In a healthy hand, finger and thumb movements are initiated by muscles in the wrist. Contraction of these muscles causes a pull on the flexor and extensor tendons, which tug on attached bones to allow the fingers to bend or straighten. Injury to these tendons can render finger joints useless and are particularly common in contact sports, in which players' fingers can become caught on others' uniforms and become stretched beyond their endurance. Similarly, rock climbing and other activities that demand excessive hand strength may also cause excessive outward pressure of the fingers that in turn can tear the tendon.
When a tendon tears, the severed parts slide away from each other as a result of lost tension in the tendon sheath. This makes it impossible for the tendon to heal independently and prompts the need for surgical intervention. Such intervention involves suturing the tendon to reattach the severed pieces and facilitate any other reconnections. It is typically most successful when it occurs within seven to 10 days following the injury.