Functional Anatomy of the Hand
Original Editor - Ewa Jaraczewska
Top Contributors - Ewa Jaraczewska and Jess Bell
Introduction[edit | edit source]
The hand, positioned at the end of the upper limb, is a combination of complex joints whose function is to manipulate, grip and grasp, all made possible by the opposing movement of the thumb.
Key Terms[edit | edit source]
Axes: lines around which an object rotates. The rotation axis is a line that passes through the centre of mass. There are three axes of rotation: sagittal passing from posterior to anterior, frontal passing from left to right, and vertical passing from inferior to superior. The rotation axes of the foot joints are perpendicular to the cardinal planes. Therefore, motion at these joints results in rotations within three planes. Example: supination involves inversion, internal rotation, and plantarflexion.
Bursae: reduce friction between the moving parts of the joints. A bursa is a fluid-filled sac. There are four types of bursae: adventitious, subcutaneous, synovial, and sub-muscular.
Capsule: one of the characteristics of the synovial joints. It is a fibrous connective tissue which forms a band that seals the joint space, provides passive and active stability and may even form articular surfaces for the joint. The capsular pattern is "the proportional motion restriction in range of motion during passive exercises due to tightness of the joint capsule."
Closed pack position: the position with the most congruency of the joint surfaces. In this position, joint stability increases. For example, the closed pack position for the interphalangeal joints is full extension.
Degrees of freedom: the direction of joint movement or rotation; there is a maximum of six degrees of freedom, including three translations and three rotations.
Ligament: fibrous connective tissue that holds the bones together.
Open (loose) pack position: position with the least joint congruency where joint stability is reduced.
Planes of movement: describe how the body moves. Up and down movements (flexion/extension) occur in the sagittal plane. Sideway movements (abduction/adduction) occur in the frontal plane. The transverse plane movements are rotational (internal and external rotation).
Hand Structure[edit | edit source]
The structure of the human hand includes 27 bones: eight carpal bones, five metacarpal bones, and fourteen digital bones, including fingers and thumb. The bony segments of the hand are arranged in a series of longitudinal and transverse arches. The bones of the five digital rays are part of the longitudinal arches. There are two transverse arches: the proximal and the distal. The proximal transverse arch is made up of carpal bones. The metacarpal heads of the fingers belong to the distal transverse arch.[1]
The Carpus (Carpal Bones)[edit | edit source]
Proximal raw:
The scaphoid (navicular): belongs to the proximal raw of the carpal bones. Located the most laterally. Its palmar surface contains the tubercle, the muscles' attachment point and the anatomical snuffbox floor.
The lunate: part of the proximal raw of the carpal bones. It articulates with the scaphoid on the lateral and the triquetrum on the medial side.
The triquetrum: other names include triquetral, triangular, or cuneiform bone. It is a triangular and pyramidal-shaped bone located in the proximal raw, on the medial side of the wrist. It contains multiple articulation surfaces: lateral for the lunate, anterior for the pisiform, and distal for the hamate.
Distal raw:
The trapezium: located in the distal raw of the carpal bones, on its radial side. It has four articulations for the first metacarpal, second metacarpal, scaphoid and trapezoid bones. This bone is part of the mechanism responsible for the wide mobility of the human hand, where the articulation between the first metacarpal and the trapezium allows for the opposable thumbs function.
The trapezoid: The lesser multangular bone is another name for this bone. This is the smallest bone of the distal raw of the carpal bones. It gives structure to the palm of the hand.
The capitate: the largest and most central carpal bone belonging to the distal raw. It articulates with the bases of the 2nd and 3rd metacarpal bones, forming part of the common carpometacarpal joint in the hand. In addition, it articulates with the following: scaphoid and lunate on the proximal, trapezoid on the lateral, and the hamate on the medial surfaces.
The hamate: sits on the medial side of the distal row of carpal bones. The hook of the hamate is the bony process extending from the palmar surface. This carpal bone forms the medial border of the carpal tunnel.
The Metacarpus (Metacarpal Bones)[edit | edit source]
Five bones- the metacarpals, make up the metacarpus. Each metacarpal bone articulates with one or more carpal bones:
- First metacarpal articulates with the trapezium
- Second metacarpal articulates with the trapezium, trapezoid and capitate
- Third metacarpal articulates with the capitate
- Fourth and fifth metacarpal articulate with the hamate
Additionally, the second to fifth metacarpals articulate with each other.
The Phalanges[edit | edit source]
Long finger bones are known as phalanges. Apart from the thumb (the pollex), which only has distal and proximal bones, each phalanx has three bones: the distal, middle and proximal phalanx. The middle and proximal phalanges consist of a base, a body, and the head, which is the distal part of the phalanx. [2]
The thumb: the typical position of the thumb is pronation and approximately 80 degrees of flexion in relation to the remaining metacarpals of the hand. This position allows opposition of the thumb to the digits.[1]
The index finger: second the most important finger of the hand. It is able to abduct, adduct, flex and extend. The index finger participates in precision pinch and directional grip. [1]
The long finger: is centrally positioned, which makes it involved in power grip and precision movements.[1]
The ring finger: weak and only randomly used in precision grip or pinch manoeuvres. When lost, it leads to the least amount of impairment in the hand.[1]
The small finger: the weakest of all fingers, but important in grasping while spanning an object manoeuvres due to its ability to abduct.[1]
Bones, Articulations and Kinematics of the Hand[edit | edit source]
Bones and Articulations[edit | edit source]
Bones | Articulations | Characteristics | Key palpation points |
---|---|---|---|
Distal row of carpal bones
Proximal bases of five metacarpal bones |
The carpometacarpal joints (CMC):[3]
|
The mobility of the CMC joints increases from radial to ulnar sides of the hand.[3]
1CMC (TMCJ) is located on the radial aspect of the wrist. Does not contain bony stabilizers. Instead, the stability is provided by five internal ligaments: dorsal radial, posterior oblique, the first intermetacarpal, ulnar collateral, and anterior oblique ligaments. 2CMC and 3CMC: belong to the central column of the hand, relatively rigid. 1CMC, 4CMC, 5 CMC: relative mobility, with 4CMC and 5CMC contributing the most to hand mobility. |
|
Metacarpal bones
Proximal phalanges |
Metacarpophalangeal (MCP) joints | Consider being the most important joint for hand function as they contribute 77% of the total arc of finger flexion[1] | |
Proximal, middle, and distal phalanges | Interphalangeal joints
|
The function of the interphalangeal joints of the hand is to permit fine motor movements in the digits. It includes providing flexion towards the palm. |
Hand Kinematics[edit | edit source]
Hand biomechanics consists of seven fundamental manoeuvres needed for basic functions. They involve specific motions which must occur at the wrist, thumb and fingers:[1]
- The precision pinch, or the terminal pinch, is used to pick up a small object, like a pen.
- Motion required: flexion of the interphalangeal (IP) joint of the thumb and the distal IP (DIP) joint of the index finger.
- The oppositional pinch, or the subterminal pinch with the thumb opposition. The index finger's pulp connects with the thumb's pulp needed to hold a piece of paper.
- Motion required: Extension of the IP and DIP joints.
- The key pinch requires stability provided by the index finger, the optimal length of the digit and a metacarpal phalangeal joint (MCP).
- Motion required: thumb adduction to the radial aspect of the index finger’s middle phalanx.
- The chuck grip, or a directional grip, is used to perform the action that requires an application of rotational and axial forces like when using a screwdriver.
- Motion required: a combined motion of the index finger, long finger, and thumb.
- The hook grip allows one to hold a briefcase by its handle. No thumb function is required in this manoeuvre.
- Motion required: finger flexion at the IP joints and extension at the MCP joints.
- The power grasp is needed to grip a club or a bat.
- Motion required: fingers and thumb flexion, thumb opposition relative to the other digits
- The span grasp manoeuvre is based on the stability of the thumb, metacarpophalangeal (MCP) and interphalangeal (IP) joints. The span grasp is utilised when grabbing a ball.
- Motion required: 30 degrees flexion of DIP joints and the proximal IP (PIP) joints, thumb abduction towards the palm
Joint | Type of joint | Plane of movement | Motion | Kinematics | Closed pack position | Open pack position |
---|---|---|---|---|---|---|
The carpometacarpal joints (CMC) | 1CMC:
Synovial, saddle joint. 2CMC/3CMC: Synarthrotic with almost no movement under physiological conditions. 4CMC/5CMC: Synovial, saddle joint. |
1CMC:
Flexion/extension occurs in the frontal plane as the thumb is rotated at 90 degrees in relation to the plane of the hand [5] Abduction/adduction occurs in the sagittal plane External/internal rotation (axial rotation) where the axis is the length of the thumb Thumb opposition: all thumb movements combined together
2CMC/3CMC: Nonaxial, translational movements. 4CMC/5CMC: Sagittal (flexion/extension) Frontal (abduction/adduction) |
1CMC:
Flexion/extension Abduction/adduction Axial rotation 2CMC/3CMC: Nonaxial, translational movements only. 4CMC/5CMC: Flexion/extension Abduction/adduction |
1CMC: [5] Flexion/extension: total motion of 40-50 degrees
Abduction/adduction: total motion of 80 degrees Axial rotation: total motion of 70-110 degrees 2CMC/3CMC: Nonaxial, translational movements only. 4CMC:[6] Flexion/extension: 10/0 degrees Abduction/adduction: 5/0 degrees. 5CMC:[6] Flexion/extension: 20/0 degrees Abduction/adduction: 13/0 degrees
|
1CMC: maximum opposition
|
1CMC:slight flexion
|
Metacarpophalangeal (MCP) joints | Condyloid joint | Sagittal
Frontal |
Flexion/extension
Abduction/ adduction Mild to moderate rotation of the digit. |
Thumb MCP:
Flexion/extension: 55 degrees/35 degrees Abduction/adduction: 25-30 degrees total range Second to fifth MCP: Flexion: 90 degrees Extension: 10-30 degrees Abduction/adduction: 25-30 degrees |
Thumb MCP: maximum opposition
|
Slight flexion |
Interphalangeal joints (IP)
|
Hinge | Sagittal | Flexion/Extension | Thumb:
Flexion: 90 degrees Extension: 10-15 degrees Second to fifth PIP: Flexion: 70-100 degrees (depends on the digit, with digit 5 having the least flexion range of motion) Extension: 2-5 degrees Second to fifth DIP: Flexion: 50 degrees Extension: 15 degrees |
Full extension | Slight flexion |
Hand Passive Range of Motion[edit | edit source]
Watch this video to learn about the thumb passive range of motion assessment using a goniometer:
Watch this video to learn about the fingers' passive range of motion assessment using a goniometer:
Ligaments of the Hand[edit | edit source]
Ligaments Supporting Carpometacarpal Joints[edit | edit source]
Trapeziometacarpal Joint (TMCJ) Ligaments[edit | edit source]
Key ligaments | Origin | Insertion | Action/role | Key palpation points |
---|---|---|---|---|
Anterior oblique ligament (AOL) ("beak ligament"):[9]
|
Palmar tubercle of the trapezium | Volar beak of the first metacarpal base at the palmar and ulnar surface | A static stabilizer of TMCJ
Prevents dorsoradial subluxation of thumb metacarpal during key pinch[10] Degeneration of AOL frequently leads to osteoarthritis of the first CMC joint.[11] |
|
Posterior oblique ligament (POL) | Dorsal-ulnar aspect of the trapezium | The dorsal-ulnar aspect of the thumb metacarpal and the palmar-ulnar tubercle | Secondary role in CMC joint stability
Prevents radial translation |
|
Ulnar collateral ligament (UCL) | distal and ulnar margin of the flexor retinaculum insertion onto the trapezial ridge | superficial and ulnar to the superficial anterior oblique ligament on the volar-ulnar tubercle of the first metacarpal base. | Prevents the thumb from side-to-side movement | |
First intermetacarpal ligament (1stIMCL) | Dorsoradial aspect of the second metacarpal, radial to the extensor carpi radialis longus tendon insertion | Volar-ulnar tubercle of the first metacarpal base | Connects the thumb metacarpal bone to the index finger metacarpal | |
Dorsoradial ligament (DRL) | Dorsoradial tubercle of the trapezium | Dorsal edge of the base of the thumb metacarpal.[12] | The strongest and stiffest of TMCJ ligaments
The primary stabiliser of the TMCJ. [12] Proprioceptive function due to rich innervation |
Carpometacarpal Joints 2-5 (2CMC-5CMC) Ligaments[edit | edit source]
Key ligaments | Origin | Insertion | Action/role | Key palpation points |
---|---|---|---|---|
Palmar (volar) carpometacarpal ligaments | Palmar (volar) surfaces of the distal row of carpal bones:
2CMC:trapezium and trapezoid 3CMC:trapezium/trapezoid, capitate, hamate 4CMC:capitate and hamate 5CMC:hamate |
Palmar (volar) four medial metacarpal bases | CMC joint stabilisers | |
Dorsal carpometacarpal ligaments | Dorsal surfaces of the distal row of carpal bones:
2CMC:trapezium and trapezoid 3CMC:trapezoid and capitate 4CMC:capitate and hamate 5CMC:hamate |
Dorsal four medial metacarpal bases | ||
Interosseous ligament:
Lateral band(LB) Medial band(MB) |
Inferior aspect of the distal margins of the capitate and hamate bones:
LB: capitate MB: hamate |
Third and fourth metacarpal bases:
LB: third metacarpal base MB: fourth metacarpal base |
Ligaments Supporting Metacarpophalangeal Joints[edit | edit source]
Key ligaments | Origin | Insertion | Action/role | Key palpation points |
---|---|---|---|---|
Collateral ligaments:
Proper collateral ligaments (PCL) Accessory collateral ligaments (ACL) |
PCL: posterior tubercles on the dorsolateral aspect of the metacarpal head
ACL: proximal to the metacarpal head |
PCL: palmar aspect of the adjacent proximal phalanx, distal to the base
ACL: distal third of the palmar (volar) plate |
Stabilises the joint medially and laterally
Limits flexion and extension |
|
Deep transverse metacarpal ligaments (2-5MCP only) | Run across the palmar aspect of the second to fifth metacarpophalangeal joints.[13] | Stabilises the transverse metacarpal arch | ||
Palmar ligament (volar plate) | The palmar aspect of the metacarpal neck
The palmar surface of the base of the adjacent proximal phalanx |
Blends with the collateral ligament | Prevents hyperextension of the MCP joint |
Ligaments Supporting Interphalangeal Joints[edit | edit source]
Key ligament | Origin | Insertion | Action/role | Key palpation points |
---|---|---|---|---|
Collateral ligaments
|
Head of the more proximal phalanx | Volar third of the middle phalanx bases
AL: Attaches to the fibres of the palmar ligament |
Provide radio-ulnar stability
Prevent excessive adduction-abduction movements of the interphalangeal joints. |
|
Palmar ligament (volar plate) | The palmar surface of the base of the distal phalanx | Blends with the accessory collateral ligaments | Prevents hyperextension of each IP joint |
Additional Structures[edit | edit source]
Pulleys of the Hand[edit | edit source]
Thickened areas of the flexor tendon sheath. The sheath holds the flexor tendons near the bone and converts the force generated in the muscle-tendon unit into movement at the phalanges. It helps maintain the tracking of the flexor tendons to the fingers during flexion and extension. There are two types of pulley systems in the hand:
- Annular pulleys are well-defined thickened tendon sheath areas going across the tendons.
- Cruciform pulleys provide the necessary flexibility for approximation of the annular pulley at flexion and maintain the integrity of the flexor sheaths.
You can read more on the hand pulleys here.
Muscles of the Hand[edit | edit source]
Hand muscles can be grouped into the extrinsic and intrinsic divisions:[4]
- Extrinsic division: muscles that originate on the forearm
- Intrinsic division: muscles that originate within the hand and are divided into four groups:
- The interossei: dorsal interossei,palmar interossei
- The lumbricals
- The hypothenar muscles controlling the fifth finger
- The thenar muscles controlling the thumb
Hand muscles can also be grouped according to their function into finger flexors, extensors, abductors and adductors.
The table below presents the hand muscles according to their function:
Finger Flexors[edit | edit source]
Muscle | Origin | Insertion | Innervation | Action |
---|---|---|---|---|
Dorsal interossei | Adjacent metacarpal shafts | The bases of the proximal phalanges and the extensor apparatus. | Abduct the fingers
Assist in flexion of the MCP joints | |
Palmar interossei | The first palmar interosseous: the medial side of the second metacarpal
The second and third interossei: the lateral side of the fourth and fifth metacarpals |
Proximal phalanx on the same side The extensor apparatus | Flexion the 2,4 and 5 MCP joints | |
Lumbricals | Tendons of the flexor digitorum profundus | Extensor apparatus on the second to fifth fingers | Flexion of MCP joints
Extension of the IP joints | |
Flexor digitorum profundus | Ulnar shaft
The interosseous membrane |
Distal phalanges of fingers two to five through four tendons | Flexion of the MCP, PIP, and DIP joints | |
Flexor pollicis longus | The anterior surface of the shaft of the radius | Distal phalanx of the thumb | Flexion of the thumb MCP and IP joints | |
Flexor digitorum superficialis
|
Innervation of the Hand[edit | edit source]
Vascular Supply of the Hand[edit | edit source]
Relevant Clinical Conditions[edit | edit source]
Clinical Relevance[edit | edit source]
- Swan neck deformity, characterised by hyperextension of the PIP joint and flexion in the distal Interphalangeal joint (DIP), is usually caused by a relative over-activity in the extensors of the PIP joint, or a laxity at the volar plate.
- Boutonniere deformity is a flexion deformity, usually occurring at the attachment of the central slip. It is commonly the result of:
- Finger pulley injuries
Resources[edit | edit source]
- bulleted list
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or
- numbered list
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References[edit | edit source]
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Duncan SFM, Saracevic CE, Kakinoki R. Biomechanics of the Hand. Hand Clinics 2013; 29(4): 483-492
- ↑ Hacking C, Gaillard F, Worsley C, et al. Phalanges of the hands. Reference article, Radiopaedia.org. Available from https://radiopaedia.org/articles/phalanges-of-the-hands [last access 7.09.2023]
- ↑ 3.0 3.1 Ayhan Ç, Ayhan E. Chapter 13 - Kinesiology of the wrist and the hand. Angin S, Şimşek IE (editors). Comparative Kinesiology of the Human Body. Academic Press, 2020: pages 211-282.
- ↑ 4.0 4.1 Xuan D. Exploring Hand Anatomy. Plus 2023
- ↑ 5.0 5.1 Vasković J. Trapeziometacarpal joint. Available from https://www.kenhub.com/en/library/anatomy/trapeziometacarpal-joint. [last access 14.09.2023]
- ↑ 6.0 6.1 Rad A. Carpometacarpal (CMC) joints. Available from https://www.kenhub.com/en/library/anatomy/carpometacarpal-cmc-joints [last access 14.09.2023]
- ↑ TheUpperHand. Thumb (Range of Motion) Goniometry. Available from: https://www.youtube.com/watch?v=OzukYU2OIKg [last accessed 16/9/2023]
- ↑ TheUpperHand. Finger (Range of Motion) Goniometry. Available from: https://www.youtube.com/watch?v=JX5dO7n4-Lg [last accessed 16/9/2023]
- ↑ Ladd AL, Weiss AP, Crisco JJ, Hagert E, Wolf JM, Glickel SZ, Yao J. The thumb carpometacarpal joint: anatomy, hormones, and biomechanics. Instr Course Lect. 2013;62:165-79
- ↑ Iyengar K, Sree DV, Loh WYC. Clinical practice algorithm for Eaton's injury of the thumb. J Clin Orthop Trauma. 2020 Jul-Aug;11(4):537-541.
- ↑ Kamalasekar K, Ravikanth R. First Carpometacarpal Joint Anatomy and Osteoarthritis: MR Imaging Overview. Indian J Radiol Imaging. 2022 Jan 10;31(4):1012-1015
- ↑ 12.0 12.1 Cardoso FN, Kim HJ, Albertotti F, Botte MJ, Resnick D, Chung CB. Imaging the ligaments of the trapeziometacarpal joint: MRI compared with MR arthrography in cadaveric specimens. AJR Am J Roentgenol. 2009 Jan;192(1):W13-9.
- ↑ Grujičić R. Metacarpophalangeal (MCP) joints. Available from https://www.kenhub.com/en/library/anatomy/metacarpophalangeal-mcp-joints [last access 16.09.2023]