Elbow Biomechanics and Osteology Quiz

Elbow Biomechanics

• The elbow joint encompasses the ulnohumeral, radiocapitellar, and proximal radioulnar joints.
• It plays a crucial role in daily activities, acting as a lever arm for hand positioning and a fulcrum for forearm leverage.
• Functional range of motion (ROM) for flexion/extension is 0-150 degrees, and supination/pronation is 50 degrees.
• Normal carrying angle is 5-10 degrees for males and 10-15 degrees for females, decreasing with flexion.
• In an extended elbow, 40% of weight is through the ulnohumeral joint, and 60% is through the radiohumeral joint.

Osteology & Arthrology

• The humerus shaft features a spiral groove posteriorly, housing the radial nerve, approximately 13 cm proximal to the trochlea's articular surface.
• The distal humeral flare encompasses the medial and lateral epicondyles.
• The trochlea is spool-shaped and located medially, while the capitellum is located laterally.
• The sublime tubercle on the ulna is where the medial ulnar collateral ligament attaches distally.
• The distal humerus contains medial and lateral columns.
• The joint surfaces are anteriorly tilted by approximately 30 degrees relative to the humeral shaft.
• The elbow exhibits a 6-degree valgus rotation and an internal rotation of 5 degrees.
• The axis of rotation centers at the trochlea and capitellum, passing through the anteroinferior medial epicondyle.

Joint Type

• The radiohumeral articulation is a pivot joint, with the radial head covered by cartilage (approximately 240 degrees). The lateral 120 degrees lack cartilage.
• The ulnohumeral articulation is a hinge joint.
• The coronoid fossa on the distal humerus accommodates the coronoid tip, especially during deeper flexion.
• The coronoid tip aids in preventing posterior dislocations.
• The elbow capsule is maximally distended at 70-80 degrees of flexion.
• The distal attachment of the anterior capsule is 6 mm distal to the coronoid tip.
• The coronoid is an intra-articular structure.

Muscles of the Elbow

• Flexors: biceps (distal attachment at the radial tuberosity), brachialis (attachment 11 mm distal to the coronoid tip).
• Extensors: triceps, brachioradialis.

Ligaments & Stability

• Primary static stabilizers: ulnohumeral joint (coronoid), medial collateral ligament (MCL).
  • The MCL consists of anterior, posterior, and transverse bundles; it resists valgus and distractive stresses.
  • Its origin is from the anteroinferior aspect of the medial epicondyle. Its insertion is on the sublime tubercle of the medial coronoid process.
• Lateral collateral ligament complex (LCL): radial collateral ligament (RCL), lateral ulnar collateral ligament (LUCL).
• LCL primarily resists varus and external stress during full elbow motion.

Secondary Static Stabilizers

• Radiocapitellar joint: functions as a constraint to valgus stress. The radial head provides approximately 30 degrees of valgus stability (most important at 0-30 degrees of flexion/pronation).
• Capsule: provides significant stability, most important at 0-30 degrees of flexion/pronation. The greatest contribution happens when the elbow is fully extended.
• Dynamic stabilizers: muscles crossing the elbow joint (anconeus, brachialis, triceps, biceps) provide compressive stability.

Nerves of the Elbow

• Musculocutaneous nerve: originates from the lateral cord of the brachial plexus, exiting laterally distal to the biceps tendon and terminating as the lateral antebrachial cutaneous nerve (LABC). It innervates the biceps and brachialis.
• Radial nerve: originates from the posterior cord of the brachial plexus, running between the brachialis and brachioradialis muscles, and is located superficial to the joint capsule at the radiocapitellar joint level.
• Median nerve: originates from the medial/lateral cords of the brachial plexus, traveling with the brachial artery and situated superficially to the brachialis muscle at the elbow joint level. It does not branch in the upper arm and provides innervation to the elbow joint..
• Ulnar nerve: originates from the medial cord of the brachial plexus, passing medial to the brachial artery, piercing the medial intermuscular septum and entering the posterior compartment, traveling posteriorly to the medial epicondyle through the cubital tunnel.

Blood Supply of the Elbow

• The brachial artery, located medially in the upper arm, enters the cubital fossa on the lateral side, with its contents including the biceps tendon, brachial artery, and median nerve (on the medial side).
• It splits into the radial and ulnar arteries at the elbow level. Branches include the superior and inferior ulnar collateral and nutrient/muscular branches (supratrochlear).

Kinematics

• Motion vectors: flexion/extension (axis of rotation at trochlea center), pronation/supination (axis through capitellum, radial head, and distal ulna).
• Joint reaction force: the short, inefficient lever arms contribute to elbow stress. This plays a role in degenerative changes.
• Center of rotation (COR): line through isometric points on capitellum (about trochlea) for flex/ext; pronation/supination axis drawn from capitellum through radial head to distal ulna.

Free Body Diagram

• Free body diagrams demonstrate elbow inefficiencies (sum M=0, 5B=15W, B=3W). Static loads are similar to body weight; dynamic loads are greater.

Arthrodesis

• Optimal unilateral arthrodesis position: 90 degrees of flexion, 0-7 degrees of valgus.
• Optimal bilateral arthrodesis position: one elbow at 110 degrees of flexion for feeding, one elbow at 65 degrees of flexion for perineal hygiene.

Test your knowledge on the complex biomechanics and osteology of the elbow joint. This quiz covers essential concepts such as joint roles, range of motion, and anatomical features. Perfect for students and professionals in physical therapy and kinesiology.