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Tendon Transfers for Low Median Nerve Lesions

- See:
    - combined injuries of the median and ulnar nerves:
    - nerve repair
    - median nerve repair at the wrist

- Discussion:
    - patient's ability to oppose is weak, and the FPL provides most of the strength in flexion;
    - loss of the radial two lumbricals is not clinically significant;
    - opposition is attempted but cannot be done because of atrophy of the opponens and APB;
          - thumb abduction strength will decrease on average by 70%, but in some cases losses will not be thissevere if there is retention 
                  of function of the FPB;
    - thumb may remain supinated;
    - in general, 1/3 of patients do not need opponensplasty since adequate thumb abduction is gained from other muscles;
    - "opponens symptom:"
          - based on the observation that loss of the opponens muscle function, the EPL and the EPB cannot fully extend the thumb MP joint;
          - it is due to the integral functional relationship between the EPL and the opponens muscle;

- Prerequisites for tendon transfers:
    - strong FPL and a strong EPL;
    - absence of wide web space;
    - adequate thumb sensation;
    - stable metacarpophalangeal joint (w/ adequate extension) (if this is not case, then consider a concomitant MP fusion);
    - stable pulley in region of the pisiform bone;
    - strong motor for transfer;
    - normal function of the FDS (if this is considered for transfer);
    - polyneuropathy: (AML, MS, or Charcot Marie Tooth);
         - consider ECRL opponenplasty or palmaris longus opponenplasty rather than opponenplasty w/ a more distal and weaker motor;
    - with any attempted opponensplasty, it is important the the transfer lie in the direction of the APB;

- Camitiz Procedure:

- Riordan Opponensplasty: (ring FDS to APB):
         - procedure is contraindicated if flexor tendons have been previously lacerated;
         - this operation provides opposition, improves pinch, & ensures better utilization of extensor and flexor muscles;
         - FDS in ring finger is transected at base of digit & is isolated at wrist;
         - tendon is passed around the FCU, and then thru a pulley (created from 1/2 of the FCU tendon at
                its insertion) and is then passed subcutaneously to the proximal phalanx of the thumb;
                - typically 1/2 of the FCU is harvested 4 cm from its origin which is then sutured back to its insertion;
                - this modification avoids the complication of lateral pulley migration;
         - distal end is anchored into the proximal phalanx and the lateral band of extensor mechanism;
                - some surgeons advocate passing the FDS around the pisiform (or appropriate pulley), and then
                        tunneling the tendon obliquely across the palm to the posterior aspect of the
                        metacarpal neck where it is sutured to the EPB (1 cm from its insertion);
                - alternatively consider passing the tendon around the radial collateral ligament (from dorsal to volar)
                        which facilitates tensioning and allows secure repair;
                - some will split the tendon and will transfer one half to bone and the other half to the lateral band of the thumb;
                - insertion site is partially determined by whether the MP joint flexes or extends w/ a goal of having a neutral position;
                        - w/ extension, then move the insertion volarly;
                        - w/ flexion, then move the insertion dorsally;
         - tensioning:
                - thumb should be left abducted (positioned between the index and middle finger), and should
                        appear to be slightly overtensioned;
         - complications:
                - swan neck deformity at the donor site
         - references:
                - Superficial radial nerve compression following flexor digitorum superficialis opposition transfer: a case report.

- Extensor Indicis Proprius Transfer: (EIP to APB)
         - procedure of choice if finger flexors had previously been cut and required tendon repair;
         - this is also the transfer of choice with a high median nerve palsy;
         - this may be the procedure of choice w/ an insensate thumb;
         - tendon is elevated thru several short incisions until there is complete mobilization up to the musculocutaneous junction;
         - the tendon is passed around the ulnar border of the ulna and then across the palm;
         - references:
                - Extensor indicis proprius opponensplasty.
                - Independent index extension after indicis proprius transfer: excision of juncturae tendinum.

- Huber Opponensplasty: (ADQ to APB)
         - this type of opponenplasty is often reserved for high median nerve palsy or for congenital deficiencies;
         - note that the ADQ will probably provide only 25% of the normal APB strength, but does provide a cosmetic fullness that is lost 
                w/ thenar atrophy;
                - this may be combined w/ FDS transfer;
         - technical considerations:
                - make an ulnar sided incision over the hypothenar area which curves radially over the pisiforrm, and then should curve back ulnarly 
                       over the wrist crease;
                - note that the FDQ must be protected as the ADQ is divided;
                       - inclusion of the FDQ in the transfer may lead to limited flexion of the little finger;
                - carefully expose the distal tendon insertion of the ADQ;
                       - release the insertion as distally as possible;
                - free the muscle so that it remains attached only to the pisiform (origin);
                - make a subcutaneous tunnel towards the thenar eminence and ensure that there is suffficient room for the tendon;
                - distal end is anchored into the proximal phalanx and the lateral band of extensor mechanism;
                - a possible complication includes iatrogenic ulnar tunnel syndrome;
         - references:
                - Opposition of the thumb and its restoration by abductor digiti quiniti transfer.
                - Abductor digiti quinti opponensplasty.

- Misc:
     - some surgeons adovcate insertion of a K wire across the MP joint prior to opponens transfer;
           - this allows the thumb to be held in proper position (since there is often an adduction and a supination deformity) and makes it 
                 easier to achieve proper tensioning

Restoration of strong opposition after median-nerve or brachial plexus paralysis.

Abductor digiti quinti opponensplasty.

Tendon transfer for median and ulnar nerve paralysis.

The effects of low median nerve block on thumb abduction strength.