Elbow joint is a complex structure which is combination of 3 joints:
· Ulnohumeral joint
· Radiocapitellar joint
· Proximal radioulnar joint
The ulnohumeral joint surface has approximately 30° of anterior tilt relative to humeral shaft. It has also 6° of valgus and 5° of internal rotation on average.
The rotation axis uf ulnohumeral joint is centered at trochlea and capitellum. It passes through anteroinferior medial epicondyle.
Ulnohumeral joint: hinge joint (flexion-extension)
Radiocapitellar joint: pivot joint (rotation)
The coronoid tip of ulna serves as a butress to prvent posterior dislocation. In deep flexion of the elbow, the coronoid tip goes towards to the coronoid fossa of distal humerus. Coronoid process is an intraarticular structure. The capsule attachment is approximately 6mm distal to tip of the coronoid.
Approximately 240° of radial head surfac is covered with cartilage. 1/3 of lateral surface has no cartilage surface. This is the safe zone for internal fixation of radial head/neck fractures.
The spiral groove of the humeral shaft contains radial nerve. The groove is located approximately 13cm proximal to articular surface of trochlea.
Elbow stability
The stability of the elbow joint is maintainde by static (primary and secondary) and dynamic stabilizers.
Dynamic stabilzers are consisted of muscles that crosses the elbow joint, which provides compression effect by muscle contraction and helps joint stability.
· Triceps
· Biceps
· Brachialis
· Anconeus
Primary static stabilizers
· Osseoes anatomy – articular congruity of ulnohumeral joint. The coronoid process serves as an important restraint to elbow instability. Loss of >50% of coronoid height results in elbow instability.
· Medial/ulnar collateral ligament (MCL):
o MCL is the primary static restraint against valgus stress.
o MCL is consisted of anterior bundle, posterior bundle and transverse bundle.
o MCL origins from anteroinferior medial epicondlye and inserts to sublime tubercle of coronoid process.
o Anterior bundle of the MCL is the most important structure preventing valgus instability.
o The posterior bundle of the MCL forms the floor of the cubital tunnel. The contracture of this bundle causes flexion limitation. It is the main restraint to valgus instability in elbow flexion.
· Lateral collateral ligament (LCL) has 4 components:
o Radial collateral ligament (RCL)
o Lateral ulnar collateral ligament (LUCL)
o Annular ligament
o Accesory collateral ligament
LUCL is the main structure to prevent varus instability. Annular ligament provides stability to proximal radioulnar joint.
Radiocapitellar joint (proximal radius) serves as a secondary constraint against valgus stress (provides 30% of the valgus stability). This effect is most important at first 30° of elbow flexion.
Other secondary static stabilizers are joint capsule and origins of flexor and extensor tendons.
Intraarticular injections to the elbow can be performed through the soft spot triangle formed by:
· Lateral epicondyle
· Olecranon
· Radial head
Neurovascular anatomy of the elbow joint
Brachial artery is medially located in the upper arm. It inters cubital fossa laterally then splits into radial and ulnar arteries.
Contents of the cubital fossa (from lateral to medial): biceps tendon, brachial artery, median nerve.
Borders of cubital fossa:
· Brachioradialis – lateral
· Pronator teres – medial
· Distal humers – proximal
Ulnar nerve, median nerve, radial nerve and musculocutaneous nerve are the major nerves that cross elbow joint.
Ulnar nerve originates from medial cord of brachial plexus. In the upper arm, it runs medial to brachial artery. It pierces medial intermuscular septum at the level of arcade of Struthers and enters posterior compartment. It crosses elbow joint in the cubital tunnel, between olecranon and medial epicondyle. It has no branches in the upper arm. It gives its first motor branch to FCU, distal to the elbow joint.
Radial nerve runs in the spiral groove of the humerus, approximately 13cm proximal to trachlear joint surface. The nerve pierces lateral intermuscular septum 7.5cm proximal to trochlea and runs between brachialis and brachioradialis muscles. Distally, it is located superficial to the joint capsule at the level of radiocapitellar joint.