Radius, Ulna, and Manus

Radius, Ulna, and Manus General Information

• The radius and ulna are bones of the forearm (skeleton antebrachii).
• The movements of the radius and ulna include rotation and pronation/supination.
• The maximum rotation in humans is 180°, in cats is 90°, and in dogs is 45°.

Radius

• The radius presents a radial head that is transversely widened with a radial articular facet.
• The trochlear notch forms part of the radius.
• Cats have a simple cupula, dogs have a cupula with a medial groove, and ungulates have three parallel depressions.
• In carnivores, the radius is complemented medially by the ulna.
• The radial tuberosity is located on the medial aspect and is where the biceps brachialis muscle tendon inserts.
• The relief for ligamentous insertion is on the lateral aspect.
• The articular circumference is caudal.
• The diaphysis (corpus radii) is compressed in a craniocaudal direction and slightly curved in its length.
• The cranial surface of the radius is smooth, and its distal part is grooved for the passage of the extensor tendons.
• The caudal surface of the radius is fused to the ulna or roughened (CARN & PIG) for the insertion of the interosseous ligament.
• The interosseous space (spatium interossea antebrachii) can be proximal or distal.
• The distal epiphysis ("radial trochlea") has extensor grooves for the passage of the extensor tendons.
• The articular surface of the radius towards the carpus (facies articularis carpea) is a transverse elongated and weakly divided cavity (carn), or two cavities bordered by two condyles on the palmar side (ung).
• The transverse crest (crista transversa) is caudal.
• The styloid process of the radius (processus styloideus radii) is for the insertion of ligaments.
• The ulnar notch (incisura ulnaris radii) is lateral and present in carnivores and pigs.
• In ruminants the distal part of the ulna is completely fused with the radius.
• In horses, the distal part of the ulna is incorporated within the radius, becoming the lateral styloid process (processus styloideus ulnae).

Ulna

• The ulna's proximal epiphysis includes the olecranon.
• The olecranon tuberosity (tuber olecrani) furnishes insertion to the triceps brachii muscle.
• The trochlear notch (incisura trochlearis) is a collaboration between the ulna and radius.
• The anconeal process (processus anconeus) fits into the olecranon fossa of the humerus.
• Lateral and medial coronoid processes are present, with the medial being more developed in carnivores.
• The radial notch (incisura radialis ulnae) joins with the articular circumference of the radius.
• The diaphysis (corpus ulnae) has a triangular cross-section.
• The ulna is smaller than the radial diaphysis.
• The ulna runs caudal to the radius and is attached by soft tissue membranes or bony fusion.
• The interosseous space/s exists between both diaphysis.
• The distal epiphysis (caput ulnae) presents a styloid process.
• The articular circumference for the radius is present in carnivores and pigs.
• In horses, the distal extremity is fused to the radius, forming the lateral styloid process of the radius.
• Ruminants have a discrete tuberosity of the radius.
• The distal articular surface in ruminants is strongly oblique.
• Pig skeletons have short, stout bones that fuse late with an ulna more developed than the radius.
• A pig skeleton will have only one interosseous space, and a strangled distal end of the ulna.
• The distal articular surface of the ulna for a pig is very oblique
• In carnivores, the two bones (radius and ulna) are independent and mobile to one another.
• Carnivores have a discrete tuberosity of the radius and evident lateral relief of insertion.
• The quadrilateral olecranon in carnivores is divided by a groove.
• The medial coronoid processes in carnivores is always much more developed.
• In dogs, the radius articulates proximally with the lateral lip of the trochlea and with the capitulum.
• In cats, the radius articulates proximally only with the capitulum.

Manus

• Manus refers to the forepaw
• Carpus, metacarpus, digits, and numeration are all components
• Functions of the Manus include gripping, digging, climbing, flying, swimming and locomotion
• Manus can be defined by its load bearing configuration: palmigrade, digitigrade, or unguligrade
• Onguligrade can be further broken down; artiodactyla and perissodactyla
• The carpus has antebrachiocarpal and carpometacarpal joints.
• It is arranged in two rows: proximal (antebrachial) and distal (metacarpal).
• The proximal row contains the radial carpal bone (scaphoid bone), intermediate carpal bone (lunate bone), ulnar carpal bone (pyramidal bone), and accessory carpal bone (pisiform bone).
• The distal row is composed of first carpal bone (trapezium bone), second carpal bone (trapezoid bone), third carpal bone (capitate bone), and fourth carpal bone (hamate bone).
• The carpus as a whole has a carpal groove, and carpal tunnel
• It also has a proximal articular surface that is regularly convex (dorsopalmar direction) and a distal articular surface that can either be fat (EQ&RUM) or depressed (dorsopalmar direction) (PIGS&CARN)
• The canon bone is formed via the fusion of the 3rd and 4th metacarpal (Mc III+IV) in ruminants
• Intercapital notch and two heads are present in the epiphysis

Phalanges

• The digits have a digital skeleton.
• The proximal phalanx (phalanx proximalis) or os compedale (UNG) is the pastern bone.
• The middle phalanx or os coronale (UNG) is the crown bone.
• The distal phalanx or os ungulare (UNG) is the coffin bone, which may have proximal sesamoid bones and distal sesamoid bone.
• Proximal phalanx is a long bone with articular surface, inverse conformation, as well as two cavities/one groove

Sesamoid bones

• Sesamoid bones are small, complementary to the joints, and develop in the neighborhood of tendons
• The proximal sesamoid bones are double (inconstant digit I): metacarpalphalangeal joint, palmar aspect
• The ossa sesamoidea dorsalia (CARN) (proximal sesamoid bones) have a palmar surface marked by a smooth groove and is covered by a layer of cartilage [scutum proximale] for the flexor tendons
• Distal sesamoid bone (CARN): the distal interphalangeal joint (palmar aspect) for the passage of the deep digital flexor tendon over the palmar surface of the bone facilitated by fibrous cartilage [scutum distale]

Elbow/humeroradioulnar joint

• The joint involves the humerus, radius, and ulna.
• The oblique ligament arises on the proximal edge of the supratrochlear foramen and crosses the cranial, flexor surface of the elbow joint distomedial to the tendons of the mm. biceps brachii and brachialis, where it may split in two.
• The trochlear notch of ulna provides stability.
• It is a composite joint, humeral surface is key.
• It is typical hinge joint or ginglymus (CARN)
• Humeroulnar joint, humeroradial joint, and proximal radioulnar joints are common joint capsules

Radioulnar joints

• In carnivores there are two separate synovial radioulnar joints that work via:

• *Anular ligament of the radius, Interosseous membrane of the antebrachium, Interosseous ligament of the antebrachium, Radioulnar ligament

• Humeroulnar + humeroradial + proximal radioulnar joints

• *on the caudal aspect, the capsule inserts along the proximal border of the olecranon fossa

• on the cranial aspect has one pouch extends medially under the biceps muscle and one laterally under the common digital extensor muscle

• The proximo radiuoulnar joins communicates communicates freely with the elbow joint

• The distal radioulnar joint is the extension of the antebiachiocarpal.joint