Monday, November 12, 2007

Tendon Transfers for Pure Median Nerve Palsy

Low Median Nerve Palsy

When the median nerve is injured at the wrist level, there are often tendon injuries at the same time to complicate the picture. In any median nerve injury there is sensory loss that affects the important sensitive areas of the volar (palm-side) surfaces of the thumb and index finger (used to pick up objects). Transfer of islands of sensitive skin should be planned and done prior to tendon transfer so that scarring doesn't make mobilization of the neurovascular bundles more difficult.

In a pure median palsy the deficits are:

  • Loss of the abductor pollicis brevis (APB)
  • Loss of the opponens of the thumb

The adductor muscles are normal. A new tendon will be needed which abducts and pronated the thumb. An opponensplasty will be needed. Burkhalter in 1973 describe transferring the EIP (extensor indexus pollicus) to the APB, which is the most common transfer (photo credit). The advantages of this transfer include no requirement for a pulley or tendon graft, no loss of grasp force, and avoidance of dissection in scarred tissue. The disadvantage is that the length of the EIP is just enough to transfer to the APB. When the EIP is mobilized, the extensor hood overlying the index finger should be repaired to prevent an extension lag.

A flexor sublimis tendon is another option for this transfer as it is long enough to reach its new insertion without a graft (Bunnell opponensplasty). The ring FDS is divided at its insertion and passed around the ulnar border of the palmar aponeurosis. A pulley can be created from the FCU or PL. This transfer cannot be used in a high median nerve injury because the ring FDS is paralyzed.

High Median Nerve Palsy

This is a very disabling condition.

Deficits:

  • Loss of index and long finger flexion
  • Loss of wrist flexors
  • Loss of forearm pronation
  • Loss of thumb flexion
  • Sensory Loss

It is important to prevent long term contractures. The adduction contractures can be prevented with an opponens splint. A fixed supination deformity may develop despite bracing due to the strong deforming forces of the Extensor Pollicus Longus and adductor.

Some options for restoration of function:

  • There is almost complete loss of grasp except in the ring and little fingers. If the ulnar-supplied half of the profundus (FDP)is strong and active, the profundus tendons of the index and long fingers can be connected to the tendons of the ring and little finger in the forearm, proximal to the wrist using a side to side repair. This will allow the ulnar-supplied profundus to flex all four fingers. If needed, the FDP of index & long fingers may be reinforced by transfer of extensor carpi radialis longus (ECRL) to give them more strength. (photo credit)
  • To balance the wrist flexion, the flexor carpi ulnaris (FCU) tendon can be split and attached half to the flexor carpi radialis (FCR) and half to its own FCU insertion.
  • The thumb flexion can be restored by using the ECRL can be detaches at its insertion, pulled out halfway up the forearm, and tunneled anteriorly to be anastomosed to the flexor pollicis longus (FPL). Alternatively, the FPL can be reinforced by using the Brachioradialis.
  • Abduction of the thumb can be restored using the extensor carpi ulnaris (ECU). The ECU is brought around the ulnar side of the forearm and extended by means of a free graft. This will also help with pronation of the forearm. Other options include the Burkhalter (as above) EIP to the APB

Sometimes it is necessary to include either arthrodesis of the MP joint or the distal IP joint of the thumb, depending of the stability.

The basic concept to remember in tendon transfer surgery, as advocated by Brand, is achieving balance in the extremity. Balance surpasses strength. One must strive to achieve equality in the distribution of forces, relocation, and replacement of tendons.

References

Tendon Transfers by Linda L Zeineh, MD--eMedicine Article

Tendon Transfer Principles and Mechanics by Premal Sanghavi, MD --eMedicine Article

High Median Nerve Lesions--Wheeless' Orthopaedics Online

Tendon Transfers for Low Median Nerve Lesions: Camitiz Procedure--Wheeless' Orthopaedics Online

Atlas of Hand Surgery By Sigurd Pechlaner--Google eBooks

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