Dr Jason Crane
Department of Orthopaedics
Tygerberg Academic Hospital
Tendon transfer is a surgical procedure that involves moving the insertion of a tendon muscle unit from one location to another location. Tendon transfer surgery is salvage surgery. A tendon transfer can be used to restore grasp, improve the position of the hand in space, and to prevent deformity, dislocations and contractures1.
In the normal hand the transition from one stable position to another is rhythmic, and groups of muscles act in proper phase and co-operate with one another. The proper timing of muscle action and exertion of the proper tension by the muscles are controlled at the unconscious level and by conscious effort. Some patterns of muscle group movement act in such endless co-ordinated repetition that they are synergistic (work together). Fingers flex when the wrist is extended and fingers extend when the wrist is flexed, this synergistic balance is important for the functioning and coordination of the hand as a unit.
When a major muscle in the hand is paralysed, in addition to loss of power the synergistic balance of the hand is disrupted. Any muscle whose antagonist is paralysed contracts unopposed and eventually develops a fixed contracture.
Prerequisites to surgery1,2
All wounds must be healed and devoid of any infection. Adequate soft tissue coverage must be present with pliable tissues and minimal fibrosis. Tendons will only glide through mobile, unscarred healthy tissue. Flaps should be pre-formed and have undergone complete healing before a tendon transfer is attempted.
Precede transfers with maximum joint mobilization through intensive hand therapy; improved active range of movement will never be gained from a tendon transfer. For the pull of a tendon to be effective across a joint, skeletal stabilization is necessary. If indicated an arthrodesis, of the joint crossed by the tendon, should be achieved prior to the tendon transfer.
Wherever possible, restoration of at least protective sensibility should precede tendon transfers. Sometimes restoring precision sensibility on a limited but critical surface such as the pulp of the thumb, by a neurovascular sensory island transfer may be an important adjunct to power redistribution.
The following principles form the foundation of the surgical approach4,6
Tendon transfers for specific palsies
The variety of circumstances encountered is endless and will be equalled by almost as many variations in details of reasonable solutions, but all are based on established principles. Examples are presented to illustrate such principles with no pretence of an encyclopaedic coverage of all circumstances2.
Radial nerve palsies
Low Radial nerve palsies
The losses of low radial nerve lesions are those of a posterior interosseous nerve palsy, requiring restoration of active metacarpophalangial (MP) finger extension through extensor digitorum communis (EDC), thumb extension through extensor pollicis longus (EPL) and for rarely required requirements, first metacarpal abduction through abductor pollicis longus (APL). Active wrist extension remains intact.
High Radial nerve palsies
High radial nerve palsies cause in addition to the defects of low lesions, total loss of wrist extension because of paralysis of the extensor carpi radialis brevis (ECRB), extensor carpi radialis longus (ECRL) and extensor carpi ulnaris (ECU). ECRB is the prime wrist extensor because it has the most central insertion and therefore is more a wrist extensor than deviator.
Primary nerve repair must be attempted, but while waiting for possible reinnervation an option to use a transfer as an internal splint is available. Pronator teres (PT) to ERCB is carried out at the time of nerve repair in an end-to-side fashion, eliminating the need to wear a splint during nerve regeneration.
The Following options are available
PT to ECRB for wrist extension
Flexor carpi radialis (FCR) to EDC for finger MP extension
Palmaris longus (PL) rerouted to EPL for thumb extension
This method maintains Flexor carpi ulnaris (FCU) as an ulnar wrist flexor, which is important to heavy laborers.
However the patient is unable to fully extend their fingers and wrist simultaneously. The PL is only present in 70% of the population3.
PT to ECRB for wrist extension
FCU to EDC for finger MP extension
PL to rerouted EPL for thumb extension
This method requires little patient training and rehabilitation, which produces good predictable results. However the patient is unable to fully extend their fingers and wrist simultaneously. The transfer can only be performed if the PL is present. This transfer produces a dominance of radial forces across the wrist weakening the overall grip strength3.
PT to ECRL and ECRB
Flexor Digitorum Superficialis (FDS) III to EDC
FDS IV to Extensor Indicis and EPL
FCR to APL and EPB
This method gives the patient the ability to extend their wrist and fingers simultaneously. It allows for independent control of their thumb and index fingers for an effective pinch grip3. However the Boyes transfer creates a potential flexion or extension deformity at the proximal interpahalngeal joints of the donor (FDS) fingers. This transfer does not use synergistic tendons, which could result in a potentially difficult rehabilitation. As the FDS tendons pass through the interosseous membrane, there is a potential for adhesions.
The arm must be immobilised in maximum wrist extension with the forearm in pronation for three weeks. This is then changed to a static splint with the wrist in extension and the fingers free for a further three weeks2.
Ulnar Nerve Palsies
The major problems after ulnar nerve palsy are deformity, weakened grip, asynchronous motion and loss of lateral finger mobility. A third to a half of the hand strength and 80% of the pinch strength is lost.
Low Ulnar nerve palsies
The losses that occur with low ulnar nerve palsies are that of paralysis of all the interosseous muscles as well as the lumbricals to the ring and small fingers. Paralysis of the adductor pollicis is particularly disabling, due to the resulting weak pinch grip. There is a lost of medial protective sensation due to the loss of sensation to the medial one and a half fingers.
There is a characteristic claw deformity of the ring and little fingers.This is due to imbalance of the forces at the three joints of each finger. The lumbrical muscles, and the interossei, flex the metacarpal phalangeal joint (MCPJ) and extend the proximal interphalangeal joint (PIPJ) and distal interphalangeal joint (DIPJ). If they are not working, the action of the unmodified long flexors and extensors produce hyperextension of the MCPJ and flexion of the interphalangeal joints.
Whenever possible, nerve exploration with neurolysis or nerve repair is the treatment of choice. Static or dynamic splints can be used as conservative treatment to correct the resultant deformity of intrinsic muscle paralysis.
For irreversible paralytic loss of the intrinsic muscles the following options are available.
For the restoration of pinch grip, ECRB or Brachioradialis can be used with a tendon graft that is passed through the third intermetacarpal space and inserted into the radial side of the thumb MCP joint. Alternatively FDS from the ring or middle can be transferred to the abductor insertion of the thumb. To recreate index finger abduction, a slip of APL is inserted into the lateral band of the index finger.
High Ulnar nerve palsies
The function of FDS to the ring and little finger, as well the FCU is lost, resulting in little additional loss over that of a low lesion.
As the FDP's of ring and small fingers normally function in conjunction with the median innervated FDP's of the middle finger, transferring them to be united side-by-side into the latter gives an excellent functional restoration. FCU's loss is not noticeable and needs no treatment.
Median Nerve Palsies
Functional impairment from a median nerve lesion is primarily the result of lost skin sensibility on the working surfaces of the thumb, index and middle finger, those used for precision manipulation, rather than the loss of muscle function.
Low median nerve palsies
The main function that needs to be replaced is opposition of the thumb. Opposition is a combination movement with simultaneous rotation of the thumb into pronation and abduction away from the palm. Three muscles are used for this function, abductor pollicis brevis, opponens pollicis and superficial head of flexor pollicis brevis.
The most commonly used donors are1,4
To recreate volar sensibility to the thumb and finger pulps a neurovascular island flap can be taken from the dorsal surface of the hand.
Post operative care
Place the forearm in a wrist extension splint with the thumb in abduction for about three weeks. The thumb may then be mobilized free for a further 3 weeks.
Upper median nerve palsies
As well as that of opposition, the functions that need to be replaced are pronation of the forearm, flexion of the thumb and flexion of the index finger. Weak flexion of the middle finger is usually possible because of the crossover fibres from the ulnar nerve.
Interphalangeal flexion of the index and middle finger can be restored by suturing their FDP tendons side-to-side into the profundus tendons of the ring and small finger. When greater power is needed ECRL can be transferred to the entire FDP group. Brachioradialis or extensor indicis can be transferred to FPL to restore thumb flexion. The power of brachioradialis is suitable but the excursion is less than ideal.
Tendon transfers for combined nerve palsies
If loss of function to any two of the three major nerves to the hand occurs, reconstruction approaching normality is absolutely precluded. A major simplification of mechanical design is necessary if the available functioning units are to be combined into a useful and effective reconstruction scheme. In the case of median nerve injuries, loss of perfect sensibility, without which fine manipulations are impossible, limits functional recovery even if good muscle rebalancing has been achieved2.
Postoperative management for tendon transfers²
Postoperative care is crucial to the outcome of tendon transfers and close co-operation with the hand therapist is essential. Immobilization is usually indicated for a minimum of 3 weeks after tendon transfer and tenodesis. The period of immobilization will depend on the robustness of the repair. A stout Pulvertaft weave permits early mobilization with fewer risks of adhesions. If the joints are stiff postoperatively, they must be mobilized, but active joint manipulation must be avoided.
Flexor tendon transfers can safely be subjected to guarded and unresisted active movement after 3 to 4 weeks, but extensor tendons are immobilized for at least 4 to 6 weeks. This is not because they heal differently, but because powerful, intact flexor antagonists oppose extensor tendons. Completely unrestricted use is not encouraged for any transfer until 8 to 10 weeks postoperatively. The patient will need to train the tendon transfer to work in the new position. The best therapy is to use the hand for normal and work related activities as soon as possible after the wounds have healed and the tendon junctions are secure.
As long as basic principles are adhered to and transfers are kept as simple as possible, a move favourable outcome can be expected with less complications and a shorter period of rehabilitation. This is salvage surgery and the patient must have a realistic expectation of the functional outcome.