Hand Osteology and Joints

Hand Osteology and Joints

• The hand consists of five digits, each containing multiple joints
• The carpometacarpal (CMC), metacarpophalangeal (MCP), and interphalangeal (IP) joints are all present
• Fingers 2 through 4 each have a proximal (PIP) and distal (DIP) interphalangeal joint, while the thumb has only one IP joint
• The metacarpals are numbered 1 through 5, moving radially to ulnarly
• Metacarpal 1 (the thumb) is the shortest and stoutest, while metacarpal 2 is usually the longest
• The remaining metacarpals (3-5) decrease in length ulnarly
• Metacarpal bases are proximal and articulate with different numbers of carpal bones
• The heads of metacarpals 2-5 form the knuckles on the hand's dorsal side
• The distal end of all metacarpals have large convex heads
• Posterior tubercles on the metacarpals serve as attachment sites for the MCP joint's collateral ligaments
• The first metacarpal is in a different plane and rotated about 90 degrees medially, with the palmar surface facing the midline, enabling thumb opposition for grip and pinch
• Proximal and middle phalanges feature a concave base and convex head
• Palmar surfaces of middle and proximal phalanges have a slightly concave longitudinal profile
• Distal phalanges have a concave base and a distal tuberosity

Arches of the Hand

• Three arch systems support the concavity of the hand
• 2 transverse arches
• 1 longitudinal arch
• Concavity control allows for grasping, gripping, and object manipulation
• The proximal transverse arch comprises of the distal row of carpal bones
• It is a static, rigid arch that that forms a portion of the carpal tunnel
• The capitate bone serves as the keystone
• It gains reinforcement from bone contacts and intercarpal ligaments
• Distal transverse arch goes through the MCP joints
• Sides of the distal transverse arch are mobile
• Transverse flexibility enables the 1st, 4th, and 5th metacarpals to "fold" around the more stable 2nd and 3rd
• The keystone for the distal transverse arch gets formed by the MCP joints of the 2nd and 3rd metacarpals
• The longitudinal arch follows the general shape of the 2nd and 3rd rays
• The arch's proximal end is rigidly linked to the carpals via the CMC joints
• Provides longitudinal stability to the hand
• The arch's distal end is mobile
• Keystone of the arch can be found at the 2nd and 3rd MCP joints

Thumb Movements

• Thumb motions include flexion, extension, abduction, adduction, and opposition

CMC Joints

• The distal carpals articulate with the base of the metacarpals at these joints
• Gliding movements are only permitted
• Anterior (palmar), posterior (dorsal), and intermetacarpal ligaments provide stability
• The open-packed position is midway between flexion and extension
• The closed-packed position is fingers in full flexion
• The 2nd and 3rd metacarpals have relatively restricted movement
• The 1st, 4th, and 5th metacarpals are more mobile
• Mobility facilitates manipulation of diverse items
• The 4th and 5th CMC joints have greater mobility
• Observed by looking at the metacarpal heads while making a fist
• Jt capsules, dorsal CMC ligaments, palmar CMC ligaments, and intermetacarpal ligaments support the joints
• Dorsal ligaments are better developed and more comprehensive compared to palmar ligaments
• The 2nd CMC joint consists of the base of the 2nd metacarpal with the distal trapezoid, and exhibits smaller articulations with the capitate and trapezium.
• The base of the 3rd metacarpal has a joint with distal capitate
• The 4th CMC joint has a base of the 4th metacarpal with a distal hamate, displaying a smaller articulation with the capitate
• The 5th CMC joint's base of is linked with with the distal hamate

1st Carpometacarpal (CMC) Joint

• It's a saddle-shaped joint with reciprocally shaped joint surfaces
• The articulation exists between the 1st metacarpal base and the distal trapezium
• Flexion, extension, adduction, abduction, and opposition are allowed at the joint
• The joint capsule has a large and lax size
• Stability stems from muscular activity and ligamentous support
• The open-packed position is characterized by being midway between abduction and adduction, as well as midway between flexion and extension
• The closed-packed position involves full opposition
• The radial collateral ligament is strong and taut during opposition, flexion, and abduction
• It is the key stabilizer of the opposed CMC joint
• The ulnar collateral ligament remains taut during abduction and extension
• The anterior (palmar) oblique ligament, is thin and weak, and taut when in full extension
• The posterior oblique ligament works similarly to the radial collateral ligament

Arthrokinematics of the 1st CMC Joint

• Flexion involves a medial (ulnar) roll and glide of the 1st metacarpal on the trapezium
• Extension entails a lateral (radial) roll and glide of the 1st metacarpal on the trapezium
• Abduction is achieved through a palmar roll and dorsal slide of the 1st metacarpal on the trapezium
• Adduction includes a dorsal roll and palmar slide of the 1st metacarpal on the trapezium

MCP, PIP, & DIP Joints

• MCP = Metacarpophalangeal
• PIP = Proximal Interphalangeal
• DIP = Distal Interphalangeal
• MCP joints are formed between the convex heads of metacarpals and concave proximal surface of proximal phalanges
• 2nd though 5th metacarpals articulate at biaxial joints with their respective phalanges
• Widened proximal bases articulate with carpals
• Jts allow flexion, extension, abduction, and adduction
• From 1st to 5th MCP, flexion ROM increase
• Joint capsules are lax and stability gets derived from collateral ligaments
• Extension generally has general laxity
• Collateral ligaments become taut in 70–90° of flexion
• Open-packed position is slight flexion
• Closed-packed position is full opposition (thumb)/full flexion (fingers)
• Collateral ligaments cross joints in an oblique way
• The dorsal cord is thicker and stronger, while the accessory portion is thinner, fan-shaped, and attached to the palmar (volar) plate
• Dense fibrocartilage, called volar (palmar) plates are on the palmar side of jts
• Bases get attached to the proximal phalanx
• Necks of metacarpals are part of the attachment process
• Capsule blends with the volar part, which resists overextension and improves jt stability
• Flexible attachments allow the sliding of the plate proximally on the metacarpal head when the MCP joint flexes
• Deep transverse metacarpal ligaments comprised of three ligaments that interconnect and loosely bind the 2nd to 5th metacarpals into a wide, flat structure
• Proximal phalanx performs a palmar (anterior) roll and slide along metacarpal during flexion
• Activation of the flexor digitorum profundus (FPD) happens during flexion
• Dorsal capsule plus the radial collateral ligament creates tension

MCP Arthrokinematics During Extension

• The proximal phalanx rolls and slides dorsally on the metacarpal
• It results from coactivation of ED and finger's intrinsic muscles
• The palmar plate becomes taut, and the cord portion of the radial collateral ligament develops slack
• Abduction gets driven by activating the 1st dorsal interosseus muscle (DI1)
• The ulnar collateral ligament becomes taut, whereas the radial collateral ligament becomes slack
• Proximal phalanx performs rolls and slides in the equivalent direction to the digits
• The thumb's MCP joint has a hinge design that permits flexion and extension
• Both the bone structure supports and enhances stability
• Ligamentous support gets acquired through anterior (palmar) and collateral ligaments
• An existing convex head of the metacarpal plus a concave surface on the base of the phalanx facilitates stabilization
• Greater ROM is correlated to Volar plate increases articular surface stretch

1st MCP and IP Joint Arthrokinematics

• The phalanx slides and rolls in the same direction at both joints, which means that flexion generates a volar roll and slide, whereas extension produces a dorsal roll and slide

Interphalangeal (IP) Joints

• They're hinge joints, which enable extension and flexion
• Stability comes from the the form of the osseous surfaces
• PIP joints are quite stable in every position
• Capsules are composed of a volar plate, collateral ligaments, and extensor expansion
• The collateral ligaments become maximally taut when the finger is flexed at 25° with the PIP
• DIP joints are less stable than PIP joints
• Open-packed position happens with minimal flexion
• Full extension comprises the closed-packed position
• Proximal interphalangeal (PIP) Joint articulations exist between proximal phalanges and middle phalanges
• Heads of the proximal phalanx have two condyles separated by a shallow groove
• Middle phalanx has two shallow concave facets divided by a centre ridge
• The IP jt capsule gets reinforced by radial and ulnar ligamentous bands
• The collateral ligament's cord parts reduce adduction and abduction with with PIP bending
• Accessory parts blend with and strengthen the palmar plate
• Proximal-lateral areas along the palmar aspect that are responsible for stabilizing ligaments
• These structural areas will provide Check-rein strength.
• Assist in resisting hyperextension
• Mobile, thickened fibrocartilaginous structure
• Serves as a restraint to hyperextension

DIP Joints

• Articulations occur between the bases and heads of the middle phalanges
• DIP jt structure/tissues are comparable with the PIP structure
• No check-rein ligaments are present
• MCP, PIP, and DIP articulation in the ulnar digits happens better overall
• The PIP jts enable extremely limited hyperextension
• MCP and DIP joints enable some degree of hyperextension
• Virtually continuous quiescent stabilization exists due to collateral ligaments with IP joints at the target level for range of motion
• Arthrokinematics for DIP joints and PIP joints mirror

Musculature of Hand

• The muscles with distal and proximinal attachments to the hand
• Muscles of the hand with attachments proximal to the forearm/humerous
• Hand movements work best if movements coordinate between extrinsic muscles,intrinsic muscles,plus wrist musculature

Intrinsic Muscles of the Hand

• Thenar Eminence: abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis
• Hypothenar Eminence: abductor digiti minimi, flexor digiti minimi, opponens digiti minimi, and palmaris brevis
• Other: adductor pollicis (2 heads), lumbricals (4), and interossei (4 palmar & 4 dorsal)

Extrinsic Muscles of the Hand

• Flexors of the digits: flexor digitorum superficialis, flexor digitorum profundus, and flexor pollicis longus
• Extensors of the fingers: extensor digitorum, extensor indicis, and extensor digiti minimi
• Extensors of the thumb: extensor pollicis longus, extensor pollicis brevis, and abductor pollicis longus

Extrinsic Flexors of the Digits

• Flexor Digitorum Superficialis (FDS): responsible for flexion of the PIP joints while also assisting in flexing every joint
• Flexor Digitorum Profundus (FDP): responsible for flexing at every crossing joint while performing primary functions by flexing the distal joint
• Flexor Pollicis Longus (FPL): responsible for flexion of the thumb IP joints.
• The muscle belly of the FDS lies deep to the 3 wrist flexors & pronator teres
• The FDS has four tendons that cross at the wrist and enter palmar side of the hand
• Splits near proximal phalanx allowing access and passage to the FDP as well
• After tendon splits it crosses the PIP joints and connects on either the end of the palmar at the middle phalanx

Flexor Digitorum Profundus (FDP)

• Muscles from within the belly reach the deepest areas for all the muscles at the forearm
• Each tendon is connected directly by the FDS allowing attachment on the palmar surface to the distal phalanx
• Sole source of flexion activity for flexor stabilization that is independent of joints that cross it
• Motion limited with interconnection on both tendons plus single fingers

Flexor Pollicis Longus (FPL)

• Located close and side by side from FDP at the surface muscles with the forearm
• Extracellular membrane passes through the wrist attaching distally towards lateral side on the distal joints on the thumb side
• Force of flexion with exertion with motion by torque (rotation) during MCP for thumb use

Flexor Structures of the Hand

• Surrounds FDS/FDP that extend to capral tunnel
• Ends inside primary hand area
• Tendons get found and connected at the 5th digit
• FPL tendons extend to tip
• Flex tendons get secured due to fibrous coatings

Flexor pulleys

• Flexor tendons get weaved across every sheath
• Tendons get coated deeply as well all the way up.
• Nutrients can supply more due to sheathing.
• Synovials also lubricate the tendons too.

Flex Pulleys:

• Every finger area has 5 annular pulleys numbered as A5 going across
• The more important, the A2 and A4 connect to where the bone is by each finger.
• The rest of the area has pulleys that attach directly inside these areas including C1-3 that secure in distinct areas and are thin/flexible
• For thumbs, ligaments give support for this as well.

Passive Flexor Elements Include

• Connects tendons at areas around the joint to hold together
• The A1 and A4 pulleys keep bowstringing from tendons going bad during tension
• The altered bio-mechanics of the finger flexion could then get severed or over time worn down resulting in elite climbers having finger issues related

Proximal Stabilization During Finger Flexion

• Extensor tendons help by joining and helping synergistic activity to single areas.
• ED contracts to stabilize MCP.
• Distal tension will get amplified more with FDS but needs stabilized with ECRL ED EDBC more than force
• The extrinsic digit extensors are the extensor digitorum (ED), extensor indicis (EI), and extensor digiti minimi (EDM), which sometimes has two tendons

Extensor Mechanism

• The attachment point exists in most muscles that are on the fingers and distal to wrist with the extensor assembly
• Small parts of the ED tendons will get combined with connecting muscles
• The lateral areas branch out for distal areas to attach
• Forces to the end parts could allow these extensions to do transfer for the best finger use

Extensor Mechanism Function

• The most identifiable aspect out is a hooded structure that has fiber support built in and connects transverse points allowing constant tension to the joint to keep in place

Parts of The active extension mechanism

• There are fibers connecting and stabilizing ED as well around it making every part connected with the transverse fibers
• Running all sides will allow these stabilizers to have best tension and support. Connective sides can allow good mobility and fusion to fibers
• Ret Lig prevent pull on joints and also enable muscle activation

Active Component of Extension

• Dorsal interossei, palmar interossei, and lumbricals participate
• Interossei muscles arise from side of MCP plus phalanxes attaching around it
• Fibers get formed into side band structures in a connecting form mostly that connects areas around them. Also attaching the lateral muscles all connected through side cords that enable every force and allow fibers to travel effectively to the finger as much as possible. Lats travel to joints too
• Every part works in support of the thumb too as much as possible allowing every kind of strength as best

Lumbricals

• Strong support for tendons for joints on the hand that will help connect and protect the rest of the finger that will have a lot of mobility and also support stabilization in each joint
• The lumbricals function with strong and synergistic effects that can give best performance of the thumb All these connections perform their peak action with synergy and control all different phases

Retinacular Ligaments

• Will run side by side and allow support with the joint as the major objective
• By assisting each muscle, it allows full control and motion of the hand preventing injury and giving support so muscles don’t take full force

Hyperextension of MCP

• Prevents force while preventing flexion while both parts need each ability and synergistic ability to maintain its posture

Synergistic Movement

• Tendons have active functions that allow each one to keep the synergistic motion in play along where most function is generated and most power will get delivered

Structure of thumb extension

• Extensors, like the EPL helps stabilize the thumb from losing joint support
• Synergistic work is made to happen to provide best performance and support between both

Extrinsic Musculature of the thumb

• Flexor Pollicis Longus (FPL) flexes at the thumbs IP JT for bending at thumbs
• The EPB (extensor Poll Brev), enables extension motion while taking from hand the support is required
• EPL, provides stability and extensions at the joint.
• Pull motions provided by these muscles help hand use

Active movements with thumbs

• ABD/AD can enable the thumb for peak Rom
• Thumb function is key to every hand motion such as grasping This allows stabilization also