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Lecture 16

FORS 3331 Lecture 16: Dr. Ferraro - FORS 3331 - Spring 2017 - Lecture 16

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Forensic Science
FORS 3331
Joseph V.Ferraro

Baker | FORS 3331| Spring 2017 | Lecture 16 | Page 1 LECTURE 16: THE HAND Minus the Fingers Overview – In this lecture we’ll tackle the bones of the hand (excluding the fingers [phalanges]) – That is, we’ll cover the wrist bones (carpals) and the palm bones (metacarpals) – The hand is comprised of 27 bones o 8 carpals o 5 metacarpals o 14 phalanges – The hand has 5 rays, each of which has one metacarpal and two or more phalanges o Ray 1: pollex or thumb o Ray 2: index finger o Ray 3: middle finger o Ray 4: ring finger o Ray 5: little finger, “pinky” – A refresher on directional terminology for the hand: o Anterior = Palmar o Posterior = Dorsal o Medial = Ulnar o Lateral = Radial – The wrist has eight (8) carpal bones arranged in two (2) rows o Most of these ossify from a single center o Proximal row (from radial to ulnar): scaphoid, lunate, triquetral, pisiform ▪ The scaphoid and lunate articulate with the radius at the distal radial articular surface o The distal row (from radial to ulnar): trapezium, trapezoid, capitate, and hamate ▪ Thesearticulateproximallywiththefirstrowofcarpalsanddistallywiththebases of the metacarpals Carpal Tunnel – Bony projections from the pisiform (I), hamate (I), scaphoid (m), and trapezium (m) stick out ventrally on the palm (2 medial, 2 lateral) – Between these projections extends a ligamentous band, the flexor retinaculum – This band retains the hand’s extrinsic flexor tendons against the wrist o Preventing them from popping out like taut bowstrings when the wrist is flexed – Together, the flexor retinaculum and carpal bones enclose a passageway – the carpal tunnel – Inflammation of these tendons will press on the median nerve and may cause pain, numbness, and paralysis of the first 3 ½ rays o Thumb to the radial side of the ring finger – This is called carpal tunnel syndrome Baker | FORS 3331| Spring 2017 | Lecture 16 | Page 2 The Carpals The Scaphoid – One of the largest carpals – Most lateral and proximal position o Between the radius and the trapezium at the base of the thumb – Spoon-shapedwithamajorconcavesurfacefortheheadof the convex surface that articulates with the distal radius – Thetubercleisabluntprojectionfortheflexorretinaculum Siding The Tubercle Method – Orient the concave surface towards you with the tubercle oriented superiorly – The tip of the tubercle points toward the side the bone comes from The Snail Method – Orient so the tubercle is the “head” – The convex “shell” is superior – The smooth indentation of the capitate will be facing you – Whichever side of the “snail’s shell” falls on is the side the bone comes from The Lunate – Shaped like a crescent half moon – Theconcavesurfacearticulateswiththeheadofthecapitate and the large rounded side articulates with the distal radius – Weird Factoid: etymologically speaking, “croissant” and “crescent” stem from the same root Siding The Croissant Method – Orient the bone so that the most convex and rugose side points away from you o i.e. with the open side of the croissant facing you – Make sure the well-defined half-circular articular surface for the triquetral is pointing up – The other side looks more like a poorly-defined rainbow – The triquetral surface will point toward the side the bone is from The Triquetral – 3 bone from the radial side in the proximal row – Also called the cuneiform – It has three articular facets (hence the name); o One with the lunate o One with the hamate o A circular isolated elevated one with the pisiform Baker | FORS 3331| Spring 2017 | Lecture 16 | Page 3 Siding The Pisiform Articular Surface Method – Orient the bone with the circular pisiform facet facing superiorly – Spin the bone until you see the right angle formed by the other two articular facets – The facet for the pisiform will be on the side that the bone is from The Pisiform – A pea-shaped bone with one circular articular facet for the triquetral – The non-articular body is an attachment for the flexor retinaculum – Factoid:thisbonedevelopswithintheflexorcarpiulnaristendon,so it’sactuallyasesamoidbone – You will not have to side the pisiform The Trapezium – Also called the greater multangular – The largest face is saddle-shaped for a distal articulation with MC1 o The first metacarpal o AKA the thumb – The long, raised, narrow tubercle/crest is the attachment for the flexor retinaculum Siding The Crucifix Method – Orient the bone so that you see a somewhat misshapen cross – The groove is on the side of the tubercle that the bone is from The Trapezoid – Also called the lesser multangular – The smallest carpal bone in the distal row – It is boot-shaped and articulates distally with MC2 o The second metacarpal o AKA the index ray Siding The Boot Method – Orient the bone with the sole of the “boot” facing inferiorly and the “v” on the
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