Must Know
- An internervous plane runs between muscles supplied by different nerves, so neither muscle is denervated when the plane is opened.
- An intermuscular plane between muscles sharing one nerve is safe when both are supplied well proximal to the dissection.
- A muscle split is safe only where it lies distal to, or away from, the entry point of its nerve.
- Deltopectoral plane separates deltoid (axillary nerve) from pectoralis major (medial and lateral pectoral nerves).
- Posterior shoulder plane separates infraspinatus (suprascapular nerve) from teres minor (axillary nerve).
- Kocher plane at the elbow separates anconeus (radial nerve) from extensor carpi ulnaris (posterior interosseous nerve).
- Henry plane at the forearm separates brachioradialis (radial nerve) from flexor carpi radialis or pronator teres (median nerve).
- Smith-Petersen plane separates sartorius and rectus femoris (femoral nerve) from tensor fasciae latae and gluteus medius (superior gluteal nerve).
- Lateral and anterolateral hip approaches, posterior hip, lateral femur, medial parapatellar knee and anterior tibia have no true internervous plane.
Shoulder and Humerus
| Approach | Superficial plane | Deep plane | Structures at risk |
|---|
| Anterior shoulder (deltopectoral) | Deltoid (axillary) and pectoralis major (medial and lateral pectoral) | Subscapularis divided or elevated off lesser tuberosity | Musculocutaneous nerve, axillary nerve, cephalic vein |
| Posterior shoulder | Deltoid detached from scapular spine or split | Infraspinatus (suprascapular) and teres minor (axillary) | Axillary nerve and posterior circumflex humeral artery below teres minor, suprascapular nerve at base of spine |
| Lateral proximal humerus (deltoid split) | No true plane, deltoid split in line of fibres | Subdeltoid bursa to humerus | Axillary nerve 5 to 7 cm below the acromion tip |
| Anterior (anterolateral) humeral shaft | Deltoid and pectoralis major proximally | Brachialis split, lateral fibres radial nerve, medial fibres musculocutaneous nerve | Radial nerve in spiral groove and in the distal third, axillary nerve, anterior circumflex humeral vessels |
| Posterior humerus | No true plane, triceps heads all radial nerve | Lateral and long heads separated, medial head split | Radial nerve and profunda brachii in spiral groove, ulnar nerve deep to medial head distally |
- Musculocutaneous nerve enters coracobrachialis from its medial side about 5 to 8 cm below the coracoid. Stay lateral to the conjoint muscles.
- Inferior traction on coracobrachialis stretches the musculocutaneous nerve and can paralyse elbow flexion.
- Axillary nerve runs posterior to anterior on the deep surface of deltoid. Posterior retraction of deltoid is safe.
- Retractors hooked around the lateral humerus can compress the axillary nerve under deltoid.
- Axillary nerve lies just below the inferior border of subscapularis. External rotation moves it away before tenotomy.
- The anterior circumflex humeral vessels (three sisters) mark the lower border of subscapularis.
- Cephalic vein has no valves between it and the superior vena cava. A damaged vein is ligated to avoid embolism.
- Staying in the infraspinatus and teres minor interval protects the quadrangular space contents.
- The quadrangular space holds the axillary nerve and posterior circumflex humeral artery. The radial nerve passes through the triangular interval.
- Axillary nerve fibres fan anteriorly, so dividing the nerve paralyses deltoid in front of the injury.
- Forceful medial retraction of infraspinatus stretches the suprascapular nerve around the lateral edge of the scapular spine.
- Anteroposterior drills or screws through an anterior humeral plate can injure the radial nerve behind the middle third.
- Lever retractors around the humeral shaft are avoided as they can crush the radial nerve.
- Distally the radial nerve pierces the lateral intermuscular septum to lie between brachioradialis and brachialis.
- Long triceps split does not denervate the muscle because branches enter close to the origins and run within the muscle.
- In the posterior approach, do not reach bone in the proximal two thirds until the radial nerve is identified.
Elbow and Forearm
| Approach | Superficial plane | Deep plane | Structures at risk |
|---|
| Posterolateral elbow (Kocher) | Anconeus (radial) and extensor carpi ulnaris (posterior interosseous) | Capsule and annular ligament incised | Posterior interosseous nerve distal to annular ligament, radial nerve if joint opened anteriorly |
| Anterior radius (Henry) | Brachioradialis (radial) and flexor carpi radialis distally or pronator teres proximally (median) | Supinator, pronator teres, flexor digitorum superficialis, pronator quadratus detached from radius | Posterior interosseous nerve in supinator, superficial radial nerve under brachioradialis, radial artery |
| Posterior radius (Thompson) | No true plane, extensor carpi radialis brevis and extensor digitorum (both posterior interosseous) proximally | Supinator elevated or nerve dissected out, abductor pollicis longus and extensor pollicis brevis cross the shaft | Posterior interosseous nerve in supinator |
| Ulna (subcutaneous border) | Extensor carpi ulnaris (posterior interosseous) and flexor carpi ulnaris (ulnar) | Muscles stripped off ulna epiperiosteally | Ulnar nerve and artery under flexor carpi ulnaris |
- Pronation carries the posterior interosseous nerve medially and away from a posterolateral elbow exposure.
- The posterior interosseous nerve is safe while the dissection stays proximal to the annular ligament.
- The posterior interosseous nerve may lie on bare radial neck opposite the bicipital tuberosity, so retractors go directly on bone.
- Full supination exposes the supinator insertion on the anterior radius for subperiosteal release.
- Releasing supinator from the anterior radius and retracting it laterally carries the nerve safely in its substance.
- Traction on the mobile wad stretches the superficial radial nerve under brachioradialis.
- In about a quarter of people the posterior interosseous nerve touches the dorsal radius just below the bicipital tuberosity.
- A dorsal plate placed high on the radius can trap the nerve, so it is dissected out in supinator before plating.
- The ulnar artery runs on the radial side of the ulnar nerve beneath flexor carpi ulnaris.
- The ulnar nerve is most at risk proximally, where it passes between the two heads of flexor carpi ulnaris.
Wrist
| Approach | Superficial plane | Deep plane | Structures at risk |
|---|
| Dorsal wrist | Skin between radial and ulnar cutaneous nerve territories | No true plane, extensor compartments all posterior interosseous, usually third and fourth compartment interval | Superficial radial nerve branches, radial artery laterally |
| Volar distal radius | Flexor carpi radialis (median) and brachioradialis (radial) | Pronator quadratus elevated from its radial border | Radial artery and venae comitantes laterally, median nerve ulnar to flexor carpi radialis |
- Extensor muscles are supplied near the elbow, so separating their tendons at the wrist is safe.
- Taking the incision straight down to retinaculum before raising flaps keeps cutaneous nerves in the full fat layer.
- Cutaneous nerve branches are found most often over the second extensor compartment.
- Cut cutaneous nerves cause painful neuroma more than troublesome numbness.
- Staying radial to flexor carpi radialis, with pronator quadratus as a cushion, protects the median nerve.
Spine
| Approach | Superficial plane | Deep plane | Structures at risk |
|---|
| Anterior cervical (Smith-Robinson) | Platysma split, no true plane (facial nerve supply high in neck) | Sternocleidomastoid and carotid sheath (accessory nerve) laterally, strap muscles (ansa cervicalis), trachea and oesophagus medially | Recurrent laryngeal nerve, sympathetic chain and stellate ganglion, carotid sheath, vertebral artery, inferior thyroid artery |
| Posterior lumbar | Midline between right and left erector spinae | Both sides supplied segmentally by posterior primary rami | Segmental lumbar vessels near facets, posterior rami with them, epidural venous plexus, nerve roots and dura |
| Anterior retroperitoneal lumbar | Medial to or under rectus abdominis (segmental supply) | Retroperitoneum swept off psoas and spine | Superior hypogastric (presacral) plexus, sympathetic chain, middle sacral artery, aorta, vena cava, iliac vessels, lumbar vessels |
- Retractors are seated under the medial edge of longus colli to protect the recurrent laryngeal nerve, trachea and oesophagus.
- Dissection onto vertebral body stays subperiosteal from the midline, away from transverse processes, to avoid Horner syndrome.
- The vertebral artery lies in the transverse foramina and is seen only if the dissection strays laterally.
- Self retaining retractors are kept off the carotid sheath. Rounded hand held retractors are used instead.
- Losing some posterior rami to cautery does not fully denervate erector spinae because supply is segmental.
- Presacral plexus injury impairs sexual function. Blunt dissection and selective bipolar cautery reduce the risk.
- Middle sacral artery bleeds at L5 to S1 and is tied off.
- At L4 to L5 the great vessels are freed by ligating lumbar vessels, never cut flush with the aorta.
Hip
| Approach | Superficial plane | Deep plane | Structures at risk |
|---|
| Anterior (Smith-Petersen) | Sartorius (femoral) and tensor fasciae latae (superior gluteal) | Rectus femoris (femoral) and gluteus medius (superior gluteal) | Lateral femoral cutaneous nerve, ascending branch of lateral femoral circumflex artery, femoral nerve if plane lost medially |
| Anterolateral (Watson-Jones) | No true plane, tensor fasciae latae and gluteus medius share superior gluteal nerve | Gluteus medius and minimus retracted or partly released from trochanter | Femoral nerve from medial retraction, femoral vessels from misplaced acetabular retractors |
| Lateral (Hardinge type) | Fascia lata split | Gluteus medius split above the superior gluteal nerve limit, vastus lateralis split lateral to femoral nerve supply | Superior gluteal nerve 3 to 5 cm above the trochanter, femoral nerve and vessels, transverse branch of lateral femoral circumflex artery |
| Posterior (Southern, Moore) | Gluteus maximus split in line of fibres (inferior gluteal supply enters medially) | Short external rotators detached | Sciatic nerve, inferior gluteal artery below piriformis, medial femoral circumflex artery near quadratus femoris |
- The lateral femoral cutaneous nerve crosses sartorius, usually superficial to it, about 2.5 cm below the anterior superior iliac spine.
- The lateral femoral cutaneous nerve may branch early and has a variable course.
- The femoral nerve lies medial to rectus femoris, with the artery medial to the nerve in the femoral triangle.
- The femoral nerve is the most lateral structure of the femoral bundle and suffers retractor neurapraxia most often.
- Anterior acetabular retractors sit on bone at 1 o clock on a right hip and 11 o clock on a left hip.
- A stay suture at the apex of the gluteus medius split stops it extending into the superior gluteal nerve.
- The sciatic nerve can divide in the pelvis, so a small looking nerve prompts a search for the other division.
- Sciatic nerve injury in the posterior approach usually comes from retractor compression, seldom from division.
- Uncontrolled inferior gluteal artery bleeding retracting into the pelvis may need internal iliac ligation through the abdomen.
Femur, Knee and Tibia
| Approach | Superficial plane | Deep plane | Structures at risk |
|---|
| Lateral femur | Fascia lata split | No true plane, vastus lateralis split or lifted off lateral intermuscular septum | Perforating branches of profunda femoris |
| Medial parapatellar knee | Medial retinaculum | No true plane, interval between vastus medialis and rectus femoris (both femoral) | Infrapatellar branch of saphenous nerve, patellar tendon insertion |
| Anterior tibia | Subcutaneous medial surface | No true plane, extensor compartment elevated epiperiosteally | Long saphenous vein and saphenous nerve |
| Posteromedial proximal tibia | Medial to medial head of gastrocnemius | Between bone and gastrocnemius | Saphenous nerve and vein, popliteal vessels if too lateral |
- Vastus lateralis is supplied high in the thigh, so a distal split does not denervate it.
- Splitting vastus lateralis bluntly helps find perforators before they are torn.
- Dividing the infrapatellar branch leaves numbness lateral to the incision and risks neuroma.
- A cut infrapatellar branch is resected and buried in fat, not repaired, to limit neuroma.
- An avulsed patellar tendon is hard to reattach and delays rehabilitation.
Ankle and Foot
| Approach | Superficial plane | Deep plane | Structures at risk |
|---|
| Anterior ankle | Extensor hallucis longus and extensor digitorum longus (both deep peroneal) | Capsule incised in the same interval | Deep peroneal nerve and anterior tibial artery, superficial peroneal nerve branches |
| Posteromedial ankle | Behind medial malleolus, flexor retinaculum opened | Tibialis posterior and flexor digitorum longus retracted | Posterior tibial artery and tibial nerve |
| Lateral malleolus | Subcutaneous bone, no plane needed | Higher up, peroneus tertius (deep peroneal) and peroneus brevis (superficial peroneal) | Sural nerve, terminal branches of peroneal artery deep to fibula |
- At the ankle joint the extensor hallucis longus tendon crosses the anterior neurovascular bundle.
- Above the ankle the bundle lies between tibialis anterior and extensor hallucis longus.
- Sural nerve injury causes neuroma and numbness of the lateral foot border. The nerve is also a graft source.
- Peroneal artery branches bleed after tourniquet release, so the tourniquet comes down before closure.
- In children the tibial nerve is large and flexor digitorum longus tendon small, so structures are identified before any tendon is cut.
Pelvis and Acetabulum
| Approach | Superficial plane | Deep plane | Structures at risk |
|---|
| Anterior iliac crest graft | Crest itself, muscles attach to it but none cross it | Abdominal muscles (segmental) off inner table, gluteus medius, minimus and tensor fasciae latae (superior gluteal) off outer table | Anterior superior iliac spine and inguinal ligament attachment |
| Posterior iliac crest graft | Outer lip of crest | Gluteus maximus (inferior gluteal) and gluteus medius (superior gluteal) off outer table | Cluneal nerves, superior gluteal vessels and sciatic nerve at the sciatic notch |
| Pubic symphysis (Pfannenstiel) | No true plane, rectus abdominis split but segmentally supplied | Space of Retzius opened behind pubis | Bladder, especially when adherent after injury |
| Anterior sacroiliac joint | No true plane, iliacus stripped from inner table | Subperiosteal onto anterior sacral ala | L4 and L5 roots and lumbosacral trunk, sacral roots at the foramina, lateral femoral cutaneous nerve |
| Posterior sacroiliac joint | No true plane | Gluteus maximus and medius partly detached from origins | Inferior and superior gluteal nerves and vessels, sacral roots from screws |
| Ilioinguinal (acetabulum) | No true plane, external oblique aponeurosis opened | Three windows around iliopsoas and the femoral vessels | Femoral nerve, femoral vessels, corona mortis, inferior epigastric vessels, lateral femoral cutaneous nerve, spermatic cord, bladder |
| Posterior acetabulum (Kocher-Langenbeck) | No true plane, gluteus maximus split well distal to its nerve entry | Short external rotators detached | Sciatic nerve, inferior gluteal artery, superior gluteal nerve and artery |
- The iliac crest is a true internervous plane because muscles attach to it from both sides and none cross it.
- Taking the anterior superior iliac spine with a graft lets the inguinal ligament retract and risks an inguinal hernia.
- Cluneal nerves are posterior rami of L1 to L3. Keeping the posterior crest incision within 8 cm of the posterior superior iliac spine spares them.
- Working only cephalad to a line dropped from the posterior superior iliac spine perpendicular to the table keeps clear of the sciatic notch.
- The superior gluteal artery exits the notch on bone above piriformis and retracts into the pelvis if cut.
- Breaching the thick bone of the sciatic notch weakens the pelvic ring. Graft from the false pelvis above it does not.
- L4 and L5 roots and the lumbosacral trunk cross the sacral ala about 1.5 cm medial to the sacroiliac joint. They mark the medial limit.
- Usually only one screw fits safely in the sacral side of an anterior sacroiliac plate.
- Lateral window. Lateral to iliopsoas, exposes the internal iliac fossa back to the anterior sacroiliac joint.
- Middle window. Between iliopsoas and the femoral vessels, exposes the quadrilateral plate.
- Medial window. Medial to the femoral vessels, exposes the superior pubic ramus and symphysis.
- The femoral vessels are mobilised inside their sheath as one bundle, which lowers the chance of thrombosis.
- Hip flexion slackens iliopsoas and the femoral nerve, so both retract with less stretch.
- Corona mortis joins obturator vessels to the inferior epigastric or external iliac vessels. It is found and tied in the medial window.
- The inferior epigastric artery crosses medial to the deep inguinal ring and is ligated in the ilioinguinal approach.
- In the Kocher-Langenbeck approach the knee stays flexed so traction does not stretch the sciatic nerve.
- A bifid sciatic nerve, or one piercing piriformis, needs the piriformis tendon cut before a trochanteric flip.
- The superior gluteal neurovascular bundle tethers gluteus medius and is at risk between gluteus minimus and piriformis.
- The book describes no Stoppa (anterior intrapelvic) approach.
Hand
| Approach | Superficial plane | Deep plane | Structures at risk |
|---|
| Carpal tunnel (volar) | No internervous plane, anatomic dissection | Flexor retinaculum divided on the ulnar side of the median nerve | Palmar cutaneous branch of median nerve, recurrent motor branch, superficial palmar arch |
| Ulnar nerve at the wrist (Guyon canal) | No internervous plane | Fascia radial to flexor carpi ulnaris, then volar carpal ligament | Ulnar nerve and artery at both of those incisions |
| Volar zigzag (Bruner) to flexor tendons | No true plane, skin supplied from both sides | Fibrous flexor sheath | Digital nerves and arteries if flaps raised too far dorsally, flap tip necrosis |
| Midlateral finger | Line between dorsal and volar digital nerve territories | Behind the neurovascular bundle to the sheath | Palmar digital nerve and artery if the incision drifts volar |
| Volar scaphoid | No true plane, only flexor carpi radialis (median) moved | Between flexor carpi radialis and radial artery proximally | Radial artery, superficial palmar branch of radial artery |
| Dorsolateral scaphoid | No true plane, extensor pollicis longus and brevis share the posterior interosseous nerve | Capsule opened in the snuffbox | Superficial radial nerve over extensor pollicis longus, dorsal carpal branch of radial artery to proximal pole |
| Dorsal phalanges and interphalangeal joints | No true plane | Skin and subcutaneous flap raised as one layer | Flap necrosis if undermined |
- The palmar cutaneous branch of the median nerve leaves about 5 cm above the wrist on the ulnar side of flexor carpi radialis.
- Angling the carpal tunnel incision toward the ulnar side protects the palmar cutaneous branch.
- The thenar motor branch varies in origin. Dividing the retinaculum ulnar to the median nerve keeps away from it.
- The superficial palmar arch lies level with the distal edge of the fully abducted thumb. Blind distal cutting endangers it.
- In the finger the digital artery lies dorsal to the digital nerve.
- Midlateral incisions start just dorsal to the dorsal ends of the interphalangeal creases.
- In the palm the digital nerves lie just deep to the palmar aponeurosis, so it is split along its fibres.
- The superficial palmar branch of the radial artery crosses the volar scaphoid field and is tied to prevent haematoma.
- The dorsal carpal branch of the radial artery supplies the proximal scaphoid pole and is preserved when opening the dorsal capsule.
- An infected hand is splinted with metacarpophalangeal joints at 80 degrees and interphalangeal joints at 10 degrees of flexion.
- That position holds the collateral ligaments at full length so they do not contract.
- Transverse web space incisions risk both digital nerves. Longitudinal ones spare the nerves but can scar the web.
- The book gives no separate extensor tendon approach beyond the dorsal wrist and dorsal phalangeal exposures.
Foot
| Approach | Superficial plane | Deep plane | Structures at risk |
|---|
| Posterolateral ankle | Peroneus brevis (superficial peroneal) and flexor hallucis longus (tibial) | Deep to flexor hallucis longus onto the posterior tibia and fibula | Sural nerve with short saphenous vein |
| Anterolateral ankle and hindfoot | Peroneal muscles (superficial peroneal) and long extensors (deep peroneal) | Same interval carried down to bone | Deep peroneal nerve and anterior tibial artery, superficial peroneal nerve branches |
| Lateral hindfoot | Peroneus tertius (deep peroneal) and peroneal tendons (superficial peroneal) | Same interval carried down to the hindfoot joints | Skin flap necrosis, sural nerve |
| Lateral subtalar (posterior talocalcaneal) | No true plane, peroneal tendons share the superficial peroneal nerve | Peroneal tendons retracted forward | Sural nerve |
| Lateral calcaneus (extensile) | No plane, subcutaneous bone | Full thickness flap raised on bone | Sural nerve if flap extends too far proximally, wound breakdown |
| Dorsal midfoot | No plane, longitudinal incisions | Directly to bone | Cutaneous nerves, insertions of the invertors and evertors |
| Dorsomedial first metatarsophalangeal joint | No true plane | Capsule | Extensor hallucis longus, dorsal digital nerve, flexor hallucis longus under proximal phalanx |
| First web space (lateral release) | No plane, adductor hallucis supplied proximally | Through the web to the lateral sesamoid | Terminal deep peroneal nerve branches, digital nerve under the transverse metatarsal ligament |
- The sural nerve and short saphenous vein are kept together as a unit to avoid painful neuroma.
- Sural nerve injury leaves numbness on the lateral border of the foot where the shoe rubs.
- Calcaneal skin takes its blood supply from below, so the lateral flap is raised full thickness on bone.
- Surgery on the calcaneus waits for swelling to settle to reduce wound breakdown.
- Superficial peroneal nerve branches run just under the skin over the front of the ankle.
- In the anterolateral approach dissection stays on bone to protect the deep peroneal nerve and anterior tibial artery.
- In bunions extensor hallucis longus bowstrings lateral to the joint and flexor hallucis longus is displaced laterally.
- Flexor hallucis longus sits in a groove under the proximal phalanx and is cut by careless subperiosteal stripping.
- At the lesser metatarsophalangeal joints the plantar nerves and vessels lie below the deep transverse metatarsal ligament.
- Cutting both digital arteries to one toe, through two adjacent web spaces, can leave the toe ischaemic.
Safe Zones for External Fixation
| Bone and level | Safe pin route | Structure at risk |
|---|
| Humerus proximal third | Lateral half pins | Axillary nerve 5 to 7 cm below the acromion, brachial artery and median nerve beyond the medial cortex |
| Humerus middle third | Anterior half pins | Radial nerve behind the bone, radial nerve at the lateral septum about two thirds down the arm |
| Humerus distal third | Lateral to medial at the elbow | Ulnar nerve behind the medial epicondyle |
| Ulna whole length | Subcutaneous border | Ulnar nerve near the elbow |
| Radius proximal third | Avoided unless open | Posterior interosseous nerve |
| Radius middle third | Dorsal half pins, mini open | Superficial radial nerve, radial artery |
| Radius distal third and wrist | Lateral half pins through small open incisions, second metacarpal dorsally | Superficial radial nerve, radial artery anterior to pins, extensor tendons and interossei |
| Pelvis, iliac crest | Just behind the anterior superior iliac spine between the two tables | Lateral femoral cutaneous nerve |
| Pelvis, supra-acetabular | Anterior inferior iliac spine between sartorius and tensor fasciae latae, at least 2 cm above the joint | Hip capsule, lateral femoral cutaneous nerve |
| Femur whole length | Lateral half pins | Profunda femoris proximally, femoral artery medially in the middle third, knee synovium distally |
| Fibula proximal third | Avoided | Common peroneal nerve at the fibular neck |
| Tibia whole length | Anteromedial subcutaneous surface | Posterior tibial artery and tibial nerve if the far cortex is overpenetrated |
| Hindfoot and forefoot | Calcaneal transfixion pin medial to lateral, first metatarsal half pin | Posterior tibial bundle behind the medial malleolus, tibialis anterior tendon |
- Half pins stop just past the far cortex. Transfixion pins and wires cross the whole limb and tether soft tissue on both sides.
- Stiffness rises with more pins, wider pin spread, larger pins, more bars and bars closer to the skin.
- Tight skin around a pin leads to low grade infection and loosening, so pin incisions are generous.
- The humerus is the hardest bone to pin safely because its neurovascular bundles hug the bone.
- Lateral pins in the distal humerus near the septum share the danger of lateral to medial nail locking bolts.
- Forearm fractures rotate, so the posterior interosseous nerve position near the radial neck cannot be predicted.
- Distal radial pins go in at about 45 degrees to the frontal and sagittal planes.
- Iliac crest pins enter through the outer cortex only and are pushed by hand to find the path between the tables.
- Supra-acetabular pins hold better than iliac crest pins but are harder to place.
- Lateral femoral pins tether fascia lata and vastus lateralis, which stiffens the knee.
- Distal femoral transfixion pins can enter the knee and risk septic arthritis.
- The tibia is triangular, so the middle of its subcutaneous surface lies in front of both neurovascular bundles.
- The calcaneal pin goes in from the medial side, posterior and distal to the neurovascular bundle.
Source. Hoppenfeld S, deBoer P, Buckley R. Surgical Exposures in Orthopaedics. The Anatomic Approach. 5th ed. Philadelphia, Wolters Kluwer, 2017. Chapters 5, 7, 12 and 13.
Positioning Hazards
- Prone spine. Longitudinal bolsters leave the abdomen free so epidural veins drain to the vena cava and bleed less.
- Prone spine. Shoulders no more than 90 degrees abducted and slightly forward flexed to relax the brachial plexus.
- Prone spine. Pad ulnar nerve at the elbow and median nerve at the wrist.
- Prone spine. No pressure on the eyes and head not below the body, to lower postoperative visual loss risk.
- Lateral hip. Pad bony prominences, as elderly skin breaks down easily.
- Supine lateral hip. Greater trochanter at the table edge lets buttock fat fall away from the incision.
- Lateral malleolus. A sandbag under the buttock rotates the limb medially and brings the fibula forward.
- Henry forearm. Partial exsanguination leaves blood in vessels so they are easier to see.
- Anterior cervical. A roll between the scapulae extends the neck and the head turns away from the incision.
More on approach extensions
- Anterior hip approach extends distally between vastus lateralis and rectus femoris onto the anterior femur.
- Deltopectoral approach extends proximally by releasing deltoid from the anterior clavicle.
- Anterior humeral approach extends proximally into the deltopectoral interval and distally into the Henry forearm interval.
- Henry approach can expose the whole length of the radius.
- Posterior humeral approach can be combined with an olecranon osteotomy for distal humeral fractures.
Numbers to Remember
- Musculocutaneous nerve. Enters coracobrachialis 5 to 8 cm below the coracoid.
- Axillary nerve. 5 to 7 cm below the acromion tip on the deep surface of deltoid.
- Superior gluteal nerve. 3 to 5 cm above the tip of the greater trochanter.
- Lateral femoral cutaneous nerve. Crosses sartorius about 2.5 cm below the anterior superior iliac spine.
- Posterior interosseous nerve. Touches dorsal radial neck in about 25 percent.
- Acetabular retractor. 1 o clock right hip, 11 o clock left hip.
Memory Aids
- Pronate for Kocher, supinate for Henry. Pronation moves the nerve away posterolaterally. Supination exposes supinator anteriorly.
- Split below, not across. Deltoid, gluteus medius and vastus lateralis splits are safe only within their nerve distance limits.
- Smith-Petersen two layers. Femoral nerve medial (sartorius, rectus). Superior gluteal nerve lateral (tensor, medius).
Exam Traps
- Posterior retraction of deltoid does not endanger the axillary nerve. Lateral retractors around the humerus do.
- Brachialis has dual supply, so its midline split is an internervous plane.
- Thompson approach has no true internervous plane because both bordering muscles take the posterior interosseous nerve.
- Anterolateral (Watson-Jones) hip has no internervous plane since tensor fasciae latae and gluteus medius share one nerve.
- The femoral nerve, not the artery, is the most lateral structure in the femoral triangle.
- Platysma is supplied by the facial nerve, not a cervical root.
- Peroneus tertius takes the deep peroneal nerve. Peroneus brevis takes the superficial peroneal nerve.
Source
Hoppenfeld S, deBoer P, Buckley R. Surgical Exposures in Orthopaedics. The Anatomic Approach. 5th ed. Philadelphia, Wolters Kluwer, 2017.
Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 17 October 2026.
