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Structure and Function of the Wrist
Chapter 6 Structure and Function of the Wrist Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Wrist Structure Terminology
Two major articulations Radiocarpal joint Midcarpal joint Palmar Synonymous with anterior Dorsal Synonymous with posterior Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Osteology: Distal Radius and Ulna
Form a concavity that articulates with the convex (proximal) row of carpal bones Concavity is bordered laterally by the radial styloid process and medially by the ulnar styloid process Radial tubercle (Lister’s tubercle) Bone projection on dorsal aspect of distal radius; guides direction of several wrist and thumb extensor muscle tendons Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Osteology: Carpal Bones
Proximal row includes: Scaphoid, lunate, triquetrum, and pisiform Distal row includes: Trapezium, trapezoid, capitate, and hamate Bones within proximal row are loosely joined; strong ligaments tightly bind distal row Distal row stability provides an important rigid base for articulations with metacarpal bones Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Osteology: Carpal Tunnel
Partly formed by transverse carpal ligament bridging palmar side of carpal bone Serves as passageway that helps protect median nerve and tendons of extrinsic flexor muscles of digits Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Joint Structure: Radiocarpal Joint
Proximal part consists of concave surface of radius and adjacent articular disc Distal part consists primarily of the convex articular (proximal) surfaces of scaphoid and lunate Approximately 80% of force that crosses wrist passes through scaphoid, lunate, and radius Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Joint Structure: Radiocarpal Joint – cont’d
Ulnar-located carpal bones and distal ulna are less likely to fracture from falls because they are not in the direct path of weight bearing Ulnocarpal space Relatively wide space between distal ulna and ulnar carpal bones Helps buffer forces that cross wrist Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Joint Structure: Midcarpal Joint
Midcarpal joint separates proximal and distal rows of carpal bones Most prominent articulation is formed between head of capitate and socket formed by distal surfaces of scaphoid and lunate Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
Ligaments of the Wrist Wrist joints are enclosed within fibrous capsule, thickened by extrinsic and intrinsic ligaments Extrinsic ligaments have proximal attachments outside carpal bones but attach distally within carpal bones Intrinsic ligaments have both proximal and distal attachments located within carpal bones Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Extrinsic Ligaments of the Wrist
Dorsal radiocarpal ligament Resists extremes of flexion Attaches between radius and dorsal side of carpal bone Radial collateral ligament Resists extremes of ulnar deviation Strengthened by muscles such as abductor pollicis longus and extensor pollicis brevis Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Extrinsic Ligaments of the Wrist – cont’d
Palmar radiocarpal Resists extremes of wrist extension Thickest ligament of wrist Ulnar collateral Resists extremes of radial deviation Helps stabilize distal radioulnar joint Part of ulnocarpal complex Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Intrinsic Ligaments of the Wrist
As a group, intrinsic ligaments: Interconnect various carpal bones Help transfer forces between hand and forearm Maintain natural shapes of radiocarpal and midcarpal joints, thereby minimizing joint stress during movement Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
Wrist Instability Normally, wrist remains stable when compressed, even under substantial forces Damage from large force or typical wear and tear from aging can significantly destabilize this region Goals for a weak, painful wrist typically include strengthening, relief of pain, education on ways to protect the wrist, and splinting Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
Osteokinematics Osteokinematics of wrist involve flexion-and-extension and ulnar-and-radial deviation Wrist typically does not spin in circular motion relative to fixed radius Portions of radiocarpal joint naturally block this twisting motion Pronation and supination are motions of forearm—not hand or wrist Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Osteokinematics – cont’d
Wrist movement’s axis of rotation pierces capitate head Axis runs medially laterally for flexion and extension and anteriorly posteriorly for radial and ulnar deviation Rotation of capitate to direct overall path of entire hand Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Sagittal Plane: Flexion and Extension
From neutral position, wrist flexes about degrees and extends about degrees Total flexion normally exceeds extension by about 15 degrees Extension limited by tension in thicker palmar carpal ligaments and carpal bones making contact with dorsal side of distal radius Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Frontal Plane: Radial and Ulnar Deviation
On average, from neutral position: Full ulnar deviation allows about degrees Radial deviation allows about degrees Maximum ulnar deviation is normally twice that of radial deviation, mostly because of void created by ulnocarpal space Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Arthrokinematics: Central Wrist Column
Series of articulations, or links, between the radius, lunate, capitate, and third metacarpal bone Radiocarpal joint Articulation between radius and lunate Midcarpal joint Articulation between lunate and capitate Carpometacarpal joint Rigid articulation between capitate and base of third metacarpal Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Arthrokinematics: Extension and Flexion
Wrist extension Simultaneous convex-on-concave rotations at both radiocarpal and midcarpal joints Kinematics occur as roll and slide in opposite directions simultaneously at radiocarpal and midcarpal joints Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Arthrokinematics: Extension and Flexion – cont’d
Full wrist extension elongates palmar radiocarpal ligaments, palmar capsule, and wrist and finger flexor muscles Helps stabilize wrist in extended position; useful when weight is borne through upper extremity Arthrokinematics of wrist flexion are similar but occur in reverse fashion Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Ulnar and Radial Deviation of Wrist
Motions of ulnar and radial deviation occur through simultaneous convex-on-concave rotations, at both radiocarpal and midcarpal joints Radial deviation at wrist is limited; radial aspects of carpal bones abut against styloid process of radius, thereby limiting extent of radial deviation across wrist Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Muscle and Joint Interaction
Innervation of wrist muscles Radial nerve courses down posterior aspect of forearm and supplies all muscles that extend wrist Median and ulnar nerves travel down anterior aspect of forearm and innervate all primary wrist flexor muscles Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Function of Muscles of the Wrist
Wrist muscles can be classified into: Primary set that attaches to wrist or nearby regions Secondary set that bypasses wrist and attaches more distally to digits All muscles of wrist cross axes of rotation located at capitate bone and therefore produce movement at wrist Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Function of Muscles of the Wrist – cont’d
Flexion and extension occur about the medial-lateral axis of rotation Radial and ulnar deviation occurs about an anterior-posterior axis of rotation Specific action of each wrist muscle determined by location of its tendon relative to each axis of rotation Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Wrist Extensors: Extensor Carpi Radialis Brevis
Proximal attachment Lateral epicondyle of humerus—common extensor tendon Distal attachment Base of third metacarpal—dorsal aspect Innervation Radial nerve Actions Wrist extension Radial deviation Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Wrist Extensors: Extensor Carpi Radialis Longus
Proximal attachment Lateral epicondyle of humerus—common extensor tendon Distal attachment Base of second metacarpal—dorsal aspect Innervation Radial nerve Actions Wrist extension Radial deviation Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Wrist Extensors: Extensor Carpi Ulnaris
Proximal attachment Lateral epicondyle of humerus—common extensor tendon Distal attachment Base of fifth metacarpal—dorsal aspect Innervation Radial nerve Actions Wrist extension Ulnar deviation Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Functional Consideration: Wrist Extensor Activity during a Grasp
Wrist extensors position and stabilize wrist for activities involving fingers e.g., making strong fist or grasp Contraction of wrist extensors is necessary to prevent wrist from “collapsing” into flexion because of strong flexion pull of extrinsic finger flexor muscles Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
Functional Consideration: Wrist Extensor Activity during a Grasp – cont’d Wrist extensor muscles, therefore, must contract every time a grasp is made; if not, wrist collapses into unwanted flexion Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
Functional Consideration: Wrist Extensor Activity during a Grasp – cont’d Person with paralyzed wrist extensor muscles usually has difficulty making a grip, even when finger flexor muscles are normal Because wrist extensors are paralyzed, gripping results in finger flexion combined with wrist flexion Unless strength is returned to wrist extensor muscles, wrist extension splint is required to brace the wrist in extension Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Wrist Flexors: Anatomy
Primary wrist flexors include: Flexor carpi radialis, flexor carpi ulnaris, and palmaris longus Secondary set wrist flexors include: Extrinsic flexors to the digits (flexor digitorum profundus, flexor digitorum superficialis, and flexor pollicis longus) Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Wrist Flexors: Flexor Carpi Radialis
Proximal attachment Medial epicondyle of humerus—common flexor tendon Distal attachment Base of second metacarpal—palmar aspect Innervation Median nerve Actions Wrist flexion Radial deviation Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Wrist Flexors: Flexor Carpi Ulnaris
Proximal attachment: medial epicondyle of humerus—common flexor tendon Distal attachment: base of fifth metacarpal and pisiform—palmar aspect Actions Wrist extension Ulnar deviation Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Wrist Flexors: Palmaris Longus
Proximal attachment Medial epicondyle of humerus—common flexor tendon Distal attachment Transverse carpal ligament and palmar apneurosis Innervation Median nerve Action Wrist flexion Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Functional Consideration: Synergistic Action of the Wrist Muscles
Simultaneous activity of flexor carpi radialis radially and flexor carpi ulnaris is required for pure wrist flexion Strong activation of all three flexors is usually required in conjunction with making a power grip Palmaris longus also helps stabilize proximal attachment of many intrinsic hand muscles Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Radial and Ulnar Deviators
Primary set of radial deviators Extensor carpi radialis longus and extensor carpi radialis brevis Secondary set of radial deviators Extensor pollicis longus, extensor pollicis brevis, flexor carpi radialis, abductor pollicis longus, and flexor pollicis longus Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Radial and Ulnar Deviators – cont’d
Muscles in both sets radially deviate wrist Extensor pollicis brevis has greatest moment arm of all radial deviators but typically has small torque production Abductor pollicis longus and extensor pollicis brevis provide important stability to radial side of wrist along with radial collateral ligament Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Functional Consideration: Grasping and Controlling Objects in the Hand
Radial and ulnar deviator muscles are frequently used for activities that involve grasp and control of objects held within hand Because of strong functional association between flexor and extensor carpi ulnaris muscles, injury to either muscle can disrupt overall muscular action of ulnar deviation For example, rheumatoid arthritis often causes inflammation and pain in extensor carpi ulnaris tendon Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
Summary Wrist joint is actually composed of two separate joints: radiocarpal joint and midcarpal joint Although only 2 degrees of freedom are allowed at the wrist, simple flexion/extension or radial/ulnar deviation motion requires motion at both joints Most often, wrist muscles are responsible for positioning hand Copyright © 2014, 2009 by Mosby, an imprint of Elsevier Inc.
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