The palmar interossei or volar are three short, unipennate muscles on the palmar surface of the hand and along with the dorsal interossei muscles. These occupy the spaces between the metacarpal bones.These are attached to the index, ring, and little fingers. They are smaller than the dorsal interossei of the hand. Palmar interossei muscles are strong Adductors of Fingers and assists in flexion of the metacarpophalangeal joints and extension of the interphalangeal joints.
- The first palmar interossei also known as pollical palmar interosseous and it originates at the media palmar surface of the first metacarpal. It is often considered as rudimentary.
- The second palmar interosseous originates at the medial surface of the base of the second metacarpal.
- The third and fourth palmar interossei originate at the lateral aspect of the fourth and fifth metacarpals.
- The 1st interossei inserts into the base of the proximal first phalanx
- The 2nd inserts onto the medial portion of the extensor hood of the first digit as well as the base of the first phalanx.
- The 3rd and 4th interossei inserts into the lateral aspect of their respective extensor hood.
The palmar interossei receive nerve supply from the deep branch of the ulnar nerve. The deep branch of the ulnar nerve arises from nerve roots of C8 and T1.
Palmar interossei muscles receive arterial blood supply from the palmar metacarpal arteries and drains into the palmar metacarpal veins. The palmar metacarpal arteries derive from the deep palmar arch, which is comprised of the terminal portion of the radial artery and the deep branch of the ulnar artery.
Adduct fingers towards centre of third digit or middle finger. Flex metacarpophalangeal joint while extending interphalangeal joints.
The palmar interossei receive innervation from the deep palmar branch of the ulnar nerve.so,
1.) Injury to the ulnar nerve can manifest as weakness or even atrophy of the interossei muscles and is mainly caused by :
- nerve root impingement
- brachial plexus compression
- nerve entrapment at the elbow, forearm, or wrist.
2.) Ulnar nerve entrapment is the second most prevalent compression neuropathy with which patients present. Depending on which nerve fibers are compromised, patients may have weakness in adduction of the fingers. The lumbricals are the major contributors to flexion at the metacarpophalangeal joints as well as extension at the DIP and PIP joints; however, the interossei also play a minor role in these movements.
- Electromyographic and nerve conduction velocity studies are used to evaluate the ulnar nerve pathology and to rule out other diagnosis.
- In a positive Wartenberg’s sign, patients are instructed to adduct all fingers. A positive test will produce abduction of the fifth finger relative to all other digits, implying weakness of the third palmar interosseous muscle and fourth lumbrical.
Method: A patient can be instructed to hold a sheet of paper between any of the second through fifth digits to examine the palmar interossei, with dropping of the piece of paper indicative palmar interossei weakness.
Strengthening of muscles and treatment of related injuries is recommended.
- Valenzuela M, Bordoni B. Anatomy, Shoulder and Upper Limb, Hand Palmar Interosseous Muscle. In: StatPearls. StatPearls Publishing, Treasure Island (FL); 2019.
- Susman RS, Nyati L, Jassal MS. Observations on the pollical palmar interosseous muscle (of Henle). The Anatomical Record: An Official Publication of the American Association of Anatomists. 1999 Feb 1;254(2):159-65.
- Lane R, Nallamothu SV. Claw Hand. InStatPearls [Internet] 2019 Apr 9. StatPearls Publishing.
- PTPT621. Test for Wartenberg Sign. Available from https://www.youtube.com/watch?v=Pj2cwCp_4uU [last accessed 20/9/2020]