Anatomy I

How many bones are in the hand?

19 major bones of the hand: 5 metacarpals and 14 phalanges There are 5 metacarpals, one of each digit and are commonly named I for the thumb, II for index, III for middle, IV for ring and V for the small finger. Each one has a base, a body or shaft, and a head (listed proximal to distal).

1st CMC joint (trapeziometacarpal joint) is between the base of the thumb MC and the trapezium. What movement is allowed here and why?

1st CMC joint (trapeziometacarpal joint) is between the base of the thumb MC and the trapezium. Axial rotation (opposition) is allowed here due to soft tissue restraints being somewhat lax. This rotation is what makes the thumb useful and functional.

If the interosseous muscles are paralyzed what flexes the MCP joints?

According to electromyographic studies, the lumbricals contribute little to MCPJ flexion. However, if the interossei are paralyzed the lumbricals can initiate MCP joint flexion. MCP joint flexion is achieved through the FDS and FDP. NOTE: the FDS and FDP (extrinsic muscles) flex the IP joints first. When the PIP/DIP are fully flexed the MCP joint will flex

Metacarpophalangeal Joints (MCP) (MPJ) Where is the abduction/adduction point of reference?

Adduction and abduction point of reference is the middle finger and the middle finger either radially or ulnarly deviates

All CMC joints are synovial meaning it is a type of joint that:

All CMC joints are synovial meaning it is a type of joint that is surrounded by a thick flexible membrane forming a sac into which is secreted a viscous fluid that lubricates the joint.

Dorsal interosseous muscles have how many muscle bellies?

All dorsal interossei have two muscle bellies. They insert into bone (proximal phalanx) and soft tissue (extensor mechanism).

The interosseous muscles are innervated by what nerve?

All interossei are innervated by the ulnar nerve

PIP jt What is the transverse retinacular ligament and it's origin and insertion

Anatomy: originates on the flexor tendon sheath at the PIP and inserts on the lateral edges of the conjoined bands Function: prevents excessive dorsal shift of the lateral bands when the PIPJ extends and when in flexion they assist with pulling the lateral bands volarly over the PIP

PIP jt Oblique Retinacular Ligament: (might also see it termed oblique retinacular ligament of Landsmeer) Function, origin and insertion

Anatomy: the ORL originates from the proximal phalanx and then inserts into the terminal extensor tendon crossing the collateral ligaments Function: It links the motion of the DIP and PIP

Carpometacarpal Joints (CMC) Are the most ____________joints in the hand

Are the most proximal joints in the hand

As the PIP joint flexes, the ____________ ______________ _____________ folds and the VP migrates proximally allowing joint flexion

As the PIP joint flexes, the accessory collateral ligament folds and the VP migrates proximally allowing joint flexion

As the PIP joint flexes, the tension on the____________ _______________ _______________ increases because it stretches over the wide area of the proximal phalanx

As the PIP joint flexes, the tension on the proper collateral ligament increases because it stretches over the wide area of the proximal phalanx

Metacarpophalangeal Joints (MCP) (MPJ) Which motion is permitted only passively

Axial rotation is permitted only passively

Proximal Interphalangeal Joint (PIP Joint) Check-rein ligaments

Check-rein ligaments are the longer proximal attachment of the volar plate and tighten as the middle phalanx extends and limits hyperextension

There are two portions of the collateral ligaments: proper or true (band) and accessory (fan) ligaments Clinically, which ligament must we respect in relation to pathology?

Clinically, the proper collateral ligament is the ligament we must respect in relation to pathology

Contraction of lumbricals will relax what muscle?

Contraction of lumbricals will relax the flexor digitorum profundus as it draws the lateral band proximally and pulls the FDP distally It is well accepted in the literature that when the lumbrical is contracted, the FDP is relaxed; when the FDP is contracted, the lumbrical is relaxed

Extensor mechanism, also known as:

Digital dorsal mechanism/hood Extensor expansion Extensor assembly Extensor apparatus Dorsal aponeurosis Aponeurotic sleeve

Arches of the Hand Distal transverse arch:

Distal transverse arch: Courses across the hand, distally. At the level of the metacarpal heads and is also a dorsal convexity

What muscles are synergists to the lumbrical muscles?

Dorsal interosseous Palmar interosseous FDP FDS

BG What clinical examination test indicates rupture to the central slip?

Elson's test https://www.youtube.com/watch?v=G9HY0qXWUvE Very interesting phenomenon and easy test to do before a deformity makes the injury apparent

Peripheral Nerves of the Hand Ulnar Nerve Enters the hand through what structure?

Enters through Guyon's canal

Ligaments of the Thumb CMC: Ulnar collateral ligament Origin and insertion

Extends from the transverse carpal ligament to the palmar-medial base of 1st metacarpal Volar and medial aspects of the CMC joint

BG The proper collateral ligament (CL) is taught in full extension hence why it is important to always place MPs in full extension after injury to recover. True or False

FALSE - the Proper CL at MCP in full extension are Loose and in flexion proper CL is taut. Orthotics and positioning should place the MCP in flexion to put the CL on tension and prevent shortening of this important ligament

BG As the extensor tendon crosses the MCPJ it attaches to the proximal phalanx. True or False

False - It is not functionally attached to the proximal phalanx but to the extensor hood mechanism and ultimately the DIPJ

Distal Interphalangeal Joint (DIP Joint) Triangular Ligament Origin and insertion? Function?

Function: Counteracts pull of the ORL and prevents subluxation of the common extensor mechanism Anatomy: triangular in shape and is located distal to the PIPJ

PIP jt Volar plate Function, origin and insertion

Function: prevent hyperextension Anatomy: thickening of joint capusule volar to the MP joint; origin is the head of the metacarpal and insertion is via the checkrein ligaments Biomechanics: loose in flexion and tight in extension

What is the functional purpose of the ORL ligament?

Functional importance is not totally known but it is believed to coincide with DIP joint and PIP joint movement

What does it mean if DIP joint passive motion is resisted when PIP joint is extended?

If DIP joint passive motion is resisted when PIP joint is extended versus flexed, then the ORL is tight or contracted since the ORL is tightened when the PIPJ is extended

If the ORL is tight what happens to the DIP joint?

If the ORL is tight, the DIP joint cannot flex or will have difficulty flexing

In about 3% of cases the first dorsal interosseous is innervated by what nerve?

In about 3% of cases the first dorsal interosseous is innervated by the median nerve

Vascular Supply to the Hand In the fingers, the palmar digital nerves lie superficial to what structures?

In the fingers, the palmar digital nerves lie superficial to the palmar digital arteries

Vascular Supply to the Hand In the palm, the superficial arterial arch and its branches lie superficial to what structures?

In the palm, the superficial arterial arch and its branches lie superficial to the common palmar digital nerves

The thenar muscles are innervated by what nerve?

Innervated by the recurrent branch of the median nerve (motor branch of median nerve distal to carpal tunnel)

BG What exercise is most important for a patient who is developing a boutonniere deformity?

Isolated DIPJ flexion with the PIPJ held in extension

Peripheral Nerves of the Hand Median Nerve Just distal to carpal tunnel it forms what structure?

Just distal to carpal tunnel it forms the recurrent branch of the median nerve (motor portion innervating the thenars) and the digital branches (common palmar digital nerves and proper digital nerves)

Arches of the Hand Longitudinal arch:

Longitudinal arch: Courses the length of the hand. The dorsal convexity of the metacarpal and phalanges forms this arch

In regard to the IP joints, how do the lumbricals function?

Lumbricals are primary extensors of the IP joints, irrespective of MCP joint position

Lumbricals assist with what functional movement?

Lumbricals assist with pinch by exerting force to the base of the finger which will oppose the thumb

When a full fist is achieved the lumbricals may do what?

Lumbricals may be pulled into carpal canal & recede proximally to the distal end of radius when a full fist is achieved

What is the origin and insertion of the lumbrical muscles?

Lumbricals originate from the FDP and insert into the radial lateral band of each finger First two lumbricals originate from the FDP of the index and middle fingers (median nerve innervated) 3rd lumbrical arises from the FDP of the middle and ring fingers (ulnar nerve innervated) 4th lumbrical from FDP of ring and little (ulnar nerve innervated)

Ligaments of the Thumb CMC: What is the Beak ligament (anterior oblique ligament) and what is its function?

Major stabilizing factor for the 1st CMC joint Interconnects the palmar tubercle (beak) of the metacarpal base and the distal part of a ridge on the tubercle of the trapezium Tight in abduction, extension, and opposition

When are the lumbricals are at their maximum length?

Maximum length of lumbricals is when you have a full fist

PIP jt Oblique Retinacular Ligament: (might also see it termed oblique retinacular ligament of Landsmeer) Pathophysiology

May be involved with Dupuytren's and contracture of it may contribute to displacement of the lateral bands and boutonniere injury

In relation to the MCP joints, how do the lumbricals function?

May contribute to or help with MCP joint flexion Ensures MCP joint flexes prior to the IP joint and allows for grabbing large objects Lumbricals are being pulled by the FDP Assist with MCP joint flexion; interossei are the primary MCP joint flexors Flexor digitorum profundus also contributes to MPJ flexion When MCP joints are stabilized, lumbricals may assist with abduction of the finger

BG What structures run through the carpal tunnel?

Median nerve Flexor pollicus longus Flexor digitorum profundus Flexor digitorum superficialis 10 structures in total...

Metacarpophalangeal Joints (MCP) (MPJ) What is the shape of the metacarpal head?

Metacarpal head is biconvex, cam-shaped so it extends further volarly than dorsally and is wider volarly than dorsally

What are intrinsic muscles?

Muscles that originate and insert within the hand are intrinsic muscles.

Thenar Muscles A good way to remember the thenar muscles is that they spell OAF

O=Opponens pollicis A=Abductor pollicis brevis F=Flexor pollicis brevis

ORL contraction or tightness may cause what structures to displace? This can lead to what pathology?

ORL contraction or tightness may cause lateral band displacement, which can lead to a boutonniere deformity.

Describe the lumbrical muscles

Originate from soft tissue and insert into soft tissue Contribute to the dorsal mechanism Its own antagonistic structure Fibers run longitudinally Workhorse of the hand

Lumbricals originate from and insert into what?

Originates from flexor digitorum profundus (FDP) Inserts into the dorsal mechanism

Peripheral Nerves of the Hand Superficial Radial Nerve passes superficially through what structures?

Passes superficially to the anatomic snuff box and EPL Purely cutaneous

Peripheral Nerves of the Hand Median Nerve passes through what structure?

Passes through carpal tunnel as the most volar structure

PIP jt What happens when the Transverse Retinacular Ligaments is attenuated?

Pathology: attenuation of these ligaments leads to excessive dorsal position of the lateral bands and ultimately a swan neck or with a contracture of the transverse retinacular ligament and attenuation of the triangular ligament will lead to translation of the lateral bands and a boutonniere deformity.

Distal Interphalangeal Joint (DIP Joint) Triangular Ligament Pathology

Pathology: contracture leads to swan neck deformity

The Elson's test essentially isolates the central band/slip of the extensor tendon complex Describe Elsons test

Position the patient's PIP in 90-degrees flexion. This normally keeps the central band taut and the lateral bands loose. Ask the patient to extend the PIP, while the provider's finger applies counterforce at the middle phalanx. NORMAL Elson's test: Results in active extension of the PIP joint and a floppy DIP. ABNORMAL Elson's test: Results in no active extension of the PIP joint and a slightly extended, taut DIP.

Describe the interosseous muscles

Primary MCP joint flexor

Arches of the Hand Proximal transverse arch:

Proximal transverse arch: Courses across the hand, proximally. Formed by the base of the metacarpals being less wide volarly than dorsally

Peripheral Nerves of the Hand Superficial Radial Nerve is purely:

Purely cutaneous

Digital Dorsal Mechanism Sagittal bands are ______________ fibers coming off of the common extensor tendon

Sagittal bands are transverse fibers coming off of the common extensor tendon

Sagittal plane: Frontal (coronal) plane: Transverse (horizontal) plane:

Sagittal plane: Divides the body vertically into right and left parts Frontal (coronal) plane: Divides the body vertically into front and back portions Transverse (horizontal) plane: Divides the body horizontally into superior and inferior portions

When are the lumbricals are the shortest length?

Shortest length of lumbricals is when the hand is fully extended

Metacarpophalangeal Joints (MCP) (MPJ) Soft tissue restraints limit motion to:

Soft tissue restraints limit motion to flexion/extension and adduction/abduction

Some believe that the ORL may be involved with what pathology?

Some believe that the ORL may be involved with Dupuytren's contracture causing PIP joint flexion and DIP joint extension

Oblique Retinacular Ligament (ORL) What is it and what are its origins and insertions?

Sometimes referred to as Landsmeer's ligament ORL arises at the level of proximal phalanx A cord that runs from the sheath of the flexors (PIP joint level) to the terminal extensor tendon Continues to the terminal extensor tendon Volar to the axis of the PIP joint

Superior: Inferior: Anterior (ventral): Posterior (dorsal): Medial: Lateral: Ipsilateral: Contralateral:

Superior: above another structure Inferior: below another structure Anterior (ventral): toward the front of the body Posterior (dorsal): toward the back of the body Medial: toward the midline of the body Lateral: away from the midline of the body Ipsilateral: on the same side of the body Contralateral: on the opposite sides of the body

Distal Interphalangeal Joint (DIP Joint) What pulley attaches at the level of the DIP?

The A5 pulley is attached to the volar plate at this level

How does the thumb MP jt differ from MP it's of the digits, and how is it similar?

The CL and articular surface are the same but the volar plate of the thumb contains 2 sesamoid bones and the space between makes a trough for the flexor pollicis longus.

Proximal Interphalangeal Joint (PIP Joint) The PIP joint is stabilized dorsally and laterally by what structures?

The PIP joint is stabilized dorsally by the central band and triangular membrane and laterally by the lateral bands and retinacular ligaments

Joint Capsule of the MCP/MP The volar plate can slide in what direction?

The VP can slide proximally with flexion because it is thin and able to fold proximally, but distally it is thick and rigid The volar plate is slack in extension and taut in hyperextension

The distal transverse arches are at the level of the metacarpal heads and form a dorsal convexity. This arch is bigger than the proximal transverse arch due to the metacarpal heads being farther apart than the bases.

The __________ ________________ ____________ are at the level of the metacarpal heads and form a dorsal convexity. This arch is bigger than the proximal transverse arch due to the metacarpal heads being farther apart than the bases.

At the MCP joints: The ____________ _____________________ __________________ loosens when the MCP joints are flexed, and they tighten in extension

The accessory collateral ligament loosens when the MCP joints are flexed, and they tighten in extension

Adductor Pollicis Is not a what?

The adductor pollicis is not a thenar muscle

Thumb Extensor Mechanism What two muscles join the extensor hood to form the terminal tendon?

The adductor pollicis muscle and EPL join the extensor hood to form the terminal tendon

The common extensor tendon trifurcates over the dorsum of the proximal phalanx to what three structures?

The central portion of the tendon is termed the central slip The central slip crosses the PIPJ and attaches to the dorsal base of the middle phalanx The radial and ulnar slips past palmar to join the intrinsic tendons from the interroseous and lumbrical muscles to form the lateral bands

Digital Dorsal Mechanism The common extensor tendon is sustained in a central position at the MP joint level by what structures?

The common extensor tendon is sustained in a central position at the MP joint level by radial and ulnar attachments to the sagittal bands

Digital Dorsal Mechanism The common extensor tendon trifurcates over the dorsum of what joint?

The common extensor tendon trifurcates over the dorsum of the proximal phalanx

Peripheral Nerves of the Hand The deep branch of the ulnar nerve is what kind of nerve?

The deep branch is a motor nerve Major motor nerve of the hand

The extensor mechanism is an elaboration of the __________ ____________ ___________ tendon on the dorsum of each phalanx. The __________ _________ _________ and the ____________ _____________ ____________insert into the extensor mechanisms of the second and fifth digits, respectively.

The extensor mechanism is an elaboration of the extensor digitorum communis (EDC) tendon on the dorsum of each phalanx. The extensor indicis (EI) and the extensor digit minimi (EDM) insert into the extensor mechanisms of the second and fifth digits, respectively.

The fibers from the triangular aponeurosis will form what structure?

The fibers from the triangular aponeurosis will then form the extensor terminal tendon at the distal phalanx which then forms the terminal tendon

How is the first dorsal interosseous muscle different from the other three?

The first dorsal interossei is a little different from the other three because the insertion is mostly bone for both bellies

The heads of the metacarpals are all similar. The ________________ ________________ is rounded. Prominent dorsal tubercles are on each side of the head, proximal to the anterior surface.

The heads of the metacarpals are all similar. The articular surface is rounded. Prominent dorsal tubercles are on each side of the head, proximal to the anterior surface.

The lateral bands are very important for what?

The lateral bands are very important for balance in the hand/fingers

The lateral bands cross the lateral aspect of the finger proximal to PIP joint and are joined to form what structure?

The lateral bands cross the lateral aspect of the finger proximal to PIP joint and are joined to form the triangular aponeurosis (triangular ligament)

Joint Capsule of the MCP/MP The medial and lateral edges of the VP act as an attachment for what structures?

The medial and lateral edges of the VP act as an attachment for the tendon sheaths and A1 pulley

How is the metacarpal of the thumb is different than digits II-V?

The metacarpal of the thumb is different than digits II-V—the thumb metacarpal is shorter and is anteriorly situated compared to the others and is rotated 90 degrees for opposition. The base of the thumb metacarpal is formed into a shallow saddled which is all anterior surface. The most medial aspect of the base sticks out more proximally and presents with a triangular beak. The base of the 4 metacarpals (digits II-V) has an irregular shape and are less wide volarly. This shape contributes to the proximal transverse arch of the hand.

The palmar and dorsal interossei insert into what structure?

The palmar and dorsal interossei insert into the extensor mechanism

Describe the PIP jt

The phalangeal head has a groove and the phalangeal base has a ridge and they contribute to joint stability and limit motion to flexion/extension

At the IP joints: What are the primary stabilizers of the PIP it?

The proper collateral ligament (PCL) and accessory collateral ligament (ACL) are primary stabilizers of the PIP

At the MCP joints: The ____________ _____________________ __________________ loosens when the MCP joints are extended, and they tighten in flexion

The proper collateral ligament loosens when the MCP joints are extended, and they tighten in flexion

Vascular Supply to the Hand The radial artery proceeds dorsal and becomes what structure?

The radial artery proceeds dorsal and becomes the deep and superficial palmar arches

The shaft of each metacarpal is triangular in shape.The ______________ _____ _____ _________________is volarly situated and has more dense bone than the dorsal part of the shaft. The shape of the shaft contributes to the longitudinal arch and provides room for intrinsic musculature and other soft structures.

The shaft of each metacarpal is triangular in shape.The peak of the triangle is volarly situated and has more dense bone than the dorsal part of the shaft. The shape of the shaft contributes to the longitudinal arch and provides room for intrinsic musculature and other soft structures.

Distal Interphalangeal Joint (DIP Joint) What structures cross this joint volarly? Dorsally?

The structures that cross the joint volarly; flexor digitorum profundus and dorsally: the lateral bands

Thumb Extensor Mechanism The terminal tendon crosses what joint and attaches where?

The terminal tendon crosses the dorsal surface of the IP joint to attach to the dorsal base of the distal phalanx

Thumb Extensor Mechanism When the EPL is absent, the thumb extensor mechanism will do what?

The thumb extensor mechanism will bring the IP joint into neutral extension via the abductor pollicis brevis when the EPL is absent

Thumb Extensor Mechanism The thumb extensor tendons are retained in a central position at the MCP joint level by what structures?

The thumb extensor tendons are retained in a central position at the MCP joint level by radial and ulnar attachments to the sagittal bands

Question What carpal articulates with the thumb?

The trapezium. Another mnemonic to remember sequence: The Thumb articulates with the trapezium

What structure holds the lateral bands in place and prevents volar slippage?

The triangular aponeurosis holds the lateral bands in place and prevents volar slippage

Vascular Supply to the Hand The ulnar artery enters Guyon's canal and continues as what structures?

The ulnar artery enters Guyon's canal and continues as the superficial palmar arch, which gives off the common palmar digital arteries

Proximal Interphalangeal Joint (PIP Joint) The volar plate

The volar plate is the attachment for the A3 pulley which stabilizes the flexor tendons and is essential for digit function

Thenar muscles are chiefly responsible for what motion?

Thenar muscles are chiefly responsible for opposition of the thumb (flexion and medial rotation of the thumb when grasping or touching the fingers)

At the IP joints: When the IP joints are flexed, the collateral ligaments are in a more relaxed position but if the PIP is immobilized in excessive flexion the position allows the ligaments to become stout and stiff. Therefore what is recommended during immobilization?

Therefore it is recommended a small amount of tension (orthotic at 0-15 degrees of flexion) will maintain the ligament length and help preserve joint motion and prevent joint stiffness as the proper collateral ligament is still tight and will help the PIPJ to be stable.

During thumb opposition, the thenar muscles are assisted by what muscles?

These muscles are assisted in this action by the adductor pollicis and flexor pollicis longus

The hypothenar muscles are innervated by what nerve?

They are all innervated by the ulnar nerve

Thumb Extensor Mechanism With an extensor pollicus longus rupture the patient is unable to lift his or her thumb off the table. This motion is termed what?

This motion is termed retropulsion

How many hypothenar muscles are there?

Three hypothenar muscles form the hypothenar eminence and move the fifth digit They lie in the hypothenar compartment with the fifth metacarpal bone

Muscles of the hand How many muscles are in the thenar eminence?

Three thenar muscles produce the thenar eminence and move the thumb

Thumb CMC (1st CMC) is different than digits 2-5 CMC joints because

Thumb CMC (1st CMC) is different than digits 2-5 CMC joints. It allows for significant motion while there is virtually no motion at digits 2-5 CMC.

Joint Capsule of the MCP/MP Describe the collateral ligament of the MP jt

Triangular Has 2 parts (accessory and proper/cord are the two parts) Fibers of the CL extend more distally and form the strongest part of the CL Generally speaking the CL is loose in extension allowing MCP abduction and adduction Proper are taut in Flexion and slack in extension while the accessory ligaments are located more volar so they are lax in flexion and taut in extension As proximal phalanx is flexed the proper CL is taut in full flexion due to shape of MC head. Tightness prevents full abduction and adduction. VP also serves as an attachment and accessory (or the fan part of the CL) and stabilizes long finger flexors.

BG True or False: The critical corner of the PIPJ is where the accessory and proper collateral ligaments, and volar plate all converge at the middle phalanx.

True

True or False: The anterolateral edge of the trapezium has an overhang, referred to as the beak, which is part of the tunnel for the flexor carpi radialis (FCR)?

True

BG True or False: Knowing the position of the collateral ligaments will ensure you will always respect them during positioning

True: For example, if a patient presents with a cast and the MCP joints are straight and the IP joints are flexed then you must get the cast cut back to allow full MCP joint flexion. Otherwise, the MCP joint collateral ligaments will become shorter and stout, causing active/passive MCP joint flexion to become painful and difficult, if not impossible. Also, in this position you will cause interossei tightness and perhaps lumbrical tightness. In the same breath, if the PIPJ and DIPJ collateral ligaments are not respected and left to flex or dangle over the edge of a cast, fluent movement at the PIPJ and DIPJ is lost and a stiff hand is usually the result.

First dorsal interossei has two muscle bellies: What are they and what are their functions?

Ulnar belly flexes, abducts, and pronates the index MCP joint Radial muscle belly helps to radially adduct the thumb MCP joint Together muscle bellies help extend the index PIPJ and DIPJ

BG What is the most common ligament injured in the thumb?

Ulnar collateral ligament

Describe the ulnar and radial sides of the thumb MP jt

Ulnar side of the extensor hood is stronger and heavier and formed by the aponeurosis (layers of flat, broad tendons) of the adductor pollicis - this supports the joint against abduction forces Radial side of the hood is formed by the tendons of the abductor pollicis brevis and flexor pollicis brevis Both sides then blend dorsally with the EPB and EPL

Unlike the thenar muscles, the adductor pollicis is innervated by what nerve?

Unlike the thenar muscles, the adductor pollicis is innervated by the deep branch of the ulnar nerve

Virtually no motion is permitted at the __________ _____ _________CMC joints. There is a small amount of motion at the 4th and 5th CMC joints that is important for gripping and manipulation of objects.

Virtually no motion is permitted at the 2nd and 3rd CMC joints. There is a small amount of motion at the 4th and 5th CMC joints that is important for gripping and manipulation of objects.

PIP jt Oblique Retinacular Ligament: (might also see it termed oblique retinacular ligament of Landsmeer) Test for ORL tightness:

When the ORL is tight it does not allow for passive DIPJ flexion with the PIPJ passively extended; conversely if the PIPJ is in flexion the DIP can flex

What happens to the ORL ligament when the PIP joint is flexed ? When it is extended?

When the PIP joint is flexed, the ORL relaxes allowing DIP joint flexion. When the PIP joint extends, the ORL tightens facilitating DIP joint extension, linking PIP joint and DIP joint motion

When the PIP joint is in full extension, the ACL are taut and because of the VP attachment, __________________________ is not permitted.

When the PIP joint is in full extension, the ACL are taut and because of the VP attachment, hyper-extension is not permitted.

Dorsal Reinforcement of the MCP Joint Sagittal bands

are the fibers on the sides of the extensor hood and they help centralize the extensor tendon - they originate on the palmar plate and insert on the extensor mechanism

Joint Capsule of the MCP/MP The VP gives stability of the tendons and prevents what?

bowstringing of the tendons allowing for better biomechanical function of the tendons

Joint Capsule of the MCP/MP encompasses the joint space and attaches to the sides of both:

encompasses the joint space and attaches to the sides of both articular surfaces

Dorsal Reinforcement of the MCP Joint Extensor hood

flat layer of fibers that are perpendicular and oblique to the bone and sweep around to the edges of the volar plate

Dorsal Reinforcement of the MCP Joint Deep transverse metacarpal ligament

functions to prevent the metacarpal heads from splaying apart or abduction.

Dorsal Reinforcement of the MCP Joint Natatory Ligament (superficial transverse metacarpal ligament)

functions to resist abduction

The lumbrical muscles are innervated by what nerve?

index and long innervated by median nerve, ring and little innervated by ulnar nerve

The terminal tendon crosses what joint and attaches where?

it crosses the dorsal surface of the DIP joint to attach to the dorsal base of the distal phalanx

BG The word lumbrical is latin for the lumbricus meaning what?

little worm... 4 wormlike muscles in the palm

Thumb Extensor Mechanism At the MCP level, the extensor pollicis brevis (EPB) lies radial to what structure and attaches where?

the extensor pollicis brevis (EPB) lies radial to the extensor pollicis longus (EPL) and attaches to the dorsal base of the proximal phalanx

Joint Capsule of the MCP/MP Volar side forms a strong plate of fibrocartilage called:

the volar plate (VP)