The carpometacarpal (CMC) joints are five

joint A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw ...

s in the

wrist In human anatomy, the wrist is variously defined as (1) the Carpal bones, carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known ...

that articulate the distal row of

carpal bones The carpal bones are the eight small bones that make up the wrist (or carpus) that connects the hand to the forearm. The term "carpus" is derived from the Latin carpus and the Greek καρπός (karpós), meaning "wrist". In human anatomy, th ...

and the proximal bases of the five

metacarpal bones In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones ...

. The CMC joint of the thumb or the first CMC joint, also known as the trapeziometacarpal (TMC) joint, differs significantly from the other four CMC joints and is therefore described separately.

Thumb

RightHumanAnteriorDistalRadiusUlnaCarpals

The carpometacarpal joint of the

thumb The thumb is the first digit of the hand, next to the index finger. When a person is standing in the medical anatomical position (where the palm is facing to the front), the thumb is the outermost digit. The Medical Latin English noun for thumb ...

(''pollex''), also known as the first carpometacarpal joint, or the trapeziometacarpal joint (TMC) because it connects the trapezium to the first metacarpal bone, plays an irreplaceable role in the normal functioning of the thumb. The most important joint connecting the wrist to the metacarpus, osteoarthritis of the TMC is a severely disabling condition; up to twenty times more common among elderly women than in average. Pronation-supination of the first metacarpal is especially important for the action of opposition. The movements of the first CMC are limited by the shape of the joint, by the capsulo-ligamentous complex surrounding the joint, and by the balance among involved muscles. If the first metacarpal fails to sit well 'on the saddle', for example because of

hypoplasia Hypoplasia (from Ancient Greek ὑπo- ''hypo-'' 'under' + πλάσις ''plasis'' 'formation'; adjective form ''hypoplastic'') is underdevelopment or incomplete development of a tissue or organ.subluxated (i.e. slightly displaced) towards the

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

. The capsule is sufficiently slack to allow a wide range of movements and a distraction of roughly 3 mm, while reinforcing ligaments and tendons give stability to the joint. It is slightly thicker on its dorsal side than on the other. The first carpometacarpal joint is a frequent site of

osteoarthritis Osteoarthritis (OA) is a type of degenerative joint disease that results from breakdown of joint cartilage and underlying bone which affects 1 in 7 adults in the United States. It is believed to be the fourth leading cause of disability in the w ...

postmenopausal Menopause, also known as the climacteric, is the time in women's lives when menstrual periods stop permanently, and they are no longer able to bear children. Menopause usually occurs between the age of 47 and 54. Medical professionals often d ...

women.

Ligaments

The description of the number and names of the ligaments of the first CMC varies considerably in anatomical literature. describe three intracapsular and two extracapsular ligaments to be most important in stabilizing the thumb: ; Anterior oblique ligament (AOL): A strong, thick, and intracapsular ligament originating on the palmar tubercle of the trapezium to be inserted on the palmar tubercle of the first metacarpal. It is taut in abduction, extension, and pronation, and has been reported to have an important retaining function and to be elongated or absent in CMC joint arthritis. ; Ulnar collateral ligament (UCL): An extracapsular ligament, the UCL is located ulnarly to the AOL. It has its origin on the flexor retinaculum and is inserted on the ulnopalmar tubercle of the first metacarpal. It is taut in abduction, extension, and pronation, and often found elongated in connection to CMC joint arthritis. The importance ascribed to the UCL varies considerably among researchers. ; First intermetacarpal ligament (IML): Connecting the bases of the second and first metacarpals, this ligament inserts onto the ulnopalmar tubercle of the first metacarpal where its fibers intermingle with those of the UCL. It is taut in abduction, opposition, and supination. It has been reported to be the most important restraining structure of the first CMC joint by several researchers. Some consider it too weak to be able to stabilize the joint by itself, yet accept that together with the UCL it represents an important restraining structure. ; Posterior oblique ligament (POL): An intracapsular ligament stretching from the dorsoulnar side of the trapezium to the ulno-palmar tubercle of the first metacarpal. Not considered an important ligament to the first CMC joint, it tightens during forced adduction and radial abduction. ; Dorsoradial ligament (DRL): Like the previous ligament, the DRL is not considered important to the first CMC. It connects the dorsal sides of the trapezium and the first metacarpal. Early, anatomically correct drawings of the ligaments of the first carpometacarpal joints were produced by .

Movements

In this articulation the movements permitted are flexion and extension in the plane of the palm of the hand, abduction and adduction in a plane at right angles to the palm, circumduction, and opposition. * It is by the movement of opposition that the tip of the thumb is brought into contact with the volar surfaces of the slightly flexed fingers. This movement is effected through the medium of a small sloping facet on the anterior lip of the saddle-shaped articular surface of the greater multangular (trapezium). The flexor muscles pull the corresponding part of the articular surface of the metacarpal bone on to this facet, and the movement of opposition is then carried out by the adductors. * Flexion of this joint is produced by the

flexor pollicis longus The flexor pollicis longus (; FPL, Latin ''flexor'', bender; ''pollicis'', of the thumb; ''longus'', long) is a muscle in the forearm and hand that flexes the thumb. It lies in the same plane as the flexor digitorum profundus. This muscle is uniqu ...

and brevis, assisted by the

opponens pollicis The opponens pollicis is a small, triangular muscle in the hand, which functions to oppose the thumb. It is one of the three thenar muscles. It lies deep to the abductor pollicis brevis and lateral to the flexor pollicis brevis. Structure The opp ...

and the

adductor pollicis In human anatomy, the adductor pollicis muscle is a muscle in the hand that functions to adduct the thumb. It has two heads: transverse and oblique. It is a fleshy, flat, triangular, and fan-shaped muscle deep in the thenar compartment beneath ...

. * Extension is effected mainly by the

abductor pollicis longus In human anatomy, the abductor pollicis longus (APL) is one of the extrinsic muscles of the hand. Its major function is to abduct the thumb at the wrist. Its tendon forms the anterior border of the anatomical snuffbox. Structure The abductor p ...

, assisted by the extensores pollicis longus and brevis. * Adduction is carried out by the adductor; abduction mainly by the

and brevis, assisted by the extensors.

Range of motion Range of motion (or ROM), is the linear or angular distance that a moving object may normally travel while properly attached to another. It is also called range of travel (or ROT), particularly when talking about mechanical devices and in mechanic ...

for the first CMC is 53° of flexion/extension, 42° of abduction/adduction, and 17° of rotation. ; Planes and axes of movements The thumb's MP and CMC joints abduct and adduct in a plane perpendicular to the palm, a movement also referred to as "palmar abduction." The same joints flex and extend in a plane parallel to the palm, also referred to as "radial abduction," because the thumb moves toward the hand's radial side. Abduction and adduction occur around an antero-posterior axis, while flexion and extension occur around a lateral axis. For ease of orientation, the thumbnail can be considered as resting in the thumb's frontal plane. Abduction and adduction of the first CMC (and MP) joint(s) occur in this plane; flexion and extension of the first CMC, MP, and IP joints occur in a plane that is perpendicular to the thumbnail. This remains true regardless of how the first metacarpal bone is being rotated during opposition and reposition.

Sexual dimorphism

Male and female thumb CMC joints are different in some aspects. In women, the trapezial articular surface is significantly smaller than the metacarpal surface, and its shape also differs from that of males. While most thumb CMC joints are more congruent in the radioulnar direction than the dorsovolar, female CMC joints are less globally congruent than male joints.

Evolution

A primitive autonomisation of the first ray took place in dinosaurs, while a real differentiation appeared in primitive primates approximately . The shape of the human TMC joint dates back about 5 million years ago. As a result of evolution, the human thumb CMC joint has positioned itself at 80° of pronation, 40° of abduction, and 50° of flexion in relation to an axis passing through the stable second and third CMC joints.

Fingers

* The second metacarpal articulates primarily with the

trapezoid A quadrilateral with at least one pair of parallel sides is called a trapezoid () in American and Canadian English. In British and other forms of English, it is called a trapezium (). A trapezoid is necessarily a Convex polygon, convex quadri ...

and secondarily with the trapezium and

capitate The capitate bone is a bone in the human wrist found in the center of the carpal bone region, located at the distal end of the radius and ulna bones. It articulates with the third metacarpal bone (the middle finger) and forms the third carpomet ...

. * The third metacarpal articulates primarily with the capitate, * The fourth metacarpal articulates with the capitate and

hamate The hamate bone (from Latin hamatus, "hooked"), or unciform bone (from Latin ''uncus'', "hook"), Latin os hamatum and occasionally abbreviated as just hamatum, is a bone in the human wrist readily distinguishable by its wedge shape and a hook-l ...

. * The fifth metacarpal articulates with the hamate. Among themselves, the four ulnar metacarpals also articulates with their neighbours at the

intermetacarpal articulations The intermetacarpal joints are in the hand formed between the metacarpal bones. The bases of the second, third, fourth and fifth metacarpal bones articulate with one another by small surfaces covered with cartilage. The metacarpal bones are conne ...

Ligaments

These four CMC joints are supported by strong transverse and weaker longitudinal ligaments: the

dorsal carpometacarpal ligaments The dorsal carpometacarpal ligaments, the strongest and most distinct carpometacarpal ligaments, connect the carpal and metacarpal bones on their dorsal surfaces. * The second metacarpal bone receives two fasciculi, one from the greater, the other ...

and the volar or

palmar carpometacarpal ligaments The Palmar carpometacarpal ligaments (or volar) are a series of bands on the palmar surface of the carpometacarpal joints that connect the carpal bones to the second through fifth metacarpal bones. The second metacarpal is connected to the trap ...

. The interosseous ligaments consist of short, thick fibers, and are limited to one part of the carpometacarpal articulation; they connect the contiguous inferior angles of the capitate and hamate with the adjacent surfaces of the third and fourth metacarpal bones.

Movements

The carpometacarpal joints of second through fifth digits are

arthrodial A plane joint (arthrodial joint, gliding joint, plane articulation) is a synovial joint which, under physiological conditions, allows only gliding movement. Plane joints permit sliding movements in the plane of articular surfaces. The opposed sur ...

. The movements permitted in the second through fifth carpometacarpal joints most readily observable in the (distal) heads of the metacarpal bones. The range of motions in these joints decrease from the fifth to the second CMCs. The second to fifth joints are synovial ellipsoidal joints with a nominal

degree of freedom Degrees of freedom (often abbreviated df or DOF) refers to the number of independent variables or parameters of a thermodynamic system. In various scientific fields, the word "freedom" is used to describe the limits to which physical movement or ...

(flexion/extension). The second and third joints are however almost essentially immobile and can be considered to have zero degrees of freedom in practice, but capable of anteroposterior gliding (translation) movements.Wise, Christopher H. "Orthopaedic Manual Physical Therapy: From Art to Evidence" F.A. Davis, 2015, p. 573.Neumann, Donald A. "Kinesiology of the Musculoskeletal System - E-Book: Foundations for Rehabilitation" Elsevier Health Sciences, 2013, p. 250. The second and third CMC however also capable of small degree of flexion-extension motion (11 degrees of flexion-extension motion for the second, while 7 degrees for the third).Skirven, Terri M., A. Lee Osterman, Jane Fedorcyzk, Peter C. Amadio "Rehabilitation of the Hand and Upper Extremity, 2-Volume Set E-Book: Expert Consult" Elsevier Health Sciences, 2011, p. 412. These two CMC provide the other three CMCs with a fixed and stable axis. While the mobility of the fourth CMC joint thus is perceptible, the first joint is a

saddle joint A saddle joint (sellar joint, articulation by reciprocal reception) is a type of synovial joint in which the opposing surfaces are reciprocally concave and convex. It is found in the thumb, the thorax, the middle ear, and the heel. Structure In ...

with two degrees of freedom which except flexion/extension also enable abduction/adduction and a limited amount of opposition. Together the movements of the fourth and fifth CMCs facilitates for their fingers to oppose the thumb.

Function

The function of the finger carpometacarpal joints and their segments overall is to contribute to the palmar arch system together with the thumb. The proximal transverse arch of the palm is formed by the distal row of carpal bones. The concavity of this arch is augmented at the level of the metacarpal heads by the flexibility of the first, fourth, and fifth metacarpal heads around the fixed second and third metacarpal heads; a flexible structure called the distal transverse arch. For each finger there is also a longitudinal arch. Together, these arches allow the palm and the digits to conform optimally to objects as we grasp them (so-called palmar cupping). Furthermore, as the amount of surface contact is maximized, stability is enhanced and sensory feedback increases. The

deep transverse metacarpal ligament The deep transverse metacarpal ligament (also called the deep transverse palmar ligament) is a narrow fibrous band which runs across the palmar surfaces of the heads of the second, third, fourth and fifth metacarpal bones, connecting them togethe ...

stabilises the mobile parts of the palmar arch system. As the fingers are being flexed, palmar cupping is contributed to by muscles crossing the carpometacarpal joints when they act on the mobile parts of the palmar arch system. The oblique

opponens digiti minimi muscle The opponens digiti minimi (opponens digiti quinti in older texts) is a muscle in the hand. It is of a triangular form, and placed immediately beneath the palmaris brevis, abductor digiti minimi and flexor digiti minimi brevis. It is one of t ...

acts on the fifth carpometacarpal joint and is the only muscle that act on the carpometacarpal joints alone. It is optimally positioned to flex and rotate the fifth metacarpal bone about its long axis. Palmar arching is further increased when lexor carpi ulnaris(which is attached to the pisiform) and intrinsic hand muscles attached to the transverse carpal ligament acts on the arch system. The fixed second and third carpometacarpal joints are crossed by the radial wrist muscles (

flexor carpi radialis In anatomy, flexor carpi radialis is a muscle of the human forearm that acts to flex and (radially) abduct the hand. The Latin ''carpus'' means wrist; hence flexor carpi is a flexor of the wrist. Origin and insertion The flexor carpi radialis is ...

extensor carpi radialis longus A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates such as the koala (which has two opposable thumbs on each "hand ...

, and

extensor carpi radialis brevis In human anatomy, extensor carpi radialis brevis is a muscle in the forearm that acts to extend and abduct the wrist. It is shorter and thicker than its namesake extensor carpi radialis longus which can be found above the proximal end of the exte ...

). The stability of these two carpometacarpal joints is a functional adaptation that enhances the efficiency of these muscles at the midcarpal and

radiocarpal joint In human anatomy, the wrist is variously defined as (1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known as the carpal ...

Synovial membranes

The synovial membrane is a continuation of that of the intercarpal joints. Occasionally, the joint between the hamate and the fourth and fifth metacarpal bones has a separate synovial membrane. The synovial membranes of the wrist and carpus are thus seen to be five in number: * The first passes from the lower end of the ulnar to the ulnar notch of the

, and lines the upper surface of the articular disk. * The second passes from the articular disk and the lower end of the radius above, to the bones of the first row below. * The third, the most extensive, passes between the contiguous margins of the two rows of carpal bones, and sometimes, in the event of one of the interosseous ligaments being absent, between the bones of the second row to the carpal extremities of the second, third, fourth, and fifth metacarpal bones. * The fourth extends from the margin of the greater multangular to the metacarpal bone of the

. * The fifth runs between the adjacent margins of the triangular and pisiform bones. Occasionally the fourth and fifth carpometacarpal joints have a separate synovial membrane.

Clinical significance

Osteoarthritis Osteoarthritis (OA) is a type of degenerative joint disease that results from breakdown of joint cartilage and underlying bone which affects 1 in 7 adults in the United States. It is believed to be the fourth leading cause of disability in the w ...

of the carpometacarpal joints is a type of

joint disease An arthropathy is a disease of a joint. Types Arthritis is a form of arthropathy that involves inflammation of one or more joints, while the term arthropathy may be used regardless of whether there is inflammation or not. Joint diseases can be cla ...

that results from breakdown of joint cartilage and underlying

bone A bone is a Stiffness, rigid Organ (biology), organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red blood cell, red and white blood cells, store minerals, provid ...

. When it affects the thumb it is termed

trapeziometacarpal osteoarthritis Trapeziometacarpal osteoarthritis (TMC OA) is, also known as osteoarthritis at the base of the thumb, thumb carpometacarpal osteoarthritis, basilar (or basal) joint arthritis, or as rhizarthrosis. This joint is formed by the trapezium (bone), trape ...

Carpometacarpal bossing Carpometacarpal bossing (or metacarpal/carpal bossing) is a small, immovable mass of bone on the back of the wrist. The mass occurs in one of the joints between the carpus and metacarpus of the hand, called the carpometacarpal joints, where a smal ...

is the presence of a small immovable protuberance over the joint.

Notes

References

* * * * * * *

External links

* - carpometacarpal joint * - carpometacarpal ligaments * {{Authority control Upper limb anatomy Joints