Median Nerve Palsy

Anatomy

  • Contains fibers from C6,7,8 & T1
  • Composed of lateral and medial roots from lateral and medical cords respectively

In axilla and arm –

  • Medial and lateral roots join to form Median nerve on the anterolateral side of 3rd portion of axillary artery
  • Courses distally in the medial intermuscular septum on anterior surface of brachial artery at middle level of arm
  • It then lies medial to brachial artery at level of elbow – here it is below the bicipital aponeurosis and superficial to brachialis muscle
  • (NO branches in arm)

In cubital fossa –

  • Nerve passes below bicipital aponeurosis and then continues to pass between two heads of Pronator Teres (Here it is separated by ulnar artery by deep (ulnar) head of PT.
  • Here it gives off muscular branches and AIN
  • After which it cross ulnar artery and passes beneath the tendinous band between two head of FDS- to enter the septum between FDS and FDP.
  • From here it continues in midline of forearm.
  • About 5cms from flexor retinaculum the nerve appears to lateral edge of FDS
  • It then lies between tendons of FDS & FCR and beneath tendon of PL before entering carpal tunnel

In the Carpal Tunnel

  • Nerve becomes palmar to tendons of FDS and lies immediately deep to flexor retinaculum
  • During travel in tunnel for about 2.5-3.0cm the median nerve becomes large and flattened
  • At distal edge of retinaculum, nerve divides into ulnar and radial terminal trunks
  • Radial trunk divides into thenar motor branch and 1st common digital nerve
  • Ulnar trunk divides into 2nd, 3rd and common digital nerve

Anterior Interosseous Nerve (AIN)

  • Originates from median nerve 5cm distal to medial epicondyle
  • Passes between FDP & FPL on interosseous membrane and supplies these two muscles
  • Further it courses between Pronator Quadratus and interosseous membrane and supplies PQ
  • It ends in articular branches of wrist
  • (AIN supplies radial side of FDP used for flexion of index and middle fingers]

 

Surface marking

In arm

  • with arm abducted, a line can be drawn from a point on the lateral wall of axilla, just posterior to the eminence of coracobrachialis and passing along medial bicipital groove to a point in the distal portion of cubital fossa

In forearm

  • With elbow extended, a line drawn from distal end of cubital fossa to point between the tendon of FCR and PL at wrist.
  • Nerve is found along this line

 

 

Motor supply of Median Nerve

PT

FCR

PL

FDS

FDP

FPL

PQ

Abductor Pollicis Brevis (APB)

FPB (Superficial head)

OP

Lumbrical – 1st and 2nd

 

AIN – Motor supply to FPL and FDS to index and middle

sensory distribution

MCNF – Medial cutaneous Nerve of forearm

LCNF- lateral cutaneous nerve of forearm

RN – Radial nerve sensory branch

MN- median nerve sensory branch

PCNF- posterior cutaneous nerve of forearm (Radial nerve)

 

 

Palmar cutaneous branch of median nerve –

– given off from radial side of median nerve

– 8.5cm proximal to the wrist crease

– Courses between FCR and PL

– pierces fascia (antebrachial fascia) 4.5cm proximal to wrist crease

– Reaches the wrist- superficial to flexor retinaculum and divides into several branches to supply thenar eminence and palm- central part

 

Ques-Low vs High Median nerve palsy?

Ans – Median nerve injury is classified into high or low depending on whether injury is proximal or distal to innervation of forearm muscles.

 

Function lost:

Low median nerve injury:

  • Loss of thenar function and opposition

High median nerve injury:    

  • Loss of thenar function and opposition
  • Loss of FDS to all fingers
  • Loss of FPL
  • Loss of index FDP

Functional loss

  • Loss of oppositional and oppositional pinch
  • Diminished grip strength
  • Loss of PT and PQ is compensated by shoulder rotation.
  • FCR is lost, but wrist function maintained by FCU
  • Loss of fine motor control and prehension
  • Sensory loss- is in critical area of hand and palm. For this reason, even if motor recovery is not possible and tendon transfers are required, median nerve should be repaired or reconstructed or sensory transfer in hand considered to restore this critical area of sensibility.

 

Causes of median nerve palsy

Above elbow:   

  1. Brachial plexus injury –  Trauma,   SOL
  2. Humerus Fracture
  3. Ligament of Struthers compression
  4. Crutch Compression
  5. Sleep palsy
  6. Anterior dislocation of humerus

At elbow:

  1. Compression due to joint effusion
  2. Pronator Teres syndrome
  3. Ventral dislocation of radial head

At forearm:

  1. AIN syndrome
  2. Deep laceration

At Wrist:

  1. Carpal tunnel syndrome
  2. Laceration

Other causes:

  1. Aneurysm
  2. Gout
  3. Diabetes
  4. Thyroid disorder
  5. Pregnancy
  6. Genetics

 

Median nerve injury Signs

  • Ape-hand deformity: hyperextended and adducted thumb
  • Thenar hypotrophy
  • Pointing index finger: inability to flex index on making fist
  • Inability to make “OK” sign
  • Pain, paresthesia, numbness in sensory distribution of median nerve
  • Loss of opposition
  • Phallen test and Reverse Phallen test: Patient holds wrist in maximum palmar flexion for up to 2 minutes- this increases pressure on carpal tunnel and provokes paresthesia in the area of median nerve
  • Maximum extension of wrist provokes similar provocation – Reverse Phallen.

 

Goal of tendon transfer in median nerve injury

  • Low median nerve injury- Restoration of thumb opposition
  • High median nerve injury- above + restoration of FPL and index FDP

 

Biomechanics of thumb opposition

  • Trapezio-metacarpal joint- Abduction + Flexion + Pronation [AFP]
  • (Palmar abduction+ Flexion + Pronation)
  • Prime muscle of Opposition – Abductor Pollicis Brevis
  • Aided by FPB and OP

 

History of Opponensplasty

  • Steindler – 1st Opponensplasty (radial slip of FPL)
  • Cook – used EDM
  • Ney – FCR or PL to EPB
  • Huber (1921)- ADM
  • (Nicolayson- 1922)
  • Bunnell (1924), Camitz (1929) used PL
  • Royal and Thomson – Superficialis transfer
  • Caplan and Aguirre (1956) –EIP

 

Critical points for tendon transfer

  • Tendon transfer not to be done in unhealed wound
  • Tendon transfer not to be done in joint function limitation
  • Tendon transfer should not pass through scarred tissue, and skin graft or skin incision
  • Other principles of Tendon transfer should be followed

 

Prevention and preoperative treatment of contracture:

In median nerve palsy and complete thumb intrinsic paralysis- thumb may adopt supinated and adducted position. Thus 1st web space contracture can occur.

 

Prevention:

Physiotherapy – passive thumb abduction and opposition

Splint – Abduction splint

 

Treatment of established first web space contracture:

Two possible causes

  • Contracture of skin and deep fascia on its exterior surface
  • Contracture of dorsal capsule of CMCJ (resists opposition but permits abduction)

Treatment:

  • Physiotherapy
  • Splint
  • Surgical release

Surgical release:

  • Dorsal web space incision
  • Fascia over Adductor pollicis and FDI released
  • Skin is widened with SSG or Flap
  • Capsule contracture of CMCJ- incision over base of joint
  • Severe contracture- rotational osteotomy at base of 1st metacarpal and trapezoidectomy

 

 

Pulley formation –

  • Line of lull of transfer should pass parallel to APB muscle
  • So, all extrinsic opponensplasties should pass around a stout, fixed pulley in the region of pisiform on ulnar border of wrist
  • Forearm extensor can pass over ulna or through interosseous membrane
  • Forearm flexor- pulley created on ulnar border of wrist

 

Insertion for opponensplasty

  • Single insertion
  • Double insertion – one for opposition and other for MP joint stabilization or preventing IPJ flexion

Single insertion is better, following single function principles.

Single insertion

  • into APB
  • used in isolated median nerve palsy

Dual insertion

  • APB insertion + Dorsal MP capsule or thumb extensor expansion
  • Useful in completely intrinsic minus thumb

IMG-20190505-WA0038

Four standard opponensplasty

  • Superficialis ooponensplasty- Royle Thomson technique or Bunnell technique
  • EIP (Burkhaulter)
  • Huber transfer (ADM)
  • Camitz procedure (PL)

 

Assessment of outcome of opponensplasty

Sundararaj and Mani –

Excellent – Opposition to ring or little finger with IPJ extended

Good – Opposition to middle or index finger with IPJ extended

Fair – IPJ flexes during opposition

Poor – No opposition restored

 

Superficialis Opponensplasty

Ring finger FDS is widely used.

Ring FDS harvest:

  • Royle & Thomson divided FDS tendon at its insertion into middle phalanx
  • North & Littler- suggested division of FDS through a window between A1 and A2 pulley (before its bifurcation)

Drawback of Royle & Thomson method – dividing FDS at its insertion

  • Involves lot of dissection in flexor sheath – fibrosis
  • Destroys vincula – disrupts blood supply to FDP
  • PIP joint capsule may be damaged – contracture

Benefits of North & Littler method

  • Avoid injury to flexor sheath and PIPJ capsule
  • Leaves 3cm of FDS tendon that glides freely within the flexor sheath

Complication of donor digit

  • DIPJ extension lag
  • PIPJ fixed flexion deformity
  • Swan neck deformity

These complications are avoided if FDS is harvested through incision in distal palm

 

Pulley formation –

Options

  • Passing FDS around FCU- problem of proximal migration
  • Distally based strip of FCU (based on its attachment to pisiform)
    • Problems
      • Raw surface over FCU- will cause adhesion
      • Radial migration can occur (FCU strip can be attached to ECU tendon to prevent radial migration)
    • Angle between distal edge of flexor retinaculum and ulnar border of palmar aponeurosis
    • Window in flexor retinaculum

 

 

Choosing a site of pulley formation-

 

Transfer’s line of action passes through –

Pisiform – maximum abduction and opposition but small amount of MCPJ flexion

Distal to pisiform – More thumb flexion, less abduction

Proximal to pisiform – more palmar abduction

 

Superficialis transfer (Royle & Thompson)

Incision 1: 3cm longitudinal incision at the base of the palm on the medial border of hypothenar eminence.

Ulnar border of palmar aponeurosis exposed and retracted radially.

FDS of ring finger identified, as it emerges from carpal tunnel proximal to superficial palmar arch

FDS of ring finger is then divided through a separate transverse incision (2nd incision) at base of digit.

FDS then delivered into palmar wound, keeping it ulnar to palmar aponeurosis.

 

Third incision at dorsum of thumb MP joint.

Subcutaneous tunnel created between this and palmar incision

FDS then passed through this tunnel superficial to palmar aponeurosis and carpal tunnel (and hence acting as a pulley for FDS)

This is then inserted into APB.

 

Tension of suture –

Should be maximum with thumb in full opposition and wrist in neutral

Postop-Immobilization for 4-6 weeks with thumb in full opposition

 

Bunnell’s technique

Ring FDS harvested as described above.

Distally based FCU pulley is made- distal portion of FCU exposed and split into 2 – for 4 cm proximal to its insertion at pisiform

One part cut and sutured back onto its base at pisiform- forming a loop

Ring FDS is delivered via the wrist incision and passed through FCU pulley and subcutaneous tunnel into insertion to dorsal thumb

FDS passes over EPL over dorsum of thumb and then passes through a drill hole in the base of PP of thumb in ulnar to radio palmar dissection

Transfers’ tension if set with thumb in full opposition and wrist is neutral.

Bunnels superficialis transfer

 

EIP Opponensplasty

Favored by Burkhaulter

Preferred to superficialis transfer as it does not weaken grip

  • First Incision: Short incision over dorsum of index MP joint. EIP is divided immediately proximal to extensor hood. (EIP is ulnar to EDC)
  • Second incision: On the ulnar side of distal forearm on the dorsum. EIP is delivered into this incision (EIP tendon is retrieved out of extensor retinaculum)
  • Third incision: Over dorsoradial aspect of thumb MPJ
  • Subcutaneous tunnel then created passing from extensor surface of forearm, passing around ulnar border of wrist, across the palm to reach the incision of thumb
  • EIP then passed through the tunnel and attached to APB tendon (in case of isolated Median nerve palsy)
  • Suturing done with thumb in maximum opposition and wrist in 30deg flexion.
  • In combined median and ulnar nerve palsy, transfer is attached sequentially to APB tendon, MPJ capsule, EPL tendon over proximal phalanx (Riordan).
  • This attachment restricts IPJ flexion and thus helps FPL flex MPJ more effectively substituting FPB function

 

  • Post op: Immobilization in wrist in flexion and thumb in full opposition for 3-4 weeks.

EIP transfer

 

ADM opponensplasty (Huber)

This transfer also improves hands appearance by increasing the bulk of thenar eminence.

  • Incision: Mid-lateral incision over ulnar border of little finger
  • Incision extended proximally and radially to distal palmar crease and then incision turns ulnarly across as it crosses the distal palmar crease
  • ADM divided from its insertion (It has 2 insertions- one at base of Proximal phalanx and second into extensor apparatus)
  • ADM freed of soft tissue attachments by retrograde dissection towards its origin at pisiform
  • Pitfall- great care must be taken not to damage this neurovascular pedicle which is on its dorso-radial aspect.
  • Once neurovascular pedicle is isolated ADM is freed up more proximally elevating its origin from pisiform. While retaining an attachment on the FCU tendon by dissecting a slip of FCU proximally
  • Next incision- over thumb MPJ dorsoradially
  • Subcutaneous tunnel created to this area immediately proximal to pisiform
  • This dissection is easier if done through another incision made in the thenar crease at base of thenar eminence
  • ADM is then turned 180° on its long axis to reduce tension on its neurovascular pedicle (as if turning page of a book)
  • ADM passed through subcutaneous tunnel and then attached to APB insertion.
  • Postop immobilization: Thumb in full opposition for 4 weeks
  • The position of wrist is not critical as transfer does not cross this joint
  • Difficult transfer
  • ADM barely reached APB insertion risk of damage to neurovascular bundle
  • This is to be done when other opponensplasties are not possible.
  • Origin of ADM at pisiform may be preserved, but then it will require short tendon graft

Huber transfer

 

Palmaris longus opponensplasty –

  • Described by Camitz
  • Simple procedure
  • Done usually in severe carpal tunnel syndrome – leading to loss of abduction and opposition
  • Procedure can be performed in regional anesthesia
  • It restores palmar abduction rather than opposition
  • Not recommended in traumatic median nerve palsy, as PL may be injured as well.
  • Transfer usually performed with carpal tunnel release- Abduction is restores till the median nerve recovers

 

Technique:

  • PL is confirmed (by opposing the thumb to little finger and flexing the wrist)
  • Incision – longitudinal incision starting 2cm proximal to distal wrist crease and progressing till proximal palmar crease in line of ring finger
  • Identify and avoid injury to palmar cutaneous branch of median nerve
  • PL tendon is freed in forearm- into the palm with 1cm wide strip of palmar aponeurosis
  • 2nd incision over dorsoradial aspect of MP joint
  • PL is tunneled into the incision and attached to APB tendon insertion
  • Suturing done with thumb in full opposition, MP joint extended and wrist in neutral

Post-op immobilization:

  • Light cast holding wrist in neutral and thumb opposed for 4 weeks.
  • Followed by night splint for 1 week

 

Other Opponensplasties

  • ECU
  • ECRL
  • EDM
  • EPL
  • FPL

 

Postop management –

  • Thumb immobilized in opposition for 3 weeks
  • For EIP transfer – additional wrist flexion is required in immobilization
  • For FDS- wrist is kept in neutral
  • If transfer’s tendon is inserted to APB or extensor mechanism then IPJ is kept in full extension
  • Splint discontinued after 3 weeks
  • Splint can be continued for longer period if more complex nerve injury.
  • Combined high median and ulnar nerve injury, Charcot Marie Tooth disease and Leprosy- Splint for 3 months

Preferred Opponensplasties –

PL for CTS (Carpal Tunnel Syndrome)

EIP for other

ADM when others cannot be done

 

Outcome

  • Outcome depends on whether
  • underlying neurologic pathology is progressive or static
  • Disability attributable to the isolated loss of opposition
  • Disability attributable to other problems such as sensory loss or other motor loss (More sensory deficit means less likely benefit from reconstructive surgery)

 

High median nerve palsy –

Aims of tendon transfer –

  • Restoration of opposition
  • Restoration of index finger flexion
  • Restoration of thumb flexion

 

Extrinsic donor available

  • ECRL
  • ECU
  • BR

 

Usual transfer

  • BR to FPL
  • ECRL to Index FDP (or side to side suturing to other FDP)
  • ECU to Opponensplasty

 

Restoration of Opposition

In high median nerve palsy – EPL, EIP, EDM are more readily available

 

Restoration of index flexion

  • Side to side suturing of index FDP and conjoint middle, ring and little finger FDP in distal forearm- this restores index finger flexion but does not restore strength
  • ECRL to index finger FDP- if independent index flexion is wanted and strength is required on radial side of hand
  • ECRL to index finger FDP should not be too tight- flexion contracture will occur
  • Tension should be just adequate that tenodesis effect is not restricted

 

Restoration of thumb flexion

BR to FPL transfer –

  • BR needs to be extensively released of soft tissue attachments to achieve good excursion
  • The tension should not be tight- it should be possible to passively extend all three joints of thumb with wrist flexed
  • BR transfer warrants 45deg elbow flexion during adjustment of tension
  • Since BR is an elbow flexor primarily, following the transfer to FPL the thumb flexion is maximally achieved when elbow is extended

 

Postoperative Splintage

  • For high median nerve palsy-
    • wrist 20° flexion
    • Thumb palmar abduction and flexion
    • Index in intrinsic plus position (Alone if ECRL to FDP transfer, or all fingers in intrinsic plus position if side to side suturing of FDP tendons done)

 

 

 

(Credits : Dr Anoop S (SR, MCh plastic Surgery, VMMC & SJH, New Delhi). Dr. Rohit M (SR, MCh plastic Surgery, VMMC & SJH, New Delhi)- Illustrations)

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