RADIAL NERVE PALSY AND TRANSFERS

Radial nerve palsy is a condition resulting from damage to the radial nerve at any point along its anatomical length. The radial nerve is the most frequently injured major nerve of the upper extremity, and radial nerve palsy typically results from fractures of the humerus. Other possible etiologies include elbow fracture, lacerations, and iatrogenic injury during upper limb surgery. Cases are classified based on their location, with injuries proximal to the elbow referred to as high radial nerve palsy and injuries distal to the elbow referred to as low radial nerve palsy. The majority of patients experience injury distal to the innervation of the triceps muscle. A tendon transfer is a surgical procedure used to treat these injuries that usually involves the release of the tendon at its anatomic insertion site, rerouting the tendon, and finally reattaching it to a new insertion site either in another tendon or in a bone. It is a commonly used procedure that may be needed for non-repairable radial nerve palsies, when there is a loss of muscle and tendon secondary to trauma, or slowly progressing neurological disease.^1-4

Related Anatomy^2,5

• Radial nerve
  • Largest nerve in the upper limb
  • Branch of the brachial plexus arising from the posterior cord with fibers originating from the C5, C6, C7, C8, and T1 nerve roots
  • Proximal to the elbow, it bifurcates into a superficial and deep branch:
    • Superficial branch: purely sensory; runs under the brachioradialis muscle at the radial side of the forearm; at radial styloid, it divides further into 2–3 sensory branches that innervate the skin of the proximal two-thirds of the lateral three and a half fingers and dorsum of the hand
    • Deep branch: purely motor; represented by the posterior interosseous nerve (PIN); it further divides into additional branches and innervates the supinator, extensor digitorum communis (EDC), extensor digiti quinti (EDQ), and extensor carpi ulnaris (ECU); it then sends branches to the abductor pollicis longus (APL), extensor pollicis longus (EPL), extensor pollicis brevis (EPB) and and extensor indicis proprius (EIP)

Signs and Symptoms⁵

• Typical symptoms of radial nerve palsy include:
  • Debilitating motor dysfunction of the hand: primarily an impaired ability to extend the wrist, fingers, and thumb
  • Loss of grip strength
  • Inability to stabilize the wrist during power grip
  • Loss of cutaneous sensibility in regions innervated by the radial nerve
• A tendon transfer is usually indicated when there is no potential for radial nerve palsy to improve, including those that are physically irreparable (eg, root avulsions, injuries not improved after direct nerve repair or grafting, and failed nerve transfers)
• Other indications for tendon transfer include:
  • Radial nerve palsies that present too late for muscle reinnervation to occur due to fibrosis of the motor end plate
  • Loss of muscle or tendon following trauma
  • Central neurologic deficits
  • Tendon ruptures in patients with rheumatoid arthritis

Physical Examination and Work-up^2,3

• Before considering a patient for a tendon transfer, the clinician should obtain an accurate history and perform a physical examination
• The physical examination includes detailed muscle testing and range of motion (ROM) assessments of the wrist, hand, and finger; an inventory of both the functioning and nonfunctioning muscle-tendon units should be performed
  • Both motor function and sensation must be evaluated to identify any deficits present, distinguish between lesion types, and determine appropriate indications for correction
  • Detailed examinations go to muscle testing by nerve or to specific muscle examinations in the exam test and signs section. (add links)
• Radial nerve palsies can usually be diagnosed by the physical exam alone, but electrodiagnostic testing may also be needed
  • Electromyography (EMG) and nerve conduction velocity (NCV) testing can be used for determining the exact location and extent of the initial injury
  • Electromyography (EMG) and nerve conduction velocity (NCV) testing can also be used for detecting signs of early nerve recovery.

Basic Science and Principles of Tendon Transfers

• When evaluating a patient for a tendon transfer and planning out the procedure, several core principles must be considered. Adhering to these principles will increase the chances of a successful outcome, while not doing so can lead to a failure. The core principles of tendon transfers are described below. ⁵

1. Synergy^3,5

• Synergy principle: certain muscle groups usually work together to perform a function or movement (e.g. wrist flexion and finger extension; wrist extension and finger flexion)
• Finger flexion and wrist flexion are not synergistic movements
  • Therefore, a wrist flexor transferred to restore finger extension will adhere to synergetic principles, while a wrist flexor transferred for finger flexion will not function synergistically.
• Synergistic transfers are usually easier to train and are preferable to non-synergistic transfers; therefore, it is advised to perform synergistic transfers whenever possible, although non-synergistic transfers may be the only option available in some cases

2. Passive mobile joints^2,3,5

• Tendon transfers cannot mobilize stiff joints, and the procedure will fail if a joint is too stiff
• Passive mobility is therefore a prerequisite to tendon transfer: the joints controlled by the transferred tendon must have nearly full passive ROM before the procedure to achieve optimal post-tendon transposition
• The donor muscles must be tested for strength before performing transfer procedures.
• Pre-operative hand therapy is often needed to improve passive ROM if it is not normal.
• In some cases, joint release may be necessary before the tendon transfer

3. Soft tissue equilibrium^3,5

• Tendon transfers must pass through a healthy bed of soft tissue that is free of scar tissue, inflammation, and edema. A healthy soft tissue bed allows the tendon to glide freely with pliable skin and minimizes adhesions.
• In most cases, this will entail the transfer passing through healthy subcutaneous fatty tissues
• After a soft tissue injury, the surgeon must allow sufficient time to pass for inflammation and edema to fully subside before performing tendon transfers.
• If a healthy, soft bed is not present and/or the transfer must pass through an area in which severely scarred tissue is present, the surgeon can either excise the scar and reconstruct the bed with a flap or plan an alternative transfer through a healthier bed of tissue

4.Adequate strength^3,5

• The strength of the donor muscle-tendon unit being must be strong enough to allow the desired movement(s) but must not be so strong that it disrupts the extensor/flexor balance.
  • When the donor is too weak, movement and function will not be adequate
  • When the donor is too strong, movements become unbalanced and there is inappropriate posture at rest
• Therefore, the strength of the muscle-tendon unit should be either normal or near normal and under voluntary control in pre-operative testing: this equates to a muscle grade of 4/5 or 5/5. Strength at 5/5 is ideal because the transferred muscle will usually loose a grade after transfer.

• Grading of muscle strength:

  Grade	Strength	Description
  5*	Normal	Completes full range of motion against maximal finger resistance
  4*	Good	Tolerates moderate resistance
  3	Fair	Completes full range of motion with no resistance
  2	Poor	Completes partial range of motion
  1	Trace	Slight contractile activity
  0	Zero	No contractile activity
  *The distinction between Grades 4 and 5 is based on comparison with the normal hand and, barring that, extensive experience in testing the hand.

• For additional information see the standard muscle testing options in the examination section below.

5. Sufficient amplitude¹

• A muscle’s amplitude is a function of its sarcomere length
• The transferred muscle-tendon unit must have enough amplitude to successfully perform the function of the tendon being replaced
  • The sarcomere length and work capacity of the muscle being transferred must provide enough muscle shortening during contraction to provide adequate shortening of the muscle-tendon unit and produce the needed ROM of the joints that need to be mobilized

• The flexor carpi ulnaris (FCU) has the greatest work capacity of the wrist motors, but due to its significant role in wrist function, using it for tendon transfers has been called into question

6. Straight line of pull^1,5

• Transferred tendons must have a straight line of pull from their origin through unscarred soft tissue to the new insertion point
• Changes in direction can create points of friction, which reduces the potential force, power, and amplitude of the transferred muscle-tendon unit: changing direction by only 40° will lead to a significant decrease in force
• Tendon transfers cannot perform two separate functions at once, especially if the line of pull is not straight
• If there is a second point of insertion because the tendon has been split to insert on two separate insertion sites and half of the tendon does not follow a straight vector, then no force will be directed to this second insertion point. There are rare exceptions to this rule such as a Stiles-Bunnell intrinsic transfer.  This means usually each transfer such have only one function not two.

7. Expendable donor^3,5

• The donor muscle-tendon unit must be expendable, meaning another tendon—or tendons—is left intact that can continue to adequately perform the original function of the transferred muscle-tendon unit
• Restoring a given movement only to lose another equally important movement in the process is not beneficial.
• Example: if one of the wrist flexors (eg, the flexor carpi radialis [FCR]) is transferred, then the FCU must be intact and functioning normally so wrist palmar flexion function is preserved after the transfer

8. Tension of the transfer⁵

• The amount of passive tension set is a critical component of the procedure: the surgeon should ensure that the tension in the transfer is slightly tight and be aware of the recommended positioning of the elbow, wrist, and digits when adjusting this tightness
• The surgeon should also use the wrist tenodesis effect to gently test the transfer passively before finalizing the tightness of the tendon transfer insertion into its new origin

9. Donor of adequate excursion^1,3,5,6

• The excursion of the donor muscle-tendon unit should be adequate enough to achieve the desired hand movement, meaning the excursion of the transferred tendon is comparable to that of the recipient tendon
• Excursion of various muscles
  • Wrist extensors and flexors: 33 mm
  • Finger extensors: 50 mm
  • Finger flexors: 70 mm
• The tenodesis effect of the wrist can add another 20–30 mm of finger tendon excursion

10. Single function per transfer^3,5,6

• A single tendon should only be used to restore a single function, as attempting to restore multiple functions compromise strength and movement
• One exception is that a single muscle-tendon unit can restore the same movement in more than one digit. (see #6)

Other

• Incisions used for tendon transfers should not parallel the route of the transferred tendon because this will increase the chance of adhesions and loss of tendon gliding.
• Use transverse incisions so there is less opportunity for the transferred tendon to scar to the surgical incision
• Tendon transfers will often adhere to the first fibrous structures that they touch, so ideally the first fascial (collagen) structure should be at the new insertion site of the transferred tendon.  This fact also means that transfers are not reliably be use to produce forearm rotation.

Timing and planning^1,4

• Timing of tendon transfers for radial nerve palsy is classified as either early or late
  • Early tendon transfer
    • Act as an internal splint
    • Performed within 12 weeks of injury
  • Late tendon transfer
    • Performed to restore function when recovery is unlikely
    • Can be performed between 6–18 months after injury
• Determining the optimal timing should be contingent on several factors, including:
  • The etiology of the injury
  • The patient’s prognosis
  • A clear indication that the injured nerve will not regenerate and the innervation has been temporarily lost
  • Patient preference

• If functional recovery is not possible, transfers should be performed immediately after the patient is ready; if it’s expected that nerve regeneration will occur, the surgeon should wait until it’s possible to determine the level of functional recovery
• Planning for tendon transfers must include making an inventory of those muscle-tendon units that are functioning normally and those that are no longer functioning or have been removed by injury

• The surgeon must do appropriate muscle testing to determine the muscle grade of each remaining muscle-tendon unit.  For additional information see the standard muscle testing options in the examination section below.High vs. low radial nerve palsy⁶
• High radial nerve palsy
  • Proximal to the elbow
  • Leads to the following deficits:
    • Wrist extension (due to denervation of brachioradialis, ECRl, ECRB, and ECU
    • Finger MP extension (due to denervation of EDC, EIP, and extensor digit minimi (EDM)
    • Thumb radial abduction and extension (due to denervation of EPL)
    • Sensation in the superficial radial nerve distribution
• Low radial nerve palsy
  • Distal to the elbow
  • Affect muscles innervated by PIN
  • Leads to the following motor deficits:
    • Weakness in wrist extension (due to denervation of the ECU)
      • ECRL innervation is often maintained, which leads to radial deviation with wrist extension
    • Weakness in finger MP extension (due to denervation of EDC, EIP, and EDM
    • Thumb radial abduction and extension weakness (due to denervation of EPL)
  • Sensory deficits are uncommon because they occur distal to the superficial radial nerve branching off the radial nerve

This patient is a 29 y. o. male who sustained an open midshaft humerus fracture secondary to a gunshot wound two years ago. The wound and fracture are now healed but the patient cannot extend his fingers, thumb or wrist. He has a chronic wrist drop. Hand therapy and splinting have improved his situation some but not helped enough. He is seeking advice regarding surgical treatment options.

Postoperative care and rehab⁵

• Regardless of what procedure is performed, an elbow splint or cast is needed after surgery
  • The elbow should be flexed at 90° degrees, forearm pronated, and wrist extended at 30°
  • The thumb should be abducted and extended, and the MP joints of the fingers extended
  • The interphalangeal (IP) joints of the fingers should be left free
  • The splint can be changed at 1–2 weeks for a wound check then be refitted
• All patients must undergo an extensive rehabilitation program with a hand therapist
• In the first four post-operative weeks, rehabilitation should focus on maintaining ROM of the shoulder and IP joints
• During weeks 4–6, the aim of exercises will be to mobilize single joints while keeping tension off the transfer
  • The mobilization phase will begin with active ROM exercises and gradually advance to gentle passive ROM exercises
  • Patients must wear their splint when not performing exercises
  • At week 6, the therapist will begin to focus on activating the muscles used in the tendon transfer and initiate muscle retraining; simultaneous flexion of the wrist and fingers should still be avoided at this stage so that excessive tension is not placed on the transfers
  • Electrical stimulation and biofeedback may also be used at this time
• At eight weeks, strengthening exercises begin and the splint can be weaned off
• At 12 weeks, patients can resume full activity

• Infection
• Bleeding
• Blood vessel or nerve damage
• Hand stiffness or weakness
• Tendon rupture at repair site
• Tendon adhesions
• Transfer weakness⁶

• In general, tendon transfers for radial nerve palsy can lead to excellent results in wrist, thumb, and finger ROM³
  • In one study of 15 patients treated with tendon transfers, 11 reported a high level of satisfaction and excellent wrist, thumb, and finger ROM⁷
• The FCR transfer, FCU transfer, and FDS transfer have all been found to elicit good, reliable outcomes in several studies. None of these procedures has been definitively found to be superior to another.⁵
• The Merle d’Aubigné procedure has also been supported in the literature as a reliable technique capable of producing good outcomes.⁵
• After a double wrist flexor transfer, wrist flexion is often reduced, but overall results are good.⁵

• The power of a muscle is related to his cross-sectional area. The transferred muscle will most likely lose some power; therefore, only muscles rated 4+ or better should be considered acceptable donor motors.¹
• A muscles work capacity is calculated as the product of the muscle power times its amplitude.¹
• There is still controversy regarding the optimal timing for tendon transfers. Most experts agree it’s necessary to wait until sufficient time has elapsed to determine that further nerve recovery will not occur, but some new research suggests that immediate transfers should be performed in certain situations (eg, a gap of >4 cm between nerve ends, when the nerve is in a deep wound of scar tissue, and with major tissue loss).²

1. Leddy, JP and Leddy, TP. (1997). Tendon Transfers in the Hand and Forearm, in Dee R et al (Eds.) Principles of Orthopaedic Practice. New York: McGraw-Hill, 1152-1158.
2. Bumbasirevic, M, Palibrk, T, Lesic, A, et al. Radial nerve palsy. EFORT Open Rev 2016;1(8):286-294. PMID: 28461960
3. Seiler, JG, 3rd, Desai, MJ and Payne, SH. Tendon transfers for radial, median, and ulnar nerve palsy. J Am Acad Orthop Surg 2013;21(11):675-84. PMID: 24187037
4. Ratner, JA, Peljovich, A and Kozin, SH. Update on tendon transfers for peripheral nerve injuries. J Hand Surg Am 2010;35(8):1371-81. PMID: 20684937
5. Sammer, DM and Chung, KC. Tendon transfers: part I. Principles of transfer and transfers for radial nerve palsy.Plast Reconstr Surg 2009;123(5):169e-177e. PMID: 19407608
6. Carl, DJ and Habusta, SF. Hand Tendon Transfers. In: StatPearls. Treasure Island (FL): 2020. PMID: 29083655
7. Ropars, M, Dreano, T, Siret, P, et al. Long-term results of tendon transfers in radial and posterior interosseous nerve paralysis. J Hand Surg Br 2006;31(5):502-6. PMID: 16928411
8. Weber RV, Mackinnon SE. Nerve transfers in the upper extremity. J Hand Surg Am. 2004; 4(3): 200-213.