the octeal joint belongs to the complex group, since it combines three articulations of three different bones at once: the radius, ulna and humerus. That is why the anatomy of the human elbow joint is incredibly complex, because it should be considered in the context of three different joints, united by one joint capsule.
All kinds of diseases, developmental abnormalities and injuries can also affect one of the sections of the elbow or all at once – it depends on the severity and localization of the pathology. In order to consistently understand this issue, it is necessary to study in detail each component of the elbow, its features and structure – only in this way can we understand the basics of the anatomy of this most important articulation of the upper limb.
Elbow joint: bone anatomy and function
The human elbow is formed by three bones of different volume and density – ulna, radial (their proximal part) and shoulder (respectively, distal).
This bone is a clear example of the dense and incredibly strong tubular bones of the human body, the shape of which smoothly changes from perfectly round at the top to triangular at the bottom. Such features allow the distal end to ideally mate with the bones of the forearm, the medial end to adjoin the ulna, and the lateral end, respectively, to the radius. In this case, the medial surface has a smoother structure, and the lateral surface is spherical, which largely explains the physiology and features of the trajectory of movement of the elbow.
The surface of the humerus is covered with pits and depressions of various shapes and sizes, due to which a tight interaction of the elements of the elbow joint is formed. So, for example, small holes are located above the medial surface, into which, when bending, the processes of the ulna – the coronal and ulnar – fall. These processes, as it were, fix the elbow in the grooves, supporting the articular capsule and protecting it from injury. In the medial and lateral epicondyles, which are quite easy to feel at the distal end of the bone, the attachment points of the muscle fibers and the ligamentous apparatus are located. And the spiral groove serves as the location of the radial nerve, which innervates the tissues of the upper limb.
The triangular ulna is more voluminous and powerful than the radius. At the upper end, it has a significant thickening with a block-shaped notch, to which the humerus is tightly adjoined, as if covering it. The lateral edge, respectively, is adjacent to the radius.
The surface of the ulna is also heterogeneous, and for good reason. On the anterior and posterior surfaces of the block-shaped notch, there are two processes that limit the mobility of the elbow and ensure the normal physiology of the joint – the coronary and ulnar. They are followed by a special tuberosity, which is necessary for a stronger attachment of the shoulder muscle. And below, at the distal end, there is a head with another process – the medial styloid, due to which the articulation of the ulnar and radial bones is partially supported.
If desired, the anatomy of the ulna can be seen not only in pictures, but also on your own hand – this bone can be easily and painlessly felt under the skin along its entire length, starting with a dense muscular skeleton in its upper part and ending with a tendon bag in the lower section. A certain anatomical structure, coupled with an adequate amount of muscle and adipose tissue of the arm, even allows you to see the head of the bone, which normally protrudes slightly on the inner posterior surface. All this greatly facilitates the identification of injuries and anomalies in the structure of the upper limb – with the proper skill of the physician, the correct diagnosis can be made even before the X-ray is taken, which is required to clarify the clinical picture rather than for diagnosis.
The radius bone together with the ulnar bone forms the forearm, however, unlike the latter, it is less strong and has a thickened lower, not upper, section. This structure allows you to achieve a balance in the structure of the forearm and elbow joint. The small diameter and vulnerability of this bone requires special protection from the body, therefore, as a rule, it is surrounded by well-developed muscle fibers throughout its entire length, securely fixed in pits and tuberosities. All this allows not only to prevent the occurrence of injuries and injuries, but also to develop mobility, slightly expanding the possibilities of the normal physiology of the elbow joint.
|Credit: Kenhub | Source: Elbow joint Anatomy|
Sections that form the elbow joint
Since the elbow belongs to complex joints and consists of three bones connected in pairs to each other, in anatomy it is customary to distinguish three interconnected parts of this joint, surrounded by one joint capsule:
- Shoulder joint . It is formed by the block-like structure of the humerus and the notch of the ulna, which normally join and fit snugly together like puzzle pieces. It allows for movement with the forearm, bending and unbending the arm.
- Brachioradial joint . This articulation is formed at the point of contact of the glenoid fossa of the radial and condylar heads of the humerus. In shape, it belongs to spherical, but the features of the anatomical structure allow you to make movements not in three, but only in two projections (flexion – extension plus rotation), since the third is limited by the presence of the adjacent ulna and a strong ligamentous apparatus.
- Proximal radioulnar joint . The cylindrical articulation of the radius and ulna supports the capabilities of the elbow, providing mobility of the arm along the longitudinal axis, that is, its rotation.
Blood supply and innervation of the adjacent area
Full nutrition of the elbow joint is carried out due to the powerful circulatory network that surrounds it. Arterial blood enters the muscle fibers adjacent to the articular surface from the superior and inferior collateral ulnar arteries, as well as the recurrent, median and radial arteries. Having enriched cells and tissues with oxygen and nutrients necessary to maintain physiological functions, it is sent through the veins of the same name to the basins of the veins of the upper extremities – brachial, ulnar and radial. The lymph flow of the elbow joint passes in a similar way, moving through the lymphatic vessels to the elbow lymph nodes.
The innervation of the capsule, which unites the sections of the elbow joint, is carried out by the largest nerve fibers of the hand – the branches of the ulnar, radial and median nerves. This explains the high sensitivity of the tissues adjacent to the elbow and the particular soreness of the injuries received.
Muscles and ligaments of the elbow joint
The features of the structure and the huge functionality of the upper limbs are largely possible due to the peculiarities of the anatomy of the human elbow joint. It is this articulation that supports mobility and ensures the full activity of the upper limb, therefore, the musculo-ligamentous apparatus of the elbow simply cannot have a simple structure. Let’s consider each of these elements in order to understand the relationship between the anatomical structure and physiological capabilities of the elbow joint.
The greater strength, physical capacity and flexibility of the hand are provided largely due to the muscles acting on the elbow joint. Since the movements allowed in the elbow affect two planes – flexion / extension and pronation / supination – all muscle fibers can be conditionally divided into 3 weighty groups:
1. Muscles-flexors of the elbow joint
Such a movement is possible due to the contraction of muscle fibers, which, as it were, pull up the forearm, reducing the angle formed by it and the shoulder. The most powerful flexor of the upper limb is the biceps parallel to the humerus. In addition, this largest muscle is able to partially participate in forearm supination and palm rotation.
Additional muscles that carry out flexion of the arm are the shoulder and brachioradialis. They (although considered auxiliary), when injuring the biceps, are able to compensate for the lost functions, performing arm movements in full.
2. Extenders of the upper limb
The flexor antagonist muscles perform exactly the opposite function, increasing the angle between the free end of the forearm and the upper limb shoulder. These include the triceps (triceps) and ulnar muscles, as well as the forearm fascia tenor. The triceps, like the biceps, is parallel to the humerus, but it is not located in front, but posteriorly, from the olecranon to the scapula. Together with the ulnar muscle fibers, it, by contracting, causes the extension of the forearm in the elbow joint until the olecranon process fixes the humerus (the maximum allowable physiological extension of the arm).
3. Rotational muscles
This group is responsible for arm rotation – pronation and supination. Pronators, which rotate the forearm inward and outward at the elbow, include the round and square pronators, as well as partly the brachioradialis muscle. And the second group – instep supports, performing movements with the forearm from the inside, – unites the instep support, brachioradial muscle and biceps.
The common joint capsule surrounding the elbow is not strong enough to hold all the large bones of the upper limb in a single joint, especially on the inner side. High loads on the arms during physical work and sports training would invariably lead to injuries of the elbow, if not for a strong ligamentous apparatus that reliably holds the elbow and ensures its limited mobility. It includes the following fibers:
- The radial collateral ligament connects the epicondyle of the humerus and the head of the radius, then splits into two beams and, covering the head in a kind of ring, is fixed on the radial notch of the ulna. In the process of vital activity, the upper part of this ring is gradually intertwined with the tendons responsible for extension, partially fulfilling their function and preventing overstretching; and deep fibers form a single structure with an annular ligament.
- The ulnar collateral ligament extends from the medial epicondyle of the humerus to the block-like notch of the ulna. Together with the radial collateral ligament, this ligament limits the mobility of the elbow, preventing lateral movement.
- The annular ligament is a kind of “sealing ring” that covers the articular circumference of the radial head, additionally fixing it at the ulna.
- The square ligament connects the ulna to the radial neck, securely fixing them to each other and preventing divergence or overstretching.
Speaking about the ligamentous apparatus of the human elbow joint, it is impossible not to mention the interosseous membrane – a special structure that anatomically, although not related to the ligaments, but performs a single function with them, fixing the bones of the forearm in the parts of the joint. It fills a small gap formed by the surfaces of the radius and ulna, and forms a strong radial syndesmosis. The tightly intertwined fibers of this membrane have special holes through which the vessels and nerves of the elbow pass, and the edges serve as an attachment point for some muscle fibers.
Human elbow physiology
The normal physiology of the human elbow joint implies quite extensive mobility: even without special training, the bones of the forearm and shoulder can rotate 90 °, bend at an angle of up to 150 ° and unbend another 10 ° in the opposite direction (that is, as if outside the elbow). Moreover, these degrees are not the limit – with a certain skill and careful training, the mobility of the elbow joint can be increased several times, clearly demonstrating the almost limitless capabilities of the human body.
It should be borne in mind that this functionality requires special attention when stressing the elbow joint. Although it belongs to the overhanging group and does not formally serve as a support, the size and number of loads does not decrease from this. In particular, this is due to physical work, lifting weights, sports training and other types of activity in which the upper limbs are involved. As a result, any careless movement performed without proper preparation and warming up of the ligamentous-muscular apparatus can be fraught with painful elbow injury requiring long-term treatment. Therefore, you should take care of your own body and regularly strengthen it with gradually increasing loads within the framework of physical exercises – this is the only way to develop elbow joints, making your hands truly strong, enduring and flexible.