Thoracic Limb

II Thoracic Limb

Chapter II Thoracic Limb

31 BONES - THORACIC LIMB II Thoracic Limb Locate the regions of the thoracic limb on an articulated limb. A • Thoracic limb: also called the 1. Shoulder region pectoral (PEK-toh-ral) limb or forelimb. 1. Shoulder region: area con- A. Scapula taining the scapula and humeral joint. 2. Brachium or arm: area con- B. Humerus taining the humerus. 3. Antebrachium or forearm: B area containing the ulna and 2. Brachium radius. or arm 4. Manus: area containing the carpal, metacarpal, digital, and sesamoid bones. II - 4a. Carpus: the structure made I up of carpal bones between the E. Interosseous space E forearm and metacarpus. D - 4b. Metacarpus: formed by 3. Antebrachium the metacarpal bones. C. Radius D. Ulna - 4c. Digital region: contains C the phalangeal bones. Med H. Accessory carpal bone Lat H F F. Carpal bones G. Radial carpal bone 4a. Carpus Dew claw I. Metacarpal bones 4. Manus J. Prox. phalanx I J 4b. Metacarpus M. Prox. sesamoid bones K. Middle phalanx K L. Dist. phalanx L 4c. Digits

I, II. Bones, Right thoracic limb, lateral & medial views

Review in general the bones of the thoracic limb using an carpus and digits in the metacarpus. articulated skeleton and individual bones. J. Proximal phalanx (P1): articulates with the metacarpal A. Scapula: the flat, triangular bone of the shoulder defining bone of the same number. the shoulder region. K. Middle phalanx (P2): the second bone of a digit. B. Humerus: the largest bone in the thoracic limb in the L. Distal phalanx (P3): the third bone of a digit. arm/brachium. M. Proximal sesamoid bones: two bones per weight bear- C. Radius: the weight-bearing bone of the ing digit on the palmar aspect of the metacarpophalangeal forearm/antebrachium. joint (one for the dew claw). D. Ulna: the long, thin bone of the forearm serving mainly N. dewclaw(II): first digit that doesn't bear weight. for muscle attachment and formation of the elbow joint. E. Interosseous space: the void between the ulna and ra- CLINICAL: dius. • Osteosarcoma: tumor of F. Carpal bones: the 2 rows of short bones making up the bone. It often metastasizes carpus. to the lungs; take chest radio- G. Radial carpal bone (II): located on the medial side of the graphs before any surgery. proximal row of carpal bones. • Physes/growth plates: all the physes of H. Accessory carpal bone: located on the lateral and palmar thoracic limb long bones close by 1 year sides of the proximal row of carpal bones. of age (except the proximal physis of the I. Metacarpals or metacarpal bones: the bones between the humerus (twelve to thirteen months).

32 II Thoracic Limb SCAPULA C D. Supraspinous fossa D B E B. Spine

H C. Acromion F

* * 3 2 G. Glenoid cavity 1* III. Left scapula, E. Infraspinous fossa ventral view 4

I. Left scapula, lateral view G 2*

H. Supraglenoid 1* tubercle H

F. Subscapular fossa

II. Left scapula, * * Defined in legend (LPI: lower priority item) medial view G 3

Study the bones of the thoracic limb on an articulated 1. Scapular notch (I, II): the indention in the cranial border at the level of the neck where the suprascapular n. crosses skeleton and on individual bones. This will help you 2. ^Neck (I, II): the constricted part of the scapula joining the articular angle when dissecting the muscles to understand their to the rest of the scapula attachments and functions. 3. ^Coracoid process (kor-ah-koid) (II, III): the small process on the medial side Thoracic (shoulder, pectoral) girdle: consists of only of the supraglenoid tubercle for the attachment of the coracobrachialis m. 4. Serrated surface (II): the dorsal part of the costal surface for the attachment the two scapulae in the domestic species as they of the serratus ventralis m. usually lack clavicles. The limb is attached to the ^ More important (LPI) body by muscles (syssarcosis) and not by a conven- D. Supraspinous fossa (soo’-pra-SPY-nus) (I, III): the area cranial tional joint. to the scapular spine providing attachment for the supraspinatus A. CLAVICLE (KLAV-i-kul) (collar bone): absent m. or rudimentary (oval cartilaginous plate) in most E. Infraspinous fossa (I, III): the area caudal to the spine providing dogs. The cat and some large dogs have a clavicle, attachment for the infraspinatus m. which is a separate bone seen radiographically. It F. Subscapular fossa (II, III): most of the medial (costal) surface of doesn't articulate with the shoulder as in humans, the scapula providing attachment for the subscapular m. but is embedded in the brachiocephalic m. So the G. Glenoid cavity: the shallow cavity that articulates with the thoracic limbs are not spread laterally but are under head of the humerus to form the shoulder joint. the body as needed for four-legged motion. H. Supraglenoid tubercle: the process near the cranial glenoid B-H. SCAPULA (SCAP-yoo-lah) or shoulder blade: cavity, providing attachment for the biceps brachii m. he flat, triangular bone of the shoulder. • Scapular cartilage: the thin band of cartilage on the dorsal border B. Spine of the scapula (I, III)#: the long projection of the scapula in the dog that is lost when bones are prepared dividing the scapula’s lateral surface and ending (not shown). as the acromion. CLINICAL: C. Acromion (a-KROH-mee-on) (I, III): the expanded • Articular scapular fractures: requires accurate distal end of the spine of the scapula where the reduction and internal fixation or DJD# develops. deltoid m. arises. • Supraglenoid tubercle fracture: biceps # (Roman numeral) in parentheses after a structure indicate in which brachii m. origin. Treat: single lag screw or illustration it is labeled (often on facing pages). Absence indicates # Degenerative joint disease the structure is in all illustrations. tension ban.

33 HUMERUS II Thoracic Limb B B, C. Greater tubercle, E. Intertubercular (bicipital) groove D Point of shoulder A C, B

2* D. Lesser 1* tubercle

F. Deltoid tuberosity A. Head II. Right humerus, proximal view 3* 3* 6* 5*

I. Right humerus, I. Olecranon fossa cranial view G H 4* I 7* 7* III. Right humerus, distal view G H. Med. (flexor) H epicondyle G. Lat. (extensor) * * IV. Right humerus, * * epicondyle 6 5 5 6 G * Defined in legend caudal view G-I. Humeral condyle * Defined in legend (LPI) G-I Study the humerus on an articulated skeleton and on in- 1.^ Neck (collum) (IV): joins the head to the rest of the bone dividual bones. 2. Insertion of the infraspinous tendon (I) A-J. HUMERUS (HYOO-mer-us): the arm or brachial 3. ^Brachial (musculospiral, spiral) groove (I, IV): spirals from the caudal to the lateral to the cranial surface of the humerus carrying the bra- bone is the largest bone of the thoracic limb. It articulates chialis m. and radial n. proximally with the scapula, forming the shoulder joint, 4. Lateral supracondylar crest (I): passes proximally from the lateral and articulates distally with the radius and ulna, forming epicondyle and gives rise to the extensor carpi radialis m. the elbow joint. 5, 6. Articular surface of the condyle: divided into trochlea and capitulum. 5.^ Trochlea (I, III, IV): the medial part of the articular surface crossed by A. Head (II, IV): the rounded process directed caudally to a groove for the trochlear notch of the ulna articulate with the smaller glenoid cavity of the scapula, 6. ^Capitulum (I, III, IV): the lateral part of the condyle that articulates thus, forming the shoulder joint. with the head of the radius B. Greater tubercle (I, II, IV): the palpable, large process cran- 7. Supratrochlear foramen (I): the opening between the olecranon and radial fossa in the dog. It may not be present as nothing passes through it. iolateral to the humeral head for muscle attachments. - C. Point of the shoulder (I, II): the palpable surface feature of the forearm. It is known as the extensor epicondyle. formed by the cranial part of the greater tubercle. - H. Medial (flexor) epicondyle (I, II, IV): the large, caudally D. Lesser tubercle (I, II, IV): the process medial to the directed projection that prevents medial luxation of the humeral head. elbow. It is functionally known as the flexor epicondyle E. Intertubercular (bicipital) groove (I, II): the sulcus be- as it is the attachment for the forearm flexor muscles. tween the greater and lesser tubercles through which the - I. Olecranon fossa (IV): the caudal excavation on the distal tendon of the biceps brachii m. runs. humerus receiving the anconeal process of the ulna on F. Deltoid tuberosity (I): the small process on the lateral side extension of the elbow. of the humerus for the insertion of the deltoideus m. CLINICAL: G-I. Humeral condyle: the entire cylindrical, distal extrem- • Humeral fractures: majority in the middle and ity of the humerus (there is only 1). distal third where there is a chance of radial n. - G. Lateral (extensor) epicondyle (I, III, IV): the lateral damage. Treat with open reduction and internal side of the humeral condyle giving rise to the extensors fixation.

34 II Thoracic Limb RADIUS & ULNA E E. Point of the elbow, 3* G. Anconeal process 3* G G D F. Trochlear notch D F 1* F D. Olecranon 1* * H 4 4* H. Med. coronoid process

C C. ULNA A A A. RADIUS J. Interosseous space

II. Left ulna and radius, cranial view 7*

B. Styloid process (radius) I III. Right ulna: cranial view I. Styloid process and radius, caudal view I. Left ulna and radius, lateral view I FOREARM ANTEBRACHIUM B or : formed by the ulna and 1. ^Head of the radius (I, III): articulates with the humerus (capitulum) radius. In the domestic species, the ulna is caudal to the by a articular fovea and the ulna radius in the proximal forearm and lateral to it distally. 2. Grooves (II): the three sulci on the cranial surface of the distal extremity of the radius, from medial to lateral for the oblique carpal extensor, A. RADIUS: the rod-like, main weight-bearing bone of the extensor carpi radialis, and common digital extensor tendons forearm. It articulates proximally with the humerus and 3. ^Olecranon tuberosity (I, II): the large process of the olecranon ulna to form the elbow joint, and articulates distally with for attachment of the triceps brachii m. the carpal bones to form the antebrachiocarpal joint. 4. Lateral coronoid process (I, III): the craniolateral distal end of the trochlear notch B. Styloid process of the radius (II, III): the distal point of Radius other structures: neck, articular fovea, body, distal extremity the radius located on the medial side. (trochlea), carpal articular surface. Ulna- other structures: body. C. ULNA (I, III): the long, thin bone serving mainly for * Defined in legend (LPI: low priority item) muscle attachment and formation of the elbow joint. ^ More important (LPI) D. Olecranon (oh-LEK-ra-non): the proximal part of the J. INTEROSSEOUS SPACE (I): the space between the ulna ulna providing a lever arm for the extensor muscles (triceps and radius. brachii m.) of the elbow. CLINICAL: E. Point of the elbow: the proximal ulna (olecranon • Ununited anconeal process: doesn't fuse with tuberosity [8]). It is a landmark located at the 5th the rest of the ulna by 6 months of age. Remove intercostal space in the standing animal. or reattach it with a screw. F. Trochlear (semilunar) notch (TROHK-lee-ar): the • Premature closure of distal ulnar physis: causes "C-shaped" depression that cups the condyle of the bowstring (cranial and medial) deformity of the humerus to help in formation of the elbow joint. radius, carpal valgus, and elbow subluxation. G. Anconeal process: the beak-like, proximal end of • Olecranon fractures: requires a tension band the trochlear notch which fits in the olecranon fossa appliance (two IM pins and figure eight wire) to of the humerus when the elbow is extended. H. Medial coronoid process (II): the craniomedial, distal counteract the pull of the triceps brachii m. end of the trochlear notch. • Radial and ulnar fractures: are often open. Simple I. Styloid process of the ulna: the distal end of the ulna. fractures are often treated with casts.

35 CARPUS II Thoracic Limb Accessory R carpal bone R U

Cr. Radial carpal bone Cu: Ulnar carpal bone Cr Cu C2 C2 C4 C3 C4 C3

Mc2 U R Mc1 Mc5 Mc3 Mc5 Ca C2 I. Left carpus, Cr II. left carpus, lateral view dorsal view Cu A. Sesamoid bone of the oblique carpal extensor tendon C1. 1st carpal bone C4 Mc1

Mc4

III. Left carpus, palmar view Cr. Radial carpal bone Cu. Ulnar carpal bone Ca. Accessory carpal bone Paw or Manus: the distal part of the thoracic limb con- • Distal (metacarpal) row: sisting of the carpus, metacarpus, phalanges and their R. Radius C1. 1st carpal bone (III) U. Ulna associated sesamoid bones. C2. 2nd carpal bone Mc1-5. Metacarpal 1-V CARPUS (KAR-pus): the carpal bones, the compound C3. 3rd carpal bone joint formed by these bones, or the region (including soft C4. 4th carpal bone: on the lateral side of the distal row structures) between the forearm and metacarpus. of carpal bones. Carpal bones: the 2 rows of bones forming the carpus. A. Sesamoid bone of the oblique carpal extensor (abduc- • Proximal (antebrachial) row: consists of the radial tor pollicis longus) tendon (III): the sesamoid bone on the carpal, ulnar carpal, and accessory carpal bones. medial side of the carpus in carnivores. - Cr. Radial (intermedioradial) carpal bone: in carnivores, it is the fused intermediate carpal bone of other CLINICAL: domestic species and the radial carpal bone. It is located • Carpal fractures: due to high-rise falls or on the medial side of the proximal row. jumping from trucks. They cause acute lameness. - Cu. Ulnar carpal bone: the lateral and smallest bone Oblique radiographs may be needed to see in the proximal row. fractures. Remove small chip fractures, stabilize - Ca. Accessory carpal bone: the oval plate on the lateral larger fragments with lag screw or multiple side of the carpus that projects behind (palmar to) the Kirschner wires. Partial carpal arthrodesis carpus. It is a landmark for the lateral and palmar (fusion) may be used for more involved fractures. aspect of the carpus. It also forms the lateral wall of • Sesamoid bone of the oblique carpal extensor tendon the carpal canal. (A): do not mistake it for a chip fracture in a radiograph.

36 II Thoracic Limb METACARPAL BONES R U a b

Mc1 Cr Cu C1 C4 Metacarpal one c Mc5

PS Mc2

Mc4 e Mc3 d A DS

II. Left manus/paw, A. Sagittal ridge dorsal view P2

I. Left metacarpal bones, palmar view

Mc1. Metacarpal I (I, II) III. Metacarpal, Mc2. Metacarpal II (I, II) Cr. Radial carpal bone distal end Mc3. Metacarpal III (I, II) Cu. Ulnar carpal bone Mc4. Metacarpal IV (I, II) e Ca. Accessory carpal bone Mc5. Metacarpal V (I, II) * Defined in legend (LPI) A. Sagittal ridge R. Radius d PS. Proximal (palmar) sesamoid bones (II) U. Ulna METACARPUS: the region of the manus between the carpus DS. Dorsal sesamoid bone R. Radius (I) Mc1-5. Metacarpal 1-V and digits. Carnivores have the generalized pattern of 5 U. Ulna (I) metacarpal bones numbered I-V from medial to lateral. P1. Proximal phalanx (I) Cr. Radial carpal bone (I) Mc2-5. Metacarpal II, III, IV, V (I, II): weight-bearing P2. Middle phalanx (I) Cu. Ulnar carpal bone (I) metacarpal bones. P3. Distal phalanx (I) C1-4 (I-IV). Numbered carpal Mc1. Metacarpal I (Mc1) (I, II): smaller than others, it bears bones no weight and has only one associated proximal sesamoid a. Base (II): the proximal extremity that articulates with the carpus b. Articular surface (II): undulating for the distal row of carpal bones bone. It is part of the dewclaw. Unlike the first metatarsal c. Shaft/body (II) bone in the rear limb, it is always present in the front limb. d. Head/trochlea (II, III): the distal extremity of Mc III articulating with the A. Sagittal ridge (II, III): the projection on the head of proximal phalanx and proximal sesamoid bones. It consists of two condyles the distal end of the metacarpal bones between the two separated by a sagittal ridge (A) - e. Condyles (medial and lateral) (II, III): articular areas condyles. It fits in a groove on the proximal end of the on either side of the sagittal ridge for the proximal phalanx proximal phalanx. and two proximal sesamoid bones

CLINICAL: • Sagittal ridge (A): can act like a screw driver • Metacarpal/metatarsal fractures: when in the groove of the proximal phalanx, resulting fixed, metacarpal/metatarsals3 and 4 must in a P1 fracture (most common in horses). be aligned properly for weight bearing.

37 II Thoracic Limb DIGITS 1 R U R U Ca Cr Cr Cu S

Mc1 Mc I Single palm. sesamoid bone

I P1 Mc5 Mc4 P3

E. Palm. sesamoid bones F. Dors. sesamoid bone P1. Prox. phalanx

P1 II P2. Middle phalanx Iii. Abaxial side P2

P3. Distal phalanx G. Horny claw D P3 V D

i I. Right manus, dorsal view I . Axial side G IV III II. Right manus, palmar view I. Axis of limb I. Axis of limb DIGITS: regional subdivision of the manus and pes that - D. Flexor tubercle/process/eminence (I, II, III, V): where correspond to the fingers and toes of man. There are five the deep digital flexor m. (DDF) attaches. digits in the generalized digital pattern, numbered from E. Proximal sesamoid bones (II, IV): small bones on the medial to lateral (1-5 or I-V). A digit generally consist of palmar side of the metacarpophalangeal joints (thus often three phalanges, a number of sesamoid bones, tendons, called palmar sesamoids). There are 2 for each of the main ligaments, vessels, nerves, and skin. weight-bearing digits and one for the dewclaw. They are DIGITAL BONES: consist of three phalanges and their called proximal for comparative anatomy, even though sesamoid bones, except the dewclaw(only two phalanges). there are no distal sesamoid bones in the carnivores. The P1. Proximal phalanx (FAY-lanks), PI or P1: the first phalanx dog has a cartilaginous nodule on the palmar side of the has a shallow groove articulating with the sagittal ridge distal interphalangeal joint. This correspond to the clinically of the corresponding metacarpal bone. significant distal sesamoid bone (navicular bone) in horses. P2. Middle phalanx, PII or P2: the second phalanx with F. Dorsal sesamoid bone (I, III): tiny bony nodules in the similar structures as the proximal phalanx, but shorter. It common digital extensor tendon of the four weight-bearing is not present in the first digit (dewclaw). digits at the metacarpophalangeal joint. P3. Distal phalanx, PIII, or P3: G. Horny claw: the fingernail-like structure covering the - A. Ungual process: the tapered, cone-shaped process ungual process. covered by the horny claw. H. Dewclaw or paradigit (I): a digit not bearing weight. It - B. Ungual crest: the crescent-shaped shelf of bone on the is the first digit and the first metacarpal bone. The first lateral and dorsal part the root of the horny claw. digit is reduced in size (having only two phalanges, the - C. Extensor process (I, III)#: the elevation on the dorso- proximal and distal, and one proximal sesamoid bone). proximal part of the distal phalanx of the four main digits. Some dog breeds have double dew claws. It provides insertion for the tendons of the common digital I. Axis of the limb (I): passes between the 3rd and 4th digits extensor m. (long digital extensor m. in the hind limb). and metacarpal bones. Ii. Axial side: side toward the axis. #(Roman numeral- IV): in parentheses after a structure indicate in which illustration it is labeled ii (often on facing pages). Absence indicates the structure is in all illustrations. A bold numeral I . Abaxial side: surface away from the axis. indicates the best illustration for a structure. On this page they also label the digits.

38 II Thoracic Limb DIGITS 2 E. Palm. sesamoid bones Single palm. sesamoid bone

Abaxial Axial P1

Digits are made of phalanges, 2* phalanges make up digits 1* P3 F. Dors. sesamoid bones I

P1. Prox. phalanx * 2 4*

I D. Flexor process

P2. Middle B * phalanx 1* 5 II V 3 A

4* IV III C. Extensor process G IV Left digits, D B. Ungual crest palmar view P3. Distal phalanx

Cr. Radial carpal bone (I, II) (I, II) II * Cu. Ulnar carpal bone 5 Ca. Accessory carpal bone (II) V S. Sesamoid bone of the oblique IV carpal extensor tendon (II)

III A. Ungual process G. Horny claw R. Radius (I, II) U. Ulna (I, II) Mc1-5. Metacarpal 1-V III. Left digits, dorsal view 1. Base (III, IV): proximal extremity of P1 and P2. 2. Axial groove of P1 (III, IV): the sulcus on the proximal articular surface of P1 for the sagittal ridge of its corresponding metacarpal bone. 3. Body (III, IV): shaft of P1 and P2 CLINICAL: 4. Head (III, IV): distal trochlea of P1 and P2 are • Dewclaw removal: common elective surgery saddle-shaped with a sagittal groove. in dogs, usually performed 5. ^Ungual groove (III, IV): holds the root of the claw. in the neonate. Other structures: proximal articular surface, palmar • Polydactyly: extra digits, tubercle, palmar groove. common in cats. * Defined in legend (LPI: lower priority item) ^ More important (LPI)