Tendon injury

Most mountain biking tendon injuries occur in the fingers. The injury usually occurs during a fall, either from jamming the finger or bending it back too far. Rarely, a tendon injury results from a direct blow, such as smacking your knuckle between the handlebar and a tree.

Tendon injuries range from mild strain to complete rupture of the tendon. With a mild strain, there is pain with motion, but no swelling, deformity, or limitation of motion. With a rupture, signs of serious injury (swelling, inability to use, severe pain, or limited motion) will be present.

A ruptured tendon won't heal properly unless managed by the doctor. Even minor tendon injuries can result in tendinitis and long-term pain. This biker (riding without bar ends), veered into an aspen. The index finger was hit directly over the middle knuckle (proximal interphalangeal joint or PIPJ). He's trying to straighten the finger, but the middle knuckle keeps popping up. This is a rupture of the central slip of the extensor tendon.
Deformity due to torn tendon.
Deformity due to torn tendon.

See the doctor if:
    there's deformity or severe swelling
    the part can't be used normally after an hour of rest
    there's continued severe pain
    there's numbness or weakness below the injured area.

Immediate care:
The treatment of a sprain is "RICE:" Rest, Ice, Compress, and Elevate. Immediately elevate the injured part and apply an ice bag. Once the area is thoroughly cooled, apply an elastic wrap (if practical) to compress the injury. Finger tendon strains may need to be splinted.

Ongoing care:
Rest the injured part for two days. If it's a finger injury, use a splint. For the first 48 hours, repeat ice and elevation 1/4 of the time (for example, 30 minutes of ice every two hours). As the pain subsides, return to activities. The rule is: "If it hurts, don't do it." You can usually stop using the elastic wrap after 2 to 3 days.

Watch for:
If the injured area doesn't improve promptly, see the doctor.