Morphological characteristics: why is it a compound joint?
According to anatomical classification, the elbow joint belongs to the category of compound joints. This means that more than two articular surfaces participate in its formation, and structurally it includes exactly three separate articulations. All three of these elements are not isolated from one another, but reside within a single joint cavity surrounded by a common capsule.
The articulatio cubiti includes the following articulations:
- Humeroulnar joint (articulatio humeroulnaris). By the shape of its articular surfaces, it is a classic ginglymus (hinge) joint.
- Humeroradial joint (articulatio humeroradialis). According to its geometric shape, this is a spheroid (ball-and-socket) articulation. However, despite its spheroid shape, its functional capabilities (range and directions of movement) are significantly restricted by adjacent anatomical structures.
- Proximal radioulnar joint (articulatio radioulnaris proximalis). This articulation is classified by shape as a trochoid (pivot) joint.
Features of the joint capsule
All three of the aforementioned articulations (humeroulnar, humeroradial, and proximal radioulnar) are enclosed by a single common joint capsule. The attachment line of this capsule runs strictly along the edges of the articular surfaces of the bones forming the joint.
A most important topographical and functional feature of the elbow joint capsule is the unevenness of its tension. Anteriorly and posteriorly, the joint capsule is loose. This anatomical property is directly related to ensuring freedom of movement during flexion and extension, since the loose areas of the capsule do not impede the excursion of the bones.
Ligamentous apparatus of the elbow joint
The stability of the compound elbow joint and the retention of the bones in the correct anatomical position are ensured by a robust complex of ligaments. This complex includes structures that restrict lateral displacement and secure the radius.
Main ligaments of the elbow joint:
- Ulnar collateral ligament (ligamentum collaterale ulnare).
- Radial collateral ligament (ligamentum collaterale radiale).
- Annular ligament of the radius (ligamentum anulare radii). This ligament plays a key role in holding the proximal end of the radius close to the ulna.
Biomechanics: axes and types of movement
Despite the presence of a spheroid element (the humeroradial articulation), overall the elbow joint functions with certain limitations, and movements within it occur around two main axes.
Available movements in articulatio cubiti:
- Flexion and extension of the forearm occur around the frontal axis. This function is primarily provided by the humeroulnar and humeroradial components.
- Pronation and supination (rotation of the forearm) occur around the vertical axis. The cylindrical proximal radioulnar joint, in combination with the humeroradial joint, is responsible for these rotational movements.
Briefly: answers to topical questions
Where does the capsule of the elbow joint attach on the humerus?
The joint capsule of the elbow is common to all three of its articulations (humeroulnar, humeroradial, and proximal radioulnar) and attaches along the margins of the articular surfaces.
Anteriorly and posteriorly, the joint capsule is loose. Longitudinal bundles of the articular muscle of the elbow (m. articularis cubiti), which originate from the anterior surface of the distal epiphysis of the humerus, weave into the anterior wall of the capsule and tension it during movements, preventing its entrapment.
Which ligaments reinforce the elbow joint?
The elbow joint is reinforced by three main ligaments that provide lateral stabilization and fixation of the radius.
- Ulnar collateral ligament (lig. collaterale ulnare) — provides lateral stabilization of the joint.
- Radial collateral ligament (lig. collaterale radiale) — provides lateral stabilization of the joint.
- Annular ligament of the radius (lig. anulare radii) — fixes the head of the radius.
Which muscles perform forearm flexion at the elbow joint?
Forearm flexion at the elbow joint is performed by three main muscles of the anterior and lateral groups.
- Biceps brachii (m. biceps brachii) — is a powerful flexor of the forearm.
- Brachialis (m. brachialis) — acts as the main flexor of the forearm.
- Brachioradialis (m. brachioradialis) — also participates in flexing the arm at the elbow joint.
Which arteries form the articular network of the elbow (rete articulare cubiti)?
The articular network of the elbow (rete articulare cubiti) is formed by anastomoses between recurrent and collateral arteries in the anterior and posterior elbow regions.
- Superior and inferior ulnar collateral arteries (a. collateralis ulnaris superior et inferior) — branches of the brachial artery.
- Radial and middle collateral arteries (a. collateralis radialis et a. collateralis media) — branches of the deep brachial artery.
- Radial recurrent artery (a. recurrens radialis) — a branch of the radial artery.
- Anterior and posterior ulnar recurrent arteries (a. recurrens ulnaris anterior et posterior) — branches of the ulnar artery.
- Interosseous recurrent artery (a. interossea recurrens) — a branch of the posterior interosseous artery.
Which muscles perform forearm supination at the elbow joint?
Forearm supination at the elbow joint is performed by two main muscles that ensure the rotation of the radius around the ulna.
These include:
- Biceps brachii (m. biceps brachii) — is a powerful supinator and flexor of the forearm.
- Supinator (m. supinator) — a specialized muscle of the posterior compartment of the forearm responsible for supination.
Remember the three joints inside the elbow easily with the rule: Humeroulnar, Humeroradial, Proximal radioulnar.
Class and exam questions
Why is the elbow joint called compound?
Because it includes three separate articulations at once (humeroulnar, humeroradial, and proximal radioulnar), which are enclosed by a single common joint capsule.
Which parts of the elbow joint capsule are most vulnerable?
The joint capsule is loosest anteriorly and posteriorly, whereas it attaches securely along the margins of the articular surfaces.
Around which axes are movements possible in the elbow joint?
Movements occur around the frontal axis (flexion and extension) and around the vertical axis (pronation and supination).
What else to study on this topic
- Detailed structure of the articular surfaces of each of the three bones
- Exact attachment sites of the collateral ligaments
- Mechanism of movement restriction in the ball-and-socket humeroradial joint
- Functional interaction of the proximal and distal radioulnar joints during pronation and supination
Study the complete topic in the Anatomy course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on the "Elbow joint" topic and 1,363 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 295 video lessons by subject
Other topics in the "Arthrology" section
Free video lessons: AnatomyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.