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.
Much of what we know today about tendon transfers was learned in treating paralyzed limbs associated with polio and injured soldiers during World Wars I and II.
Pathoanatomy of Specific Nerve Injuries
High radial nerve injuries occur above the elbow and lead to deficits in:
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:
High median nerve injury occurs proximal to the elbow joint and leads to weakness of:
Low median nerve injuries occur distal to the elbow resulting in the following motor and sensory deficits:
High ulnar nerve injuries occur proximal to the elbow leading to deficits in:
Low ulnar nerve injuries occur at the level of the wrist leading to deficits in:
Motor strength and sensory testing will distinguish lesions and appropriate indications for correction according to above categories.
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. Abnormal EMG findings 3 months from time of injury indicate a low likelihood of spontaneous recovery and tendon transfers may be considered.
Principles of Tendon Transfer
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.
Radial Nerve Injury
Low Median Nerve Injury
High Median Nerve Injury
Ulnar Nerve Palsy
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.
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. 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.