ELBOW COMPLEX
Sagar Naik, PT
ELBOW COMPLEX S a g a r N a ik ik , The elbow complex consists of the elbow joint (humeroulnar & humeroradial articulations) and the proximal and distal radioulnar joints.
Elbow Joint: Articulation: This occurs between the trochlea and capitulum of the humerus and the trochlear notch of the ulna and the head of the radius. The articular surfaces are covered with hyaline cartilage. Articulation between the ulna and humerus at the humeroulnar joint occurs primarily as a sliding motion of the trochlear notch of the ulna on the trochlea. In trochlea. In extension, sliding continues until the olecranon process enters the olecranon fossa. In flexion, the trochlear ridge of the ulna slides along the trochlear groove until the coronoid process reaches the floor of the coronoid fossa in full flexion. Articulation between the radial head and the capitulum at the humeroradial joint involves sliding of the shallow concave radial head over the relatively large convex surface of the capitulum. In full extension, no contact occurs between the articulating surfaces. In flexion, the rim of the radial head slides in the capitulotrochlear groove and enters the radial fossa as the end of the flexion range is reached. Type: Synovial hinge joint. Capsule: Anteriorly Capsule: Anteriorly it is attached above to the humerus along the upper margins of the coronoid and radial fossae and to the front of the medial and lateral epicondyles and below to the margin of the coracoid process of the ulna and to the annular ligament, which surrounds the head of the radius. Posteriorly it is attached above to the margins of the olecranon fossa of the humerus and below to the upper margin and sides of the olecranon process of the ulna and to the annular ligament. Ligaments: Collateral ligaments are located on the medial and lateral sides of hinge joints to provide medial/lateral stability to the joint and to keep joint surfaces in apposition. The two main ligaments associated with the elbow joints are the medial (ulnar) and lateral (radial) collateral ligaments. The medial The medial (ulnar) collateral ligament (MCL) is triangular and consists principally of three strong bands: 2
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Sagar Naik, PT
(1) The anterior band , which passes from the medial epicondyle of the humerus to the medial margin of the coronoid process. (2)The posterior band , which passes from the medial epicondyle of the humerus to the medial side of the olecranon. (3)The transverse band , which passes between the ulnar attachments of the two preceding bands. Scientist have identified three components in the anterior portion of the ligament: a) fibres that arise from the anterior surface of the medial condyle that are taut in full extension; b) fibres that arise from below the tip of the medial epicondyle that are taut from 90 of flexion to full flexion; and c) fibres that arise from the inferior edge of the medial epicondyle that are always taut throughout the full range of motion and limit the extremes of extension. The third group of fibres is known as “ guiding bundle.” The posterior MCL limits elbow extension but plays a less significant role than the anterior MCL in providing valgus stability for the elbow. The transverse MCL assists in providing valgus stability and helps to keep the joint surfaces in approximation. The lateral (radial) collateral ligament (LCL) is triangular and is attached by its apex to the lateral epicondyle of the humerus and by its base to the upper margin of the annular ligament. The LCL provides reinforcement for the humeroradial articulation, offers some protection against varus stress in some positions of the elbow, and assists in providing resistance to distraction of the joint surfaces. Some fibres of the LCL remain taut throughout the flexion ROM with either a varus or valgus moment applied. Synovial Membrane: This lines the capsule and covers fatty pads in the floors of the coronoid, radial, and olecranon fossae; it is continuous below with the synovial membrane of the proximal radioulnar joint. Nerve Supply: Branches from the median, ulnar, musculocutaneous, and radial nerves. °
Axis of Motion: The axis for flexion and extension is relatively fixed and passes through the center of the trochlea and capitulum bisecting the longitudinal axis of the shaft of the humerus. When the upper extremity is in the anatomic position, the long axis of the humerus, and the long axis of the forearm form an acute angle medially when they meet at the elbow. The angulation is due to the configuration of the articulating surfaces and results in a normal valgus angulation of the forearm in relation to the humerus. This angle is called the carrying angle and is slightly greater in women than men. The average angle in men is about 5 , whereas in women it is about 10 to 15 . An increase in the °
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Sagar Naik, PT
carrying angle is considered to be abnormal, especially if it occurs unilaterally. When the angle is increased beyond the average, it is called cubitus valgus. Normally, the carrying angle disappears when the forearm is pronated and the elbow is in full extension and when the forearm is flexed against the humerus in full elbow flexion. The configuration of the trochlear groove determines the pathway of the forearm during flexion and extension.
Range of Motion: A number of factors determine the amount of motion that is available at the elbow joint. These factors include The type of motion (active or passive). The position of the forearm (pronation or supination). The position of the shoulder. The range of active flexion at the elbow is usually less than the range of passive motion, because the bulk of the contracting flexors on the anterior surface of the humerus interfere with the approximation of the forearm with the humerus. The position of the forearm also affects the flexion ROM. When the forearm is in either pronation or midway between supination and pronation, the ROM is less than it is when the forearm is supinated. The position of the shoulder may affect the ROM available to the elbow. Two joint muscles, such as the biceps brachii and the triceps, that cross both the shoulder and elbow joints may become actively or passively insufficient when a full ROM is attempted at both joints. Passive tension in the triceps may limit elbow flexion when the shoulder is simultaneously moved into full flexion. Concomitantly, the biceps brachii, if active, may lose tension as it attempts to shorten over both the joints. Passive tension created in the long head of the biceps by shoulder hypertension may limit full elbow extension. If the triceps is producing the elbow extension, the long head may become actively insufficient. Other factors that limit the ROM and help to provide stability for the elbow are the configuration of the joint surfaces, the ligaments, and joint capsule. The elbow has inherent articular stability at the extremes of extension and flexion. In full extension the humeroulnar joint is in a close-packed position. In this position, bony contact of the olecranon process in the olecranon fossa limits the end of the extension range and the configuration of the joint structures help to provide valgus and varus stability. The bony components, medial collateral ligament, and anterior joint capsule contribute equally to resist valgus stress in full extension. Approximation of the coronoid process with the coronoid fossa and of the rim of the radial head in the radial fossa limits 4
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Sagar Naik, PT
extremes of flexion. If the anterior portion of the medial collateral ligament becomes lax through overstretching, medial instability will result when the elbow is in flexed positions. Also, the carrying angle will increase. Cocontractions of the flexor and extensor muscles of the elbow, wrist, and hand help to provide stability for the elbow during forceful motions of the wrist and fingers and in activities in which the arms are used to support the body weight.
Flexors Muscle Action: The role that the three-flexor muscles play in motion at the elbow is determined by a number of factors, including The location of the muscles. Position of the elbow and adjacent joints. Position of the forearm. The magnitude of the applied load. The type of muscle contraction. The speed of motion. Brachialis: The brachialis is inserted close to the joint axis and therefore is considered to be a mobility muscle. The moment arm (MA) of the brachialis is greatest at slightly more than 100 of elbow flexion, and, therefore, its ability to produce torque is greatest at that particular elbow position. The brachialis is inserted on the ulna and, therefore, is unaffected by changes in the forearm position brought about by rotation of the radius. As a one-joint muscle, the brachialis is not affected by the position of the shoulder. According to electromyography (EMG) studies, the brachialis muscle works in flexion of the elbow in all positions of the forearm, with and without resistance. It is also active in all types of contractions during slow and fast motions. Biceps Brachii: The biceps brachii is considered to be a mobility muscle because of its insertion close to the joint axis. The moment arm (MA) of the biceps is largest between 80 and 100 of elbow flexion and, therefore, the biceps is capable of producing its greatest torque in this range. The biceps is active during unresisted elbow flexion with the forearm supinated and when the forearm is midway between supination and 5
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Sagar Naik, PT
pronation in both concentric and eccentric contractions, but it tends not to be active when the forearm is pronated. When the magnitude of the resistance increases much beyond limb weight, the biceps is active in all positions of the forearm. The biceps with both heads crossing two joints may become actively insufficient when full flexion of the elbow is attempted with the shoulder in full flexion especially when the forearm is supinated. Brachioradialis: The brachioradialis is inserted at a distance from the joint axis and therefore during muscle contraction, the largest component of muscle force goes toward stability. The peak moment arm (MA) for the brachioradialis occurs between 100 and 120 of elbow flexion. The brachioradialis shows no electrical activity during eccentric flexor activity when the motion is performed slowly with the forearm supinated . Activation of the brachioradialis during concentric contractions is greater than during eccentric contractions particularly when the range of elbow flexion is between 0 and 60 . The brachioradialis shows no activity during slow, unresisted, concentric elbow flexion. When the speed of the motion is increased, the brachioradialis shows moderate activity if a load is applied and the forearm is in either a position midway between supination and pronation or in full pronation. The brachioradialis does not cross the shoulder and therefore is unaffected by the position of the shoulder. The pronator teres as well as the palmaris longus, flexor digitorum superficialis, flexor carpi radialis, and flexor carpi ulnaris are weak elbow flexors. °
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Extensors Muscle Action: The effectiveness of the triceps as a whole is affected by changes in the position of the elbow but not by changes in position of the forearm because the triceps attaches to the ulna and not the radius. The long head of the triceps crosses two joints; therefore, activity of the long head is affected by changing shoulder joint positions. The long head becomes actively insufficient when full elbow extension is attempted with the shoulder in hyperextension. In this instance the muscle is shortened over both the elbow and shoulder simultaneously. 6
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Sagar Naik, PT
The medial and lateral heads of the triceps are not affected by the position of the shoulder. The medial head is active in unresisted active elbow extension. All three heads are active when heavy resistance is given to extension or when quick extension of the elbow is attempted in the gravity-assisted position. The maximum isometric torque that the triceps can generate is at an elbow position of 90 of elbow flexion. However, the total amount of extensor torque generated at 90 varies with the position of the shoulder and the body. The triceps is active eccentrically to control elbow flexion as the body is lowered to the ground in a push-up. The triceps is active concentrically to extend the elbow when the triceps acts in a closed kinematic chain such as in a push-up. The triceps may be active during activities requiring stabilization of the elbow. For example, it acts as a synergist to prevent flexion of the elbow when the biceps is acting as a supinator. The other extensor of the elbow, the anconeus, assists in elbow extension and apparently also as a stabilizer during supination and pronation. °
Superior Radioulnar Joints: Articulation: Between the circumference of the head of the radius and the annular ligament and the radial notch on the ulna. Type: Synovial pivot joint. Capsule: The capsule encloses the joint and is continuous with that of the elbow joint. Ligaments: The three ligaments associated with the proximal radioulnar joint are the annular and quadrate ligaments and the oblique cord. The annular ligament is a strong band that forms four-fifths of a ring that encircles the radial head. It is attached to the anterior and posterior margins of the radial notch on the ulna and forms a collar around the head of the radius. It is continuous above with the capsule of the elbow joint. It is not attached to the radius. The quadrate ligament extends from the inferior edge of the ulna’s radial notch to insert in the neck of the radius. The quadrate ligament reinforces the inferior aspect of the joint capsule and helps to maintain the radial head in apposition to the radial notch. The quadrate ligament also limits the spin of the radial head in supination and pronation. The oblique cord is a flat fascial band on the ventral forearm that extends from an attachment just inferior to the radial notch on the ulna to insert just below the bicipital tuberosity on the radius. The fibres of the oblique cord are at right angles to the fibres of the interosseous membrane. 7
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Sagar Naik, PT
Synovial Membrane: This is continuous above with that of the elbow joint. Below it is attached to the inferior margin of the articular surface of the radius and the lower margin of the radial notch of the ulna. Nerve Supply: Branches of the median, ulnar, musculocutaneous, and radial nerves.
Inferior Radioulnar Joint: Articulation: Between the rounded head of the ulna and the ulnar notch on the radius. Type: Synovial pivot joint. Capsule: The capsule encloses the joint but is deficient superiorly. Articular Disc: This is triangular and composed of fibrocartilage. It is attached by its apex to the lateral side of the base of the styloid process of the ulna and by its base to the lower border of the ulnar notch of the radius. It shuts off the distal radioulnar joint from the wrist and strongly unites the radius to the ulna. Ligaments: The dorsal and palmar radioulnar ligaments, as well as the interosseous membrane, which stabilizes both proximal and distal joints, reinforce the distal radioulnar joint. The dorsal and palmar ligaments are formed by longitudinally oriented collagen fiber bundles originating from the dorsal and palmar aspects of the ulnar notch of the radius. The two ligaments extend along the margins of the articular disc to insert on the ulnar fovea and base of ulnar styloid process. The interosseous membrane is described simply as a broad collaginous sheet that runs between the radius and ulna. The fibres of the central band run distally and medially from the radius to the ulna. Maximum strain in the fibres of the central band occurs when the forearm is in a neutral position (midway between supination & pronation). The fibres in central band are relaxed in both the supinated and pronated positions. The interosseous membrane provides stability for both the superior and inferior radioulnar joints. When under tension, the membrane not only binds the joints together, but also provides for the transmission of forces from the hand and distal end of the radius to the ulna. Synovial Membrane: This lines the capsule passing from the edge of one articular surface to that of the other. Nerve Supply: Anterior interosseous nerve and posterior interosseous nerve.
Axis of Motion: The axis of motion for pronation and supination is a longitudinal axis extending from the centre of the radial head to the centre of the ulnar head. 8
ELBOW COMPLEX
Sagar Naik, PT
In supination the radius and ulna lie parallel to one another, whereas in pronation, the radius crosses over the ulna. There is very little motion of the ulna during pronation and supination. The ulnar head moves distally and dorsally in pronation and proximally and medially in supination. Therefore, at the distal radioulnar joint, ulnar head glides in the ulnar notch of the radius from the dorsal lip of the ulnar notch in pronation to a position on the palmar aspect of the ulnar notch in full supination.
Range of Motion: A total ROM of 150 has been ascribed to the radioulnar joints. The range of motion of pronation and supination is assessed with the elbow in 90 of flexion. This position stabilizes the humerus so that radioulnar joint rotation may be distinguished from rotation that is occurring at the shoulder joint. Limitation of pronation when the elbow is extended may be caused by passive tension in the biceps brachii. Pronation in all positions is limited by bony approximation of the radius and ulna and by tension in the dorsal radioulnar ligament and the posterior fibres of the medial collateral ligament of the elbow. Supination is limited by passive tension in the palmar radioulnar ligament and the oblique cord. The quadrate ligament limits spin of the radial head in both pronation and supination, and the annular ligament helps to maintain stability of the proximal radioulnar joint by holding the radius in close approximation to the radial notch. °
Muscle Action: The pronators produce pronation by exerting a pull on the radius, which causes its shaft and distal end to turn over the ulna. The pronator teres is a two joint muscle that has a slight role in elbow flexion although its major action is at radioulnar joints. As a two-joint muscle, the pronator teres may become actively insufficient when a full range of pronation is attempted simultaneously with the full range of shoulder flexion. The pronator teres contributes some of its force toward stabilization of the proximal radioulnar joint. The translatory component of the force produced by the pronator teres helps to maintain contact of the radial head with the capitulum. The pronator quadratus, a one-joint muscle, is unaffected by changing positions at the elbow. The pronator quadratus is active in unresisted and resisted pronation and in slow or fast pronation. The deep head of the pronator quadratus also acts to maintain compression of the distal radioulnar joint. The supinators, like pronators, acts by pulling the shaft and distal end of the radius over the ulna. The supinator muscle acts alone during unresisted 9
ELBOW COMPLEX
Sagar Naik, PT
slow supination in all positions of the elbow or forearm. The supinator also can act alone during unresisted fast supination when the elbow is extended. However, activity of the biceps is always evident when supination is performed against resistance and during fast supination when elbow is flexed to 90 . Activity of the biceps is most evident when using a screwdriver to drive a screw into the wood. The anconeus muscle is active in supination and pronation.
Effects of Immobilization and Injury: The joints and muscles of the elbow complex may be subjected to the effects of immobilization and injury. Immobilization may cause decrease in muscle strength. If the flexors happen to be weakened more than the extensors, the flexors may not be able to counteract the pull of the extensors and the elbow joint may hyperextended during extension. Also the flexor muscles contributions to joint compression would be decreased, and therefore joint stability would be diminished. Prolonged immobilization of the elbow in 90 of flexion results in adaptive shortening of the elbow flexors and lengthening of the elbow extensors. Consequently the elbow ROM in extension is limited. Injuries to the elbow are fairly frequent and these injuries usually disrupt normal function.
Compression Injury: Resistance to longitudinal compression forces at the elbow is provided for mainly by the contact of bony components; therefore, excessive compression forces at the elbow leads to bony failure. Falling on the hand when the elbow is in a close-packed position may result in the transmission of forces through the bones of the forearm to the elbow. If the forces are transmitted through the radius as may happen with a concomitant valgus stress, a fracture of the radial head may result from impact of the radial head on the capitulum. If the force from the fall is transmitted to the ulna, a fracture of either the coronoid or olecranon processes may occur from impact of the ulna on the humerus. If neither the radius nor the ulna absorbs the excessive force through a fracture, then the force may be transmitted to the humerus and may result in a fracture of the supracondylar area.
Distraction Injury: Ligaments and muscles provide for resistance of the joints of the elbow complex to longitudinal traction. A distraction force of sufficient magnitude exerted on the radius may cause the radius to slip out of the annular 10
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Sagar Naik, PT
ligament. Small children are particularly susceptible to this type of injury because the radial head is not fully developed. Lifting a small child up into the air by one or both hands or yanking a child by the hand is the usual causative mechanism and therefore the injury is referred to as nursemaid’s elbow. However, the distractive pull will rarely cause problems if the child is expecting the pull and has contracted the compressive elbow flexors. When the pull is unexpected, the muscles are not ready to provide the appropriate stabilization.
Varus/Valgus Injury: The medial collateral ligament (MCL) and lateral collateral ligament (LCL), articular configuration, and the joint capsule provide resistance to medial and lateral stresses at the elbow. If either one of the ligaments is overstretched, one aspect of the joint will be subjected to abnormal tensile stresses and the other to abnormal compressive forces. The MCL is subjected to tensile stress during the backswing or “cock up” portion of throwing a ball. If the stress on the MCL is repetitive, such as in baseball pitching, the ligament may become lax and unable to reinforce the medial aspect of the joint. The resulting medial instability may cause an increase in the normal carrying angle and excessive compression of the radial head on the capitulum. If the abnormal compression forces on the articular cartilage are prolonged, these forces may interfere with the blood supply of the cartilage and result in avascular necrosis. Repetitive microtrauma from valgus stress can cause epiphyseal plate fractures of the proximal radius.
Overuse and Other Injuries: The use of a racquet greatly increases the length of the forearm lever (resistance arm) and subjects the elbow complex structures to great stresses. The classic tennis elbow (epicondylitis of the lateral epicondyle) is caused by repeated forceful contractions of the wrist extensors, primarily the extensor carpi radialis brevis. The tensile stress created at the origin of the extensor carpi radialis brevis may cause microscopic tears that lead to inflammation of the lateral epicondyle. Repeated tensile stress on the inelastic tendon may result in microscopic tears at the musculotendinous junction and result in tendinitis. Repetitive microtrauma injury can lead to mucinoid degeneration of the extensor origin and subsequent failure of the tendon. Medial tendinitis or medial epicondylitis (Golfer’s Elbow) may be caused by forceful repetitive contractions of the pronator teres, flexor carpi radialis, and occasionally by the flexor carpi ulnaris. These muscles are 11
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Sagar Naik, PT
involved in the tennis serve when the combined motion of the elbow extension, pronation, and wrist flexion is used. Other injuries to the elbow complex that may occur as a result of muscular contraction include nerve compression and bony fracture or dislocation. Repetitive forceful contraction of the flexor carpi ulnaris may compress the ulnar nerve as it passes through the cubital tunnel between the medial epicondyle of the humerus and the olecranon process of the ulna. The resting injury, called cubital tunnel syndrome, results in impaired motion of the thumb and fourth and fifth digits. Sudden forceful contractions of the biceps brachii when the forearm is supinated and flexed at 90 may cause a rupture of the biceps tendon, or fracture or dislocation of the radius. °
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