The document summarizes the muscles and structures on the back of the forearm. There are seven superficial muscles including the brachioradialis, extensor carpi radialis longus and brevis. Deep to these are five deep muscles. Key structures discussed include the extensor retinaculum which holds the extensor tendons in place at the wrist. The extensor digitorum and extensor indicis pass through the retinaculum and fan out over the back of the hand. Near the fingers, the extensor tendon divides and attaches via slips to the dorsal surfaces of the finger bones.

1. Back of Forearm

2. Superficial Muscles
There are seven superficial muscles on the back of the forearm

3. Extensor Retinaculum
• The deep fascia on the back of the wrist is thickened
• Holds the extensor tendons in place
• Oblique band, directed downwards & medially
Attachments
Laterally: Lower part of the sharp anterior border of the radius.
Medially:
i. Styloid process of the ulna
ii. Triquetral
iii. Pisiform

6. BRACHIORADIALIS

8. ECRL
ECRB
ECRL

9. ECRB

10. 1
2
3
4

11. 1
2
3
4

15. Deep Muscles
There are five deep muscles

21. 1
2
3
4
1.The extensor digitorum and extensor indicis pass through the same
compartment of the extensor retinaculum, and have a common synovial
sheath.

23. 1
2
3
4
• 4 tendons of the extensor digitorum emerge from undercover of the extensor
retinaculum and fan out over the dorsum of the hand
• Tendon to the index finger is joined on its medial side by the tendon of the extensor
indicis
• Tendon to the little finger is joined on its medial side by the two tendons of thea
extensor digiti minimi.

24. On the dorsum of the hand, adjacent tendons are variably connected
together by 3 intertendinous connections directed obliquely downwards
and laterally.
The medial connection is strong
The lateral connection is weakest and may be absent
The four tendons and three intertendinous connections are embedded
in deep fascia,
and together form the roof of the subtendinous (subaponeurotic) space
on the dorsum of the hand.

25. Dorsal Digital Expansion/Extensor Expansion
• Is a small triangular aponeurosis (related to each tendon of the
extensor digitorum) covering the dorsum of the proximal phalanx.
• Its base, which is proximal, covers the metacarpophalangeal (MP)
joint.
• The main tendon of the extensor digitorum occupies the central part
of the extension, and is separated from the MP joint by a bursa.
• The posterolateral corners of the extensor expansion are joined by
tendons of the interossei and of lumbrical muscles.
• The corners are attached to the deep transverse metacarpal
ligament.
• The points of attachment of the interossei (proximal) and lumbrical
(distal) are often called 'wing tendons'

26. The dorsal digital expansion of right index, middle, ring and little
fingers. Note the insertions of the lumbricals and interossei into it

27. Near the proximal interphalangeal joint, the extensor tendon divides into
a central slip and two collateral slips.
The central slip crosses the proximal interphalangeal joint, and is
inserted on the dorsum of the base of the middle phalanx.
The 2 collateral slips are joined by the remaining thick margin of the
extensor expansion. They join each other and are inserted on the
dorsum of the base of the distal phalanx.
The retinacular ligaments (link ligaments) extend from the side of the
proximal phalanx, and form its fibrous flexor sheath, to the margins of the
extensor expansion to reach the base of the distal phalanx

28. The muscles inserted into the dorsal digital expansions of:
Index finger:
1st dorsal interosseous, 2nd palmar interosseous, 1st lumbrical,
extensor digitorum slip, and extensor indicis
Middle finger:
2nd & 3rd dorsal interossei, 2nd lumbrical, extensor digitorum slip
Ring finger:
4th dorsal interosseous, 3rd palmar interosseous, 3rd lumbrical and
extensor digitorum slip
Little finger:
4th palmar interosseous, 4th lumbrical, extensor digitorum slip and
extensor digiti minimi