74. Wrist
From Primary Surgery
Contents |
74. The wrist
74.1 Introduction
One of the ways in which we use our hands is to protect our bodies from falling. Our outstretched hands are very good at doing this, but in doing so our wrists are particularly likely to get hurt in a variety of ways, which depend on how old we are. This chapter is entirely concerned with these injuries.
0-5 years
A young child usually has a greenstick fracture of the lower third of his radius, and sometimes of his ulna also (73.6a). If his injury is severe, he may break both his forearm bones transversely just above his wrist (73.8).
5-10 years
In an older child fractures of the lower quarter of the radius and ulna are more often complete (73.8), and the fragments may overlap.
10-15 years
A child of this age typically has a fracture separation of his distal radial epiphysis (73.9).
Adults
An adult is liable to two major groups of fractures at the lower ends of his forearm-those caused by hyperextension (common) of his wrist, and those caused by hyperflexion (unusual). These are most easily distinguished in a lateral X-ray.
(1) Hyperextension fractures comprise: (a) The common hyperextension (Colles) fracture in which the fracture line runs across the lower end of the radius parallel to the articular surface, with the distal fragment displaced posteriorly. (b) The much less common posterior marginal fracture in which the fracture line enters the joint. (c) Sometimes the distal fragment of the radius is comminuted.
(2) Hyperflexion fractures are rare. A lateral X-ray shows the fracture line running obliquely across the distal end of the radius. In (a) Smith's fracture, it does not enter the joint, but in (b) Barton's fracture, it does.
There is also a group of minimal fractures, including fractures of the radial styloid in which manipulation is rarely needed, and which you can immobilize as for a hyperextension fracture.
Falling on an outstretched hand occasionally causes injuries
of the carpal bones: (1) The distal row of carpal bones can dislocate
on the proximal row (intercarpal dislocation, 74.5), or (2) the
lunate can dislocate. The wrist is seldom sprained, so that a sprain is more likely to be a fracture of the scaphoid or of the
triquetrum. Fractures of the triquetrum are difficult to see in
an X-ray, so they are seldom diagnosed. Fortunately, they heal
spontaneously.
Occasionally the wrist can become dislocated on the forearm. Reduce the dislocation immediately by exerting traction in the long axis of the forearm and hand.
EXAMINING THE WRIST
Observe the patient's wrist for swelling and deformity, and feel for warmth and tenderness.
Dorsiflexion
Ask him to put the palms of his hands together, as in a position of prayer, and then to raise his elbows. This will let you compare the dorsiflexion in his wrists.
Palmar flexion
Ask him to put the backs of his hands together and to depress his elbows. This will allow you to compare palmar flexion in his wrists.
Other movements
Ask him to tuck his elbows into his sides. How far can he pronate and supinate them and deviate them in a radial or ulnar direction?
CAUTION! Have you examined his elbow? He may also have a fracture of the head of his radius.
SIGNS FOR PARTICULAR FRACTURES OF THE WRIST
Extension fractures (Colles fractures)
Look at the back of the patient's wrist. Put the tip of one of your index fingers into the gap between his radial styloid and his wrist. Put the tip of your other index finger into the gap between his ulnar styloid and his wrist. This will show you the position of the two styloids clearly. The radial styloid is normally distal to the ulnar one. It is displaced proximally in an extension fracture. Its replacement is a useful sign of adequate reduction.
Examine both his wrists as if you were feeling his radial pulses. Has the normal concavity in front of his injured radius been filled out by a tender haematoma?
Is there a dinner fork deformity of his wrist? This is only present if backward displacement is gross, and is also seen in fractures of the lower quarter of the radius and ulna in children.
Flexion fractures (Smith's and Barton's fractures)
Ask him to hold out his arm. Is his hand displaced anteriorly on his forearm, as in Fig. 74-7?
Fractures of the scaphoid (74.4)
Three signs for this fracture are shown in Fig. 74-2.
(A) Hold the patient's hand with your left hand, and put the tip of your finger in the normal depression just distal to the end of his radius, between the two extensor tendons of his thumb (his `anatomical snuffbox'). His scaphoid will be directly under i t. Deviate his hand towards his ulna, and press. If he winces, he has probably fractured his scaphoid. The radial nerve passes over the snuffbox, and having this pressed can also be painful, so compare both sides carefully. Occasionally, there is mild swelling in the anatomical snuffbox.
(B) Does moving the patient's wrist cause him pain only at the extreme of its range?
(C) Ask him to clench his fist and deviate it radially. Percuss the head of his middle metacarpal. This is painful when his scaphoid is fractured. There may also be tenderness over the knuckles of his index and middle fingers, but none over those of his ring and little fingers.
Carpal dislocation
Both carpal dislocations (intercarpal dislocation and dislocation of the lunate) produce a painful, swollen, Immobile wrist. In addition, if a patient's lunate is dislocated, he may have any of these four special signs.
(1) Is there tenderness and an abnormally deep hollow on the back of his wrist just distal to his radius, in line with his first finger? Normally, the lunate occupies this hollow. If the lunate is dislocated this hollow is deep and abnormally tender.
(2) Ask him to clench both his fists. Compare their backs. If his middle metacarpal looks slightly shorter, his lunate may be dislocated (or his middle metacarpal may be fractured).
(3) Feel the volar aspect of his wrist, between his thenar and hypothenar eminences. If this is tender, and slightly full compared with the opposite side, his lunate may be dislocated. Percuss the fullness. This may produce paraesthesia in distribution of his median nerve.
(4) Examine his median nerve (75.3). A dislocated lunate may paralyse it, or produce numbness and tingling.
X-RAYS
The routine views are an AP and a lateral. If you take a lateral view routinely you will not confuse flexion and extension fractures. If you suspect a fracture of the scaphoid, ask for oblique views. A lateral view is the easiest one in which to see displacements of the lunate, and the oblique view gives you another opportunity to see a fracture of the scaphoid. These three views can usually be taken on the same film. CAUTION! If you suspect a scaphoid fracture, but the Xray is negative, repeat it in 7 to 10 days.
COMPARE HIS INJURED WRIST WITH HIS NORMAL ONE
74.2 Extension (Colles) fractures
These are the most common human fractures. The patient falls on his outstretched hand, he hyperextends his wrist, he fractures the lower end of his radius, and he sometimes fractures the tip of his ulnar styloid in one of the following three ways.
In all of them he complains of a swollen wrist, and of the signs described in Section 7.1.
(1) In the classical extension fracture he has a single transverse fracture about 2 cm from the lower end of his radius, which does not involve the surface of his wrist joint. The distal fragment is in one piece, shifted dorsally, tilted dorsally and radially, and impacted on the shaft. In the developing world these fractures are seen in adults of any age, and are not typically injuries of older women as they are elsewhere.
(2) In a T-shaped fracture the fracture line extends distally into the wrist joint, and divides the distal fragment into two.
(3) In a comminuted fracture the distal fragment is in many pieces.
X-rays are highly desirable, but not absolutely essential. You
need them to make sure that the patient has not also got a fractured
scaphoid, or some other injury of his carpus. If you are
not sure what fracture he has, rely: (1) on the nature of the injury
(flexion or extension) and remember that, (2) if there is any
displacement, the distal fragment will be displaced backwards
in an extension fracture, and forwards in a flexion one.
If a fracture is impacted in a reasonably good position with only moderate shift, and less than 15° of dorsal angulation, don't try to reduce it. Leaving it alone will let it heal faster, and will avoid the risk of anaesthesia. It will enable active movements to start earlier and thus reduce stiffness. Reducing a more severely displaced fracture is usually easy, but applying a cast in a way that will prevent the fragments slipping is not so easy, so follow the instructions carefully. Poor reduction is more often due to putting on the cast badly, than to manipulating the fracture incorrectly. Radial instead of ulnar deviation of the distal fragment is the common mistake. Prevent this by making sure the patient's hand is in moderate ulnar deviation when you apply the cast. Two methods of reduction are described; the disadvantage of the first one is that it takes a little longer.
FULL PRONATION WITH MODERATE FLEXION AND MODERATE ULNAR DEVIATION EXTENSION (COLLES) FRACTURES OF THE WRIST IF THE DISTAL FRAGMENT IS COMMINUTED OR T-SHAPED
If there is less than 15° of dorsal tilt and comminution is
mild, apply a volar splint for protection and to relieve pain.
Encourage the patient to start active movements of his fingers
immediately.
If displacement or comminution is moderate or severe, management depends on his age. if he is young, attempt reduction as described below. if he is oId, apply a backslab for a few days, and then encourage active movements as soon as pain allows.
If the distal fragments are in only two pieces and look as if they could be fixed internally, refer him if you can, especially if he is young.
If active immediate movements are indicated but pain is too great to allow them, apply an anterior plaster slab or a backslab for about 3 weeks, until the pain has lessened. enough to allow the patient to begin using his wrist. if possible, hold the slab in place with crepe bandages. Remove the slab for periods of exercise and then reapply it. if you have no crepe bandages, use a plaster bandage, and split it (70.6).
IF THE DISTAL FRAGMENT OF THE RADIUS IS IN ONE
PIECE IF THERE IS MINOR DISPLACEMENT of the distal fragment,
with less than 15° of dorsal tilt, don't reduce it. Apply a slab
to the front of the patient's arm and wrist and start active
movements, as above, as soon as the pain allows.
IF THERE IS MORE SEVERE DISPLACEMENT with more than 15° of dorsal angulation of the distal fragment, or the patient is in severe pain, or there are signs of pressure on his median nerve, reduce the fracture immediately, as follows.
ANAESTHESIA (BOTH METHODS)
(1) Local anaesthesia of the fracture haematoma is very effective if the fracture is recent (A 5.6). its disadvantages are that: (a) it converts a closed fracture into an open one, with the possible risk of infection, and (b) it does not relax the muscles. Using careful aseptic precaution, insert the needle on the back of the patient's forearm well above his wrist. Aim the needle obliquely, as in Fig. 74-5, so that it enters the fracture cavity; aspirate to make sure you are in the haematoma, then inject 10 ml, not more, of 2% Iignocaine without adrenaline and wait 15 minutes. (2) Intravenous forearm block (A 6.19). (3) Supraclavicular block (A 6.17). (4) Axillary block (A 6.18).
===FIRST METHOD FOR REDUCiNG AN EXTENSION FRACTURE
OF THE WRIST===
Lie the patient down. Suspend his arm from a drip stand, using clove hitches (Fig. 73-10) round his thumb, and index or middle finger. Put a strap round his upper arm, and apply 5 kg traction to it.
Wait 10 minutes while the traction corrects the impaction. At the end of this time the distal fragment will usually be free and you can move it into position with the minimum of effort.
Apply anterior and posterior plaster slabs. Suspension will have secured a suitable degree of moderate ulnar deviation, so you have only to make sure that you apply the plaster in moderate flexion and full pronation.
Don't let the anterior slab come further than the patient's distal palmar crease. Make sure the tip of his thumb can touch his index finger.
If possible, hold the slab in place with a crepe bandage. If you don't have a crepe bandage, pad his arm and hold the slabs in place with a plaster bandage. Split this while the cast is still damp.
If the fracture is unstable, continue the cast up his upper arm with the elbow at 90°. For stable or minimally displaced fractures, forearm slabs are enough.
SECOND METHOD FOR REDUCING AN EXTENSION FRACTURE OF THE WRIST
The following description assumes that the patient has a fracture of his right wrist.
Anaesthetize him and lie him down.
DISIMPACTION
Ask an assistant to hold the patient's arm just above his elbow.
Hold his fingers in one of your hands and his thumb in the other.
Exert traction on his fingers and thumb (1) while your assistant
pulls his elbow in the opposition direction (2). The
younger he is the stronger the pull you need. Pull steadily for
a minute timed by the clock. You will feel the fragments disimpact,
and will sometimes hear them do so.
CORRECT THE DEFORMITY
Abduct his forearm, stand with your back to him, and pronate his wrist.
Put your left thenar eminence (3) over the displaced distal fragment, with your fingers and thumb round the ulnar border of his wrist.
Put your right hand beneath his distal forearm with your right hypothenar eminence just proximal to the fracture line (4) Curl the fingers of your right hand round his lower forearm. Using your right hypothenar eminence as a fulcrum, move the lower fragment into a position of moderate flexion and moderate ulnar deviation all in one movement (5).
If the ulnar styloid is fractured, disregard it.
IMMOBILIZE THE FRAGMENTS
Apply a plaster backslab (6) with its corners cut (7) to allow movement of the patient's elbow, fingers, and thumb.
While your assistant bandages on the slab, hold the patient's fingers in one hand (8) and his thumb in the other (9). Lean backwards, exert gentle traction, and his wrist will fall into moderate ulnar deviation.
While the slab is still soft, move back to the inner side of the arm, and apply the same grip as you used to correct the deformity (10), but without applying any pressure. Allow the plaster to set while you maintain this grip.
CAUTION ! (1) Make sure his wrist is fully pronated, moderately flexed, and moderately ulnar deviated. (2) His MP joints must be free. If the slab extends too far distally it will splint them in extension, and give him a stiff useless hand.
CHECK X-RAYS
The AP view should show that you have corrected the alignment.
The lateral view should show that the articular surface of the patient's radius is no longer facing dorsally. It should be facing 5 to 10° anteriorly, but a strictly vertical position is acceptable. If reduction is unsatisfactory, have one further attempt at manipulation. if you make further attempts in your efforts to get a good X-ray, the clinical result will only be worse.
POSTOPERATIVE CARE FOR AN EXTENSION FRACTURE (both methods)
Put the patient's arm in a triangular sling, with his elbow flexed at more than 90°. If his fingers become painful, tell him to return immediately, or to split the bandage with a pair of scissors. Encourage him to move his fingers, elbow, and shoulder actively, using the exercises in Fig. 71-7. Early shoulder movements are especially important because they will prevent the common complication of a stiff shoulder.
In a few days, or at the next fracture clinic, complete the cast around his forearm.
Where possible, X-ray him again 7 to 10 days later, so that if redisplacement has occurred, there will still be time to correct it. This is important in a younger patient, but if an older patient's fracture redisplaces, leave it, and encourage active movements.
A young adult Keep the cast on for 6 weeks. An old adult Remove the cast after 3 weeks, and encourage him to move his wrist.
DIFFICULTIES WITH EXTENSION FRACTURES
If the patient's fracture has united, but his WRIST IS DEFORMED with an ugly radial deformity, pain, and limited rotation, you can refer him for excision of the head of his ulna, together with 2 cm of its adjacent shaft (Darrach's operation). This is a simple procedure with good results, so it is better than trying to remanipulate a badly reduced extension fracture with radial deviation. The pain over the head of his ulna will eventually improve, but it may last a year.
If he Is SUDDENLY UNABLE TO EXTEND HIS THUMB
some weeks or months after the accident, he has probably
ruptured the tendon of his extensor pollicis longus. This
sometimes happens suddenly long after the accident. Refer
him to have it repaired.
74.3 Flexion fractures of the wrist (Smith's and Barton's fractures)
In these two fractures the patient falls on his flexed wrist to produce the characteristic deformity shown in Fig. 74-7, in which his hand is displaced anteriorly on his forearm. In a lateral Xray, the fracture line runs obliquely across the distal end of his radius, instead of being parallel to its articular surface, as is usual in an extension fracture. Also, the distal end of the radius is displaced anteriorly in contrast to the posterior displacement of an extension fracture. In a Smith's fracture the fracture line does not extend into the joint, but in a Barton's fracture it does. In both the fragments are difficult to reduce and hold in place.
Although these two fractures should be easy to diagnose, they are so rare that they are often mistaken for extension fractures. In Barton's fracture the fragments can seldom be held in a cast, so that open reduction and plating is usually necessary, but in Smith's fractures closed reduction may succeed. The fragment is displaced anteriorly, so that the patient's wrist must be held in dorsiflexion, and his hand supinated (the opposite to an extension fracture). If you treat either of these fractures badly, the loss of wrist movement will be severe.
FLEXION FRACTURES OF THE WRIST
If the fracture involves the articular surface (Barton's fracture), refer the patient for internal fixation. if you cannot refer him, treat him as for a Smith's fracture described below. SMITH'S FRACTURE Use local anaesthesia as for an extension fracture. Ask an assistant to apply traction in the axis of the patient's forearm.
While traction is being applied, supinate and dorsiflex his wrist fully. Apply a plaster slab to the front of his forearm, from just above his elbow to the proximal crease of his palm, and bind it on with a crepe bandage. Or failing this, pad his forearm and hold the slab on with a circular plaster bandage, split it, as for an extension fracture.
Take an X-ray to see if the fracture is reduced.
If the fracture is reduced, complete the cast on the third day; encourage him to use his hand, and keep his shoulder moving. Remove the cast after 6 weeks.
If the fracture is not reduced, have one more attempt at reduction. If this fails, refer him for internal fixation immediately.
DIFFICULTIES WITH EXTENSION FRACTURES
If the DISTAL FRAGMENT SLIPS, it will do so anteriorly and proximally, but this may not interfere with function. If the slipping is significant, refer the patient for the application of a plate.
74.4 Fractures of the scaphoid
These can occur at any age, even in children, but they are particularly common in young men. The patient falls on his hand and forcibly dorsiflexes the joint between the proximal and distal rows of his carpal bones. The scaphoid, which forms part of both rows, breaks across its distal pole, or its neck.
Fracture of the distal pole (tuberosity) of the scaphoid
is a minor injury, because the detached fragment has a good
blood supply and unites readily. Treat this fracture by encouraging
early active movements.
Fracture of the neck of the scaphoid is a more common and more serious injury, because non-union is frequent. The patient's wrist is normal, except for pain at the extremes of movement, and local tenderness in the anatomical snuffbox over his scaphoid. He may complain that his wrist continues to hurt after a `sprain', but because the pain is so mild, he may continue to use his hand, with the result that this fracture is often missed.
The signs in Section 74.1 should make you suspect the diagnosis, particularly pain on pressing the `anatomical snuffbox'.
Take an AP, a lateral, and two oblique X-rays at 30° and
60°. The fracture line is a fine crack in the neck of the scaphoid
which you can easily miss. Look for it on a dry film in a good
light with a magnifying glass. If there is clinical evidence of
a fractured scaphoid, but the X-ray is negative, apply a scaphoid
cast and take another film after removing the cast 7 to 10 days
later. The fracture line will then be much more obvious. If clinical
signs are strongly suggestive, but the X-ray is still negative,
assume that the patient has a scaphoid fracture, and treat it.
Neither fragment is significantly displaced, so they need not be reduced, but they do need to be splinted. If they are going to unite successfully: (1) splinting must be prolonged for 10 weeks, (2) the cast must be close fitting (there must be no movement at the mid-carpal joint), and (3) the cast must go above the elbow.
Non-union is the main difficulty with these fractures. This may be due to: (1) a poorly applied cast which allows movement at the mid-carpal joint, (2) interrupted splinting, (3) splinting for too short a time, or (4) aseptic necrosis of the proximal fragment, especially if it is small. All bandages and casts for the scaphoid, except the one we have described, are almost certainly useless, so whenever you apply a scaphoid cast, do so as in Fig. 74-10.
IF THE X-RAY OF A SPRAINED WRIST' IS NEGATIVE,
BUT SYMPTOMS PERSIST, REPEAT IT 10 DAYS LATER
FRACTURE OF THE NECK OF THE SCAPHOID
In 15% of cases the patient has some other injury, so examine his wrist carefully. Anaesthesia is unnecessary.
APPLYING A SCAPHOID CAST
Put a stockinette tube over the patient's lower arm and hand. Skilled surgeons usually apply an unpadded circular cast. If you are inexperienced, apply a thin layer of cotton wool.
Apply the cast from above the patient's elbow to just above his knuckles. Bring it just proximal to his distal palmar crease. Hold his elbow at 90°. Dorsiflex his wrist, and bring his thumb across his palm as if he were holding a glass. The plaster on his thumb should reach just short of its IP joint. Mould it firmly round his first metacarpal.
As soon as the cast is on, and before it has set, grasp his hand, so as to squeeze the cast from front to back, as in D, Fig. 74-10. Squeezing the cast like this will prevent his hand moving and straining the fracture line. If he can flex or extend his wrist even a little, the cast is useless. His wrist will not swell, so don't split the cast. Encourage him to use all the j oints outside the cast. This will soon make it soft, so renew it as necessary.
THE POSTOPERATIVE CARE OF A SCAPHOID FRACTURE
At 6 weeks, renew the cast, but this time bring it below the patient's elbow. At 10 weeks, remove the cast and take another X-ray.
If his fracture has united, allow him to use his wrist progressively. If his fracture has not united, proceed as follows.
(1) If wrist movements are very important to him, refer him.
If you cannot refer him, apply another cast for 3 more weeks. Twelve weeks in a cast is the maximum time. If you leave it on longer than this, his wrist will become excessively stiff and osteoporotic.
(2) If wrist movements are less important to him, remove the cast, and allow a false joint to form. Often, there are no symptoms, even if the fragments fail to unite.
(3) If, later, he continues to have unacceptable disability, refer him for bone grafting, or removal of the avascular fragment.
DIFFICULTIES WITH A FRACTURED SCAPHOID
If the fracture has NOT UNITED and the PROXIMAL FRAGMENT LOOKS VERY DENSE on the X-ray, it has probably undergone avascular necrosis. It can be excised, but the operation is difficult. If you cannot refer him, encourage him to disregard his disability and use his hand as much as he can.
If you have NO PLASTER, aim for a pseudarthrosis and start active movements immediately.
REGARD A SPRAINED WRIST IS A FRACTURED
SCAPHOID UNTIL PROVED OTHERWISE
74.5 Carpal dislocations
In these rare injuries, the patient falls on his hand and dorsiflexes his wrist violently, so that the second row of carpal bones dislocates on the first row. His lunate remains in its normal place in the proximal row, and in its normal place in relation to the radius. Sometimes the injury stays like this so that he has an intercarpal dislocation. But, if the distal row of carpal bones now springs forwards again, it may push his lunate forwards, out of its position in the proximal row, and away from its normal relation with the radius. He now has an anterior dislocation of his lunate. Rarely, the lunate dislocates posteriorly.
These dislocations are important, because you can usually reduce them. If you don't, severe disability follows, and the greater the delay, the worse it becomes. Exactly the same kind of injury fractures the scaphoid, so in injuries of the lunate, always look for a fractured scaphoid. Distinguishing between these two lunate injuries clinically can be difficult. The lateral X-ray is the critical one.
LOOK CAREFULLY AT THE LATERAL X-RAY
74.5a Intercarpal dislocation (perilunate dislocation)
This makes the patient's wrist swell. Neither he nor you can move his wrist, and its antero-posterior diameter is increased. His styloid processes are in their normal places. His radial pulse and the concavity of the lower end of his radius are normal, and you cannot localize tenderness anywhere.
The X-rays are difficult to interpret. Take a lateral view and compare it with one of his normal wrist. In an intercarpal dislocation the lunate is more or less in its normal place in relation to the radius, and is facing in its proper direction, but its distal cup-shaped articular surface is not in contact with the dome-shaped surface of the capitate. Instead, the patient's hand and his carpus lie in a plane posterior to his radius. This dislocation is less easy to see in an AP view. A useful sign is an increase in the normal space between the lunate and the scaphoid, as shown in B, Fig. 74-12.
The methods for reducing both these injuries are similar. The first step is to exert strong traction on the patient's hand. In an intercarpal dislocation, press over the back of his wrist and then flex it. In a dislocation of his lunate, press over the front of his wrist and then extend it.
INTERCARPAL DISLOCATION
Anaesthetize the patient. Bend his elbow to 90°, and secure his upper arm to the table with a bandage, as in C, Fig. 74-12. Supinate his forearm, and ask an assistant to pull strongly on his fingers for 10 minutes.
While your assistant is maintaining very strong traction, place both your thumbs against the back of the patient's wrist. Push forwards, and at the same time slowly flex his wrist (not illustrated).
Take an X-ray to make sure you have not dislocated his lunate by mistake. Look carefully to make sure that he has not also fractured his scaphoid. If reduction fails, refer him. POSTOPERATIVE CARE If he has not fractured his scaphoid, apply a splint for 2 weeks to allow some healing, then encourage active movements immediately.
If he has fractured his scaphoid, apply a scaphoid cast, and split it. In a few days, when swelling has subsided, replace it with an unsplit cast.
DISASTER WITH AN INTERCARPAL DISLOCATION
If the DIAGNOSIS WAS MISSED, this may be because nobody listened to what the patient said. If he says "There is something wrong with my hand"; believe him, even though his X-ray seems normal. if the dislocation was overlooked at the time of the injury, refer him for open reduction. If this is not possible, his wrist movements will remain limited and painful.
74.5b Dislocation of the lunate
This is the second stage of an intercarpal dislocation. The displaced distal row of carpal bones springs back and rotates the lunate forwards. As it does so, the posterior radio-lunate ligament ruptures, but the anterior one remains intact. The displaced lunate presses on the patient's median nerve, and if it is not replaced, he may lose the function in it permanently. The patient falls and injures his wrist, after which it is swollen and painful, and he can can only move it a little. His fingers remain partly flexed, and will not straighten. He may have any of the four signs in Section 74.1.
In a lateral X-ray, the proximal dome-shaped surface of the patient's lunate faces posteriorly, and is no longer in contact with his radius. Its distal cup-shaped surface faces anteriorly, and is no longer in contact with his capitate. His capitate and the carpus are in the same plane as his radius. Signs in the AP view are characteristic, but are often missed. The normal lunate appears to have four sides in an AP view, but when it is dislocated, it seems only to have three. So look for a triangular lunate. Look also for a widened space between the scaphoid and the lunate. Normally they touch. Dislocations of the lunate are so easily missed that the lunate is the first bone to look at in any X-ray of the wrist.
DISLOCATION OF THE LUNATE
Try to reduce a patient's lunate as soon as you can, before his median nerve is permanently injured. Every few hours make a difference. After 2 weeks, closed methods usually fail.
CLOSED REDUCTION
Give the patient a general anaesthetic that will relax the muscles of his arm completely. Bend his elbow to 90° and fix his upper arm with a bandage to the table as in Fig. 74-12.
Supinate his forearm, and ask an assistant to pull strongly on the patient's fingers for 10 minutes (1).
After 10 minutes of traction and while it is still being maintained, place both your thumbs against the front of the patient's wrist over his lunate, and press hard posteriorly (2) while dorsiflexing his wrist (3). Then flex his wrist while keeping up traction and pressure (not illustrated). If this fails, refer him for open reduction. If this is impossible, encourage early active movements. If he is lucky, he may have comparatively little disability.
POSTOPERATIVE CARE
If his scaphoid has been fractured, apply a scaphoid cast. If it has not been fractured, encourage active movements from the start, and splint it only for the relief of pain. Irritation to his median nerve will improve quickly after you have replaced his lunate.
Alternatively, hang 5 kg of traction round the patient's upper arm, as for the first method for an extension fracture (74.2) of his wrist. Then try to manipulate his wrist.
IN AN X-RAY OF THE WRIST LOOK FIRST AT THE LUNATE
