ULNAR NERVE PALSY AND TENDON TRANSFERS

DR. N .BENTHUNGO TUNGOEMS(ORTHOPEDICS), PGCENTRAL INSTITUTE OF ORTHOPEDICS, NEW DELHI

Ulnar nerve: introduction

Spinal roots: C8-T1. Motor functions: Innervates the muscles of the hand (apart

from the thenar muscles and two lateral lumbricals), flexor carpi ulnaris and medial half of flexor digitorum profundus.

Sensory functions: Innervates the anterior and posterior surfaces of the medial one and half fingers, and the associated palm area.

Anatomy of ulnar nerve: In the arm, the ulnar nerve lies anterior to the triceps muscle. It travels through the cubital tunnel at the

elbow, and then passes between the two heads of the FCU, which it innervates. As it courses distally, it lies on the volar aspect of the FDP, and innervates the FDP to the small and ring

fingers. Approximately 7 cm proximal to the wrist, it gives off a dorsal sensory branch, which provides sensibility to the

ulnar aspect of the dorsal hand. At the wrist, the main nerve passes into Guyon’s canal along with the ulnar artery. Within Guyon’s canal it

divides into deep and superficial branches. The superficial branch gives sensibility to the small finger and the ulnar half of the ring finger. The deep motor branch innervates the hypothenar muscles, the ulnar two lumbricals, the interossei, the

adductor pollicis, and the deep head of the flexor pollicis brevis (FPB). The most distal motor branch innervates the first dorsal interosseous. Anomalous ulnar nerve anatomy is common in the forearm and hand.

The Martin-Gruber connection is seen when the median nerve contributes motor fibers to the ulnar nerve in the forearm, resulting in median nerve innervation of intrinsic hand muscles. This anomaly can result in intact intrinsic hand function following proximal ulnar nerve injury.

The Riche-Cannieu anomaly is a connection between the motor branch of the ulnar nerve and the recurrent motor branch of the median nerve in the hand, with ulnar to median innervation.3 This anomaly can result in preservation of thenar function after median nerve injury at the wrist or more proximally.

Motor Functions The Anterior Forearm

In the anterior forearm, the muscular branch of the ulnar nerve supplies two muscles:

Flexor carpi ulnaris – Flexes and adducts the hand at the wrist. Flexor digitorum profundus (medial half ) – Flexes the fingers.  The remaining muscles in the anterior forearm are innervated by the median nerve.

The Hand The majority of the intrinsic hand muscles are innervated by the deep branch of the

ulnar nerve. The hypothenar muscles (a group of muscles associated with the little finger) are

innervated by the ulnar nerve. It also innervates some other muscles of the hand: Medial two lumbricals Adductor pollicis Interossei of the hand

Sensory Functions There are three branches of the ulnar nerve

that are responsible for its cutaneous innervation.

Two of these branches arise in the forearm, and travel into the hand: Palmar cutaneous branch: Innervates the skin

of the medial half of the palm. Dorsal cutaneous branch: Innervates the skin

of the medial one and a half fingers, and the associated palm area.

The last branch arises in the hand itself: Superficial branch – Innervates the palmar

surface of the medial one and a half fingers

Clinical findings: Ulnar nerve palsy is a more devastating injury than radial nerve palsy. In both high and low ulnar nerve palsy, key pinch is lost because of absent adductor pollicis and first

dorsal interosseous muscle function. Clawing occurs as a result of paralysis of the interosseous muscles in the presence of functioning

extrinsic finger flexors. Clawing causes a loss of active IPJ extension and MCPJ flexion, which prevents the patient from cupping thehand around objects.

In addition, integration of MCPJ and IPJ flexion is lost. In the normal hand, integrated finger flexion begins at the MCPJ powered by the intrinsic muscles,

followed by flexion of all three finger joints powered by the FDP and FDS, folding the fingers smoothly into the palm.

In ulnar nerve palsy, MCPJ flexion is not initiated by the intrinsic muscles, and finger flexion begins at the IPJ’s, followed by late MCPJ flexion. This results in a rolling motion of the fingers, which prematurely closes them before they reach the palm, making it difficult to grasp objects.

In addition to the above findings, high ulnar nerve palsy results in loss of the FCU and FDP to the ring and little fingers. This causes diminished grip strength as well as the loss of ulnar deviation with wrist flexion.

A small benefit of diminished FDP function is that clawing is less severe than in low ulnar nerve palsy, in which the FDP to the ring and small fingers remains intact.

Unlike radial nerve palsy, the sensory deficit in ulnar nerve palsy is clinically disabling. Protective sensation in the ulnar nerve distribution is important for preventing injury when the hand is

placed in resting positions.

Mode of injury and assossciated clinical findings: Injury at the Elbow:

 The nerve is most vulnerable to injury at the medial epicondyle, so fracture of the medial epicondyle is the most common way of damaging the ulnar nerve

Motor functions: Flexor carpi ulnaris and medial half of flexor digitorum profundus paralysed. Flexion of the wrist can still occur, but is accompanied by abduction.

The interossei are paralysed, so abduction and adduction of the fingers cannot occur. Movement of the little and ring fingers is greatly reduced, due to paralysis of the medial two lumbricals.

Sensory functions: All sensory branches are affected, so there will be a loss of sensation over the areas that the ulnar nerve innervates.

Characteristic signs: Patient cannot grip paper placed between fingers.

INJURY AT THE WRIST MOTOR FUNCTIONS:

The interossei are paralysed, so abduction and adduction of the fingers cannot occur. Movement of the little and ring fingers is greatly reduced, due to paralysis of the medial two lumbricals.  The two muscles in the forearm are unaffected.

SENSORY FUNCTIONS: The palmar branch and superficial branch are usually severed, but the dorsal

branch is unaffected. Sensory loss over palmar side of medial one and a half fingers only.

Characteristic signs: Patient cannot grip paper placed between fingers. For long-term cases, a hand deformity called ‘Ulnar Claw’ develops.

Ulnar claw consists of: Hyper-extension of the metacarpophalangeal joints of the little and ring fingers – this

is because of the paralysis of the medial two lumbricals, and the now unopposed action of the extensor muscles

Flexion at the interphalangeal joints (if the lesion has occurred close to the elbow, this might not be evident, as the flexor digitorum profundus will be paralysed)

Bouvier’s test:

Bouvier’s test involves passively correcting the MCPJ hyperextension, and checking for improved IPJ extension.

If the patient’s flexed IPJ posture improves, then Bouvier’s test is positive, and the clawing is defined as simple.

If the IPJ’s remain flexed even after passive correction of the MCJP hyperextension, then Bouvier’s test is negative, and the clawing is defined as complex.

Clinical assessment of ulnar nerve:1. Flexor carpi ulnaris (C7–T1)

assessment, stabilizing the pisiform: While the patient abducts the

ipsilateral fifth digit, observe and palpate the flexor carpi ulnaris’ tendon just proximal to the wrist. The flexor carpi ulnaris contracts to stabilize the pisiform so that the abductor digiti minimi may function.

2. Flexor carpi ulnaris (C7-T1) assessment, wrist flexion

: Have the patient flex his or

her wrist against resistance in an ulnar direction, which is the primary action of this muscle.

3. Flexor digitorum profundus (C8, T1) assessment: This muscle is tested in

thesame fashion as its median innervated half, except to evaluate the ulnar nerve contribution

one uses the fifth digit. To test, immobilize the proximal interphalangeal joint while the patient flexes the distal interphalangeal joint against resistance.

4. Palmaris brevis (C8, T1) assessment:

Test this muscle by having the patient forcibly abduct the fifth digit and then instructing them to “contract” the hypothenar eminence simultaneously.

Skin corrugation should occur.

5. Abductor digiti minimi (C8, T1) assessment:

This muscle is tested when the patient abducts the fifth digit against resistance.

One should keep in mind that this muscle is delicate, the patient’s resistance is easily overcome even with normal strength.

6. Flexor digiti minimi (C8, T1) assessment : This muscle is tested by

immobilizing the interphalangeal joints of the fifth digit and having the patient flex the metacarpal-phalangeal (knuckle) joint against resistance.

One cannot isolate this muscle’s function, however, because flexion of the fifth digit’s metacarpal-phalangeal joint is performed by not only theflexor digiti minimi, but also by the fourth lumbrical and the interossei.

7. Opponens digiti minimi (C8, T1) assessment:

Have the patient hold the volar pads of the distal thumb and fifth digit together. While the patient maintains this position, try to force the proximal digit and distal fifth metacarpal away from the thumb.

8. Third and fourth lumbrical (C8, T1) assessment:

Immobilize the metacarpalphalangeal joints of these two fingers in hyperextension and then test extension of the proximal interphalangeal joints against resistance.

9. First dorsal interosseous (C8, T1) assessment

: On a flat surface, the patient abducts his or her index finger

against resistance. Contraction or atrophy of the

first dorsal nterosseous muscle can be observed and palpated on the dorsum of the hand.

9. Second palmar interosseous (C8, T1) assessment

: On a flat surface, the patient adducts the index finger against resistance.

10. Adductor pollicis assessment:

Ask the patient to grasp a book between extended thumb and index finger.

If the ulnar nerve is intact, he will grasp with extended thumb taking full advantage of adductor pollicis and first palmar interossei,

In ulnar nerve injury, the patient will hold the book by flexing the thumb with the help of flexor pollicis longus.(FROMENT’S SIGN)

11. Test for palmar interossei: Card Test

A card inserted between two extended fingers and the patient is asked to grasp it between the fingers while the clinician gently tries to pull the card.

Goals of tendon transfer in ulnar nerve pasly:

The primary goals of tendon transfer procedures for ulnar nerve palsy are restoration of

small and ring finger DIPJ flexion (in cases of high ulnar nerve palsy),

restoration of key pinch, correction of clawing, integration of MCPJ and IPJ flexion, and improvement in grip strength.

1. Restoring small and ring finger DIP joint flexion:

Restoration of small and ring finger DIPJ flexion can be achieved by adjacent suturing of their respective FDP tendons to the functioning middle finger FDP.

The index finger FDP should not be included in the adjacent suturing in order to preserve its independent functioning

Adjacent suturing of ring and small finger FDP to middle finger FDP for restoration of DIPflexion in ulnar palsy.

2. Restoring key pinch: In the normal hand, key pinch is the result of combined first dorsal interosseous

and adductor pollicis function

Both the ECRB (Smith) and brachioradialis (Boyes)are strong donor MTU’s that can be used to restore key pinch, and that do not leave a functional deficit when harvested.

They must be lengthened by tendon grafts and then passed between the 2nd and 3rd metacarpals into the palm. Here they are routed towards the thumb, using the 2nd metacarpal as a pulley, and inserted on the adductor pollicis insertion.

The direction change that occurs at the 2nd metacarpal pulley orients the tendon along the original direction of pull of the adductor pollicis.

ECRB (with tendon graft) transfer to adductor pollicis insertion for restoration of key pinch inulnar palsy.

3. Correction of clawing This requires correction of MCPJ hyperextension, the problem that initiates clawing. Procedures can be categorized as static or dynamic. If Bouvier’s test is positive,

static procedures may be successful. Dynamic tenodesis can be performed, as popularized by Fowler and Tsuge.

A tendon graft is looped through the extensor retinaculum at the wrist. The two free ends of the tendon graft are passed through the intermetacarpal spaces into the palm, along the course of the lumbricals, and out to the fingers where they are inserted to the lateral bands. When the wrist is flexed, an active tenodesis effect occurs, resulting in MCPJ flexion and IPJ extension.

Dynamic tenodesis with tendon graft for correction of clawing.

Brand, Riordan, and others described the use of wrist-level motors to treat clawing and integrate finger flexion as well as augment grip strength.

The FCR, ECRL, ECRB, or brachioradialis may be used. These MTU’s require a free tendon graft which is split into two or four slips to pass through the intermetacarpal spaces into the corresponding lumbrical canals.

The insertion can be into the lateral band, the proximal phalanx, or the A1 or A2 pulley.

The main advantage of these tendon transfer procedures over the superficialis transfers is that they improve rather than worsen grip strength.

ECRB transfer (extended with tendon graft to all four fingers) for correction of clawing.

modified Stiles-Bunnell procedure There are a number of tendon transfer procedures available that provide

dynamic correction of clawing, integrate MCPJ and IPJ flexion, and in some cases augment grip strength.

These can be divided into superficialis transfers and transfers powered by wrist motors.

In the modified Stiles-Bunnell procedure, the middle finger superficialis tendon is divided distally in the finger and retrieved into the palm. It is then split into four slips.

Each slip is then passed along the path of the lumbrical, volar to the deep transverse metacarpal ligament, and back into the finger, where it is inserted on the lateral band.

The main drawback of superficialis transfers is that although they reliably correct clawing and integrate finger flexion, they do not improve grip strength, and may even result in further weakening of an already diminished grip.

Modified Bunnell’s procedure:

Zancolli lasso insertion technique: Zancolli described a “lasso” insertion, wherein the FDS is passed through the A1 pulley, then sutured back onto itself, resulting in improved MCPJ flexion while avoiding PIPJ hyperextension.

Zancolli Lasso Procedure: A transverse incision was made at the level of the distal palmer crease. The flexor tendon sheaths were exposed from the middle of the metacarpal to the middle of the proximal

phalanx. The proximal pulley was identified by its thick, glistening fibrous strands. The flexor tendon sheath was opened proximal to the pulley by making a T-shaped incision. Distally the

digital fibrous tunnel was opened in an L-shaped incision at the level of the proximal arciform ligament. The flexor tendons were identified through the distal opening. The flexor digitorum superficialis tendon of the middle finger was hooked up and cut as distally as feasible

without injuring the profundus tendon that lies beneath it. The distal cut end was allowed to retract. The tendon was withdrawn through a small curved incision at the base of the palm along the thenar

crease. The tendon was split into 4 slips, one slip for each finger. The slips were passed deep to the palmar aponeurosis along the flexor sheath with the help of a tendon

tunneller. The slips were then passed under the proximal pulley of the corresponding finger and through the opening distal to the pulley, and the tendon was taken out and brought palmar to the pulley and proximally.

The slip was sutured to the same slip (thus forming a lasso) under proper tension with the metacarpophalangeal joint in 20º to 30º flexion and the wrist in 30º flexion.

Any excess tendon slip was cut off. This procedure was performed for all 4 fingers starting from the index finger, using the flexor digitorum superficialis of the middle finger