Updated: 12/27/2021

Elbow Anatomy & Biomechanics

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  • Introduction
    • Joint includes
      • ulnohumeral joint
      • radiocapitellar joint
      • proximal radioulnar joint
    • Elbow function
      • crucial for activities of daily living
      • acts as a lever arm when positioning the hand
      • functions as a fulcrum for forearm lever
  • ROM
    • Functional ROM
      • 30° to 130 flexion/extension
        • total ROM is 0-150 degrees
      • 50° supination/pronation
    • Normal carrying angle
      • normal valgus carrying angle
        • 5-10° for males
        • 10-15° for females
        • this diminishes with flexion
    • Axial loading
      • in extended elbow
        • 40% of weight is through ulnohumeral joint
        • 60% of weight is through radiohumeral joint
  • Osteology & Arthrology
    • 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
          • 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
    • Arthrology
      • 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
  • Muscles of the Elbow
    • Flexors
      • 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
    • Extensors
      • triceps
  • Ligaments & Stability of Elbow
    • Primary static stabilizers
      • 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
    • Secondary static stabilizers
      • 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
    • Dynamic stabilizers
      • includes muscles crossing elbow joint
        • anconeus
        • brachialis
        • triceps
        • biceps
      • they provide compressive stability
  • Nerve of the Elbow
    • 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
    • Radial nerve
      • 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
    • Median nerve
      • 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
    • Ulnar nerve
      • 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
  • Blood Supply of Elbow
    • Brachial artery
      • 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
    • Principle branches
      • superior/inferior ulnar collateral
      • nutrient/muscular
      • supratrochlear
  • Kinematics
    • Motion vectors
      • 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
    • Joint reaction force
      • 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
    • Center of rotation (COR)
      • 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
    • Free body diagram demonstrate inefficiencies of elbow
      • sum M = 0
      • 5B = 15W
      • B = 3W
    • Static loads are close to body weight
    • Dynamic loads are greater than body weight
  • Arthrodesis
    • Optimal position
      • 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
  • Diagnostic Injections
    • Intra-articular injection best given in soft spot formed by
      • lateral epicondyle
      • the olecranon
      • radial head
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Evidence (8)
Private Note