1. Volar Approach to the Distal Radius

   The volar approach to the distal radius provides excellent exposure of the volar aspect of the distal radius. Its use is almost exclusively in the treatment of distal radial fractures and its popularity has increased greatly in recent years since the advent of locking plates.

   Other uses include the following:

   1. Bone grafting for nonunions of the distal radius

   2. Osteotomies of the distal radius

   3. Excision of the radial styloid or release of the brachioradialis

The approach is very similar to the lower end of the anterior approach to the radial shaft (page 148) but it utilizes the plane between the radial artery and the flexor carpi radialis and not the plane between the radial artery and brachioradialis. The exposure of the distal radius is therefore more ulnarward and retraction of the radial artery is not required to access the more central portions of the distal radius and wrist joint.

 

Position of the Patient

 

Place the patient supine on an operating table. Rest the forearm on a hand table in the supinated position so that the palm faces upward. Use an exsanguinating bandage (Fig. 5-15).

 

Landmarks and Incision

Landmarks

Palpate the styloid process of the radius. It is the most distal part of the lateral side of the radius. Then move in an ulna direction to palpate the tendon of flexor carpi radialis which is thick and immobile. The flexor carpi radialis muscle and tendon lie radial to the palmaris longus muscle at the level of the wrist and just to the ulnar side of the radial pulse.

Incision

Make a longitudinal incision overlying the tendon of flexor carpi radialis. Begin just above the skin crease of the wrist and extend the incision up the volar aspect of the forearm. The length of the incision will depend on the nature of the fracture pathology and the length of the plate to be used for fixation—7 cm is usually sufficient (Fig. 5-16).

Internervous Plane

 

The plane lies between the flexor carpi radialis supplied by the median nerve and the brachioradialis muscle supplied by the radial nerve.

 

Superficial Surgical Dissection

 

Incise the subcutaneous fat in the line of the skin incision. Incise the deep fascia overlying the tendon of flexor carpi radialis (Fig. 5-17). Identify the radial artery radially and the tendon of flexor carpi radialis ulnarly. Develop a plane between these two structures to expose the fascia overlying the pronator quadratus muscle (Figs. 5-18 and 5-19).

 

 

 

Figure 5-15 Position of the patient for volar approaches to the distal radius.

 

 

Figure 5-16 Incision for volar approach to wrist. The 5- to 7-cm incision overlies the tendon of flexor carpi radialis and ends just above the wrist joint crease.

 

 

 

Figure 5-17 The fascia over the tendon of flexor carpi radialis is incised and the radial artery is identified in the radial edge of the wound.

 

 

 

Figure 5-18 The tendon of flexor carpi radialis is retraced ulnarly to reveal the pronator quadratus muscle.

 

 

Figure 5-19 The pronator quadratus muscle is divided to expose the underlying volar aspect of the distal radius.

 

 

 

Figure 5-20 The pronator quadratus muscle is divided in the line of the skin incision to reveal the volar aspect of the distal radius.

 

Deep Surgical Dissection

 

The volar aspect of the distal radius is covered by the pronator quadratus muscle. Several techniques can be used to reach the bone of which three will be described. No technique has been proven to give better long-term function although minimally invasive techniques may give a slightly faster return to function.10,11

1. Complete muscle detachment

   Identify the insertion of the muscle into the anterolateral border of the radius beginning just below the radial styloid process. Detach this insertion by sharp dissection. Similarly detach the insertion of the muscle to the anterior surface of the distal end of the radius raising up a triangular flap of muscle. This technique gives the opportunity to close the muscle flap after surgery protecting the more superficial flexor muscles from an anteriorly applied plate.

2. Minimally invasive technique

   Identify the insertion of the muscle into the anterior surface of the distal end of the radius and detach it from the bone by sharp dissection. Leaving the lateral insertion intact tunnel underneath the muscle to expose the anterior surface of the bone. This technique is more soft tissue friendly but gives less exposure of the fracture site. Screws have to be inserted through stab incisions in the muscle.

3. Classical technique

Divide the pronator quadratus muscle in the line of the skin incision and elevate it from the anterior surface of the bone. This technique is more destructive and may be associated with slower initial recovery. Repair of the muscle is usually not possible (Fig. 5-20).

 

 

Dang

 

 

Vessels

The radial artery lies close to the lateral border of the wound and can be incised accidentally at any time during the dissection. Therefore, take care to identify and protect the artery. It is surrounded by venae comitantes and these may be easier to identify than the artery if an exsanguinating

tourniquet is used.

Nerves

The median nerve lies on the ulnar side of the approach and is protected as long as one stays radial to the flexor carpi radialis. If one strays ulnarward or do not use the pronator quadratus and its subperiosteal reflection to protect the structures on the ulnar side of the wrist, then the median nerve will be encountered and may be at risk of damage.

 

How to Enlarge the Approach

 

The incision can be extended usefully proximally and distally. Proximally, extend the skin incision along the line of the flexor carpi radialis muscle. Identify the proximal border of the pronator quadratus muscle following the internervous plane between median nerve innervated structures and radial nerve innervated structures (flexor carpi radialis and brachioradialis respectively). The exposure can also be extended distally by incising the wrist capsule and following the line of the flexor carpi radialis tendon. The tubercle of scaphoid is palpated in the distal most aspect of the incision and the wrist joint can be opened with visualization of the articular surface of the scaphoid. (See Volar Approach to the Scaphoid, page 50.)

 

Volar Approach to the Carpal Tunnel and Wrist

 

 

Decompression of the median nerve within the carpal tunnel is one of the most common operations of the hand. Two anatomic structures, the motor and palmar cutaneous branches of the median nerve, determine how the tunnel is approached. Both structures vary considerably in the paths they take; they are so unpredictable that “blind” procedures, which are acceptable elsewhere, must be avoided. If treated by open surgery the tunnel must be decompressed through a full incision and under direct vision. The uses of the incision include the following:

1. Decompression of the median nerve12,13

2. Synovectomy of the flexor tendons of the wrist

3. Excision of tumors within the carpal tunnel

4. Repair of lacerations of nerves or tendons within the tunnel

5. Drainage of sepsis tracking up from the midpalmar space

6. Open reduction and internal fixation of certain fractures and dislocations of the distal radius and carpus, including volar lip fractures of the radius and transscaphoid perilunate dislocations

 

Position of the Patient

 

Place the patient supine on an operating table. Rest the forearm on a hand table in the supinated position so that the palm faces upward. Use an exsanguinating bandage (see Fig. 5-15).

 

Landmarks and Incision

Landmarks

The thenar crease runs around the base of the thenar eminence. The proximal transverse skin crease of the wrist overlies the wrist joint. The tendon of the palmaris longus muscle bisects the anterior aspect of the wrist. Its distal end bisects the anterior surface of the carpal tunnel. It is easy to palpate in the distal forearm if the patient is instructed to pinch the fingers together and flex the wrist.

Incision

Begin the incision just to the ulnar side of the thenar crease, about one-third of the way into the hand. Curve it proximally, remaining just to the ulnar side of the thenar crease, until the flexion crease of the wrist is almost reached: To avoid problems in skin healing, do not wander into the thenar crease itself. Then, curve the incision toward the ulnar side of the forearm so that the flexion crease is not crossed transversely (Fig. 5-21).

 

Internervous Plane

 

There is no internervous plane. The approach is a true anatomic dissection in which the major nerves are identified, dissected out, and preserved. No muscles are transected except, on occasion, some fibers of the abductor pollicis brevis and palmaris brevis that cross the midline.

 

Superficial Surgical Dissection

 

Carefully incise the skin flaps. Remember that the palmar cutaneous branch of the median nerve, which usually presents on the ulnar side of the flexor carpi radialis, has a variable course. Dissection should be carried out

meticulously, with particular attention paid to the location of the nerve (see Fig. 5-21). After the fat is incised, the fibers of the superficial palmar fascia come into view; divide them in line with the incision.

Retract the curved flaps medially, exposing the insertion of the palmaris longus muscle into the flexor retinaculum (the transverse carpal ligament; Fig. 5-22). Retract the tendon toward the ulna and identify the median nerve between the tendons of the palmaris longus muscle and the flexor carpi radialis muscle. The nerve lies closer to the palmaris longus than to the flexor carpi radialis (Fig. 5-23).

Pass a blunt, flat instrument (such as a McDonald dissector) down the carpal tunnel between the flexor retinaculum and the median nerve (Fig. 5-24). Carefully incise the retinaculum, cutting down on the dissector to protect the nerve. Make the incision on the ulnar side of the nerve to avoid possible damage to its motor branch to the thenar muscle. Divide the entire length of the retinaculum (Fig. 5-25).

 

Deep Surgical Dissection

 

Identify the motor branch of the median nerve. It usually arises from the anterolateral side of the median nerve just as the nerve emerges from the carpal tunnel. The motor branch then curves radially and upward to enter the thenar musculature between the abductor pollicis brevis and flexor pollicis brevis muscles. Sometimes, however, the motor branch arises within the tunnel and pierces the flexor retinaculum to reach the thenar musculature. In these rare cases, the motor nerve itself may have to be decompressed before the patient’s symptoms will be relieved fully (see Fig. 5-25).

 

 

Figure 5-21 The incision for the volar approach to the wrist. The incision should be made on the ulnar side of the palmaris longus tendon to protect the palmar cutaneous branch of the median nerve.

 

 

Figure 5-22 The skin is retracted, and the deep fascia and tendon of the palmaris longus are inspected.

 

 

Figure 5-23 The deep fascia is incised. The palmaris longus is retracted toward the ulna, revealing the median nerve as it enters the carpal tunnel.

 

 

Figure 5-24 A spatula is placed under the transverse carpal ligament to protect the median nerve as the ligament is incised.

 

 

Figure 5-25 The transverse carpal ligament is released on the ulnar side of the nerve to avoid damage to the motor branch of the thenar muscle.

 

It rarely is necessary to gain access to the volar aspect of the wrist joint. If this is required, mobilize the median nerve in the carpal tunnel and retract it radially to avoid stretching its motor branch. Next, mobilize and retract the flexor tendons in the carpal tunnel (Fig. 5-26). Incising the base of the tunnel longitudinally exposes the volar aspect of the carpus. Extending the incision proximally provides access to the volar aspect of the wrist joint and the distal radius (Fig. 5-27). The most convenient approach for access to the volar aspect of the distal radius is the volar approach to the distal radius or the distal portion of the anterior approach to the radius (see Chapter 4).

 

 

Dang

 

 

Nerves

The palmar cutaneous branch of the median nerve arises 5 cm proximal to the wrist joint and runs down along the ulnar side of the tendon of the

flexor carpi radialis muscle before crossing the flexor retinaculum. The greatest threat to this nerve occurs if the skin incision is not angled to the ulnar side of the forearm (see Fig. 5-21).

The motor branch of the median nerve to the thenar muscles exhibits considerable anatomic variation. The risk to the nerve is minimized if the incision is made into the carpal tunnel on the ulnar side of the median nerve (see Applied Surgical Anatomy of the Volar Aspect of the Wrist and Fig. 5-39).

Vessels

The superficial palmar arch crosses the palm at the level of the distal end of the outstretched thumb. Blind slitting of the flexor retinaculum may damage this arterial arcade if the instrument passes too far distally. The arch is in no danger if the flexor retinaculum is cut carefully under direct observation for its entire length (see Figs. 5-21 and 5-39). Minimally invasive approaches to divide the flexor retinaculum rely on arthroscopic visualization of the anatomical structures to ensure their preservation.

 

How to Enlarge the Approach

Extensile Measures

 

Proximal Extension. The approach can be extended to expose the median nerve. To accomplish this, extend the skin incision proximally, running it up the middle of the anterior surface of the forearm (Fig. 5-28). Incise the deep fascia of the forearm between the palmaris longus and flexor carpi radialis muscles. Retract the flexor carpi radialis in a radial direction and the palmaris longus in an ulnar direction, exposing the muscle belly of the flexor digitorum superficialis muscle in the distal two-thirds of the forearm (Fig. 5-29). The median nerve adheres to the deep surface of the flexor digitorum superficialis, held there by fascia. Thus, if the flexor digitorum superficialis is reflected, the nerve goes with it (Fig. 5-30).

 

 

Figure 5-26 The median nerve is retracted radially and the flexor tendons are retracted toward the ulna, revealing the distal radius and joint capsule. An incision then is made into the capsule to expose the carpus.

 

 

Figure 5-27 Incise the joint capsule to expose the carpus.

 

 

 

Figure 5-28 Extend the wrist incision proximally to expose the distal forearm and median nerve.

 

 

Figure 5-29 Incise the fascia on the forearm between the palmaris longus and the flexor carpi radialis to expose the tendons and muscles of the flexor digitorum superficialis.

 

 

 

Figure 5-30 Reflect the flexor digitorum superficialis and note that the median nerve moves with it, because it is attached to the muscle via the posterior fascia of the muscle.

 

Distal Extension. The skin incision can be extended into a volar zigzag approach for any of the fingers, providing complete exposure of all the palmar structures (see Volar Approach to the Flexor Tendons and Fig. 5-45).

Volar Approach to the Ulnar Nerve

The volar approach is used for exploration of the ulnar nerve at the wrist. It is used primarily to decompress the canal of Guyon in cases of ulnar nerve compression. It also permits exploration of the ulnar nerve in cases of trauma. The approach is freely extensile proximally, allowing exposure of the nerve all the way up the forearm.

 

Position of the Patient

 

Place the patient supine on the operating table. Rest the hand on a hand table in the supinated position, so that the palm faces upward. Use an exsanguinating soft bandage, then inflate a tourniquet (see Fig. 5-15).

 

Landmarks and Incision

Landmarks

The hypothenar eminence is a readily palpable group of muscles on the ulnar border of the hand. The proximal transverse skin crease of the wrist overlies the wrist joint.

Incision

Make a curved incision, following the radial border of the hypothenar eminence and crossing the wrist joint obliquely at about 60 degrees. Extend the incision onto the volar aspect of the distal forearm. The incision should be about 5 to 6 cm long (Fig. 5-31).

 

Internervous Plane

 

There is no internervous plane. The approach is a true anatomic dissection in which the nerve and vessels are dissected out and preserved.

 

Superficial Surgical Dissection

 

Deepen the incision in the line of the skin incision and identify the tendon of the flexor carpi ulnaris in the proximal end of the wound (Fig. 5-32). Take care to identify and preserve the palmar cutaneous branch of the ulnar nerve which lies close to the plane of dissection in most patients. Mobilize the tendon by incising the fascia on its radial border, and retract the muscle and tendon in an ulnar direction to reveal the ulnar nerve and

artery (Fig. 5-33).

 

 

 

Figure 5-31 Incision for the exposure of the ulnar nerve in the canal of Guyon.

 

 

Figure 5-32 The volar carpal ligament is seen as a continuation of the deep palmar fascia and fibers of the flexor carpi ulnaris.

 

 

Figure 5-33 The volar carpal ligament is isolated and the nerve is protected in preparation for sectioning of the volar carpal ligament.

 

Deep Surgical Dissection

 

Trace the nerve and artery distally, incising overlying fibrous tissue, the volar carpal ligament. During this procedure, take great care to protect the nerve and vessel. The ulnar nerve now is exposed across the wrist joint; the canal of Guyon is decompressed (Fig. 5-34).

 

 

Dang

 

 

Nerves

The ulnar nerve is vulnerable during two phases of the dissection:

1. When the fascia on the radial side of the flexor carpi ulnaris is incised to allow retraction of the muscle, during superficial surgical dissection

2. When the volar carpal ligament is incised, during deep surgical dissection

If care is taken during these two phases of the procedure, the nerve should be safe.

 

How to Enlarge the Approach

Extensile Measures

 

Proximal Extension. Extend the skin incision proximally on the anterior aspect of the forearm, running it longitudinally up the middle of the forearm (Fig. 5-35). Incise the deep fascia in line with the incision and identify the radial border of the flexor carpi ulnaris. Develop a plane between the flexor carpi ulnaris muscle (which is supplied by the ulnar nerve) and the flexor digitorum superficialis muscle (which is supplied by the median nerve), retracting the flexor carpi ulnaris toward the ulna to reveal the ulnar nerve. This incision can expose the ulnar nerve almost to the level of the elbow joint (Fig. 5-36), where it passes between the two heads of the flexor carpi ulnaris muscle. If the nerve is exposed for a long distance, take care to preserve as many small vessels attaching to it as possible.

 

 

 

Figure 5-34 The roof of the canal has been incised, revealing the ulnar nerve and artery.

 

 

 

Figure 5-35 Explore the ulnar nerve proximally in the forearm.

 

 

 

Figure 5-36 Develop the plane between the flexor carpi ulnaris and the flexor digitorum superficialis. In the depth of the wound, the ulnar nerve is visualized running under the flexor carpi ulnaris.

 

Applied Surgical Anatomy of the Volar Aspect of the Wrist

 

 

 

Overview

 

The carpal tunnel is a fibroosseous canal on the volar surface of the carpus. Its base is formed by the deeply concave surface of the volar aspect of the carpal bones, and its roof is formed by the flexor retinaculum (Fig. 5-37). The ulnar nerve runs over the surface of the flexor retinaculum; it is enclosed in its own fibroosseous canal, the canal of Guyon (Fig. 5-38).

 

Landmarks and Incision

 

The four attachments of the flexor retinaculum all are palpable (Figs. 5-42 and 5-43A):

1. The pisiform. This is located on the ulnar border of the wrist. The pisiform is a mobile sesamoid bone lying within the tendon of the flexor carpi ulnaris muscle. The bone was sometimes used by artisans to tap nails into soft wood or leather. Historically stress fractures were noted in cobblers who used to use the pisiform for this purpose. Acute fractures have been described in contact sports athletes14,15 and pisotriquetral arthrosis may be a cause of ulnar wrist pain.16

2. The hook of the hamate. This is slightly distal and radial to the pisiform. To locate it, place the interphalangeal joint of the thumb on the pisiform, pointing the tip toward the web space between the thumb and the index finger, and rest the tip of the thumb on the palm. The hook of the hamate lies directly under the thumb. Because it is buried under layers of soft tissue, one must press firmly to find its rather shallow contours. The deep branch of the ulnar nerve lies on the hook, and neurapraxia of the nerve has been described in cases of fracture.17

3. The ridge of the trapezium. The trapezium lies on the radial side of the carpus where it articulates with the first metacarpal. To palpate the ridge, identify the joint between the trapezium and the thumb’s metacarpal bone by moving the joint passively. The ridge feels like a prominent lump on the volar aspect of the trapezium (see Fig. 5-43A).

4. The tubercle of the scaphoid. This small protuberance is barely palpable just distal to the distal end of the radius on the volar aspect of the wrist joint (see Figs. 5-42 and 5-43A).

On its radial side, the retinaculum also attaches across the groove on the trapezium, converting the groove into a tunnel through which the

tendon of the flexor carpi radialis muscle runs before it attaches to the base of the second and third metacarpals (see Figs. 5-42 and 5-43A).

 

 

 

Figure 5-37 Superficial anatomy of the wrist and palm. Note the course of the cutaneous branch of the median nerve. The longitudinal bands of the palmar aponeurosis are continuations of the palmaris longus tendon.

 

Superficial Surgical Dissection and Its Dangers

 

Three structures run across the surface of the flexor retinaculum (see Fig. 5-37):

1. Tendon of the palmaris longus. The palmaris longus is a vestigial muscle of no functional importance. Its tendon is used frequently for tendon grafting. It is important to test for the presence of this tendon before surgery, because it is absent in about 10% of the population. The tendon also is used as an anatomic landmark for the injection of steroid into the

   carpal tunnel. If the patient is asked to flex the wrist against resistance while pinching his fingers together the tendon of the palmaris longus (if it is present) is easily palpable together with the thicker and more radially located tendon of the flexor carpi radialis. The easily defined gap between the two tendons is the site where the needle should be inserted for injection of the carpal tunnel. The needle should be inserted here dorsally and distally at an angle of almost 45 degrees. Note also that because the carpal tunnel is a distensible space, if problems are encountered in injecting it, then the tip of the needle either is still in the flexor retinaculum or is imbedded in one of the tendons in the tunnel.

   Fluid inserted through correctly positioned syringes should enter the space without encountering much resistance to pressure.

2. Palmar cutaneous branch of the median nerve. The course of the palmar cutaneous branch of the median nerve may vary in four important ways (see Fig. 5-37)18,19,20:

   1. Normally, the nerve branches off 5 cm proximal to the wrist. It runs along the ulnar side of the tendon of the flexor carpi radialis before crossing the flexor retinaculum. On rare occasions, the nerve actually may be enclosed by parts of the flexor retinaculum and, thus, may run in a tunnel of its own on the wrist.

       

       

      Figure 5-38 The palmar aponeurosis and fascia have been elevated to reveal the transverse carpal ligament. The fascia of the forearm and the expansions of the flexor carpi ulnaris (volar carpal ligament) are left intact where they form the roof of the tunnel of Guyon. The canal of Guyon looking from proximal to distal (inset). The transverse carpal ligament forms the floor of the tunnel of Guyon; the roof is formed by the volar carpal ligament, which is a condensation of the fascia of the forearm and expansions of the flexor carpi ulnaris tendon. The canal is formed

      medially by the pisiform bone and laterally by the hook of the hamate bone.

       

       

       

      Figure 5-39 The palmar aponeurosis has been resected further distally to expose the superficial palmar arterial arch. The transverse carpal ligament also has been resected. The median nerve lies superficial to the tendons of the profundus, but at the same level with the superficialis muscle tendons. Note the motor branch of the median nerve to the thenar muscles. The location of its division from the median nerve is quite variable.

       

      The nerve divides into two major branches, medial and lateral, while crossing the flexor retinaculum. The lateral is the larger branch. Both supply the skin of the thenar eminence.

   2. Less often, the nerve arises from the median nerve in two distinct branches, which travel separately across the wrist.21

   3. The palmar cutaneous branch may arise within the carpal tunnel and

      penetrate the flexor retinaculum to supply the skin of the thenar eminence.

   4. The palmar cutaneous branch may be absent, replaced by a branch derived from the radial nerve, the musculocutaneous nerve, or the ulnar nerve.21

      The skin incision described above avoids cutting the nerve by angling across the distal forearm in an ulnar direction. One must be aware, however, that considerable variability exists in the course of the nerve. Because damage can result in the formation of a painful neuroma, transverse incisions on the volar aspect of the distal forearm must be avoided. (Compression lesions of the nerve have been reported, but these are rare.)22,23

3. Ulnar nerve and palmar cutaneous branch of ulnar nerve.24 The ulnar nerve runs down the volar surface of the distal forearm under cover of the flexor carpi ulnaris muscle (see Fig. 5-38). The ulnar artery lies on its radial side. The tendon of the flexor carpi ulnaris inserts into the pisiform, which then joins with the hamate and fifth metacarpal via ligaments. Just proximal to the wrist, the artery and nerve emerge from under the tendon to pass over the flexor retinaculum (the transverse carpal ligament) of the wrist (see Fig. 5-38).

 

 

Figure 5-40 The palmar aponeurosis has been elevated up to its attachment to the digital flexor sheaths. Its deeper attachments to the volar plate and bone have been cut. The flexor tendons and digital nerves are shown in continuity, as are the superficial palmar arch and the thenar and hypothenar muscles. Note that the digital nerves and vessels go deep or dorsal to the natatory ligaments.

 

Flexor Pollicis Brevis. Origin. The muscle’s superficial part arises from the distal edge of the flexor retinaculum and the tubercle of the trapezium, a bone in the wrist. It passes along the radial side of the tendon of the flexor pollicis longus. The deeper (and medial) portion of the muscle is very small, and arises from the ulnar side of the first metacarpal bone between the oblique part of the adductor pollicis and the lateral head of the first dorsal interosseous muscle. Insertion. The superficial head is inserted into the radial side of the base of the proximal phalanx of the thumb; in its

tendon of insertion there is a sesamoid bone. The deep head is inserted into the ulnar side of the base of the first phalanx with the adductor pollicis. Action. Flexor of the metacarpophalangeal joint of the thumb. Nerve supply. Superficial head—median nerve (motor or recurrent branch). Deep head—deep branch of ulnar nerve.

Abductor Pollicis Brevis. Origin. Flexor retinaculum and tubercle of scaphoid. Insertion. Radial side of base of proximal phalanx of thumb. Action. Abduction of thumb at metacarpophalangeal joint and rotation of proximal phalanx of thumb. Nerve supply. Median nerve (motor or recurrent branch).

 

 

 

Figure 5-41 Portions of the thenar and hypothenar muscles have been resected to reveal their layering. The ulnar nerve passes between the origin of the abductor digiti minimi and the flexor digiti minimi. In the thenar region, the course of the flexor pollicis longus is seen as it crosses between the two heads of the flexor

pollicis brevis. Portions of the long flexors of the fingers have been resected to show their layering. The superficial palmar arch runs superficial to the tendons, whereas the deep palmar arch is immediately deep to the tendons. Note that potential spaces develop on the undersurface of the flexor tendons and their sheaths, and on the deep intrinsic muscles of the hand, the interosseous on the hypothenar side and the adductor pollicis on the thenar side. A septum that runs from the undersurface of the flexor tendons to the third metacarpal divides the two spaces. More distally, the superficial transverse ligament has been resected, revealing the course of the lumbricals and the digital vessels that run superficial or palmar to the deep transverse metacarpal ligaments.

 

Adductor Pollicis. Origin. Oblique head from bases of second and third metacarpals, trapezoid, and capitate. Transverse head from palmar border of third metacarpal. Insertion. Ulnar side of base of proximal phalanx of thumb via ulnar sesamoid. Action. Adduction of thumb. Opposition of thumb. Nerve supply. Deep branch of ulnar nerve.

Opponens Pollicis. Origin. Flexor retinaculum. Insertion. Radial border of thumb metacarpal. Action. Opposition of metacarpal bone of thumb. Nerve supply. Median nerve (motor or recurrent branch).

 

 

Figure 5-42 The deepest layer of the palm is revealed. The deep palmar arterial arch lies deep to the long flexor tendons and superficial to the interosseous muscles. It crosses the palm with the deep branch (motor branch) of the ulnar nerve. The nerve supplies all the interosseous muscles. More distal, the interosseous muscles are seen running deep (dorsal) to the deep transverse ligament. The deep transverse metacarpal ligaments attach to the palmar plate, which is seen on the fifth metacarpal. The pulleys of the thumb are seen in relationship to the digital nerves.

 

 

 

Figure 5-43 A: The bones of the wrist and palm and the proximal metacarpals are seen in relationship to the creases of the wrist. The necks of the metacarpals are at the level of the distal palmar crease. The distal wrist crease runs from the proximal

portion of the pisiform to the proximal portion of the tubercle of the scaphoid and marks the proximal level of volar carpal ligament. The proximal transverse palmar crease is at the radiocarpal joint. B: Kaplan’s cardinal line. Used to locate the motor branch of the median nerve to the thenar muscles.

 

At this level, the anatomic arrangement of these structures can be remembered by the mnemonic “ANT”: The artery is the most lateral structure, then the nerve, and, finally, the tendon of the flexor carpi ulnaris (see Fig. 5-38).

The palmar cutaneous branch arises in the forearm. It travels lateral to the ulnar artery in 75% of patients. The nerve perforates the fascia of the anterior forearm just proximal to the distal wrist crease. In the palm, the nerve travels superficial to the superficial palmar arch in most cases. It is therefore at risk during decompression of the ulnar nerve in the Canal of Guyon.

At the wrist, the nerve is particularly vulnerable to damage by lacerations. The grim triad of lacerations of the tendon of the flexor carpi ulnaris, the ulnar artery, and the ulnar nerve is a common sequela of falling through a window with the ulnar border of the wrist flung forward to protect the face.

As the nerve crosses the flexor retinaculum, it is covered with a tough fibrous tissue that is continuous with the deep fascia of the forearm, the volar carpal ligament. The tunnel thus formed, the canal of Guyon, has four boundaries: A floor, the flexor retinaculum (transverse carpal ligament); a medial wall, the pisiform; a lateral wall, the hamate; and a roof, the volar carpal ligament (distal fascia of the forearm; see Fig. 5-38).

Around the pisiform, the ulnar nerve divides into two branches. The superficial branch supplies the palmaris brevis muscle and the skin of the small finger and ulnar half of the ring finger. The deep branch supplies all the small intrinsic muscles of the hand, except those of the thenar eminence and the radial two lumbricals (see Figs. 5-39 to 5-42).

 

Deep Surgical Dissection and Its Dangers

Median Nerve

The median nerve crosses the volar aspect of the distal forearm deep to the flexor digitorum superficialis muscle. Just above the wrist, it becomes superficial and lies between the tendons of the palmaris longus and flexor carpi radialis muscles. It enters the palm by traversing the carpal tunnel (see Fig. 5-38).

Within the tunnel, the nerve lies superficial to the tendons of the flexor digitorum profundus and flexor pollicis longus muscles. The superficialis tendons lie toward the ulnar side of the nerve. At the distal border of the flexor retinaculum, the nerve divides into two branches (see Figs. 5-39 and 5-40).

1. The medial branch sends cutaneous branches to the adjacent sides of the ring and middle fingers, and to the adjacent sides of the middle and index fingers.

2. The lateral branch sends cutaneous branches to the radial side of the index finger and to both sides of the thumb. The lateral branch usually also sends off the motor, or recurrent, nerve (see Fig. 5-39), which is the key surgical landmark and major surgical danger in carpal tunnel decompression.

The motor nerve supplies the muscles of the thenar eminence. Its course may take any one of eight significant variations22,25:

1. The classic course (seen in 50% of patients). The branch arises from the volar radial aspect of the median nerve distal to the radial end of the carpal tunnel. The nerve hooks radially and upward to enter the thenar muscle group between the flexor pollicis brevis and abductor pollicis brevis muscles.

2. The position of the motor branch can be estimated by drawing one vertical line from the web space between the middle and index fingers, drawing another from the radial origin of the first web space, then connecting to the hook of the hamate (Kaplan’s cardinal line). The intersection of these two lines marks the entrance of the motor branch into the thenar muscles (see Fig. 5-43B).26

3. A variation that occurs in about 30% of patients. The branch arises from the anterior surface of the nerve within the carpal tunnel. It passes through the tunnel with its parent nerve and hooks around the distal end of the flexor retinaculum to enter the thenar group between the flexor pollicis brevis and abductor pollicis brevis muscles.

4. A variation that occurs in about 20% of patients. The branch arises from the anterior surface of the nerve within the carpal tunnel. It travels radially to pierce the flexor retinaculum and enter the thenar group of muscles between the abductor pollicis brevis and flexor pollicis brevis muscles.27

5. A rare variation. The branch arises from the ulnar side of the median

   nerve.28 It crosses the median nerve within the tunnel, then hooks around the distal end of the flexor retinaculum to enter the thenar muscle group. It also may pass through the flexor retinaculum and lie anterior to it.29

6. Another rare variation. The nerve arises from the anterior surface of the median nerve within the carpal tunnel. At the distal end of the flexor retinaculum, the branch hooks radially over the top of the retinaculum. The nerve crosses the distal part of the retinaculum almost transversely before entering the thenar group of muscles.

7. A very rare variation (multiple motor branches).30 Double nerves may follow any of the courses described above.

8. A third rare variation (high division of the median nerve).31 The nerve may divide into medial and lateral branches high up in the forearm. The thenar branch, originating from the lateral branch, may leave the carpal tunnel either in the conventional manner or by piercing the flexor retinaculum on its radial side.

All these variations should be considered when the nerve is exposed. If the tunnel is opened on the ulnar side of the nerve, the motor branch will be preserved unless it lies on the same side. Patients with exceptionally rare variations usually have large palmaris brevis muscles, which should alert the surgeon to the possibility during the approach.22

Flexor Digitorum Superficialis

Within the carpal tunnel, the tendons to the middle and ring fingers are superficial to the tendons of the index and little fingers. This arrangement dictates correct repair in cases of multiple tendon laceration (see Figs. 5-38 and 5-41).

Flexor Digitorum Profundus

The tendons of the flexor digitorum profundus lie deep to the tendons of the flexor digitorum superficialis. The tendon to the index finger is separate; the other three still may be attached partially to each other as they pass through the carpal tunnel (see Fig. 5-41).

Flexor Pollicis Longus

The tendon of the flexor pollicis longus lies deep to that of the flexor carpi radialis and is found on the most radial aspect of the canal at the same depth as the profundus tendons (see Fig. 5-41).

Flexor Carpi Radialis

The flexor carpi radialis tendon perforates the flexor retinaculum to lie in the groove of the trapezium before it inserts into the bases of the second and third metacarpals. It does not pass through the carpal tunnel (see Fig. 5-42).