Biomechanics of Elbow Joint (Part 1) PDF

Biomechanics of Elbow Joint (Part 1) Dr. Ahmed Abd El-Moneim Lecturer of Physical Therapy & Osteopathic Medicine Beni-Suef University Coordinator of Prosthetics & Orthotics...

Biomechanics of Elbow Joint (Part 1) Dr. Ahmed Abd El-Moneim Lecturer of Physical Therapy & Osteopathic Medicine Beni-Suef University Coordinator of Prosthetics & Orthotics Technology Program (BTU) Diploma of Osteopathic Medicine, IAO (Belgium) Diploma of Therapeutic Nutrition, NNI  Elbow and Forearm Complex  The elbow and forearm complex consists of three bones and four joints.  The humero-ulnar and humeroradial joints form the elbow. – The motions of elbow flexion and extension provide a means to adjust the overall functional length of the UL. This mechanism is used for many activities, such as feeding, reaching, and personal hygiene.  The radius and ulna articulate with each other within the forearm at the proximal and distal radio-ulnar joints. – These articulations allows the palm to be turned up (supinated) or down (pronated), without requiring shoulder motion.  Elbow and Forearm Complex  Supination and pronation can be performed in conjunction with, or independent from, elbow flexion and extension.  The interaction between the elbow and forearm joints adds significantly to the versatility of hand placement, enhancing the overall function of the UL. Elbow and Forearm Complex  General Features of The Humeroulnar and Humeroradial Joints  Although both joints contribute to the kinematics of flexion and extension, each has a different role in maintaining the overall three-dimensional stability of the elbow. – The humero-ulnar joint provides much of its stability through the tight fit between the trochlea and trochlear notch. – The less congruous humeroradial joint, provides elbow stability through a buttressing of the radial head against the capitulum, in conjunction with its many capsuloligamentous connections.  General Features of The Humeroulnar and Humeroradial Joints  Early anatomists classified the elbow as a ginglymus or hinged joint owing to its predominant uniplanar motion of flexion and extension.  The term modified hinge joint is more appropriate because the ulna experiences a slight amount of axial rotation (rotation around its own longitudinal axis) and side-to-side motion as it flexes and extends.  Valgus Angle of The Elbow  Elbow flexion and extension occur around a near medial-lateral axis of rotation, passing through the vicinity of the lateral epicondyle, and through the convex members of the articulation.  From medial to lateral, the axis courses slightly superiorly owing to the distal prolongation of the medial lip of the trochlea. This asymmetry in the trochlea causes the ulna to deviate laterally relative to the humerus.  The natural frontal plane angle made by the extended elbow is referred to as normal cubitus valgus (The carrying angle = The valgus angle tends to keep carried objects away from the side of the thigh during walking). Valgus Angle of The Elbow  Valgus Angle of The Elbow  An average cubitus valgus angle in healthy men and women = 13 degrees.  Women had a greater valgus angulation than men by about 2 degrees.  Regardless of gender, valgus angle is greater on the dominant arm.  The carrying angle naturally increases with age.  Valgus Angle of The Elbow  The extended elbow may exhibit an excessive cubitus valgus that exceeds about 20 or 25 degrees.  In contrast, the forearm may less commonly show a cubitus varus (gunstock) deformity, where the forearm is deviated toward the midline.  Valgus = turned outward (abducted) & Varus = turned inward (adducted).  A marked varus or valgus deformity may result from trauma, as a severe fracture through the growth plate of the distal humerus in children.  Excessive cubitus valgus may overstretch and damage the ulnar nerve as it crosses medial to the elbow. Valgus Angle of The Elbow  Periarticular Connective Tissue  The articular capsule encloses the humeroulnar joint, the humeroradial joint, and the proximal radioulnar joint.  The articular capsule is thin and reinforced anteriorly by oblique and vertical bands of fibrous tissue. A synovial membrane lines the internal surface of the capsule.  The articular capsule is strengthened by collateral ligaments. These ligaments provide an important source of multiplanar stability to the elbow, mainly within the frontal plane.  The medial collateral ligament (MCL) consists of anterior, posterior, and transverse fiber bundles. Periarticular Connective Tissue  Periarticular Connective Tissue  The anterior fibers are the strongest and stiffest of the MCL. These fibers provide the most significant resistance against a valgus (abduction) producing force to the elbow. – The anterior fibers arise from the anterior part of the medial epicondyle and insert on the medial part of the coronoid process of the ulna. – Because these thin fibers span both sides of the axis of rotation, at least some are taut throughout the full range of flexion and extension. – When considered as a group, the anterior fibers of the MCL provide articular stability throughout sagittal plane movement. Periarticular Connective Tissue  Periarticular Connective Tissue  The posterior fibers of the MCL are less defined than the anterior fibers and are fanlike thickenings of the posteriormedial capsule. – The posterior fibers attach on the posterior part of the medial epicondyle and insert on the medial margin of the olecranon process. – The posterior fibers resist a valgus-producing force, as well as become taut in the extremes of elbow flexion.  The transverse fibers of the MCL cross from the olecranon to the coronoid process of the ulna. – Because these fibers originate and insert on the same bone, they provide only limited articular stability.  Periarticular Connective Tissue  In addition to the MCL, the proximal fibers of the wrist flexor and pronator group of muscles also resist a valgus-producing strain at the elbow, most notably by the flexor carpi ulnaris. For this reason, these muscles are considered dynamic medial stabilizers of the elbow.  Periarticular Connective Tissue  The MCL is susceptible to injury when the extended elbow is violently forced into excessive valgus, from a fall onto an outstretched and supinated upper extremity. The ligamentous injury may be associated with: 1) Compression fracture within the humeroradial joint or anywhere along the length of the radius bone that accepts most of the compression force applied through the wrist. 2) Injury to the ulnar nerve or proximal attachments of the pronator– wrist flexor muscles. 3) Excessive hyperextension of the elbow, injuring the anterior capsule. Periarticular Connective Tissue  Periarticular Connective Tissue  The MCL is susceptible to injury from non–weight-bearing, repetitive, valgus-producing strains placed on the elbow. – This injury is common in athletes involved in overhead activities, most notably baseball pitchers. – Pain and valgus instability are evident during the late cocking and acceleration phase of throwing, when the valgus-producing torques at the elbow are at their greatest.  Periarticular Connective Tissue  The lateral collateral ligament complex of the elbow originates on the lateral epicondyle and splits into two fiber bundles: 1) The radial collateral ligament, fans out to merge with the annular ligament, with some fibers blending with the proximal attachments of the supinator and extensor carpi radialis brevis muscles. 2) A second thicker fiber bundle, called the lateral (ulnar) collateral ligament (LUCL), attaches distally to the supinator crest of the ulna.  The lateral location of both ligaments provides resistance against a varus- producing force at the elbow. Periarticular Connective Tissue  Periarticular Connective Tissue  The relative posterior location of the LUCL renders most of its fibers taut at full flexion.  By attaching to the ulna, the LUCL functions along with the anterior fibers of the MCL as the primary frontal plane “guy wires” to the elbow.  As a pair, the LUCL and anterior fibers of the MCL provide the primary soft tissue resistance against excessive varus and valgus movements, respectively, throughout the full range of flexion and extension.  Periarticular Connective Tissue  The stout distal attachment of the LUCL to the ulna forms a sling that supports the radial head, helping to prevent excessive external rotation of the proximal forearm relative to the humerus. – The importance of this function becomes apparent in some severe injuries that completely disrupt the LUCL. The radial head often dislocates from under the capitulum by twisting in a posterior and lateral direction, resulting in a posterior-lateral rotary instability of the elbow complex.  The LUCL is respected for its ability to provide both frontal and horizontal plane stability at the elbow. Periarticular Connective Tissue