1. Supple joints before transfer.
2. Tissue equilibrium
3. Adequate strength (donor)
4. Adequate excursion (donor)
5. Expendable donor
6. Straight line of pull
7. Synergism
8. One tendon – One function
Supple Joints
Applying an active motor to a passively mobile joint is the fundamental tenet of a tendon transfer. No amount of transferred power will mobilize a stiff joint. Extensive physiotherapy, the judicious use of splints and corrective surgery are often needed to correct stiffness or contracture prior to tendon transfer procedures. Once a plateau or end point has been reached, then the definitive transfer is performed, understanding that the active range of motion will, at best, match the passive range of motion.
Tissue Equilibrium
The elastic energy inherent in the transfer should be maximally applied to the passively mobile joint that the transfer is designed to move. Any residual oedema, firm scar or joint stiffness will result in an increased resistance to the muscle force and therefore, a compromised result. This optimal tissue condition is termed “tissue equilibrium”. Reducing post operative oedema and scar formation is equally important.
Gentle dissection through a fatty subcutaneous bed offers the best pathway for a transferred tendon. Curved incisions should be used to place tendon junctures beneath flaps rather than beneath incisions [3].
Adequate Donor Strength
The transferred musculotendinous unit must have enough strength to perform its desired function. While there has been excellent basic science work on muscle strengths by the masters (Brand, Boyes), these tables are often not practical and easily usable [1, 2]. Form follows function and therefore one can assume that tendons of similar cross sectional size have similar strength.
A transferred muscle should be of near normal strength, as Omer has shown that it will be lose one grade from 5 to 4 or from 4 to 3 [3]. Surgeons are often advised to beware a muscle that has recovered strength following denervation or paralysis. These muscles might appear strong enough but often suffer fatigability.
Adequate Donor Excursion
The transferred musculotendinous unit should have an excursion similar to that of the tendon it is replacing. Surgeons are advised to commit the following excursion values to memory. Wrist flexors and extensors – 3 cm, finger extensors (including EPL) – 5 cm and finger flexors – 7 cm (3, 5, 7 rule) [2] (See Table 2.2).
Table 2.2
Tendon excursion
Tendon | Excursion (cm) |
|---|---|
Wrist flexors | 3 |
Wrist extensors | 3 |
Finger extensors | 5 |
Finger flexors | 7 |
Tendons of similar excursion are often not available. Extensive mobilization of the fascial attachment of the muscle can increase the excursion. A good example is the FCU to EDC transfer. A 3 cm excursion can be increased to the desired 5 cm by dissecting the muscle free from its broad attachment to the ulna. Furthermore, the body can adapt to excursion differences by utilizing the tenodesis effect. By flexing the wrist, the effective excursion on the transferred FCU is increased, thereby facilitating finger extension. The fact that wrist flexion (FCU) and finger extension are in-phase or synergistic also adds to the success of the transfer (see section “Synergism”).
Expendable Donor
It goes without saying that every donor muscle to be transferred should either be expendable or, after careful clinical assessment, shown to be less important than the recipient muscle targeted. Fortunately, there are two wrist flexors and three wrist extensors which means that function remains following the use of one of these tendons for transfer.
Straight Line of Pull
In order to minimize the energy loss of the transfer, the transfer tendon should assume as straight a line as possible from the donor motor to the recipient. Excessive use of a redirectional pulley should be avoided where possible.
Synergism
This is a very important concept to understand. In the normal balance of the hand, as the wrist flexes, so the fingers extend and as the wrist extends, the fingers flex into a fist. Transfers that take advantage of this co-contractile synergism are destined to be superior to those that are out of phase.
A classic example of this is the wrist flexor (FCU or FCR) to EDC transfer in high radial nerve palsy. Any attempt to extend the fingers is associated with a reflex of spontaneous tendency to flex the wrist which thereby augments the transfer. In so doing, the brain does not have to relearn the action centrally.
Another way to understand this point is the notion that if the active transfer does not work or gets stuck down in scar tissue, then the transfer will still function as a tenodesis affect.
One Tendon – One Function
A transferred tendon should not be split into two separate insertion points. It would be extremely difficult to set up the tension in both limbs of the transfer so that two actions will be performed simultaneously. Secondly, to expect one tendon transfer to perform a function at two or more contiguous joints is subjecting that transfer to increased risk of failure. An example is expecting a transferred wrist flexor to extend both the wrist and the fingers.
Surgical Algorithm (Table 2.3)
Table 2.3
Surgical algorithm
1. What is lost? |
2. What is available? |
3. Is the hand suitable for a tendon transfer? |
4. Is the patient suitable for a tendon transfer? |
What Is Lost?
Careful clinical assessment will reveal which joint functions need to be reconstructive. It is more important to identify the functional deficit rather than a list of all the muscles that are not actively contracting.
What Is Available?
Often, the algorithm ends here. If no motors are available for transfer, then no reconstructive options are available. If multiple donors are available, then the principles as discussed above will guide the preferred and correct choice.
Is the Hand Suitable for a Tendon Transfer?
Once a donor muscle has been selected, the next critical assessment is to decide whether the patient and/or the patient’s hand are suitable for a tendon transfer. In order for the transferred muscle to perform a locomotor function, the joint that is mobilized by the donor muscle must be supple and capable of an easy passive range of motion. Surgery should be delayed until physiotherapy has restored full passive mobility.
The second critical criterion to assess in the hand is the sensibility to the anatomical structure to be reanimated. A tendon transfer to a poorly sensate hand will often result in a suboptimal clinical and functional outcome. This is because the brain will tend to exclude these areas from functional activity, and hence movement because of their reduced sensory feedback.
Is the Patient Suitable for a Tendon Transfer?
Tendon transfer surgery can be technically challenging and careful attention must be applied to the post operative rehabilitation. Young children and patients with impaired cognitive functioning will struggle with a complicated post operative physiotherapy regimen. Cerebral palsy patients are a unique group that can be difficult to assess. They often have many combined factors mitigating against tendon transfers. These might include spasticity, poor sensibility, altered cognitive functioning and failure of the developing brain to incorporate the use of the affected limb.
Radial Nerve Palsy
Anatomy
The radial nerve is the terminal branch of the posterior cord of the brachial plexus. It passes in a posterior direction around the humerus where it runs between the medial and lateral heads of triceps in the spiral groove. At this level it is closely applied to the bone and, as such, is liable to injury when the humerus shaft is fractured. The three heads of triceps are innervated proximally in the upper arm and this muscle is usually not affected in the more common causes of radial nerve palsy. At the mid-humerus level the radial nerve is immediately posterior to the bone and at the level of the junction between the middle and distal thirds of the humerus; the nerve lies immediately lateral to the bone. An understanding of the relevant surface anatomy of the radial nerve is important when planning surgical incisions or inserting external fixation pins.
Just proximal to the cubital fossa of the elbow the nerve lies between biceps and brachioradialis muscles. At this level it gives off branches to Extensor Carpi Radialis Longus and Brachioradialis (BR). The nerve now splits into the superficial branch and the Posterior Interosseous Nerve (PIN). The superficial branch is a purely sensory nerve which lies on the deep surface of BR until the distal one third of the forearm. The PIN passes lateral to the proximal radius between the two heads of supinator muscle which it supplies. After it leaves the supinator muscle the PIN splits into its terminal branches supplying all the extensor muscles.
Assessment
In high radial nerve palsy there is loss of all extensor function below the elbow (BR, ECRL, ECRB, EDC, EIP plus EDQ, EPL, APL, EPB) (See Table 2.4). This should be differentiated from posterior interosseous nerve palsy or low radial nerve palsy where BR & ECRL are preserved. These patients present with weak but intact wrist extension in marked radial deviation (Fig. 2.1).
Table 2.4
Muscles supplied by radial nerve
Fig. 2.1
Marked radial deviation on attempted wrist extension due to intact BR and ECRL in PIN palsy
High Radial Nerve Palsy
These patients present with three distinct clinical deficits.
Loss of wrist extension
Loss of thumb extension
Loss of finger extension
Most authors would agree that the preferred technique to restore wrist extension is by transferring the pronator teres. This reliable transfer is complicated only by the short donor tendon of pronator teres which needs to be elongated by a strip of periosteum at the time of harvest. In the unlikely scenario where the pronator teres cannot be used, then options include utilizing the FDS tendon from the middle and/or ring finger or performing a single FCU transfer to reconstruct wrist extension, finger extension and thumb extension [4].
Loss of function in EPL, APL and EPB results in an inability to retropulse the thumb out of the palm. The poorly positioned thumb now interferes with cylindrical grasp and the ability to release larger objects. As in the case of wrist extension transfers, reconstruction of thumb extension is mostly concurred by various authors. The EPL is rerouted out of the 3rd compartment and anastomosed to the palmaris longus. This transfer usually results in a satisfactory ability to clear the thumb out of the plane of the palm. In patients who do not have palmaris longus (12 %), the best option is to include EPL with the tendon transfer to the finger extensors as a mass action transfer. Wrist flexion will result in simultaneous metacarpophalangeal joint extension and extension/retropulsion of the thumb.
The most controversial aspect of radial nerve palsy reconstruction revolves around the restoration of finger extension. The use of a wrist flexor (FCU or FCR) to achieve finger extension, results in a transfer that is both strong enough as well as being in-phase with the normal tenodesis effect of the hand. Boyes advocated the use of finger flexors (FDS 4) to motor EDC but few clinicians make use of this technique today [5, 6].
Jones initially described the use of FCU as a motor [7] but many, including Brand [8], feel strongly that FCU is critical for the normal kinematics of the wrist as it is the main motor for flexion–ulna deviation in the “dart throwers” or hammering motion. Despite these concerns, Raskin and Shaw Wiglis et al. failed to show any loss of wrist flexion strength or function after FCU harvest [9].
Many authors are of the opinion that the FCR transfer (Brand) is easier, quicker and associated with less intra-operative dissection. Mobilization of FCU requires a substantial incision and dissection because FCU is a unipennate muscle with strong fascial attachments to the ulna periosteum along its entire length. In the rare event, where the wrist flexor is expected to power wrist, finger and thumb extension, then FCU would be a reasonable donor to sacrifice.
Goal | Transfer |
|---|---|
1. Wrist extension | PT to ECRB |
2. Finger extension | FCR to EDC (Brand) |
Or FCU to EDC (Jones) | |
Or FDS to EDC (Boyes) | |
3. Thumb extension | PL to EPL (rerouted) |
Or if no PL (12 %) then FCR/FCU to EDC + EPL | |
Or FDS to EPL |
Low Radial Nerve Palsy
These patients present with intact wrist extension through the maintained functioning of ECRL. Because of this, they do however tend to extend into radial deviation which is made worse by the lack of tone in ECU. To take away the remaining ulna deviator in the form of FCU would exacerbate the radial deviation acutely. For this reason, where there is debate over the choice of wrist flexor to power finger extension in high radial nerve palsy, in posterior interosseous nerve palsy there is NO underlying debate. Only FCR should be utilized. Thought should be given to rerouting the transfer around the ulna border of the forearm to balance the radial deviation moment at the wrist.
Surgical Technique (Fig. 2.2)
Fig. 2.2
Line drawing of radial nerve tendon transfer. (a) Incisions as discussed in text. (b) First the FCR is transferred around the radial border of the forearm and anastomosed to the EDC tendons by a Pulvertaft weave just distal to the musculotendinous junction. Then the PL is transferred to the rerouted EPL. Finally the PT is transferred to the ECRB
The following surgical technique describes the FCR set of tendon transfers. An S-shaped curvy linear incision is made on the volar radial aspect of the mid forearm approximately 8 cm long. The midpoint of this incision is at the insertion of pronator teres and is situated over the radial artery and the volar border of brachioradialis. This utilitarian incision will be utilized to dissect PT, ECRB, FCR and PL.
As per the standard Henry approach, the deep fascia is incised at the medial edge of BR. The radial artery and vein lie immediately deep to the fascia at this point and will be retracted in an ulna direction. The oblique fibres of PT are identified coursing from the medial epicondyle to the mid volar radius. The distal/ulna and proximal/radial edges of the muscle and tendon are identified and dissected off the adjacent epimysium.
The PT tendon and a 2 cm strip of periosteum are elevated off the radius by sharp dissection in a proximal to distal direction. Gentle traction of the tendon will allow substantial mobilization of the pronator teres muscle. Eventually, the deep head blends into the common flexor muscles making further dissection hazardous. A 3 cm excursion of the PT is confirmed and is considered adequate.
A separate transverse incision is made over the volar wrist crease. Care is taken to identify and protect the palmar cutaneous branch of the median nerve. The PL is separated from its dense fascial attachments and transected distally. The FCR tendon is identified and mobilized by passing a tendon hook around it and delivering a loop of tendon out of the wound. By flexing the wrist and tensioning the tendon, the FCR can be transected as far distally as possible. These tendons are delivered into the 1st incision and the 2nd incision (transverse wrist) is closed with a subcuticular suture. As this incision is sutured in the flexion crease, it heals with a pleasing cosmetic result.
Through the same utilitarian incision, the volar skin flap is elevated to expose the tendons of PL and FCR. The dorsoradial flap is elevated and with the help of passive pronation, the tendons of ECRL, ECRB and BR are identified. Care must be taken to preserve the superficial branch of the radial nerve lying initially on the deep aspect of brachioradialis and then passing distally between the BR tendon volarly and the combined tendons of ECRL and B dorsally. Even though the radial nerve innervated muscles might not be functioning, there might be some sensation passing through the radial sensory nerve and for this reason, it needs to be protected. These two tendons often run in the same fascial sheath and must be carefully separated. Remember that the ECRL lies lateral to the ECRB on its way to the base of index finger metacarpal.
Pearl
ECRL is Lateral
The third incision is C-shaped and curved longitudinally, starting at Lister’s tubercle with its apex over the interosseous membrane. An 8 cm incision will easily suffice. Full thickness skin flaps are elevated with complete exposure of the extensor retinaculum. A large window is made in the proximal aspect of the retinaculum and this is flapped in an ulna direction. The EPL tendon is identified and transected proximally. The retinaculum is opened over the EPL distally to deliver the cut proximal end out of the 3rd dorsal compartment. This tendon is now rerouted over the 2nd compartment in preparation for transfer.
A subcutaneous dissection is performed from the 1st incision to the 3rd and the FCR and PL tendons are passed through. The 4th compartment consisting of the EDC tendons together with the EIP is mobilized and tractioned to confirm there are no adhesions limiting excursion and to confirm that all the MP joints are extending. Occasionally the little finger lags and the EDM (5th compartment) may need to be incorporated into the transfer. Now the transfers are performed.
The PL is sutured to the rerouted EPL and FCR is sutured to the EDC tendons. Various anastomoses can be performed including the Pulvertaft weave [10], the spiral technique [11], the Lasso technique and the side to side suture [12]. What is more important is the tension of the transfer and the bulk of the repair site. There have been many descriptions of methods of setting the tension in these transfers. There are two issues that need to be addressed. Firstly, the MP joints should achieve passive extension as the wrist is brought into flexion (the tenodesis effect) and secondly, in wrist extension, the fingers should be easily able to achieve a full fist. Failure to address the later point can seriously compromise flexion causing a larger functional impairment than a loss of extension.
The technique I prefer is to set the tension with the wrist in 20° extension and the MP joints in 0° extension. With this static position held, the tendons are tractioned gently to a maximum length and then the FCR is released approximately 1 cm. Two or more horizontal mattress sutures are placed and the tenodesis effect is checked. Any laxity or tightness can be corrected. The PL to EPL transfer often has a tendency to lag post operatively and for this reason a conscious effort is made to tension this transfer slightly tighter with the wrist in 45° of dorsiflexion. The 3rd incision can now be closed with subcuticular absorbable sutures.
The final aspect of the procedure involves suturing the pronator teres to ECRB. This component of the overall transfer is performed last to allow intraoperative checking of the tenodesis effect to assess the correct tension of the first two transfers. ECRB is mobilized and tractioned fully until the wrist extends to 60°. A tight weave between the tendon of PT and ECRB is performed. When released, the wrist should not drop below a 30° extended position. If it does, then the transfer should be tightened. The incision is now closed.
A volar below elbow plaster slab is applied with the wrist 60° extended and the MP joints in 0° extension. The IP joints are left free and the thumb is held with a volar plaster of Paris slab in a position of maximum retropulsion. After 3 weeks, the plaster is removed and the wrist supported in a volar splint. This splint is removed every 2 h to allow only active flexion of the wrist and fingers. Once flexion of the fingers into the palm is achieved (usually 1 or 2 weeks), a lively extensor splint is worn for a further 3 weeks. This splint should also be removed 2 hourly for wrist flexion and extension exercises to facilitate the tenodesis affect.
Timing of Radial Nerve Tendon Transfers
Radial nerve palsy complicates a fracture of the humeral diaphysis in approximately 10 % of cases. Other well described causes include Saturday night palsy, gunshot injuries and sharp penetrating injuries. The management of the radial nerve with an associated humerus shaft fracture is controversial. Between 70 and 90 % of these injuries will recover spontaneously and therefore primary exploration per se is not indicated.
The one exception is an open fracture of the humerus where the incidence of a transected nerve is greater than 50 % [13]. The rest will be treated expectantly. If after 6 months, there has been no recovery then intervention is required. Most would advocate exploration and grafting. It needs to be clearly explained to the patient that, while the results nerve grafting are good [14], the recovery can be extremely prolonged (6–9 months on average).
Following a radial nerve tendon transfer procedure, the patient can reliably expect extensor function to the upper limb to be reconstructed. Return to work and avocational activities can be anticipated by 3 months.
Pearl: Outcome in Adults and in Children
Primary nerve repair is better than tendon transfer in both.
Children: Nerve grafting has better results than tendon transfer.
Adults: Nerve grafting has similar results to tendon transfer (but much longer recovery time).Related posts:
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