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ts of forearm

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anatomical transverse section of forearm showing flexor and extensor compartments radius ulna interosseous membrane

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forearm anatomy

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transverse section forearm anatomy flexor extensor compartments radius ulna

Transverse section of the forearm

Cross-section of posterior forearm extensors
A transverse section shows the forearm divided by the radius, ulna, interosseous membrane, deep fascia, and intermuscular septa into flexor and extensor compartments.

1. Bones and membrane

  • Radius: lateral side, or thumb side
  • Ulna: medial side, or little-finger side
  • Interosseous membrane: strong fibrous sheet joining the two bones; separates deep flexor and extensor structures and transmits forces between radius and ulna.

2. Anterior compartment - flexor-pronator compartment

Located anterior to the radius, ulna, and interosseous membrane.
Superficial muscles
  • Pronator teres
  • Flexor carpi radialis
  • Palmaris longus
  • Flexor carpi ulnaris
  • Flexor digitorum superficialis
Deep muscles
  • Flexor digitorum profundus
  • Flexor pollicis longus
  • Pronator quadratus, near the distal forearm
Nerves and vessels
  • Median nerve: usually between flexor digitorum superficialis and profundus
  • Ulnar nerve and ulnar artery: medial side, near flexor carpi ulnaris
  • Radial artery: lateral side, deep to brachioradialis
  • Anterior interosseous nerve and artery: on the anterior surface of the interosseous membrane

3. Posterior compartment - extensor-supinator compartment

Located posterior to the radius, ulna, and interosseous membrane.
Superficial muscles
  • Extensor digitorum
  • Extensor digiti minimi
  • Extensor carpi ulnaris
  • Extensor carpi radialis longus and brevis
  • Brachioradialis, on the lateral side
Deep muscles
  • Supinator
  • Abductor pollicis longus
  • Extensor pollicis brevis
  • Extensor pollicis longus
  • Extensor indicis
Nerve and vessels
  • Posterior interosseous nerve, the continuation of the deep branch of radial nerve
  • Posterior interosseous artery

Easy orientation in a diagram

  • Anterior side: bulk of flexor muscles, median and ulnar neurovascular bundles
  • Posterior side: extensor muscle mass
  • Lateral/radial side: brachioradialis and radial artery
  • Medial/ulnar side: flexor carpi ulnaris with ulnar nerve and artery
The forearm is conventionally described as having anterior flexor and posterior extensor compartments, as summarized in this cross-sectional anatomy review.

Diagram of topographical anatomy of forearm with Regions.

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An accurate educational labelled diagram of the topographical anatomy of the forearm, shown in two full-length views side by side: anterior (flexor) view and posterior (extensor) view, elbow at top and wrist at bottom. Clearly label regions: cubital fossa, anterior forearm flexor-pronator region, posterior forearm extensor-supinator region, lateral radial region, medial ulnar region, radial styloid, ulnar styloid, wrist. Include concise surface landmarks: brachioradialis, flexor carpi radialis, palmaris longus, flexor carpi ulnaris, extensor digitorum, extensor carpi ulnaris, and indicate radial artery and ulnar nerve/artery at the distal forearm. Use anatomically correct relative locations, clinical anatomy textbook style.

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labelled surface anatomy regions of forearm anterior posterior diagram radial ulnar flexor extensor

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forearm anatomy

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forearm surface anatomy regions anterior posterior radial ulnar landmarks

Topographical anatomy of the forearm

Labelled topographical anatomy of the forearm, anterior and posterior regions
Main surface regions
  1. Cubital fossa: triangular depression on the anterior aspect of elbow.
  2. Anterior antebrachial region: flexor-pronator compartment.
  3. Posterior antebrachial region: extensor-supinator compartment.
  4. Lateral or radial region: thumb-side border, marked proximally by brachioradialis and distally by the radial artery.
  5. Medial or ulnar region: little-finger-side border, with the ulnar nerve and artery becoming superficial near the distal forearm.
  6. Carpal or wrist region: distal boundary, with the radial and ulnar styloid processes as palpable landmarks.
In the distal anterior forearm, the flexor carpi radialis tendon lies lateral to palmaris longus, a useful clinical surface landmark. Gray's Anatomy for Students describes these tendons as landmarks for locating vessels and nerves in the distal forearm. The division into anterior flexor and posterior extensor regions is also summarized in this forearm anatomy overview.

Diagram of the puncture of the joints

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Transverse section of the forearm

Cross-section of posterior forearm extensors
A transverse section shows the forearm divided by the radius, ulna, interosseous membrane, deep fascia, and intermuscular septa into flexor and extensor compartments.

1. Bones and membrane

  • Radius: lateral side, or thumb side
  • Ulna: medial side, or little-finger side
  • Interosseous membrane: strong fibrous sheet joining the two bones; separates deep flexor and extensor structures and transmits forces between radius and ulna.

2. Anterior compartment - flexor-pronator compartment

Located anterior to the radius, ulna, and interosseous membrane.
Superficial muscles
  • Pronator teres
  • Flexor carpi radialis
  • Palmaris longus
  • Flexor carpi ulnaris
  • Flexor digitorum superficialis
Deep muscles
  • Flexor digitorum profundus
  • Flexor pollicis longus
  • Pronator quadratus, near the distal forearm
Nerves and vessels
  • Median nerve: usually between flexor digitorum superficialis and profundus
  • Ulnar nerve and ulnar artery: medial side, near flexor carpi ulnaris
  • Radial artery: lateral side, deep to brachioradialis
  • Anterior interosseous nerve and artery: on the anterior surface of the interosseous membrane

3. Posterior compartment - extensor-supinator compartment

Located posterior to the radius, ulna, and interosseous membrane.
Superficial muscles
  • Extensor digitorum
  • Extensor digiti minimi
  • Extensor carpi ulnaris
  • Extensor carpi radialis longus and brevis
  • Brachioradialis, on the lateral side
Deep muscles
  • Supinator
  • Abductor pollicis longus
  • Extensor pollicis brevis
  • Extensor pollicis longus
  • Extensor indicis
Nerve and vessels
  • Posterior interosseous nerve, the continuation of the deep branch of radial nerve
  • Posterior interosseous artery

Easy orientation in a diagram

  • Anterior side: bulk of flexor muscles, median and ulnar neurovascular bundles
  • Posterior side: extensor muscle mass
  • Lateral/radial side: brachioradialis and radial artery
  • Medial/ulnar side: flexor carpi ulnaris with ulnar nerve and artery
The forearm is conventionally described as having anterior flexor and posterior extensor compartments, as summarized in this cross-sectional anatomy review.### Topographical anatomy of the forearm
Labelled topographical anatomy of the forearm, anterior and posterior regions
Main surface regions
  1. Cubital fossa: triangular depression on the anterior aspect of elbow.
  2. Anterior antebrachial region: flexor-pronator compartment.
  3. Posterior antebrachial region: extensor-supinator compartment.
  4. Lateral or radial region: thumb-side border, marked proximally by brachioradialis and distally by the radial artery.
  5. Medial or ulnar region: little-finger-side border, with the ulnar nerve and artery becoming superficial near the distal forearm.
  6. Carpal or wrist region: distal boundary, with the radial and ulnar styloid processes as palpable landmarks.
In the distal anterior forearm, the flexor carpi radialis tendon lies lateral to palmaris longus, a useful clinical surface landmark. Gray's Anatomy for Students describes these tendons as landmarks for locating vessels and nerves in the distal forearm. The division into anterior flexor and posterior extensor regions is also summarized in this forearm anatomy overview.Which joint puncture diagram do you need?Please specify the joint: shoulder, elbow, wrist, hip, knee, or multiple joints.

Diagram of zone of kanavella

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Accurate labelled medical anatomy diagram of Kanavel spaces of the hand, palmar view. Show the thumb radial bursa, little finger ulnar bursa, flexor tendon digital synovial sheaths of index, middle and ring fingers, the midpalmar space and thenar space, carpal tunnel, and Parona space in the distal forearm. Use color-coded translucent regions and arrows to show possible spread of infection from thumb and little finger through radial and ulnar bursae, including their potential communication. Clear concise labels, clean surgical anatomy textbook style.

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Kanavel spaces hand diagram radial bursa ulnar bursa thenar midpalmar Parona space

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Kanavel hand spaces anatomy

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Kanavel spaces anatomy diagram radial ulnar bursae Parona space

Kanavel spaces of the hand

Diagram of Kanavel spaces: radial bursa, ulnar bursa, thenar and midpalmar spaces, and Parona space
The term Kanavel spaces commonly refers to the synovial tendon sheaths and deep fascial spaces through which infections can spread in the hand and distal forearm.

Key structures shown

  • Radial bursa: synovial sheath surrounding the flexor pollicis longus tendon of the thumb. It continues proximally through the carpal tunnel.
  • Ulnar bursa: common flexor synovial sheath in the palm, usually continuous with the flexor sheath of the little finger.
  • Digital flexor tendon sheaths: sheaths of index, middle, and ring fingers usually end near the metacarpal neck, so they do not usually directly communicate with the ulnar bursa.
  • Thenar space: deep potential space lateral in the palm, associated with the thumb and index-finger side.
  • Midpalmar space: deep potential space medial in the palm, related to the middle, ring, and little-finger side.
  • Space of Parona: potential space in the volar distal forearm, between the flexor tendons and pronator quadratus.

Clinical importance

An infection in the thumb may spread proximally into the radial bursa, while an infection of the little finger may enter the ulnar bursa. These bursae may communicate through the carpal tunnel and the space of Parona, producing a horseshoe abscess. The thumb sheath is continuous with the radial bursa, and the little-finger sheath with the ulnar bursa. Campbell's Operative Orthopaedics also notes that the two bursae may communicate.
Kanavel signs are different: they are the four clinical findings of pyogenic flexor tenosynovitis, namely fusiform digit swelling, tenderness along the flexor sheath, resting flexion, and pain on passive extension. The NCBI review of pyogenic flexor tenosynovitis describes the clinically important bursal and Parona-space connections.

Puncture of the joints

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Educational multi-panel medical diagram titled Common Joint Aspiration (Arthrocentesis) Landmarks. Include labelled surface-anatomy panels for shoulder, elbow, wrist, knee and ankle. Show patient positioning, bony landmarks, and a needle icon pointing toward each joint space, without showing skin penetration, blood, or injection. Shoulder: posterior approach near posterolateral acromion. Elbow: posterolateral soft spot. Wrist: dorsal radiocarpal joint space. Knee: superolateral approach at patella. Ankle: anteromedial tibiotalar joint space. Add a clear note: trained clinician, sterile technique, ultrasound guidance where appropriate. Accurate clinical anatomy textbook style.

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labelled diagram common joint aspiration arthrocentesis shoulder elbow wrist knee ankle landmarks

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arthrocentesis ultrasound guidance systematic review

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joint aspiration arthrocentesis shoulder elbow wrist knee ankle landmarks procedure guideline

Common joint puncture sites - arthrocentesis

Educational diagram of common joint aspiration landmarks: shoulder, elbow, wrist, knee, and ankle
Joint puncture (arthrocentesis) is performed to obtain synovial fluid, especially from an acutely hot, swollen joint to assess for infection, crystals, or bleeding.
JointCommon landmark approach
ShoulderAnterior approach just inferior and lateral to the coracoid process, or a posterior approach near the posterolateral acromion
ElbowPosterolateral “soft spot” bounded by the olecranon, radial head, and lateral epicondyle
WristDorsal radiocarpal joint space, commonly between the extensor tendons
KneeSuperolateral approach adjacent to the patella, targeting the suprapatellar recess
AnkleAnteromedial tibiotalar approach, medial to the tibialis anterior tendon
Joint aspiration requires accurate anatomy, sterile preparation, informed consent, and a trained clinician. Ultrasound can help confirm an effusion and guide needle placement, particularly where landmarks are difficult or a landmark-guided attempt yields no fluid. A 2025 systematic review found ultrasound-guided knee arthrocentesis was associated with improved procedural outcomes compared with landmark-guided aspiration (PMID: 39889185).
Firestein & Kelley's Textbook of Rheumatology identifies diagnostic aspiration of a hot, swollen joint as the most common indication for arthrocentesis. The MSD shoulder procedure guide and MSD elbow procedure guide describe the relevant landmarks and safety precautions.
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