Module 1: Comparative Functional Anatomy and Biomechanics Article E-1 Learning Objectives At the end of this section the learner will be able to: Describe the bones of the equine thoracic Describe the joints of the equine thoracic and their movements Describe the supportive structures of the equine thoracic Describe the synovial structures of the equine thoracic 1
Fig 1.1 The Equine Thoracic Limb Cranial View 1. Scapula 2. Spine of Scapula 4. Humerus 5. Lateral tuberosity 6. Deltoid tuberosity 7. Lateral epicondyle 9. Radius 10. Carpus 12. Metacarpal III 13. Phalanges Proximal (P1) Middle (P2) Distal (P3) Modifications in the bones of the fore No clavicle Scapula: Large cartilage of prolongation which is incorporated into whither for muscle attachment No acromion Scapula spine is thickened from the scapula tuberosity Humerus: Short and thick Deep musculospiral grove Large tuberosities for attachments: Greater an lesser tuberde, both have cranial and caudal parts. Cranial greater tuberosity is the point of shoulder Intermediate tuberde helps prevent biceps from slipping laterally Large deltoid tuberosity Fig 1.2 Lateral and medial views of the bones of the left fore from the elbow distally 4. Humerus 7. Ulna 8. Olecranon process 9. Head of the Radius 10. Carpal bones 11. Accessory carpal bone 12.Tuberosity of Metacarpal III 12. Metacarpal III 14. Metacarpal IV 14. Metacarpal V 15. Proximal Sesamoid bones (x2) 16. Proximal phalanx (P1) 17. Middle phalanx (P2) 18. Distal phalanx (P3) 19. Distal sesamoid bone (x1) Lat. view Med. view 2
Modifications in the bones of the fore Radius: Flattened craniocaudally Medial surface is mostly subcutaneous Ulna: Shaft greatly reduced Fused with radius by interosseus ligement (ossifies in adult) Carpal bones: Large accessory carpal bone Prox row radial intermediate, ulnar and accessory carpal Distal row 2 nd, 3 rd, 4 th carpal Bones of the lower (same in the thoracic and pelvic ) Metacarpals: Cannon bone is only weight bearing element Strong with reduced medullary cavity MII & MIV (Splint Bones) are greatly reduced. Fibrous attachment to MII, which ossifies later Bones of the lower (same in the thoracic and pelvic ) Phalanges: Prox phalanx (long pastern) Decreased medullar cavity, grooved prox to conform to condyle of MII Middle phalanx (short pastern) No medullar cavity, partly enclosed in hoof Palmar fibrocartilage for ligament and tendon insertion Distal phalanx (coffin bone/pedal bone) Wedge-shaped, enclosed in hoof, perforated by many vascular foramina Extensor process porx Med & lat palmar processes caudally Solar surface concave forming semilunar crest on caudal border for attachment DDFT Lat cartilages extend prox from palmar processes, palpable above heels 3
Bones of the lower (same thoracic and pelvic ) Sesamoids Proximal Pared articulating with MII dorsal Axial surface joined by thick intersesamoidean ligament Distal/navicular Boat shaped, Articulated with PII and PIII Provides bearing surface for DDFT which places it under massive compressive stress Fig. 1.3 Bones of the lower (saggital section) 1. Metacarpal III 4. Proximal sesamoid 5. Proximal phalanx (P1) 7. Middle phalanx (P2) 9. Distal phalanx (P3) 10. Distal sesamoid Scapulo-trunk Type: Synsarcotic joint with no bony attachments (no clavicle) ROM: Glide - Rotation To inrease ROM of thoracic Supporting structures: Series of muscles that sling the trunk from the scapula. This allows for shock absorption and increase ROM. 4
Shoulder/ glenohumeral Type : Ball and socket joint Glenoid cavity of the scapula and head of humerus Glenoid fossa on scapula deepened by glenoid labrum ROM: Mostly Flexion (FL) and Extension (EXT) Rotation (ROT) Minimal Adduction (ADD) and Abduction (ABD) Supporting structures Four muscles form collateral support; Subscapular, Supraspinatus, Coracobrachialis and Infraspinatus Shoulder/ glenohumeral cont. Articulating structures: Biceps tendon lies over the cranial aspect of joint and is held against humerus by transverse humeral retinaculum Synovial structures and tendon sheaths: Bursa to biceps tendon is cranial to joint and does NOT communicate with joint capsule in horse. Bursa under infraspinatus tendon at greater tubercle of humerus. 3 7 Fig 1.4 and 1.5 Deep structures of the Glenohumeral Joint 3. Biceps tendon 5. Lat tuberosity of humerus 7. Bicipital bursa v. mm Biceps brachii z. Tendon of mm Infraspinatus 38. mm Subclavius 5
Elbow (humeroradial, humeroulnar, radioulnar) Type: Hinge joint Humeral condyle and the radius head and semilunar notch of elbow Proximal radioulnar joint communicates with main elbow simple pivot joint Humeroradial main weight bearing joint ROM: FL & EXT No movt proximal radioulnar joint Elbow (humeroradial, humeroulnar, radioulnar) cont. Supporting structures: Medial and lateral collateral ligaments. These limit rotation when elbow flexed. Synovial structures and tendon sheaths: The joint capsule extends to form synovial pouched underlying some of muscle insertions. Bursa under triceps attachment Fig 1.6 Deep structures of the Elbow joint 4. Humerus 4. Lateral collateral ligament of elbow 7. Ulna 8. Olecranon tuberosity 9. Radius 39. mm Brachialis 6
Carpal joint Type: Hinge joint Radiocarpal (RC) trochlea of radius and carpals Midcarpals (MC) proximal and distal carpals Carpomatacarpals (CMC) - carpal bones (II IV) and metacarpals (II IV) Intercarpals (IC) carpals of same row ROM RC FL & EXT (up to 90⁰) and slight ROT and glide MC FL & EXT (up to 45⁰) CMC little planar mvt and IC no planar mvt Carpal joint cont. Supporting structures: Strong carpal ligament (Extends to DFT as carpal/ accessory check ligament restricts over ext) Dorsal carpal ligament (ext retinaculum) Collateral ligaments Intercarpal ligaments Ligament from accessory carpal to MC Articulating structures: Flexor retinaculum anchors flexor tendons to palmar aspect of joint Carpal joint cont. Synovial structures and tendon sheaths: Common fibrous capsule separate synovial compartments with narrow communication between middle and distal compartments Sheaths or bursa associated with most of the tendons in carpal area. Common synovial sheaths for deep and superficial digital flexor tendons. 7
Fig 1.7 and 1.8 Supporting structures, synovial structures and tendon sheaths of the Carpus g d. mm Lateral digital extensor e. mm Extensor carpi ulnaris f. mm Long digital abductor g. Extensor retinaculum j. Tendon of mm Extensor carpi radialis k. Tendon of mm Extensor digiti communis (common digital extensor) j k Joints of the thoracic Metacarpo-phalangeal (fetlock) Type: Hinge Third metacarpal and proximal phalanx and proximal sesamoid bones ROM FL & Ext During FL small amounts of abd/add and axial rot Supporting structures: Collateral ligaments Interosseus muscle/suspensory ligament Proximal sesamoidean ligaments: Intersesamoidean and lat & med collateral sesamoidean Distal sesamoidean ligaments Metacarpo-phalangeal (fetlock) cont. Articulating structures: Paired proximal sesamoids Synovial structures and tendon sheaths: Extensive joint capsule extending under extensor tendon. Digital sheaths associated with superficial and deep digital flexors. 8
Reprinted with permission from the University of Wisconsin Digital Collection Fig 1.9 and 1.10 Supporting structures, synovial structures and tendon sheaths of the fetlock mm Interosseous (suspensory ligament Straight sesamoidean ligament Oblique sesamoidean ligament Collateral sesamoidean ligament Lateral collateral ligament of fetlock Proximal sesamoidean ligament Tendon of Common digital extensor Fetlock joint capsule Proximal Scutum Fig 1.11 Ligaments of the Pes 12. Interosseous (suspensory) ligament 15. Med and Lat collateral sesamoidean ligaments 16. Palmar annular ligament 17. Proximal digital annular ligament 18. Distal digital annular ligament Interphalangeal joint Type: Hinge joint PIP - Pastern - proximal and middle phalanx DIP - coffin joint - middle phalanx, distal phalanx, hoof cartilage and navicular bone ROM: FL & Ext Axial rot & lat mvts Supporting structures : Proximal interphalangeal joint (PIP) - lat & med collaterals. Paired abaxial and axial palmar ligaments (4 - prevents ext beyond 180 0 ) Distal interphalangeal joint (DIP) - med & lat collaterals. Collateral navicular ligaments. Distal navicular ligaments. 9
Interphalangeal joint cont. Articulating structures: Distal sesamoid (navicular bone) Synovial structures: Separate navicular (podotrochanteric) bursa. Fig 1.12 Supporting structures of the PIP and DIP Palmar ligament of pastern Central ligament of pastern Collateral ligament of pastern Common collateral ligament Dorsal ligament of coffin Collateral ligament of coffin Collateral sesamoidean ligament Distal sesamoidean ligament 10