Comprehensive guide to the Thompson dorsal approach for proximal and mid-shaft radius exposure - surgical anatomy, posterior interosseous nerve protection, and exam preparation
Reviewed by OrthoVellum Editorial Team
Orthopaedic clinicians and medical editors • Published by OrthoVellum Medical Education Team
True Internervous | PIN at Risk | Proximal/Mid-Shaft Exposure
The posterior interosseous nerve (PIN) is at highest risk in this approach (3-11% temporary palsy). PIN enters supinator muscle proximally, spirals around radial neck, and exits at distal supinator border. Protection: (1) Full forearm pronation, (2) Subperiosteal dissection only, (3) Avoid superior dissection beyond radial head.
ECRB (radial nerve) laterally and EDC (posterior interosseous nerve) medially. This is a true internervous plane - splitting between muscles supplied by different terminal branches of the radial nerve. ECRB gets superficial branch, EDC gets deep branch (PIN).
Full pronation is mandatory throughout dissection. Pronation moves the PIN laterally and anteriorly, away from the radius. This creates maximum distance between nerve and operative field. Any supination during dissection dramatically increases nerve injury risk.
The supinator muscle wraps around proximal radius and contains the PIN within its substance. NEVER dissect through supinator - always stay subperiosteal. PIN exits supinator at its distal border (approximately 5cm distal to radial head). Subperiosteal elevation protects the nerve.
| Clinical Scenario | Thompson Approach | Alternative Approach | Key Decision Factors |
|---|---|---|---|
| Proximal radius shaft fracture | Excellent - ideal indication | Volar Henry approach (distal radius only) | Thompson for proximal 2/3, Henry for distal 1/3 |
| Radial head/neck fracture | Good - with PIN precautions | Lateral Kocher approach | Thompson allows better shaft access if needed |
| Distal radius fracture | Not recommended - too distal | Volar Henry approach | PIN risk without benefit at distal radius |
| Combined radius and ulna fractures | Thompson for radius + separate ulna approach | Single-incision approaches | Separate approaches preserve soft tissue attachments |
Memory Hook:THOMPSON approach requires maximal pronation and subperiosteal technique to protect the posterior interosseous nerve
Memory Hook:PIN safety depends on pronation and subperiosteal dissection - never violate the supinator muscle
Memory Hook:RADIAL nerve divides into superficial (sensory) and deep PIN (motor) branches - Thompson works between territories
The Thompson approach (also called the dorsal approach to the radius) is a true internervous approach providing excellent exposure of the proximal and middle thirds of the radius. First described by Thompson in 1918, it remains the gold standard for proximal radial shaft fractures and radial head/neck pathology requiring plate fixation.
Historical development:
Clinical significance:
Why Thompson Not Henry for Proximal Radius
The Thompson (dorsal) approach is preferred over the Henry (volar) approach for proximal radius because: (1) Thompson provides direct posterior access to common fracture displacement direction, (2) Henry approach requires dissection through multiple muscle layers volarly and risks radial artery, (3) Thompson is internervous while Henry splits pronator teres (median nerve territory), (4) Plate placement on dorsal radius is biomechanically superior for most fracture patterns.
Internervous plane:
Anatomical boundaries:
Understanding radial nerve anatomy is critical for safe execution of the Thompson approach.
Radial nerve division:
Posterior interosseous nerve (PIN) course:
| Location | Relationship to Radius | Protection Strategy |
|---|---|---|
| Radial neck (proximal) | Spirals around radial neck from medial to lateral | Avoid superior dissection beyond radial head |
| Within supinator (middle) | Embedded in supinator muscle substance | Subperiosteal dissection only - never through muscle |
| Distal supinator border | Emerges 5cm distal to radial head, lateral to radius | Safe zone - nerve has exited at this level |
Supinator muscle:
Effect of forearm position on PIN:
PIN wrapped tightly around radial neck, closest to bone Minimal distance between nerve and surgical field HIGH RISK position - never dissect in supination
PIN partially relaxed but still close to radius Some distance created but not maximal Suboptimal positioning for dissection
PIN moved laterally and anteriorly, maximum distance from radius Supinator muscle relaxed, nerve protected MANDATORY position for Thompson approach
Surface anatomy and landmarks:
Muscles in the approach:
Extensor carpi radialis brevis (ECRB): Lies lateral (radial) in the approach. Muscle belly visible, tendon runs to base of 3rd metacarpal. Supplied by radial nerve directly (not PIN).
Extensor digitorum communis (EDC): Lies medial (ulnar) in the approach. Muscle belly with four tendons to fingers. Supplied by posterior interosseous nerve.
Critical distinction: Splitting between these muscles creates internervous plane. Never confuse EDC with ECRB - they have different nerve supplies.
Vascular anatomy:
The Thompson approach utilizes a true internervous plane between muscles supplied by different terminal branches of the radial nerve.
The Plane:
Clinical Significance:
This is a true internervous approach because ECRB and EDC receive innervation from different terminal branches of the radial nerve. The radial nerve divides at the level of the lateral epicondyle into:
Why Thompson is True Internervous
The Thompson approach is truly internervous because it works between ECRB (radial nerve territory) and EDC (PIN territory). This differs from approaches that split a single muscle or work between muscles with the same nerve supply. True internervous dissection minimizes denervation and preserves muscle function on both sides of the interval.
Identifying the interval:
The internervous nature of this approach is a key advantage over muscle-splitting or muscle-dividing approaches.
Fractures:
Tumor pathology:
Infection:
Other indications:
The Thompson approach provides excellent access to proximal and mid-shaft radius pathology.
Clinical assessment:
PIN function testing:
Imaging protocol:
AP and lateral forearm views AP and lateral elbow views (assess radial head) AP and lateral wrist views (assess distal radioulnar joint) Assess: fracture location, displacement, comminution, associated injuries
Indications: radial head fractures, proximal radius comminution, malunion 3D reconstruction helpful for surgical planning Assess articular involvement and fragment size
If complex deformity or malunion Template for reconstruction
Surgical planning:
Assessing PIN Function Preoperatively
Complete PIN examination requires testing all muscles supplied: (1) Extensor digitorum - extend all fingers at MCP (patient makes fist then extends), (2) Extensor pollicis longus - extend thumb IP joint against resistance, (3) Extensor indicis proprius - extend index finger independently, (4) Abductor pollicis longus - abduct thumb in plane of palm. Document normal function preoperatively - if post-op deficit occurs, you have baseline for comparison.
Equipment checklist:
Patient position:
Arm positioning:
Tourniquet:
Imaging setup:
Skin preparation:
Proper positioning with maximal forearm pronation is the foundation for safe PIN protection.
Incision planning:
Subcutaneous dissection:
Key landmarks:
Expose deep fascia overlying extensor muscles Fascia appears white and glistening Identify raphe between ECRB and EDC
Palpate interval between ECRB (lateral, firmer) and EDC (medial, softer) Natural cleavage plane exists between muscles Incise fascia in line with muscle fibers
Use blunt dissection (fingers or scissors) to develop interval ECRB retracts laterally, EDC retracts medially Minimal force required if correct plane identified
Finding the Correct Internervous Interval
The ECRB-EDC interval can be identified by: (1) ECRB has a thicker, more prominent muscle belly laterally, (2) EDC is thinner and more tendinous medially with visible multiple tendons, (3) Palpate with finger - a natural groove exists between the muscles, (4) ECRB tendon inserts on base of 3rd metacarpal (palpate distally to confirm), (5) EDC has four tendons to fingers (visible if exposure extended). If uncertain, trace tendons distally to confirm identity.
Correct identification of the ECRB-EDC interval is critical for true internervous dissection.
| Complication | Incidence | Prevention/Management |
|---|---|---|
| PIN palsy (posterior interosseous nerve injury) | 3-11% (usually temporary) | Maximal pronation, subperiosteal dissection, avoid superior extension. Most recover 3-6 months with observation. |
| Superficial radial nerve injury | 2-5% (sensory only) | Protect during superficial dissection, ligate veins carefully. Numbness over dorsal thumb/hand. Usually resolves. |
| Infection (superficial or deep) | 1-3% | Prophylactic antibiotics, sterile technique, hemostasis. Treat with antibiotics or debridement if needed. |
| Heterotopic ossification | 5-10% | Gentle soft tissue handling, ROM exercises early. Excision if limits function after maturation. |
| Nonunion (fracture failure to heal) | 3-5% | Stable fixation, avoid excessive periosteal stripping. Bone graft and revision if occurs. |
| Malunion (angulation or rotation) | 2-5% | Verify reduction intraoperatively with imaging. Corrective osteotomy if symptomatic. |
| Hardware prominence/irritation | 10-15% | Low-profile plates, avoid prominent screw heads. Hardware removal after healing if symptomatic. |
| Radioulnar synostosis | Less than 1% (rare) | Avoid periosteal stripping between radius and ulna. Excision if causes limited rotation. |
Posterior interosseous nerve (PIN) palsy:
PIN palsy prevention strategy:
PIN palsy presents as: (1) Inability to extend fingers at MCP joints (hand droops when wrist extended), (2) Inability to extend thumb at IP joint, (3) PRESERVED wrist extension (ECRL and ECRB are radial nerve, not PIN), (4) No sensory loss (PIN is pure motor). Differential diagnosis: Radial nerve palsy includes wrist drop and dorsal hand numbness. If PIN palsy recognized, document carefully, reassure patient most recover, arrange EMG at 6 weeks, provide night splint to prevent MCP flexion contractures.
Superficial radial nerve injury:
Hardware-related complications:
Sugar-tong splint: elbow 90 degrees, forearm neutral Elevation to reduce swelling Finger and shoulder ROM exercises Wound check at 10-14 days, suture/staple removal Verify PIN function at first visit
Transition to removable forearm splint or brace Begin elbow and forearm ROM exercises (gentle) Active-assisted wrist ROM No lifting, no weight-bearing on affected arm X-rays at 6 weeks to assess healing
Progressive ROM exercises for elbow, forearm, wrist Light strengthening exercises (1-2 kg weights) Proprioception and coordination exercises X-rays at 12 weeks - expect bridging callus
Progressive strengthening to full strength Return to unrestricted activities once healed Consider hardware removal if prominent (after 12 months minimum) Final follow-up at 6 months with X-rays
Early post-operative monitoring:
Splinting protocol:
Return to activities:
Long-term outcomes:
Practice these scenarios to excel in your viva examination
"A 35-year-old male sustains a displaced proximal radial shaft fracture in a fall. X-rays show 50% displacement with dorsal angulation. You are planning Thompson approach for ORIF. What are the key anatomical considerations and how do you protect the posterior interosseous nerve?"
"During a Thompson approach for mid-shaft radius fracture, you find the fracture extends more distally than expected on imaging, into the distal third. The fracture reduction requires plating that would extend beyond your typical Thompson exposure. What are your options and how do you proceed?"
"You performed a Thompson approach for proximal radius fracture ORIF. In recovery, the patient has loss of finger and thumb extension at MCP joints, but wrist extension is preserved. What is your diagnosis, differential, and management plan?"
Internervous Plane Question
Q: What is the internervous plane in the Thompson approach to the radius?
A: The Thompson approach works between extensor carpi radialis brevis (ECRB) and extensor digitorum communis (EDC). ECRB is supplied by the radial nerve (superficial branch), while EDC is supplied by the posterior interosseous nerve (deep branch of radial). This is a true internervous plane.
PIN Anatomy Question
Q: Where does the posterior interosseous nerve exit the supinator muscle?
A: The PIN exits the supinator muscle at its distal border, approximately 5cm distal to the radial head. This represents the safe distal limit of the Thompson approach. Dissection beyond this level risks direct nerve injury.
Forearm Position Question
Q: Why is maximal pronation important during the Thompson approach?
A: Maximal pronation moves the PIN laterally and anteriorly, away from the radius, creating maximum distance between the nerve and the surgical field. This is the single most important maneuver for protecting the PIN during Thompson approach.
PIN Palsy Recognition Question
Q: How do you distinguish PIN palsy from radial nerve palsy clinically?
A: PIN palsy: Loss of finger MCP extension and thumb extension, but PRESERVED wrist extension (ECRL/ECRB intact). Radial nerve palsy: Includes wrist drop (ECRL/ECRB affected) plus finger/thumb extension loss plus sensory loss over dorsal hand. Preserved wrist extension indicates PIN injury distal to radial nerve branching.
Supinator Dissection Question
Q: What is the key technique to avoid PIN injury during Thompson approach?
A: Strict subperiosteal dissection - staying directly on the radius bone and elevating the supinator muscle as a complete mass without dissecting through it. The PIN is contained within the supinator, so subperiosteal elevation protects the nerve. Never dissect through the supinator muscle belly.
Public System Coverage:
Therapeutic Guidelines (eTG) recommendations:
PBS (Pharmaceutical Benefits Scheme):
Australian epidemiology:
Australian Orthopaedic Association (AOA) guidelines:
Workers compensation considerations:
Training and education:
High-Yield Exam Summary