Anatomy of elbow and forearm Flashcards
Describe the surface anatomy markers of the elbow and forearm
- elbow:
- lateral epicondyle
- medial epicondyle
- olecranon
- radial head
- wrist:
- radial styloid
- lister’s tubercle: EPL runs around it to thumb
- ulnar styloid
Describe the features of the humerus (as it relates to elbow and forearm)
- head
- anatomical neck, and surgical neck
- greater and lesser tuberosity
- bicipital groove
- shaft
- deltoid tuberosity
- olecranon fossa - proximal to trochlea on posterior aspect, radius head sits here. In elbow extension, the tip of the ulnar olecranon process lodges into this fossa.
- coronoid fossa - proximal to trochlea on anterior aspect. During flexion of the elbow, the coronoid process of the ulna lodges into the coronoid fossa. Lateral to the coronoid fossa and superior to the capitulum is another depression referred to as the radial fossa. It is so named as the margin of the head of the radius lodges there in full flexion.
- radial fossa - proximal to capitulum. the fossae accommodate the humerus and ulna during flexion or extension
- capitulum: located laterally (not visible posteriorly). Articulates with radius. Unlike the trochlea, it doesn’t cover the posterior surface. It articulates with the head of the radius. In extension, the inferior surface is in contact with the radiusbut in the flexed position the radial head slides towards the anterior aspect of the humerus.
- trochlea: located medially. Articulates with ulna. When the elbow is in the extended position, the posterior and inferior aspects of the trochlea are in contact with the ulna. However, when the elbow is flexed the posterior part is no longer in contact, as the trochlear notch slides towards the anterior aspect of the humerus.
- medial epicondyle: constitutes the CFO
- lateral epicondyle: constitutes the CEO
Make elbow joint stable as compared to GH, thus it stiffs easily.
Describe the radius and ulna briefly
The radius and ulna are the two bones of the forearm. They articulate proximally with the humerus at the elbow, and distally with the carpal bones at the wrist. In the anatomical position, the radius is positioned on the lateral aspect of the forearm, while the ulna is found medially.
The radius and ulna articulate with each other at the proximal and distal radioulnar joints, while their bodies are connected by an interosseous membrane. These two joints allow the radius to move around the ulna, allowing for a palm facing up (supinated) or palm facing down (pronated) positioning of the forearm.
Describe the features of the radius
Key features of the radius include:
- head: The discoid head of the radius articulates superiorly with the capitulum of the humerus, contributing to the formation of the elbow joint. At the same time, the head of the radius also articulates with the ulna forming the proximal radioulnar joint. In this joint, the circumference of the head of the radius is situated on the radial notch of ulna.
- neck
- radial tuberosity/biceps tuberosity: where biceps inserts
- styloid process: The lateral aspect of the distal radius forms a ridge and terminates distally as the radial styloid process.
- ulnar notch: The distal end of the radius widens to form three smooth, concave surfaces. The medial aspect of the distal radius forms a concavity known as the ulnar notch, which articulates with the distal ulna.
Describe key features of the ulna
Key features of the ulna include:
- olecranon
- trochlear notch
- coronoid process: Projecting anteriorly from the proximal portion of the ulna is the coronoid process. The coronoid process aids in stabilizing the elbow joint and preventing hyperflexion of the forearm.
- head: The distal end of the ulna tapers to form the disc-like head of the ulna. The head of the ulna does not articulate with the carpal bones and is therefore not a component of the wrist joint
- radial notch
- ulnar tuberosity: Inferior to the coronoid process is the tuberosity of ulna, which functions as an attachment point for the brachialis muscle.
- styloid process: Projecting from the head of the ulna is a small bony protrusion known as the styloid process of ulna.
Describe the elbow joint
The elbow joint is not a simple synovial hinge joint.
The elbow joint is really a combination of ulno-humeral joint, radio-humeral, and proximal radioulnar joint. It is thus described as a composite trochoginglymoid joint – a rotating (ginglymoid) articulation at radioulna joint with
a hinge joint (trochoid) at the ulnohumeral and
radiohumeral joints.
The humeroulnar joint is between the trochlea on the medial aspect of the distal end of the humerus and the trochlear notch on the proximal ulna. The humeroradial joint is formed between the capitulum on the lateral aspect of the distal end of the humerus with the head of the radius. The proximal ends of the radius and ulna articulate with each other at the proximal radioulnar joint.
Functionally, the elbow is a hinge joint, allowing movement in only one plane: flexion and extension. Yet, it also facilitates motion in the hand in the form of supination and pronation of the forearm.
Check image for key points.
Note also: distal radioulnar joint
The distal radioulnar joint is a synovial joint between the distal ends of the radius and ulna.
This is a uniaxial pivot joint that allows the movements in one degree of freedom; pronation-supination.
The distal radioulnar joint is the articulation between the crescent-shaped convex distal head of ulna and the concave ulnar notch of radius. Both surfaces are lined by the hyaline cartilage.
The joint contains a triangular fibrocartilaginous articular disc.
The joint is enclosed by a fibrous capsule.
Describe ligaments supporting elbow
There are three main ligaments that support the elbow joint: the ulnar collateral ligament, radial collateral ligament and annular ligament.
The medial collateral ligament has three bands:
- anterior (strong)
- posterior (weaker)
- oblique
The MCL is crucial for combatting valgus stress. The anterior band of MCL is especially crucial for this.
The annular ligament runs around the radial head from the anterior and the posterior margin of the radial notch, to approximate the radial head to the radial notch and enclose the radial circumference. It encircles 80% of the radial head and functions to maintain the relationship between the head of the radius and the humerus and ulna.
Function:
- Holding the proximal radius against the ulna as it fits strongly around the radial head,
- It permits for free rotation of radial head as it’s internal surface is lined with cartilage.
Note that the radial is synonymous with the lateral collateral ligament. Similarly the ulnar is synonymous with the medial collateral ligament.
Describe the CEO and CFO
Tendons attach around the elbow at two sites:
- common extensor origin: CEO - a blend of muscles whose tendons attach to the lateral epicondyle
- ECRB
- EDC
- ECU
- EDM
- #clinicallyrelevant : tennis elbow, or lateral epicondylitis
- Damage to the tendinous insertion common wrist and finger extensors
- Pain and tenderness at common extensor origin and Lateral epicondyle
- Pain with wrist and finger extension
- Treated with rest and stretching, physiotherapy and cortisone injection
- Rarely requires surgery to cut tendon
- common flexor origin: CFO - a blend of muscles whose tendons attach to the medial epicondyle
- Pronator Teres
- Flexor Carpi Radialis
- Flexor Digitorum Superficialis
- Palmaris Longus
- Flexor Carpi Ulnaris
- # clinicallyrelevant : golfer’s elbow or medial epicondylitis
- damage to the tendinous insertion common wrist and finger flexors
- pain and tenderness at common flexor origin and medial epicondyle
- pain with wrist and finger flexion
- treated with rest and stretching, physiotherapy and cortisone injection
- rarely requires surgery
List the muscles of the forearm
Flexor muscles
There are 5 superficial and 3 deep muscles of the forearm.
Superficial
All superficial muscles attach to common flexor origin.
- Pronator Teres - has two heads (CFO, deep ulna) - median n.
- Flexor Carpi Radialis - ulnar n.
- Flexor Digitorum Superficialis:
- Middle and Ring are superficial
- Index and Little are deep
- Test: Hold back other fingers to eliminate FDP
- Palmaris Longus ^[not in all people]
- Flexor Carpi Ulnaris - ulnar n.
#### Deep
The deep muscles do NOT cross the elbow
- Flexor Digitorum Profundus:
- passes deep in the Carpal Tunnel
- passes through the slips of Superficialis
- inserts into the Volar surface base of Distal Phalanx
- Test: Flexion of the distal Phalanx
- Flexor Pollicis Longus ^[no need for superficialis as compares to the phalanges; two phalanges vs three]
- Pronator Quadratus
Note on flexor Digitorum Superficialis (FDS) and Profundus:
- Superficialis is Four separate muscles and Tendons
- Profundus is one muscle and four separate tendon … you can’t contract them independently
### Summary
There are twelve muscles on the dorsal aspect of the forearm:
- 2 Anconeus and supinator
- 3 Pass on the radial Border to wrist/forearm:
- Brachioradialis
- ECRL: from the distal Lateral Humerus
- ECRB: from CEO
- 3 From the CEO:
- Extensor Digitorum Comminus
- Extensor Digiti Minimi
- Extensor Carpi Ulnaris
- 3 Emerge from between
- Abductor Pollicis Longus
- Extensor Pollicis Brevus
- Extensor Pollicis Longus
- 1 Distally to the forefinger (index)
- extensor indicis proprius: enables independent movement of the index finger
