When considering tendon transfers it is vital that passive motion of any joints involved is optimized and the soft-tissue envelope is supple. Beyond this, there are six key principles that underpin tendon transfer in relation to the donor and recipient muscles. These can be remembered with the mnemonic SPEEPS: Single function, Power (adequate), Expendable, Excursion, Pull, Synergistic. When considering a transfer, each transferred tendon should ideally restore a single function. The donor must be adequately powered; so, ideally the transferred muscle/tendon will have similar power to the unit being replaced. Medical Research Council (MRC) grade for the donor muscle should ideally be grade V, although grade IV can also be adequate. The donor muscle must be expendable (e.g., one wrist flexor or extensor should be preserved). The excursion or amplitude of the transferred tendon should be similar to the excursion being replaced, but it does not have to be greater. The line of pull or vector should be similar between donor and recipient action and avoid pulleys wherever possible. The transferred donor and recipient muscles should ideally be synergistic. For example, finger flexion is optimal with wrist extension; so, using a wrist extensor for finger flexion is advantageous when it comes to rehabilitation.1,2
2. Richards RR. Tendon transfers for failed nerve reconstruction. Clin Plast Surg 2003;30(2):223–245, vi The most common indication for tendon transfer is nerve injury. This may be required because repair or grafting of the nerve is not possible, due to delay or extent of injury, or because the distance to reinnervation is too long (e.g., some brachial plexus injuries). Tendon transfer may also be indicated when previous attempts at repair have failed, or to reduce the need for splinting when nerve recovery is awaited (e.g., PT to ECRB for wrist control while a radial nerve repair recovers). The other options listed each represent potential reasons for tendon transfer. Medical diseases where limb function is impaired, such as poliomyelitis or leprosy, represent potential indications for tendon transfer, but the disease must be well controlled before undertaking surgery.1,2
Although sometimes very useful, tendon transfers can also be unpredictable in spasticity, such as in cerebral palsy. This is particularly true where spasticity is variable, such as in athetoid movements. Where a deficit or ability is variable, tendon transfer should be avoided. Diabetes mellitus is not a significant contraindication to tendon transfer, but glycemic control should be optimized as for any surgery. A stable deficit post-poliomyelitis can respond well to a tendon transfer where a suitable donor is available; however, sufficient recovery time should have elapsed before surgery is considered. Rheumatoid arthritis can provide many opportunities for a tendon transfer, such as EIP to EPL or crossed intrinsic transfer during MCP joint realignment. It is important to address the underlying cause first by controlling the disease medically, debriding active synovitis and excising osteophytes, or addressing other bony prominences (such as a prominent ulnar head). A tendon transfer can be helpful if repair or grafting of a tendon defect has failed; however, any causes for the first failure should be addressed (e.g., prominent hardware, abnormal bony prominences, poor patient compliance with therapy, or infection).1–3
Tendon transfers are more commonly performed as delayed procedures, as there are many factors to optimize before surgery, such as allowing any recovery to develop, allowing scar tissue to improve, or infection to settle. One good indication for an immediate tendon transfer is to augment function while waiting for prolonged nerve recovery, or where the prognosis for nerve or muscle recovery is poor. A good example of this is using a PT to ECRB transfer to act as an internal wrist splint for a patient with a high radial nerve injury while recovery is awaited. This potentially frees the patient from an external splint and puts the hand in a better position for using the remaining median and ulnar innervated muscles.1 Tendon transfers can be helpful in leprosy, but the disease must be controlled first.2,3 An immediate PL transfer for thumb abduction/opposition (Camitz procedure) is sometimes used in carpal tunnel syndrome with thenar wasting, which is more common in elderly patients or others expected to make a poor recovery. In a young, healthy patient with only partial thenar wasting, it would be more common to simply decompress the carpal tunnel and allow a period of recovery before considering a tendon transfer. When resurfacing a scarred limb, it is usual to allow the soft-tissue envelope to mature and soften before undertaking tendon transfers, as there is a high risk of adhesions and poor excursion if an immediate transfer is done. Following an immediate distal nerve repair, such as the ulnar nerve at the wrist, recovery is expected to occur much sooner than with a proximal injury, so tendon transfer in this setting is unlikely to be required. It is usual to perform these transfers with regional block; however, there are reports of doing this safely and effectively under local anesthetic, the so-called wide awake local anesthetic surgery (WALANT).2,3
Common options for restoration of thumb opposition/flexion include a radial innervated EIP transfer around the ulnar border of the hand, or a proximal median nerve innervated ring finger FDS transfer. The FDP should not be sacrificed because of the unacceptable digital flexion deficit that would result. The Huber transfer uses abductor digiti minimi as a transfer across the palm to restore thumb abduction/ opposition. It is more commonly performed in children, where it can be helpful in addressing thumb hypoplasia. It is less common in adults, as there are other options which may be simpler, and the cosmetic appearance can be disappointing because of the bridge of muscle crossing the palm. The PL can also be transferred with a strip of palmar fascia to augment length (Camitz transfer). However, the vector would be poor and the length insufficient if passed around the FCU, and in this scenario the PL may well have been injured. The FCR is not a good pulley to route an FDS transfer for thumb opposition/abduction around as the vector is incorrect.1–4
case? Although a transfer of the ring finger FDS tendon to the lateral bands could provide good correction of clawing, it would leave the ring finger unacceptably weak, since the FDP to this digit has been denervated and is not fully recovered. Many patients manage perfectly well with a long-term ulnar claw splint, or with no intervention at all; so, it is important to check whether they are content with a splint before embarking on complex reconstruction. Options C and E can also be used successfully in ulnar palsy.1
When considering tendon transfers, it is important to understand the expected timescale for nerve regeneration after repair/graft and the likely extent of nerve and muscle recovery, otherwise an unnecessary transfer might be undertaken. The ECRL and the ECRB are supplied very proximally; hence, there should be some wrist extension by 4 months. Although there may be signs of EDC reinnervation, it is unlikely to be strong at this stage. EPL recovery occurs late and may still remain sufficient up to 1 year after injury, as the PIN motor branch enters the muscle more distally in the forearm. Nerve recovery is typically 1 mm/day. EMG studies can be helpful to demonstrate early signs of reinnervation before significant clinical signs of recovery. If EPL displayed early recovery on EMG, a transfer would usually be postponed. Re-repair of a recovering nerve will sacrifice the recovered function and prolong the time to reinnervation of distal muscles. It is therefore unlikely to produce a superior outcome.1
Tendon transfers are tailored to each individual patient and according to surgeon experience and preference. One of the core principles is to avoid creating an unacceptable donor deficit. Scenario D would give good wrist and digital extension but at the unacceptable cost of preventing adequate wrist flexion, because both wrist flexors have been used (FCU and FCR). All of the other combinations address the deficits following radial nerve palsy without severe donor morbidity. PT is usually transferred to ECRB in radial nerve injuries to provide wrist extension, but ECRL and ECU are not usually reconstructed. FCR may be transferred to EPB and APL together to provide thumb extension and abduction. FCU or FCR may be used to provide digital extension by transfer to EDC; however, it is preferable not to sacrifice FCU in most scenarios. PL or FDS ring may be used to provide thumb extension by transfer to EPL.1–4
after a mid-forearm laceration that required repair of both the median and ulnar nerves 4 years earlier. Which thumb opposition. A radial nerve-innervated EIP transfer1 will be preferable to either a PL or FDS transfer for thumb opposition/ abduction, as these muscles are innervated by the median nerve and may also have had direct damage to the muscle belly at the time of injury. A Huber transfer,2,3 which uses the abductor digiti minimi muscle, is innervated by the ulnar nerve and is unlikely to have recovered well, given that the patient still has other signs of intrinsic muscle denervation. “One tendon transfer, one function” is one of the core principles when planning a series of transfers, and it is always sensible to review compliance with physiotherapy before undertaking complex upper limb reconstruction. While previously denervated muscles may be used if adequately recovered, it is preferable to use an uninjured donor where possible and MRC grade III power is insufficient for use as a transfer.
Scenario E demonstrates a violation of one of the core principles of tendon transfer, that is, joints must already be supple enough for functional range of motion before tendon transfer is undertaken. There will likely be a failure to correct, an early recurrence of the original deformity, or adhesions leading to stiffness if a transfer is performed in this scenario. Therefore, the PIP joint should be released as a first stage, with a delayed lateral band transfer once a stable range of joint movement is obtained and the soft-tissue envelope has settled again.1,2 Scenarios A through D demonstrate tendon transfers that may be appropriate. It is often sensible to perform an early tendon transfer, despite anticipated nerve recovery to improve quality of life, if this spares the patient from requiring an external splint and the recovery time is likely to be prolonged. As such, PT to ECRB transfer can allow a patient with radial nerve palsy to manage without a bulky wrist splint; likewise, a tibialis posterior to anterior transfer can obviate the need for a foot drop splint in patients with common peroneal nerve injury.3 EPL rupture can occur with distal radius fractures due to direct injury or ischemia in the third extensor compartment. The EIP passes through a different compartment and is therefore unlikely to rupture following transfer to the EPL. Transfers can be routed beneath a flap reconstruction, but the soft-tissue envelope must be soft and pliable.
This patient demonstrates spontaneous rupture of the EPL tendon with inability to extend the IP joint. This can occur in advanced rheumatoid arthritis where attrition rupture develops from synovitis or abrasion on bony spurs along the course of the EPL, particularly under the extensor retinaculum and over the carpus. The advantage of using the EIP tendon is that index finger extension can be maintained by the EDC and the path of the tendon transfer avoids some of the areas of previous damage. It is a straightforward procedure to undertake with minimal exposure required. The distal EPL is identified by making a longitudinal incision over the first metacarpal. The EIP is identified at the index MCP joint and is differentiated from the EDC tendon by its more ulnar position and insertion. A small incision allows this tendon to be divided at the extensor expansion. A second, proximal incision over the base of the second metacarpal allows the tendon to be retrieved before being rerouted subcutaneously to the distal stump of the EPL. A Pulvertaft weave is performed with the thumb and wrist in full extension. It is, of course, important to ensure that the EDC to the index finger is intact before transferring the EIP, as there may be multiple tendon ruptures in rheumatoid arthritis. Other tendon transfers for EPL rupture include ring finger FDS and palmaris longus. The FCR is sometimes used for APL and EPB but not EPL. The EDC is usually avoided, as this would give a mass extension action to the digits and thumb. The FDP tendon harvest would sacrifice the DIP joint flexion, which is not generally acceptable.1