Osteology and joints of the upper limb Flashcards
What are the 3 types of bone present in the hand?
Carpal bones (Most proximal) – A set of eight irregularly shaped bones. These are located in the wrist area. Metacarpals – There are five metacarpals, each one related to a digit Phalanges (Most distal) – The bones of the fingers. Each finger has three phalanges, except for the thumb, which has two.
How many carpal bones are there? Name them laterally to medially, proximally to distally.
8:
-In the proximal row, the bones are (lateral to medial):
Scaphoid
Lunate
Triquetrum
Pisiform (a sesamoid bone, formed within the tendon of the flexor carpi ulnaris)
-In the distal row, the bones are (lateral to medial):
Trapesium
Trapezoid
Capitate
Hamate (has a projection on its palmar surface called the hook of hamate)
-Proximally, the scaphoid and lunate articulate with the radius to form the wrist joint. In the distal row, all of the carpal bones articulate with the metacarpals.
Which carpal bones are most often broken? How are they normally broken? State the clinical relevance.
- Scaphoid and lunate. The most common mechanism of injury in both cases is FOOSH (falling on an outstretched hand).
- The scaphoid is more commonly fractured. Characteristically there is pain and tenderness in the anatomical snuffbox. A fracture needs to be fixed quickly, as the blood supply to the proximal part of the bone can be cut off, causing it to undergo avascular necrosis. Patients with an undiagnosed scaphoid fracture are very likely to develop wrist arthritis.
- A lunate fracture occurs when falling on a outstretched hand causes hyperextension at the wrist. It is can be associated with some median nerve damage.
Describe the metacarpal bones.
The metacarpal bones articulate proximally with the carpals, and distally with the proximal phalanges. They are numbered, and each associated with a digit:
Metacarpal I – Thumb (pollex)
Metacarpal II – Index finger (index)
Metacarpal III – Middle finger (medius)
Metacarpal IV – Ring finger (anularis)
Metacarpal V – Little finger (digitus minimus)
Each metacarpal consists of a base, shaft and a head. The medial and lateral surfaces of the metacarpals are concave, allowing attachment of the interosseus muscles.
Describe the two most common fractures of the metacarpals,
- Boxer’s fracture – A fracture of the 5th metacarpal neck. It is usually caused by a clenched fist striking a hard object. The distal part of the fracture is displaced posteriorly, producing shortening of the affected finger.
- Bennett’s fracture – A fracture of the 1st metacarpal base, extending into the carpometacarpal joint. It is caused by hyperabduction of the thumb.
Where is the clavicle situated?
The clavicle (collarbone) extends between the sternum and the acromion of the scapula.
What is the classification of the clavicle? What is its function?
It is classed as a long bone, and can be palpated along its length. In thin individuals, it is visible under the skin. The clavicle has three main functions:
- Attaches the upper limb to the trunk.
- Protects the underlying neurovascular structures supplying the upper limb.
- Transmits force from the upper limb to the axial skeleton.
Describe the bony landmarks of the clavicle.
The clavicle is a slender bone with an ‘S’ shape. Facing forward, the medial aspect is convex, and the lateral aspect concave. It can be divided into a sternal end, a shaft and an acromial end.
-Sternal (medial) End:
The sternal end contains a large facet – for articulation with the manubrium of the sternum at the sternoclavicular joint.
The inferior surface of the sternal end is marked by a rough oval depression for the costoclavicular ligament (a ligament of the SC joint).
-Shaft:
The shaft of the clavicle acts a point of origin and attachment for several muscles – deltoid, trapezuis, subclavius, pectoralis major, sternocleidomastoid and sternohyoid
-Acromial (lateral) End:
The acromial end houses a small facet for articulation with the acromion of the scapula at the acromioclaviclar joint. It also serves as an attachment point for two ligaments:
o Conoid tubercle – attachment point of the conoid ligament, the medial part of the coracoclavicular ligament.
o Trapezoid line – attachment point of the trapezoid ligament, the lateral part of the coracoclavicular ligament.
o The coracoclavicular ligament is a very strong structure, effectively suspending the weight of the upper limb from the clavicle.
Describe a fracture of the clavicle, and state its clinical significance.
- A function of the clavicle is to transmit forces from the upper limb to the axial skeleton. Thus, the clavicle is the most commonly fractured bone in the body. Fractures commonly result from a fall onto the shoulder, or onto an outstretched hand.
- The most common point of fracture is the junction of the medial 2/3 and lateral 1/3. After fracture, the lateral end of the clavicle is displaced inferiorly by the weight of the arm, and medially, by the pectoralis major. The medial end is pulled superiorly, by the sternocleidomastoid muscle.
- The suprascapular nerves (medial, intermedial and lateral) may be damaged by the upwards movement of the medial part of the fracture. These nerves innervate the lateral rotators of the upper limb at the shoulder – so damage results in unopposed medial rotation of the upper limb – the ‘waiters tip’ position.
What is the humerus and what does it do?
- The humerus is the bone that forms the upper arm, and joins it to the shoulder and forearm.
- The proximal region articulates with the scapula and clavicle, forming part of the shoulder joint. Distally, the humerus articulates with the forearm bones (radius and ulna), to form the elbow joint.
- The humerus acts as an attachment site for many muscles and ligaments, resulting in various raised roughening on the bony surface.
What are the important anatomical features of the proximal region of the humerus?
- The proximal region of the humerus articulates with the scapula to form the glenohumeral joint (shoulder joint).
- The important anatomical features of the proximal humerus are the head, anatomical neck, surgical neck, greater and lesser tubercles and intertubercular sulcus. A tubercle is a round nodule, and signifies an attachment site of a muscle or ligament.
- The head of the humerus projects medially and superiorly to articulate with the glenoid cavity of the scapula. The head is connected to the tubercles by the anatomical neck, which is short in width and nondescript.
- The greater tubercle is located laterally on the humerus. It has a anterior and posterior face. The greater tubercle serves as attachment site for 3 of the rotator cuff muscles (supraspinatus, infraspinatus and teres minor).
- The lesser tubercle is much smaller, and more medially located on the bone. It only has an anterior face. It is a place of attachment for the last rotator cuff muscle – subscapularis.
- Separating the two tubercles is a deep depression, called the intertubercular sulcus, or groove. The tendon of the long head of biceps brachii runs through this groove. The edges of the intertubecular sulcus are known as lips. Tendons of the pectoralis major, teres major and latissimus dorsi attach to the lips of the intertubecular sulcus.
- The surgical neck runs from the tubercles to the shaft of the humerus.
What is the clinical importance of a surgical neck fracture of the humerus?
- This is a frequent site of fracture (hence the name), this occurs by a direct blow to the area, or by falling on an outstretched hand.
- It is important to consider the regional anatomy of this area to assess which vessels and nerves are a risk of damage. The key structures of concern is this scenario are the axillary nerve and posterior circumflex artery.
- Damage to the axillary nerve will result in paralysis to the deltoid and teres minor muscles; the patient will not being able to abduct their arm.
- The axillary nerve also innervates the skin over the lower deltoid (known as the regimental badge area), and so sensory innervation here could be lost.
What are the important anatomical features of the shaft of the humerus?
-The shaft of the humerus contains some important bony landmarks such as the deltoid tuberosity and radial groove, and is the site of attachment for various muscles.
-On the lateral side of the humeral shaft is a roughened surface where the deltoid muscle attaches. This is known is as the deltoid tuberosity.
-The radial groove is shallow depression that runs diagonally down the posterior surface of the humerus, parallel to the deltoid tuberosity. The radial nerve and profunda brachii artery lie in this groove.
-Other than the deltoid, the following muscles attach to the humerus:
Anteriorly: Corocobrachialis, deltoid, brachialis, brachioradialis
Posteriorly: Medial and lateral heads of the triceps
What is the clinical relevance of a mid-shaft fracture of the humerus?
- A mid-shaft fracture could easily damage the radial nerve and profunda brachii artery, as they are tightly bound in the radial groove.
- The radial nerve innervates the extensors of the wrist. In the event of damage to this nerve, the extensors will be paralysed. This results in unopposed flexion of the wrist occurs, known as ‘wrist drop’.
- There is also some sensory loss over the dorsal (posterior) surface of the hand, and the proximal ends of the lateral 3 and a half fingers dorsally.
What are the important anatomical features of the distal region of the humerus?
- The distal part of the humerus articulates with the ulna and radius at the elbow joint. Here, the bone adopts a flattened, almost 2-D shape.
- The lateral and medial borders of the humerus form medial and lateral supraepicondylar ridges. The lateral supraepidcondylar ridge is more roughened, as it is the site of attachment for many of the extensor muscles in the posterior forearm.
- Immediately distal to the supraepicondylar ridges are the lateral and medial epicondyles –projections of bone. Both can be palpated at the elbow (the medial more so, as it is much larger). The ulnar nerve passes into the forearm along the posterior side of the medial epicondyle, and can also be palpated there.
- The trochlea articulates with the ulna. It is located medially, and extends onto the posterior of the bone. Lateral to the trochlear is the capitulum, which articulates with the radius.
- Also found on the distal portion of the humerus are three depressions, known as the coronoid, radial and olecranon fossae. They accommodate the forearm bones during movement at the elbow.
What is the clinical significance of a distal humeral fracture?
- Supracondylar fractures and medial epicondyle fractures are common fracture types of the distal humerus. A supraepicondylar fracture occurs by falling on a flexed elbow. It is a transverse fracture, spanning between the two epicondyles.
- Direct damage, or swelling can cause interference to the blood supply of the forearm from the brachial artery. The resulting ischaemia can cause Volkmann’s ischaemic contracture – uncontrolled flexion of the hand, as flexors muscles become fibrotic and short. There also can be damage to the medial, ulnar or radial nerves.
- A medial epicondyle fracture could damage the ulnar nerve, a deformity known as ulnar claw is the result. There will be a loss of sensation over the medial 1 and 1/2 fingers of the hand, on both the dorsal and palmar surfaces.
What is the radius, and what does it do?
The radius is a long bone in the forearm. It lies laterally and parallel to ulna, the second of the forearm bones. The radius pivots around the ulna to produce movement at the proximal and distal radio-ulnar joints.
What are the 4 articulations of the radius?
- Elbow Joint – Partly formed by an articulation between the head of the radius, and the capitulum of the humerus.
- Proximal Radioulnar Joint – An articulation between the radial head, and the radial notch of the ulna.
- Wrist Joint – An articulation between the distal end of the radius and the carpal bones.
- Distal Radioulnar Joint – An articulation between the ulnar notch and the head of the ulna.
Describe the proximal region of the radius. What are the important bony landmarks?
- The proximal end of the radius articulates in both the elbow and proximal radioulnar joints.
- Important bony landmarks include the head, neck and radial tuberosity:
- Head of Radius – A disk shaped structure, with a concave articulating surface. It is thicker medially, where it takes part in the proximal radioulnar joint.
- Neck – A narrow area of bone, which lies between the radial head and radial tuberosity.
- Radial Tuberosity – A bony projection, which serves as the place of attachment of the biceps brachii muscle.
Describe the shaft of the radius.
- The radial shaft expands in diameter as it moves distally. Much like the ulna, it is triangular in shape, with three borders and three surfaces.
- In the middle of the lateral surface, there is a small roughening for the attachment of the pronator teres muscle.
Describe the distal region of the radius.
- In the distal region, the radial shaft expands to form a rectangular end. The lateral side projects distally as the styloid process. In the medial surface, there is a concavity, called the ulnar notch, which articulates with the head of ulna, forming the distal radioulnar joint.
- The distal surface of the radius has two facets, for articulation with the scaphoid and lunate carpal bones. This makes up the wrist joint.
What are the 3 most common radial fractures?
- Colles’ Fracture – The most common type of radial fracture. A fall onto an outstretched hand causing a fracture of the distal radius. The structures distal to the fracture (wrist and hand) are displaced posteriorly. It produces what is known as the ‘dinner fork deformity’.
- Fractures of the radial head – This is characteristically due to falling on an outstretched hand. The radial head is forced into the capitulum of humerus, causing it to fracture.
- Smith’s Fracture – A fracture caused by falling onto the back of the hand. It is the opposite of a Colles’ fracture, as the distal fragment is now placed anteriorly.
What is the clinical relevance of the presence of the interosseous membrane between the radius and ulna? Give 2 examples of fractures that involve both the radius and ulna.
-The radius and the ulna are attached by the interosseous membrane. The force of a trauma to one bone can be transmitted to the other via this membrane. Thus, fractures of both the forearm bones are not uncommon.
-There are two classical fractures:
o Monteggia’s Fracture – Usually caused by a force from behind the ulna. The proximal shaft of ulna is fractured, and the head of the radius dislocates anteriorly at the elbow.
o Galeazzi’s Fracture – A fracture to the distal radius, with the ulna head dislocating at the distal radio-ulnar joint.
Describe the scapula.
- The scapula is also known as the shoulder blade. It articulates with the humerus at the glenohumeral joint, and with the clavicle at the acromioclavicular joint. In doing so, the scapula connects the upper limb to the trunk.
- It is a triangular, flat bone, which serves as a site for attachment for many (17!) muscles.
- In this article, we shall look at the bony landmarks on the costal, lateral and posterior surfaces of the scapula.
Describe the costal surface of the scapula.
- The anterior surface of the scapula is termed ‘costal’, this is because it is the side facing the ribcage.
- This side of the scapula is relatively unremarkable, with a concave depression over most of its surface, called the subscapular fossa. The subscapularis muscle, one of the rotator cuff muscles, originates from this side.
- Originating from the superolateral surface of the costal scapula is the coracoid process. It is a hook-like projection, which lies just underneath the clavicle. The short head of the biceps brachii and the pectoralis minor attach here, while the corocobrachialis muscle originates from this projection.
Describe the lateral surface of the scapula.
- The lateral surface of the scapula faces the humerus. It is the site of the glenohumeral joint, and of various muscle attachments.
- Glenoid fossa – A shallow cavity, which articulates with the humerus to form the glenohumeral joint. The superior part of the lateral border is very important clinically, as it articulates with the humerus to make up the shoulder joint, or glenohumeral joint.
- Supraglenoid tubercle – A roughening immediately superior to the glenoid fossa, this is the place of attachment of the long head of the biceps brachii.
- Infraglenoid tubercle – A roughening immediately inferior to the glenoid fossa, this is the place of attachment of the long head of the triceps brachii.
Describe the posterior surface of the scapula.
- The posterior surface of the scapula faces outwards. It is a site of attachment for the majority of the rotator cuff muscles of the shoulder.
- Spine – The most prominent feature of the posterior scapula. It runs transversely across the scapula, dividing the surface into two.
- Infraspinous fossa – The area below the spine of the scapula, it displays a convex shape. The infraspinatus muscle originates from this area.
- Supraspinous fossa – The area above the spine of the scapula, it is much smaller that the infraspinous fossa, and is more convex in shape. The supraspinatus muscle originates from this area.
- Acromion – projection of the spine that arches over the glenohumeral joint and articulates with the clavicle.
What is the clinical relevance of fractures of the scapula?
- Fractures of the scapula are relatively uncommon, and if they do occur, it is an indication of severe chest trauma. They are frequently seen in high speed road collisions, crushing injuries, or sports injuries.
- The fractured scapula does not require much intervention, as the tone of the surrounding muscles holds the pieces in place for healing to occur.
What is winging of the scapula?
- The serratus anterior muscle originates from ribs 2-8, and attaches the costal face of the scapula, pulling it against the ribcage. The long thoracic nerve innervates the serratus anterior.
- If this nerve becomes damaged, the scapula protrudes out of the back when pushing with the arm. The long thoracic nerve can become damaged by trauma to the shoulder, repetitive movements involving the shoulder or by structures becoming inflamed and pressing on the nerve.
What is the ulna and where does it articulate?
- The ulna is a long bone in the forearm. It lies medially and parallel to the radius, the second of the forearm bones. The ulna acts as the stablising bone, with the radius pivoting to produce movement.
- Proximally, the ulna articulates with the humerus at the elbow joint. Distally, the ulna articulates with the radius, forming the distal radio-ulnar joint.
Describe the proximal portion of the ulna and its bony landmarks.
- The proximal end of the ulna articulates with the trochlea of the humerus. To enable movement at the elbow joint, the ulna has a specialised structure, with bony prominences for muscle attachment.
- Important landmarks of the proximal ulna are the olecranon, coronoid process, trochlear notch, radial notch and the tuberosity of ulna.
- Olecranon – A large projection of bone that extends proximally, forming part of trochlear notch. It can be palpated as the ‘tip’ of the elbow. The triceps brachii muscle attaches to its superior surface.
- Coronoid Process – This ridge of bone projects outwards in a anterior manner, forming part of the trochlear notch.
- Trochlear Notch – Formed by the olecrannon and coronoid process. It is wrench shaped, and articulates with the trochlea of the humerus.
- Radial Notch - Located on the lateral surface of the trochlear notch, this area articulates with the head of the radius.
- Tuberosity of Ulna – An roughening immediately distal of the coronoid process. It is where the brachialis muscle attaches.
Describe the shaft of the ulna.
-The ulnar shaft is triangular in shape, with three borders and three surfaces. It is moves distally, it decreases in width.
-The three surfaces:
o Anterior – Site of attachment for the pronator quadratus muscle distally.
o Posterior – Site of attachment for many muscles.
o Medial – Unremarkable.
-The three borders:
o Posterior – Palpable along the entire length of the forearm posteriorly
o Interosseous - Site of attachment for the interosseous membrane, which spans the distance between the two forearm bones.
o Anterior – Unremarkable.
Describe the distal portion of the ulna.
- The distal end of the ulna is much smaller in diameter that the proximal end. It is mostly unremarkable, terminating in a rounded head, with distal projection – the ulnar styloid process.
- The head articulates with the ulnar notch of the radius to form the distal radio-ulnar joint.
What is the clinical relevance of an ulna fracture?
- A fracture of the ulna alone (not involving the radius) usually occurs as a result of the ulna being hit by an object. The shaft is the most likely site of fracture. In this situation, the normal muscle tone will pull the proximal ulna posteriorly.
- Less commonly, the olecrannon process can be fractured. This is caused by the patient falling on a flexed elbow. The triceps brachii can displace part of the fragment proximally.
What is the acromioclavicular joint?
The acromioclavicular joint is a plane type synovial joint. It is located where the lateral end of the clavicle articulates with the acromion of the scapula. The joint can be palpated during a shoulder examination; 2-3cm medially from the ‘tip’ of the shoulder (formed by the end of the acromion).
Describe the articulating surfaces of the acromioclavicular joint.
The acromioclavicular joint consists of an articulation between the lateral end of the clavicle and the acromion of the scapula. It has two atypical features:
The articular surfaces of the joint are lined with fibrocartilage (as opposed to hyaline cartilage).
The joint cavity is partially divided by an articular disc – a wedge of fibrocartilage suspended from the upper part of the capsule.
Describe the joint capsule of the acromioclavicular joint.
The joint capsule consists of a loose fibrous layer which encloses the two articular surfaces. It also gives rise to the articular disc. The posterior aspect of the joint capsule is reinforced by fibres from the trapezius muscle.
As would be expected of a synovial joint, joint capsule is lined internally by a synovial membrane. This secretes synovial fluid into the cavity of the joint.
