Introduction
A recent epidemiologic study reported an annual incidence of traumatic upper-extremity nerve injuries of 17 persons in 100,000 with an average age of 38 years and a male:female ratio of 2:1. Laceration is the most common mechanism of injury, and the ulnar nerve is the most frequently affected nerve. Injury to a major peripheral nerve of the arm or forearm poses several challenges to the person affected, ranging from mild discomfort to lifelong functional impairment. The socioeconomic impact of upper-extremity nerve injuries is substantial. In its most severe form, that is, discontinuity of a nerve due to full transection of all axons and their sheaths, the risk of major, lasting functional deficit is considerable. Even with appropriate and early nerve repair, outcomes vary depending on several factors including distance from the injury site to the affected muscles, age, general health, and access to rehabilitation. Treatment options include nerve repair and nerve transfers in the early period after injury. After about one year, however, these options are no longer available and “musculotendinous transfers” (commonly known simply as “tendon transfers”) become the mainstay of reconstruction.
The principles and general guidelines for tendon transfers are described in many hand surgery textbooks and reviews. In this chapter, we summarize current strategies, based on physiologic and biomechanical studies, for tendon transfers that minimize functional loss and restore control and performance of the hand after injuries to the radial, median, and/or ulnar nerve. This review includes transfer of healthy muscles as well as weaker and reinnervated donors for postural control of hand intrinsic functions. Below is a list of these principles together with considerations and some personal reflections and recommendations of the authors of this chapter.
Principles and general guidelines
Correction of muscle-joint contracture
In any patient with cervical spinal cord injury or peripheral nerve palsy, the joints must be kept supple: soft-tissue contracture is far easier to prevent than to correct . Maximum passive motion of all joints must be present before a tendon transfer is undertaken because, in general, a tendon transfer cannot move a stiff joint effectively. Occasionally, a tendon transfer may act as an “internal splint” and can, over time, correct a muscle-tendon-joint contracture. This effect has been observed, for example, with the deltoid-triceps tendon transfer with passive elbow extension deficit and passively powered tenodesis. The “House procedure” to correct proximal interphalangeal (PIP) joint flexion contracture is another such example.
Adequate strength
The muscle selected as the donor for transfer must be strong enough to perform its new function in its new, changed position. Selecting the appropriate motor is important because a muscle may, at least initially, lose some strength after transfer. In general, it is not advisable to transfer a muscle that has been reinnervated. However, the exception may be when the reinnervated muscle is transferred more for postural reasons, when less power is needed. For example, a reinnervated extensor digiti minimi (EDM) can be transferred to abductor pollicis brevis (APB) to restore thumb abduction after a successful supinator to posterior interosseous nerve (PIN) transfer procedure. Postoperatively, immediate controlled activation is employed to (1) maintain muscle strength, (2) prevent atrophy and muscle-tendon adhesions, and (3) facilitate motor relearning.
Muscle architecture and amplitude of motion
Excursion of the donor musculotendinous unit is important. Together with the selection of a suitable donor muscle, sufficient excursion is probably the most critical factor in determining the success of any transfer surgery. Excursion is particularly important when the new motor will power a joint that has a large range of motion or will power a tendon acting over several joints. To obtain adequate excursion, release of the donor muscle needs to be sufficient and, sometimes, must be extensive. Incomplete amplitude of the entire musculotendinous unit will result in a poor outcome no matter how complete the release of the distal tendon is.
The choice of donor muscle in tendon transfer surgery needs to include consideration of the muscle architecture. By “muscle architecture” is meant the length of the individual muscle fibers and the physiologic (not anatomical) cross-sectional area (CSA) ( Fig. 21.1 ). Muscle excursion is proportional to fiber length, or, more accurately, fiber bundle length, and muscle force is proportional to CSA. At surgery, it is important to always release the entire musculotendinous unit from surrounding fibrous connections to achieve sufficient excursion and optimal direction of pull. Different donor units require different amounts of such release to gain mobility. Usually, a donor with a large excursion should be selected. However, the arrangement of muscle bundles varies within and between muscles. For example, a wrist flexor, such as flexor carpi ulnaris (FCU), with an excursion of 30 to 40 mm cannot substitute fully for a finger extensor with an excursion amplitude of 60 mm. Yet, an extensive release (15 cm in an adult arm) can allow for the longer muscle fibers proximally to provide greater excursion and, thus, force production over a wider range of joint motion ( Fig. 21.2 ). , Although the true amplitude of a tendon cannot be increased, its effective amplitude can be estimated in different ways ( Box 21.1 ).
- 1.
Select architecturally matching donor muscles. In other words, if the action to be restored will require a large excursion, a muscle with long fibers (a relatively small pennate angle) is preferred.
- 2.
A natural tenodesis effect can be enhanced by converting a muscle from monoarticular to biarticular or multiarticular. For example, a monoarticular pronator teres transferred to the extensor pollicis longus, abductor pollicis longus, and extensor digitorum communis can in addition be enhanced by flexing the wrist.
- 3.
When necessary, extensive mobilization of the musculotendinous unit from its surrounding fascial attachments can be employed to increase its excursion substantially.
Line of pull
To be most effective as a transfer, the musculotendinous unit must pass in a direct line from its origin to the insertion of the tendon being substituted. This straight line of pull reduces friction and, hence, the risk of adhesions, thus facilitating postoperative motor training.
One tendon, one function and exceptions
A single transferred tendon cannot be expected to perform entirely opposing actions simultaneously (e.g., both flex and extend the same joint). If a musculotendinous unit is inserted into tendons that have different functions, the force of the donor transfer is dissipated and less effective than if motoring a single tendon. In some cases, dual actions obtained by one transfer can be achieved. Such an example is restoration of both thumb flexion and forearm pronation by transfer of the brachioradialis (BR) to the flexor pollicis longus (FPL) through the interosseus membrane (IOM) in patients lacking sufficient forearm pronation power. , Another example is restoration of intrinsic thumb control after median nerve injury. By differential insertion (dorsally and palmarly) of the two EDM tendon slips into different parts of the APB tendon, it is possible to restore palmar abduction and, simultaneously, add pronation movement of the thumb to achieve the normal trajectory of thumb movement against to the radial aspect of the midphalanx of the index for key pinch.
Synergism
Synergism occurs when muscles contract simultaneously to augment the effectiveness of each individual muscle. The use of synergistic muscles (e.g., finger flexors acting in concert with wrist extensors and finger extensors with wrist flexors) has been advocated for transfer. However, there are many examples of well-functioning, nonsynergistic donors being used successfully in tendon transfer surgery—for example, BR and pronator teres (PT) in high median and radial nerve lesions, respectively. In general, functional relearning is quicker and easier after synergistic muscle transfer, whereas nonsynergist transfers generally involve more protracted and therapist-guided motor relearning.
Expendable donor
The severance of a donor tendon for transfer must not result in an unacceptable loss of function. Sufficient muscle power must remain to perform the original function of that donor muscle. For example, when harvesting flexor carpi radialis (FCR) to be transferred to extensor digitorum communis (EDC), it is imperative to verify sufficient power of at least one remaining wrist flexor (e.g., FCU).
Stress-relaxation of the donor muscle before attachment
When detached from its insertion, a musculotendinous unit has an intrinsic passive stress-relaxation that must be considered before tendon transfer ( Fig. 21.3 ). Therefore it is important to let the muscle stress-relax before tendon-to-tendon attachment and tensioning is performed at the site of insertion. Stress-relaxation in human skeletal muscle requires 2 to 5 minutes. Consequently, the surgeon must wait for this length of time before final suturing of the transfer to its insertion.
Correct tendon-to-tendon suture
A reliable tendon-to-tendon attachment is crucial to immediate postoperative training in tendon transfer surgery. A double-sided running suture, back and forth, with 3 to 5 cm tendon–tendon overlap is sufficient ( Fig. 21.4 ). This suture has a strength of more than 200 N and allows immediate and active postoperative training without risk of rupture. Early postoperative rehabilitation improves tendon gliding, prevents atrophy of the transferred muscle, and facilitates relearning.
Timing of tendon transfer
Transfers should not be undertaken until the local tissues are in optimal condition. The term tissue equilibrium is often used to describe this state and refers to the absence of wound reaction, with resolution of soft-tissue induration, fully mobile joints, and scars that are as soft and mobile as they are expected to become. Typically, tendon transfers function best when routed between subcutaneous fat and the deep fascial layer. In contrast, tendon transfers are less likely to function well when routed through an area of scar. Occasionally, it is useful to provide two substitutes for a vital motor function by tendon transfer simultaneously with repair of the injured nerve, particularly when the reinnervation time is expected to be long (e.g., after a high radial nerve injury).
Establish your own “toolbox” of tendon transfers
We recommend using a limited number of standardized transfers and performing them well instead of “experimenting” with new and challenging procedures, especially if requiring a lengthy learning curve. Also, we endorse learning the “art” of augmenting tendon transfers by addition of active and passive tenodeses.
Get involved in postoperative training
Be sure to communicate any surgical circumstances that require special attention to the hand therapists. Address in writing any deviation from standard protocols. In this overview, we refer to the cited articles for specifics of postoperative training. In general, early, unloaded active training several times per day (3–4) is recommended. Custom-made splints protect the transfer at night and between training sessions.
Radial nerve palsy
By definition, the nerve injury in a high radial palsy is proximal to the forearm and that causing a low palsy is distal to the elbow and involves the posterior interosseous nerve. The clinical presentations are different.
The clinical pattern of radial nerve palsy
The most important functional motor deficits in high radial nerve palsy are the inability to extend the wrist, the fingers, and the thumb at the metacarpophalangeal (MCP) joints and to radially abduct the thumb at the carpometacarpal (CMC) joint ( Box 21.2 ). The most critical deficit is the patient’s inability to control wrist stability, causing a break of the kinetic chain affecting the entire function of the hand. Wrist stability is vital for the transmission of flexor muscle force to the fingers. When wrist extension power is lacking, grip strength is markedly impaired. Similarly, abductor pollicis longus (APL) is vital to maintaining the kinetic chain of the thumb by radially abducting and stabilizing the first CMC (CMC1) joint. Stabilizers of both the wrist and CMC1 are important to the opening phase of reaching out to grasp, when they are synchronized with finger extension. In radial nerve palsies, failure of finger MCP extension can be partially compensated by PIP and distal interphalangeal (DIP) joint extension, provided by the median and ulnar nerve innervated lumbricals. However, the lumbricals are not sufficiently tensioned if wrist extension is missing. Intact finger flexors will disable any attempt to achieve a “tenodesis extension” of the finger MCPs in the presence of paralyzed EDC muscles.
Two important motor deficits in high radial nerve palsy:
- 1.
Inability to extend the wrist and fingers.
- 2.
Inability to extend the thumb at the metacarpophalangeal (MCP) joints and to radially abduct the thumb at the carpometacarpal (CMC) joint.
- 1.
Two schools of thought in decision-making for a transfer:
- 1.
Early postinjury tendon transfer performed simultaneously with repair of the radial nerve.
- 2.
Delayed tendon transfers when reinnervation (or lack of innervation) of the brachiloradialis (BR) and extensor carpi radialis longus (ECRL) has occurred within a defined time limit, usually up to 9 months.
- 1.
Donor and recipients in tendon transfers:
- 1.
Pronator teres to extensor carpi radialis brevis (PT-ECRB) for wrist extension,
- 2.
Flexor carpi radialis to extensor digitorum communis (FCR–EDC) for finger extension,
- 3.
Palmaris longus to extensor pollicis longus (PL-EPL) for thumb extension.
- 1.
Taken together, restoration of wrist extension, thumb extension/abduction, and finger extension are of paramount importance to function and should be undertaken at a suitable point in time (see below).
The optimal time to perform tendon transfers for high radial nerve palsy remains debated ( Box 21.2 ). There are essentially two schools of thought: (1) early postinjury tendon transfer performed simultaneously with repair of the radial nerve and (2) delayed tendon transfers when reinnervation (or lack of innervation) of the “above elbow” innervated muscles, viz. the BR and extensor carpi radialis longus (ECRL) has occurred within a defined time limit, usually up to 9 months. The choice of strategy depends on the level, type, and severity of the lesion. The prognostically most “favorable” injury is a partial, clean-cut lesion a few centimeters proximal to the motor branches to the BR and ECRL.
We advocate approach number one for several reasons. First, early restoration of wrist extension provides immediate wrist stability and power grip. Second, the functional loss is minimal and motor relearning can start early while awaiting reinnervation. Third, should nerve suture be successful, further strengthening of wrist extension will not affect general hand performance negatively.
Common tendon transfers in radial nerve palsy
Although several different alternatives exist, , , our most recent strategy typically includes the following tendon transfers: pronator teres to extensor carpi radialis brevis (PT-ECRB), flexor carpi radialis to extensor digitorum communis (FCR–EDC), and palmaris longus to extensor pollicis longus (PL-EPL) ( Box 21.2 ) ( Figs. 21.5–7 ).
Rationale for choice of procedures
Wrist extension.
With all three wrist extensors, viz. ECRB, ECRL, and extensor carpi ulnaris (ECU) missing, the demand for a strong donor is obvious. PT is the strongest muscle in the forearm (see Fig. 21.1 ) and can relatively closely match the composite force of the three extensors, having approximately 60% of their combined strength. However, its excursion is less than all three of the individual wrist extensors. PT is nevertheless the best choice to secure wrist extension stability and strength. To get maximal benefit from the PT transfer, it is imperative to maximize its mobility by an extensive release ( Fig. 21.5 ). ,
Finger extension.
To satisfy the need for sufficient musculotendinous excursion to enable finger extension, regardless of wrist position, and to avoid extensive musculotendinous release, the FCR presents a logical choice. Alternatively, the FCU could be used as a donor ( Fig. 21.7 ). However, the extensive release is necessary to obtain satisfactory excursion and the excessive strength of the FCU, which is the second strongest muscle in the forearm (see Fig. 21.1 ). These considerations on the FCU make the choice of the FCR more sensible, particularly in cases with a posterior interosseus nerve lesion with consequent loss of ECU function.
Thumb extension.
When present, the PL is an obvious choice to restore lost thumb extension ( Fig. 21.7 ). Mechanically, the PL acts as a wrist flexor, so its action is synergistic with thumb extension. It is one of the weakest muscles in the forearm but has an almost identical force-excursion profile to the extensor pollicis longus (EPL) , ( Fig. 21.1 ), and it is well suited to replacing thumb extension as well as abduction after insertion into a rerouted EPL tendon.
Our preferred choices and techniques
Transfer of PT to ECRB ( Fig. 21.6 A) ( Fig. 21.7 A).
Through a straight, longitudinal, 6 to 8 cm incision centered over the dorsoradial aspect of the middle portion of the radius, the PT is detached together with a distal 2 cm (or more when feasible) periosteal strip. The latter makes distal reattachment easier. The ECRB tendon, including its intramuscular portion, is identified and divided. The PT tendon is released in a proximal direction. The ulnar head of the PT is small, mainly tendinous, and it is a minor contributor to the force of the PT and restricts the excursion of the transfer. If present, the separate ulnar head of the PT is identified and divided. The main PT is then secured to the ECRB using the technique described above. Note that if there is a strong tendency of ulnar deviation of the wrist because of the harvesting of the FCR (see below), suturing of the ECRB side-to-side to the ECRL may be considered to bring the sum of the wrist extension moment slightly more radial.
Transfer of FCR to EDC (see Fig. 21.6 B and Fig. 21.7 B).
Through a traverse volar incision, the FCR tendon is transected at the wrist crease and mobilized proximally (easily) to about the midforearm, where it is identified through a separate transverse palmar incision. A dorsal incision is made just proximal to the extensor retinaculum to expose the EDC and EPL tendons. The FCR tendon is tunneled subcutaneously and obliquely from the proximal palmar incision around the radial side of the forearm into the dorsal wrist incision using the same dorsolateral incision as for the PT-ERCB exposure. The donor FCR is then passed obliquely through the EDC tendons proximal to the extensor retinaculum and secured to all of the individual EDC tendons using the technique described above.
Transfer of PL to EPL (see Fig. 21.6 C and Fig. 21.7 C).
Through the same volar wrist incision used to harvest the FCR, the PL tendon is divided and withdrawn through the same transverse midforearm incision as for the FCR tendon. It is then tunneled subcutaneously along the distal, radial aspect of the forearm to an incision over the base of the first metacarpal. The EPL tendon is divided at its musculotendinous junction, withdrawn from the third dorsal extensor tendon compartment, and passed subcutaneously to the incision at the base of the thumb metacarpal, where it is secured to the PL tendon using the technique described above. If the PL is absent, the EPL tendon can either be powered by the superficialis flexor of the ring finger (FDS4) passed through the IOM or included with the EDC tendons in the FCR transfer. In the latter case, the FCR would power both finger and thumb extension. Technical points for tendon transfers in radial nerve palsy are summarized in Box 21.3 .
PT-ECRB
- 1.
PT has two heads: the greater humeral head (PT H ) originating from the medial supracondylar ridge of humerus and the ulnar head PT U originating from the medial side of the coronoid process of the ulna.
- 2.
Excursion limitation may arise from the short nature of PT U muscle fibers and its more tendinous structure.
- 3.
Release, or excision, of PT U may be necessary before transfer to achieve maximal PT H amplitude ( Fig. 21.5 ).
- 4.
Any tendency to excessive ulnar deviation due to wrist flexor imbalance can be compensated by side-to-side suturing of the ECRB to the ECRL.
FCR-EDC
- 1.
The FCR is detached through the same transverse volar wrist incision as the PL.
- 2.
No extensive proximal release is needed.
- 3.
Pass the FCR tendon through the same dorso-lateral incision as for the PT-ERCB exposure.
PL-EPL
- 1.
Detach the PL through the same transverse volar wrist incision as the FCR.
- 2.
Tunnel the PL subcutaneously along the distal, radial aspect of the forearm.
- 3.
Divide the EPL proximal to Lister’s tubercle and reroute it radially, subcutaneously, and outside of the third extensor compartment.
- 4.
Suture the PL to the EPL over the proximal part of the first metacarpal.
- 5.
The PL is a stiff muscle —no need to overstretch.
Median nerve palsy
Median nerve lesions are typically separated into two categories, viz. high and low median nerve palsy, , with the functional loss depending on the level of the lesion. High median nerve palsies include lesions at the upper arm, elbow, and proximal forearm level. Low median nerve palsies result from injury at the distal forearm and wrist. The major problem of low median nerve palsy is the loss of motor of the opponens pollicis. However, the FPL function is still intact in low median nerve palsy, so thumb opposition is mostly possible, which does not need a transfer. Transfer is justified if opposition is weak or incompetent ( Box 21.4 ). The major contents below is for high median nerve palsy.
High median nerve palsy:
Nerve injury proximal to the mid-forearm. Major consequences: loss of FPL function and loss of opposition, and sometimes loss of forearm pronation. The methods:
- 1.
Restoring function of the AIN-innervated muscles (FPL and FDP 2/3): (1) BR to FPL transfer, and (2) FDP 2/3 function can be reconstructed by side-to-side coupling to the FDP 4/5. In selected cases, the synergistic ECRL tendon can be a donor for FPL or FDP 2/3 function.
- 2.
Restoring forearm pronation: Biceps rerouting to change its function from supination to pronation; Alternatively, a BR to FPL transfer via the dorsal route through the IOM.
- 3.
Reconstruction of opposition: The strongest muscle for opposition is the APB. In all opposition transfers, the insertion of the tendon transfer is the distal APB tendon. The EIP is a frequent donor, passed subcutaneously around the ulna or through the IOM. Transfers of the FDS3 and 4 are suitable for median nerve lesions distal to the nerve branches to the FDS, passing the FDS around the FCU near its insertion at the pisiform. The Camitz transfer is a PL transfer either routed around the palmar aponeurosis or through a slit in the ulnar side of the flexor retinaculum.
- 4.
The ADM muscle transfer can be used when complex forearm injuries with extensive scarring might interfere with gliding of the other extrinsic donor tendons.
- 1.
Low median nerve palsy:
Nerve injury at the distal forearm or the wrist. A transfer is needed if thumb opposition is incompetent (see above 3 and 4 for methods).
Authors’ advice:
- 1.
A more differentiated approach must be chosen for reconstruction of thumb opposition. We prefer to use the FDS 4 as the donor. FDS 4 is intentionally activated together with thumb opposition and, consequently, serves as an appropriate donor option.
- 2.
If the FDS 4 cannot be used, our second choice is the EDM transferred through the interosseus membrane in a straight line to APB. The EIP alternative for opposition transfers has the drawback that the tendon can be too short to reach the APB aponeurosis.
- 1.
Clinical presentation of high median nerve palsy and goals
The most common motor deficits are loss of pinch and grip strength, weakened forearm pronation, and inability to oppose the thumb. Three main goals of reconstruction need to be met in median nerve palsy.
- 1.
Grasp and pinch function should be restored. To achieve this objective, reconstruction of the paralyzed anterior interosseous nerve (AIN) innervated muscles, viz. the FPL and flexor digitorum profundus (FDP) to the index and middle fingers (FDP2/3), must be restored.
- 2.
Forearm pronation should be restored. Most daily hand activities are undertaken with a pronated forearm, with pronation being essential to the hand reaching its target, such as grasping cutlery, manipulating a keyboard, or shaking hands, easily.
- 3.
Thumb opposition is imperative for all hand functions and should be restored. Opponens pollicis (OP) and abductor pollicis brevis (APB) reconstructions serve this purpose.
Treatment methods: After high median nerve injury
Multiple tendon transfer procedures in different combinations have been proposed over the years. , , , , , Below, we summarize some of those used most and those which the authors of this article have the most experience.
Restoring function of the AIN-innervated muscles (FPL and FDP 2/3).
The combined loss of thumb flexion and opposition and flexion of the index and middle fingers is functionally significant, since all pinch and grasp configurations are no longer possible. Reconstruction of these extrinsic median-innervated functions is, therefore, of utmost importance. Our primary choice for restoring FPL function is by transferring the BR musculotendinous unit. FDP 2/3 function can easily be reconstructed by side-to-side coupling to the FDP tendons of the ring and little finger (FDP 4/5). Both transfers can be carried out through forearm access on the flexor side. The side-to-side suture technique, performed according to Fridén using cross-stitches with braided, non-resorbable 3.0 TiCron, is preferred (see Fig. 21.4 ). , This tendon-to-tendon attachment technique provides maximal strength and allows for early active rehabilitation. , The necessity for controlling the surgical attachment length and the position of the patient’s limb at the time of tendon transfer deserves special attention. In selected cases, the synergistic ECRL tendon can serve as the donor for FPL or FDP 2/3 function.
Restoring forearm pronation.
Forearm pronation is rarely completely lost in high median palsies with paresis of the PT and pronator quadratus (PQ) muscles. The brachioradialis, FDP, and ECU muscles can maintain a residual level of pronation function. However, if this function fails completely, important activities of daily living can no longer be carried out. In these cases, reconstruction of pronation is necessary. In these circumstances, biceps rerouting to change its function from supination to pronation is a reliable surgical procedure. Technically, it is important not to detach the tendon from its insertion to the radius. With a long Z-shaped tenotomy, the distal tendon insertion is preserved, and the required additional length is achieved. The distal tendon slip is routed radially around the radius to achieve pronation and then sutured in a stable side-to-side fashion to the proximal slip with the necessary lengthening ( Fig. 21.8 ).
Alternatively, restoration of forearm pronation may be combined with powering of the FPL by a BR to FPL transfer via the dorsal route, in which the BR is passed through the IOM.
Reconstruction of thumb opposition.
Without the ability to oppose the thumb, the important functions of pinch grip and fist closure when grasping are not possible. When planning this reconstruction, the direction of the pull of the transferred tendon is of particular importance. The strongest muscle for opposition function is APB. Therefore in all opponensplasties, the insertion site of the tendon transfer is the distal APB tendon. Proximally, to mimic APB, the direction of the pull of the transferred tendon should originate at the flexor retinaculum and the FCU tendon sheath. ,
Opponensplasty using an extensor indicis proprius transfer.
The extensor indicis proprius (EIP) tendon is frequently used as a donor for reconstruction of opposition function ( Figs. 21.9 , 21.10 ). Transfer subcutaneously around the ulna or through the IOM are both described, and both achieve an ideal vector. The EIP transfer creates no loss of strength when clenching a fist, as is the case with other donors such as FDS. Furthermore, using the EIP keeps the FDS in reserve for other transfers. In individual cases, extension of the EIP tendon, with a PL or extensor pollicis brevis (EPB) tendon, can be necessary.
Opponensplasty using a flexor digitorum superficialis transfer.
Flexor digitorum superficialis (FDS) tendons are suitable donors for median nerve lesions distal to the nerve branches to the FDS at the midlevel of the forearm ( Fig. 21.10 ). The powerful FDS 3 and 4 tendons serve as good donors. Care must be taken in cases with an additional high ulnar nerve lesion and loss of FDP 4/5 function. Here, FDS 4 harvest must be avoided; otherwise, the ring finger loses all flexor function. After distal transection of a FDS tendon, fixation of the distal tendon remnants to the palmar plate with a single stitch is recommended to avoid hyperextension of the PIP joint. The ulnar edge of the palmar aponeurosis can be chosen as the turning point of the transferred tendon. However, passing the FDS tendon around the FCU tendon near its insertion at the pisiform bone provides a better vector and is preferred. To maintain the position of the turning point here, a loop can be formed with a distally based strip of the FCU tendon, through which the FDS tendon runs ( Fig. 21.10 ).
