Muscles are attached firmly to bone and connective tissue at one end and generally insert in bones via tendons. Tendons are white fibrous cords that are lined with a loose tissue (paratenon) and which sometimes run through a fibrous tube (tendon sheath). Tendons have the ability to glide over bone and through tissues. Muscle contraction is therefore transmitted via the tendons causing intervening joints to move. Muscles that bend the fingers and wrist are termed "flexor" and those that straighten the fingers and wrist, "extensors".
Tendon injuries are very common and usually caused by accidents involving glass or knives (open injury). These injuries can cause damage to single or multiple tendons as well as neighbouring structures such as nerve, blood vessels and bone. Tendons can also snap if overstressed such as occurs in sports (closed injury). The complete division or detachment of a tendon causes immediate loss of its function, which is permanent unless it is repaired. Patients are usually immediately aware of difficulty in moving a finger but some injuries may be less obvious where there is some duplication in the function of muscles. Partial cuts of tendons will not be obvious but can be suspected if use of the tendon causes pain.
Assessment of tendon injuries requires careful examination during which the doctor will ask how the injury occurred and then systematically tests each and every tendon as well as nerves that may have been damaged. When examining the limb, the doctor will look for the following signs.
Position The exact position of the cut will indicate
which structures may have been injured. The doctor will also consider
the nature of the injuring agent. Slicing injuries from knives
and saws produce fairly predictable damage but stabbing injuries
particularly from glass can damage structures at some distance
from the site of entry.
Posture When relaxed, the hand lies in a characteristic posture
with the thumb-tip held slightly flexed and fingers held in a
cascade. Any change in the resting posture can suggest tendon
or even nerve damage.
Passive movement Gentle pressure on each fingertip can
reveal loss of tension or floppiness of a joint. Tendon function
can be assessed by gentle pressure over the muscles in the forearm,
which will normally cause some movement of the relevant tendon.
An alternative way of testing the finger tendons is for the doctor
to move the wrist, which causes finger movement.
Active movement The best way of testing a tendon is for
the doctor to ask the patient to use the tendon by moving or tensing
the relevant joint.
Treatment
Not all tendon injuries need to be repaired. In particular, closed ruptures of the extensor tendons such as cause a mallet finger are probably best managed by a period of splinting unless there is a large associated fracture fragment.
The situation is, however, different for open injuries. If the
doctor considers it likely or even possible that there is tendon
or nerve damage, arrangements will be made for either (i) further
examination by a more senior or specialised doctor and/or (ii)
surgical exploration of the wound. This type of surgery is generally
undertaken in Orthopaedic or Specialist Hand Units because of
its complexity. Arrangements may therefore be made for referral
to this Unit to enable the injury to be explored and repaired
by the most appropriate Team. If surgical exploration is indicated,
it should be performed soon after injury but it is not essential
that it occur on the day of injury.
If a cut tendon is not repaired, its function is permanently lost. This may cause deformity, loss of movement and weakness. Delay in treatment especially beyond a month can make subsequent attempts at repair difficult or even impossible depending on the length of delay and the tendon(s) injured. If unrepaired, the tendon ends retract and get stuck in scar tissue; the muscle shortens and withers; the tunnels through which the tendons run shrink; and the joints affected can stiffen. Late secondary reconstruction can be performed but the surgery is more complex and the results are poorer.
Surgery
Exploration of the wound will often occur with the patient awake (local or regional anaesthetic) but more complex injuries would be explored whilst the patient is asleep (general anaesthetic). The surgeon will apply a tourniquet to the limb to prevent bleeding, which makes the operation much easier. It is likely that the wound will be made larger by the surgeon to enable a thorough inspection of the structures in the vicinity as well as to retrieve tendon ends that tend to spring apart when cut. The operation can be technically demanding particularly with the flexor tendons and involve microsurgery if nerves require repair. The cut tendons are retrieved and stitched toget