Osteology Flashcards
Why is clavicle S-shaped, and how does this influence its fracture pattern?
• S-shape balances strength and flexibility.
• It distributes forces from arm to the axial skeleton and allows shoulder movement.
• Fractures commonly occur at the middle-third which is the weakest point, due to force concentration.
• After a fracture, medial fragment : pulled upward and lateral : pulled downward by the arm’s wt. & shoulder muscles.
Why is the medial third of clavicle least fractured?
The medial third of the clavicle is the least commonly fractured because it is strongly supported by the sternoclavicular and costoclavicular ligaments and its connection to the sternum. This provides significant stability, making fractures in this region rare.
Importance of coracoid process in shoulder joint stability?
The coracoid process stabilizes the shoulder joint by providing attachment for muscles (pectoralis minor, biceps brachii, coracobrachialis) and ligaments (coracoacromial and coracoclavicular), preventing dislocation and supporting joint integrity.
Why is the surgical neck of the humerus, prone to fractures and which structures are at risk?
The surgical neck of the humerus is prone to fractures because it is a narrow, weak area subjected to stress during falls.
Structures at risk:
1. Axillary nerve – may be injured, leading to deltoid muscle weakness and loss of sensation over the shoulder.
2. Posterior circumflex humeral artery – risk of bleeding and ischemia.
Clinical significance of the radial groove of humerus.
The radial groove of the humerus is clinically significant because it houses the radial nerve and the deep brachial artery.
• Fractures in the midshaft of the humerus can damage the radial nerve, leading to wrist drop (inability to extend the wrist and fingers) and sensory loss in the dorsum of the hand.
• Injury to the deep brachial artery may cause compromised blood supply to the arm.
What anatomical factors predispose the scaphoid bone to avascular necrosis?
The scaphoid bone is predisposed to avascular necrosis (AVN) due to its unique blood supply:
1. Retrograde Blood Flow:
• The scaphoid receives blood primarily from branches of the radial artery, which enter at the distal pole and travel proximally.
• This retrograde flow means the proximal pole has the least blood supply.
2. Proximal Pole Vulnerability:
• Fractures, especially at the waist of the scaphoid, can disrupt the blood flow to the proximal pole, leading to ischemia and AVN.
Explain why Colle’s fracture presents with a ‘dinner fork’ deformity
A Colles’ fracture occurs due to a fall on an outstretched hand, causing a fracture of the distal radius with:
1. Dorsal displacement and angulation of the distal fragment.
2. Dinner fork deformity due to backward tilt of the wrist.
It often involves ulnar styloid fracture and can risk complications like median nerve compression or stiffness.
What is the role of the interosseous membrane in the forearm?
The interosseous membrane in the forearm serves several important functions:
1. Connects the radius and ulna: It helps maintain the proper alignment of these bones during movement.
2. Transfers forces: It transmits forces from the hand to the upper arm, reducing stress on the individual bones.
3. Muscle attachment: Provides attachment for muscles, particularly those involved in forearm movement.
4. Stabilizes the forearm: It contributes to the stability of the forearm during actions like gripping and lifting.
Why is the pisiform considered a sesamoid bone and what is its functional significance?
The pisiform is considered a sesamoid bone because it develops within the tendon of the flexor carpi ulnaris muscle, rather than from cartilage like typical bones.
Functional Significance:
1. Increases mechanical advantage: It acts as a fulcrum, improving the efficiency of the flexor carpi ulnaris in wrist flexion and adduction.
2. Protects tendons: It helps reduce friction between the tendon and the carpal bones.
Why does the ulnar styloid process rarely fracture compared to the radial styloid?
The ulnar styloid process rarely fractures compared to the radial styloid because:
1. Location: The ulnar styloid is more protected by the ulna and is less exposed to direct trauma.
2. Less mechanical stress: The radial styloid, being on the lateral side of the wrist, is more prone to forceful impacts (e.g., during falls on an outstretched hand), while the ulnar styloid is more medial and shielded.
3. Structural difference: The radial styloid is a more prominent bony structure compared to the smaller ulnar styloid.
Functional significance of the olecranon process in elbow stability.
The olecranon process plays a crucial role in elbow stability:
1. Acts as a lever: It provides attachment for the triceps brachii muscle, which is essential for elbow extension and contributes to stability during arm movements.
2. Forms part of the hinge joint: The olecranon fits into the olecranon fossa of the humerus during elbow extension, acting as a bony stopper to limit hyperextension and stabilize the elbow.
3. Prevents dislocation: It helps maintain proper alignment and prevents dislocation of the ulna from the humerus during arm movements.
How does the presence of bicipital groove aid in tendon stability?
The bicipital groove (also known as the intertubercular sulcus) aids in tendon stability by:
1. Providing a secure channel: It houses the long head of the biceps brachii tendon, keeping it stable and preventing displacement during arm movements.
2. Guiding tendon movement: The groove helps the tendon glide smoothly as the arm moves, minimizing friction and wear.
3. Preventing tendon subluxation: The anatomical shape of the groove helps prevent the tendon from sliding out of place, especially during flexion and rotation of the shoulder.
