Flexor Tendon Injuries

What are the flexor tendons?
Flexor tendons are the elastic cord like structures which arise from the muscles in the forearm, running into the hand, and attached to the bones of the fingers. When the muscle contracts, the tendons pull on the bones of the fingers to allow the hand to close into a fist.

In the fingers, the tendons run within a fibrous tunnel made up of pulleys. This tunnel is designed to prevent the tendon from pulling away from the bone when a force is applied. There are two flexor tendons to each finger and one to the thumb. In the finger, the deep tendon has to pass though a gap in the superficial tendon to run smoothly past it and on to the end of the finger. The two tendons fit very tightly into the tunnel, making repair of these structures in the fingers particularly tricky for surgeons.

What is the cause? 
There are two ways that the flexor tendons can be injured:

1) Closed injuries – if too much force is applied to a tendon, then it can rupture away from the bone and spring back up the finger or even into the forearm. A good example of this is the ‘jersey finger’ which rugby players are prone to. Tendons may also rupture if the tendon itself is diseased or weakened for other reasons, for example in rheumatoid arthritis.

2) Open injuries – These are by far the more common type of tendon injury in Fife, and are caused by penetration of the tendon by something sharp, usually a knife or piece of glass.

What are the symptoms?
The main symptom (other than pain from the wound) is an inability to pull the finger into a full fist, with weakness of grip strength. If the superficial tendon only is divided, or if the tendon is only partially divided, then even these symptoms may not be present.

Within the digits, the nerves and blood vessels to the fingers lie very close to the tendons, and there is often damage to these structures in open injuries, giving rise to some altered sensation within the finger.

How is the diagnosis made?
The diagnosis is made on clinical examination. With the hand relaxed, the fingertips all run in a curve, known as the normal lie of the hand. The position of the lie changes with a change in wrist movement, and this usually makes it obvious if there is a major issue with a tendon.

Sometimes the diagnosis is more subtle, with the hand appearing relatively normal. In this case, examination of the finger may reveal an inability to bend either the fingertip joint of the finger, or to bend the knuckle joint of the finger with the other fingers straight.

What is the natural history?
Tendons will only heal if the two ends of the tendon are opposed. When a tendon is cut, the muscle contraction pulls one end of the tendon away from the other end, leaving a gap of anything from a few millimetres to 15cm! Tendons therefore never heal when they are completely divided and separated.

The end result of a tendon injury which has not been treated is generally poor. People with an injury to one of the two finger tendons often have good overall function, but grip strength is reduced compared to normal. If both tendons are severed, the finger points straight and cannot be moved. The finger then catches on things and generally gets in the way of the function of the hand.

Before modern surgery techniques were developed, loss of both tendons in a finger generally resulted in an amputation of the finger.

What is the treatment? 
Surgical repair is almost always recommended for a tendon injury, provided the diagnosis is made within the first few weeks. At operation, the two tendon ends are opposed, and a strong suture known as a ‘core suture‘ is used to tie the ends of the tendon together. The core suture is made of a tough nylon or polymer thread, and used to ‘grasp‘ the tendon on either side. The repair is only as strong as the suture that holds it together, and surgeons have spent years trying to work how how best to do this.

Anyone who has mended an item of clothing will know that a single stitch will snap, but it the stitch is repeated over and over then the repair is much stronger. In addition, if the stitch is placed too near the hole, then it is liable to cut out. The same is true for flexor tendon repair – surgeons use 4 strands of suture rather than 2, and the sutures are placed well away from the cut ends.

The 4-strand Adelaide repair. Dotted line represents suture within the tendon

The Adelaide core suture, illustrated above in a pig’s tendon, is the one used in Fife to repair a flexor tendon. There is usually an additional running stitch around the edge of the tendon to prevent it from fraying. After the tendon is repaired, a Plaster of Paris cast is applied. It is usually quite safe to move the fingers within this plaster splint, and hand therapy is commenced within a week of the surgery. The therapist will remove the plaster and make a splint for the hand, with the aim of starting to move the tendons without putting too much strain on the repair. The splint prevents the fingers from fully straightening and loading the repair.

A typical splint that may be used

Hand therapy aims to balance protection of the tendon within the splint, with gradual loading or movement of the tendon with exercises. The splint is usually worn all the time for the first 6 weeks following repair and at night only for another 6 weeks. It is usually safe to start using the hand without restriction by 3 months after the repair.

What are the complications of treatment?
Flexion contracture of the finger – Although therapy aims to regain full movement in the affected finger or fingers, most patients end up with slight loss of ability to fully straighten the finger after flexor tendon repair. This does not usually impact on function or outcome.

Rupture of the tendon repair – Despite the care taken to produce a strong repair and to protect the repair while it heals, some tendon repairs rupture. This can be a technical problem with the repair, or more commonly it results from an inadvertent fall or sudden unexpected loading of the repair. Rupture of the repair is usually accompanied by a snapping sensation, and immediate loss of movement in the finger. This complication can be a bit of a disaster for the tendon repair, and may require surgery to restore the repair.

Adhesion formation – Where movement is poor, or where the initial injury was a crush rather than a cut, the tendon can scar down to its surrounding tissue. This makes movement of the tendon very limited, although strength may be unaffected. Surgery is recommended where adhesions are a problem, and this is done well after the tendon has healed, in order that immediate full movement can be started following the surgery, and further adhesions prevented.

General surgical complications – You can read about general complications of surgery here.

Does anything else affect tendon healing?
Smoking – Smoking unfortunately has a massive negative impact on tendon healing, and it is really important to stop smoking in order to allow the tendon to heal. Poor results and ruptures seen after this type of surgery are often related to smoking.

Diabetes – Poor blood sugar control should be avoided in order to maximise healing potential and avoid adhesions and infection.

General diet – It is worth supplementing vitamins C and D after a tendon repair in order to optimise tissue healing.

© Fife Hand Service 2021

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