Specialised Structures on the Hand

Question 1

Carpal tunnel + flexor retinaculum

Answer 1

• Scaphoid tubercle + trapezium to pisiform + hook of hamate
• Contains long (finger + thumb) flexor tendons
• Attachment site for muscles e.g. PL, all 3 thenar mm, AbdDM, ODM
• Carpal bones sit at the floor of the tunnel, flexor retinaculum sits along the top = roof of tunnel (they sit directly above carpal bones)
• Provides a single space for transmission of 9/10 tendons + median nerve (FDSx4, FDP x4, FPL
• FCU + palmaris longus = not in carpal tunnel = sit superficial to the flexor retinaculum
• FCR = has its own tunnel

Question 2

Fibrous Flexor Sheath/ ligaments + Synovial Sheaths

Answer 2

• The finger flexors are surrounded by a continuous synovial membrane, reinforced by annular + cruciate ligaments
• Sheath acts to: i) facilitate smooth gliding of tendons ii) create a mechanical adv + iii) maintains tendon health (nutrition) via synovial fluid supply
• Holds the tendon so its sits directly on the bone + palmar plates
• The synovial sheath/ membrane produces synovial fluid
• The fibrous flexor sheath, comprised of annular + cruciate fibres, reinforces it & prevents bowstringing

Question 3

Palmar Aponeurosis (fascia)

Answer 3

• Strengthens the hand for gripping
• Protects underlying vessels + nerves
• Vertical septa fibres – form compartments
• Consists of longitudinal bands + horizontal fibres – dense regular connective tissue – connected to skin & flexor retinaculum

Question 4

Extensor Retinaculum + Extensor tunnels (6 of them)

Answer 4

• Multiple compartments in contrast to flexor side
• 6 compartments numbered starting from radial to ulna direction
• Separates + retains the alignment of the thumb + finger extensors
• Prevents bowstringing to increase mechanical efficiency
• ALSO PREVENTS BOWSTRINGING

Question 5

Extensor tunnels (whats in each)

Answer 5

Tunnel 1: APL + EPB
Tunnel 2: ECRL + ECRB
Tunnel 3: EPL
Tunnel 4: EI + ED
Tunnel 5: EDM
Tunnel 6: ECU

Question 6

Extensor Synovial Sheaths

Answer 6

Same function as flexor synvoial sheaths

Question 7

Intertendinous connections

Answer 7

• Fascial interconnections b/w the 4 finger extensor tendons
• Plays some role in distributing forces b/w extensor tendons
• EDM + EI = are loose tendons = do not connect to the ED = do not connect also to intertendinous connections
• Help w/ the alignment of the tendons, help prevent excessive splaying of the tendons or movt of the tendons over the MCP joints

Question 8

Extensor tendon insertion - Dorsal Digitial Expansion

Answer 8

• The extensor tendons split into 3 parts at the proximal phalanges:
  1. central slip inserts onto the middle phalanx
  2. lateral slips on both sides rejoin at the distal phalanx to insert.
• They displace volarly in flexion & return to dorsum in finger extension
• Lumbricals, from the FDP tendon, insert onto the radial (lateral) band. They create MCP flexion by pulling the dorsal aspect of the finger into flexion
• The palmar + dorsal interossei muscles also insert on the Dorsal Digital expansion
• Anything that pulls on the DDE is going to extend the PIP + DIP joints