Tendon transfers are utilized to reestablish balance to a disabled, damaged, or devoid neuromuscular-motor unit. They are indicated for rejuvenation of muscular function after peripheral nerve damage, trauma to the brachial plexus or spinal cord, or irrecoverable injury to tendons/muscles. The goal is to equalize the surrounding musculotendinous forces and restore functional activity. Tendon transfers are most commonly used in the hand and forearm to address radial, median, or ulnar nerve dysfunction. Understanding the principles for transfer can ensure maximal benefit and optimize postoperative results. Nerve transfers may be an alternative option depending on the nature and chronicity of the injury.
17 Nerve Palsies and Tendon/Nerve Transfers for Injuries at or Distal to the Elbow
I. Principles of Tendon Transfer
Injuries to the major nerves of the hand and upper extremity result in loss of function secondary to muscle paralysis, atrophy, and lack of sensibility.
Depending on the chronicity and type of injury, nerve repair may not be an option. Tendon transfers are an option to reestablish motor function.
Core principles of tendon transfers
Preoperative prevention of contracture: Full passive range of motion (ROM) of affected joints is required.
Preoperative tissue equilibrium: Scar tissue from previous trauma must be fully mature to provide a smooth bed for the transfer to function.
Adequate strength: Donor tendons must be from a muscle with appropriate strength.
Amplitude of motion: Excursion of the transferred tendon should match the required length of recipient tendon motion.
Flexors and extensors of the wrist have 30 mm of excursion.
Digital extensors have 50 mm of excursion.
Digital flexors have 70 mm of excursion.
Straight line of pull: Transferred tendons should be in as straight a line as possible from origin to insertion to reduce friction and optimize force transmission.
One function: A tendon should be transferred to execute a single action.
Synergism: Synergistic action of donor and recipient tendons should be considered (e.g., wrist flexion and finger extension are synergistic).
Expendable donor: Sacrifice of the donor tendon should not result in a loss of function, so there must be a separate muscle-tendon junction providing similar function.
II. Requirements for Tendon Transfers
Passive ROM of all surrounding joints with supple web space skin.
Radiographs to confirm no/minimal arthritic changes of surrounding joints.
Ensure patient can be compliant with postoperative restrictions and occupational therapy protocols.
III. Tendon Transfers for Median Nerve Palsy
Injuries are characterized as “high” or “low” depending on whether they occur above or below the anterior interosseous nerve (AIN) branch in the forearm.
Low median nerve palsy
Thenar intrinsics including the opponens pollicis (OP), abductor pollicis brevis (AbPB), and the superficial head of the flexor pollicis brevis (FPB) are affected in addition to sensory innervation to the thumb/index/long/partial ring fingers.
Loss of thumb opposition is the primary motor deficit:
Opposition is multiplanar including abduction, pronation, and flexion.
Some opposition may be preserved by anatomically variable contributions from the ulnar nerve (Riche-Cannieu anastomosis).
The deep head of the FPB and the adductor pollicis (AdP) are innervated by the ulnar nerve, which may allow satisfactory compensation.
Tendon transfer to restore opposition (► Table 17.1):
Palmaris longus (PL) to AbPB/OP: PL is tunneled subcutaneously and attached to the AbPB/OP at the base of the thumb (a.k.a. Camitz transfer).
Extensor indicis proprius (EIP) to AbPB/OP: This will restore opposition even in the setting of a high median nerve palsy. EIP is transected on the dorsal aspect of the index finger just distal to the metacarpophalangeal (MCP) joint but proximal to the extensor hood, and freed proximal to the extensor retinaculum at the wrist. It is then routed subcutaneously in a volar ulnar direction over the flexor carpi ulnaris (FCU) to the AbPB/OP. Wrist is maintained in flexion for attachment.
Flexor digitorum sublimis (FDS) from the ring finger to AbPB/OP: The FDS to the ring finger is brought proximally and routed through a pulley created by a radial slip of FCU tendon (to create appropriate vector of pull) and then tunneled subcutaneously to the AbPB/OP.
Abductor digiti minimi (AbDM) to AbPB/OP (a.k.a. Huber transfer): AbDM is supplied by a neurovascular pedicle at the most dorsoradial aspect of its proximal origin which must be protected during dissection and from being kinked as the tendon is tunneled to the APB. This option is usually used in children.
Postoperatively, a thumb spica splint is placed with the thumb in palmar abduction for 2 to 4 weeks and then protected ROM exercises are begun with occupational therapy.
High median nerve palsy
The pronator teres (PT), flexor carpi radialis (FCR), FDS to all fingers, index and middle finger flexor digitorum profundus (FDP), flexor pollicis longus (FPL), and pronator quadratus (PQ) are affected, in addition to those affected in low median palsy.
The anterior interosseous nerve (AIN) off the main median nerve innervates some of the forearm musculature; therefore, AIN palsy mimics median nerve palsy, but spares the intrinsic muscles of the hand and has no associated sensory changes.
Loss of forearm pronation, thumb interphalangeal (IP) joint flexion, index finger flexion, and variable loss of long finger flexion are the main additional motor deficits. FCU provides wrist flexion in the absence of FCR.
Extensor carpi radialis longus (ECRL) to index finger (IF) FDP: The purpose of this transfer is to restore pinch. ECRL is identified in the distal forearm inserting at the base of the index finger metacarpal and transferred to the index finger FDP in the volar aspect of the forearm. A dorsal blocking splint is placed postoperatively to protect the repair, and active ROM is avoided for 4 weeks.
Brachioradialis (BR) to FPL to restore thumb IP joint flexion: The BR is identified at its insertion on the radial styloid, tunneled under the radial artery, and attached to the FPL deep to the FCR tendon. A thumb spica splint is placed postoperatively and active ROM is begun at 4 weeks (► Table 17.2).