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The range of adduction is 2-3 times that of abduction.
The range of adduction is 2-3 times that of abduction.
True
The range of adduction is less in supination than in pronation.
The range of adduction is less in supination than in pronation.
False
The range of abduction and adduction is maximal when the wrist is fully flexed.
The range of abduction and adduction is maximal when the wrist is fully flexed.
False
The distal end of the radius angles about 25° down, toward the ulnar direction.
The distal end of the radius angles about 25° down, toward the ulnar direction.
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Radial deviation is limited by bony impingement of the carpus against the styloid process of the radius.
Radial deviation is limited by bony impingement of the carpus against the styloid process of the radius.
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The distal articular surface of the radius is angled proximally about 10° in the dorsal direction.
The distal articular surface of the radius is angled proximally about 10° in the dorsal direction.
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Extension of the wrist is considered the close-packed position.
Extension of the wrist is considered the close-packed position.
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Active extension is initiated at the proximal carpal row.
Active extension is initiated at the proximal carpal row.
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The distal carpal row glides in the opposite direction to the motion of the hand when reaching the neutral position.
The distal carpal row glides in the opposite direction to the motion of the hand when reaching the neutral position.
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Individual physiological bony variations do not affect wrist motion.
Individual physiological bony variations do not affect wrist motion.
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The wrist complex consists of two compound joints: the radiocarpal and the midcarpal.
The wrist complex consists of two compound joints: the radiocarpal and the midcarpal.
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The shoulder joint does not contribute to the placement of the hand in space.
The shoulder joint does not contribute to the placement of the hand in space.
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The carpal bones include the radius and the ulna.
The carpal bones include the radius and the ulna.
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The distal row of carpal bones includes the trapezium, trapezoid, capitate, and hamate.
The distal row of carpal bones includes the trapezium, trapezoid, capitate, and hamate.
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The main function of the wrist is to maximize torque production for the hand.
The main function of the wrist is to maximize torque production for the hand.
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The intercarpal joints exist between the carpal bones.
The intercarpal joints exist between the carpal bones.
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The wrist has been described as one of the simplest joints of the body.
The wrist has been described as one of the simplest joints of the body.
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Fine adjustment of grip is a significant contribution of the wrist.
Fine adjustment of grip is a significant contribution of the wrist.
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The wrist complex does not affect the approach of the hand to an object.
The wrist complex does not affect the approach of the hand to an object.
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In wrist flexion, the joints are in a loose-packed position and bones are splayed.
In wrist flexion, the joints are in a loose-packed position and bones are splayed.
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Radial deviation occurs mostly at the radiocarpal joint.
Radial deviation occurs mostly at the radiocarpal joint.
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During ulnar deviation, the capitate bone rolls in a radial direction.
During ulnar deviation, the capitate bone rolls in a radial direction.
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Tension in ligaments does not influence the movement of the carpal bones.
Tension in ligaments does not influence the movement of the carpal bones.
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The scaphoid, lunate, and triquetrum bones slide radially during ulnar deviation.
The scaphoid, lunate, and triquetrum bones slide radially during ulnar deviation.
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The radial side of the carpus limits the amount of radial deviation due to impingement against the styloid process of the radius.
The radial side of the carpus limits the amount of radial deviation due to impingement against the styloid process of the radius.
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The passive tension in ligaments increases during ulnar deviation.
The passive tension in ligaments increases during ulnar deviation.
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The distal inverted V system of ligaments is formed by the palmar radiocarpal and palmar ulnocarpal ligaments.
The distal inverted V system of ligaments is formed by the palmar radiocarpal and palmar ulnocarpal ligaments.
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Both radial and ulnar deviations occur through different arthrokinematics.
Both radial and ulnar deviations occur through different arthrokinematics.
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Tension in stretched collateral ligaments helps determine the end range of radial and ulnar deviation.
Tension in stretched collateral ligaments helps determine the end range of radial and ulnar deviation.
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The wrist remains stable throughout life in most healthy persons.
The wrist remains stable throughout life in most healthy persons.
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The lunate is the least frequently dislocated carpal bone.
The lunate is the least frequently dislocated carpal bone.
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A fracture in the 'waist' region of the scaphoid can cause a mechanical disruption between the scaphoid and lunate.
A fracture in the 'waist' region of the scaphoid can cause a mechanical disruption between the scaphoid and lunate.
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The scaphoid and adjoining ligaments must be intact for optimal wrist function.
The scaphoid and adjoining ligaments must be intact for optimal wrist function.
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Volar intercalated segment instability (VISI) occurs when the lunate dislocates with its distal articular surface facing dorsally.
Volar intercalated segment instability (VISI) occurs when the lunate dislocates with its distal articular surface facing dorsally.
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The distal articular surface of the lunate faces dorsally in dorsal intercalated segment instability (DISI).
The distal articular surface of the lunate faces dorsally in dorsal intercalated segment instability (DISI).
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The wrist experiences a rotational collapse when compressed from one end.
The wrist experiences a rotational collapse when compressed from one end.
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The ulnar tilt of the radius contributes to the carpus translating in a radial direction.
The ulnar tilt of the radius contributes to the carpus translating in a radial direction.
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Injury to the dorsal intercarpal ligament is not typically involved in wrist instability.
Injury to the dorsal intercarpal ligament is not typically involved in wrist instability.
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The palmar radiocarpal ligament resists the tendency of the carpus to translate in an ulnar direction.
The palmar radiocarpal ligament resists the tendency of the carpus to translate in an ulnar direction.
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The FCU muscle is less effective in ulnar deviation than the FCR muscle is in radial deviation.
The FCU muscle is less effective in ulnar deviation than the FCR muscle is in radial deviation.
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The proximal attachments of the primary wrist flexors are located on and near the MEC of the humerus.
The proximal attachments of the primary wrist flexors are located on and near the MEC of the humerus.
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During active wrist flexion, the FCR and FCU act together as antagonists.
During active wrist flexion, the FCR and FCU act together as antagonists.
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The FDP muscle is more consistently effective as a wrist flexor than the FDS muscle.
The FDP muscle is more consistently effective as a wrist flexor than the FDS muscle.
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In the neutral wrist position, the ECRL and AbPL have the largest radial deviation torque.
In the neutral wrist position, the ECRL and AbPL have the largest radial deviation torque.
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The transvers carpal ligament stabilizes the tendons of the wrist flexors and enhances their effectiveness during flexion.
The transvers carpal ligament stabilizes the tendons of the wrist flexors and enhances their effectiveness during flexion.
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Study Notes
The Wrist Complex
- The wrist joint is comprised of the radiocarpal and midcarpal joints, collectively known as the wrist complex
- Each joint proximal to the wrist helps improve the placement of the hand, increasing its range of motion
- The shoulder offers a dynamic base of support; the elbow allows hand extension or approach toward the body; the forearm adjusts the hand's trajectory towards an object
- The wrist's primary function is to control and adjust the length-tension relationships of multiarticular extrinsic hand muscles.
- The wrist muscles are designed for balance and control to set and maintain optimal position, rather than for maximizing torque production.
Wrist Complex Orientation
- The carpal bones, arranged from radial to ulnar:
- Proximal Row: Scaphoid (S), Lunate (L), Triquetrum (Tq), and Pisiform (P)
- Distal Row: Trapezium (Tr), Trapezoid (Tz), Capitate (C), and Hamate (H)
- The radiocarpal joint connects the radius and radioulnar disc to the scaphoid, lunate, and triquetrum
- The midcarpal joint is the articulation between the scaphoid, lunate, and triquetrum with the distal carpal row (trapezium, trapezoid, capitate, and hamate)
- Intercarpal joints exist between the carpal bones
Wrist Movements
- Adduction range is 2-3 times greater than abduction
- Adduction range is greater in supination than pronation
- Abduction and adduction range is least when the wrist is fully flexed or extended, due to tension in carpal ligaments
- Maximal range of abduction and adduction occurs in the reference position or slightly flexed position, as the ligaments are relaxed
Bony Structure
- The distal end of the radius has two significant biomechanical aspects:
- Ulnar tilt: Angles 25° upwards, allowing for greater ulnar deviation than radial deviation (radial deviation limited by bony impingement)
- Palmar tilt: Distal articular surface angles 10° proximally towards the palm, contributing to greater flexion than extension at the wrist
Arthrokinematics of Flexion-Extension
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Full Flexion to Neutral: Active extension starts at the distal carpal row and firmly attached metacarpals, driven by wrist extensor muscles.
- Distal carpals glide on the relatively fixed proximal bones.
- Distal carpal row glides in the same direction as hand motion.
- This contradicts the convex-concave rule, reflecting the complexity of the midcarpal joint surface.
- When reaching neutral position, the ligaments spanning the capitate and scaphoid create a close-packed position.
-
Extension beyond Neutral: Continued extension force moves the combined unit of the distal carpal row and scaphoid over the relatively fixed lunate and triquetrum.
- Fully flexed wrist joints are loose-packed and allow only minimal radial or ulnar deviation.
Arthrokinematics of Ulnar and Radial Deviation
- Ulnar and radial deviations occur through synchronous convex-on-concave rotations at both radiocarpal and midcarpal joints.
-
Ulnar Deviation:
- Midcarpal joint contributes more than the radiocarpal joint
- Scaphoid, lunate, and triquetrum roll ulnarly and slide radially at the radiocarpal joint
- Capitate rolls ulnarly and slides slightly radially at the midcarpal joint
-
Radial Deviation:
- Similar arthrokinematics as ulnar deviation
- Limited by bony impingement of the radial side of the carpus against the radius' styloid process
- 85% of radial deviation occurs at the midcarpal joint
Carpal Stability
- Muscle drives arthrokinematics, while ligaments control and guide them.
- Four ligaments form a double-V system:
- Distal inverted V: Medial and lateral legs of the palmar intercarpal ligament
- Proximal inverted V: Palmar ulnocarpal and palmar radiocarpal ligaments
- All four legs are under tension even in the neutral position
- Ulnar deviation: Increases tension in the lateral leg of the palmar intercarpal ligament (PICL) and palmar ulnocarpal ligament fibers.
- Radial deviation: Increases tension in the medial leg of the (PICL) and palmar radiocarpal ligament fibers.
- Gradual increase in ligament tension controls movement and provides dynamic stability to carpal bones.
- Tension in stretched collateral ligaments assists the double-V system in determining the range of radial and ulnar deviation.
Carpal Stability (cont.)
- The wrist consists of a mobile proximal row of carpal bones sandwiched between the forearm (radius) and the distal row, which are relatively rigid.
- Wrist stability is maintained by ligament resistance, tendon forces, and the shape of carpal bones.
- The lunate is the most frequently dislocated carpal bone.
- The scaphoid is crucial for the mechanical link between the lunate and distal carpal bones.
- The radius' ulnar tilt creates a natural tendency for carpal translation towards the ulnar side, countered by the palmar radiocarpal ligament fiber direction.
Rotational Collapse of the Wrist
-
The proximal row of carpal bones is susceptible to rotational collapse in a "zigzag" manner when compressed from both ends.
-
Dorsal Intercalated Segment Instability (DISI):
- Scaphoid fracture in the "waist" region and scapholunate ligament tearing disrupt the mechanical link.
- The inherently less stable lunate may dislocate or sublux, so its distal articular surface faces dorsally.
- Other injured ligaments may include the dorsal intercarpal or dorsal radiocarpal ligaments.
-
Volar Intercalated Segment Instability (VISI):
- Injury to the lunotriquetral ligament can cause lunate dislocation, with its distal articular surface facing volarly.
-
This rotational collapse mechanism is less likely on the radial side, due to stronger ligamentous and bony structures.
Function of Wrist Flexors
- The primary wrist flexors originate near the medial epicondyle (MEC) of the humerus and the ulna's dorsal border.
- The transverse carpal ligament, similar to the extensor retinaculum, stabilizes wrist flexor tendons, preventing excessive bowstringing during flexion.
- The FCU muscle envelops the pisiform, a sesamoid bone. This arrangement increases the mechanical advantage (MA) for flexion, and the tendon crosses the wrist at a greater distance from the axis than the FCR, making the FCU more effective for ulnar deviation.
- The FCU has the greatest wrist flexion torque among the three primary flexor muscles.
- During active wrist flexion, the FCR and FCU act as synergists while opposing each other's deviation abilities.
Function of Wrist Flexors (cont.)
- Secondary flexor muscles:
- FDS and FDP primarily flex the fingers.
- FPL primarily flexes the thumb.
- The FDS muscle consistently functions as a wrist flexor more than the FDP.
- This is logical, as the FDP crosses more joints, becoming easily actively insufficient.
- The FPL tendon position suggests a contribution to both wrist flexion and radial deviation if distal joints are stabilized.
- In the neutral wrist position, the abductor pollicis longus and extensor pollicis brevis have a small moment arm for wrist flexion.
Function of Radial Deviators
- In the neutral wrist position, the ECRL and AbPL have the largest radial deviation torque.
- The extensor pollicis brevis has a relatively small torque production.
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Description
Explore the intricate anatomy and functions of the wrist complex, including the radiocarpal and midcarpal joints. Understand how the shoulder, elbow, and forearm work together to enhance hand movement and the mechanics of wrist muscles. Test your knowledge of carpal bones and their arrangement.
