6. ECU
c. Anatomic snuffbox i. Fovea radialis
1. Anterior/ radial border: APL/ EPB 2. Posterior/ ulnar border: EPL 3. Floor: scaphoid trapezium 4. Content: radial artery
d. No man’s land
i. The area where the finger flexor tendons are tightly enclosed within the tenosynovium ii. Located in the palm between the distal palmar crease and the creases of the PIP in the
palm
iii. Generally, primary repair of the tendons in this region is contraindicated iv. Increase in chance of infection, no coating of flexor tendon
v. zones
1. Distal phalanx
2. Refer above no mans land 3. Lumbricals origin
4. Carpal tunnel
5. Proximal to carpal tunnel e. Extensor assembly
i. Tendinous system
1. Tendons of extrinsics extensors 2. Almost all intrinsic muscles, except:
a. PB, OP, ODM, ADM, FDM
ii. Retinacular system: Fascia and ligaments (to retain and stabilize tendons and skin) iii. Function
1. Extends the digits in different positions of finger flexion 2. Provides shortcut to allow full flexion
iv. Remember:
v. Motor input into the lateral bands for each finger:
1. Extrinsic extensors 2. Lumbricals 3. 2 interossei vi. Central band
1. Serves as the back bone of the extensor mechanism 2. Transmits extensor force from the ED across the IP joint 3. Boutonniere deformity
vii. Lateral band
1. Transmit extensor force from the ED, lumbricals, and interossei across the PIP and DIP joint
2. Mallet finger lesion viii. Dorsal hood transverse fibers
1. Stabilize the ED tendon over the dorsal aspect of the MCP joint from a sling around the proximal end of the proximal phalanx, thereby assisting the ED in extending the MCP joint
ix. Dorsal hood oblique fibers
1. Transfer force from the lumbricals and interossei to the lateral bands of the extensor mechanism, thereby assisting with extension of the PIP and DIP joints x. Oblique retinacular ligament: Helps coordinate movement between the PIP and DIP of the
fingers.
f. Flexor Pulleys
i. Annular pulleys:
1. Attached to the shafts of the proximal and distal phalanges and to the sides of the volar plates of the MCP, PIP, and DIP joints at the junction with the extensor hood and the retinaculum.
2. Prevents bow stringing effect of long flexor tendons during flexion.
ii. Cruciate pulleys
1. Attach on the shafts of the phalanges and cross to from distal attachments on the volar plates of the PIP and DIP joints.
iii. These pulleys prevent bowstringing of the long flexor tendons during flexor activities iv. Severance of a pulley causes loss of finger motion.
g. Power and precision grips
Grip Description Finger function Thumb function Example of uses
Precision Lateral
pinch grip Aka. Key grip. The least precise.
Small object placed between the index finger and thumb.
Index Finger is abducted at the MCP joint and partially flexed at the MCP and IP joint. Muscles include FDP, FDS, and first dorsal interossei
Thumb is abducted and IP joint is flexed.
Muscles include FPL, FPB, and adductor pollicis prehension grip. Pads of distal 2nd and 3rd digits contact pad of thumb for the purpose of picking up or grasping objects
MCP and PIP joint flexion.
Possible DIP flexion. The FDS performs the task if the DIP is in extension, but if the DIP is partially flexed, the FDP is also activated.
Interossei work to provide MCP abduction and adduction.
Thumb is positioned in opposition, flexed at MCP and IP joints and adduction at CMC joint. Muscles include adductor pollicis working with FPB to stabilize the first metacarpal while FPL flexes the thumb joints
Grasping a coin, using a writing utensil such as pen or pencils
Tip to Tip
grip Aka. Tip prehension grip. Thumb faces one of the fingers. Most often used is index finger.
Purpose of picking up or manipulating small objects
The finger used is in flexion at all 3 joints. Some lateral movement of the MCP towards the ulnar side occurs to allow the finger to meet the thumb with the fingertip facing a radial direction. FDP plays a greater role.
Thumb is in opposition with flexion at MCP and IP. Thumb is also adducted so the tip is aligned with opposing finger’s tip. FPL plays an important role in this grip
Picking up a small object such as a pin, bead, or strand of hair.
Power Hook
Grip Finger digits provide this grip. Use primarily to support or carry an object
Fingers and palm are primary contributors. Primary function from FDS and FDP
secondarily with IP joint flexion especially at the PIP.
Thumb does not contribute to this grip.
Held in extension away from the hand.
Carrying a barbell off the floor
Cylinder
Grip Grasp objects that are cylindrical in shape and large enough that the thumb does not touch the fingers. The fingers and palm are on one side of the object and thumb is on the opposite side.
Flexion of MC and IP with activity of FDP. The FDS assists when increased forces are required.
Interossei muscles flex MCP joints and move in an ulnar direction and counteracted by Radiocollateral ligements.
Fingers lie adjacent and parallel to each other with contact with adjacent fingers
Thumb position varies.
Often it flexes and adducts acting as a vice to secure the object to fingers and palm. Rotation to provide opposition at CMC joint but depends on the width of the grip.
Holding a beverage container or a telephone receiver incorporates the cylinder grip.
Spherical
Grip Grasp round objects.
Fingers are spread apart more than in the cylinder grip. Interossei work more in this grip. The grasp is adjusted to the size and shape of the spherical object.
MCP abducted and partially flexed. Abductor and Adductor interossei co-contract to stabilize MCP joints. Extrinsic flexor muscles work to flex the fingers. ED contracts to counteract the flexor force and control release of object.
Thumb position varies according to size and weight of the object.
Thumb opposed the other fingers and is flexed at MCP and may be flexed at IP joint. Adductor pollicis and other thenar muscles are active.
Holding a ball or an apple
Fist grip Aka. Digital palmar prehension pattern.
Palm and fingers flex around the object and the thumb wraps around from the other direction to enclose the object.
Objects grasped are usually not large since the thumb closes over the object and often incontact with the digits.
All three joints of the digits are flexed. Digits are usually parallel to one another. Firm grasping is provided by the FDS and FDP.
Thumb is held in adduction against the object or in opposition to fingers. Thumb is used to provide a counterforce against the finger flexors to maintain the object in the hand.