Thenar and Hypothenar Muscles Of The Hand

Original Editor - Saumya Srivastava

Top Contributors - Saumya Srivastava, Kim Jackson, Leana Louw and Amanda Ager


Introduction

The complex integrity of the human hand is one of the factors that sets our species apart from other primates and animals. The movement of opposition played an important role in human evolution. This was made possible as more muscles attach to the thumb in modern humans than our ancestral primates[1]. Although the muscles of the human hand are found in one or more extant non–human primates, it is the combination of such which makes up for the uniqueness of our dexterity[1]

This page outlines the thenar and hypothenar muscles of the hand.

Description

When the human hand is viewed from the palmar side, 2 "fleshy" mounds can be observed[2].

  • Thenar eminence - fleshy part at the base of the thumb, made up of 3 muscles which control the movements of the thumb.
  • Hypothenar eminence - fleshy part at the base of the fifth digit (little finger), made of 4 muscles which contract to manifest motion through the little finger.

The muscles of the thenar and the hypothenar eminence along with the adductor compartment make up the intrinsic muscles of the hand. Their origin and insertion is within the carpal and metacarpal bones and are surrounded by ligaments, and fascia of the hand. They help with fine motor movements of the hands.[3]

The extrinsic muscles of the hand originate outside the hand, commonly the forearm, and insert into hand structures.

Thenar Eminence (TE) Muscles

The muscles of the TE are -[3]
  • Opponens Pollicis the largest of the 3 muscles
    • Origin - at the tubercle of the trapezium
    • Insertion - lateral margin of the metacarpal of the thumb
    • Nerve - recurrent branch of the median nerve
    • Artery - Superficial palmar arch from the radial artery
    • Function - performs opposition by flexing and medially rotating the metacarpal on the axis of the trapezium.
  • Abductor Pollicis Brevis positioned anteriorly to the opponens pollicis
    • Origin - tubercles of the scaphoid and trapezium
    • Insertion - lateral aspect of the proximal phalanx of the thumb
    • Nerve - recurrent branch of the median nerve
    • Artery - Superficial palmar arch from the radial artery
    • Function - primary muscle providing opposition. Also leads to abduction of the thumb which is drawing the thumb away from the midline
  • Flexor Pollicis Brevis
    • Origin - tubercle of the trapezium via the deep head, and the associated flexor retinaculum via the superficial head
    • Insertion - lateral aspect of the proximal phalanx of the thumb
    • Nerve - dual innervation with fibers from both the median ( superficial head) and ulnar ( deep head) nerves
    • Artery - branches of the radial artery; superficial palmar artery, branches of the princeps pollicis artery and radialis indicis artery
    • Function - flexion at the metacarpophalangeal and carpometacarpal joints leading to opposition of the thumb and, if continued, produces the medial rotation of thumb

Hypothenar Eminence (HE) Muscles

The HE muscles are[3] -
  • Opponens Digiti Minimi
    • Origin - the hook of hamate and associated transverse carpal ligament
    • Insertion - lateral aspect of the proximal phalanx of the thumb
    • Nerve - Deep branch of ulnar nerve (C8, T1)
    • Artery - Ulnar artery
    • Function - flex and laterally rotate the 5th metacarpal about the 5th carpometacarpal joint
  • Abductor digiti minimi
    • Origin - pisiform bone and the tendon of flexor carpi ulnaris
    • Insertion - the ulnar base of the proximal phalanx of the small finger
    • Nerve - Deep branch of ulnar nerve (C8, T1)
    • Artery - Ulnar artery
    • Function - abduction of the 5th finger, as well as flexion of its proximal phalanx
  • Flexor digiti minimi brevis
    • Origin - the hook of hamate and associated transverse carpal ligament
    • Insertion - the base of the proximal phalanx of the small finger
    • Nerve - Deep branch of ulnar nerve (C8, T1)
    • Artery - Ulnar artery
    • Function - flexes the little finger at the metacarpophalangeal joint
  • Palmaris brevis
    • Origin - the transverse carpal ligament
    • Insertion - on the skin of the medial palm
    • Nerve - Deep branch of ulnar nerve (C8, T1)
    • Artery - Ulnar artery
    • Function - tenses the skin of the palm on the ulnar side during a grip action and deepens the hollow of the palm
[4]


Clinical relevance

Fine motor movements are provided by the intrinsic muscles, which include the 3 thenar muscles and 4 hypothenar muscles. The extrinsic muscles provide strength to the hand[3]. The largest of the thenar muscles, opponens pollicis, along with hypothenar muscle, opponens digiti minimi, leads to opposition between little finger and thumb[3]. Palmaris brevis permits the wrinkling of the skin on the palmar surface of the hand[3]. It also deepens the hollow of the palm and protects the neurovasculature of the ulnar canal, which contains the ulnar nerve[5]

Although majority of the injuries resulting in hand deformity and malfunction are due to the involvement of the extrinsic muscles, intrinsic muscle injuries are yet relevant. Median nerve compression at carpal's tunnel will affect the muscles of the thenar compartment. Blunt trauma lesions of the insertion of opponens pollicis can cause the action of thumb opposition and supination to be significantly altered despite intact innervation[3].

As the ulnar nerve serves the hypothenar muscles, damage or compromise to the nerve leads to atrophy of the HT eminence and can be used as a identifying marker for proximal hand ulnar nerve compromise[2]. Another consequence of the ulnar nerve passing through the hook of the hamate and pisiform bone (the Guyon's canal), compression at this level leads to atrophy, numbness, tingling, and pain in the hypothenar eminence along with fourth and fifth digits[2]. This is much like the 'carpel tunnel syndrome' but in this case the ulnar nerve is involved. Cyclist are prone to this kind compression.

Arterial injury to the ulnar artery can also affect the HT eminence due to insufficient collateral blood flow, leading to a condition called 'hypothenar hammer syndrome'. Depending on flow compromise, necrosis of the HT eminence can also occur. Individuals that work with tools needing tight gripping and repetitive pounding can suffer with such injury as the action of gripping and pounding causes recoil impact on the vascular blood supply in the hypothenar eminence[2]

Proximal compromise of the nerve and/or the artery will show symptomatic changes in the hypothenar eminence in both the resting and active presentation of the hand. A loss or decrease of sensation and the feeling of pins and needles (paraesthesia) in the HT eminence can also indicate a C8 spinal root lesion on the ipsilateral side due to the dermatomal distribution for C8[2]. .

[6]


Assessment

When ulnar nerve compromise occurs at the Guyon's canal it causes weakness with abduction and adduction of the fingers, flexion at the MCP and extension at the PIP, and adduction and flexion at the MCP of the thumb. Hypothenar muscles are also not spared due to their innervation by the ulnar nerve[3].

In Carpel Tunnel Syndrome (CTS), where median nerve compromise occurs, thenar muscles can show wasting as they are innervated by the median nerve. If noted, other CTS tests like the Phalen's sign and the Tinel's test should be conducted. Phalen's sign is positive when numbness and tingling occurs when the patient raises the hands out in front of him or herself, flexes the wrist and places the dorsal wrists together, while flexed, for about 60 seconds. Tinel's test is positive when numbness and tingling is experienced when the examiner taps the medial aspect of the wrist, at the median nerve.

For a complete wrist and hand examination, see Wrist and Hand Examination

[7]
[8]


Treatment

In most acute case injuries, rest, icing, pain relief, support and activity modification helps with recovery. Where there is residual weakness of the muscles or mild to moderate neurological compromise, physiotherapy can aid in acquiring normal Hand Function

[9]


[10]


In case of functional malfunction of the hand needing surgery, the knowledge of the anatomy of the thenar and hypothenar eminence becomes vital for a safe and optimal approach [2].

When the ulnar artery is involved, the understanding of the collateral blood flow is very important because if not established post surgery, can lead to not only the necrosis of the hypothenar muscles but also the nerves and the tissues of that region[2].

Ulnar nerve repair needs the knowledge of its course in the Guyon's canal because if compression not release or if injury occurs during surgery, atrophy of the hypothenar eminence along with loss of sensory and motor function in the region the ulnar nerve innervation will occur[2].

References

  1. 1.0 1.1 Diogo R, Richmond BG, Wood B. Evolution and homologies of primate and modern human hand and forearm muscles, with notes on thumb movements and tool use. J Hum Evol. 2012;63(1):64-78. doi:10.1016/j.jhevol.2012.04.001
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 Nguyen J, Duong H. Anatomy, Shoulder and Upper Limb, Hand Hypothenar Eminence. In: StatPearls. Treasure Island (FL): StatPearls Publishing; August 13, 2020.
  3. 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Okwumabua E, Sinkler MA, Bordoni B. Anatomy, Shoulder and Upper Limb, Hand Muscles. In: StatPearls. Treasure Island (FL): StatPearls Publishing; July 31, 2020.
  4. Muscles Of The Hand Thenar & Hypothenar Groups - Everything You Need To Know - Dr. Nabil Ebraheim. Available from: http://www.youtube.com/watch?v=BTEjO6F1-vI
  5. Moore CW, Rice CL. Structural and functional anatomy of the palmaris brevis: grasping for answers. J Anat. 2017;231(6):939-946. doi:10.1111/joa.12675
  6. Treating Trigger Points - Thenar Eminence. Available from: http://www.youtube.com/watch?v=IuHYdiFH5Co
  7. Recognizing Thumb Muscle Atrophy - Carpal Tunnel Syndrome. Available from: http://www.youtube.com/watch?v=ffCnKlZVJvQ
  8. How to Tell What is Causing the Numbness in Your Hands (5 Common Causes). Available from: http://www.youtube.com/watch?v=GHdN55Hj32E
  9. Thenar Strengthening Exercises. Available from: http://www.youtube.com/watch?v=GqDmTfrwNag
  10. Hand/finger Strengthening Exercises with putty. Available from: http://www.youtube.com/watch?v=exi9ifuss98