TheraLife^� Wrist

Carpal Tunnel Syndrome

Vincent R. Hentz, M.D.    Professor of Functional Restoration- Hand Surgery

Stanford University, School of Medicine.

Carpal tunnel syndrome is the name given to signs and symptoms that are a consequence of above normal pressure on a particular nerve that lies just under the skin on the palmar side of the wrist. This nerve, called the median nerve passes beneath a tight ligament at the wrist, together with the tendons that move the fingers. It is the most superficial structure passing through the unyielding carpal tunnel. This tunnel is formed by a ring of wrist bones that comprise the sides and roof of the tunnel and the transverse carpal ligament that forms the floor of the tunnel.

The nerve is subject to compression when the tunnel is constricted or, more frequently, when swelling of soft tissues within the tunnel occurs. There is abundant tissue called "synovium" around the flexor tendons as they pass through the carpal tunnel. This tissue serves to lubricate the tendons so that they glide easily back and forth as our fingers move.

Carpal tunnel syndrome is most frequently the result of synovial edema or thickening from a variety of causes. Any condition that crowds the carpal tunnel may result in the syndrome. For example, displaced bone after wrist fracture, ganglion, tumor, anomalous muscles, and fluid retention syndromes may be primary causes of median nerve compression at this site. The symptom complex and physical signs of median nerve compression within the carpal tunnel are predictable. Various levels of tingling, numbness, and even absence of feeling over the median nerve sensory distribution in the hand are classic. Generally, the region of median nerve sensibility consists of the palmar aspect of the thumb, index, long, and radial one half of the ring finger, but there may be some variation of this pattern in individual patients. Atrophy of the muscles about the thumb is the classic finding when the median nerve is sufficiently compressed for a long period of time.

Frequently, the patient is awakened at night by uncomfortable tingling and numbness in the hand. The wrist may drop into flexion during sleep and increase compression on the median nerve. The symptoms generally abate if the patient shakes the hand and moves the wrist about. Forcibly holding the wrist in flexion may create a tingling sensation in the thumb, index and middle fingers, the fingers supplied sensation by the median nerve. When the wrist is held in the flexed position and the fingers begins to tingle within one minute, this is referred to as a "positive Phelan's test." Tapping on the palmar surface of the wrist may result in a shock-like sensations in the median-innervated digits.

When the findings are classic for carpal tunnel syndrome in the absence of a history of wrist trauma, pregnancy, amyloidosis, or other systemic disorders, non-specific swelling of the synovial tissues of the flexor tendons within the carpal tunnel is probably the basis of the compression. Sometimes night splinting and anti-inflammatory drugs relieve the symptoms. If not, the physician may choose to inject a steroid medication such as cortisone into the carpal tunnel area for its anti-inflammatory effect. Relief of carpal tunnel symptoms after such injection tends to confirm the diagnosis. Persistent symptomatic carpal tunnel syndrome is best treated by a surgical procedure whose goal is complete division of the ligamentous floor of the carpal tunnel to release the compression. Two principle types of surgical procedures are performed today. An older method utilizes an incision made in the tissues of the palm of the hand. The transverse ligament is viewed (this is termed "dissection") directly and then it is divided under direct vision. This method and its several variations are loosely termed "open" technique. A more recent surgical procedure employs a specially constructed telescopic lens that permits indirect visualization of the transverse carpal ligament through a tiny incision. These techniques are referred to as "endoscopic" techniques. Each will be described.

Open Technique

Most surgical procedures to treat carpal tunnel syndrome can be performed today as outpatient procedures under either local (novocaine) or general anesthesia (fully asleep.) There has long been interest in utilizing an incision that provides both adequate exposure to permit safe and complete sectioning of the transverse carpal ligament and a cosmetically acceptable and symptom free scar. A variety of incisions varying primarily in the length and placement of the incision have been recommended. Most avoid incisions that cross proximal to the wrist crease as we have come to appreciate that scar hypertrophy could be minimized if the incision did not cross proximal to the wrist flexor crease. Several variations are discussed and illustrated.

Release of carpal tunnel compression by section of the transverse carpal ligament is best performed with the patient under local or regional anesthesia. The incision is important, since straight, longitudinal incisions crossing the wrist creases lead often to hypertrophic scarring.

Surgery must be undertaken only by skilled surgeons because there are several troublesome complications that may occur unless proper care is taken. These complications include injury to the branches of the median nerve .

The axis of the incision is along a line drawn from the center of the wrist at the distal wrist flexor crease to the radial border of the ring finger.

Figure 2

This line corresponds to the proximal extent of the natural crease between thenar and hypothenar prominences. , The incision begins proximally at the distal flexor crease of the wrist and follows the thenar crease for about 1.5 cms.

The skin is incised and the subcutaneous fat is bluntly spread from side to side as the surgeon searches for crossing branches of the palmar cutaneous nerve from the median nerve.

Figure 3

A less consistently present ulnar corollary of this nerve may be present and branches originating from this cutaneous nerve should be sought and left uninjured. This is the most important step in reducing the incidence of painful incisional neuromas. Once the fatty tissues have been swept aside, the longitudinally oriented fibers of the palmar fascia are exposed. These fibers are sharply incised over the extent of the incision.

A small curved scissor is placed with plane of blade opening held parallel to the transversely oriented fibers of the transverse carpal ligament. The tips of the scissors are gently pushed between these fibers until an opening is created.

Figure 4

The opening is extended distally by small increments and along the axis established at the beginning of the procedure (centrum of wrist toward radial border of the ring finger.) The scissors are used to dissect any tissue attachments existing between flexor tendons and underside of ligament. The median nerve is well radial to the line of incision of the transverse carpal ligament. After about 5-7 mm of the proximal ligament is divided, there is sufficient exposure to divide by small increments, the remainder of the ligament under direct vision.

Figures 5 & 6

After assuring that the nerve has been completely released in the palm, attention is directed to releasing the the antebrachial fascia just proximal to the wrist crease. This fascia is divided for a distance of 2 to 21/2 cm proximal to the wrist crease on the little finger side of the palmaris longus tendon if this is present.

Figure 7

The nerve is examined for irregularities and the canal is examined for the presence of tumors, aberrant muscles or exuberantly hypertrophic synovium.

If there is a great deal of boggy, hypertrophic synovium, a limited synovectomy may be indicated. If the nerve has sustained additional injury or, by virtue of long-term compression, appears to be collared by unyielding scar, a scar release is in order. The admonition today seems to be to handle or otherwise disturb the nerve as little as possible.

After completeness of release has been firmly established, the wound is closed by reapproximating the palmar fascia in the proximal palm, and then suturing the skin.

Figure 8

Figure 9

A light volar plaster splint or short gauntlet type cast is fitted by the surgeon to immobilize the wrist in some degree of wrist extension. The splint may be removed safely within five to seven days. Some surgeons will not recommend postoperative splinting.

Other incisions described for effecting release of median nerve compression include a somewhat shorter longitudinally located palmar incision. Such an incision coupled with a second incision made transversely, proximal to the wrist, allows exposure of the nerve first proximally and then distally as the ligament is released.  If a full, direct exposure above and below the extremes of the transverse carpal ligament is desired, the incisions above may be joined in such a way to avoid a longitudinal incision across the palmar wrist crease.

Postoperative Period

The dressings and the sutures are removed within several days of surgery. A small removable brace may be advised for night time use and some type of exercise for the operated hand is usually prescribed. This are typically very simple exercises performed at home.

Initially following surgery, the hand may feel somewhat weakened. With user and exercise, strength is usually regained by the 6th to 8th week.

Many people who undergo carpal tunnel release are able to resume their work within one or two days. Individuals who perform heavy labor or who must perform extensive keyboard activities may not be able to resume work so quickly. Several weeks of exercise and recovery are required to allow these individuals to return to full work activity.

Many of the most troublesome symptoms may be immediately relieved following surgery. If night awakening with numb and tingling fingers has been a prominent preoperative symptom, following surgery this may be relieved rapidly. Other symptoms may persist for much longer or even indefinitely. If the muscles around the thumb have become atrophied as a consequence of prolonged nerve compression, after release of compression, these muscle may never regain their normal strength and appearance. If sensation is severly altered by nerve compression, its recovery after nerve decompression may take many months or even years. Occasionally, absent sensation persists indefinitely.

Endoscopic Carpal Tunnel Release

Indications and Contraindications

Since an endoscopic approach provides limited visibility of the contents of the carpal canal, the technique is indicated only when there is no particular need to examine the carpal canal or manipulate the contents. There are several contraindications. These are discussed in terms of the advantages and disadvantages of the technique.

The advantages of the endoscopic technique are said to include the following:

• Skin incisions are kept off the prime contact surface of the proximal palm (the so-called "heel" of the hand) This lessens the possibility of injury to small sensory branches of the palmar cutaneous nerves from either the median nerve or ulnar nerve. Injuries to these branches may result in neuroma hypersensitivity in the critical area.
• Patients regain grip and pinch strength more rapidly. With the endoscopic technique, the palmar fascia is left relatively undisturbed. Leaving these supporting structures unaltered may result in fewer changes to the origins of the thenar muscles. Maintaining this layer intact may reduce the extent of the changes in the moment arms of the tunnel's flexor tendons that occur as a consequence of release of the transverse carpal ligament. Some authors believe that these factors are important in the postoperative recovery of grip and pinch strength.
• There is less postoperative discomfort.

The disadvantages of the endoscopic technique to release the transverse carpal ligament include the following:

• There are many contraindications to the use of the procedure. The procedure is contraindicated for patients whose nerve compression symptoms are a consequence of an inflammatory condition such as rheumatoid arthritis, amyloidosis or gout. The inflammed tissues or deposits obscure the surgeons view. Previous surgery or injury to the carpal canal will restrict exposure
• The surgeon has a very limited view. There is no option of examining the contents of the carpal canal in a search for unusual etiologies of median nerve compression such as intra-tunnel ganglions or aberrant muscles. The nerve itself cannot be visualized to determine whether some adjunctive procedure such as neurolysis might be indicated
• There is controversy regarding whether the technique is inherently more risky than other techniques performed through more extensive exposures. Cited risks include bruising of the median nerve by the dissecting instruments or the endoscopic device as these are passed into the carpal canal, inadvertant injury to adjacent flexor tendons, laceration of the superficial arterial palmar arch, laceration of the common digital nerve to the third web space, laceration of a sensory nerve branch crossing from the ulnar sensory nerve to the common digital nerve to the third web space and even laceration of the median nerve itself. Advocates of the technique point out that all of these complications have also been reported in association with the more traditional open surgical techniques.
• There is concern over whether this technique results in "complete" release of all compressive structures. Various cadaver studies involving post endoscopic release dissections have demonstrated suspicious areas of palmar fascia at the distal margin of the transverse carpal ligament that represent sites of potential residual constriction.
• The procedure may add an unnecessary expense.

Great experience has been gained with the single portal technique using the Agee endoscopic device (3M) and this technique will be illustrated

Preparation

The procedure may be performed under local, regional or general anesthesia. Advocates of local anesthesia feel that this adds a safety factor in that the patient will complain if the surgeon applies too much pressure on the median nerve during instrumentation. We prefer either local skin infiltration anesthesia with some sedation, or low dose intravenous regional anesthesia under a forearm tourniquet control.

Assembling the Device

Prior to the incision, the instrument is assembled and tested for picture clarity and color, light source brightness level, and proper location of the fiber optic and camera cables. The blade trigger is tested to be sure it raises and releases properly.

Procedure

The skin surface landmarks are identified. These include the pisiform and hook of hamate, the palmaris longus, flexor carpi ulnaris and flexor carpi radialis tendons at the wrist, and the various transverse skin creases at the wrist.

Figure 10

It is ideal if the small transverse incision at the wrist falls into a pre-existent skin crease. Usually the most distal crease is too distal because an incision here exposes the fat of then hypothenar eminence which may boil into the wound obscuring view. The most proximal crease is typically too far proximal to be ideal since the antebrachial fascia in this area, especially in women, may be very thin and not easily identified as a surgical plane of dissection. The ideal incision is a line between these two creases and if a natural crease does not exist, the incision may be placed as indicated in the illustration. A reference line is drawn from the center of the wrist to the center of the ring finger.

The area of the skin incision is infiltrated with local anesthesia, avoiding leakage into the carpal canal. The skin is incised and longitudinal blunt dissection exposes longitudinally directed structures such as small nerve branches or venules. These are retracted laterally and the antebrachial fascia is identified. Since its fibers are transversely oriented, it is relatively easy to distinguish from other fascial layers. A one square centimeter area is cleaned of attachments to surrounding structures.

Two longitudinally directed parallel incisions are made with the incisions about one cm apart. Their proximal ends are connected creating a distally based flap of fascia.

Figure 11

A two-pronged hook retracts this flap distally and any synovial attachments from the contents of the canal are dissected off the underside of this flap. The initial synovial clearing dissection can be continued with the scissors under direct vision.

The surgeon then cradles the patients hand in his or her non-dominant hand with the surgeons thumb placed as illustrated. The patient's wrist is maintained in a neutral position while the various instruments are used, first to dissect any synovial attachments to the transverse carpal ligament, thus clearing a path for visualization of the underside of the transverse carpal ligament. The dilators are used to further create a safe passage for the endoscope. The technique is a bimanual one with the surgeon's nondominant thumb assessing what the dominant hand and its instrument are doing and confirming proper location. The dilator also serves as a device to determine that the pathway is being created within the carpal canal and not within Guyon's canal. The dilator is described as a hamate finder, since it can tell the surgeon the location of the hook of the hamate and confirm that the dilator is within the proper canal.

The endoscope is inserted with gentle distal pressure. Insertion is made easier by moistening the plastic of the protective sleeve and the skin just proximal to the incision 

Figure 12

How much pressure is tolerable is a matter of experience. If the patient is awake and the median nerve unanesthetized, the patients response to this maneuver is helpful. If the surgeon is concerned about the pressure required to pass the sleeve into the canal, either the procedure should be abandoned in favor of an open technique or the procedure modified by withdrawing the endoscope and dividing the most proximal margin of the transverse carpal ligament under direct vision and then reintroducing the endoscope.

The sleeve is advanced under direct vision via the monitor maintaining some upward pressure so that the flat edges of the sleeve hug the underside of the ligament. The ligament is readily identifiable by virtue of its transversely oriented collagen bundles. The sleeve is carefully passed until the distal margin of the ligament is visualized. Pressure over this point by the nondominant thumb helps in identifying a frequently present fat pad located just distal to the distal edge of the ligament.

The tip of the sleeve is positioned at the distal edge of the ligament. The blade is slightly raised to determine its point of contact and any adjustments to position made. Then the trigger is depressed completely raising the blade to its full height and the point of penetration is determined. The assembly with blade fully elevated is then carefully withdrawn about 7 - 10 mm and the shape of the resultant incision analyzed.

Figure 13

If the "V" apex of the incision is directed proximally, this indicates complete release of the distal part of the ligament. If the "V" is pointing distally, this indicates that some part of the distal ligament must be revisualized and divided with a second short pass of the blade.

Once the distal ligament has been completely released, the elevated blade is positioned at the apex of the incision in the ligament and again fully elevated and slowly withdrawn under direct vision across the full extent of the ligament. The blade is lowered, the sleeve is reinserted and the completeness of the proximal release is determined. Frequently another short pass or two of the blade, usually only partly raised, will be necessary. The dissector can be passed into the canal and the extent of the release can be confirmed.

To complete the procedure, the skin and subcutaneous tissues over the antebrachial fascia proximal to the wrist crease are dissected as was described for the open technique.

Some surgeons prefer to reinsert the endoscope into the now capacious carpal canal and, then deflate the tourniquet. The canal is observed with the endoscope for evidence of brisk arterial bleeding that might indicate that the superficial transverse arterial arch has been injured.

The skin incision is closed with a subcuticular pull-out suture and a standard hand dressing and palmar splint are applied to maintain the wrist is slight extension. The splint and suture are removed one week later and therapy is begun.