TBL5 - Bones of the Anterior Arm Flashcards
What two structures are found on the distal end of the humerus?
1) The distal end of the humerus makes up the condyle of the humerus. The condyle has two articular surfaces:
a) a lateral capitulum (L. little head) for articulation with the head of the radius
b) a medial, spool-shaped or pulley-like trochlea (L. pulley) for articulation with the proximal end (trochlear notch) of the ulna
Where are the lateral & medial epicondyles? Where are the coronoid & olecranon fossae?
1) The inferior end of the humeral shaft widens and then ends distally in the especially prominent medial epicondyle and the lateral epicondyle, providing for muscle attachment
2) Anteriorly, the coronoid fossa receives the coronoid process of the ulna during full flexion of the elbow. Posteriorly, the olecranon fossa accommodates the olecranon of the ulna during full extension of the elbow
Describe the head, neck, and tuberosity of the radius. What does the radial head articulate with?
1) Proximally, the smooth superior aspect of the discoid head of the radius is concave for articulation with the capitulum of the humerus during flexion and extension of the elbow joint. The head also articulates peripherally with the radial notch of the ulna; thus the head is covered with articular cartilage
2) The neck of the radius is a constriction distal to the head
3) The oval radial tuberosity is distal to the medial part of the neck, and demarcates the proximal end (head and neck) of the radius from the shaft
Describe the olecranon, coronoid process, & tuberosity of the ulna
1) For articulation with the humerus, the ulna has two
prominent projections:
a) the olecranon, which projects proximally from its posterior aspect (forming the point of the elbow), and serves as a short lever for extension of the elbow
b) the coronoid process, which projects anteriorly
2) Inferior to the coronoid process is the tuberosity of the ulna for attachment of the tendon of the brachialis muscle
How is the trochlear notch formed? What does the trochlear notch articulate with?
1) The olecranon and coronoid processes form the walls of the trochlear notch, which in profile resembles the jaws of a crescent wrench as it “grips” (articulates with) the trochlea of the humerus
2) The articulation between the ulna and humerus primarily allows only flexion and extension of the elbow joint, although a small amount of abduction–adduction occurs during pronation and supination of the forearm
What bones come together when the forearm is flexed? What bones come together when the forearm is extended?
1) When the forearm is flexed, the coronoid fossa receives the coronoid process
2) During extension of forearm, the olecranon fossa accommodates the olecranon
What two ligaments strengthen the elbow joint capsule on either side? What is the anular ligament and what does it do?
1) The lateral side is strengthened by the radial collateral ligament
2) The medial side is strengthened by the ulnar collateral ligament
3) The anular ligament of the radius encircles and holds the head of the radius in the radial notch of the ulna
4) The radial collateral ligament with the anular ligament form the proximal radio-ulnar joint and permit pronation and supination of the forearm
How does posterior dislocation of the elbow joint typically occur and why is the distal humerus driven anteriorly? Which nerve may be damaged?
1) Posterior dislocation of the elbow joint may occur when children fall on their hands with their elbows flexed. Dislocations of the elbow may also result from hyperextension or a blow that drives the ulna posterior or posterolateral
2) The distal end of the humerus is driven through the weak anterior part of the fibrous layer of the joint capsule as the radius and ulna dislocate posteriorly. The ulnar collateral ligament is often torn, and an associated fracture of the head of the radius, coronoid process, or olecranon process of the ulna may occur
3) Injury to the ulnar nerve may occur, resulting in numbness of the little finger and weakness of flexion and adduction of the wrist
What is the most common cause of subluxation of the radial head in preschool children? Which ligament is commonly damaged and how is the injury treated?
1) Preschool children, particularly girls, are vulnerable to transient subluxation (incomplete dislocation) of the head of the radius (also called “nursemaid’s elbow” and “pulled elbow”). The history of these dislocations is typical
2) The child is suddenly lifted (jerked) by the upper limb while the forearm is pronated (e.g., lifting a child). The child may cry out, refuse to use the limb, and protect their limb by holding it with the elbow flexed and the forearm pronated
3) The sudden pulling of the upper limb tears the distal attachment of the anular ligament, where it is loosely attached to the neck of the radius. The radial head then moves distally, partially out of the “socket” formed by the anular ligament. The proximal part of the torn ligament may become trapped between the head of the radius and the capitulum of the humerus
4) Treatment of the subluxation consists of supination of the child’s forearm while the elbow is flexed. The tear in the anular ligament heals when the limb is placed in a sling for 2 weeks
What are the steps that occur to repair a bone after a fracture?
1) In bone, as in other tissues, immediate responses to injury are inflammation and edema. Torn blood vessels near the fracture cause bleeding from the marrow cavity and surrounding tissues. Within a few hours, a blood clot, or hematoma, forms at the site
2) Infiltration of fibroblasts and new capillaries from periosteum is followed by migration of leukocytes, monocytes, and macrophages to form granulation tissue. Osteoprogenitor cells from both periosteum and endosteum also migrate and proliferate at the wound site
3) This tissue becomes more fibrous and then develops around and between fragment ends to form a bridge, or callus, to unite the fragments
How do angiogenic capillary sprouts from the periosteal capillaries selectively induce osteoprogenitor cell differentiation?
1) After a fracture, internal callus—between ends of bone fragments and marrow cavities (composed of trabecular bone)—and external callus—around opposing ends of bone fragment (composed of hyaline cartilage)—temporarily stabilize and bind together bone fragments
2) Because osteoprogenitor cells in the callus are pleuripotent, their fate depends on vascularity and oxygen tension of their immediate microenvironment: cells close to blood vessels become osteoblasts, which directly form trabeculae of new woven bone
3) In contrast, pleuripotential cells far from capillaries, at a lower oxygen tension, differentiate into chondroblasts, which become chondrocytes that form hyaline cartilage. This cartilage typically develops externally in the callus and is later replaced by woven spongy bone by a process similar to endochondral bone formation
What changes occur to the external callus of a bone once it is damaged in a fracture?
Macrophage-derived osteoclasts degrade the cartilaginous callus and osteoblasts reconstruct the callus with trabecular bone
What do trabecular bone in the internal and external callus do after a fracture has begun repair?
1) Trabecular bone of the internal callus restores the damaged marrow cavity
2) Trabecular bone in the external callus transforms into compact bone to complete the fracture repair
How might mesenchymal stem cell technology be beneficial for the reconstruction of fractured bones?
Because they are able to differentiate into osteogenic cell lineages that can become osteoblasts, mesenchymal stem cells from umbilical cord, bone marrow, and other sites can be harvested and cultured for use in fabrication of tissue-engineered bone for reconstruction of bone defects
