Anatomy
The flexor tendons are found on the palm side of the hand.  They are connected to the forearm muscles that move the fingers.
The tendons emanate from the ends of these muscles and travel through a canal at the wrist called the carpal tunnel, traverse the palm, and then travel on the palm side of the fingers to attach to the bone at the end of the fingers.  When the muscle contracts, this entire unit shortens and the finger therefore flexes, or bends, down to the palm.
Each finger has two flexor tendons; one travels to the bone at the end of the finger (the distal phalanx), and the other travels to the middle joint of the finger (the middle phalanx) and attaches to this bone.  There is a separate muscle-and-tendon unit for the thumb, which has but a single flexor tendon.

Injury
Deep lacerations of the wrist, palm, or fingers can partially or completely divide the flexor tendons.  Should both tendons be completely divided, the finger is unable to bend at any of the joints.
Flexor tendons have an elastic property, especially the end attached to the muscle in the forearm.  When they are divided, they tend therefore to retract and separate further.

Treatment
A divided tendon in the finger, palm, wrist, or forearm should be repaired in order to restore the ability of the finger to flex (bend toward the palm).

Surgery
Because of the retraction of a tendon after it has been divided, repair of the tendon requires an incision that must be extended some distance away from the laceration.  Once the tendon is located, the two divided ends are brought together.
There are a great many techniques for repairing the tendon ends, but almost all of these involve using a "core" or internal stitch of a strong nylon or braided material and a peripheral or edging suture composed of a finer material.

Patented Device
Our group has developed and patented a new device called a tendon suture anchor.  This is attached to each end of the divided tendon and firmly holds the two tendon ends together.  This device almost doubles the strength of the tendon repair.

Healing after Surgery
Therapy is an integral and essential part of the postoperative regimen.  If a repair is strong enough, then movement of the finger can be begun within days after surgery.  This avoids finger stiffness and allows the tendon gliding to be restored.  Finger stiffness and lack of gliding are the two most common and severe complications, resulting in loss of flexion function of the involved finger.  Therapy is generally needed for several months following repair.
Customary or normal use of the finger or hand can usually start two to three months following surgery.
If movement is too vigorous or forceful, then the sutures will break and the tendon repair will come apart.  If therapy is not vigorous enough, then the finger will become stiff.  A strong repair that will withstand flexion forces, and an experienced therapist who will safely provide the exercise program, are therefore essential.