Hand

Learning Objectives

After reading this post you will know:

  • The origin, insertion, nerve supply and action of intrinsic muscles of hand.
  • Palmar spaces – midpalmar space, thenar space and pulp spaces of hand.
  • Details of lumbricals and interossei muscles.
  • Cutaneous innervation of hand.
  • Anatomical snuff box of hand.
  • Extensor expansion/dorsal digital expansion.

Q.  Name the intrinsic muscles of the hand and give their nerve supply.

A.  Intrinsic muscles of the hand ( total – 20 muscles) are grouped into five groups.

  1. Thenar muscles:
  • Abductor pollicis brevis
  • Flexor pollicis brevis
  • Opponens pollicis brevisAdductor pollicis ( does not form thenar eminence)

      2. Hypothenar muscles:

  • Abductor digiti minimi
  • Flexor digiti minimi
  • Opponens digiti minimi
  • Palmaris brevis

      3. Four Lumbricals ( one for each digit except thumb)

      4. Four Palmar interossei ( third digit /middle finger does not have palmar interrossei).

      5. Four dorsal interrossei ( thumb and the fifth digit/little finger do not have dorsal interrossei, whereas middle finger has two dorsal interrosei)

 Nerve supply: The intrinsic muscles of the hand are on the palmar aspect and are innervated by  branches of the ulnar and median nerves.

  • Five muscles are supplied by the median nerve:
    • Muscles forming thenar eminence:
    • Abductor pollicis brevis
    • Flexor pollicis brevis
    • Opponens pollicis brevis and
    • 1st and 2nd lumbricals
  • Fifteen muscles are supplied by ulnar nerve
    • Four hypothenar muscles
    • 3rd and 4th lumbricals
    • Four parmar  interrossei
    • Four dorsal interrossei
    • Adductor pollicis

Q. Write short notes on :

  1. Lumbricals
  2. Interrossei muscles of hand
  3. Spaces of the hand
  4. Anatomical snuff box
  5. Extensor expansion/Dorsal digital expansion
  6. Radial and ulnar bursa and digital synovial sheath

A. 1.. Lumbricals

  • Arise from the tendons of the flexor digitorum profundus
  • Are numbered 1st, 2nd, 3rd and 4th from lateral to medial side.
  • Lumbrical 1st and 2nd take origin from lateral side of the tendons of flexor digitorum profundus.
  • Lumbricals 3rd and 4th take origin from the adjacent sides of the tendons of flexor digitorum profundus.
  • They are inserted into the lateral side of the dorsal digital expansion of  2nd to 5th digits.
  • Medial 2 lumbricals are innervated by the ulnar nerve and lateral 2 lumbricals by the median nerve.
  • Flex the metacarpophalangeal joints and extend the interphalangeal joints.

   2.Interrossei muscles

Four dorsal interossei:

  • There is one dorsal interossei for index and ring finger and two dorsal interossei for the middle finger. They are numbered 1-4 from lateral to medial side.
  • They are bipennate .
  • They take origin from the adjacent sides of the shafts of the metacarpal bones.
  • Are inserted into the dorsal digital expansion (DGE) and base of proximal phalanx of the difgits ( 1st and 2nd on the lateral side of DGE and 3rd and 4th on the medial side of DGE.
  • They are the abductors  of digits (Dorsal ABduct = DAB).
  • All are supplied by deep branch of ulnar nerve.

Three palmar interossei

  • There is one palmar interossei for index, ring and little finger. They are numbered 1-3 from lateral to medial side.
  • They are unipennate.
  • They take origin from  the anterior aspect of metacarpals 2, 4 and 5,
  • They are inserted into dorsal digital expansion (DGE) of the difgits ( 1st on the medial side of DGE and  2nd and 3rd on thelateral side of DGE.
  • They are the adductors of digits (Palmar ADduct = PAD).
  • They  are  innervated by the deep branch of ulnar nerve.

Palmar and dorsal interossei

3. Spaces of the hand: The disposition of fascia and fascial septa in the hand results in the formation of  potential spaces. These spaces are surgically important as they may get infectected and distended with pus.

Following are the important spaces on the palmar aspect :

  • Midpalmar space
  • Thenar space
  • Pulp spaces of the fingers

Midpalmar space:

  • Shape  is triangular.
  • Location : in the medial half of the hollow of the palm.
  • Extent :
    • proximally till the distal margin of flexor retinaculum,
    • Distally till the distal palmar crease.
  • Boundaries:
    • Anterior: Palmar aponeurosis and flexor tendons of middle three digits ( enclosed in ulnar bursa).
    • Posterior; Fascia covering interossei and middle three metacarpals.
    • Lateral : Intermediate palmar septum (extending from  the  palmar aponeurosis to the 3rd metacarpal).
    • Medial : Medial palmar septum ( extending from the palmar aponeurosis to the 5th metacatpal).
  • Communications :
    • Proximally may communicate with the forearm space of Parona through carpal tunnel.
    • Distally with the medial three web spaces ( subcutaneous spaces in the interdigital cleft) through the medial three lumbrical canals (fascial sheaths of lumbricals).
  • Dranaige in case of infection : Pus from this space can be drained by incision in the 3rd and 4th web spaces.

Thenar space:

  • Shape : triangular
  • Location : in the outer half of the hollow of the palm.
  • Extent :
    • proximally till the distal margin of flexor retinaculum.
    • Distally till the proximal transversel palmar crease
  • Boundaries:
    • Anterior: Palmar aponeurosis and flexor tendon of index finger and tendon of flexor pollicis longus ( enclosed in radial bursa)and 1st lumbrical.
    • Posterior; Fascia covering adducor pollicis.
    • Lateral : lateral palmar septum  (extending from  the  palmar aponeurosis to the 1st  metacarpal).
    • Medial : Intermediate palmar septum ( extending from the palmar aponeurosis to the 3rd  metacatpal).
  • Communications :
    • Distally with the 1st web space ( subcutaneous space in the interdigital cleft) through the  1st  lumbrical canal.
  • Drainage in case of infection : Pus from this space can be drained by incision in the 1st web space.

midpalmar and thenar spaces

 Pulp spaces of the fingers:

  • Are the subcutaneous spaces on the palmar aspect of the tips of the fingers and the thumb.
  • They are filled with subcutaneous fatty tissue that is divided into compartments by the numerous fibrous septa which extend from the skin to the distal phalanx.
  • Boundaries:
    • Anterior ; skin and superficial fascia
    • Posterior; distal 2/3rd of the distal phalanx.
  • Terminal branches of the digital artery course through the spaces to supply the diaphysis of the distal phalanx.
  • Infection of the pulp spaces is known as ‘ Whitlow‘.
  • If neglected, the whitlow may lead to the necrosis of distal 4/5th of the distal phalanxThis is due to the fact that the diaphysis of the distal phalanx (distal 4/5th) is supplied by the branches of the digital artery that traverse through the pulp space. The rising tension due to accumulation of pus may occlude these branches of the digital artery resulting in avascular necrosis of the distal 4/5th of the terminal phalanx. As the proximal 1/5th (epiphysis) of the distal phalanx receives blood supply proximal to the pulp space, it is not affected.
  • Pus from the pulp space is drained by lateral incision which opens all the compartments.

pulp space of fingers

 4. Anatomical snuff box:

  • It is a triangular depression seen on the lateral aspect of dorsum of hand when the thumb is extended.
  • It is bounded by:
    • Laterally by  tendons of abductor pollicis longus and extensor pollicic brevis.
    • Medially by the tendon of extensor pollicis longus.
    • Roof is formed by skin and superficial fascia containing cephalic vein and superficial branch of radial nerve.
    • Floor is formed by scaphoid and trapezium bones.
    • Proximally it is limited by styloid process of radius.
  • Content : Radial artery.
  • Clinical significance: 
    • Tenderness in the anatomical snuff box indicates fracture of scaphoid bone.
    • The cephalic vein at this site is often used for giving intravenous fluids.
    • Pulsation of the radial artery can be felt here.

anatomical snuff box

5. Extensor expansion/Dorsal digital expansion

  •  It is a triangular aponeurosis  of extensor dgiitorum longus (EDL) which   coves the metacarpophalangeal joint and the dorsal surface of proximal phalanx.
  • The tendons of the  lumbricals and interossei are inserted via it.
  • It forms a functional unit to for coordinated action of  EDL, lumbricals and interossei muscles  to perform  extension at the  proximal and distal interphalangeal joints.
  • The expansion  divides into three bands at its distal end:
    • Lateral bands pass on either side of the proximal phalanx and are attached to the dorsal surface of the  base of  the distal phalanx.
    • Median band is  attached on the dorsal surface of the  base of the middle phalanx.

extensor expansion

6. Radial and ulnar bursa

Ulnar bursaRadial and ulnar bursa of hand

  • It is a common synovial sheath that encloses the tendons of flexor digitorum superficialis(FDS) and flexor digitorum profundus(FDP) as they pass deep to the flexor retinaculum..
  • It extends proximally into the forearm upto 5cm, proximal to flexor retinaculum.
  • Distally it extends into the palm upto the middle of the shaft of the metacarpals.
  • The distal end of ulnar bursa is continuous with the digital synovial sheath of the little finger.

Radial bursa

  • It is the synovial sheath that encloses the tendon of flexor pollicis longus as it passes deep to the flexor retinaculum..
  • It extends proximally into the forearm upto 5cm, proximal to flexor retinaculum.
  • Distally it  is continuous with the digital synovial sheath of the thumb.

Digital synovial sheaths

  • These are the synovial sheaths that enclose the flexor tendons of digits as they pass deep to fibrous flexor sheaths.
  • They extend from the heads of the metacarpals to the distal phalanges of the digits.
  • Digital synovial sheath of little finger is continuous with the ulnar bursa.
  • Digital synovial sheath of thumb is continuous with the radial bursa.

Function: Function of  ulnar bursa, radial bursa and digital synovial sheaths is to reduce friction and allow smooth movement of the flexor tendons as they pass deep to the flexor retnacum or fibrous flexor sheaths.

Clinical significance:  In case of infection of little and  thumb the infection can spread to forearm space of Parona ( between flexor digitorum profundus and interosseous membrane.) as they are continuous with the ulnar and radial bursa respectively. However, as the digital synovial sheaths of index a, middle and ring finger do not communicate with ulnar bursa, therefore infection from these digigits do not pass to palm and forearm. this is the reason for pricking the ring finger of non-dominant hand for withdrawing blood.

Q. Draw labelled diagram to show the:

  • Cutaneous innervation of hand

cuaneous innervation of hand

  • Formation and branches of superficial and deep palmar arches.

superficial and deep palmar arches of hand

 

 Q. Write in a tabulated form

  • Origin, insertion, action and nerve supply of thenar muscles.

thenar muscles

MuscleOriginInsertionActionNerve supply
Abductor pollicis brevisFlexor retinaculum Tubercle of scaphoi Crest of trapezium Lateral side of base of proximal phalanx of thumbAbduction of thumbMedian nerve
Flexor pollicis brevisFlexor retinaculum Trapezoid and Capitate bones Base of proximal phalanx of thumbFlexion of thumbMedian nerve
Opponens pollicisFlexor retinaculum and crest of trapeziumLateral half of palmar surface of 1st metacarpal.Opposition of thumb (pulls thumb medially and forwars towards the fingersMedian nerve
Adductor pollicis (is not part of thenar eminence)Oblique head from bases of 2nd and 3rd metacarpals Transverse head from shaft of 3rd metacarpalMedial aspect of base of proximal phalanx of thumbAdduction of thumbDeep branch of ulnar nerve

  

  • Origin, insertion, action and nerve supply of hypothenar muscles.

hypothenar muscles of hand

MuscleOriginInsertionActionNerve supply
Abductor digiti minimiFlexor retinaculum Pisiform Base of proximal phalanx of little finger.Abduction of little fingerDeep branch of ulnar nerve
Flexor digiti minimiFlexor retinaculum Pisiform Base of proximal phalanx of little fingerFlexion of little fingerDeep branch of ulnar nerve
Opponens digiti minimiFlexor retinaculum Medial border of 5th metacarpal. Pulls little finger forwardDeep branch of ulnar nerve
Palmaris brevisFlexor retinaculum Skin of palm of medial sideWrinkles skin of pam to improve gripsuperficial branch of ulnar nerve
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