Jeffrey B. Friedrich and Scott H. Kozin
DEFINITION
The median nerve can be compromised by any number of causes, including trauma, tumor, chronic compression, or synovitis.
Palsy of the median nerve can result in motor or sensory deficits, or both, within the distribution of this nerve.
ANATOMY
The median nerve enters the forearm between the two heads of the pronator teres muscle.
The median nerve travels down the forearm between the flexor digitorum superficialis and profundus muscles to enter the carpal tunnel.
Along its course, the anterior interosseous nerve branches from the median nerve to provide innervation to the flexor pollicis longus, flexor digitorum profundus (FDP) to the index, and the pronator quadratus muscles.
The median nerve proper provides innervation to the flexor carpi radialis, pronator teres, flexor digitorum superficialis (FDS), palmaris longus, and FDP to the long finger.
The palmar cutaneous branch arises from the median nerve 5 cm proximal to the wrist joint, crosses the wrist volar to the transverse carpal ligament, and supplies sensibility to the thenar eminence.
Just proximal to the wrist, the median nerve becomes superficial and travels within the carpal tunnel.
The recurrent motor branch originates from the central or radial portion of the median nerve during its passage through the carpal tunnel. The recurrent branch usually passes distal to the transverse carpal ligament to innervate the thenar muscles. The nerve can also pass through the transverse carpal ligament (occurs in 5% to 7% of individuals).6
The thenar muscles are the opponens pollicis, flexor pollicis brevis, and abductor pollicis brevis. The flexor pollicis brevis muscle receives dual innervation from both the recurrent branch and the deep motor branch of the ulnar nerve.
The median nerve terminates into multiple sensory branches, which supply sensibility to the thumb, index, long, and ring (radial side) fingers. The sensory branches to the radial side of the index and radial side of the long fingers possess a minor motor component that sends a small branch that innervates the adjacent lumbrical muscle.
PATHOGENESIS
Most injuries to the median nerve occur at the wrist and affect the thenar muscles. The resultant functional loss is lack of thumb opposition.
Compression injuries are most common and are usually attributed to prolonged carpal tunnel syndrome.
Carpal tunnel compression may also be secondary to tumor, adjacent synovitis, or fracture-dislocation.
Penetrating or perforating injuries may directly damage the median nerve.
Pediatric causes include lipofibrohamartoma of the median nerve or Charcot-Marie-Tooth disease, a demyelinating process that has a preference for the median and ulnar nerves (FIG 1).6
High median nerve injuries are rare. Similar causes exist, including trauma and nerve compression.
NATURAL HISTORY
With a median nerve compression neuropathy (ie, carpal tunnel syndrome), palsy of the median nerve is insidious in onset and manifestation. Over a period of months to years, patients can progress to decreased median nerve function as well as sensory changes in the dermatome of this nerve.
Acute injuries to the median nerve at the wrist or elbow have a traumatic onset followed by sensory or motor changes, or both.
PATIENT HISTORY AND PHYSICAL FINDINGS
Compressive neuropathy of the median nerve
Patients report pain, numbness, and tingling in the thumb, index, middle, and sometimes ring ringer of the affected hand. They frequently describe problems with fine coordination of the hand, notably problems with pinch. Patients often report pain and numbness that awakens them at night.
Physical examination findings include thenar muscle wasting and diminished thumb opposition (defined as the combination of palmar abduction, metacarpophalangeal [MCP] joint flexion, and thumb pronation).
FIG 1 • Left hand of 16-year-old boy with Charcot-Marie-Tooth disorder resulting in median nerve palsy. Note inability to oppose thumb with attempt to touch small fingertip. (Courtesy of Shriners Hospital for Children, Philadelphia.)
Additional signs include the Tinel sign, the Phalen sign, the carpal tunnel compression sign, and increased two-point discrimination in the thumb, index, and long fingers.
High median nerve neuropathies have similar findings, in addition to loss of forearm pronation and flexion of the thumb, index, and long fingers.
Acute median nerve injury
There is nearly always a wound on the upper extremity, usually on the volar wrist.
Physical findings include diminished sensibility in the thumb, index, and long fingers; increased two-point discrimination in those fingers; and an inability to touch the thumb tip to the small finger (ie, loss of opposition).
Depending on the level of injury, patients may display diminished sensibility of the thenar eminence of the thumb, signifying an injury proximal to the palmar cutaneous branch of the median nerve, or a concomitant injury to the palmar cutaneous branch.
Higher median nerve neuropathies have similar findings, in addition to loss of forearm pronation and flexion of the thumb, index, and long fingers.
Patients with median nerve palsy will not be able to oppose thumb to small finger. There may be some palmar abduction due to function of the abductor pollicis longus or extensor pollicis brevis muscles, but this will be minor. The ulnar-innervated deep head of the flexor pollicis brevis muscle will still function, creating MCP joint flexion but not true opposition.
Inability to make an “OK” sign indicates anterior interosseous nerve injury and high median nerve pathology.
The clinician should ask the patient to try to touch thumb to small finger with the wrist flexed. Due to median nerve palsy, the patient will likely not be able to fully touch the thumb to the small finger. However, if the palmaris longus is present, it will be visible as it tents up the skin over the volar wrist.
The patient is asked to spread his or her fingers apart and hold them against adduction pressure on the small finger. The examiner feels for resistance and palpates the hypothenar eminence at the same time. There should be resistance to adduction force on the small finger, and firmness of the hypothenar eminence should be appreciated.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Radiographs
Plain radiographs are helpful in determining the nature of fractures or dislocations after acute trauma to the upper extremity.
Specific carpal tunnel radiographic views may demonstrate osteophytes within the carpal tunnel, but they are not routinely performed.
Electrodiagnostic studies
In the setting of compressive neuropathy of the median nerve, nerve conduction studies typically show increased motor and sensory latencies in the median distribution.
In advanced stages of compressive neuropathy, electromyography demonstrates fibrillation potentials in various muscles tested, most commonly the abductor pollicis brevis. These fibrillation potentials signify denervation of the tested muscle.
Advanced high median nerve neuropathy reveals fibrillation potentials in more proximal muscles, such as the flexor carpi radialis and the pronator teres.
DIFFERENTIAL DIAGNOSIS
Carpal tunnel syndrome
Anterior interosseous syndrome
Pronator syndrome
Wrist synovitis
Direct injury to the median nerve
Tumor compression of the median nerve
Charcot-Marie-Tooth disease
Brachial plexus injury
Stroke or other brain injury
NONOPERATIVE MANAGEMENT
Patients with demonstrable carpal tunnel syndrome can undergo a trial of splinting, wrist corticosteroid injection, or both.
Work modification is indicated in patients with compressive neuropathy as a result of overuse for both carpal tunnel and pronator syndromes.
Anti-inflammatory and immunomodulatory medications are indicated in patients with wrist synovitis secondary to inflammatory arthropathy.
SURGICAL MANAGEMENT
The chief surgical modality for a low or high median nerve palsy that has not responded to surgery or other interventions is tendon transfer.3,6
Typically, in a low median nerve palsy, the only function that requires restoration via tendon transfer is thumb opposition, which is a combination of palmar abduction, MCP joint flexion, and thumb pronation.
In a high median nerve palsy, the additional loss of flexion of the thumb, index, and long fingers requires tendon transfer. In addition, lack of pronation may require tendon transfer.
Preoperative Planning
The surgeon must ensure that there is good passive range of motion of the joints to be mobilized.
In longstanding median nerve palsy, the thumb MCP and carpometacarpal joints can become quite stiff.
Physical therapy must be employed to loosen these joints and increase their range of motion.3 This can usually be accomplished in 3 to 6 weeks.
A thorough assessment of muscle function and strength is made before selecting a transfer, especially in the setting of combined nerve deficits.
When performing an opponensplasty, the donor tendon and attachment site are individualized to the particular patient, his or her injury, his or her needs, and the donor muscle–tendon availability. As the attachment site moves more dorsal, the amount of pronation and thumb extension is increased.
Donor options for opponensplasty include:
FDS
Abductor digiti minimi (Huber)
Extensor indicis proprius (EIP)
Palmaris longus (Camitz). The palmaris transfer is associated with more abduction and less opposition compared to other opposition transfers.3
Other less common donors include the extensor pollicis longus, extensor carpi ulnaris, extensor carpi radialis brevis, and extensor digitorum quinti.4
Opponensplasty attachment site options include the following:3
Abductor pollicis brevis tendon. This yields a lot of thumb abduction and some opposition.
Extensor pollicis brevis or longus tendons. This yields thumb abduction, pronation, and MCP joint extension.
Single attachment options
Riordan's technique involves interweaving the transferred tendon into the abductor pollicis brevis tendon, with continuation onto the extensor pollicis longus tendon distal to the MCP joint.
Littler's technique attaches the transferred tendon into the abductor pollicis brevis tendon.
Bunnell's method involves passing the tendon through a small drill hole made at the proximal phalanx base from the dorso-ulnar to palmar-radial direction to provide pronation of the thumb.
Dual attachment options
These are designed to rotate (pronate) the thumb and either passively stabilize the MCP joint or minimize interphalangeal joint flexion.
There is a theoretical benefit in patients with combined median and ulnar nerve deficits who lack all thumb intrinsic function.
Some authors question the utility of dual insertion techniques since the transfer will only function predominantly on the tighter of the two insertions.
In Brand's technique, one half is woven through the abductor pollicis brevis tendon and then passed distal to the MCP joint and attached to the extensor pollicis longus tendon.
In the Royle-Thompson method, a slip is passed through a drill hole made in the metacarpal neck, from radial to ulnar, with the metacarpal pulled into as much opposition as possible. This slip is tied to the other half that is initially passed dorsally over the extensor hood at the MCP joint and through a small tunnel in the fascia and periosteum at the base of the proximal phalanx.
High median nerve palsies require additional restoration of thumb, index, and long finger flexion. On occasion, reestablishment of pronation is required.
Flexion of the index and long fingers can be accomplished by side-to-side transfers of the FDP tendons of the index and long to the ring and small. We transect the recipient tendons proximal to the wrist and weave them into the donor tendons.
Thumb flexion can be restored by transfer of the brachioradialis to the flexor pollicis longus.
Loss of pronation can be overcome by rerouting the biceps around the radius, which converts the biceps from a supinator into a pronator.
Positioning
The patient is positioned supine on the operating table.
The affected limb is abducted at the shoulder and placed on an attached hand table or armboard.
Approach
The approach to opponensplasty for median nerve palsy depends on two factors: the donor tendon and the site of attachment.
TECHNIQUES
LOW MEDIAN NERVE TRANSFERS
Flexor Digitorum Superficialis Transfer (Authors' Preferred Technique6)
Separate the radial half of the tendon longitudinally from the ulnar half, creating a distally based strip of tendon graft.
Loop the tendon graft distally and pass it through the distal portion of the FCU near the pisiform insertion to create a pulley.
Make a palmar transverse skin incision over the first annular pulley of the ring finger.
Identify the A1 pulley and incise it longitudinally. Isolate the FDS tendon.
Apply traction to the FDS tendon to flex the proximal interphalangeal joint (TECH FIG 1A), and divide the FDS tendon transversely just proximal to its bifurcation while protecting the FDP tendon.
Make a second zigzag incision at the volar ulnar distal forearm in the region of the flexor carpi ulnaris (FCU) tendon insertion.
Isolate the FCU and the ring finger FDS tendons and protect the ulnar neurovascular bundle.
Divide the radial half of the FCU tendon transversely about 4 cm proximal to its insertion onto the pisiform.
TECH FIG 1 • A. Isolation of ring finger flexor digitorum superficialis (FDS) to be transferred for thumb opposition. B. Ring finger FDS passed through the flexor carpi ulnaris, which now serves as the pulley for the transferred tendon. C. Creation of the subcutaneous tunnel between the ulnar wrist and thumb incisions, through which the FDS tendon will be passed. D. Ring finger FDS tendon shown passing through both the flexor carpi ulnaris tendon and the subcutaneous tunnel. E. Suture fixation of the FDS tendon to the abductor tendon and extensor hood of the thumb. (Courtesy of Shriners Hospital for Children, Philadelphia.)
Pull the cut ring finger FDS tendon into the volar ulnar forearm incision and pass it through the constructed pulley (TECH FIG 1B).
Make a third incision on the radial aspect of the thumb MCP joint.
Create a subcutaneous tunnel between this incision and the wrist incision (TECH FIG 1C).
Pass the ring FDS tendon through this tunnel to the thumb incision (TECH FIG 1D).
Place the thumb into opposition with the small finger.
Secure the FDS tendon to the thumb with a 3-0 or 4-0 braided polyester suture (TECH FIG 1E).
The attachment sites usually include the abductor tendon plus or minus the dorsal capsule and extensor pollicis brevis tendon.
Protect the ulnar sensory nerve to the small finger.
Divide the ADM insertion sites, including a portion of the lateral band to increase its overall length.
Dissect the muscle proximally to the pisiform (TECH FIG 2A).
Release the origin from the pisiform; identify and protect the neurovascular bundle (on the dorsoradial side).
Make a longitudinal incision on the radial aspect of the thumb MCP joint.
Use blunt dissection to create a subcutaneous tunnel in the palm.
Pass the ADM through the tunnel to the thumb MCP joint (TECH FIG 2B).
Secure the ADM tendon to the thumb using 3-0 or 4-0 braided polyester suture (TECH FIG 2C).
Abductor Digiti Minimi Transfer (Huber) 4
Make an oblique or zigzag incision beginning distally on the ulnar border of the small finger proximal phalanx, curving radially along the radial border of the hypothenar eminence.
Separate the abductor digiti minimi (ADM) muscle from the flexor digiti minimi. Dissect the ADM distally to its insertion into the proximal phalanx and lateral band.
TECH FIG 2 • A. Isolated and dissected abductor digiti minimi (ADM) muscle–tendon unit, to be used for transfer for thumb opposition (Huber transfer). B. Passage of the ADM muscle–tendon unit through the previously created subcutaneous tunnel to the thumb. C. Final position of thumb after suture fixation of the ADM to the thumb. Note opposition and palmar abduction. (Courtesy of Shriners Hospital for Children, Philadelphia.)
Extensor Indicis Proprius Transfer 4
Make a longitudinal incision on the dorsum of the index finger MCP joint.
Locate the EIP tendon deep and ulnar to the extensor digitorum communis tendon to the index finger (TECH FIG 3A).
Identify the EIP tendon along with the extensor hood.
Divide the EIP tendon on the proximal edge of the extensor hood. The EIP tendon can be elongated by taking a 3to 4-mm slip of extensor mechanism along the proximal phalanx. Repair the rent in the extensor hood with interrupted 4-0 braided polyester suture.
Make a longitudinal incision on the dorso-ulnar aspect of the wrist, just proximal to the point where the dorsal sensory branch of the ulnar nerve crosses near the ulnar styloid.
Carry dissection from this incision radially until the proximal EIP tendon can be identified (just distal to the extensor retinaculum) (TECH FIG 3B).
Divide the distal extensor retinaculum over the fourth compartment to release the EIP tendon.
Bring the EIP tendon out through the ulnar wrist incision (TECH FIG 3C).
Make another small longitudinal incision on the radial edge of the pisiform.
Make a fourth incision over the thumb MCP joint.
Create a subcutaneous tunnel from the ulnar wrist incision to the pisiform incision, then on to the thumb MCP joint incision, using blunt dissection.
Pass the EIP tendon first through the pisiform incision, then on to the thumb incision (TECH FIG 3D).
Suture the EIP tendon to the thumb using a 3-0 or 4-0 braided polyester suture.
TECH FIG 3 • A. Isolation of extensor indicis proprius (EIP) tendon ulnar and deep to the extensor digitorum communis tendon to the index finger. B. Wrist incision through which the proximal aspect of the EIP is found and isolated. C. The EIP tendon is brought out through the previously created ulnar wrist incision. D. Passage of EIP tendon through the subcutaneous tunnel between ulnar wrist incision and thumb incision.
Palmaris Longus Transfer (Camitz10)
Confirm the presence of a palmaris longus (PL) tendon by having the patient attempt to oppose the thumb to the small fingertip with the wrist flexed.
Make a longitudinal incision beginning at the distal wrist crease and continuing distally to the proximal palmar crease. This incision may be “zigzagged” at the wrist to prevent scar contracture.
Dissect the PL tendon proximally to distally.
Take a small (about 1 cm square) patch of palmar aponeurosis along with the PL tendon.
Make an incision over the dorsum of the thumb MCP joint.
Create the subcutaneous tunnel between the PL tendon and the MCP joint with blunt dissection.
Pass the PL tendon through the tunnel to the thumb incision.
Finally, secure the PL tendon to the thumb with 3-0 or 4-0 braided polyester suture.
HIGH MEDIAN NERVE TRANSFERS
Brachioradialis Transfer
Make a long radial incision from the radial styloid to the brachioradialis muscle belly.
Release the brachioradialis tendon from the radial styloid and mobilize it along the forearm to optimize available excursion (TECH FIG 4).7
Identify the flexor pollicis longus tendon deep to the flexor carpi radialis tendon.
Weave the harvested brachioradialis tendon into the flexor pollicis longus using a tendon braider and multiple weaves.
Determine proper tension of the transfer by placing the wrist in flexion and extension and judging tenodesis lateral pinch position and thumb release, respectively.
Biceps Rerouting
Biceps rerouting is our preferred technique for supple supination deformities of the forearm to correct the forearm position and to apply a pronation moment.
Surgery is performed under general anesthesia and an upper arm tourniquet is used. The upper extremity is prepared and draped in the usual sterile fashion. The limb is exsanguinated and the tourniquet inflated.
Design a Z-incision with a horizontal limb across the antecubital fossa (TECH FIG 5A).
Identify the lateral antebrachial cutaneous nerve lateral to the biceps tendon and protect it (TECH FIG 5B).
Isolate the biceps tendon and incise the lacertus fibrosis while protecting the underlying median nerve and brachial artery.
TECH FIG 4 • Brachioradialis harvested as donor for transfer to the flexor pollicis longus tendon (red loop) to restore lateral pinch. (Courtesy of Shriners Hospitals for Children, Philadelphia.)
TECH FIG 5 • A. Skin incision for biceps rerouting. B. Isolation of the biceps tendon and lacertus fibrosis. The lateral antebrachial cutaneous nerve is just lateral to the tendon. C. Biceps tendon is traced to its insertion into radial tuberosity. D. Z-plasty of the biceps tendon is planned along its entire length to ensure sufficient tendon length for passage around the radius. E. Z-plasty of entire biceps tendon. The distal Z-plasty is left attached to the insertion site and the proximal Zplasty is left attached to the muscle belly. F. A curved clamp facilitates tendon rerouting around the radius. G. Tendon is passed through interosseous space and around the radius. H. Distal limb is repaired back to proximal limb using a tendon weave augmented with nonabsorbable suture. (Courtesy of Shriners Hospital for Children, Philadelphia.)
Trace the biceps tendon to its insertion into the radial tuberosity by careful dissection and placement of the forearm into supination (TECH FIG 5C).
Plan a Z-plasty of the biceps tendon along its entire length to ensure sufficient tendon length for passage around the radius (TECH FIG 5D).
Leave the distal Z-plasty attached to the insertion site and leave the proximal Z-plasty attached to the muscle belly (TECH FIG 5E).
Carefully reroute the distal attachment around the radius through the interosseous space to create a pronation force. A curved clamp, such as a Deborah cast clamp or Castaneda pediatric clamp, facilitates tendon passage (TECH FIG 5F,G).
Protect the supinator muscle and posterior interosseous nerve to prevent injury.
Place the elbow in 90 degrees of flexion and the forearm in pronation. Repair the rerouted distal tendon back to the proximal tendon that is still attached to the biceps muscle using a tendon weave augmented by nonabsorbable suture (TECH FIG 5H).
Close the subcutaneous tissue and skin in routine fashion. Apply a long-arm cast with the elbow in 90 degrees of flexion and the forearm in pronation. The cast is worn for 5 weeks.
POSTOPERATIVE CARE
A bulky hand dressing and short-arm plaster splint is placed with the wrist in flexion and the thumb in full opposition.
Immediate hand therapy commences to maintain motion in the fingers, especially the ring finger after FDS harvest.
If the ring finger tends to position into flexion, a proximal interphalangeal joint extension splint is fabricated for nighttime wear.
In contrast, a ring finger that tends to swan-neck secondary to loss of the FDS tendon requires a silver ring splint to prevent deformity until the remaining FDS scars along the volar aspect of the proximal interphalangeal joint.
After 2 to 3 weeks, the plaster splint is removed and therapy is initiated. Longer periods of immobilization may yield scarring of the FDS tendon within the reconstructed pulley.
An Orthoplast splint is fabricated to maintain mild wrist flexion and thumb opposition. The splint is removed four to six times a day to encourage tendon gliding exercises and retraining of the transferred tendon.
Similar occupational therapy principles are applied after other opposition transfers as described, including the palmaris longus, EIP, abductor digiti minimi, and other transfers.
Patients are instructed in other modalities, including scar management, muscle–tendon re-education, and incorporation of the transfer into activities of daily living.
OUTCOMES
In general, opposition transfers are successful: most patients regain opposition adequate to perform normal daily activities such as writing, buttoning clothes, and other fine manipulation tasks (FIG 2).9
Burkhalter et al2 reported excellent results in 57 of 65 cases of EIP opponensplasty; excellent results were defined as those with 75% function compared to the opposite normal thumb or those with less than a 20-degree difference between the plane of the opposite thumbnail and the plane of the palm with good power.
Jacobs and Thompson,5 using a variety of donor tendons (mainly FDS IV and FDS III tendons), pulley designs, and insertion techniques, reported 77 good or excellent, 9 fair, and 17 poor results. Similar results were obtained with the FDS IV and FDS III tendons.
In a comparison of FDS versus EIP opponensplasty, Anderson et al1 compared 50 EIP to 116 FDS ring finger opponensplasty cases. Their analysis demonstrated that the EIP opponensplasty was best in supple hands, while the FDS opponensplasty was more suitable in less pliable hands.
COMPLICATIONS
Suboptimal transfer outcome due to stiff joints
Selection of suboptimal or weak muscle–tendon unit for transfer
Incorrect vector of pull due to lack of or poor selection of pulley
Rupture of transferred tendon
Tendon adhesions
Loss of grip strength after FDS ring finger transfer
Difficulty with muscle–tendon re-education, especially with tendon transfers that are not synergistic. For example, EIP transfer is more difficult to learn compared to FDS tendon transfer.
FIG 2 • Postoperative photo of patient from Figure 1. This demonstrates good thumb opposition after ring finger flexor digitorum superficialis transfer for thumb opposition. (Courtesy of Shriners Hospital for Children, Philadelphia.)
REFERENCES
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2. Burkhalter W, Christensen RC, Brown P. Extensor indicis proprius opponensplasty. J Bone Joint Surg Am 1973;55A:725–732.
3. Cooney WP. Tendon transfer for median nerve palsy. Hand Clin 1988;4:155–165.
4. Davis T. Median nerve palsy. In Green D, Hotchkiss R, Pederson W, et al, eds. Green's Operative Hand Surgery, 5th ed. Elsevier, 2005: 1131–1160.
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6. Kozin SH. Tendon transfers for radial and median nerve palsies. J Hand Ther 2005;18:208–215.
7. Kozin SH, Bednar M. The excursion of the brachioradialis muscle during tetraplegia reconstruction. J Hand Surg Am 2001; 26A:510–514.
8. Rath S. Immediate active mobilization versus immobilization for opposition tendon transfer in the hand. J Hand Surg Am 2006; 31A:754–759.
9. Sundararaj GD, Mani K. Surgical reconstruction of the hand with triple nerve palsy. J Bone Joint Surg Br 1984;66B: 260–264.
10. Trumble T. Tendon transfers. In Trumble T, ed. Principles of Hand Surgery and Therapy, 1st ed. Saunders, 2000:343–360.