Elbow Biomechanics PDF

Elbow Biomechanics Dr. Bassem Khalifa Assistant Professor of Orthopedic Physical Therapy  INTRODUCTION o Joint includes ▪ ulnohumeral joint ▪ radiocapitellar joint ▪ proximal radioulnar joint o Elbow function ▪ crucial for activities of daily living...

Elbow Biomechanics Dr. Bassem Khalifa Assistant Professor of Orthopedic Physical Therapy  INTRODUCTION o Joint includes ▪ ulnohumeral joint ▪ radiocapitellar joint ▪ proximal radioulnar joint o 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 o Functional ROM ▪ 30° to 130 flexion/extension ▪ total ROM is 0-150 degrees ▪ 50° supination/pronation o Normal carrying angle ▪ normal valgus carrying angle ▪ 5-10° for males ▪ 10-15° for females ▪ this diminishes with flexion o Axial loading ▪ in extended elbow ▪ 40% of weight is through ulnohumeral joint ▪ 60% of weight is through radiohumeral joint  OSTEOLOGY & ARTHROLOGY o 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  o 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 o 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 o Extensors ▪ triceps  LIGAMENTS & STABILITY OF ELBOW o 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 o 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 o Dynamic stabilizers ▪ includes muscles crossing elbow joint ▪ anconeus ▪ brachialis ▪ triceps ▪ biceps ▪ they provide compressive stability  NERVE OF THE ELBOW o 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 o 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 o 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 o 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 o 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 o Principle branches ▪ superior/inferior ulnar collateral ▪ nutrient/muscular supratrochlear  KINEMATICS o 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 o 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 o 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 o Free body diagram demonstrate inefficiencies of elbow ▪ sum M = 0 ▪ 5B = 15W ▪ B = 3W o Static loads are close to body weight o Dynamic loads are greater than body weight  ARTHRODESIS o 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