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About OSTA of 1. TA of forearm with regions 2. TA of hand with regions 3. TS of forearm 4. The muscles of forearm and hand 5. The layers of each region 6. The bundle of vessels and nerves of forearm 7. How we will do amputation of forearm and hand 8. The technique of exoarticulation of wrist and carpal, intercarpal, interphalangeal joints 9. The puncture of the joints 10. The zone of kannavella

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This is a broad operative surgical topographic anatomy (OSTA) unit of the forearm and hand. I can take one area at a time.
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This is a broad operative surgical topographic anatomy (OSTA) unit of the forearm and hand. I can take one area at a time.This OSTA unit covers the topographic and operative anatomy of the forearm and hand:
  1. Topographic anatomy of the forearm
    • Anterior (flexor) and posterior (extensor) regions
    • Fascial compartments, intermuscular septa, bones, and spaces
  2. Topographic anatomy of the hand
    • Palmar and dorsal regions
    • Thenar, hypothenar, central palmar, and adductor spaces
    • Digital anatomy
  3. Cross-section of the forearm
    • Arrangement of flexor, extensor, and lateral compartments
    • Relation of radius, ulna, interosseous membrane, nerves, and vessels
  4. Muscles of the forearm and hand
    • Forearm flexors, pronators, extensors, supinators
    • Intrinsic hand muscles: thenar, hypothenar, lumbricals, interossei, adductor pollicis
  5. Layers of each region
    • Skin
    • Superficial fascia
    • Deep fascia
    • Muscular layers
    • Neurovascular structures
    • Bones and joints
  6. Forearm neurovascular bundles
    • Radial artery with superficial radial nerve
    • Ulnar artery with ulnar nerve
    • Median nerve
    • Anterior and posterior interosseous vessels and nerves
    • Major surface projections and surgical relations
  7. Forearm and hand amputation
    • Principles: viable skin flaps, preservation of maximum functional length, atraumatic handling, hemostasis, bone shortening/smoothing, nerve management, and tendon balancing
    • Choice of flap depends on injury level and viable tissue, rather than a single universal incision
  8. Disarticulation techniques
    • Wrist joint
    • Carpometacarpal joints
    • Intercarpal joints
    • Metacarpophalangeal joints
    • Interphalangeal joints
      Focus: landmarks, capsule and ligament division, protection of tendons/vessels/nerves, and flap planning.
  9. Joint puncture
    • Wrist joint aspiration/injection landmarks

Quick answer

OSTA: Forearm and Hand - high-yield outline

1. Topographic anatomy of the forearm

The forearm extends from the elbow to the wrist and is divided into:
  • Anterior region: flexor-pronator compartment
  • Posterior region: extensor-supinator compartment
  • Lateral/radial region: mobile wad, including brachioradialis and radial wrist extensors
Boundaries
  • Medial: subcutaneous posterior border of ulna
  • Lateral: radius
  • Deep: radius, ulna, and interosseous membrane
  • Superficial: skin, superficial fascia, deep fascia

2. Topographic anatomy of the hand

The hand is divided into:
  • Palmar region
    • Thenar region
    • Hypothenar region
    • Middle palmar region
    • Digital regions
  • Dorsal region
  • Fingers
The palmar skin is thick, firmly fixed by fibrous septa, and contains no hair or sebaceous glands. The dorsal skin is thin and mobile.

3. Cross-section of the forearm

A transverse section shows three fascial compartments:
CompartmentMain contentsMain nerve
AnteriorFlexors and pronatorsMedian nerve, with ulnar nerve medially
PosteriorExtensors and supinatorRadial nerve branches
LateralBrachioradialis, ECRL, ECRBRadial nerve
The interosseous membrane connects radius and ulna, stabilizes them, and separates anterior from posterior interosseous vessels and nerves.

4. Muscles of the forearm and hand

Anterior forearm: flexor-pronator group

Superficial layer
  • Pronator teres
  • Flexor carpi radialis
  • Palmaris longus
  • Flexor carpi ulnaris
Intermediate layer
  • Flexor digitorum superficialis
Deep layer
  • Flexor digitorum profundus
  • Flexor pollicis longus
  • Pronator quadratus
Innervation is mainly by the median nerve. Exceptions:
  • Flexor carpi ulnaris: ulnar nerve
  • Medial half of flexor digitorum profundus: ulnar nerve

Posterior forearm: extensor-supinator group

Superficial layer
  • Brachioradialis
  • Extensor carpi radialis longus and brevis
  • Extensor digitorum
  • Extensor digiti minimi
  • Extensor carpi ulnaris
Deep layer
  • Supinator
  • Abductor pollicis longus
  • Extensor pollicis brevis and longus
  • Extensor indicis
Innervation: posterior interosseous nerve, a deep branch of the radial nerve.

Intrinsic muscles of the hand

Thenar
  • Abductor pollicis brevis
  • Flexor pollicis brevis
  • Opponens pollicis
    Mainly recurrent branch of median nerve.
Hypothenar
  • Abductor digiti minimi
  • Flexor digiti minimi brevis
  • Opponens digiti minimi
    Ulnar nerve.
Central group
  • Lumbricals
  • Palmar interossei: adduct fingers toward middle finger
  • Dorsal interossei: abduct fingers away from middle finger
  • Adductor pollicis: ulnar nerve
Mnemonic: PAD = palmar interossei adduct; DAB = dorsal interossei abduct.

5. Layers of important regions

Anterior forearm, superficial to deep

  1. Skin
  2. Superficial fascia: superficial veins and cutaneous nerves
  3. Deep antebrachial fascia
  4. Superficial flexor muscles
  5. Flexor digitorum superficialis
  6. Deep flexor muscles
  7. Radius, ulna, interosseous membrane

Palm, superficial to deep

  1. Thick palmar skin
  2. Dense subcutaneous tissue with fibrous septa
  3. Palmar aponeurosis
  4. Superficial palmar arterial arch and digital nerves
  5. Flexor tendons and synovial sheaths
  6. Deep palmar arterial arch
  7. Interossei, metacarpals

Dorsum of hand

  1. Thin mobile skin
  2. Loose subcutaneous tissue with dorsal veins and cutaneous nerves
  3. Deep fascia
  4. Extensor tendons
  5. Metacarpals and interossei

6. Major vessels and nerves of the forearm

Radial neurovascular bundle

  • Radial artery runs in the lateral forearm, deep to brachioradialis in the upper part.
  • At the wrist, it lies between the tendons of brachioradialis and flexor carpi radialis.
  • It enters the hand through the anatomical snuffbox and forms most of the deep palmar arch.
  • The superficial branch of the radial nerve accompanies it in the upper forearm but becomes superficial near the wrist.

Ulnar neurovascular bundle

  • The ulnar artery enters the forearm deep to pronator teres and travels with the ulnar nerve distally.
  • At the wrist, both pass superficial to the flexor retinaculum through Guyon's canal.
  • The ulnar artery contributes mainly to the superficial palmar arch.

Median nerve

  • Travels in the anterior compartment between flexor digitorum superficialis and profundus.
  • Passes through the carpal tunnel beneath the flexor retinaculum.
  • Supplies thenar muscles and sensation to the lateral 3½ digits.

Important wrist landmarks

  • Radial pulse: lateral to tendon of flexor carpi radialis.
  • Ulnar nerve and artery: lateral to pisiform in Guyon's canal.
  • Median nerve: deep to palmaris longus, entering carpal tunnel.

7. General principles of forearm and hand amputation

These operations require a trained hand or trauma surgeon. General principles are:
  1. Preserve the maximum useful length.
  2. Retain viable, sensate skin for durable coverage.
  3. Plan flaps away from pressure-bearing scars where possible.
  4. Control arteries and veins carefully.
  5. Divide nerves cleanly under gentle traction, allowing them to retract into healthy soft tissue.
  6. Smooth and shorten bone ends enough for tension-free closure.
  7. Balance flexor and extensor tendons when possible.
  8. Avoid closure under tension and ensure good soft-tissue padding.
  9. Consider early reconstruction or replantation when appropriate, especially in thumb and multiple-digit injuries.
A thumb is functionally very important. Attempts to preserve thumb length and function are prioritized whenever feasible.

8. Disarticulation procedures

Wrist disarticulation

  • Joint is between distal radius/ulna and proximal carpal row.
  • Preserve long palmar flap if viable because palmar skin is tough and weight-bearing.
  • Divide capsule and collateral ligaments, disarticulate the carpus from radius and ulna.
  • Protect and manage radial and ulnar vessels, median and ulnar nerves, and tendons.

Carpometacarpal disarticulation

  • Done at joints between metacarpal bases and carpal bones.
  • The thumb carpometacarpal joint is saddle-shaped and has different mechanics from the other CMC joints.
  • Important concern: preserving as much thumb and first web space as possible.

Metacarpophalangeal disarticulation

  • Incision and flaps should preserve useful palmar skin.
  • Extensor tendon, collateral ligaments, volar plate, and capsule are divided.
  • The metacarpal head should be preserved if possible when maintaining hand contour/function is desired.

Interphalangeal disarticulation

  • Performed at proximal or distal interphalangeal joint.
  • Preserve a longer volar flap because the volar pad gives durable sensate coverage.
  • Divide extensor tendon dorsally and flexor tendon/volar plate on the palmar side, then release collateral ligaments.

9. Joint puncture of the wrist

Wrist aspiration or injection is typically performed from a dorsal approach because major palmar vessels and nerves are avoided.
A common landmark is the dorsal radiocarpal interval:
  • Between the extensor pollicis longus tendon and extensor digitorum communis tendons, or
  • Near the interval between extensor carpi radialis longus/brevis and extensor digitorum tendons.
Key precautions:
  • Use strict aseptic technique.
  • Avoid extensor tendons and superficial radial nerve branches.
  • Do not puncture through cellulitis, infected skin, or an abscess.
  • Suspected septic arthritis requires urgent specialist assessment and aspiration.

10. Kanavel spaces and Kanavel signs

The term may refer to either Kanavel's fascial spaces or Kanavel signs.

Kanavel's deep fascial spaces of the palm

Important potential spaces that permit spread of infection:
  • Thenar space: lateral/deep palmar space, related to the thumb and index finger flexor apparatus.
  • Midpalmar space: medial/deep palmar space, related to flexor tendons of middle, ring, and little fingers.
  • Parona's space: potential space in the distal forearm between flexor tendons and pronator quadratus. It can communicate with the hand through the carpal tunnel.
  • Ulnar bursa: common flexor synovial sheath of the little finger and flexor tendons.
  • Radial bursa: synovial sheath surrounding flexor pollicis longus.
Infection can spread from the thumb through the radial bursa, across the palm, and toward the little finger via the ulnar bursa. This is sometimes called a horseshoe abscess.

Kanavel signs of pyogenic flexor tenosynovitis

  1. Finger held in slight flexion
  2. Fusiform swelling of the digit
  3. Tenderness along the flexor tendon sheath
  4. Severe pain with passive extension
This is a surgical emergency because delayed treatment may cause tendon necrosis, stiffness, or loss of the digit.
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