Power Grasp: Dual Channel

Electrode Placement
Application Instruction by Dr. Lucinda Baker

Electrode placement for power grasp, using dual channel stimulation. The medial condyle and the pisiform bone are marked with X's. The negative electrode of channel one is placed over the ulnar nerve just proximal to the pisiform bone. The positive electrode is connected with a dual leadwire electrode at the mid forearm. The negative electrode of channel two is placed over the extrinsic finger flexors. The positive electrode for channel two is also connected to the dual leadwire electrode at the mid forearm.

Power Grasp: Dual Channel

Video Instruction
Audio Transcript:

Electrode placement for power grasp, using dual channel stimulation. The medial condyle and the pisiform bone are marked with X's. The negative electrode of channel one is placed over the ulnar nerve just proximal to the pisiform bone. The positive electrode is connected with a dual leadwire electrode at the mid forearm. The negative electrode of channel two is placed over the extrinsic finger flexors. The positive electrode for channel two is also connected to the dual leadwire electrode at the mid forearm.

The stimulation of channel one results in metacarpal phalangeal flexion. Stimulation of channel two results in distal and proximal interphalangeal flexion. When the two channels are combined a power grasp occurs. This would be graded as a three plus out of five muscle contraction.

Power Grasp: Dual Channel

Muscle Anatomy

Muscles involved in power grasp: (extrinsic)

Flexor Digitorum Superficialis
Origin: Medial epicondyle of the humerus (common flexor tendon) as well as parts of the radius and ulna
Insertion: Anterior margins on the base of the middle phalanges of the four fingers

Flexor Digitorum Profundus
Origin: Upper 3/4 of the anterior and medial surfaces of the body of the ulna, interosseous membrane and deep fascia of the forearm
Insertion: Base of the distal phalanges of the fingers

Flexor Pollicis Longus
Origin: The middle 1/2 of the anterior surface of the radius and the adjacent interosseus membrane
Insertion: The base of the distal phalanx of the thumb

Note: It is not uncommon for the flexor digitorum superficialis to be absent from the 5th digit making it difficult to identify 5th digit injury.

Muscles involved in power grasp: (intrinsic)

Interosseous Muscles (Palmar)
Origin: Each interossei originates from a medial or lateral surface of a metacarpal
Insertion: into the extensor hood and proximal phalanx of same finger

Lumbrical Muscles
Origin: Tendon of the flexor digitorum profundus
Insertion: They pass dorsally and laterally around each finger, and inserts into the extensor hood

Power Grasp: Dual Channel

Nerve Anatomy

Nerves involved in power grasp: (extrinsic)

Flexor Digitorum Superficialis
Nerve: Median nerve
Nerve root: C8, T1

Flexor Digitorum Profundus
Nerve innervation: The medial half (acts on digits
IV & V) is innervated by the ulnar nerve. The lateral half (acts on digits II & III) is innervated by the anterior interosseous branch of the median nerve
Nerve root: C8, T1

Flexor Polliicis Longus Nerve innervation: Median nerve (anterior interosseous branch)
Nerve root: C8, T1

Nerves involved in power grasp: (intrinsic)

Interosseous Muscles (palmar)
Nerve innervation: ulnar nerve
Nerve root: C8-T1

Lumbrical Muscles
Nerve innervation: The lateral two lumbricals (of the index and middle fingers) are innervated by the median nerve. The medial two lumbricals (of the little and ring fingers) are innervated by the ulnar nerve
Nerve root: C8-T1