The Canine Elbow Anatomy

By Anna Lloyd and Kirsten Straszacker

Anatomy forms the very foundation of everything we do as Vetrehabbers, and (un)fortunately, it’s an area we should be constantly reviewing and studying!

This month, we dive into the canine elbow. We’ll discuss it’s classification, stabilisation, mobility and, of course, the anatomical structures that allow each component of movement.

Joint classification

The elbow is a composite joint that includes the humerus, radius and ulna. The humeroulnar and humeroradial joints are both hinge joints, while the proximal radioulnar joint is a pivot joint and the mid-radioulnar joint is a syndesmosis joint.

Physiological movement available

Within the humeroradioulnar joints, flexion and extension occur in the sagittal plane through the transverse axis of movement. This flexion and extension is an essential component of the functional movement of the dog, allowing the forelimb to protract and retract during a normal gait cycle. Flexion of the elbow is essential during functional movements such as jumping, climbing stairs, and lying down.

Within the radioulnar joint, pronation and supination occur in the transverse plane through the ventrodorsal axis of movement. Pronation and supination allow the dog to turn and pivot, and to adjust to changes in the surface of the terrain. It is also essential during self-grooming activities.

Stabilisation of the elbow

The elbow joint is stabilised by a series of structures. The shape of the humeroulnar portion provides stability to the joint and restricts movement to the sagittal plane. Lateral movement of the joint is restricted by the medial and lateral collateral ligaments, as well as the anconeal process that extends into the olecranon fossa of the humerus.

The annular ligament runs transversely around the radius from the lateral to the medial coronoid processes of the ulna. Other ligaments of the elbow include the olecranon ligament and the oblique ligament.

The joint capsule surrounds the entire humeroradioulnar joint, and communicates with the proximal radioulnar joint. 

The radius and ulna are primarily united by the strong interosseus ligament (Hermanson et al., 2020).

Muscles responsible for elbow extension

There are three primary muscles responsible for the extension of the canine elbow: the four heads of the Triceps Brachii, the Anconeus, and the Tensor Fascia Antibrachii.

Triceps Brachii has four heads – long, lateral, medial, and accessory. The four heads have a common insertional tendon onto the olecranon tuber, with a synovial bursa between the tendon and the prominence of the olecranon.

The long head originates on the distolateral two-thirds of the caudal border of the scapula and the infraglenoid tuberosity. The lateral head lies between the long head and the humerus, originating on the tricipital line of the humerus via an aponeurosis. It inserts on the olecranon in a short broad tendon that partially merges with the tendon of the long head, and partially with the tendon of the tensor fascia antibrachii. The medial head originates on the crest of the minor tubercle of the humerus and inserts independently on the medial portion of olecranon tuber. The accessory head originates on the proximocaudal part of the neck of the humerus and inserts on the common tendon of the olecranon tuber with the lateral and long heads.

Anconeus originates on the lateral epicondylar crest, the lateral epicondyle, and part of the medial epicondyle of the humerus. It inserts on the lateral surface of the proximal ulna.

Tensor Fascia Antebrachii originates above the axillary arch from the thickened epimysium of the lateral surface of M. Latissimus dorsi, and inserts on the common tendon of the olecranon tuber, as well as in the antebrachial fascia.

The muscles of extension are all innervated by the radial nerve (Hermanson et al., 2020).

Muscles responsible for elbow flexion

There are three primary muscles responsible for flexion of the elbow: the Brachialis, Biceps Brachii and Extensor Carpi Radialis.

Brachialis originates on the proximal portion of the brachial groove of the humerus, winding from the caudolateral to the cranial surface of the humerus as it travels distally and inserts on the ulnar tuberosity.

Biceps Brachii originates on the supraglenoid tubercle of the scapula via a long tendon of origin, which crosses over the cranial humerus through the intertubecular groove. It is held in place within the groove by a transverse band – the retinaculum transversum. It communicates with the shoulder joint capsule, which surrounds it as a tendon sheath. At the elbow, the tendon of insertion splits into two parts, inserting on the ulnar tuberosity and radial tuberosity.

Extensor Carpi Radialis originates on the lateral epicondylar crest of the humerus. As it travels distally down the radius, it splits into two tendons, which continue to travel together through a groove on the carpus covered by the extensor retinaculum and surrounded by a tendon sheath. Once past the carpus, they separate and insert on the 2nd and 3rd metacarpal bone as the longus and breves respectively.

The Brachialis and Biceps Brachii are both innervated by the musculocutaneous nerve, while the Extensor Carpi Radialis is innervated by the radial nerve.

Muscles responsible for supination and pronation of the radio-ulnar joint

Two primary muscles originating at the elbow control supination: the Supinator and the Brachioradialis.

Supinator originates on the lateral epicondyle and the lateral collateral ligament, where there is normally a sesamoid bone present, and inserts on the cranial surface of the medial border of the radius.

Brachioradialis, also known as Supinator Longus, originates on the proximal surface of the lateral epicondylar crest of the humerus and inserts on the distal 3rd and 4th region of the cranial-medial portion of the radius. Both muscles are innervated by the radial nerve.

The two muscles originating at the elbow that support pronation of the limb, include the Pronator Teres and Pronator Quadratus.

Pronator Teres originates on the medial epicondyle of the humerus and inserts on the medial border of the radius down to the middle portion.

Pronator Quadratus originates between the ulna and radius over the interosseous membrane. The fibers run obliquely, distally and medially from the ulna to the insertion on the radius. Both muscles are innervated by the median nerve.

Accessory structures of the elbow

The accessory structures of the elbow include muscles that originate from the adjacent structures of the elbow joint but do not primarily contribute to the movement of the elbow. These muscles primarily control the movement of the carpus and digits.

They are listed below in order from craniolateral to caudomedial origins:

• M. Extensor Digitorum Communis
• M. Extensor Digitorum Lateralis
• M. Extensor Carpi Ulnaris
• M. Flexor Carpi Ulnaris (Ulnar and Humeral heads respectively)
• M. Flexor Digitorum Superficialis
• M. Flexor Digitorum Profundus
• M. Flexor Carpi Radialis

The accessory structures also include a sesamoid bone in the origin of the M. Supinator, as well as a subtendinous bursa in the tendon of origin of the Triceps muscle group.

If you would like to see additional anatomical summaries like this one, comment and let us know

References

• Done, S.H., Goodey, P.C., Evans, S.A., Stickland, N.C., 2009. Color Atlas of Veterinary Anatomy, Volume 3, The Dog and Cat, 2nd Edition. Elsevier.
• Hermanson, J.W., de Lahunta, A., Evans, H.E., 2020. Miller and Evans’ Anatomy of the Dog, 5^th  Edition. Elsevier.
• https://veteriankey.com/surgical-diseases-of-the-elbow
• https://www.amazon.co.uk/FACAIA-Assembly-Anatomical-Veterinary-Educational/dp/B08R2RRHH6
• https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/elbow-joint