Joint components and biomechanics
By its structure, the elbow joint is complex. Within a single fibrous capsule, three distinct articulations function, each having its own shape and formed by specific bone surfaces:
- Humeroulnar joint (articulatio humeroulnaris). Classified as a ginglymus (hinge) joint. It is formed by the trochlea of the inferior epiphysis of the humerus and the trochlear notch of the ulna.
- Humeroradial joint (articulatio humeroradialis). Has a spheroidal (ball-and-socket) shape. It is formed by the capitulum of the humerus (capitulum humeri) and the articular facet on the head of the radius.
- Proximal radioulnar joint (articulatio radioulnaris proximalis). Represents a pivot (trochoid) joint formed by the radial notch of the ulna (incisura radialis) and the articular circumference of the radial head.
The shape of these articular surfaces collectively provides movement around two axes. Flexion and extension of the forearm occur around the frontal axis. Rotation, i.e., pronation (pronatio) and supination (supinatio), occurs around the vertical axis.
Capsule, ligamentous apparatus, and vulnerable spots
The capsule of the elbow joint is common to all three articulations. Externally, it is securely reinforced by the ligament apparatus, including the ulnar collateral ligament (lig. collaterale ulnare), radial collateral ligament (lig. collaterale radiale), and annular ligament of the radius (lig. anulare radii).
Despite the strong ligaments, the fibrous capsule has thinned areas, which in clinical practice are called "vulnerable spots":
- Sacciform recess (recessus sacciformis). In purulent joint inflammation, effusion accumulates precisely here. If the capsule ruptures in the area of the recess, the purulent process inevitably spreads into the deep fascial spaces of the forearm.
- Posterosuperior part of the capsule. Located on the sides of the olecranon (olecranon). The specific feature of this zone is that the capsule here is completely devoid of reinforcement by muscle fibers.
It is worth noting that the synovial bursae located in the posterior region of the elbow, in particular the subcutaneous olecranon bursa (bursa subcutanea olecrani), are isolated and do not communicate with the joint cavity.
Topography and landmarks
Upon external inspection, the main landmarks are the olecranon and the epicondyles of the humerus. It is important to remember their relative position: the lateral epicondyle is located 1 cm lower than the medial one.
The projection of the joint line is a transverse line that runs asymmetrically:
- 1 cm below the lateral epicondyle.
- 2 cm below the medial epicondyle.
At the level of a transverse section of the elbow joint, a complex topography of vessels, nerves, and muscles can be found. Key neurovascular bundles include the brachial vessels (a. et vv. brachiales), median nerve (n. medianus), and radial nerve (n. radialis). The ulnar nerve (n. ulnaris) together with the superior ulnar collateral artery is located in the posterior medial sulcus, where it lies directly against the joint capsule, covered only by fascia.
The joint is surrounded by numerous muscles and their tendons, including the brachialis muscle (m. brachialis), biceps brachii (m. biceps brachii) and triceps brachii (m. triceps brachii) muscles, pronator teres (m. pronator teres), brachioradialis (m. brachioradialis) and others.
Blood supply, innervation, and lymphatic drainage
The blood supply to the joint is provided by a robust arterial network around the elbow — rete articulare cubiti. Branches of three main arteries participate in its formation: the brachial (a. brachialis), radial (a. radialis), and ulnar (a. ulnaris) arteries. Venous drainage occurs via companion veins accompanying the arteries.
Innervation of the joint capsule is provided by branches of the radial, median, and ulnar nerves. Lymphatic drainage is directed through deep lymphatic pathways to the cubital and axillary lymph nodes.
Arthrocentesis of the elbow joint For therapeutic or diagnostic purposes, puncture is performed in the area of greatest accessibility of the joint cavity. The optimal access point is directly below the distal end of the m. triceps brachii tendon. Anatomically, this point corresponds to the olecranon fossa of the humerus (fossa olecrani humeri), where a spacious portion of the cavity is located directly above the apex of the olecranon.
Arterial collaterals of the cubital region
The developed arterial collateral network (rete articulare cubiti) performs a crucial compensatory function. It is designed to restore blood flow in case of stenosis, occlusion, or ligation of the main brachial artery. The network is a system of anastomoses between descending branches (from above) and ascending branches (from below).
Diagram of anastomoses of the cubital network:
| Network zone | Branch from above (source) | Branch from below (source) |
|---|---|---|
| Lateral | a. collateralis radialis (from a. profunda brachii) | a. recurrens radialis (from a. radialis) |
| Posterior (middle) | a. collateralis media (from a. profunda brachii) | a. interossea recurrens (from a. interossea communis) |
| Medial (Posterior Bundle) | a. collateralis ulnaris superior (from a. brachialis) | r. posterior a. recurrens ulnaris (from a. ulnaris) |
| Medial (Anterior Bundle) | a. collateralis ulnaris inferior (from a. brachialis) | r. anterior a. recurrens ulnaris (from a. ulnaris) |
It is clinically proven that the greatest number of collaterals are recruited when the obstruction to blood flow is located between the origin of the inferior ulnar collateral artery and the bifurcation of the brachial artery. Conversely, the most critical and unfavorable disruption of blood flow occurs above the origin of the profunda brachii artery (a. profunda brachii), as this completely cuts off the main source of blood supply to the collateral network from above.
To memorize the anastomoses of the medial surface: "The superior goes to the posterior, and the inferior goes to the anterior" (the superior ulnar collateral anastomoses with the posterior branch of the recurrent, and the inferior ulnar collateral with the anterior branch).
Class and exam questions
Where does pus spread in case of damage to the sacciform recess of the elbow joint?
When the capsule ruptures in the area of the sacciform recess, purulent effusion spreads into the deep fascial spaces of the forearm.
Does the lumen of the subcutaneous olecranon bursa communicate with the joint cavity itself?
No, the synovial bursae of the posterior elbow region, including the bursa subcutanea olecrani, do not communicate with the joint cavity.
Where is the most convenient site to perform an elbow joint puncture?
The puncture is performed directly below the distal end of the triceps brachii tendon, allowing the needle to enter the spacious part of the capsule in the area of the fossa olecrani humeri.
At what level of brachial artery ligation is the prognosis for the limb the worst?
Ligation proximal to the origin of the profunda brachii artery (a. profunda brachii) is most unfavorable, since in this case the main blood source for the superior collaterals of the articular network is shut off.
What else to study on this topic
- Detailed topography of neurovascular bundles in the transverse section of the cubital region
- Fascia of the arm and forearm: formation of sheaths for the muscles surrounding the joint
- Topography of the ulnar nerve in the posterior medial sulcus and its clinical significance
- Structure and biomechanics of the proximal radioulnar joint in conjunction with the distal one
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