Three weeks ago in their playoff series with the Miami Heat, Boston Celtics guard Rajon Rondo dislocated his elbow. Rondo was taken to the locker room, where doctors put the joint back in place.

Incredibly, Rondo returned to the game. In an even more impressive testament to his toughness, Rondo was back on the floor the very next night.

Rondo’s story brings up an important distinction I point out to my athletes every day. Learning the difference between pain and injury is essential, especially for athletes trying to get the most out of their bodies.

So what’s the difference between pain and injury? It’s not as simple as it might seem. It turns out there are some conditions in which it is simply not safe to play through pain.

Fractures are an easy example. Play with a broken bone that is not properly splinted, and you risk displacing the fracture. If the bone fragments move relative to each other or even if they move apart, then the bone might require surgery to make sure it heals properly. In some cases, displaced fractures don’t heal at all.

Another situation in which athletes should exercise caution is with joint instability. Many athletes tear their ACL each year. This ligament is the primary structure giving the knee much-needed stability for cutting and changing directions.

Some athletes with ACL tears can feel their knees buckle when they put too much pressure on them. This is a sign of what doctors call instability. In short, the joint’s alignment is becoming abnormal for a split second before the muscles can put it right again.

No problem, right? Wrong. That momentary instability can cause damage to the articular surfaces of the knee. Torn cartilage inside the knee can complicate repairing the knee and lead to arthritis later in life.

These are just a few of the situations in which an injury might make it unsafe to return to sports, no matter how tough the athlete is. With other conditions, like one called patellofemoral syndrome of the knee, the nature of the injury means that playing through the pain is safe.

Arthritis is another good example of pain without injury. Exercising with aching knees can be very painful. Despite this, exercise does not hurt the joints. In fact, it can even prevent the condition from worsening.

So before you suck it up and get back on the court or field like Rajon Rondo, check with your sports medicine specialist. Make sure you know whether you have an injury or are just suffering from pain.

Dr. James Glazer is a sports medicine physician for Coastal Orthopedics and Sports Medicine in Freeport. He serves as a consultant for the U.S. ski team.