Principle of Tendon Transfers

Anatomy and Physiology

Fundamental Biomechanics

Identifying the most appropriate muscle transfer procedure and graft requires thoroughly understanding the biomechanics of the muscle tension unit (MTU). Principles of optimal sarcomere length, force production characteristics, muscle architecture, and moment arms considerations should all be considered. This comprehensive approach can enhance individualization and functional outcomes for patients undergoing these procedures.

Laser diffraction experiments conducted by Lieber and colleagues in the 1980s revolutionized our ability to measure sarcomere length within various MTUs. This research helped reveal the optimal resting length for maximal forceful contraction of various muscle groups, with longer sarcomeres generally offering a greater range of motion. Blix curves illustrate this concept by demonstrating how sarcomere length affects tension and force production. Experimentally confirmed by Lieber et al in 1992, these curves show that muscle tension decreases rapidly as the muscle stretches beyond its resting length, with only a slight increase under passive stretch due to viscoelastic forces in muscle and connective tissues.

These findings have important implications for muscle transfer procedures, as they challenge the traditional practice of overtightening donor muscles based on the assumption that postoperative stretch occurs. In fact, overstretching can significantly compromise biomechanical effectiveness by reducing actin-myosin overlap. In extreme cases, muscle efficiency can diminish to as low as 28% of its maximum potential, causing the transferred tendon to function more through the tenodesis effect than active contraction. Conversely, excessive laxity increases sarcomere unit overlap, limiting effective excursion.[4]

The force generated by each muscle transfer is primarily determined by the physiological cross-sectional area of the muscle unit, with larger areas producing greater output. Muscle architecture, particularly the pennation angle, plays a role in this capability. Muscles with fibers parallel to the line of force generally outperform those with steep angles. Additionally, the moment arm should be considered when planning muscle transfers. A smaller moment arm allows for a greater range of motion, while a larger moment arm provides increased strength. This trade-off between range of motion and strength is essential in donor graft and transfer technique selection.

Graft (Donor) Fixation

The evolution of fixation methods in tendon repair surgery must be discussed. The Pulvertaft weave, introduced in 1954, is a standard technique involving interlacing donor and recipient tendons multiple times to provide robust and reliable fixation. However, the procedure's labor-intensive nature and potential bulk have spurred the development of innovative coaptation techniques. These advancements aim to facilitate immediate mobilization and reduce adhesion risks. Modifications to the Pulvertaft weave now focus on preserving tendon vascularity, while novel methods like spiral linking and the double-loop technique have emerged. The double-loop technique, for instance, has shown promise in biomechanical studies with significantly greater early postoperative strength, though its application is limited in areas with minimal soft tissue coverage. Similarly, the lasso technique offers comparable strength to the Pulvertaft weave but results in a thicker repair.

Recent innovations have addressed the challenge of combining strength with a lower profile. A notable example is the side-to-side coaptation technique, which has demonstrated superior strength without increased bulk, making it a promising option for early mobilization scenarios. This development represents a significant step in balancing the need for strong fixation with the desire for less invasive and bulky repairs.[5] Parallel to these advancements in tendon-to-tendon fixation, tendon-to-bone fixation has gained popularity, particularly in lower extremity procedures. This shift is largely due to improvements in implant technology. Techniques using bone anchors or interference screws are now preferred for their reduced risk of wound complications and less extensive surgical dissection.

Results from a 2018 study by Marsland et al compared the mechanical strength of interference screw fixation to the Pulvertaft weave, finding them comparable. Notably, the screw fixation displayed less variability, suggesting it may be more dependable due to reduced reliance on surgical technique. This progression from traditional methods to innovative techniques and alternative fixation approaches reflects the ongoing evolution in tendon repair surgery, with each advancement addressing specific challenges in strength, mobility, and surgical outcomes.[6]

Indications

Location-Specific Considerations for Tendon Transfer

Tendon transfer procedures come with unique indications that depend on the anatomical and functional demands of the specific location. Surgical plans must be tailored to ensure that the transferred tendon achieves optimal strength, range of motion, and effective integration within the targeted region, taking into account the distinct requirements of each site.

Upper Extremity Tendon Transfers

Upper extremity tendon transfers are crucial for restoring function lost due to peripheral nerve injuries (eg, brachial plexus injuries or radial, ulnar, and median nerve palsies), central nervous system deficits, cerebral palsy, spinal cord injuries, rheumatoid arthritis-related tendon ruptures, and disabilities caused by poliomyelitis and leprosy. These procedures help patients regain grip strength and fine motor skills, significantly improving their ability to perform daily activities.[7] In cerebral palsy affecting the upper extremity, patients commonly present with a wrist flexion deformity and excessive pronation. Corrective surgeries include transferring the flexor carpi ulnaris (FCU) to the extensor carpi radialis brevis (ECRB) to enhance wrist extension (the Green procedure), releasing the pronator teres to address forearm pronation, and realigning the thumb by releasing the spastic adductor pollicis and rerouting the extensor pollicis longus (EPL).[8] 

Extensive research results have demonstrated the effectiveness of these techniques.[9] For example, results from a 25-year study involving 134 individuals with cerebral palsy undergoing 718 procedures showed overall improvement in upper extremity function, with the best outcomes observed in patients with fair to good voluntary control. Another study comparing surgical treatment, botulinum toxin injections, and ongoing therapy in 39 children provided results showing that the surgical group demonstrated more significant improvements in wrist strength and overall movement scores. Long-term studies' results have also shown excellent patient-reported outcomes, even when positional results were mixed.[10] For pronation deformities, isolated pronator teres rerouting has emerged as the most effective and straightforward method. However, care should be taken when performing transfers in older pediatric patients near growth acceleration to avoid secondary deformities.[11][12]

When selecting donor transfers for upper extremity procedures, several key principles should be considered. Matching strength while maintaining amplitude and muscle excursion is essential to effectively mimic the line of pull and synergistic function when selecting a donor for host muscles. Excursion typically follows the Smith 3-5-7 rule: wrist flexors and extensors provide 33 mm of excursion, finger extensors 50 mm, and finger flexors 70 mm.[13] In terms of donor strength, the brachioradialis and FCU are the strongest, with a relative strength of 2. These muscles are followed by the flexor carpi radialis (FCR), wrist extensors, and finger flexors, which have a strength of 1. Finger extensors have a relative strength of 0.5, while thumb extensors, the palmaris longus, and the abductor pollicis longus (APL) have a strength of 0.1. For wrist tendon transfers, wrist flexion and extension can create a tenodesis effect of approximately 2.5 cm. Although the excursion provided by a wrist flexor alone may be inadequate for complete finger extension, wrist flexion can enhance this effect by tightening the finger extensors, thereby increasing extension through the tenodesis effect.

Tendon Transfers in Brachial Plexus Injuries

Although nerve palsies affecting the distal upper extremity have been more thoroughly researched, it is important to briefly acknowledge proximal lesions of the arm and shoulder. These conditions often require salvage procedures, which is discussed in greater detail later in this topic.

Tendon Transfers of the Shoulder

Shoulder tendon transfers enhance the coordination between the scapulothoracic and glenohumeral joints, which is fundamental to the overall mobility and stability of the shoulder. These procedures primarily address motor insufficiencies resulting from nerve injuries or muscle tears. Common pathologies include serratus anterior palsy, trapezius palsy, irreparable rotator cuff tears (RCTs), and deltoid muscle deficiency. Elhassan et al conducted a study in 2012 on the effectiveness of shoulder tendon transfers for brachial plexus injuries, examining 52 patients who underwent these procedures. The transfers utilized donor musculature from the lower trapezius, levator scapulae, and serratus anterior. Postoperatively, patients showed significant improvement in shoulder external rotation and modest gains in abduction and flexion. While pain levels and functional scores also improved, comorbid factors and the severity of the initial injury often limited the extent of recovery.[7]

Lower Extremity Tendon Transfers

Lower extremity tendon transfers address issues resulting from nerve injuries, musculoskeletal disorders, and the sequelae of conditions such as Charcot-Marie-Tooth disease, polio, and oncological disease processes. As with upper extremity procedures, the choice of technique for lower extremity tendon transfers is carefully considered. Surgeons base their decisions on the extent of muscle involvement and the specific functional deficits present, ensuring the most effective approach for each case.[14] Such transfers are often required due to complications like foot drop, most commonly caused by peroneal nerve injuries, particularly involving the common peroneal nerve. Foot drop disrupts normal gait by impairing ankle dorsiflexion and subtalar eversion, leading patients to compensate with excessive hip and knee flexion to clear the foot and avoid tripping.[15]

Various tendon transfer techniques have been developed over the years. Common procedures include the posterior tibialis tendon transfer, frequently utilized due to its effectiveness in restoring dorsiflexion and correcting foot deformities like cavovarus foot, often associated with neurological conditions such as Charcot-Marie-Tooth disease.[16] This transfer routes the posterior tibialis tendon either circumferentially about the tibia or through the interosseous membrane to the dorsum of the foot, aiming to substitute for the impaired dorsiflexors.

For more complex cases, multiple tendon transfers may be necessary, including transfers of the flexor digitorum longus (FDL) to the extensor tendons, which aim to restore a balance between the foot's flexors and extensors to improve gait and stability. In addition to addressing foot drop, tendon transfers may also be employed in cases of severe musculoskeletal injury like following oncological resections or in cases of quadriceps paralysis. Local tendon transfers of the hamstring musculature have been utilized to substitute for lost muscle function of knee extension while maintaining flexion.[17]

Technique or Treatment

Tendon Transfer in Radial Nerve Palsy

Tendon transfer procedures for radial nerve palsy aim to restore function in patients with varying degrees of radial nerve injury. These techniques, described below, are indicated for both high and low radial nerve palsies. High radial nerve palsy occurs above the elbow and affects all muscles supplied by the radial nerve. This condition results in complete loss of wrist extension, finger extension at the metacarpophalangeal (MCP) joints, thumb extension, and radial abduction. Patients also experience reduced sensation in the radial nerve distribution area. Notably, some distal interphalangeal (DIP) joint extension may persist due to the action of lumbrical and interossei muscles. Patients may also lose elbow extension if the injury extends to the brachial plexus.

Low radial nerve palsy involves the posterior interosseous nerve and presents differently from high radial nerve palsy. Patients maintain some wrist extension ability because the extensor carpi radialis longus (ECRL) remains innervated. This preserved ECRL function causes characteristic radial deviation during wrist extension. While patients experience weakness in finger MCP extension and thumb extension and abduction, they notably do not experience sensory loss because the superficial radial nerve remains unaffected.

The triple (Jones) transfer 

The triple transfer or Jones transfer is the most widely accepted approach for restoring function in cases of complete, irreversible radial nerve palsy at the wrist. This technique aims to reestablish wrist, finger, and thumb extension. The procedure involves transferring the pronator teres to the ECRB to restore wrist extension, the FCR to the extensor digitorum communis (EDC) for finger extension, and the palmaris longus to the EPL to achieve thumb extension.[18]

Merle d’Aubigne transfer

The Merle d’Aubigne transfer provides an alternative to the Jones transfer in cases of irreversible radial nerve palsy, aiming to restore wrist, finger, and thumb extension. The technique involves transferring the pronator teres to the ECRB or ECRL in the radial direction to achieve wrist extension. To facilitate finger and thumb extension, the FCU is transferred to the EPL and EDC on the ulnar side, with tendons interwoven to enhance stability and function. The palmaris longus is redirected to the extensor pollicis brevis (EPB) and APL in the radial direction, supporting thumb positioning and movement.[19]

Flexor carpi ulnaris (Jones), flexor carpi radialis (Brand), or flexor digitorum superficialis (Boyes) transfer to the extensor digitorum communis

Transferring the FCU, FCR, or flexor digitorum superficialis (FDS) to the EDC aims to restore MCP joint extension in cases of radial nerve palsy. The FCU transfer, first popularized by Jones, has drawbacks due to the sacrifice of the sole ulnar-wrist flexor motor, leading to undesirable radial deviation and the loss of ulnar deviation, impairing actions like hammering and throwing. Consequently, the FCR and FDS transfers have become preferred alternatives as they avoid the wrist deviations associated with such procedures. The choice between FDS and FCR ultimately depends on the specific patient needs, with factors such as potential excursion, ease of reeducation, and maintenance of wrist stability guiding the decision.

The FDS transfer, introduced by Boyes, offers superior tendon excursion compared to FCR and FCU, making it a potentially powerful option for restoring wrist extension. The FDS transfer technique specifically uses the FDS tendons of the ring and middle fingers to achieve multiple extension functions. The ring finger FDS is directed to the EPL and extensor indicis proprius (EIP), facilitating thumb and index finger extension. The middle finger FDS is transferred to the EDC to enable the extension of digits 2 through 5. However, this technique faces significant challenges in motor reeducation, as patients must learn to repurpose finger flexion dynamics for extension, requiring extensive training. Alternatively, the FCR transfer, advocated by Brand, maintains wrist stability without causing radial deviation. While it provides less excursion than FDS, the FCR works synergistically with the transferred function, potentially simplifying the rehabilitation process.

Palmaris longus to extensor pollicis longus transfer

The palmaris longus to EPL transfer aims to restore thumb extension and abduction. In this technique, the palmaris longus tendon is rerouted radially to align with the EPL in the same linear vector, enhancing both thumb extension and abduction.

Pronator teres to extensor carpi radialis brevis transfer

The pronator teres to ECRB transfer restores wrist extension in high radial nerve palsy cases. The procedure may be performed using an end-to-end technique for a definitive solution or an end-to-side technique to allow for potential future reinnervation of the ECRB.

Flexor digitorum superficialis to third metacarpal transfer

The FDS to thirrd metacarpal transfer represents a novel surgical technique aimed at restoring wrist extension in patients with radial nerve palsy, as described by Rondon et al in 2021. This procedure involves transferring 2 branches of the FDS from the third and fourth digits to the base of the third metacarpal, allowing for effective functional restoration.To ensure balance and prevent the creation of a net supination or pronation force, 1 tendon is routed through the interosseous membrane while the other is directed radially around the wrist. This method  offers an alternative to traditional tendon transfers, such as the pronator teres transfer, which may be at risk of compromise.[20]

Biceps-to-triceps transfer

The biceps-to-triceps transfer aims to restore elbow extension and overhead function in individuals with tetraplegia. The technique involves transferring the biceps tendon through the medial aspect of the arm to augment the triceps.[21]

Posterior deltoid-to-triceps transfer

The posterior deltoid-to-triceps transfer is designed to restore elbow extension in individuals with tetraplegia. The technique involves transposing the posterior deltoid to the triceps by removing a bone block with the attached deltoid from the humerus and a similar block from the olecranon. These blocks are positioned from cancellous bone to cancellous bone and secured with wires.[22]Current procedures for treating radial nerve palsy with tendon transfers are detailed below in Table. Summary of Tendon Transfers in Radial Nerve Palsy.

Table. Summary of Tendon Transfers in Radial Nerve Palsy

APL, abductor pollicis longus; ECRB, extensor carpi radialis brevis; ECRL, extensor carpi radialis longus; EDC, extensor digitorum communis; EPB, extensor pollicis brevis; EPL, extensor pollicis longus; FCR, flexor carpi radialis; EDC, extensor digitorum communis; FDS, flexor digitorum superficialis; FCU, flexor carpi ulnaris

Tendon Transfer in Median Nerve Palsy

Median nerve palsy is classified as either high or low, with these distinctions guiding the choice of surgical intervention. The following sections outline surgical procedures and techniques for addressing median nerve palsy and restoring thumb opposition. High median nerve palsy presents with a wide range of functional deficits, including a loss of thumb opposition, thumb interphalangeal and fingers' DIP flexion, wrist flexion, and forearm pronation. The resulting ulnar deviation during wrist flexion is due to the ulnar nerve's control of the FCU. The sensory loss extends to the radial palm and fingers, significantly impacting fine motor skills like pinching and gripping. Without restored sensation, tendon transfers may be less effective for retraining purposes. While other muscles can partially compensate for forearm pronation and wrist flexion, the loss of FDS affects all 4 fingers. However, the ulnar-innervated flexor digitorum profundus (FDP) muscles maintain flexion in the ring and small fingers.

Low median nerve palsy primarily affects the thenar muscles and sensory distribution to the radial palm. This condition spares the lumbricals and deeper forearm muscles involved in wrist and finger flexion. Although less devastating than high median nerve injuries, low median nerve palsy still significantly impacts thumb opposition, abduction, and fine touch sensation. Boatright and Kiebzak found in 1997 that a median nerve block at the wrist significantly reduced thumb abduction strength by paralyzing the abductor pollicis brevis (APB) and opponens pollicis, with losses averaging 70.3% for men and 74.3% for women. The APL's functionality did not fully compensate for these losses, highlighting the APB's critical role in thumb abduction.[23]

Opponensplasty

Opponensplasty is the primary technique to restore thumb opposition, which is critical for recovering the ability to perform pinching and grasping motions. In low median nerve palsy cases, the Camitz opponensplasty utilizes the palmaris longus tendon, often extended with a palmar fascia graft, to restore thumb abduction rather than true opposition. This technique, effective in severe carpal tunnel syndrome, uses the palmaris longus tendon and a graft to extend its reach. While it allows for no functional loss during carpal tunnel release, the palmaris longus has limited motor function and cannot fully restore true thumb opposition.

Another approach, the superficialis opponensplasty (Royle-Thompson modification), employs the FDS tendon from the ring finger, rerouted subcutaneously across the palm to attach at the base of the thumb, attempting to mimic natural opposition. The routing occurs at the level of the pisiform to maintain opposition, using a pulley from the transverse carpal ligament, palmar fascia, or FCU tendon loop to achieve the appropriate line of pull. For high median nerve palsy, the extensor indicis proprius (EIP) opponensplasty routes the EIP tendon about the ulnar hand at the level of the pisiform to attach to the APB. Recommended for high median nerve injuries, this technique provides a robust mechanism for opposition.

The Huber transfer is particularly effective in treating the congenital absence of the thenar muscles or when primary tendons like the FDS and EIP are unavailable, and also improves hand aesthetics in instances of thenar atrophy. In this procedure, the ulnar nerve-innervated abductor digiti minimi (ADM) is fully released from its insertion, rotated 180°, and reattached to the APB insertion. This transfer not only restores functional thumb movements but also adds volume to the thenar eminence, enhancing the overall appearance of the hand. Additionally, tendons such as the extensor digiti minimi (EDM), extensor carpi ulnaris (ECU), and ECRL may also be utilized as needed, often requiring tendon grafts to achieve the desired length and tension.

Brachioradialis to flexor pollicis longus transfer

The brachioradialis to flexor pollicis longus (FPL) transfer aims to restore thumb interphalangeal flexion in patients with high median nerve injuries, enhancing the thumb's ability to grip and pinch. The brachioradialis tendon is transferred to the FPL tendon to produce thumb flexion. Tendon tension is adjusted to optimize pinch strength, mimicking the thumb's natural opposition. The transfer is typically routed volarly.[24]

Dorsal brachioradialis to flexor pollicis longus transfer

This procedure aims to biomechanically restore key pinch and forearm pronation simultaneously, providing a dual function with a single muscle transfer that is particularly beneficial for patients lacking functional pronator muscles. The brachioradialis muscle is transferred dorsally, passing posterior to the radius through the interosseous membrane to coapt with the FPL tendon. This position gives the muscle a larger pronation moment arm while maintaining its ability to perform key pinch. The transfer harnesses the natural excursion of the brachioradialis muscle, aligning it to augment both pronation and thumb flexion without compromising total muscle excursion.[25]

Extensor carpi radialis longus to flexor digitorum profundus transfer

The ECRL to FDP transfer is intended to restore independent DIP flexion of the index and long fingers in cases of high median nerve injury. The ECRL tendon is rerouted to the FDP tendons of the index and long fingers. The surgical approach prioritizes meticulous placement and tension adjustment, ensuring a smooth flexion cascade and natural finger movement. This tendon transfer is carefully calibrated to achieve a comfortable, functional range of motion, allowing the fingertips to approach the palm by 1 cm when the wrist is extended. This balance optimizes flexion without compromising extension, enhancing overall grip function.

Adjacent suturing of flexor digitorum profundus tendons (median palsy)

This technique is intended to restore DIP flexion of the index and long fingers with a symmetric cascade in cases of high median nerve palsy. In this technique, the FDP tendons of the ring and small fingers are directly sutured side by side to the tendons of the index and long fingers, allowing flexion to occur as a single unit. Current procedures for treating median nerve palsy with tendon transfers are detailed below in Table. Summary of Tendon Transfers in Median Nerve Palsy. 

Table. Summary of Tendon Transfers in Median Nerve Palsy

ADM, abductor digiti minimi; APB, abductor pollicis brevis; BR, brachioradialis; DIP, distal interphalangeal joint; ECRL, extensor carpi radialis longus; EIP, extensor indicis proprius; FDS, flexor digitorum superficialis; FDP, flexor digitorum profundus; FPL, flexor pollicis longus

Tendon Transfer in Ulnar Nerve Palsy

Ulnar nerve palsy impairs hand function by weakening muscles critical for grip and pinch strength, often causing clawing posture and impaired finger movement coordination. Tendon transfer procedures for high and low ulnar nerve palsies can help restore function and improve hand mechanics. The ulnar nerve passes through several anatomical choke points where it can be compressed, including the cubital tunnel and Guyon canal. This nerve supplies the hypothenar muscles, 2 lumbricals, all interossei, adductor pollicis, and a head of the flexor pollicis brevis (FPB). High ulnar nerve palsy affects muscles proximal to the wrist, the FDP to the ring and little fingers, and the FCU, leading to significant grip weakness, loss of ulnar deviation during wrist flexion, and weakened pinch strength.

Patients with high ulnar nerve palsy exhibit clawing due to the unopposed action of the extrinsic finger extensors and flexors, resulting in hyperextension at the MCP joints and flexion at the interphalangeal joints. The condition disrupts the normal flexion sequence of the fingers and impairs grasp. Loss of the intrinsic muscles' action in the intrinsic-minus position prevents effective cupping of the hand for gripping. This palsy is further complicated by localized sensory deficits affecting the ulnar aspect of the palm and fingers, which is clinically significant for protecting the resting hand position.

Injuries at or distal to the wrist primarily affect the intrinsic hand muscles without affecting the FCU or FDP functions. Low ulnar nerve palsy causes more pronounced clawing than high ulnar nerve palsy because the FDP to the ring and little fingers is often unaffected, allowing further finger flexion. The loss of intrinsic muscle function leads to an abnormal flexion pattern, with early flexion at the interphalangeal joints and delayed MCP joint flexion due to the lack of initiation by the intrinsic finger muscles, impairing effective grasping. Similar to high ulnar nerve palsy, pinch strength is significantly diminished.

Extensor carpi radialis brevis (Smith) and brachioradialis (Boyes) transfer to adductor pollicis brevis

The Smith and Boyes transfers aim to restore thumb adduction strength, whether due to ulnar nerve palsy or other etiologies. In this technique, a tendon graft is woven through the space between the second and third metacarpals, positioned deep to the adductor pollicis, and sutured to its tendon. Proximally, the graft is tunneled subcutaneously along the dorsal side and attached to the previously harvested ECRB. The tendon graft length is adjusted to align the radial side of the thumb and the plane of the palm with a straight wrist.[26]

Adjacent suturing of flexor digitorum profundus tendons (ulnar palsy)

This procedure is designed to restore DIP joint flexion for the small and ring fingers in high ulnar nerve palsy. The FDP tendons of the ring and small fingers are sutured adjacent to the functioning middle finger FDP. The index finger FDP is excluded to preserve its independent function. Clawing may worsen, potentially requiring additional corrective measures.

Flexor digitorum superficialis transfer for thumb adduction

The flexor digitorum superficialis transfer is used to restore adductor pollicis function and pinch grip in patients with low ulnar nerve palsy. The FDS tendon is divided distally in the ring or middle finger and retrieved into the palm. The tendon is then delivered through the palm, passing deep to the flexor tendons, and inserted into the adductor pollicis tendon at the thumb. The results of a study involving 22 patients who underwent a ring flexor superficialis tendon transfer across the palm showed a significant increase in pinch strength, improving from 30% to 71% of the unaffected hand.[27]

Modified Stiles-Bunnell procedure using the flexor digitorum superficialis tendon

The Modified Stiles-Bunnell procedure aims to correct clawing and rebalance the forces at the MCP and proximal interphalangeal (PIP) joints for finger flexion. The middle finger flexor superficialis tendon is divided distally and retrieved into the palm. The tendon is then split into 4 parts and carried volarly to the deep transverse metacarpal ligament, following the path of the lumbricals, before being inserted back into the fingers on the lateral bands. Alternatives include inserting the tendon onto the proximal phalanx to prevent PIP hyperextension or using a "lasso" technique (Zancolli), where the FDS tendon is passed through the A1 pulley and sutured onto itself to increase MCP flexion and avoid PIP joint hyperextension. Notably, this procedure does not improve grip strength.

Extensor carpi radialis longus tendon transfer for clawing

The purpose of this transfer is to dynamically correct clawing caused by ulnar nerve palsy and to enhance grip strength by providing flexion at the MCP joints and extension at the DIP joints. The ECRL tendon is detached from its insertion and augmented with tendon grafts. These grafts are routed from dorsal to volar in line with the lumbricals and attached to the lateral bands, A1 pulley, A2 pulley, or proximal phalanx of the digits.

During operative planning, special attention should be given to the distinction between complex and simple clawing. Simple clawing occurs due to nonfunctional intrinsic musculature. In contrast, complex clawing may involve additional factors, such as attenuation of the central slip, volar subluxation of the lateral bands, or adhesions of the extensor tendon or joint capsule at the PIP or DIP joint. The Bouvier test is used to differentiate between the simple and complex clawing. The Bouvier test involves the tester blocking full MCP extension and assessing whether the patient can actively extend their fingers while the MCP joints remain flexed. A positive test indicates that the patient can extend their fingers, suggesting simple clawing, while a negative test indicates that they cannot extend their fingers, suggesting complex clawing that requires further evaluation. If complex clawing is due to central slip attenuation, the tendon transfer should be directed to the lateral bands rather than other insertion sites to allow for interphalangeal extension. Current procedures for treating ulnar nerve palsy with tendon transfers are detailed below in Table. Summary of Tendon Transfers in Ulnar Nerve Palsy.

 Table. Summary of Tendon Transfers in Ulnar Nerve Palsy

APB, abductor pollicis brevis; DIP, distal interphalangeal joint; ECRB, extensor carpi radialis brevis; ECRL, extensor carpi radialis longus; FDP, flexor digitorum profundus; FDS, flexor digitorum superficialis; MCP, metacarpophalangeal joint; PIP, proximal interphalangeal joint

Tendon Transfers for Wrist Conditions Arising from Other Etiologies

Tendon transfers are a valuable surgical approach for addressing a range of wrist issues stemming from various conditions. These procedures are particularly beneficial for patients dealing with multiple nerve palsies, traumatic ruptures, rheumatoid arthritis, and congenital deformities arising from cerebral palsy. The surgical techniques are discussed below. Notably, when multiple nerve palsies are present, staging procedures and selective arthrodesis are the recommended courses of action to maximize function. 

Flexor carpi ulnaris to extensor carpi radialis brevis transfer

The purpose of the FCU to ECRB transfer (Green) procedure is to improve wrist positioning in individuals with spastic cerebral palsy. The FCU tendon is attached to the ECRB tendon, routed ulnarly, and tensioned between 0° and 30° of extension.[10]

Brachioradialis rerouting

Brachioradialis rerouting aims to correct forearm pronation deformity and restore active supination in children with cerebral palsy, as described by Ozkan et al in 2004. The procedure involves releasing and lengthening the pronator quadratus and pronator teres muscles, followed by a Z-plasty division of the brachioradialis tendon. The distal end of the tendon is then rerouted from dorsal to palmar through the interosseous space and sutured back to its proximal end, resulting in an average gain of 81° in active supination.[28]

Extensor indicis proprius to extensor pollicis longus

This transfer aims to restore the original function of thumb extension and abduction following EPL rupture, often due to rheumatoid arthritis. The EIP tendon is directly transferred to the EPL tendon. This procedure is recommended for its reliability, minimal need for postoperative reeducation, and low incidence of complications.[29]

Flexor digitorum profundus-flexor digitorum superficialis-flexor digitorum profundus dual tendon transfer

The FDP-FDS-FDP dual tendon transfer procedure aims to reconstruct chronic, isolated FDP tendon injuries. This procedure is particularly useful in the presence of "lumbrical plus" phenomena where traditional reconstructions may worsen digital function. The technique involves detaching the FDS tendon from the middle phalanx and advancing it to the distal stump of the FDP. The proximal stump of the FDP is then advanced to restore appropriate lumbrical tension and sewn to the proximal FDS tendon, simplifying tensioning and avoiding the need for tendon grafts. This method also helps prevent quadriga and the paradoxical extension of the lumbrical muscle by decoupling the FDP function from the adjacent digit.[30] Other procedures for treating wrist conditions with tendon transfers are detailed below in Table. Tendon Transfers for Wrist Conditions Arising from Other Etiologies.

Table. Tendon Transfers for Wrist Conditions Arising from Other Etiologies

ECRB, extensor carpi radialis brevis; EIP, extensor indicis proprius; EPL, extensor pollicis longus; FDS, flexor digitorum superficialis; FDP, flexor digitorum profundus; FCU, flexor carpi ulnaris

Tendon Transfers in Brachial Plexus Injuries

While less researched than distal nerve palsies, shoulder and proximal upper extremity lesions also require careful consideration. Tendon transfer procedures for upper extremity injuries are often used as salvage options, which aim to restore everyday functions.   

Musculocutaneous nerve palsy

Brachial plexus injuries often compromise elbow flexion, a key function for daily activities. Various surgical techniques have been developed to restore elbow flexion, including traditional approaches such as the Steindler flexorplasty and triceps-to-biceps transfer, which produce reliable outcomes. Recent surgical innovations have expanded these options. For instance, Bertelli and colleagues demonstrated success with a hybrid technique that combines free reverse gracilis muscle transfer with Steindler flexorplasty, which has proven particularly effective in cases where initial repairs failed.[31]

The surgical repertoire also includes various local muscle transfer options, as documented by Ruhmann's team, who explored using the latissimus dorsi, pectoralis major and minor, triceps, and sternocleidomastoid muscles.[32] Additionally, Taran's group contributed to the field by developing a modified pectoralis major tendon transfer, a valuable salvage procedure for complete brachial plexus injuries.[33] The Steindler procedure involves transferring the wrist flexor group from the medial epicondyle onto the humerus to restore flexion; this can be augmented with a gracilis free-muscle graft. In the triceps-to-biceps transfer, the triceps muscle is transposed and attached to the distal tendon of the biceps, allowing for co-contraction of the triceps and biceps to provide elbow flexion while maintaining elbow extension.

Tendon Transfers of the Shoulder

Tendon transfers of the shoulder provide effective surgical solutions for restoring function in cases of nerve injury or muscle paralysis. 

Pectoralis major tendon transfer for serratus anterior muscle palsy

The pectoralis major tendon transfer aims to treat scapular winging due to serratus anterior insufficiency. The procedure has 2 main techniques: indirect and direct. The indirect technique involves harvesting gracilis and semitendinosus tendons, weaving them through the harvested sternal head of the pectoralis major, and anchoring the construct through a burr hole at the scapula’s inferior angle to mimic the serratus anterior's line of pull. The direct technique entails harvesting the sternal head of the pectoralis major with a small segment of bone and directly attaching it to the inferior angle of the scapula, which offers a bone-to-bone healing potential and less morbidity compared to the indirect method.[34]

Eden-Lange procedure

The Eden-Lange procedure aims to treat scapulothoracic abduction and medial rotation anomalies resulting from trapezius palsy. The technique involves lateralizing the insertions of the rhomboid minor and major to the infraspinatus fossa of the scapula and the levator scapulae to the scapular spine and acromion.[35] The rhomboid flip aspect of this procedure may also be performed independently.[36]

Triple tendon transfer

The triple tendon transfer (T3) procedure aims to replicate the anatomical arrangement and mechanical action of the 3 heads of the trapezius muscle, particularly addressing the internal rotation torque created by the Eden-Lange procedure and converting it into a more functional external rotation moment. This newer technique involves transferring the levator scapulae to the lateral scapular spine while the rhomboid minor and major are transferred medially to this insertion.[37]

Latissimus dorsi tendon transfer for irreparable posterosuperior rotator cuff tears

The latissimus dorsi tendon transfer procedure aims to reconstruct irreparable supraspinatus and infraspinatus tendon tears, restoring shoulder elevation and active external rotation. The technique involves isolating the tendon, releasing it from the humeral shaft, and reattaching it to the proximal greater tuberosity through a bone tunnel under the deltoid. Fixation is performed with the arm positioned at 30° of flexion, abduction, and external rotation. Both open and arthroscopic-assisted approaches are utilized.[38] Latissimus dorsi transfers significantly improve function, pain, and range of motion in shoulders with irreparable RCTs, particularly when the subscapularis muscle is intact, as evidenced by increased Subjective Shoulder Value and Constant scores during long-term follow-up.[39][40] However, the procedure shows limited benefits in cases where subscapularis function is deficient.

Modified L’Episcopo tendon transfer for isolated loss of shoulder external rotation

The Modified L’Episcopo tendon transfer is designed to rectify the isolated shoulder external rotation loss. The technique involves transferring the latissimus dorsi tendon, with or without the teres major, to the posterior distal aspect of the greater tuberosity using a single incision deltopectoral approach. This transfer has proven effective in improving anterior-posterior stability, increasing rotation, and enhancing shoulder scores. However, reverse shoulder arthroplasty may be necessary to restore external rotation in cases of advanced rotator arthropathy.[41]

Lower trapezius tendon transfer

The lower trapezius tendon transfer aims to recreate the anatomic line of pull of the infraspinatus, enhancing external rotation and overall shoulder mechanics without requiring intensive postoperative training. This procedure is particularly useful for irreparable posterior RCTs, as it provides a line of pull more similar to the native infraspinatus, distinguishing it from latissimus dorsi transfer. The technique utilizes the lower trapezius, often with an Achilles tendon allograft for attachment onto the humerus, offering an easier approach in patients with obesity and avoiding the need for biofeedback training.

Pectoralis minor tendon transfer

The pectoralis minor tendon transfer aims to address lesions involving the superior two-thirds of the subscapularis and irreparable supraspinatus tears. The technique involves transferring the pectoralis minor tendon to the lesser tuberosity along with a small cortical piece of the coracoid. This transfer has shown significant improvements in Constant scores, with most patients returning to daily activities and experiencing minimal loss in external rotation. Arthroscopically assisted methods offer promising short-term outcomes.[42]

Pedicled pectoralis major tendon transfer

The pedicled pectoralis major tendon transfer aims to reconstruct the deltoid in patients with deltoid paralysis. The technique utilizes the pectoralis major's clavicular and upper sternal heads, which are mobilized through an extended deltopectoral approach. The muscle's origins are reattached to the lateral third of the clavicle and the anterior acromion, while the insertion is reattached to the humerus at the deltoid tuberosity, effectively reconstructing the deltoid muscle to aid in shoulder function.

Upper trapezius to humerus transfer for deltoid paralysis

The upper trapezius to humerus transfer procedure aims to restore shoulder abduction and elevation in patients with deltoid paralysis. The technique involves harvesting the upper trapezius muscle from its insertion on the acromion of the scapula and transferring it to the superior greater tuberosity to enable the trapezius to assume the function of the paralyzed deltoid. Current procedures for treating the shoulder with tendon transfers are detailed below in Table. Summary of Tendon Transfers of the Shoulder. 

Table. Summary of Tendon Transfers of the Shoulder

RCT, rotator cuff tear

Lower Extremity Tendon Transfers

Lower extremity tendon transfers address various functional impairments in the lower limbs. Unlike upper extremity transfers, which often prioritize fine motor skills and dexterity, lower extremity procedures focus on ambulation and weight-bearing, often requiring more extensive structural adjustments.

Tibialis posterior tendon transfer via interosseous membrane vs circumtibial technique

This surgical intervention aims to correct chronic foot drop by enabling foot dorsiflexion. In 1996, Soares identified this procedure as an excellent treatment for foot drop from leprosy-related neuritis. In 2014, Dreher et al noted its effectiveness in addressing the foot drop component of Charcot-Marie-Tooth disease. In 2022, Baskar et al highlighted its use in Duchenne muscular dystrophy.[43][44] This tendon transfer demonstrates adequate clinical and mechanical outcomes despite reduced strength compared to the contralateral extremity. Patients experience significant improvements in ambulation without developing postoperative flat foot deformity.[45]

The posterior tibial tendon transfer procedure involves carefully detaching the tendon and rerouting it through the interosseous membrane. The choice of fixation location—typically the middle or lateral cuneiform or the cuboid bone—depends on the specific functional needs of the patient. If eversion weakness is significant, lateral attachment to the peroneus brevis or tertius can help restore balanced ankle mechanics. Surgeons may use various approaches: a subcutaneous route along the medial tibial edge, direct visualization through the interosseous membrane, or a closed technique passing from posterior to anterior. Recent evidence from a 2023 retrospective review indicates that surgeons increasingly favor the closed technique due to its association with faster recovery times. Depending on surgical goals and tissue quality, the final fixation can be achieved through tendon-to-tendon or tendon-to-bone attachment.

While tendon-to-tendon fixation has been historically prevalent, it has shown varying degrees of success. The outcomes largely depend on the technical precision of the procedure and the quality of the donor's tendon. In contrast, the more modern tendon-to-bone fixation has gained popularity for its robustness. Techniques such as using bone anchors or interference screws yield stronger, more reliable outcomes with fewer complications compared to traditional methods. These procedures require shorter tendon lengths and less invasive dissection, potentially improving postoperative outcomes.[46] In 2018, Marsland et al found that interference screw fixation and Pulvertaft weave for tibialis posterior tendon transfer in foot drop were comparable in terms of tendon displacement and load to failure, with greater reliability observed in the interference screw group.

Anterior tibial tendon transfer

The anterior tibial tendon transfer addresses dynamic supination and related structural deformities in patients with recurrent clubfoot, particularly following nonoperative treatments such as the Ponseti technique. The tibialis anterior transfer can be performed using several technical variations. The complete tendon may be rerouted beneath or above the ankle retinaculum, ultimately attaching to the dorsum or lateral midfoot. Alternatively, a split transfer technique may be employed, repositioning only the medial half of the tendon to the cuboid or peroneus tertius tendon. The primary goal of these modifications is to achieve balanced muscle forces and optimal foot positioning during gait, particularly in cases where an overly strong tibialis anterior muscle causes excessive supination. Tibialis anterior tendon transfer for relapsed clubfoot previously treated with Ponseti casting shows effective long-term prevention of deformity relapse without compromising foot function, as demonstrated in a follow-up study spanning up to 55 years.[47] In 2013, Gray et al reported similar success in treating recurrent clubfoot with anterior tibial tendon transfer.[48]

Split anterior tibialis tendon transfer

The purpose of the split anterior tibialis tendon transfer, also known as SPLATT, is to correct foot deformities in spastic equinovarus. The technique involves bisecting the anterior tibialis tendon and redirecting its lateral portion through a bone tunnel in the lateral column, typically at the cuboid or 5th metatarsal. Traditional fixation methods, such as plantar button or felt pad suturing, may be effective but produce complications, including skin ulceration and plantar sensitivity. Contemporary approaches using interference screws or suture anchors offer more secure tendon fixation while minimizing these potential complications.[49]

Bridle procedure

The Bridle procedure aims to restore dorsiflexion while maintaining a neutral foot position, preventing late varus or valgus deformity in patients with foot paralysis. The technique involves a modified posterior tibial tendon transfer that includes additional attachments to the tibialis anterior and a rerouted peroneus longus positioned anterior to the lateral malleolus. While this technique can eliminate the need for bracing, its tendon-to-tendon fixation may present higher failure rates in physically active patients.[50]

Triple tendon transfer

The triple tendon transfer can correct both foot drop and toe drop, improving overall gait mechanics and enhancing patient satisfaction. The technique involves transposing the posterior tibial tendon to the middle cuneiform while routing the flexor hallucis longus (FHL) and flexor digitorum longus (FDL) through the superior extensor retinaculum to connect with their respective extensors.[51]

Flexor hallucis longus to Achilles transfer

This transfer aims to treat insertional tendinosis by providing a healthy tendon to support or replace the degenerated Achilles tendon. The technique involves repositioning the FHL tendon to the calcaneus following Achilles debridement and calcaneal exostosis resection. This approach has demonstrated particular success in older, sedentary, overweight patients, with minimal impact on hallux function.[52]

Jones tendon transfer

The Jones tendon transfer aims to correct a clawed hallux deformity, which is characterized by an abnormally flexed position of the interphalangeal joint with metatarsophalangeal extension. The technique involves transferring the extensor hallucis longus (EHL) tendon to the neck of the first metatarsal while simultaneously fusing the interphalangeal joint of the hallux. This transfer maintains first-ray plantarflexion through the intact peroneus longus, improving toe alignment and function.[53]

Flexor digitorum longus to navicular tendon transfer for posterior tibial tendon insufficiency

The goal of this procedure is to correct flexible flatfoot deformity and alleviate foot pain unresponsive to nonsurgical treatments in stage II posterior tibial tendon deficiency. The technique involves transecting the flexor digitorum longus (FDL) tendon proximal to the knot of Henry, then transferring the tendon to the navicular bone. Fixation is achieved using either bone tunnel tendon-to-tendon fixation or transosseous interference screw fixation. Results from a retrospective review conducted by Myerson et al in 2004, which included 129 patients, demonstrated that 97% reported pain relief and 94% showed functional improvement when this tendon transfer was combined with a calcaneal osteotomy.[54]

Hamstring transfer for quadriceps paralysis

The hamstring transfer for quadriceps paralysis aims to stabilize the knee in patients with residual paralysis and quadriceps weakness, enabling them to extend and lock the knee straight for improved stability and mobility. The modified technique involves using the biceps femoris and semitendinosus tendons anchored directly to the patella.[55] Current procedures for treating the lower extremity with tendon transfers are detailed below in Table. Summary of Tendon Transfers in the Lower Extremity.

Table. Summary of Tendon Transfers in the Lower Extremity

 EHL, extensor hallucis longus; FDL, flexor digitorum longus; FHL, flexor hallucis longus

Complications

Tendon transfer surgeries can result in many complications, the most common being inadequate healing or tendon rupture, particularly in the shoulder and foot, where high biomechanical demands increase the risk. Poor healing can result in restricted range of motion, diminished strength, or persistent deformities, sometimes requiring additional surgery. Other complications, such as infection, hematoma formation, and tendon adhesions, can further delay recovery. Persistent nerve dysfunction presents another challenge, potentially causing sensory deficits or motor impairments that limit rehabilitation by reducing tolerance to therapeutic exercise. Inadequate protection of the operative limb can further compromise healing, increasing the risk of poor functional outcomes.[56] Complications such as loosening of bioabsorbable screws can lead to tendon instability and poor functional outcomes.[57] Furthermore, altered gait mechanics may result in overuse injuries or strain on other tendons and joints.[58] 

Rehabilitation Protocol

Postoperative rehabilitation protocols for tendon transfers vary based on the surgical site—upper extremity, lower extremity, or shoulder—reflecting differences in functional demands and biomechanical properties. For upper extremity tendon transfers, such as those for radial, ulnar, or median nerve injuries, rehabilitation typically involves early immobilization followed by gradually introducing active and passive range-of-motion activities followed by loading exercises when tissue healing allows. This approach prevents joint stiffness while allowing the transferred tendon to heal. Traditionally, immobilization lasts 2 to 3 weeks postoperatively, though there is a growing trend toward earlier mobilization to improve outcomes.

Due to the complexity of shoulder mechanics, shoulder tendon transfers, including those for rotator cuff and brachial plexus injuries, often require prolonged immobilization. Mobilization is introduced cautiously and staged to balance the need to restore motion and strength while protecting the repair. Activity restrictions may remain in place for up to 6 months. In contrast, lower extremity tendon transfers prioritize early weight-bearing and gait retraining to optimize ambulation, particularly for foot drop correction. Immobilization typically lasts 6 to 8 weeks, gradually progressing to full weight-bearing, strengthening, and functional gait training. 

Clinical Significance

Tendon transfers represent a pivotal advancement in reconstructive surgery, offering hope and restored functionality to patients affected by nerve damage, injuries, or congenital defects that compromise muscle function. By strategically rerouting functional tendons to replace compromised muscle units, these procedures restore essential movements and provide significant aesthetic and psychological benefits. The clinical impact of tendon transfers is far-reaching. In upper extremity cases, procedures like the triple transfer for radial nerve palsy restore critical functions of wrist, finger, and thumb extension, while the Green transfer for patients with cerebral palsy enhances independence in daily activities. Similarly, in lower extremity conditions such as peroneal nerve injuries, procedures like the posterior tibialis transfer effectively address foot drop by restoring dorsiflexion and normalizing gait patterns. Beyond immediate functional improvements, these surgical interventions are crucial in preventing long-term complications such as joint contractures and deformities, ultimately enhancing patients' quality of life through improved mobility, independence, and psychological well-being.

Enhancing Healthcare Team Outcomes

Enhancing interprofessional team outcomes in tendon transfer surgical cases requires a collaborative, interdisciplinary approach spanning preoperative, intraoperative, and postoperative phases. Preoperatively, comprehensive functional assessments by orthopedic surgeons, neurologists, and physiatrists guide surgical planning to evaluate whether and what type of tendon transfer surgery aligns with the patient's functional needs and goals. The surgical process involves a diverse team, including nurses, advanced practice providers, and others. The surgeon determines restrictions and protocol limitations for the rehabilitation process, which aim to balance the restoration of joint mobility and tendon strength while preventing joint stiffness. Occupational and physical therapists design and carry out rehabilitation plans that respect individual post-op and return-to-function needs.

Success in tendon transfer surgery hinges on a holistic approach that carefully considers patients' expectations and goals, particularly in upper extremity nerve palsies. By incorporating patients' daily activities into rehabilitation plans, healthcare teams can provide more personalized and effective care. Regular communication between surgical, rehabilitation, and nursing teams enables dynamic adjustment of therapy protocols based on patient progress, helping prevent setbacks and optimize recovery. This coordinated, patient-centered approach enhances surgical outcomes and leads to greater patient satisfaction.