Anatomy of the Hand By Dr. G kamau

Learn about the anatomy of your hand .

1. HAND DR. G. KAMAU

2. Objectives:-1) Hand spaces & their clinical significance. 2) Revise neurovascular supply to the hand & intrinsic muscles of the hand

3. The hand is a chief tactile & sensory organ,capable of fine dexterous precision grip movements ,strong grasping power grip movements, hook grip as lifting an object ,or combination of the movements. It is the terminal working tool of upper limb. The thumb is most important digit with a lot of free mobility > loss of thumb is about 50% loss of hand function.Thumb movements are adduction/abduction, flexion /extension ,rotation &opposition. For adduction/abduction of the fingers, the middle finger & its metacarpal act as imaginary reference line .The dorsal interrossei are abdutors (DAB),& palmar interossei adductors (PAD) It has intrinsic hand muscles supplied by ulnar &median nerves &extrinsic long tendon muscles from the forearm. Radial nerve does not supply the intrinsics

4. Homunculus is topographical arrangement of body areas on the brain precentral motor gyrus & postcentral gyrus sensory of cerebral cortex. Note the hand occupies a very large area on the brain especially its thumb. Note the body is inverted, except the face, the toes being on medial surface of the cerebral cortex.

5. Tissues of the hand The tissues of the hand from the palm consists of:- 1) Palmar skin is of thick similar to the sole with little mobility because of numerous interlocking fibrous septa enclosing fat. -2) Palmar aponeurosis arising from terminal end of palmaris longus . -3) Thenar / Hypothenar muscles -4)Long flexor tendons & associated lumbricals -5)Adductor Pollicis arising as transverse & oblique heads from 3 rd metacarpal. -6)The interossei ,palmer & dorsal arising from the metacarpals.

6. Nail &pulp spaces infection infections Paronychia is soft tissue adjacent to the nail infection. May be acute due to bacteria eg staphylococcus aureas but occassionally due Herpes simplex virus. Chronic may be fungal eg candida or mycobacteria . Pulp space infection or felon is very painful because the pus forms in inter- septal spaces where it becomes enclosed.It may lead to osteomyelitis of distal phalange.

7. Palmar Aponeurosis :- It is a continuation of palmaris longus . It extends, from distal border of flexor retinaculum , fanning out in a triangular fashion towards the bases of the fingers sending to each a slip.Each slip further subdivides into two bands that are attached to deep transverse ligament. Dupuytren’s contracture of palmar aponeurosis >fixed flexion contractures of fingers.

8. Thenar muscles:- They arise from flexor retinaculum :- Abductor pollicis brevis attached to radial side of base of 1 st phalange is the most prominent & radial.It abducts the thumb at the MP joint. Flexor pollicis brevis is attached via a radial sesamoid to radial border of 1 st phalange as its flexor at MP joint. Opponens pollicis is inserted to radial border of 1 st MC. All are supplied by median nerve In relaxed position of the hand, the thumb is at right angle to the palm plane./In apposition of the thumb, its MC &phalanges are rotated so that the thumb lies parallel to palm plane,Apposition mainly occur at Trapezial -metacarpal joint. In relaxed hand position also,the other fingers become progressively more flexed becoming most flexed at little finger & least at index finger. A pointing finger is a sign of long flexor tendons not working.

9. Hypothenar muscles:- All arise from flexor retinaculum . Abductor digiti minimi attached to ulnar side of base of proximal phalange> abduction of little finger to ulnar side. Flexor digiti minimi Inserted to base of proximal phalange. Opponens digiti minimi inserted to ulnar border of 5 th MC.All hypothenar muscles are supplied by deep branch of ulnar nerve.

10. Lumbricals :- Arise from the four profundus tendons passing at the radial side of MP joints. Their tendons passing through fibrous lumbrical canals reach the extensor expansion on the dorsum of proximal phalange. The two ulnar lumbricals are innervated by ulnar nerve & the two radial by median nerve. They flex the MP joints.

11. Adductor pollicis :- Transverse head arises from 3 rd MC, oblique head also from 2 nd MC to be attached via ulna sesamoid to ulna side of base of proximal phalange.It approximates the thumb to index finger.It is supplied by deep branch of ulnar nerve. Interossei :- Palmar are smaller and arise from their own MC.They adduct (PAD). Middle finger & thumb have no palmar interossei . Dorsal are larger & arise from both adjacent MC,They abduct(DAB).Supplied by deep branch of ulnar nerve,They are inserted to the proximal phalange via the extensor expansion hood.

12. Fibrous flexor sheath:- For the long flexor tendons over the metacarpal heads & phalanges. They prevent bowstringing of the long flexor tendons. FDS &FDP tendons pass through them,.The FDS tendon splits to spiral &decussate around FDP to be attached to middle phalange &FDP to distal phalange. The zones of long flexor tendons are :- Zone1 distally containing profundus . Zone2 (No man’s land) containing both FDS & FDP. Zone3 FDP where the lumbricals arise. Zone4 At carpal tunnel. Zone5 above carpal tunnel at forearm.

13. Synovial flexor sheaths:- In the carpal tunnel, the long flexor tendons are invested with a synovial sheath of parietal & visceral layers. The visceral layer sends double folds of synovium called vincula that contain blood supply to the tendon. They extend proximally into the forearm as space of Parona , anterior to pronator quadratus & distally into the fingers.FPL of the thumb & flexors of little fingers have continous synovial flexor sheaths through out ,hence their great mobility & extend 2.5 cm above the wrist in the forearm as Radial (smaller) & Ulnar bursae (larger) The synovial sheaths for index ,middle & ring fingers have interruptions where the tendons are bare &where the lumbricals arise in the palm. >Synovial sheath infection at 2 nd ,3 rd & 4 th fingers may be restricted to the fingers,but that of thumb & little fingers can spread into the wrist & distal forearm. - Space of Parona -may in infection & abscesses as proximal extension of the synovial sheath infection

14. PALMAR SPACES:- The palmer aponeurosis sends from its side fibrous septa into the :- -1)5 th MC > hypothenar space with hypothenar muscles. -2)Middle MC > midpalmar space& thenar space The midpalmar space floor is 3 rd & 4 th MC with their interossei & distally continue as lumbrical canals in the three web spaces. Infection in web spaces >to lumbrical canals > to midpalmar space. The thenar space always contain the 1 st lumbrical . Its floor is adductor pollicis .

15. Arterial arcades in the hand:- Superficial palmar arch:- This is an arterial arcade that lie below the palmar aponeurosis as a direct continuation of ulnar artery beyond the flexor retinaculum . It is completed on radial side by superficial branch of radial artery. It gives common palmar digital arteries >digital arteries at the web to adjacent fingers surfaces ulna surface of little finger,except the radial side of index finger & entire thumb. Deep palmar arch:- This is an arterial arcade mainly by the deep terminal branch of radial artery after passing between the two heads of 1 st dorsal interrossei , then between oblique & transverse heads of adductor pollicis in the palm. It gives palmar metacarpal arteries(3) which anastomose with palmar digital arteries of superficial arch; arteria radialis indicis & arteria princeps pollicis .

16. Digital nerves:- The palmar surfaces of the hand & fingers are supplied by ulna & median nerves only. Radial nerve does not supply the palm.The digital nerves accompany & are deep to digital arteries. The thumb, index , midddle fingers & radial ½ of ring fingers are supplied entirely by digital nerves from median nerve. The little finger & ulnar ½ of ring fingers are supplied by digital nerves from the superficial branch of ulnar nerve.

17. Anatomical snuff box It is visible especially when the thumb is fully extended on the radial side of wrist & thumb. It lies between EPL & EPB together with APL. It contains superficial branch of radial nerve & radial artery ,whose pulse is palpable at the box. Cephalic vein branches also. On its base ,the scaphoid can be felt together with radial styloid process , base of thumb metacarpal & trapezium. Tenderness in the snuff box could be due to # 0f waist of scaphoid , a notorious # because of AVN of proximal # fragment >causing OA of the wrist joint; delayed or non-union of the #.

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