Radial nerve palsy

Course of radial nerve?

Radial nerve is terminal branch of posterior cord, a continuation of it. It receives supply from C5-T1.

It then descends in front of subscapularis and latissimus dorsi and posterior to axillary artery.

At the level of lower border of teres major it courses posterolaterally and passes through triangular interval (between long head of triceps, teres major and humerus).

It then courses in shallow groove on posterior surface of the humerus – between lateral and medial head of triceps where it gives off branches- muscular and cutaneous.

At level of middle and lower 1/3rd of arm it penetrates lateral intermuscular septum to enter anterior compartment.

It travels between brachialis (medially) and brachioradialis & ECRL (laterally).

At the level of capitulum of humerus it divides into superficial and deep branches.

Deep branch (PIN) passes between two heads of supinator à wraps around lateral aspect of radius to reach back of forearm. [PIN emerges from supinator approx. 8cm distal to elbow joint]

After emerging from supinator it travels between superficial and deep layer of muscles of extensor compartment i.e. it passes/travels over APL & EPB and under the EDC.

It then courses on the dorsal surface of interosseous membrane underneath the EPL and EIP.

At wrist joint it is almost flattened giving sensory fibers to wrist joint and DRUJ.

Superficial branch –

Courses underneath the brachioradialis.

In the proximal third of foreram – it lies on the supinator

In the distal part it travels sequentially over pronator teres àFDS (radial side) à FPL

In the distal forearm – Approx. 7-8cm proximal to the wrist it emerges between BR & ECRL – pierces the deep fascia.

After emerging from BR it winds around radius. Travels over (crosses) the tendons of APL & EPB.

Passes through anatomical snuff box, over the extensor retinaculum and then divides into four or five dorsal digital nerves.

 

The branches of radial nerve?

Near axilla –

Medial muscular branches – medial and long head of triceps

Cutaneous branches -Posterior cutaneous n of arm (arises in axilla)

In the groove –

Posterior muscular branches – medial and lateral head of triceps

Cutaneous branches – @ the start of groove (originating almost just after first muscular branches) a branch of radial n penetrates lateral head of triceps and overlying fascia and then splits into these two nerves –

Posterior cutaneous n of forearm

Lateral cutaneous n of arm

Lateral muscular branches – branches given after radial nerve, penetrates lateral I/M septum – BR & ECRL

Branches before entering supinator –

  1. ECRB & Supinator

After emerging from supinator –

  1. Short muscular branches – EDC, ECU, EDM

Two long muscular branches –

  1. Medial – EPL & EIP
  2. Lateral – APL & EPB

 

Sequence of innervation of muscle by radial nerve?

In order of innervation from proximal to distal (helps in guiding the recovery process) –

  1. BR
  2. ECRL
  3. ECRB ↔ supinator
  4. EDC
  5. ECU
  6. EDM
  7. APL
  8. EPL
  9. EPB
  10. EIP

High or low radial nerve injury?

When injury occur above the elbow there is loss of almost all the function of radial n – this is called high radial nerve injury.

When the injury is distal to the elbow, so that only PIN is injured. In this case innervation to BR, ECRL, ECRB (variable) is preserved and hence wrist extension is preserved. When wrist extension is preserved its called Low radial nerve injury.

 

The sensory distribution of radial nerve?

In the arm – posteriorly and inferior lateral

In the forearm – posterior

In the hand – radial aspect of half of dorsum of hand, proximal portion of dorsum of radial 3 and ½ finger (excluding the tip)

 

The deficit that you will notice in radial nerve injury?

In motor loss there will be –

  1. Loss of finger extension at MCPJ
  2. Loss of wrist extension
  3. Loss of thumb extension and abduction
  4. Loss of elbow extension if nerve to triceps if also injured

In sensory, there will be loss noted in –

  1. 1st dorsal web space- also known as the autonomous zone of radial sensory nerve.
  2. Lateral 3 & ½ fingers (except distal phalanx)
  3. Posterior aspect of forearm

Surface marking of radial nerve ?

Mark points –

First point – lateral wall of axilla – lower limit

Second point – junction of upper 1/3rd and lower 2/3rd of line joining lateral epicondyle and insertion of deltoid

Third point – in front of elbow joint below level of LE approx 1 cm lateral to insertion of biceps brachii.

1st point to 2nd point – oblique course in radial groove.

2nd point to 3rd point – anterior compartment course.

In forearm –

4th point – junction of upper 2/3rd and lower 1/3rd of line along lateral border of forearm lateral to radial artery.

5th point – anatomical snuff box

3rd point to 4th point – radial nerve is straight

4th point to 5th point – radial nerve curves backwards.

 

Planning for nerve injury – nerve exploration vs nerve repair vs tendon transfer?

Nerve grows @ 1mm/day with 30 days of latency period.

In case of closed fracture its prudent to wait till the expected(calculated) time of recovery. Nerve exploration to be done if no recovery seen. if more than 3-6 months has passed from expected time of recovery without any recovery.

If more than 16-18 months has elapsed since time of injury then directly planned for tendon transfer.

 

When do you time the tendon transfer?

There are two approach for tendon transfer-

“Early” tendon transfer – tendon transfer done simultaneously with nerve repair or before the expected time of reinnervation of muscle.

“Conventional” or late tendon transfer – when reinnervation of most proximal paralysed muscles (BR & ECRL) fails to occur by three months after the expected time of reinnervation.

In early tendon transfer there can be –

“Limited” transfer – which is PT –> ECRB only

  1. Provides for internal splintage (eliminates need for external splintage) while the nerve is recovering,
  2. Provides immediate restoration of power grip (by stabilizing the wrist)
  3. If the nerve recovers it works as a helper by adding power of a normal muscle to innervated muscle.

Complete set of transfer (advocated by Brown) –

This is reasonable approach in case where prognosis of nerve repair is poor –

  1. Nerve gap >4cm
  2. There is large wound or extensive scarring or skin loss over the nerve.

Bevin advocated directly proceeding to tendon transfer without attempting nerve repair – benefit of reduced time of disability. This has not been well accepted.

 

Historical perspective of development of tendon transfer in radial nerve palsy?

First transfer was described by Franke – FCU to EDC.

Followed by Capellen – FCR to EPL

First complete set of transfer was given by Sir Robert Jones (1906)

  1. PT  –> ECRB & ECRL
  2. FCU –> EDC III-V
  3. FCR –> EPL, EIP, EDC II

He subsequently modified it in 1921 (Jones II)

And used FCR to additionally to EPB & APL

  1.  PT –> ECRB & ECRL
  2. FCU –> EDC III-V
  3. FCR –> EPL, EIP, EDC II, EPB & APL

Starr was firs to use PL to EPL transfer and left one wrist flexor intact.

Zachary convincingly proved that it’s desirable to leave at least one wrist flexor intact.

In 1949, Scuderi refined PL to rerouted EPL transfer.

These studies resulted in what is called “Standard” set of transfer –

  1. PT to ECRB
  2. FCU to EDC II-V
  3. PL to rerouted EPL

Brand proved that FCU should not be used as it is too strong, too short excursion and is prime ulnar stabilizer of wrist. He then, along with Starr described FCR transfer (which was used instead of FCU) –

  1. PT to ECRB
  2. FCR to EDC II-V
  3. PL to rerouted EPL

Boyes reasoned that FCU is a more important wrist flexor to preserve than FCR because the normal axis of movement of wrist movement is dorso-radial to volar-ulnar (a dart-throwing type of movement).

Boyes also reasoned that wrist flexors (FCU & FCR) (33mm) has inadequate excursion compared to finger extensors (50mm), and it’s better to use FDS which has better excursion (70mm).

Boyes described Superficialis transfer

  1. PT to ECRB & ECRL
  2. FDS IV to EDC
  3. FDS III to EIP & EPL
  4. FCR to APL & EPB.

 

Aims to achieve by tendon transfer in radial nerve palsy?

Aim is to achieve –

  1. Wrist extension
  2. MCPJ extension
  3. Thumb abduction and extension

 

The principles of tendon transfer?

  1. One tendon , one transfer
  2. Straight line of pull
  3. Similar amplitude of excursion
  4. Adequate strength (muscle to be transferred should be atleast >85% of its normal strength)
  5. Supple joint
  6. Synergistic muscle
  7. Expendable donor

Example of synergistic muscle – wrist flexor with finger extensor & wrist extensor with finger flexors.

 

Describe the incision and procedure of FCU set of transfer.

Incision –

First incision – directly over the FCU in distal half of forearm longitudinally. Distal end in J-shaped extension to reach PL.

FCU is transected just proximal to pisiform and freed up as far as possible through that incision.

Second incision – begins 2 cm below the medial epicondyle and angles across the dorsum of proximal forearm directed towards Lister tubercle.

Deep fascia overlying the FCU muscle is incised. Fascial attachments of FCU is completely freed up .

Upper limit of dissection of FCU muscle is 2 inches from its proximal origin where its nerve supply enters.

Third incision – begins on the volar-radial aspect of mid-forearm, passes dorsally around the radial border of forearm in the region of insertion of PT and then angles back on the dorsum.

Tendon of PT is identified in the volar aspect – followed to its insertion on the radius –tendon insertion is freed with a cuff of periosteum around 2-3 cm – muscle tendon unit freed up proximally – PT then transferred around the radius, superficial to BR and ECRL to be inserted to ECRB just distal to musculocutaneous junction .

Through dorsal incision – Kelly’s clamp is passed around the ulnar border to grab FCU and pulled into dorsal wound. (FCU muscle belly may be required to be trimmed if too bulky)

EPL is identified àdivided at its musculotendinous junction à rerouted out of Lister’s canal towards the volar aspect of wrist across anatomical snuffbox à PL transected at the wrist –muscle-tendon unit freed up proximally to allow for straight line of pull.

FCU can alternatively be passed through a window in interosseous membrane.

FCU is sutured to EDC tendons by weaving through all four EDC tendons in end to side fashion at an angle of 45° just proximal to retinaculum.

 

How will be the tension in tendons adjusted?

1st suture will be PT to ECRB – to be sutured with wrist in 45° extension with PT in maximum tension.

2nd suture is FCU to EDC – to be sutured with wrist in neutral position, with FCU in maximum tension with full extension at MCPJ.

After these two sutures – there should be full flexion of fingers with wrist extended and – full extension of digits with wrist flexed.

Final suture is PL to EPL. Both tendons are sutured under resting tension with wrist in neutral position.

Reconstruction is checked again for full movements – finger flexion with wrist extension & finger extension with wrist flexion.

 

Post-op care following tendon transfer?

Long term splint for immobilization –

  1. Forearm in – 15-30° pronation
  2. Wrist – 45° extension
  3. MCPJ – slight flexion – 10-15°

Thumb in – maximum abduction and extension

Remove sutures after around 6-7 days

Remove cast at 4 weeks – start physiotherapy.

 

Potential problems after FCU repair?

Excess radial deviation – removing the only remaining ulnar deviator can lead to radial deviation of hand, especially if ECRL is functioning well (PIN only palsy.). this is also more aggravated if PT to ECRL transfer has been done, less so if PT to ECRB transfer.

Solution –

Avoidance – if preoperatively there is already radial deviation present (PIN only palsy) – avoid FCU transfer.

After transfer – reposition ECRL insertion – i) into ECRB; ii) attach PT to ECRB & ECRL and then detach ECRL; iii) detach from 2nd metacarpal- reroute and inset into 3rd and 4th  metacarpal bone (Tubiana).

Absence of PL –

Solution – i) Use superficialis transfer; ii) include EPL into FCU to EDC transfer ; iii) include EPL, EPB, APL into FCU to EDC transfer; iv) Use BR (if low radial n palsy) to EPL; v) Use FDS III or IV.

 

Highlights of Superficialis transfer?

Incision –

Long incision on volar side of the radial aspect of mid-forearm.

Expose PT and ECRB

Remove PT with 2-3 cm of periosteum and interwoven into ECRB.

Exposure of FDS (ring and middle) –

Through transverse incision in distal palm or at base of each finger.

Tendon divided proximal to chiasma- freed up and delivered into forearm.

@ Level just proximal to pronator quadratus, two incision made of size 1 x 2 cm in I/O membrane.

“J-shaped” incision in dorsum of distal forearm –

Transverse limb from radial styloid to ulnar styloid. Vertical limb extends proximally along ulna.

Bring out FDS through I/O membrane. FDS of long finger passed radial to profundus mass and FDS of ring finger passed on ulnar side of profundus mass.

FDS III – attached to EIP & EPL

FDS IV – attached to EDC.

Setting of tension – an assistant holds wrist in 20° extension with fingers and thumb held in a fist, until all transfers are done with reasonable tension.

Transverse incision at base of thumb – free FCR tendon –-> pass it dorsally –-> attach to APL (preferably only to APL or with APL & EPB both).

 

FCR transfer highlights?

Incision –

Straight longitudinal incision in volar forearm on radial side in distal half b/w FCR & PL.

Both tendons identified, transected near their insertion, freed up to middle of the forearm.

Longitudinal incision on dorsum – extending just distal to retinaculum to mid forearm.

FCR passed around radial border of forearm through subcutaneous tunnel.

EDC tendons are identified and divided at musculotendinous junction – withdrawn distally superficial to intact extensor retinaculum to a point over distal radius and sutured to FCR

Adjusting the tension – wrist and MCPJ in neutral position – FCR sutured in maximum tension.

PT to ECRB & PL to rerouted EPL as described for others.

 

Nerve transfer option for radial nerve injury.

Median nerve to radial nerve

Fascicles of FDS or FCR to PIN & ECRB.

  1. FDS to ECRB
  2. FCR to PIN

Indications –

  1. Very proximal nerve injury – where proximal stump is not available for repair, or even if available regeneration will take a very long time.
  2. Avoiding an area of scarring
  3. Nerve injury presenting in delayed fashion
  4. Partial nerve injury – presenting with well defined motor function deficit.
  5. Level of injury is unclear (idiopathic, radiation induced injury)

 

 

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