Under these but still forming part of the superficial layer is Flexor Digitiorum Superficialis
Flexor Carpi Ulnaris
Forms medial border of forearm
O: From 2 heads
Humeral - from CFO
Ulna - Medial border of olecranon and posterior border of ulna (via an aponeurosis)
Forms a long tendon which inserts into pisiform (investing it) and onto the hook of hamate and base of the 5th metacarpal
A: flexion and ulnar deviation of the wrist
NS: Ulnar nerve C8, T1
Palmaris Longus
Not always present
Lies between FCU and FCR
O: CFO
Forms a ling tendon which passes over the flexor retinaculum to insert into the palmar aponeurosis
A: Weak wrist flexor and tightens the palmar fascia
NS: Median nerve (C8,T1)
Flexor Carpi Radialis
Most lateral of the superficial flexors (lies between palmaris longus and pronator teres)
O: CFO
Forms a long tendon which passes under the flexor retinaculum (in a separate compartment over trapezium) and inserts into the palmar aspect of the bases of the 2nd and 3rd metacarpals
A: Flexion and radial deviation
NS: Median nerve (C6,C7)
Flexor Digitorum Superficialis
Often described a being the intermediate layer
O: from 2 head
Medial – CFO, ulnar collateral ligament and medial border of coronoid
Lateral – from upper 2/3s of anterior oblique line on radius
Forms 4 tendons which pass under the flexor retinaculum (sharing a common synovial sheath with profundus)and insert into the intermediate phalanges of the 4 fingers
At the level of the MCP joint the tendons of FDS split to allow the tendons of profundus through
The 2 halves of the tendon then twist before re-uniting to form a groove for FDP
Before inserting into the intermediate phalanx the tendon splits again
A: Flexion of the PIP, MCP and wrist joints
NS: Median nerve C7,8, T1
Flexors - Deep Layer
These muscles arise from the anterior aspect of the radius, ulna and interosseous membrane
Flexor digitorum profundus
Flexor pollicis longus
Pronator quadratus
Flexor Digitorum Profundus
Deep to FDS on medial side of forearm
O: Fro medial side of coronoid process, upper ¾ of anterior and medial aspect of the ulna shaft and medial ½ of middle part of IOM
Form 4 tendons proximal to the wrist joint which pass to the distal phalanx of the 4 fingers
As the tendons pass under the flexor retinaculum they share a common synovial sheath with FDS
At the level of the MCP joints they pass through the split in FDS to reach their distal attachment on the palmar aspect of the distal phalanx
A: flexion of DIP, PIP, MCP and wrist joints
NS: Laterally via the anterior interosseous nerve (C7, 8, T1) and medially via the ulna nerve (C8,T1)
Flexor Pollicis Longus
Lateral to FDP
O: From anterior surface of radius just below the anterior oblique line but above pronator quadratus and adjacent IOM
Forms a tendon proximal to the wrist joint which passes under the flexor retinaculum in its own synovial sheath
I: Palmar aspect of base of distal phalanx of thumb
A: Flexion of IP, MCP and wrist joint
NS: Anterior Interosseous nerve (C8, T1)
The Flexor Retinaculum
Strong fibrous band of deep fascia
Attached firmly to pisiform scaphoid, trapezium and hook of hamate
Converts the anterior aspect of the carpus into a tunnel
Maintains the concavity of the carpal bones
Laterally it divides into 2 lamellae
These form a separate tunnel for the tendon of FCR
Medially the tendons of FDS, FDP, FPL and the median nerve pass under it
Synovial Sheaths
As the tendons pass under the flexor retinaculum they are all encased in a double layer of synovial membrane
The sheaths begin at the proximal wrist crease
The sheath for FDS and FDP end midway into the palm of the hand (except for the sheath passing to the little finger) - the tendons to the 2nd, 3rd and 4th fingers then have separate sheath from the MC heads
