Bones 3
Distal humeral paddle with the trochlea (medial, for the trochlear notch of the ulna) and the capitulum (lateral, for the radial head). Anteriorly the coronoid and radial fossae, posteriorly the olecranon fossa, which house the fat pads. Medial epicondyle: origin of the flexor-pronators and of the ulnar collateral ligament; lateral epicondyle: extensor-supinators and lateral collateral complex. The capitulum is the typical site of osteochondritis dissecans in young throwers (about 12–16 years); under age 10, Panner disease, an osteochondrosis of the entire capitulum, usually with a benign course.
The olecranon and the coronoid process bound the trochlear notch; laterally the radial notch receives the radial head. On the medial side of the coronoid lies the sublime tubercle (insertion of the anterior bundle of the ulnar collateral ligament); laterally, distal to the radial notch, the supinator crest (insertion of the LUCL). Anteriorly, below the coronoid, the ulnar tuberosity for the brachialis.
Disc-shaped head with a fovea (for the capitulum) and an articular circumference (for the radial notch of the ulna), encircled by the annular ligament; then the neck and the radial tuberosity, insertion of the biceps. Radial head fractures are graded with the Mason classification; in children, subluxation of the head under the annular ligament is nursemaid's elbow.
Ligaments 8
The strongest bundle. Typically injured in throwers by repetitive valgus overload. On ultrasound it is a fibrillar band deep to the common flexor tendon, also to be assessed under valgus stress; on MR arthrography, partial undersurface detachment from the sublime tubercle produces the T sign.
- Origin
- Anteroinferior surface of the medial epicondyle.
- Insertion
- Sublime tubercle of the coronoid process.
- Function
- Primary restraint to valgus between about 30° and 120° of flexion.
Fan-shaped capsular thickening; forms the floor of the cubital tunnel.
- Origin
- Posteroinferior surface of the medial epicondyle.
- Insertion
- Medial margin of the olecranon.
- Function
- Secondary restraint to valgus, especially in deep flexion, when it is taut.
Does not cross the joint: minimal contribution to stability.
- Origin
- Medial margin of the olecranon.
- Insertion
- Medial margin of the coronoid process.
- Function
- Joins the ulnar insertions of the anterior and posterior bundles; deepens the trochlear notch.
Directly deep to the common extensor tendon; in chronic lateral epicondylitis it may be involved together with the ECRB.
- Origin
- Lateral epicondyle.
- Insertion
- Annular ligament, with which it blends.
- Function
- Resists varus and keeps the radial head in contact with the capitulum.
Forms about four fifths of the osteofibrous ring around the radial head, narrower distally. In children the head can slip partly under the ligament (nursemaid's elbow).
- Origin
- Anterior margin of the radial notch of the ulna.
- Insertion
- Posterior margin of the radial notch of the ulna.
- Function
- Holds the radial head against the radial notch and allows it to rotate during pronation and supination.
Runs behind the radial head. It is the first structure injured in elbow dislocation; the pivot-shift test assesses its insufficiency.
- Origin
- Lateral epicondyle.
- Insertion
- Supinator crest of the ulna, blending with the posterior margin of the annular ligament.
- Function
- Primary restraint to posterolateral rotatory instability; restraint to varus.
Proximally it leaves a gap for the posterior interosseous vessels. Its rupture together with a radial head fracture and a distal radioulnar joint injury is the Essex-Lopresti lesion.
- Origin
- Interosseous border of the radius.
- Insertion
- Interosseous border of the ulna (fibers mostly oblique, running distally and medially).
- Function
- Transfers load from the radius to the ulna; separates the anterior and posterior compartments and gives origin to the deep muscles.
Thin fibrous band just below the annular ligament. Approximate reconstruction; rarely distinguishable on imaging.
- Origin
- Inferior margin of the radial notch of the ulna.
- Insertion
- Medial surface of the radial neck.
- Function
- Supports the capsule and limits excessive rotation of the radius.
Arm muscles 6
In the arm it is the lateral belly; above the elbow it merges with the short head into the common distal tendon, which rotates about 90° before inserting. Distal rupture typically occurs in adult men during eccentric contraction; on ultrasound it is assessed with anterior, medial and lateral approaches and in the "cobra" position. The septum between the two bellies is reconstructed: position is approximate.
- Origin
- Supraglenoid tubercle of the scapula and superior glenoid labrum; the proximal tendon crosses the shoulder and runs in the intertubercular groove.
- Insertion
- Radial tuberosity, through the common distal tendon (proximal part of the footprint, farther from the axis of rotation).
- Function
- Supinates the forearm (main supinator with the elbow flexed) and flexes the elbow; assists shoulder flexion.
In the arm it is the medial belly; above the elbow it merges with the long head into the common distal tendon, from which the bicipital aponeurosis runs medially. The septum between the two bellies is reconstructed: position is approximate.
- Origin
- Tip of the coracoid process, with a tendon shared with the coracobrachialis.
- Insertion
- Radial tuberosity, through the common distal tendon (distal part of the footprint); bicipital aponeurosis to the antebrachial fascia.
- Function
- Flexes the elbow and supinates the forearm; assists shoulder flexion and adduction.
Deep to the biceps: forms the floor of the cubital fossa and covers the anterior capsule. Innervated by the musculocutaneous nerve, with a radial nerve contribution to the lateral portion. After elbow trauma it is a typical site of myositis ossificans.
- Origin
- Distal half of the anterior surface of the humerus and intermuscular septa, mainly the medial one.
- Insertion
- Ulnar tuberosity and anterior surface of the coronoid process.
- Function
- Main elbow flexor in every forearm position; inserting on the ulna, it has no role in pronation and supination.
With the other heads it forms the distal tendon on the olecranon. Distal tendon rupture is rare and is often associated with a small avulsed bone fragment (flake sign).
- Origin
- Infraglenoid tubercle of the scapula.
- Insertion
- Olecranon (superior and posterior surfaces), through the common tendon; expansion to the antebrachial fascia.
- Function
- Extends the elbow; extends and adducts the shoulder (biarticular).
Superficial, converges into the olecranon tendon; covers the radial nerve and the deep artery of arm in the radial groove.
- Origin
- Posterior surface of the humerus, above the radial groove.
- Insertion
- Olecranon, through the common tendon; lateral expansion to the antebrachial fascia.
- Function
- Extends the elbow, especially against resistance.
Deep, covered by the long and lateral heads. Its deepest fibers insert on the posterior capsule and pull it up during extension. Snapping of its margin over the medial epicondyle (snapping triceps) can accompany ulnar nerve dislocation.
- Origin
- Posterior surface of the humerus below the radial groove, and medial and lateral intermuscular septa.
- Insertion
- Olecranon, through the common tendon; posterior capsule.
- Function
- Extends the elbow: it is the head active in every extension, even without resistance.
Flexor-pronators 7
Medial border of the cubital fossa. The median nerve passes between its two heads (pronator syndrome); the ulnar artery passes deep to the ulnar head.
- Origin
- Humeral head: medial epicondyle (common flexor origin) and medial supracondylar ridge. Ulnar head: medial margin of the coronoid process.
- Insertion
- Lateral surface of the radius at mid-shaft (pronator tuberosity).
- Function
- Pronates the forearm; assists elbow flexion.
Between the pronator teres (laterally) and the palmaris longus. The common flexor origin is the site of medial epicondylitis, less frequent than lateral; the anterior bundle of the ulnar collateral ligament runs directly deep to it. At the wrist it runs in its own tunnel next to the trapezium.
- Origin
- Medial epicondyle of the humerus (common flexor tendon).
- Insertion
- Base of the 2nd metacarpal (palmar surface).
- Function
- Flexes and abducts the wrist (radial deviation).
Short belly and long tendon to the palmar aponeurosis. Absent in about 15% of people; used as a tendon graft, for example in ulnar collateral ligament reconstruction in throwers.
- Origin
- Medial epicondyle of the humerus (common flexor tendon).
- Insertion
- Superficial surface of the flexor retinaculum and palmar aponeurosis.
- Function
- Flexes the wrist and tenses the palmar aponeurosis.
Its two heads are joined by a fibrous arch under which the median nerve and the ulnar artery pass: a possible site of median nerve compression; the nerve then descends adherent to the deep surface of the muscle.
- Origin
- Humeroulnar head: medial epicondyle (common tendon), ulnar collateral ligament and coronoid process. Radial head: oblique line and anterior border of the radius.
- Insertion
- Sides of the middle phalanx of the 2nd–5th fingers (Camper chiasm).
- Function
- Flexes the PIP joints and, secondarily, the MCP joints and the wrist.
Deep layer, under the FDS. Dual innervation: medial portion (4th–5th fingers) from the ulnar nerve, lateral portion (2nd–3rd) from the anterior interosseous nerve (median).
- Origin
- Anterior and medial surfaces of the proximal three quarters of the ulna, medial surface of the coronoid and interosseous membrane.
- Insertion
- Palmar base of the distal phalanx of the 2nd–5th fingers.
- Function
- Flexes the DIP joints and, secondarily, the PIP and MCP joints and the wrist.
The most medial of the superficial flexors. Its two heads are joined by the Osborne aponeurosis: the ulnar nerve enters the forearm passing between them and stays deep, on the FDP. The belly follows the medial and posteromedial side of the ulna, at the level of the subcutaneous posterior border (not behind the olecranon).
- Origin
- Humeral head: medial epicondyle (common tendon). Ulnar head: medial margin of the olecranon and, through an aponeurosis, proximal two thirds of the posterior border of the ulna.
- Insertion
- Pisiform and, through the pisohamate and pisometacarpal ligaments, hamate and base of the 5th metacarpal.
- Function
- Flexes and adducts the wrist (ulnar deviation).
Deep layer, lateral to the FDP: the anterior interosseous nerve descends between the two. An accessory head (Gantzer muscle), from the coronoid or the medial epicondyle, can compress the anterior interosseous nerve. Within the model window only the proximal belly is visible (reconstructed on the real bones, approximate shape); the tendon continues into the carpal tunnel.
- Origin
- Anterior surface of the radius, from below the tuberosity and the oblique line down to the pronator quadratus, and adjacent interosseous membrane.
- Insertion
- Palmar base of the distal phalanx of the thumb.
- Function
- Flexes the IP joint of the thumb and, secondarily, the MCP joint.
Extensor-supinators 10
Lateral border of the cubital fossa. The radial nerve runs in the groove between the brachioradialis and the brachialis; the superficial branch descends under its belly. An elbow flexor even though it is innervated by the radial nerve; with the ECRL and ECRB it forms the mobile wad (of Henry).
- Origin
- Proximal two thirds of the lateral supracondylar ridge of the humerus and lateral intermuscular septum.
- Insertion
- Base of the radial styloid process.
- Function
- Flexes the elbow, especially in midpronation; brings the forearm back to the neutral position.
Directly under the brachioradialis. At the wrist it runs in the 2nd compartment.
- Origin
- Distal third of the lateral supracondylar ridge of the humerus and lateral intermuscular septum.
- Insertion
- Base of the 2nd metacarpal (dorsal surface).
- Function
- Extends and abducts the wrist (radial deviation); assists elbow flexion.
Its deep origin is the main site of lateral epicondylitis: on ultrasound a thickened, hypoechoic tendon, sometimes with calcifications, Doppler hyperemia and partial tears. Its proximal tendinous margin can compress the posterior interosseous nerve.
- Origin
- Lateral epicondyle of the humerus (common extensor tendon) and radial collateral ligament.
- Insertion
- Base of the 3rd metacarpal (dorsal surface).
- Function
- Extends the wrist.
Superficial to the supinator and the posterior interosseous nerve. At the wrist it runs in the 4th compartment with the EIP.
- Origin
- Lateral epicondyle of the humerus (common extensor tendon).
- Insertion
- Extensor apparatus of the 2nd–5th fingers (middle and distal phalanges).
- Function
- Extends the fingers and the wrist.
The most medial of the superficial extensors. At the wrist it runs in the 6th compartment, in the groove of the ulna.
- Origin
- Humeral head: lateral epicondyle (common extensor tendon). Ulnar head: posterior border of the ulna, through an aponeurosis shared with the FCU and FDP.
- Insertion
- Base of the 5th metacarpal (ulnar side).
- Function
- Extends and adducts the wrist (ulnar deviation).
Two layers wrap around the radial neck, with the posterior interosseous nerve passing between them. The proximal margin of the superficial layer forms the arcade of Frohse, the main site of PIN syndrome and radial tunnel syndrome.
- Origin
- Lateral epicondyle, radial collateral ligament, annular ligament, supinator crest and fossa of the ulna.
- Insertion
- Lateral, anterior and posterior surfaces of the proximal third of the radius, between the radial tuberosity and the pronator teres insertion.
- Function
- Supinates the forearm: alone in slow movements and with the elbow extended, with the biceps against resistance.
Covers the posterolateral capsule and the annular ligament. Landmark of the Kocher lateral approach (between the anconeus and the ECU). Not to be confused with the anconeus epitrochlearis, a medial accessory muscle that can compress the ulnar nerve in the cubital tunnel.
- Origin
- Posterior surface of the lateral epicondyle, through a short tendon.
- Insertion
- Lateral surface of the olecranon and proximal quarter of the posterior surface of the ulna.
- Function
- Assists the triceps in extension; tenses the capsule and dynamically stabilizes the posterolateral side.
Thin, fusiform belly of the superficial layer, between the EDC (laterally) and the ECU (medially), often fused with the EDC. Innervated by the posterior interosseous nerve; at the wrist it runs in the 5th compartment.
- Origin
- Lateral epicondyle of the humerus (common extensor tendon), with the EDC.
- Insertion
- Extensor apparatus of the little finger.
- Function
- Extends the little finger.
Deep layer, covered by the EDC and EDM, with the posterior interosseous nerve on its surface. Further down it emerges between the ECRB and the EDC and crosses the radial wrist extensors (intersection syndrome); at the wrist, with the extensor pollicis brevis, it forms the 1st compartment (De Quervain tenosynovitis). Only the proximal part is included in the model window.
- Origin
- Lateral part of the posterior surface of the ulna below the anconeus, interosseous membrane and middle third of the posterior surface of the radius, below the supinator.
- Insertion
- Base of the 1st metacarpal (radial side).
- Function
- Abducts and extends the thumb at the trapeziometacarpal joint.
Deep layer, medial to the APL. At the wrist, in the 3rd compartment, it changes direction around Lister tubercle: a typical site of delayed rupture after distal radius fracture. Only the proximal belly is in the window.
- Origin
- Middle third of the posterior surface of the ulna (lateral part), below the APL, and interosseous membrane.
- Insertion
- Dorsal base of the distal phalanx of the thumb.
- Function
- Extends the IP joint of the thumb; adducts and retropulses it.
Arteries 12
In the medial bicipital groove, lateral to the median nerve; at the elbow, medial to the biceps tendon, under the bicipital aponeurosis. It divides into the radial and ulnar arteries just below the elbow crease, at the level of the radial neck. Caliber about 4 mm. At risk in extension-type supracondylar fractures in children.
Lateral branch of the bifurcation: descends obliquely in front of the biceps tendon, the supinator and the pronator teres, under the medial margin of the brachioradialis. Caliber about 2.5–3 mm; just below its origin it gives off the radial recurrent artery.
Passes deep to the ulnar head of the pronator teres and under the FDS arch; distally it joins the ulnar nerve under the FCU. It is the larger branch of the bifurcation (about 3 mm) and gives rise to the common interosseous artery and the ulnar recurrent arteries.
Arises from the brachial artery at mid-arm; it accompanies the ulnar nerve behind the medial intermuscular septum down to the cubital tunnel and anastomoses with the posterior ulnar recurrent artery (elbow articular network; in the model the two meet at a point). Caliber about 1.5 mm.
Arises from the brachial artery a few centimeters above the medial epicondyle, runs in front of it and anastomoses with the anterior ulnar recurrent artery (in the model they meet at a point). Caliber about 1.5 mm.
Branch of the deep artery of arm: it accompanies the radial nerve in the groove, then runs in front of the lateral epicondyle and anastomoses with the radial recurrent artery (in the model they meet at a point). Caliber about 1.5–2 mm.
Arises from the radial artery just after its origin; it ascends laterally between the brachioradialis and the brachialis, near the radial nerve, toward the lateral epicondyle, where it anastomoses with the radial collateral artery. Caliber about 1.5–2 mm.
Arises from the ulnar artery; it ascends between the brachialis and the pronator teres in front of the medial epicondyle, where it anastomoses with the inferior ulnar collateral artery. Caliber about 1.2 mm.
Arises from the ulnar artery; it passes between the FDS and FDP, then between the heads of the FCU, ascends behind the medial epicondyle with the ulnar nerve and anastomoses with the superior ulnar collateral artery. Caliber about 1.5 mm.
Short trunk from the ulnar artery, 1–2 cm below its origin; it divides into the anterior and posterior interosseous arteries at the proximal margin of the interosseous membrane. Caliber about 2 mm.
Descends on the anterior surface of the interosseous membrane, between the FDP and FPL, with the anterior interosseous nerve. Caliber about 1–1.5 mm.
Passes over the proximal margin of the interosseous membrane into the dorsal compartment and accompanies the posterior interosseous nerve between the extensor layers. Caliber about 1–1.5 mm.
Veins 11
Superficial: along the lateral border of the forearm and, above the elbow, in the lateral bicipital groove; it ascends the arm to the axillary vein. Below the elbow crease it receives the median cephalic vein and sends a share of its flow into the median cubital vein. The lateral cutaneous nerve of forearm runs beside it, medially and in the same plane (in contact for up to about 7 cm below the crease): at risk during lateral venipuncture.
Superficial, on the medial side: it ascends in front of the medial epicondyle with the branches of the medial cutaneous nerve of forearm, receives the median basilic and median cubital veins, and at about mid-arm pierces the deep fascia to continue medial to the brachial artery. It is usually the largest superficial vein of the elbow.
Oblique anastomosis between the cephalic and basilic veins in front of the cubital fossa, superficial to the bicipital aponeurosis, which separates it from the brachial artery and median nerve: the usual site for venous blood sampling. The arrangement and caliber of the connecting veins (median cubital, median cephalic, median basilic) vary greatly between individuals; in the model they are shown together.
Lateral branch of the bifurcation of the median antebrachial vein (M pattern): it ascends obliquely toward the lateral side, superficial to the lateral epicondylar muscles, and drains into the cephalic vein below the elbow crease. It crosses over the lateral cutaneous nerve of forearm, which passes beneath it.
Medial branch of the bifurcation of the median antebrachial vein (M pattern): it ascends obliquely over the bicipital aponeurosis, which separates it from the brachial artery, and drains into the basilic vein. The branches of the medial cutaneous nerve of forearm run alongside it and are at risk during medial venipuncture.
One of the two deep veins accompanying the brachial artery, joined by transverse anastomoses; it arises from the confluence of the ulnar venae comitantes and continues up to the axillary vein. On Doppler ultrasound they are seen on either side of the artery.
The second deep vein beside the brachial artery; it arises from the confluence of the radial venae comitantes and receives the perforating vein of the elbow.
Connects the median cubital vein with the deep veins, piercing the fascia next to the bicipital aponeurosis; presence and caliber vary. This is why the needle must not be inserted too deep during venipuncture (underneath lie the brachial artery and the median nerve).
On the anterior surface of the forearm, it drains the palmar venous network; toward the elbow crease it divides into the median cephalic and median basilic veins (M pattern) or drains into the median cubital vein (Y pattern). Highly variable anatomy.
Two deep veins on either side of the radial artery, joined by transverse anastomoses, that accompany the artery in the forearm; at the brachial bifurcation they join the brachial veins (venae comitantes of the brachial artery).
Two deep veins on either side of the ulnar artery, under the pronator teres and the FDS arch; they join the brachial veins at the bifurcation of the brachial artery.
Nerves 14
Mixed nerve. Behind the medial intermuscular septum, then in the cubital tunnel behind the medial epicondyle, under the Osborne ligament, and between the heads of the FCU. It gives no branches in the arm; motor to the FCU, the ulnar half of the FDP and most intrinsic hand muscles; sensory to the ulnar border of the hand, the little finger and half of the ring finger. The cubital tunnel is the second most common site of compressive neuropathy in the upper limb: on ultrasound the cross-sectional area is measured at the epicondyle (above about 10 mm² is generally abnormal, with cutoffs varying between studies) and stability is assessed in flexion.
Mixed nerve. Medial to the brachial artery; at the elbow, under the bicipital aponeurosis, then between the heads of the pronator teres and under the FDS arch. It gives no branches in the arm; motor to the forearm flexors and pronators (except the FCU and the ulnar half of the FDP), partly through the AIN, and to the superficial thenar muscles and the 1st–2nd lumbricals; sensory to the palmar surface of the thumb, index, middle and radial half of the ring finger. Compression sites: ligament of Struthers (when a supracondylar process is present), bicipital aponeurosis, pronator teres, FDS arch.
Mixed nerve. It pierces the lateral intermuscular septum and descends between the brachialis and the brachioradialis, in front of the lateral epicondyle; before dividing it supplies the triceps and anconeus (in the arm), the brachioradialis and the ECRL. At about the level of the humeroradial joint line it divides into the superficial branch (sensory) and the posterior interosseous nerve (motor).
Sensory: radial dorsum of the hand, the thumb and the proximal part of the index and middle fingers. It descends under the brachioradialis, lateral to the radial artery, and emerges in the distal third of the forearm (Wartenberg syndrome).
Motor to the supinator and the extensors of the posterior compartment (EDC, EDM, ECU, APL, EPL, EPB, EIP; often also the ECRB); no cutaneous territory. It enters the supinator under the arcade of Frohse, winds laterally around the radial neck and re-emerges dorsally among the extensors. PIN syndrome: weak finger extension without sensory loss, with the wrist extending in radial deviation (ECRL spared); radial tunnel syndrome: lateral pain without motor weakness.
The musculocutaneous nerve (mixed) descends between the biceps and the brachialis, which it supplies, and emerges lateral to the biceps tendon as the lateral cutaneous nerve of forearm, sensory to the lateral surface of the forearm. In the subcutaneous tissue it passes under the median cubital vein and runs medial to the cephalic vein, in contact with it in the first part of the forearm. It divides into an anterior (palmar) branch, toward the radial artery, and a posterior (dorsal) branch, which passes under the cephalic vein; the level of the bifurcation varies widely. At risk during surgical reattachment of the biceps and during lateral venipuncture.
Motor branch of the median nerve; it arises under the FDS arch (about 5 cm below the elbow crease) and descends on the interosseous membrane with the artery of the same name; it supplies the FPL, the lateral half of the FDP and the pronator quadratus. Kiloh-Nevin syndrome: weak flexion of the distal phalanges of the thumb and index finger (OK sign) without sensory loss.
Sensory to the skin of the medial surface of the forearm. From the medial cord of the brachial plexus; it pierces the fascia at mid-arm and accompanies the basilic vein with anterior and posterior branches. At risk during medial venipuncture and elbow surgery (neuroma).
From the medial cord (T1); sensory to the medial skin of the arm, it runs near the basilic vein.
Sensory to the skin of the posterior surface of the forearm. A branch of the radial nerve, it arises in the radial groove and pierces the lateral head of the triceps. Schematic course.
Motor branches arising from the medial side of the trunk at and just below the elbow: pronator teres (the most proximal, usually above the joint line), FCR, palmaris longus and FDS. The pronator teres and the FDS arch are possible sites of median nerve compression. Origin and caliber are schematic.
Motor branches to the FCU, which arise just distal to the medial epicondyle and enter the muscle between its two heads, and to the ulnar half of the FDP, further down. Origin and caliber are schematic.
From the radial nerve trunk, above the lateral epicondyle, branches to the brachioradialis and ECRL; the ECRB and the supinator receive branches from the terminal divisions (variable origin, possibly before the arcade of Frohse). Schematic course.
Motor branches to the biceps and brachialis, in the plane between the two muscles (the brachialis also receives a contribution from the radial nerve). The nerve continues as the lateral cutaneous nerve of forearm. Schematic course.
‹ MSK Atlas