Michael W. Bowman M.D. FACS
The flexor tendons are the tendons on the palmar side of the hand that bend or flex the fingers and thumb. There are two flexor tendons for each finger and one flexor tendon for the thumb. Tendons attach muscles to bone. The muscles for the flexor tendons of the hand are located in the forearm and become tendons just prior to the wrist joint. The long flexor tendon (flexor digitorum longus or FDL) attaches to the end of the finger at the last bone, or distal phalanx. It bends the last joint, or DIP joint. The short flexor tendon for each finger (flexor digitorum superficialis or FDS) attaches to the middle bone, or middle phalanx, of each finger. It bends the middle joint or PIP joint. Each flexor tendon is a long but tough band-like structure made of collagen. It is covered by tenosynovium, which makes the surface smooth for gliding.
The flexor tendons are contained in a tunnel called the flexor tendon sheath. At the wrist (carpus in latin) this tunnel and sheath are called the carpal tunnel. In the hand the sheath separates into 5 separate flexor tendon sheathes for each individual finger. In each finger flexor tendon sheath there are bands of thickened tissue called pulleys that help hold the tendon in place to avoid bowstringing of the tendon out of place with grip. The anatomy and mechanics in this finger flexor tendon sheath are very complex. Both the FDS and FDP tendons slide back and forth with grip and extension. The two tendons also slide past each other during different activities. The FDS tendon is more superficial in the wrist and palm. It splits near the middle PIP joint. The longer FDP tendon travels underneath the FDS and goes through that split in the FDS at the level of the PIP joint. It then travels out to the end of the finger where it attaches. This segment of the flexor tendon sheath containing the pulleys and where the flexor tendons move past each other is called “no man's land” for the difficulty of operating in this area. Both flexor tendons and the pulleys must operate correctly for you to completely flex your finger.
Lacerations on the palm side on the hand involving the flexor tendons can be devastating to the function of the hand. Repair and restoration of function after a flexor tendon injury is most often performed by hand surgery specialists for this reason. Just like fractures, all lacerations to the hand and flexor tendon lacerations are different and unique. Lacerations may be classified by location. There are 5 different zones from one to 5, starting at the fingertip and moving proximally towards the wrist. Each zone has its own problems and is treated differently. Lacerations may be classified by orientation of the laceration (longitudinally or transverse) and whether they are clean and sharp(knife or glass) or jagged (table saw or chainsaw). The wounds may be clean or dirty. There may be associated injuries such as a fracture, nerve injury or loss of skin and soft tissue coverage. Surgical planning must also take into account arthritis or stiffness of the surrounding joints, the age and general health ofthe patient, circulation and issues such as smoking or malnutrition. The ability of the patient to cooperate with the critical but complex postoperative therapy is also crucial for the success of flexor tendon surgery.
In general, treatment of flexor tendon lacerations is surgical. Exceptions may be when only the FDS is cut, leaving an intact and functional FDP, which is capable of flexing the finger. Another exception may be a small partial laceration of the flexor tendon, which is still functional and may require only therapy. A patient who has very stiff arthritic finger joints that are incapable of motion may not benefit from flexor tendon repair. Flexor tendon surgery is usually performed as an outpatient with general anesthesia or axillary block anesthesia. The laceration wound is explored to evaluate and repair any possible damage to other structures such as nerves or arteries. If a fracture is present, that is usually stabilized first by inserting small pins or screws. The flexor tendon sheath is opened in the area of the laceration and the tendons inspected. The exact repair is different in each zone. In zone one, near the end of the finger the FDP tendon may be repaired directly back to the bone with a small anchor. In zone 5, a simple repair of the tendon may be completed. In zone two or” no man's land”, the anatomy is most demanding. Usually both tendons have been lacerated as well as a pulley. In most cases both tendons must be repaired as well as the flexor tendon sheath and pulleys. This can be most challenging. Often the flexor tendon will retract into the palm or forearm due to tension from the muscle. The tendon must be retrieved and woven down the flexor sheath in order to complete the repair. The tendon and sheath must be handled delicately under magnification in order to avoid damage that will increase the risk of scar tissue or adhesions of the tendon.
After surgery is completed the hand and wrist are placed in a protective cobra splint on the top or dorsum of the hand which flexes the wrist. This is to protect the completed repair. The tendon will take 6 weeks to heal and must be absolutely protected during this time. The patient is instructed not to perform any active gripping during this time. Active gripping of any finger may pull apart and the repaired tendon, since the flexor tendons work together in concert. Basically the patient is not to use the hand all for any lifting or gripping during the 6 week period.
A very complicated but elegant program of therapy has been developed for treating flexor tendon repairs. This flexor tendon protocol is designed to allow motion of the repaired flexor tendons in the sheath without putting excess tension on the repair and pulling apart the repair. Too much motion or stress will result in tearing apart the repair. No motion will result in scarring of the flexor tendons and no motion. There must be a delicate balance between these two. Compliance with the therapy program is absolutely critical to the success of the repair. During this program the patient is allowed supervised active extension of the finger and flexion of the finger by the therapist or rubber bands attached to the finger. There is no active gripping during this time. After 6 weeks the tendon repair is sufficiently healed to remove the splint and start active range of motion and gripping exercises. In approximately 20% of our flexor tendon repair cases and additional surgery may be required to free up the flexor tendon from scar tissue (tenolysis), release of joint contracture for stiff joint or repair of a flexor tendon repair that has failed.
In cases of chronic rupture of the flexor tendon and after failed primary flexor tendon repairs a two-stage flexor tendon reconstruction is required. In that case thee scarred, damaged tendon is removed and replaced with an artificial Kevlar and Silastic tendon which is attached to the bone and muscle. Approximately 3 to 6 months later the artificial tendon is removed and replaced with a tendon graft from the leg. The hand must be protected for 6 weeks after each surgery. Dr. Bowman drained with Dr. Hunter, the inventor of this active tendon, in Philadelphia, was responsible for some of the clinical research regarding its use and was the first surgeon in Western Pennsylvania to use the active artificial tendon.