Tendon transfers for nerve palsy - Rob Lee 20/10/2005

Definition

A procedure in which the tendon of insertion or of origin of the functioning muscle is mobilised, detached or divided and reinserted into a bony part or onto another tendon, to supplement or substitute for the action of the recipient tendon


Indications for tendon transfers

Irreparable nerve damage (also early transfer whilst nerve repair heals)
Loss of function of a musculotendinous unit due to trauma or disease
In some nonprogressive or slowly progressive neurological disorders

Basic principles of tendon transfer

Correction of contracture
All joints must be kept supple because soft tissue contracture is far easier to prevent than to correct.
Maximum passive motion of all joints must be present before a tendon transfer because no tendon transfer can move a stiff joint.


One tendon, one function
A single tendon cannot be expected to simultaneously perform diametrically opposing actions, eg, flex and extend the same joint.
If a muscle is inserted into 2 tendons with separate functions, the force of amplitude of the donor tendon is dissipated and less effective than that of a muscle motored by a single tendon.

Synergism
The use of synergistic muscles: finger flexors acting in concert with wrist extensors and digital adductors; finger extensors with wrist flexors and digital abductors.
Muscle function is easier to retain after synergistic muscle transfer.

Adequate strength
The tendon chosen as a donor for transfer must be strong enough toperform its new function in its altered position.
Selecting an appropriate motor is important because a muscle will lose one grade of strength following transfer.
Do not transfer muscle that has been reinnervated or muscle that was paralyzed and has returned to function. Weak muscle is pale pink and smaller

Amplitude of motion
Consider the amplitude of tendon excursion for each muscle. A wrist flexor with an excursion of 33 mm cannot substitute fully for a finger extensor with an amplitude of 50 mm.
Although the true amplitude of a tendon cannot be increased, its effective amplitude can be augmented 2 ways. First, the natural tenodesis effect can be used by converting a muscle from monoarticular to biarticular or multiarticular. Second, extensively dissecting a muscle from its surrounding fascial attachments can increase amplitude
Amplitude can be limited by scarring and adhesions

Tendon transfers function best when passed between subcutaneous fat and the deep fascial layer; they are not likely to be functional if placed in the pathway of a scar.

Functional integrity must be preserved
the transferred musculotendinous unit must be expendable
if a tendon is split and inserted into different sites only the tighter of the two will function and the other will not

Good compliance of the overlying soft tissues (ie skin is not too tight)

Straight line of pull
In the most effective transfer, the muscle passes in a direct line from its origin to the insertion of the tendon being substituted.
Although not always possible, this configuration is desirable.

All transfers require appropriate tensioning. Transfers should be sutured at maximum tension in the position that reverses the activity that the tendons are trying to accomplish.

Acceptable distal sensation



Physics

Force – proportional to cross-sectional area of muscle (3.65x cross-sectional area)

Amplitude – proportional to length of muscle ie displacement

Work capacity – Force x amplitude = work capacity (work per unit time)

Surgical considerations in tendon transfers

In extensive paralysis of the upper limb, restore function from proximal to distal :
Stabilisation of the shoulder
Flexion of elbow
Extension of wrist
Flexion of fingers
Reestablishment of thumb grip in opposition or lateral thumb grip
Finger extension
Restoration of function of the interrossei

Timing of transfer
if no chance of functional recovery, transfers should be performed asap
following nerve injury repair, the date of expected recovery can be calculated by measuring the distance between the injury to the most proximal muscle supplied, assuming a rate of regeneration of 1mm/day. If reasonable return of function not present for 3 months after the expected, consider tendon transfer
early tendon transfers – within 12 weeks of injury


Planning
make a list of deficient functions
make a list of available donor muscles

Techniques
1. Multiple short transverse incisions rather than long longitudinal incisions
2. Careful tendon handling
3. Good soft tissue coverage over the tendon junctures
4. Joining the tendons
a) End to end anastomoses
b) End to side anastomoses
c) Side to side anastomoses
d) Tendon weave procedures

5. Achieving proper tension - no general rule, but reasonable to place limb in the position of maximal function of the tendon transfer and suture without tension



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