Hand Tendon Transfers

Anatomy and Physiology

Pathoanatomy of Specific Nerve Injuries [1][2][3]

High radial nerve injuries occur above the elbow and lead to deficits in:

1. Wrist extension with denervation of the brachioradialis, extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB), and extensor carpi ulnaris (ECU)
2. Finger MCP extension with denervation of the extensor digitorum communis (EDC), extensor indicis proprius (EIP), and extensor digit minimi (EDM)
3. Thumb radial abduction and extension with denervation of the extensor pollicis longus (EPL)
4. Sensation in the superficial radial nerve distribution.

Low radial nerve injuries occur distal to the elbow and affect muscles innervated by the posterior interosseous nerve (PIN). These injuries typically have no sensory deficits because they occur distal to where the superficial radial nerve branches off the radial nerve, but result in the following motor deficits:

1. Weakness in wrist extension as the innervation to the ECU is lost, but the ECRL innervation is often maintained leading to radial deviation with wrist extension.
2. Finger MCP extension weakness secondary to denervation of the EDC, EIP, and EDM
3. Thumb radial abduction and extension weakness secondary to denervation of the EPL.

High median nerve injury occurs proximal to the elbow joint and leads to weakness of:

1. Thumb opposition secondary to denervation of the superficial head of the flexor pollicis brevis (FPB), abductor pollicis brevis (APB), and the opponens pollicis
2. Thumb interphalangeal (IP) flexion secondary to denervation of the flexor pollicis longus (FPL)
3. Distal interphalangeal (DIP) flexion secondary to denervation of the index and long finger flexor digitorum profundus (FDP)
4. Proximal interphalangeal (PIP) flexion secondary to denervation of the flexor digitorum superficialis (FDS)
5. Forearm pronation secondary to denervation of the pronator teres and pronator quadratus
6. Wrist flexion secondary to denervation of the flexor carpi radialis (FCR), ulnar deviation occurs with wrist flexion since the flexor carpi ulnaris (FCU) is intact
7. Sensory deficits in the thumb, index, long, and radial half of the ring fingers.

Low median nerve injuries occur distal to the elbow resulting in the following motor and sensory deficits:

1. Thumb opposition secondary to denervation of the superficial head of the FPB, APB, and the opponens pollicis
2. Sensory deficits in the thumb, index, long, and radial half of the ring fingers.

High ulnar nerve injuries occur proximal to the elbow leading to deficits in:

1. Ring and small finger DIP flexion secondary to denervation of the FDP
2. Ring and small finger MCP flexion secondary to denervation of the interossei and ring and small finger lumbricals
3. Pinch strength secondary to denervation of the adductor pollicis (ADP), deep head of the flexor pollicis brevis (FPB), and 1st dorsal interosseus
4. Sensory deficits both volarly and dorsally in small finger, ulnar half of the ring finger, and on the ulnar third of the palm. 

Low ulnar nerve injuries occur at the level of the wrist leading to deficits in:

1. Ring and small finger MCP flexion secondary to denervation of the interossei and ring and small finger lumbricals
2. Pinch strength secondary to denervation of the ADP, deep head of FPB, and 1st dorsal interosseus
3. Sensory deficits on the volar aspect of the small finger and ulnar half of the ring finger.

Indications

Motor strength and sensory testing will distinguish lesions and appropriate indications for correction according to above categories.  [4][5][6]

Wrist passive tenodesis test should be performed by taking the wrist passively from flexion to extension. With a normal test, the digits transition from an extended posture in wrist flexion to a flexed posture in wrist extension with fingers maintaining symmetrical cascade. An abnormal exam can indicate isolated tendon injuries. Wrist, hand, and finger range of motion testing is important since the full passive range of motion should be achieved before tendon transfers.

Ulnar claw hand occurs because of unopposed extension forces by the EDC and EDM on the small and ring finger MP joints with no counter flexion force by the interossei and ulnar two lumbricals innervated by the ulnar nerve. The extended posture of the MP joint prevents extension forces from the EDC from being transmitted to the PIP and DIP joints. Also, the normal extensor force to the PIP and DIP joints through the extensor hood of the ring and small fingers is deficient secondary to weakness of the interossei and ulnar two lumbricals.

A low ulnar nerve palsy results in a more severe claw hand because the FDP to the ring and small fingers are intact, worsening the imbalance of flexion forces across the PIP and DIP joints.

In ulnar nerve palsy, when the patient attempts to pinch an object, the thumb MP hyperextended the, and the IP flexes in an attempt by the EPL and FPL respectively to compensate for the deficiency of the adductor pollicis, 1st dorsal interosseus, and deep head of the flexor pollicis brevis (FPB). This is called Froment sign. 

In the setting a non-displaced distal radius fracture, integrity of the EPL can be tested by having the patient place their hand flat on a table, inability to lift their thumb off of the table is consistent with an EPL rupture.

An EMG can help determine nerve injury severity and likelihood of recovery.  Unlike procedures to reinnervate muscles, tendon transfers do not depend on the viability of the motor endplate of the dysfunctional muscle and so can be performed at any time.

Contraindications

Principles of Tendon Transfer to Avoid Complications[7][8][9]

1. Choose a tendon donor for transfer that minimizes functional loss. The donor tendon must be expendable.
2. The muscle strength of the donor's tendon must be near normal as it will lose a function grade with the transfer (a tendon with 5/5 strength will decrease to 4/5 strength after transfer).
3. Excursion of donor's tendon should be similar to an excursion of recipient's tendon, wrist extension and flexion tendons have 33 mm excursion, finger extensors 50 mm of excursion, and finger flexors 70 mm of excursion (Smith 3-5-7 rule). Utilizing the tenodesis effect of the wrist can compensate for an additional 20 mm to 30 mm of finger tendon excurison. 
4. The donor tendon should be routed in the direction of pull that is line with the recipient's tendon.
5. A singe tendon transfer should aim to restore one function.
6. Soft tissue adjacent to transfer site should be stable and pliable to allow for tendon gliding.
7. The full passive range of motion of the joint controlled by the transferred tendon should be achieved before surgery.
8. Donor tendons should be in the same phase as recipient's tendons if possible (finger extensor act in phase with wrist flexors and finger flexors act in phase with wrist extensors).

Equipment

The procedure is typically performed in the operating room under general anesthesia. A tourniquet is placed high in the axilla, and the arm rests on a hand table. The operative equipment required includes a tendon passer and basic hand tray.

Technique or Treatment

Surgical Procedures

Radial Nerve Injury

1. Wrist extension achieved with transfer of PT to ECRB
2. Finger MCP extension achieved with transfer of the FCR to EDC or FDS of the long finger to the EDC
3. Thumb extension achieved with the transfer of the palmaris longus to the EPL or FDS of the ring finger to the EPL.

Low Median Nerve Injury

1. Thumb opposition achieved with the transfer of the abductor digiti minimi to the APB (Huber), extensor indicies proprius to the APB (Burkhalter), or FDS of the ring finger to the APB (Bunnell or Royle-Thompson). These are considered opponensplasty procedures as they attempt to restore thumb opposition. Palmaris longus to APB (Camitz) transfer is another well described procedure but only restores palmar abduction, not thumb opposition.

High Median Nerve Injury

1. Thumb opposition achieved with transfers described above
2. Thumb interphalangeal (IP) flexion is achieved with the transfer of the brachioradialis, ECRL, or ECU to the FPL
3. DIP and PIP flexion to the index finger can be achieved by transferring the ECRL to the FDP tendon of the index finger or by side-to-side tenodesis of the flexor digitorum profundus tendons.

Ulnar Nerve Palsy 

1. Clawing is corrected by blocking MCP hyperextension which allows for the transmission of the EDC extensor forces distally to the PIP and IP through the extensor hood.  This is accomplished by MCP capsulodesis or tenodesis. The FDS slips of the affected finger can be transected 2 cm proximal to their insertion and sutured back to themselves proximally creating a lasso around the A1 pulley (Zancolli lasso). Alternatively, the FDS of the long finger can be transected 2 cm proximal to its insertion and retracted from the tendon sheath proximally and then rerouted distally deep to the intermetacarpal ligament and inserted into the radial lateral bands of the small and ring fingers (Stiles-Bunnell). Clawing of all four digits (as seen in a combined ulnar and low median nerve palsy) can be treated using the FCR, or ECRB tendon split into two to four tails according to the number of fingers being addressed. The tails are then extended using free tendon grafts and attached to the radial lateral bands of the small, ring and long fingers and the ulnar lateral band of the index finger (Brand).
2. Power pinch (normally achieved by the ulnarly innervated adductor pollicis, 1st dorsal interossei, and deep head of the flexor pollicis brevis) can be addressed using the ECRB or FDS for an adductor plasty. The ECRB adductor-plasty is performed by detaching the ECRB from its insertion on the base of the second metacarpal and retrieving it proximal to the extensor retinaculum. A free tendon graft is then used as an extension on the end of the ECRB tendon and routed distally between the second and third metacarpals and attached to the adductor pollicis insertion on the first metacarpal. Alternatively, FDS adductor-plasty can be done using the long finger FDS. The FDS is harvested 2 cm proximal to its insertion and routed across the palm and attached to the adductor pollicis insertion.

EPL Rupture in the setting of a healed distal radius fracture is treated with EIP to EPL transfer.  When harvesting the EIP, it can be identified ulnar to the index EDC tendon at the level of the metacarpal head.

Complications

Donor tendons are attached to recipient tendons most commonly using the Pulvertaft weave. Utilizing this method, the donor tendon is woven back and forth through the substance of the recipient's tendon with each pass 90 degrees perpendicular to the previous pass and fixed to the tendon using a mattress suture of 2-0 or 3-0 ticron or fiberwire depending on surgeon preference and the size of the tendon. A minimum of three passes should be used for appropriate strength.

Complications are related mainly to an improper initial graft tensioning and repair site rupture or loosening as a result of slit propagation or knot failure. Alternative repair techniques (spiral linking and loop-tendon suture) can be used based on surgeon preference to help improve the biomechanical strength of the repair site with the tradeoff of increased bulk of the repair. [7][9]

Clinical Significance

In the forearm and hand there are over forty different muscles many of which perform overlapping functions. After an injury, some muscles may not move correctly. A tendon transfer moves a working muscle and tendon to replace a non-working muscle and tendon improving function.

Enhancing Healthcare Team Outcomes

Functional deficits in the hand arise most commonly as sequelae of radial, median, or ulnar nerve injury, but can also be secondary to brachial plexus injury, spinal cord injury, specific muscle or tendon injury, or as a result of polio. Additionally, non-displaced distal radius fractures treated non-operatively can lead to attritional rupture of the extensor pollicis longus. Tendon transfers are used to address functional deficits created by these conditions.