Elbow/مرفق./肘(Zhǒu)

The human elbow is the region surrounding the elbow-jointthe ginglymus or hinge joint in the middle of the arm. Three bones form the elbow joint: the humerus of the upper arm, and the paired radius and ulna of the forearm.

The bony prominence at the very tip of the elbow is the olecranon process of the ulna, and the inner aspect of the elbow is called the antecubital fossa.

Terminology

The now obsolete length unit ell relates closely to the elbow. This becomes especially visible when considering the Germanic origins of both words, Elle (ell, defined as the length of a male forearm from elbow to fingertips) and Ellbogen (elbow). It is unknown when or why the second "l" was dropped from English usage of the word.

Joint

The elbow-joint comprises three different portions. All these articular surfaces are enveloped by a common synovial membrane, and the movements of the whole joint should be studied together.

The combination of the movements of flexion and extension of the forearm with those of pronation and supination of the hand, which is ensured by the two being performed at the same joint, is essential to the accuracy of the various minute movements of the hand.

The hand is only directly articulated to the distal surface of the radius, and the ulnar notch on the lower end of the radius travels around the lower end of the ulna. The ulna is excluded from the wrist-joint by the articular disk.

Thus, rotation of the head of the radius around an axis passing through the center of the radial head of the humerus imparts circular movement to the hand through a very considerable arc.

Ligaments

Left elbow-joint Left: anterior and ulnar collateral ligaments Right: posterior and radial collateral ligaments The trochlea of the humerus is received into the semilunar notch of the ulna, and the capitulum of the humerus articulates with the fovea on the head of the radius. The articular surfaces are connected together by a capsule, which is thickened medially and laterally, and, to a less extent, in front and behind. These thickened portions are usually described as distinct ligaments. The major ligaments are the ulnar collateral ligament, radial collateral ligament, and annular ligament.  Synovial membrane The synovial membrane is very extensive. It extends from the margin of the articular surface of the humerus, and lines the coronoid, radial and olecranon fossæ on that bone; it is reflected over the deep surface of the capsule and forms a pouch between the radial notch, the deep surface of the annular ligament, and the circumference of the head of the radius. Projecting between the radius and ulna into the cavity is a crescentic fold of synovial membrane, suggesting the division of the joint into two; one the humeroradial, the other the humeroulnar. Between the capsule and the synovial membrane are three masses of fat: the largest, over the olecranon fossa, is pressed into the fossa by the Triceps brachii during the flexion; the second, over the coronoid fossa, and the third, over the radial fossa, are pressed by the Brachialis into their respective fossæ during extension.
Muscles The muscles in relation with the joint are: in front, the Brachialis, the Brachioradialis behind, the Triceps brachii and Anconæus laterally, the Supinator, and the common tendon of origin of the Extensor muscles medially, the common tendon of origin of the Flexor muscles, and the Flexor carpi ulnaris Movements Two main movements are possible at the elbow: The hinge-like bending and straightening (flexion and extension) between the humerus and the ulna. The complex action of turning the forearm over (pronation or supination) happens at the articulation between the radius and the ulna (this movement also occurs at the wrist joint). The hinge moves in only one plane. In the anatomical position (with the forearm supine), the radius and ulna lie parallel to each other. During pronation, the ulna remains fixed, and the radius rolls around it at both the wrist and the elbow joints. In the prone position, the radius and ulna appear crossed. Most of the force through the elbow joint is transferred between the humerus and the ulna. Very little force is transmitted between the humerus and the radius. (By contrast, at the wrist joint, most of the force is transferred between the radius and the carpus, with the ulna taking very little part in the wrist joint). Carrying angle When the arm is extended, with the palm facing forward or up, the bones of the humerus and forearm are not perfectly aligned. The deviation from a straight line occurs in the direction of the thumb, and is referred to as the “carrying angle” (visible in the right half of the picture, right). The carrying angle permits the arm to be swung without contacting the hips. Women on average have smaller shoulders and wider hips than men, which may necessitate a more acute carrying angle (i.e., less angle than that in male when measured from outside). There is, however, extensive overlap in the carrying angle between individual men and women, and a sex-bias has not been consistently observed in scientific studies. This could however be attributed to the very small sample sizes in those cited earlier studies. A more recent study based on a sample size of 333 individuals from both sexes concluded that carrying angle is a suitable secondary sexual characteristic. The angle is greater in the dominant limb than the non-dominant limb of both sexes, suggesting that natural forces acting on the elbow modify the carrying angle. Developmental, ageing and possibly racial influences add further to the variability of this parameter. The carrying angle can influence how objects are held by individuals — those with a more extreme carrying angle may be more likely to pronate the forearm when holding objects in the hand to keep the elbow closer to the body. The lateral elbow radiograph positioned to the right is a poor example of a lateral elbow joint. Although, the radius and ulna are at true lateral position at the distal radio ulnar joint the humerus is not parallel to the image receptor resulting in a closing of the joint at the trochlear olecranon articulation, thus making the image non diagnostic. Arteries and nerves The arteries supplying the joint are derived from the anastomosis between the profunda and the superior and inferior ulnar collateral branches of the brachial, with the anterior, posterior, and interosseous recurrent branches of the ulnar, and the recurrent branch of the radial. These vessels form a complete anastomotic network around the joint. The nerves of the joint are a twig from the ulnar, as it passes between the medial condyle and the olecranon; a filament from the musculocutaneous, and two from the median. Diseases Gout elbow Left: Lateral X ray of a dislocated right elbow Right: AP X ray of a dislocated right elbow The types of disease most commonly seen at the elbow are due to injury. Tendonitis Two of the most common injuries at the elbow are overuse injuries: tennis elbow and golfer's elbow. Golfer's elbow involves the tendon of the common flexor origin which originates at the medial epicondyle of the humerus (the "inside" of the elbow). Tennis elbow is the equivalent injury, but at the common extensor origin (the lateral epicondyle of the humerus). Fractures There are three bones at the elbow joint, and any combination of these bones may be involved in a fracture of the elbow.  Patients who are able to fully extend their arm at the elbow are unlikely to have a fracture (98% certainty) and an X-ray is not required as long as an olecranon fracture is ruled out.Acute fractures may not be easily visible on X-ray. Dislocation Elbow dislocations constitute 10% to 25% of all injuries to the elbow. The elbow is one of the most commonly dislocated joints in the body, with an average annual incidence of acute dislocation of 6 per 100,000 persons.Among injuries to the upper extremity, dislocation of the elbow is second only to a dislocated shoulder.  A full dislocation of the elbow will require expert medical attention to re-align, and recovery can take approximately 8-14 weeks. A small amount of people (10% or less) report near full recovery and minimal permanent restriction, but most often a permanent restriction of 5-15% movement is common. Infection Infection of the elbow joint (septic arthritis) is uncommon. It may occur spontaneously, but may also occur in relation to surgery or infection elsewhere in the body (for example, endocarditis). Arthritis Elbow arthritis is usually seen in individuals with rheumatoid arthritis or after fractures that involve the joint itself. When the damage to the joint is severe, fascial arthroplasty or elbow joint replacement may be considered. Imaging The elbow joint is a complex joint, which consists of three individual joints: humero-radial joint, humero-ulnar joint, and radio-ulnar joint. Numerous ligaments, tendons and muscles are surrounding the joint. The main indications for imaging are acute trauma and chronic overuse injuries. Not only for these indications are CT and MRI used, but also for peripheral nerve compression syndromes and other joint diseases. Conventional Radiography CR. Anterior and posterior fat pad sign. The conventional radiography is still a very useful and therefore basic diagnostic tool for the elbow joint. But “cave”: The default settings of the X-ray do not match the physiological central joint position. The standard projection in an a.p. beam requires full extension and supination of the arm. Many diseases and injuries can restrict the range of motion, so that the patient’s position could be suboptimal. Consequently could the applicability be lowered. If the joint extension range is restricted due to a traumatic event, a parallel positioning of the forearm to the board can improve the assessment of the humero-radial joint and the radius head at an a.p. projection. The lateral projection is not affected by an extension deficit because it does not require any extension of the arm. But the full supination of the forearm is still necessary. On the basis of an x-Ray it is difficult to quantify any supination deficit. Especially in this joint, the assessment of soft tissue can point to joint effusions. For example the so-called anterior and posterior fat pad sign. A special projection targeted towards the radius head can improve the judging concerning a fracture. First and foremost common after an inconspicuous standard general view but traumatic joint effusion. Other special projections like the sulcus-ulnaris projection get more and more displaced by the cross sectional imaging. Important diagnostic reference lines: Anterior humerus line AHL: The AHL intersects the medial third of the capitulum if the lateral position is exact. Consequently are extension and flexion malpositions after supracondylar fractures easier to identify. Radius capitulum axis RCA: The longitudinal axis intersects the shaft of the radius of the capitulum in all projections. But contrary to the popular opinion, the intersection is only in 75% positioned at the center of the capitulum humeri. Slight misalignment shows no radius head deformity. Nevertheless is this reference line valuable for the diagnosis. Computed Tomography The CT scans gained of considerable importance in the diagnosis of articular fractures and their therapeutic control. The patient lies in a supine position and the joint should be positioned in moderate flexion over the head. If the arm would be mounted next to the body or on the abdomen, the radiation exposure is higher and the picture is more vulnerable for artifacts. The investigation should be performed on a multidetector CT with minimum thickness, supplemented by adapted sagittal and coronal reformations. Magnetic Resonance Imaging Beyond solely the fracture diagnosis, MRI is the cross-section imaging device of choice. This applies to suspected soft tissue changes as well as for chronic overuse injuries and joint blocks. The positioning of the elbow joint is more difficult compared to CT. Surface coils are obligatory required. Ideal storage is possible with elevation of the arm at the isocenter of the magnet. It can occur that a prolonged storage of the arm towards cranial triggers shoulder impingement symptoms. Depending on the available equipment and technology examination with the arm positioned alongside of the body is possible. But that occasionally involves limitations in spectral fat saturation. A storage of the elbow joint on the belly is inappropriate. Protocol: Coronar T1 SE Coronar water-sensitive sequence (PD FSE FS, STIR) Axial PD FSE FS Facultative also sagittal PDw FSE FS. As a parameter, a layer of 2mm thickness and a FOV of 80-120mm is recommended. Basically, an investigation of musculo-skeletal problems in an extended matrix (320, 384, 448, 512) should be sought. The goal should be a pixel size of 0.4 mm. It has to be added that the sagittal plane is at an eventual “postero-lateral rotary instability”, for example after dislocation, a good choice to illustrate the centering of the radius head or changes at the olecranon. An injection of contrast agent can be helpful in epicondylitis or rare overuse syndromes. Husarik et al. examined 60 non-sympomatic volunteers on a 1.5 Tesla MR system. Sequences of choice were T1-weighted spin echo, sagittal T2-weighted fast spin echo, coronar fast spin echo inversion recovery with short time of inversion, transversal intermediate weighted with fat-saturation and coronar three-dimensional fast imaging with steady state precession (FISP) with water stimulus. The anterior ulnar collateral ligament and the radial collateral ligament were entirely visible in all of the volunteers. The posterior UCL, the lateral UCL and the ligamentum anulare AL were entirely visible on 97%, 85%, respectively, 98%. An increased signal intensity in liquid sensitive sequences has been found at the anterior UCL, posterior UCL, RCL, lateral UCL and AL on 15%, 7%, 2%, 10%, respectively, 2%. 98% showed a plica postero-lateralis but only 33% a posterior plica. 85% showed a pseudo defect of the capitulum. They concluded that the elbow ligaments and the plica postero-lateralis are throughout visible at non-symptomatic individuals on conventional MR images. Most of the physiological ligaments are thinner than 4mm and most of the physiological plicae are thinner than 3mm. Ultrasonography The arthrosonography allows a dynamic study of the soft tissue and bone surfaces. The clinical use is well established, particularly in the pediatrics and rheumatology. In order to verify an intraarticular fluid accumulation the ultrasound is the method of first choice. The evaluation of cartilage is limited. Through power Doppler neovascularizations can be detected sensitively at synovitis or epicondylitis. The examination is carried out by a linear transducer with a frequency from 7.5 up to 13 MHz. The extensioned elbow joint should be depicted ventrally and dorsally, both longitudinally and transversely. Typical indications for an ultrasonographic examination of the elbow joint: Bony destruction usure, osteophytes, non-attached joint fragment, chondromatose, osteochondrosis dissecans, avascular bone-cartilage-necrosis, intraarticular volume gain: joint effusion or synovialitis, bursitis, lesion of the distal biceps tendon, dislocation of the caput radii, elbow joint instability, changes of the humeral neck retro torsion angle, gout tophus, rheumatic node, inflammative rheumatic diseases, fractures, foreign bodies, tumor.