1212022 LECTURE3 BIOMECHANICS OF ELBOW COMPLEX Prepared by

1/21/2022

LECTURE-3 BIOMECHANICS OF ELBOW COMPLEX Prepared by: Dr. Ishaq Ahmed MSPT(KMU), BSPT(UHS), t-DPT(KMU) 1/21/2022

Elbow biomechanics �ROM flexion and extension - 0 to 140 � 30 to 130 required for most ADL �flexion-extension axis - a loose hinge. �The active ROM for elbow flexion with the forearm supinated is typically considered to be from about 135 to 145 degrees. �the range for passive flexion is between 150 and 160. �the forearm is either in pronation or midway between supination and pronation, the ROM is less than it is when the forearm is supinated. 1/21/2022

�Passive tension in the triceps may limit elbow flexion when the shoulder is simultaneously moved into full flexion �Passive tension created in the long head of the biceps brachii by passive shoulder hyperextension may limit full elbow extension 1/21/2022

Axis of forearm motion. 1/21/2022

Axis of motion: � Variation of the flexion axis throughout ROM described in terms of the screw displacement axis (SDA), which shows the instantaneous rotation and position of the axis throughout flexion. � The average SDA - shown to be in line with the anteroinferior aspect of the medial epicondyle, the center of the trochlea, and the center projection of the capitellum onto a parasagittal plane. 1/21/2022

�Variations �activity of the various muscles may influence the pattern of motion during active flexion, �differences in contours of the joint surfaces may explain differences during passive motion. �Intra individual and inter individual variations in the axes appear to be greater in the frontal plane than in the horizontal plane. 1/21/2022

�valgus-varus laxity was greatest between 0 and 40 of flexion and decreased considerably when flexion exceeded 100. �all instantaneous rotation axes nearly intersected on the medial facet of the trochlea. 1/21/2022

Carrying angle: �The average angle in full elbow extension is about 15 �This normal valgus angulation is called the carrying angle or cubitus valgus. �A varus angulation at the elbow is referred to as cubitus varus �the carrying angle disappears when the forearm is pronated and the elbow is in full extension �and when the supinated forearm is flexed against the humerus in full elbow flexion. 1/21/2022

�The configuration of the trochlear groove determines the pathway of the forearm during flexion and extension. �In the most common configuration of the groove, the ulna is guided progressively medially from extension to flexion, so that in full flexion, the forearm comes to rest in the same plane as the humerus. �In extension, the forearm moves laterally until it reaches a position slightly lateral to the axis of the humerus in full extension. 1/21/2022

Pronation-supination �The radiocapitellar and proximal radioulnar joints �The normal range of forearm rotation is 180 with �pronation of 80 to 90 and �supination of ~ 90 �Most ADL can be accomplished with 100 of forearm rotation �(50 of pronation and 50 of supination) 1/21/2022

�The normal axis of forearm rotation �the center of the radial head to the center of the distal ulna �axis of rotation shifts slightly ulnar and volar during supination �shifts radial and dorsal during pronation �The radius moves �proximally with pronation �distally with supination 1/21/2022

�The elbow has inherent articular stability at the extremes of extension and flexion. �In full extension, the humeroulnar joint is in a closepacked position. �Bony contact of the olecranon process in the olecranon fossa limits the end of the extension range, �configuration of the joint structures helps provide valgus and varus stability. �Resistance to valgus stress in extension: �The bony components, MCL, and anterior joint capsule. �Resistance to varus stress in full extension, �lateral collateral complex and joint capsule. ( half) �The bony component (half). 1/21/2022

�Resistance to joint distraction in the extended position is provided entirely by soft tissue structures. �Anterior portion of the joint capsule provides the majority of the resistance to anterior displacement of the distal humerus out of the olecranon fossa, whereas the MCL and LCL contribute only slightly. �Elbow flexion of about 80 is considered to be the elbow position at which the least amount of tension is present in the joint capsule 1/21/2022

Stability of elbow with rotation �Forearm rotation - important role in stabilizing the elbow, especially when the elbow is moved passively. �With passive flexion, the MCL deficient elbow is more stable in supination. �LCL-deficient elbow is more stable in pronation. �Elbow more stable in supination in coronoid fractures that involve more than 50% of the coronoid with or without an intact MCL. 1/21/2022

�Most simple elbow dislocations - relatively stable once reduced �MCL is completely ruptured in nearly all cases. �LCL is disrupted in most cases 1/21/2022

Coronoid � Fractures involving > 50% of the coronoid shows significantly increased varus-valgus laxity, even in the setting of repaired collateral ligaments � The coronoid plays a significant role in posterolateral stability in combination with the radial head. 1/21/2022

�Soft tissues that attach to the base of the coronoid include �Anteriorly- Insertion of the anterior capsule and brachialis �Medial- insertion of the MCL. �Reduction and fixation of coronoid fractures help to restore the actions of these stabilizers 1/21/2022

Olecranon �One study - no significant differences in elbow extensor power between olecranonectomy with triceps reattachment and open reduction internal fixation of olecranon fractures �There are significant increases in joint pressure with excision of 50% of the olecranon, which over time may contribute to elbow pain and arthritis 1/21/2022

Proximal radius �The radial head is an important secondary valgus stabilizer of the elbow (30%) �more important for valgus stability in the presence of MCL deficiency �Radial head excision also increases varus- valgus laxity and posterolateral rotatory instability, regardless of whether the collateral ligaments are intact. 1/21/2022

Soft tissue stabilization � Medial collateral ligament complex � AMCL is the primary constraint for valgus and posteromedial stability � Complete division causes valgus and internal rotatory instability throughout the complete arch of flexion with � maximal valgus instability at 70 � maximal rotational instability at 60 1/21/2022

LCL complex �The LCL is the primary constraint of external rotation and varus stress at the elbow. �complete sectioning causes varus and posterior radial head subluxation �The flexion axis of the elbow passes through the origin of the LCL so that there is uniform tension in the ligament throughout the arc of flexion. 1/21/2022

�damage to the LCL complex is the initial injury seen along the continuum of injuries resulting from elbow dislocation �In Lateral surgical approaches to the elbow for radial head fixation or replacement. �As long as the annular ligament is intact, the radial collateral ligament or the lateral ulnar collateral ligament can be cut and repaired without causing instability 1/21/2022

�When the radial head is excised in the presence of a deficient LCL, there is increased varus and external rotatory instability. �Radial head replacement in this setting improves posterolateral instability. 1/21/2022

Joint forces � significant compressive and shear forces at the elbow � Loads across the elbow - distributed � 43% across the ulnohumeral joint and � 57% across the radiocapitellar joint � Joint reaction forces vary with elbow position. � Force transmission at the radiocapitellar joint is greatest between 0 and 30 of flexion and is greater in pronation than in supination. 1/21/2022

Muscles �Muscles that cross the elbow joint act as �dynamic stabilizers as they compress the joint. �Compression of the elbow joint by the muscles protects the soft tissue constraints. �throwing an object can cause a valgus stress that is greater than the failure strength of the MCL. �The flexor-pronator muscle group contracts during the throwing motion and provides dynamic stabilization to the medial aspect of 1/21/2022 the elbow, which protects the MCL from injury

Muscles �Elbow flexors �Biceps brachii �Brachialis �Brachioradialis �Weak assistance from Pronator teres �Elbow extensor �Triceps brachii �Anconeus provides assistance 1/21/2022

Muscles �Radioulnar pronators �Pronator teres �Pronator quadratus �Brachioradialis �Radioulnar supinators �Biceps brachii �Supinator muscle �Brachioradialis 1/21/2022

Muscles �“Tennis elbow" - common problem usually involving extensor digitorum muscle near its origin on lateral epicondyle �known lateral epicondylitis �associated with gripping & lifting activities �Medial epicondylitis �somewhat less common �known as golfer's elbow �associated with medial wrist flexor & pronator group near their origin on medial epicondyle �Both conditions involve muscles which cross elbow but act primarily on wrist & hand 1/21/2022

Muscles �Anterior �Primarily flexion & pronation �Biceps brachii �Brachialis �Brachioradialis �Pronator teres �Pronator quadratus 1/21/2022

Muscles �Posterior �Primarily extension & supination �Triceps brachii �Anconeus �Supinator 1/21/2022

Nerves �All elbow & radioulnar joints muscles are innervated from median, musculotaneous, & radial nerves of brachial plexus 1/21/2022

Nerves �Median nerve - derived from C 6 & C 7 �Pronator teres �Pronator quadratus (anterior interosseus nerve) �Sensation to palmar aspect of hand & first three phalanges, palmar aspect of radial side of fourth finger, dorsal aspect of index & long fingers 1/21/2022

Nerves �Musculotaneous nerve - branches from C 5 & C 6 �Biceps brachii �Brachialis 1/21/2022

Biceps Brachii Muscle Flexion of elbow Supination of forearm Weak flexion of shoulder joint Weak abduction of shoulder joint when externally rotated 1/21/2022

Brachialis Muscle True flexion of elbow 1/21/2022

Brachioradialis Muscle Flexion of elbow Pronation from supinated position to neutral Supination from pronated position to neutral 1/21/2022

Triceps Brachii Muscle All heads: extension of elbow Long head: extension of shoulder joint; adduction of shoulder joint; horizontal abduction 1/21/2022