PAS427Class09TheHandNotes1.docx

Overview ======== - Distal-most region of the upper appendage - Intricate dexterity -- precision contractions and opposable digit allow grasping, manipulation with great deal of control - Opposition due to 90^0^ rotation of 1^st^ digit - Palmar region found anteriorly, dorsal reg...

Overview ======== - Distal-most region of the upper appendage - Intricate dexterity -- precision contractions and opposable digit allow grasping, manipulation with great deal of control - Opposition due to 90^0^ rotation of 1^st^ digit - Palmar region found anteriorly, dorsal region found posteriorly Bones of the hand ================= - Divided into 3 regions Carpal bones ------------ - The bones of the wrist - Articulate with radius, ulna through wrist joint proximally, metacarpals distally - 8 bones arranged in 2 rows of 4 - Scaphoid, lunate, triquetrium, pisiform - Trapezium, trapezoid, capitate, hamate - Interconnected through flat articulating surfaces bound by dense ligaments - Permits small degree of gliding - Subtle, but necessary for normal hand function - Joints are often tight, restrictive following cast removal for fractured forearm, wrist; limits hand movements (grasping, pulp-to-pulp opposition); part of rehabilitative therapy involves carpal joint mobilization to improve function Metacarpal Bones ---------------- - Associated with the distal palm - Composed of 5 small long bones - Base found proximally, articulating with carpal bones - Digit 1 -- saddle joint - Head found distally, articulating with phalanges - Makes up "knuckles" of the fist - Metacarpal fractures common, resulting from improper punches, punching hard surfaces; 3^rd^ metacarpal particularly vulnerable, due to its length Phalanges --------- - Associated with the fingers - Series of very small long bones - 2 in digit 1 (proximal and distal), 3 in digits 2 through 5 (proximal, middle, and distal) - Articulate with metacarpals through condyloid joints - Permits flexion, extension, abduction, adduction - Interarticulations through hinge joints - Permits flexion, extension only Fascia and Compartments ======================= - Hand enveloped in single layer of superficial fascia continuous with the fascia of the forearm - Specialized in various regions, depending on function - Fascia helps to divide hand into 5 distinct compartments; each compartment houses different set of muscles - NB: all 5 compartments associated with palmar surface; no dorsal compartments, intrinsic muscles Palmar Fascia ------------- - Covers the palmer surface - Thickest in midregion of palm, where it forms palmar aponeurosis - Dense regular connective tissue projecting distally towards digits - Due in part to insertion of plamaris longus tendon - Projects into palmar surface of digits, forming fibrous digital sheaths that envelop flexor tendons - Projects deep in palmar surface of hand dividing palm into separate compartments - Dupuytren Contracture -- fibrosis/shortening of medial aspect of palmer aponeurosis, resulting in contracture of 4^th^ and 5^th^ digits - Fibers oriented transversely just distal to the wrist - Superficial transverse fibers commonly called the palmar carpal ligament, but officially unnamed - Very thin -- similar and continuous with extensor retinaculum on posterior side - Holds all flexor tendons in place, preventing bowstringing - Deeper, thicker transverse fibers run from scaphoid/trapezium to pisiform/hook of hamate, forming the flexor retinaculum, (transverse carpal ligament) - Forms the roof of the carpal tunnel - Separates wrist/digital flexors - Wrist flexors (flexor carpi) found superficial to transverse ligament - Digital flexors (flexor digitorum) found deep to transverse ligament - Thins out drastically on either side of flexor retinaculum, where it envelops thenar and hypothenar eminences as loose aerolear connective tissue - Palmaris brevis -- small, thin muscle that runs transversely in palmar fascia over hypothenar eminence - Anchors dermis over hypothenar eminence to palmar aponeurosis - Contracts to wrinkle skin, deepen palmar furrow - Soft protection for ulnar artery/nerve Dorsal Fascia ------------- - Much thinner than palmar fascia - Thickest just distal to the wrist, where it forms the extensor retinaculum Central Compartment ------------------- - Located deep to palmar aponeurosis - Medial/lateral borders formed by deep fascial projections off palmar aponeurosis - Houses digital flexor tendons - Midpalmar space -- potential space between central, interosseous compartment - Assists with tendon gliding Thenar Compartment ------------------ - Located lateral to central compartment - Contains thenar muscles, forming fleshy tissue at base of thumb - Thenar space -- potential space between thenar, adductor compartments - Allows gliding between compartments Hypothenar Compartment ---------------------- - Located medial to central compartment - Contains hypothenar muscles, forming fleshy tissue at base of small finger Interosseus Compartment ----------------------- - Located between metacarpals - Contains dorsal, palmar interossei muscles - NB: despite name, dorsal interossei still considered part of palmar surface Adductor Compartment -------------------- - Intermediate to thenar/interosseus compartments - Contains adductor pollicis muscle Muscles of the Hand =================== Thenar Muscles -------------- - Located at base of thumb (pollicis) in thenar compartment - Common origin off flexor retinaculum, lateral carpal bones (scaphoid, trapezium) - Involved with precision movement of the thumb - Particularly important for opposition - Loss of function (e.g. deinnervation) results in muscle atrophy, loss of opposition; antagonistic muscles pull thumb into extension (ape-hand deformity) #### Flexor Pollicis Brevis - Superficial medial portion of the thenar eminence - Two headed muscle (superficial and deep) separated by FPL tendon - Inserts on proximal phalanx - Assists FPL with metacarpophalangeal flexion #### Abductor Pollicis Brevis - Superficial lateral portion of the thenar eminence - Inserts on proximal phalanx - Assists APL with metacarpophalangeal abduction #### Opponens Pollicis - Deep portion of the thenar eminence - Inserts on 1^st^ metacarpal - Contracts to generate complex movement of thumb opposition (flexion, internal rotation of 1^st^ carpometacarpal joint drawing pulp of thumb towards other fingers) Hypothenar Eminence ------------------- - Located at base of little finger (digiti minimi) in hypothenar compartment - Common origin off flexor retinaculum and carpal bones (pisiform, hook of hamate) - Involved with precise movement of little finger #### Flexor Digiti Minimi Brevis - Lies superficial and lateral (inside border) in the hypothenar eminence - Inserts on outside of proximal phalanx - Flexor of MCP joint - NB: flexor digiti minimi longus represents rare anatomical variant: not normally present in humans nor discussed in anatomical texts #### Abductor Digiti Minimi - Found superficial and medial (outside border) of hypothenar eminence - Inserts on outside of proximal phalanx - Abductor of MCP joint #### Opponens DigitiMinimi - Deep portion of the thenar eminence - Inserts on 5^th^ metacarpal - Generates opposition in little finger (flexion, internal rotation of 5^th^ carpometacarpal joint) Adductor Pollicis ----------------- - Only muscle of the adductor compartment - Belly divides into 2 heads - Oblique head -- originates off base of 2^nd^, 3^rd^ metacarpal - Transverse head -- originates off shaft of 3^rd^ metacarpal - Inserts on proximal phalanx of thumb - Adducts thumb, contributes to grip strength Lumbricals ---------- - Four small cylindrical muscles - NB: lumbrical -- earthworm - Originate off FDP tendon - Two lateral lumbricals (1 and 2) have single origin off lateral border of tendons to 2^nd^ and 3^rd^ digit - Two medial lumbricals (3 and 4) bipennate, originating off medial and lateral borders of adjacent tendons to digits 3 through 5 - Tendon cross anterior to MCP joints on their lateral sides, project posteriorly to insert on lateral bands of extensor hood - Unique insertion results in flexion of MCP joint, extension of interphalangeal joints - Commonly paralyzed following nerve damage to brachial plexus (Klumpke's palsy), medial nerve, or ulnar nerve; loss of intrinsic function (MCP flexion, IP extension) results in unopposed pull of antagonistic muscles leading to claw finger deformity (MCP extension, IP flexion); variability in specific lumbrical muscles paralyzed, depending on site of nerve damage (due to innervation by different nerves) results in different deformity presentations Interossei Muscles ------------------ - Found within the interosseus compartment - Tendons cross anterior to MCP joints to attach to base of proximal phalanges, expansion of extensor hood - Similar course to lumbrical muscles; also produce MCP flexion, IP extension - Interossei commonly paralyzed along with lumbricals (similar innervation pattern), further contributing to claw finger/hand deformity #### Palmar Interossei - Three unipennate muscles originating off sides of 2^nd^, 4^th^, and 5^th^ metacarpal bones - Come off side closest to midline - 2^nd^ -- medial - 4^th^ and 5^th^ -- lateral - Insert on side of proximal phalange closest to midline - Contract to pull digits 2, 4, 5 closer to digit 3 (adduction) - Think: 3 PAD #### Dorsal Interossei - Four bipennate muscles originating off both sides of adjacent metacarpals - Tendons insert on base of proximal phalange furthest away from midline - Arrangement permits abduction during contraction - Think: 4 DAB Long Tendons of the Hand ======================== Flexor Digitorum Tendons ------------------------ - Digital flexor tendons (from FDS and FDP) enter hand through carpal tunnel encased in common flexor sheath (ulnar bursa) - Bursal membrane separates each row of tendons, preventing friction - Think: water-filled garbage bag - In central compartment, tendons of FDS, FDP disperse to digits 2 through 5 - As tendons approach MCP joint, become encased in digital synovial sheaths similar to common flexor tendon sheaths that continues to distal insertion point - Synovial sheath of 5^th^ digit continuous with common flexor sheath; while tenosynovitis (synovial sheath infections from deep lacerations) of digits 2 through 4 remain localized, synovial sheath infection in digit 5 can spread to central compartment, carpal tunnel - Tendons and sheaths covered by fibrous sheath anteriorly that forms osseofibrous tunnel - Prevents bowstringing of tendons - Quervain tenovaginitis stenosans -- fibrous thickening of sheaths and stenosis of osseofibrous tunnel due to excessive friction in tendons; may result in tendons getting "caught" in tunnel, producing painful snapping on flexion/extension (trigger finger) - Past MCP joint, FDS tendons bifurcate, attach bilaterally to base of middle phalanges - Tendons of FDP continue along midline of digit, emerging from beneath FDS at bifurcation point, to insert on base of distal phalanges Flexor Pollicis Longus Tendon ----------------------------- - Enters hand through carpal tunnel lateral to digital flexor tendons - Curves laterally to enter thenar compartment and continues on to base of distal phalanx of 1^st^ digit - Constitutes a single tendon wrapped in a continuous tendonous sheath from carpal tunnel to distal insertion (radial bursa) Extensor Digitorum Tendons -------------------------- - Major component of dorsum of hand - Enter hand deep to extensor retinaculum to continue to digits 2 through 5 - At the MCP joint, the tendon splits, broadens into aponeurosis called extensor expansion (dorsal hood) - Central (median) bands continues along midline of digit to insert at base of middle phalanges - Partial bifurcation generates lateral bands, which diverge along proximal phalanges, converge and insert upon distal phalanges - Receive lumbrical, interossei attachment Vasculature of the Hand ======================= - Arterial supply from extensive anastomoses of radial, ulnar arteries - Poses difficulties with severe lacerations to arteries of the hand; often the brachial artery is compressed to prevent excessive bleeding during surgical repair Superficial Palmar Arch ----------------------- - Superficial arterial arcade supplied by superficial branches of the ulnar artery medially and the radially artery laterally - Ulnar \> radial - Gives off 3 common palmar branches between digits 2 through 5 - Each branch splits at MCP joint to form proper digital branches - Raynaud syndrome -- idiopathic ischemia of digital arteries, typically in response to cold, stress, resulting in pain and/or parasthesia - Course along medial/lateral sides of adjacent digits - Gives off single proper digital branch to medial side of 5^th^ digit Deep Palmer Arch ---------------- - Deep arterial arcade supplied by deep branches of the ulnar artery medially and the radially artery laterally - Ulnar \< radial - Gives off 3 palmar metacarpal branches - Anastamose with common palmer branches anteriorly - Gives off radialis indicis artery - Supplies blood to lateral aspect of 2^nd^ digit - Gives off Princeps pollicis artery - Splits to supply digital branches to the thumb Nerves of the Hand ================== Median Nerve ------------ - Enters hand through carpal tunnel - Carpal Tunnel Syndrome -- results from increased compartmental pressure in the carpal tunnel; caused by inflammation of tendons, ulnar/radial bursa or blunt force trauma; pressure causes neural degeneration of median nerve, resulting in loss of function - Gives off recurrent branch to thenar eminence; innervation of thenar muscles (except deep head of FPB) - Injury to any part of the median nerve results in loss of function of thenar eminence, progressing to ape-hand deformity without recovery - Branches into common/proper digital nerves between digits 1 through 4. - Supply motor branches to lumbricals 1 and 2 - Injury to any part of the median nerve results in loss of function of lumbricals supplying digits 2 and 3, progression to digital claw deformity for these 2 digits, exclusively ("median nerve claw") - When asked to make fist, loss of function results in incomplete flexion of digits 2 and 3 (the "Hand of Benediction" sign) - Proper digital nerves receive cutaneous innervation from digits 1 through 3, lateral half of digit 4 Ulnar Nerve ----------- - Enters hand through ulnar canal between pisiform and hook of hamate, medial to ulnar artery - Provides branches to hypothenar eminence - Deep branch courses with deep palmer arch - Supplies motor branches to interossei, adductor pollicis, deep head of FPB - Superficial branch splits to provide common digital branch between digits 4 and 5, proper digital branch to digit 5 - Gives off motor branches to 3^rd^ and 4^th^ lumbricals - Proper digital branches receive cutaneous innervation from digit 5, medial half of digit 4 - Ulnar nerve supplies majority of muscles in the hand; injury to the ulnar nerve proximal to the hand would result in extensive loss of hand function, progressing to "ulnar nerve claw" deformity; more pronounced claw deformity for digits 4 and 5 (loss of lumbricals, interossei) and less pronounced claw deformity for digits 2 and 3 (loss of interossei, only); Radial Nerve ------------ - Superficial branch enters the hand superficial to the palmar fascia - Receives cutaneous innervation to base of thumb, back of hand