Wrist Anatomy PDF

Upper Extremities Functional B Lecturer: Beáta Seregély assistant lecturer; [email protected] Semmelweis University Faculty of Health Sciences Department of Physiotherapy The wrist complex Theory Lecturer: Beáta Seregély assistant lecturer [email protected] Semmelweis Un...

Upper Extremities Functional B Lecturer: Beáta Seregély assistant lecturer; [email protected] Semmelweis University Faculty of Health Sciences Department of Physiotherapy The wrist complex Theory Lecturer: Beáta Seregély assistant lecturer [email protected] Semmelweis University Faculty of Health Sciences Department of Physiotherapy The function The wrist (carpus) consists of 2 compound joints: the radiocarpal and the midcarpal, referred to collectively as the wrist complex. Each joint proximal to the wrist serves to broaden the placement of the hand in space and to increase the degrees of freedom available to the hand. The shoulder serves as a dynamic base of support; the elbow allows the hand to approach or extend away from the body; and the forearm adjusts the approach of the hand to an object. Contrarily, the wrist major contribution is to control and adjust length-tension relationships in the multiarticular extrinsic hand muscles, which cannot be replaced by compensatory movements of the shoulder, elbow, or forearm and to allow fine adjustment of grip. The wrist muscles designed for balance and control to set and maintain the optimal position, rather than for maximizing torque production. The wrist has been called the most complex joint of the body, from both an anatomic and physiologic perspective. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Orientation at the wrist complex The carpal bones: from a radial (lateral) to ulnar direction, the proximal row includes the scaphoid (S), lunate (L), triquetrum (Tq), and pisiform (P), Left hand palmar side the distal row includes the trapezium (Tr), trapezoid (Tz), capitate (C), and hamate (H). The radiocarpal joint is formed by the radius and radioulnar disk as part of the triangular fibrocartilage complex (TFCC) proximally and by the scaphoid, lunate, and triquetrum distally. The midcarpal joint is the articulation between the scaphoid, lunate, and triquetrum proximally and the distal carpal row composed of the trapezium, trapezoid, capitate, and hamate. Intercarpal joints exist between the carpal bones. Left hand dorsal side SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Orientation at the dorsal surface The tendons of the muscles that cross the dorsal and dorsalradial side of the wrist are secured in place by the extensor retinaculum. The extensor compartments refer by Roman numerals I to VI in order from radial to ulnar are: 1st: abductor pollicis longus and extensor pollicis brevis 2nd: extensor carpi radialis longus and brevis, radially to Lister's tubercle, which separates the 2nd and 3rd compartments 3rd: extensor pollicis longus, ulnary to Lister's tub. 4th: extensor indicis and extensor digitorum 5th: extensor digiti minimi 6th (runs in the groove of the ulnar head): extensor carpi ulnaris: extensor carpi ulnaris SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. The dorsal surface Osteologic Features of the Distal Forearm Dorsal (Lister’s) tubercle of the radius Styloid process of the radius Styloid process of the ulna Distal articular surface of the radius Muscles that originate Muscles that insert there is no any Bracioradialis (side of the radius) ECRL ECRB ECU The dorsal surface of the distal radius has several grooves and raised areas that help guide or stabilize the tendons that course toward the wrist and hand. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18.  Right Orientation at the volar surface The transverse carpal ligament converts the palmar concavity made by the carpal bones into a carpal tunnel. This thick fibrous band of connective tissue is connected to four raised points on the palmar carpus, namely, the pisiform and the hook of the hamate on the ulnar side, and the tubercles of the scaphoid and the trapezium on the radial side. At the wrist level, all of the volar wrist muscles pass Left beneath the flexor retinaculum (TCL) along with the median nerve except the Palmaris Longus and the Flexor Carpi Ulnaris muscles. The flexor retinaculum prevents bowstringing of the long flexor tendons, thereby contributing to maintaining an appropriate length-tension relationship. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. The palmar/volar surface Muscles that originate Pronator quadratus (ulna) Muscles that insert Pronator quadratus (radius) Bracioradialis (side of the radius) Abductor pollicis longus Flexor carpi radialis Flexor carpi ulnaris The radiocarpal joint is moved indirectly by the muscles, as all the muscles that move the wrist are passed through it, but none, except the flexor carpi ulnaris (on pisiform), attach to the carpal bones. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Joint Structure - Radiocarpal Joint - surfaces The proximal components of the radiocarpal joint are the concave surfaces of the radius and an adjacent articular disc, which is also an integral part of the distal radioulnar joint. It composed by: the lateral concave radial facet, articulates with the scaphoid; the medial concave radial facet, articulates with the lunate; the TFCC, which articulates predominantly with the triquetrum. It also has some contact with the lunate in the neutral wrist. It lies directly beneath the ulna, blocking its the direct articulation between and the proximal carpals. The distal components of the radiocarpal joint are the convex proximal surfaces of the scaphoid and the lunate, and the triquetrum across the articular disc. As a whole it creates a biconvex (both antero posteriorly and transversally) ellipsoid (condyloid) surface. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Joint Structure - Radiocarpal Joint – wrist ligaments They are maintaining the natural intercarpal alignment and transferring forces within and across the carpus. Muscle-produced forces stored in stretched ligaments provide important control to the complex arthrokinematics of the wrist. Within them mostly in the dorsals, are mechanoreceptors help protecting the wrist. They are classified as extrinsic or intrinsic: Extrinsic ligaments have their proximal attachments on the radius or ulna, and the distal within the wrist. Intrinsic ligaments have both attachments within the wrist. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Joint Structure - Radiocarpal Joint – ligaments the radial (lateral) collateral ligament, extending from the radial styloid process to the scaphoid. It stretches during adduction and the medial ligament relaxes. Provide only modest stability, instead the extrinsic muscle does it. the ulnar (medial) collateral ligament, extending from the ulnar styloid process to the triquetrum and the pisiform. It stretches during abduction and the lateral ligament relaxes. the anterior radio-carpal ligament lying close to the centre of rotation, so no contribution. The anterior radio-carpal ligamentous complex is attached to the anterior edge of the concave distal surface of the radius and the neck of the capitate, stretches during extention. The posterior radio-carpal ligamentous complex forms a posterior strap for the joint, stretches during flexion. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Joint Structure - Midcarpal Joint - surfaces The articulation between the proximal and distal rows of carpal bones. The capsule that surrounds the midcarpal joint is continuous with each of the many intercarpal joints. The midcarpal joint can be divided descriptively into medial and lateral joint compartments. The larger medial compartment is formed by the convex (condyloid as a whole) head of the capitate and apex of the hamate, fitting into the concave recess formed by the distal surfaces of the scaphoid, lunate, and triquetrum. The lateral compartment of the midcarpal joint as a whole is formed by the junction of the slightly convex distal pole of the scaphoid with the slightly concave proximal surfaces of the trapezium and the trapezoid. The lateral compartment shows less movement than the medial. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Joint Structure - Intercarpal Joint - surfaces Joint surfaces between the carpal bones are vary in shape between nearly flat to markedly convex or concave. As a whole, the joints contribute to wrist motion through small gliding and rotary motions, occurring primarily between the bones within the proximal row of the carpus. Compared with the large range of motion permitted at the radiocarpal and midcarpal joints, motion at the intercarpal joints is relatively small but nevertheless essential for normal wrist motion and subtle posturing of the hand. Additionally, small intercarpal motions stretch several intercarpal ligaments that assist with dissipating compression forces across the wrist. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Joint Structure - Midcarpal Joint – dorsal ligaments The dorsal radiocarpal ligament courses distally in an ulnar direction, attaching primarily between the distal radius and the dorsal surfaces of the lunate and triquetrum. It reinforces the posterior side of the radiocarpal joint, helps guide the natural arthrokinematics, especially of the bones in the proximal row. provide an especially important restraint against anterior (volar) dislocation of the inherently unstable lunate. one of the richest sensory-innervated ligaments of the wrist, containing a relatively large number of mechanoceptors, so it has a dominant role in wrist proprioception. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Joint Structure - Midcarpal Joint – palmar ligaments There are several thick and strong ligaments known collectively as the palmar radiocarpal ligament. This ligament provides greater overall mechanical stability to the wrist than the thinner dorsal extrinsic ligament. Its 3 parts: Radio(scapho)capitate, long radiolunate/radiotriquetral, and short radiolunate In general, each ligament arises from the distal radius, travels distally in an obliquely ulnary. helps guide the natural arthrokinematics, provide stability, limit impingement between the dorsal radius and the carpals The palmar ulnocarpal ligament has two parts: ulnotriquetral and ulnolunate, they help indirectly secure the position of the disc (TFC). SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Joint Structure - intrinsic ligaments Essentially every intercarpal junction is bound and strengthened by intrinsic ligaments. The palmar intercarpal ligament firmly attaches to the distal one-third of the capitate. The ligament bifurcates proximally, forming two inverted V shape groups. The lateral leg attaches to the scaphoid, and the medial leg to the triquetrum. They help guide the arthrokinematics of the wrist. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Joint Structure - intrinsic ligaments The dorsal intercarpal ligament provides transverse stability to the wrist by interconnecting the trapezium and the proximal carpals. Tears or attenuation of these ligaments can result wrist instability, notably between the scaphoid and the lunate. They contain a large number of mechanoreceptors so they have a sensory role in coordinating wrist movement. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Joint Structure - intrinsic ligaments Several intermediate ligaments exist within the wrist: The lunotriquetral ligament, helps to stabilize the ulnar side of the lunate relative to the triquetrum. The primary stabilizer of the lunate, is the scapholunate ligament Scaphotrapezial and scaphotrapezoidal ligaments reinforce the articulation between the distal pole of the scaphoid with the trapezium and trapezoid. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. The long axis of the hand and the functional position of the wrist The functional position of the wrist corresponds to the position of maximal efficiency of the muscles of the fingers, especially of the flexors. This position is defined by: slight extension (dorsiflexion) of the wrist to (20) 30-45° slight ulnar deviation (adduction) to 10-15°. It is the position of the wrist that the hand is best adapted for its function of prehension. As we said the axis of the forearm in pronation is collinear with the axis of the arm and the hand, which is drawn across the radius near the ulnar notch, (approximately inline with the Lister’s tubercle) and runs through between the lunate and the scaphoid, the capitate and the third metacarpal bone and the middle finger. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Kinematics of Wrist Motion Wrist movements are combined motions of the radiocarpal and the midcarpal joints, so the axis of rotation pass through not at the radiocarpal joint, but the head of the capitate. The head of the capitate, frequently referred to as the “keystone” of the wrist, providing the rigid center of the fixed carpal arch. The axis runs in a near medial-lateral direction for flexion and extension occurring in the sagittal plane, and near anterior-posterior direction for radial and ulnar deviation take place in the coronal plane. But during flexion/extension the lunate seems to move least, so the axis rather is at the joint line between the lunate and the capitate. Wrist circumduction is a combination of the 2 before mentioned movements, the hand traces in space a conical surface. Flexion (80-85°): the palmar surface of the hand moves towards the anterior aspect of the forearm. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Kinematics of Wrist Motion Extension (70-85°): the dorsal surface of the hand moves towards the posterior aspect of the forearm. Both are maximal when the hand is neither abducted nor adducted. Passive flexion exceeds 90° in pronation, the passive extension exceeds 90°, in both pronation and supination. Adduction/ulnar deviation (30° (the axis of the hand used for measurement) -45°): hand moves towards the axis of the body, Abduction/radial deviation (15°): hand moves away from the axis of the body. The range of adduction is 2-3 times that of abduction, The range of adduction is greater in supination than in pronation, In general, the range of abduction and adduction is minimal when the wrist is fully flexed or extended, because of the tension developed in the carpal ligaments. It is maximal when the hand is in the reference position or slightly flexed, because the ligaments are relaxed. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. The bony structure guide the movements The distal end of the radius has 2 configurations of biomechanical importance. the distal end of the radius angles about 25° up, toward the ulnar (medial) direction. This ulnar tilt allows the wrist and hand to rotate farther into ulnar deviation than into radial deviation. As a result of this tilt, radial deviation is limited by bony impingement of the lateral side of the carpus against the styloid process of the radius. the distal articular surface of the radius is angled proximally about 10° in the palmar direction. This palmar tilt accounts, in part, for the greater flexion than extension at the wrist. Extension is the close-packed position. There are individual physiological bony variations. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Arthrokinematics of flexion-extension 1.From full flexion the active extension is initiated at the distal carpal row and at the firmly attached metacarpals by the wrist extensor muscles attached to those bones. The distal carpals glide on the relatively fixed proximal bones. The distal carpal row glides in the same direction as motion of the hand. It reflects the complexity of the midcarpal joint surface and the motion, and contradict the convex-concave rules. When the wrist complex reaches the neutral position, the ligaments spanning the capitate and scaphoid together in close-packed position. 2.Continued extensor force moves the combined unit of the distal carpal row and the scaphoid on the relatively fixed lunate and triquetrum. At ~ 45° of extension of the wrist complex, the scapholunate interosseous ligament brings the scaphoid and lunate into close-packed position, function as a single unit. 3.This relatively solid unit moves on the radius and TFCC. All ligaments become taut as full extension is reached and the entire wrist complex is close packed. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Arthrokinematics of flexion-extension Wrist motion from full extension to full flexion occurs in the reverse sequence. The series of hand activities necessary for activities of daily living and independence require a functional wrist motion of 10° of flexion and 35° of extension. Theoretically the arthrokinematics of extension-flexion are based on synchronous convex-on-concave rotations at both the radiocarpal and the midcarpal joints. Extension occurs at the radiocarpal joint as the convex surface of the lunate rolls dorsally on the radius and simultaneously slides in a palmar direction and at the midcarpal joint, the head of the capitate moves on the lunate in a same way, this produces full wrist extension. This two-joint system has the advantage that the significant total range of motion requiring only moderate amounts of rotation at the individual joints, each joint motion is relatively limited and so more stable. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Arthrokinematics of Ulnar and Radial Deviation In radial deviation, the carpals slide ulnarly on the radius. The carpal motion not only produces deviation of the proximal and distal carpals radially, but simultaneous flexion of the proximal carpals and extension of the distal carpals. During radial/ulnar deviation, the distal carpals, once again, move as a relatively fixed unit. In full radial deviation, both the radiocarpal and midcarpal joints are in close- packed position. The radial and ulnar deviation RoM are greatest when the wrist is in neutral flexion/extension. When the wrist is extended (close-packed position), the carpals are all locked, and very little radial or ulnar deviation is possible. In wrist flexion, the joints are loose-packed and the bones are splayed, but only little radial or ulnar deviation is possible in the fully flexed position. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Arthrokinematics of Ulnar and Radial Deviation The ulnar and radial deviation occurs through synchronous convex-on- concave rotations at both radiocarpal and midcarpal joints. During ulnar deviation, the midcarpal joint and, to a lesser extent, the radiocarpal joint contribute to overall wrist motion. At the radiocarpal joint, the scaphoid, lunate, and triquetrum roll in an ulnar direction and slide a significant distance radially. Ulnar deviation at the midcarpal joint occurs primarily from the capitate rolling in an ulnar direction and sliding slightly radially. Radial deviation occurs through similar arthrokinematics as ulnar deviation. The amount of radial deviation at the radiocarpal joint is limited because the radial side of the carpus impinges against the styloid process of the radius. Consequently, about 85% of radial deviation occurs at the midcarpal joint. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Carpal stability The arthrokinematics are driven by muscle but guided or controlled by passive tension within ligaments. 4 ligaments appear as the double-V system of ligaments. The distal inverted V is formed by the medial and lateral legs of the palmar intercarpal ligament; the proximal inverted V is formed by the palmar ulnocarpal and palmar radiocarpal ligaments. All 4 legs are under slight tension even in the neutral position. During ulnar deviation, passive tension increases in the lateral leg of the palmar intercarpal ligament (PICL) and fibers of the palmar ulnocarpal ligament. During radial deviation, tension increases in the medial leg of the (PICL) and fibers of the palmar radiocarpal ligament. A gradual increase in tension within these ligaments provides control to the movement, as well as dynamic stability to the carpal bones. Tensions in stretched collateral ligaments may assist the double-V system in determining the end range of radial and ulnar deviation. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Carpal stability Mechanically, the wrist consists of a mobile proximal row of carpal bones intercalated or interposed between two relatively rigid structures: the forearm (radius) and the distal row of carpal bones. In most healthy persons the wrist remains stable throughout life. Collapse and joint dislocation are prevented primarily by resistance from ligaments and from forces in tendons and by the shapes of the carpal bones. The lunate is the most frequently dislocated carpal bone. Beside the ligaments the scaphoid forms an important mechanical link between the lunate and the more stable, distal row of carpal bones, so the scaphoid and adjoining ligaments must be intact. The ulnar tilt of the radius creates a natural tendency for the carpus to translate in an ulnar direction, which resisted by the fiber direction of the palmar radiocarpal ligament. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Rotational collapse of the wrist Like cars of a freight train that are subject to derailment, the proximal row of carpal bones is susceptible to a rotational collapse in a “zigzag” fashion when compressed from both ends. The fracture in the “waist” region of the scaphoid, and tearing of the scapholunate ligament cause disruption of the mechanical link between the two bones. The inherently less stable lunate may dislocate, or sublux, so its distal articular surface faces dorsally. This condition is referred to clinically as dorsal intercalated segment instability (DISI). Injury to other ligaments besides the scapholunate ligament is often involved, such as the dorsal intercarpal or dorsal radiocarpal ligaments. Injury the lunotriquetral ligament, may allow the lunate to dislocate such that its distal articular surface faces in a volar orientation. This condition is referred to as volar intercalated segment instability (VISI). SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Rotational collapse of the wrist The injury to other ligaments besides the scapholunate ligament is often involved in DISI, such as the dorsal intercarpal or dorsal radiocarpal ligaments. DISI also may exist in the absence of a fractured scaphoid. Injury to both the scapholunate and the scaphotrapezial ligaments may allow the scaphoid to excessively flex (rock forward) as the lunate progressively subluxes dorsally. In addition to the scapholunate subluxation, an excessive gap typically forms between the scaphoid and lunate. In the relaxed wrist, the evidence of a gap of more than 3–5 mm used as a benchmark to suspect a clinically relevant static scapholunate dissociation. Active muscle contraction associated with grasp or bearing weight across the wrist with a DISI may force the capitate proximally between the scaphoid and lunate, thereby widening the preexisting gap. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Muscles at the Wrist The area of the red boxes is proportional to the cross-sectional area of the muscle’s belly and indicative of the maximal force. The small black dot within each red box indicates the position of the muscle’s tendon. The wrist’s axises of rotation intersect within the head of the capitate. The wrist’s axises of rotation intersect within the head of the capitate. Each muscle’s moment arm for a particular action is equal to the perpendicular distance between the particular axis and the position of the muscle’s tendon. That provide a useful method for estimating the action and relative torque potential of the wrist muscles. The ECU is an extensor and the FCU is a flexor and both are ulnar deviators. Because both muscles have similar cross-sectional areas, they produce comparable maximal force. But the ECU is more potent ulnar deviator than extensor and the FCU is both potent flexor ulnar deviator. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Function of the Muscles at the Wrist The wrist is controlled by a primary and a secondary set of muscles. The tendons of the muscles within the primary set attach distally within the carpus, or the adjacent proximal end of the metacarpals; these muscles act essentially on the wrist only. The tendons of the muscles within the secondary set cross the carpus and attach distally to the digits so they act on the wrist and the hand. At least from the anatomic position, therefore, essentially all wrist muscles are equipped with moment arms to produce torques in both sagittal and frontal planes, except the palmaris longus. The ECRL passes dorsally to the ML axis and laterally to the AP axis and produce a combination of wrist extension and radial deviation. Using this muscle for pure radial deviation would necessitate the activation of other muscles to neutralize the undesired wrist extension. So muscles of the wrist and hand rarely act in isolation when producing a meaningful movement. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Function of the wrist extensors The proximal attachments of the primary set are on and near the LEC of the humerus and dorsal border of the ulna. The main function of the wrist extensors is to position and stabilize the wrist during activities involving active flexion of the digits, particularly important in making a fist or producing a strong grip. The tendons of the muscles are secured in place by the extensor retinaculum, which prevents the underlying tendons from “bowstringing” up and away from the radiocarpal joint during active movements of the wrist. The extensor digitorum is also capable of generating significant wrist extension torque but is mainly involved with extension of the fingers. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Function of the wrist extensors The ECRB active during all grasp-and-release hand activities, except those performed in supination. The ECRL muscle shows increased activity when either radial deviation or support against ulnar deviation is required or when forceful finger flexion motions are performed. Activity of this muscle is important the maintaining the functional position of the wrist. Without this the wrist fixates in ulnar-deviated position. The ECU muscle extends and ulnarly deviates the wrist. It is active not only in wrist extension but frequently in wrist flexion as well. ECU muscle activity in wrist flexion adds an additional stability to the structurally less stable ulnar side. This is not needed on the radial side, which has more developed ligamentous and bony structural checks. It is less effective in pronation. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Function of the wrist flexors The proximal attachments of the primary wrist flexors are located on and near the MEC of the humerus and dorsal border of the ulna The transvers carpal ligament analogous to the extensor retinaculum, stabilizes the tendons of the wrist flexors and prevents excessive bowstringing during flexion. The FCU muscle envelops the pisiform, a sesamoid bone that increases the MA for flexion and its tendon crosses the wrist at a greater distance from the axis than does the FCR muscle, so the FCU muscle is more effective in its ulnar deviation than is the FCR muscle is in its radial deviation. The FCU has the greatest wrist flexion torque of the 3 primary wrist flexor muscles. During active wrist flexion, the FCR and FCU act together as synergists while simultaneously opposing each other’s deviation ability. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Function of the wrist flexors From the secondary muscles the FDS and FDP muscles are predominantly flexors of the fingers, and the FPL muscle is predominantly the flexor of the thumb. The FDS muscle seems to function more consistently as a wrist flexor than does the FDP muscle. This is logical, because the FDP muscle is a longer, deeper muscle, crosses more joints, and is therefore more likely to become actively insufficient. The position of the FPL muscle’s tendon suggests the ability to contribute to both flexion and radial deviation of the wrist if its more distal joints are stabilized. With the wrist in a neutral position, the abductor pollicis longus and extensor pollicis brevis have a small moment arm for wrist flexion. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Function of the radial deviators In the neutral wrist position, the ECRL and AbPL have the largest radial deviation torque. The extensor pollicis brevis torque production is relatively small. The AbPL and EPB provide important stability to the radial side of the wrist. The AbPL and the EPB muscles are capable of radially deviating the wrist. This radial deviation may detract from their prime action on the thumb. A synergistic contraction of the ECU muscle may be required to offset the unwanted wrist motion. When muscles producing ulnar deviation are absent, the thumb extrinsic muscles may produce a significant radial deviation deformity at the wrist. Little evidence has been found to indicate that the more centrally located EPL muscle has any notable effect on the wrist. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Function of the ulnar deviators Because of moment arm length, however, the muscles most capable of this action, by far, are the extensor carpi ulnaris and flexor carpi radialis. This strong pair of ulnar deviator muscles contracting when one strike a nail with a hammer. The wrist is driven strongly into ulnar deviation as it flexes slightly. The overall posture of the wrist at nail strike still remains biased towards extension however, a requirement for maintaining a firm grasp on the hammer. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Functional considerations, synergy of the wrist and fingers muscles The extrinsic finger flexor muscles, namely the FDP and FDS, possess a significant internal moment arm as wrist flexors, which must be counterbalance by the wrist extensor muscles. As a strong, static grip is applied to an object, such as a hammer, the wrist extensors typically hold the wrist in the functional position. This optimizes the length-tension relationship of the extrinsic finger flexors, thereby facilitating maximal grip strength. The grip strength is significantly reduced when the wrist is fully flexed. It is caused by combination of 2 factors. First the finger flexors cannot generate adequate force because they are functioning at an extremely shortened length respective to their length-tension curve. Passive insufficiency. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18. Functional considerations, synergy of the wrist and fingers muscles Second, the overstretched finger extensors, particularly the extensor digitorum, create a passive extensor torque at the fingers, which further reduces effective grip force. This combination of physiologic and biomechanical events explains why a person with paralyzed or weakened wrist extensor muscles (from a radial nerve injury for example) has difficulty producing an effective grip, even though the finger flexor muscles are fully innervated. Stabilizing the wrist in greater extension enables the finger flexor muscles to nearly triple their grip force. SU-FoHS Department of Physiotherapy Beáta Seregély assistant lecturer 2024. 09. 18.