Elbow Anatomy & Biomechanics - Shoulder & Elbow (2024)

• ulnohumeral joint

• radiocapitellar joint

• proximal radioulnar joint

• crucial for activities of daily living

• acts as a lever arm when positioning the hand

• functions as a fulcrum for forearm lever

• 30° to 130 flexion/extension

  • total ROM is 0-150 degrees

• 50° supination/pronation

• normal valgus carrying angle

  • 5-10° for males

  • 10-15° for females

  • this diminishes with flexion

• in extended elbow

  • 40% of weight is through ulnohumeral joint

  • 60% of weight is through radiohumeral joint

Osteology

• spiral groove

  • the shaft for humerus has a spiral groove posteriorly (contains radial nerve)

  • this lies approximately 13 cm proximal to the articular surface of trochlea

• distal flare

  • the distal flare of humerus includes the medial and lateral epicondyles

    • the flare accounts for half of the elbow joint

  • trochlea

    • is spool shaped and is located medially

  • capitellum

    See Also

    The Elbow Joint - Structure - Movement

    • located laterally

• sublime tubercle

  • the sublime tubercle on the ulna is where the anterior bundle of the medial ulnar collateral ligament attaches distally

• columns

  • distal humerus contains medial and lateral column

• axis and alignment

  • anterior tilt

    • the joint surface is anteriorly tilted approximately 30 deg relative to shaft of humerus

  • varus/valgus

    • 6 deg of valgus

  • rotation

    • internally rotated by 5 deg

  • axis of rotation

    • is centered at trochlea and capitellum

    • it passes through anteroinferior medial epicondyle

• joint type

  • pivot joint - the radiohumeral articulation is a pivot joint

    • radial head is covered by cartilage for approximately 240 degrees

      • the lateral 120 degrees contains no cartilage

      • this is crucial for internal fixation of radial head fractures

  • hinge joint - the ulnohumeral articulation is a hinge joint

    • coronoid fossa

      • coronoid fossa on distal humerus receives the coronoid tip in deeper flexion

    • coronoid tip

      • the coronoid tip has a buttress effect in the prevention of posterior dislocations

• capsule

  • capsule is maximally distended at 70-80 deg of flexion

  • distal attachment of anterior capsule is found 6 mm distal to tip of coronoid

    • coronoid is an intra-articular structure

• biceps

  • the distal biceps attachment is at the level of the radial tuberosity

• brachialis

  • the attachment of the brachialis 11 mm distal to the tip of the coronoid

• brachoradialis

• triceps

• ulnohumeral joint (coronoid)

  • loss of 50% or more of coronoid height results in elbow instability

• medial (ulnar) collateral ligament (MCL)

  • overview

    • the MCL is composed of the anterior, posterior and transverse bundles

    • the MCL provides resistance to valgus and distractive stresses

  • anatomy

    • origin

      • anteroinferior aspect of medial epicondyle

    • insertion

      • sublime tubercle of medial coronoid process

  • components

    • anterior bundle of MCL

      • most important restraint against valgus stresses

        • radial head is second most important

    • posterior bundle of MCL

      • the posterior bundle forms the floor of the cubital tunnel

      • primary restraint to valgus stress in maximal elbow flexion

      • if this is contracted, flexion may be limited

    • transverse bundle of MCL

• lateral collateral ligament complex (LCL)

  • overview

    • consists of the

      • radial collateral ligament (RCL)

      • lateral ulnar collateral ligament (LUCL)

        • function

          • primary restraint to varus and external stress during full arc of elbow motion

        • origin

          • posterior lateral epicondyle

        • insertion

          • crista supinatoris of proximal ulna

      • accessory collateral ligament

        • some believe that the the accessory collateral ligament and the radial collateral ligament contribute substantially to lateral elbow stability

      • annular ligament

        • provides stability to the proximal radioulnar joint

    • anatomy

      • the LCL arises from isometric point on lateral aspect of capitellum

    • function

      • optimal stability is conferred with an appropriately tensioned LCL repair

• radiocapitellar joint

  • this functions as an important constraint to valgus stress

    • the radial head provides approximately 30% of valgus stability

    • this is most important at 0-30 deg of flexion/pronation

• capsule

  • greatest contribution the capsule on stability occurs with the elbow extended

• origins of the flexor and extensor tendons

• includes muscles crossing elbow joint

  • anconeus

  • brachialis

  • triceps

  • biceps

• they provide compressive stability

Musculocutaneous nerve

• origin

  • lateral cord of the brachial plexus

• anatomy at elbow

  • it exits laterally, distal to the biceps tendon

  • it will terminate as the LABC (forearm), which is found deep to the cephalic vein

• innervation at elbow

  • it supplies the biceps and brachialis

    • the nerve runs between these muscles

• origin

  • posterior cord of the brachial plexus

• anatomy at elbow

  • it leaves the triangular interval (teres major, long head of triceps and humeral shaft)

  • found in spiral groove 13 cm above the trochlea

  • pierces lateral intermuscular septum 7.5 cm above the trochlea

    • this is usually at the junction of the middle and distal third of the humerus

    • lies between the brachialis and the brachioradialis

  • distally it is located superficial to the joint capsule, at the level of the radiocapitellar joint

• origin

  • medial/lateral cords of the brachial plexus

• anatomy at elbow

  • it courses with brachial artery, running from lateral to medial

  • lies superficial to brachialis muscle at level of elbow joint

• innervation at elbow

  • it gives branches to elbow joint

  • it has no branches in upper arm

• origin

  • medial cord of brachial plexus

• anatomy at elbow

  • runs medial to brachial artery, pierces medial intermuscular septum (at the level of the arcade of Struthers) and enters posterior compartment

  • it traverses posterior to the medial epicondyle through the cubital tunnel

• innervation at elbow

  • it gives branches to elbow joint

  • it has no branches in upper arm

  • first motor branch to FCU is found distal to the elbow joint

• is located medially in the upper arm

• it enters cubital fossa laterally

  • contents-- biceps tendon (lateral), brachial artery, median nerve (medial)

  • lateral border--brachoradialis

  • medial border--pronator teres

  • proximal border --distal humerus

• at the level of elbow it splits into the radial and ulnar arteries

• superior/inferior ulnar collateral

• nutrient/muscular

• supratrochlear

• flexion and extension

  • the axis of rotation is found at the center of trochlea

• pronation (pronator teres and quadratus) & supination (biceps and supinator)

  • the axis of motion is found at the capitellum through to the radial/ulnar heads

  • this effectively forms a cone

• there are large joint reaction forces due to short and inefficient lever arms around elbow (biceps inserts not far from center of rotation)

• this contributes to degenerative changes of the elbow

• is a line through isometric points on the capitellum about trochlea

• the axis of pronation / supination is a line drawn from capitellum, through radial head, to distal ulna

Free body diagram demonstrate inefficiencies of elbow

• sum M = 0

• 5B = 15W

• B = 3W

• in a unilateral arthrodesis

  • 90° of flexion

  • 0-7° of valgus

• in a bilateral arthrodesis

  • one elbow in 110 ° of flexion for feeding

  • one elbow in 65 ° of flexion for perineal hygiene

Intra-articular injection best given in soft spot formed by

• lateral epicondyle

• the olecranon

• radial head