Theelbow is the region between theupper arm and theforearm that surrounds theelbow joint.[1] The elbow includes prominent landmarks such as theolecranon, thecubital fossa (also called the chelidon, or the elbow pit), and thelateral and themedial epicondyles of thehumerus. The elbow joint is ahinge joint between thearm and theforearm;[2] more specifically between the humerus in the upper arm and theradius andulna in the forearm which allows the forearm and hand to be moved towards and away from the body.[3][4]The termelbow is specifically used forhumans and other primates, and in other vertebrates it is not used. In those cases,forelimb plusjoint is used.[1]
The name for the elbow in Latin iscubitus, and so the wordcubital is used in some elbow-related terms, as incubital nodes for example.
The elbow joint has three different portions surrounded by a common joint capsule. These are joints between the three bones of the elbow, thehumerus of the upper arm, and theradius and theulna of the forearm.
In any position of flexion or extension, the radius, carrying the hand with it, can be rotated in it. This movement includespronation andsupination.
When inanatomical position there are four main bony landmarks of the elbow. At the lower part of the humerus are themedial andlateral epicondyles, on the side closest to the body (medial) and on the side away from the body (lateral) surfaces. The third landmark is theolecranon found at the head of the ulna. These lie on a horizontal line called theHueter line. When the elbow isflexed, they form a triangle called theHueter triangle, which resembles anequilateral triangle.[5]
Left elbow extended and flexed
At the surface of the humerus where it faces the joint is thetrochlea. In most people, the groove running across the trochlea is vertical on the anterior side but it spirals off on the posterior side. This results in the forearm being aligned to the upper arm during flexion, but forming an angle to the upper arm during extension — an angle known as the carrying angle.[6]
Capsule of elbow-joint (distended). Anterior and posterior aspects.
The elbow joint and the superior radioulnar joint are enclosed by a single fibrous capsule. The capsule is strengthened by ligaments at the sides but is relatively weak in front and behind.[8]
On the anterior side, the capsule consists mainly of longitudinal fibres. However, some bundles among these fibers run obliquely or transversely, thickening and strengthening the capsule. These bundles are referred to as thecapsular ligament. Deep fibres of thebrachialis muscle insert anteriorly into the capsule and act to pull it and the underlying membrane during flexion in order to prevent them from being pinched.[8]
On the posterior side, the capsule is thin and mainly composed of transverse fibres. A few of these fibres stretch across the olecranon fossa without attaching to it and form a transverse band with a free upper border. On the ulnar side, the capsule reaches down to the posterior part of theannular ligament. The posterior capsule is attached to thetriceps tendon which prevents the capsule from being pinched during extension.[8]
Thesynovial membrane of the elbow joint is very extensive. On the humerus, it extends up from the articular margins and covers thecoronoid andradial fossae anteriorly and theolecranon fossa posteriorly. Distally, it is prolonged down to the neck of the radius and the superior radioulnar joint. It is supported by thequadrate ligament below the annular ligament where it also forms a fold which gives the head of the radius freedom of movement.[8]
Several synovial folds project into the recesses of the joint.[8]These folds or plicae are remnants of normal embryonic development and can be categorized as either anterior (anterior humeral recess) or posterior (olecranon recess).[9]A crescent-shaped fold is commonly present between the head of the radius and the capitulum of the humerus.[8]
On the humerus there are extrasynovialfat pads adjacent to the three articular fossae. These pads fill the radial and coronoid fossa anteriorly during extension, and the olecranon fossa posteriorly during flexion. They are displaced when the fossae are occupied by the bony projections of the ulna and radius.[8]
Left elbow-joint Left: anterior and ulnar collateral ligaments Right: posterior and radial collateral ligaments
The elbow, like other joints, hasligaments on either side. These are triangular bands which blend with the joint capsule. They are positioned so that they always lie across the transverse joint axis and are, therefore, always relatively tense and impose strict limitations on abduction, adduction, and axial rotation at the elbow.[8]
Theulnar collateral ligament has its apex on themedial epicondyle. Its anterior band stretches from the anterior side of the medial epicondyle to the medial edge of thecoronoid process, while the posterior band stretches from posterior side of the medial epicondyle to the medial side of theolecranon. These two bands are separated by a thinner intermediate part and their distal attachments are united by a transverse band below which the synovial membrane protrudes during joint movements. The anterior band is closely associated with thetendon of the superficial flexor muscles of the forearm, even being the origin offlexor digitorum superficialis. Theulnar nerve crosses the intermediate part as it enters the forearm.[8]
There are three main flexor muscles at the elbow:[10]
Brachialis acts exclusively as an elbow flexor and is one of the few muscles in the human body with a single function. It originates low on the anterior side of the humerus and is inserted into thetuberosity of the ulna.
Biceps brachii is the main elbow flexor but, as a biarticular muscle, also plays important secondary roles as a stabiliser at the shoulder and as a supinator. It originates on the scapula with two tendons: That of the long head on thesupraglenoid tubercle just above the shoulder joint and that of the short head on thecoracoid process at the top of the scapula. Its main insertion is at theradial tuberosity on the radius.
Brachialis is the main muscle used when the elbow is flexed slowly. During rapid and forceful flexion all three muscles are brought into action assisted by the superficial forearm flexors originating at the medial side of the elbow.[11]Theefficiency of the flexor muscles increases dramatically as the elbow is brought into midflexion (flexed 90°) — biceps reaches its angle of maximum efficiency at 80–90° and brachialis at 100–110°.[10]
Active flexion is limited to 145° by the contact between the anterior muscles of the upper arm and forearm, more so because they are hardened by contraction during flexion. Passive flexion (forearm is pushed against the upper arm with flexors relaxed) is limited to 160° by the bony projections on the radius and ulna as they reach to shallow depressions on the humerus; i.e. thehead of radius being pressed against theradial fossa and thecoronoid process being pressed against thecoronoid fossa. Passive flexion is further limited by tension in the posterior capsular ligament and in triceps brachii.[12]
A small accessory muscle, so called epitrochleoanconeus muscle, may be found on the medial aspect of the elbow running from the medial epicondyle to the olecranon.[13]
Elbow extension is simply bringing the forearm back to anatomical position.[11] This action is performed bytriceps brachii with a negligible assistance fromanconeus. Triceps originates with two heads posteriorly on the humerus and with its long head on the scapula just below the shoulder joint. It is inserted posteriorly on the olecranon.[10]
Triceps is maximally efficient with the elbow flexed 20–30°. As the angle of flexion increases, the position of the olecranon approaches the main axis of the humerus which decreases muscle efficiency. In full flexion, however, the triceps tendon is "rolled up" on the olecranon as on a pulley which compensates for the loss of efficiency. Because triceps' long head is biarticular (acts on two joints), its efficiency is also dependent on the position of the shoulder.[10]
Extension is limited by the olecranon reaching theolecranon fossa, tension in the anterior ligament, and resistance in flexor muscles. Forced extension results in a rupture in one of the limiting structures: olecranon fracture, torn capsule and ligaments, and, though the muscles are normally left unaffected, a bruisedbrachial artery.[12]
The blood is brought back by vessels from theradial,ulnar, andbrachial veins.There are two sets oflymphatic nodes at the elbow, normally located above the medial epicondyle — the deep and superficial cubital nodes (also called epitrochlear nodes). The lymphatic drainage at the elbow is through the deep nodes at the bifurcation of the brachial artery, the superficial nodes drain the forearm and the ulnar side of the hand. Theefferent lymph vessels from the elbow proceed to the lateral group ofaxillary lymph nodes.[14][15]
The elbow is innervated anteriorly by branches from themusculocutaneous,median, andradial nerve, and posteriorly from the ulnar nerve and the branch of the radial nerve toanconeus.[14]
The elbow undergoes dynamic development of ossification centers through infancy and adolescence, with the order of both the appearance and fusion of theapophyseal growth centers being crucial in assessment of the pediatric elbow on radiograph, in order to distinguish a traumatic fracture or apophyseal separation from normal development. The order of appearance can be understood by the mnemonic CRITOE, referring to thecapitellum,radial head, internal epicondyle,trochlea, olecranon, and externalepicondyle at ages 1, 3, 5, 7, 9 and 11 years. These apophyseal centers then fuse during adolescence, with the internal epicondyle and olecranon fusing last. The ages of fusion are more variable than ossification, but normally occur at 13, 15, 17, 13, 16 and 13 years, respectively.[16] In addition, the presence of a joint effusion can be inferenced by the presence of thefat pad sign, a structure that is normally physiologically present, but pathologic when elevated by fluid, and always pathologic when posterior.[17]
In humans, the main task of the elbow is to properly place the hand in space by shortening and lengthening the upper limb. While the superior radioulnar joint shares joint capsule with the elbow joint, it plays no functional role at the elbow.[7]
With the elbow extended, the long axis of the humerus and that of the ulna coincide.[20] At the same time, the articular surfaces on both bones are located in front of those axes and deviate from them at an angle of 45°.[21] Additionally, the forearm muscles that originate at the elbow are grouped at the sides of the joint in order not to interfere with its movement. The wide angle of flexion at the elbow made possible by this arrangement — almost 180° — allows the bones to be brought almost in parallel to each other.[7]
Normal radiograph; right picture of the straightened arm shows the carrying angle of the elbow
When the arm isextended, with the palm facing forward or up, the bones of the upper arm (humerus) andforearm (radius andulna) 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".[22]
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 tends to produce a larger carrying angle (i.e., larger deviation from a straight line than that in men). 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.[23]
The angle is greater in the dominant limb than the non-dominant limb of both sexes,[24] suggesting that natural forces acting on the elbow modify the carrying angle. Developmental,[25] aging and possibly racial influences add further to the variability of this parameter.
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 anolecranon fracture is ruled out.[27] Acute fractures may not be easily visible on X-ray.[28]
X-ray of ventral dislocation of the radial head. There is calcification of annular ligament, which can be seen as early as 2 weeks after injury.[29]
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.[30] Among injuries to the upper extremity, dislocation of the elbow is second only to adislocated shoulder.A full dislocation of the elbow will require expert medical attention to re-align, and recovery can take approximately 6 weeks.[citation needed]
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).[31]
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.[32]
Elbow pain can occur for a multitude of reasons, including injury, disease, and other conditions. Common conditions include tennis elbow, golfer's elbow, distal radioulnar joint rheumatoid arthritis, and cubital tunnel syndrome.
Tennis elbow is a very common type of overuse injury. It can occur both from chronic repetitive motions of the hand and forearm, and from trauma to the same areas. These repetitions can injure the tendons that connect the extensorsupinator muscles (which rotate and extend the forearm) to theolecranon process (also known as "the elbow"). Pain occurs, often radiating from the lateral forearm. Weakness, numbness, and stiffness are also very common, along with tenderness upon touch.[33]A non-invasive treatment for pain management is rest. If achieving rest is an issue, a wrist brace can also be worn. This keeps the wrist in flexion, thereby relieving theextensor muscles and allowing rest. Ice, heat, ultrasound, steroid injections, andcompression can also help alleviate pain. After the pain has been reduced, exercise therapy is important to prevent injury in the future. Exercises should be low velocity, and weight should increase progressively.[34] Stretching the flexors and extensors is helpful, as are strengthening exercises. Massage can also be useful, focusing on the extensortrigger points.[35]
Golfer's elbow is very similar to tennis elbow, but less common. It is caused by overuse and repetitive motions like a golf swing. It can also be caused by trauma. Wrist flexion and pronation (rotating of the forearm) causes irritation to the tendons near themedial epicondyle of the elbow.[36] It can cause pain, stiffness, loss of sensation, and weakness radiating from the inside of the elbow to the fingers.Rest is the primary intervention for this injury. Ice, pain medication, steroid injections, strengthening exercises, and avoiding any aggravating activities can also help. Surgery is a last resort, and rarely used. Exercises should focus on strengthening and stretching the forearm, and utilizing proper form when performing movements.[37]
Rheumatoid arthritis is a chronic disease that affects joints. It is very common in the wrist, and is most common at theradioulnar joint. It results in pain, stiffness, and deformities.There are many different treatments for rheumatoid arthritis, and there is no one consensus for which methods are best. Most common treatments include wrist splints, surgery, physical and occupational therapy, andantirheumatic medication.[38]
Cubital tunnel syndrome, more commonly known asulnar neuropathy, occurs when the ulnar nerve is irritated and becomes inflamed. This can often happen where the ulnar nerve is most superficial, at the elbow. The ulnar nerve passes over the elbow, at the area known as the "funny bone". Irritation can occur due to constant, repeated stress and pressure at this area, or from a trauma. It can also occur due to bone deformities, and oftentimes from sports.[39] Symptoms include tingling, numbness, and weakness, along with pain.First line pain management techniques include the use ofnonsteroidal anti-inflammatory oral medicines. These help to reduce inflammation, pressure, and irritation of the nerve and around the nerve. Other simple fixes include learning moreergonomically friendly habits that can help preventnerve impingement and irritation in the future. Protective equipment can also be very helpful. Examples of this include a protective elbow pad, and an arm splint. More serious cases often involve surgery, in which the nerve or the surrounding tissue is moved to relieve the pressure. Recovery from surgery can take awhile, but the prognosis is often a good one. Recovery often includes movement restrictions, and range of motion activities, and can last a few months (cubital and radial tunnel syndrome, 2).
The now obsolete length unitell 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) andEllbogen (elbow). It is unknown when or why the second "l" was dropped from English usage of the word.[citation needed] Theell as in the English measure could also be taken to come from the letter L, being bent at right angles, as an elbow.[40] The ell as a measure was taken as six handbreadths; three to the elbow and three from the elbow to the shoulder.[41] Another measure was thecubit (fromcubital). This was taken to be the length of a man's arm from the elbow to the end of the middle finger.[42]
The wordswenis andwagina are humorously used to describe the posterior and anterior regions of the elbow, respectively. The terms entered the slang lexicon in the 1990s and proliferated as an Internet meme.[43] Specifically,wenis refers to the loose flap of skin under the elbow (olecranal skin), whilewagina refers to the skin crease of thecubital fossa.[44]
Though the elbow is similarly adapted for stability through a wide range of pronation-supination and flexion-extension in allapes, there are some minor differences. Inarboreal apes such asorangutans, the large forearm muscles originating on the epicondyles of the humerus generate significant transverse forces on the elbow joint. The structure to resist these forces is a pronounced keel on thetrochlear notch on the ulna, which is more flattened in, for example, humans and gorillas. Inknuckle-walkers, on the other hand, the elbow has to deal with large vertical loads passing through extended forearms and the joint is therefore more expanded to provide larger articular surfaces perpendicular to those forces.[45]
Derived traits incatarrhini (apes and Old World monkeys), elbows include the loss of theentepicondylar foramen (a hole in the distal humerus), a non-translatory (rotation-only) humeroulnar joint, and a more robust ulna with a shortened trochlear notch.[46]
Theproximal radioulnar joint is similarly derived inhigher primates in the location and shape of theradial notch on the ulna; the primitive form being represented byNew World monkeys, such as thehowler monkey, and by fossil catarrhines, such asAegyptopithecus. In these taxa, the oval head of the radius lies in front of the ulnar shaft so that the former overlaps the latter by half its width. With this forearm configuration, the ulna supports the radius and maximum stability is achieved when the forearm is fully pronated.[46]
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