Hand Osteology, Joints & Movement

• The objective is to understand hand osteology and joints.
• The purpose is to also understand differences between the movement of the thumb and the 2nd through 5th fingers
• Another goal is to identify the functions of passive and active stabilizing features
• The objective is to describe the arthrokinematics of the joints of the hand.
• To be able to describe the extensor mechanism and flexor muscles/pulleys of the hand
• The goal is to learn about optimal power grip

The Hand

• It has 5 digits, each with multiple joints.
• The carpometacarpal (CMC) joints, the metacarpophalangeal (MCP) joints and the interphalangeal (IP) joints are the most important
• Fingers 2 through 4 include the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joint
• The thumb has one IP joint.

Metacarpals

• They are numbered 1 to 5 from the radial to ulnar side.
• The thumb metacarpal is the shortest and stoutest
• 2nd metacarpal is usually longest.
• Length of remaining three decreases ulnarly.
• Bases are proximal and interact articualte with one or more carpal bone(s).
• The metacarpal neck just proximal to the head.
• The heads of digits 2-5 are the "knuckles" on dorsum of hand.
• Distal end has large convex head.
• Posterior tubercles serve as attachment sites for MCP joint collateral ligaments.
• The 1st MC is oriented different than others and is rotated ~90 degrees medially relative to other MC's
• Palmar surface faces the midline
• Allows opposition

Phalanges

• Proximal and middle phalanges have concave bases and convex heads
• Distal phalanx has concave base and distal tuberosity.
• Palmar surfaces concave longitudinally.

Arches of the Hand

• Concavity is supported by three arch systems.
• The arch systems are: 2 transverse and 1 longitudinal.
• Concavity control allows grasping, gripping, and object manipulation.

Proximal Transverse Arch

• Formed by carpal distal row.
• Static, rigid arch
• Forms carpal tunnel part.
• Capitate as keystone.
• Reinforced by contacts with other bones and intercarpal ligaments.

Distal Transverse Arch

• Passes via MCP joints.
• Sides of distal arch are more mobile than proximal arch
• Flexibility in the hand happens as the 1st, 4th, and 5th metacarpals "fold" toward the more stable 2nd and 3rd.
• Keystone formed by MCP joints of 2nd & 3rd metacarpals

Longitudinal Arch

• Follows general shape of 2nd and 3rd rays
• Proximal end firmly linked to carpals by CMC joints.
• Provides longitudinal stability
• Distal arch end mobile.
• Keystone of arch defined by 2nd & 3rd MCP joints

Thumb Motions

• Flexion
• Extension
• Abduction
• Adduction
• Opposition

CMC Joints

• CMC joints are the articulations of distal carpals with metacarpal base.
• Gliding movements happen at CMC
• Stability from palmar, dorsal, and intermetacarpal ligaments.
• An open packed hand is midway between flexion and extension
• Close-packed position for hand is full flexion
• Mobility is provided by the 1st, 4th, and 5th digits
• 2nd and 3rd metacarpals are relatively rigid
• The carpometacarpal joints enhance grasp

CMC Joint Mobility

• 4th and 5th CMC joints are highly mobile.
• Mobility of the metacarpal heads can be seen when making a fist.
• Stability is dependent on joint capsules, dorsal CMC ligaments, palmar CMC ligaments, intermetacarpal ligaments

Specific CMC Joints

• Base of trapezoid articulates with the distal trapezoid with the second CMC joint.
• 3rd CMC joint has the base of the 3rd with the distal capitate.
• 4th CMC has fourth base with distal hamate.
• The base of 5th metacarpal articulates with the distal hamate with them 5th CMC

First Carpometacarpal (CMC) Joint

• Saddle joint reciprocally shaped
• Articulation among the first metacarpal base and distal trapezium.
• There is flexion and extension, adduction and abduction and opposition.
• Jt capsule is relatively large, and stability related to muscle actions and ligamentous support.
• In an Open-packed position, pt is Midway b/w ABD & ADD and midway b/w flexion and extension
• Close-packed position is in full opposition

Ligaments of the First CMC Joint

• Radial collateral is relatively thick and strong that is taut with opposition, flexion, abduction and is the prime stabilizer.
• Ulnar collateral is taut in adduction and extension Anterior (palmar) oblique has thin, weak ligament _ The anterior is taut in full extension The palmar oblique function is similar to the radial collateral

Arthrokinematics for the First CMC Joint

• With flexion, there is medial (ulnar) roll and slide of the first metacarpal on the trapezium
• With extension, there is lateral (radial) roll and slide of the first metacarpal on the trapezium.
• With abduction, there is palmar roll and dorsal slide of the first metacarpal on the trapezium.
• With adduction, there is dorsal roll and palmar slide of the first metacarpal on the trapezium.

MCP, PIP, and DIP Joints

• Metacarpophalangeal is MCP
• Proximal Interphalangeal joint is "PIP".
• Phalangeal joint is DIP.
• MCP joints happen between convex metacarpal heads and proximal phalanx concave surface.
• Digits 2-5 articulate with proximal phalanx at biaxial joints and wide proximal base articulating with carpal
• Flexion/Extension, Abduction/Adduction
• ROM increases from 1st-5th MCP.
• Joint capsules.
• Stability from collateral ligaments.
• Generally lax with extension, and become more taut with 70-90 degrees flextion
• Open-packed position in slight flexion
• Close-packed position in full opposition or full flexion

Stability of MCP Joints

• Main stabilizers include collateral ligaments and cross joint in oblique fashion that includes dorsal cord and the thinner accessory portion
• Palmar (volar) plates
• Blend with volar aspect of joint Capsule.
• Resists excessive extension and supports joint stability

With MCP joint flexion:

• Flexible attachments allow plate to slide distally on the metacarpal head without limiting motion.

Deep Transverse Metacarpal Ligaments Structure

• There are about 3 ligaments merging into wide flat structure
• Interconnect and Loosely bind the 2nd and 5th metacarpals

MCP Arthrokinematics

• With flexion, proximal phalanx rolls and slides palmarly on the metacarpal.
• Activation of FPD draws dorsal capsule and collateral cord
• With extension, The proximal phalanx both rolls and slides dorsally on top of the metacarpal
• With extension, the ED with intrinsic coactivation, and the volar plate are more taut and the cord component less taut.
• With abduction, the first dorsal interosseus muscle (DI1) is activated
• In full ABD, ulnar collateral is taut and the radial collateral more slack.
• Direction is dependent on digit

MCP Joint of Thumb

• A hinge joint
• Bony support provides inherent stability
• Movement limited to flexion & extension
• Ligamentous support from anterior and collateral ligaments.
• Articular surfaces convex and concave
• The volar plate increases articular surface ROM.

First MCP and IP Joint Arthrokinematics

• Slide and roll occur in same direction at both joints.
• Flexion: volarly roll & slide
• Extension: dorsally roll & slide

Interphalangeal (IP) Joints

• Hinge joints that are stabilized by the osseous surface
• PIP- stable in most positions
• Joint capsules are made with a volar plate, and the ligaments are maximally taut 25 degrees
• DIP less stable than the PIP
• Position with Slight Flexion during open packing
• Close pack is full extension

PIP Joints

• Articulation is done b/w proximal phalanx, the base of the middle phalanx
• The head of proximal the phalanx has condyles that were separated from a shallow groove
• The middle phalanx has shallow concave facets and is also part if the support system

Support Systems for PIP joints

• radial and ulnar collateral ligaments reinforce them with limitations happening from the collateral ligaments
• Support also from a volar plate and longitudinal support
• The Fibrous tissue support happens using check rein joints
• The support system also assists with extending from the DIP by reinfocing support

Volar Plate

• Thickened fibrocartilage
• It functions to restrain hyperextension at the IP joints
• It improves mechanical advantage and surface area of joints allowing greater ROM

DIP Joint

• Articulations b/w middle phalanx, distal phalanx
• Similar structure to the PIP joint with no check-rein ligaments

Kinematics and Arthrokinematics of PIP and DIP Joints

• Greater flexion in MCP PIP and DIP happens at the more ulnar part of the digits
• There is limited hyperextension
• Near constant tension at IP via ROM
• The arthrokinematics are like DIP and PIP

Flexion Arthrokinematics

• Flexion of PIP is initiated with roll & slide by the concave
• Flexion of DIP is initiated with roll & slide by the distal end
• Joint Capsules assists with this movement to create smooth gliding

Musculature of the Hand

• Intrinsic attachments are proximal
• Extrinsic attachments are on the epicondyles
• A mix of both is important to coordinate

Intrinsic

• The Thenar eminence flexes pollicis brevis
• The Hypothenar eminence abducts digiti minimi
• Other adductor pollicis such as lumbricals and interosseis

Extrinsic

• Flexors digitorum flex digitorums
• the extensor digitorums
• thumb extensors
• These structures help coordinate movement

Extrinsic Flexors of Digits

• Flexor Digitorum (FDS), and has the Action of flexing
• Flexor Digitorum Profundus, and this functions with all joints
• The Pollicus Longus also serves for this function

Flexor Digitorum Superficialis

• Muscle belly just deep to the 3 wrist flexors & pronator teres
• Flexor Structures of the hand include Flexor Pollicis Longus and Flexor Carpi Radalis and the digital attachments on the proximal part of the hand

Flexors

• Flexor digitorum profundus (FDP) deepest muscular plane of forearm
• only DIP flexor, passing splitFDS to palmar aspect of base of distal phalanx
• Flexor pollicis longus (FPL) is in deep plane of forearm
• crosses/attaching side of base of distal phalanx of thumb

Flexor Structures of Hand

• Structures are Ulnar synovial extending from FDS with tendons
• Ends @ distal, and radial continues to its distal place

Flexor Pulleys

• Structures embedded in pulleys, and flexor deep
• Reduces friction to tendons
• Extends with digital

Major Pulleys

• The Pulleys allow attachments of major ligaments attached and assist with volar support
• The Crucicate assist with with transverse movement -Thumb help with ligaments with movements

Flexor Pulley Function

• To help with the flexion without any pinch
• Allows even weight to distribute
• Flexor allows contractions while holding tightly together

Proximal Stabilization

• Requires the Synergistically coordination of the muscles
• This helps amplify the movement of ED

Extrinsic Extensors of Fingers

• Important structures are Extensor digitorum (ED) interconnected by junctura tendinae
• Actuators that control Extensor indicis (EI) & Extensor diagiti (edm)
• Tendons are integrated in to tissues that act as distal attachments in the fingers

The ED Muscles

• ED also controls proximal which helps move from the side for side support
• There is a large amount of oblique support during side movements

Active Components of the Extensor Mechanism

• Dorsal help stabilize proximall the distal phalanx's
• The lumbricals allow tendon and later band to attach from proximal to Distal

Intrinsic Muscles of the Fingers

• These muscles help support the abduction and flexion of the fingers
• This function is for both abduction and adduction with extension

Extensor Mechanism Summary

• Transverse provide the back bone and assists with movement of extensor tendons
• The functions help coordinate at the distal and proximal

Extension

• Contraction during joint movements, and flexion provides help for the IP area
• Coupling is important for Active extension and flexion

In Summary of The Intrinsic

• Both extension and flexion are strong supporters
• Simultaneous contractions with lumbricals produce for side support and movement

Musculature of the Thumb

• This help both the flex ion and extension
• Also provide support for abduction with longus and brevus
• Muscles can assist and and are not complete at this distal stage