling of looseness in the knee and even a loud snap at the onset of the injury. The ACL and LCL often require surgery, Ruesch said, however the MCL does not require it nor does the PCL because current reconstruction efforts to that ligament have not been perfected yet.

Ruesch said it's a tough call on whether an injury to a knee ligament is career ending.

"You can on some level equate the Motocross athlete to the football athlete," he said. "They are collision sports. Not everyone comes back from that injury. I would say probably 75 to 90 percent of people can come back."

Returning to a normal life off the bike depends on the ligament injury as well. Of course, rupturing more than one ligament is harder to rehabilitate. Add associated cartilage injury to the severity of the injury and the rider is looking at even longer lasting effects.

Ruesch said knee braces, which many, if not all riders wear, especially in races, provide some protection and are better than nothing. However, with the amount of energy absorbed by the knee during an impact a Motocross knee brace won't stop an injury. Stretching prior to riding doesn't help much either.

Ruesch said the best way to avoid knee injuries when riding a dirt bike is of course to be cautious and not to take undo risks. Additionally, riding past the point of fatigue can get you into trouble because muscles don't work as fast or effectively.

"Most skiing accidents occur when a skier is fatigued and gets a little bit lazy and puts their knee in a risky position," he said. "Mechanically if the (Motocross rider) is fit or at the peak of (physical exertion) their muscles will be strong and they won't put their knee or leg into a bad position."

Written By: AndrewT