Kaplan Approach to the Elbow (Lateral, EDC–ECRB Interval)

The Kaplan approach is the workhorse lateral approach to the elbow for radial head and capitellar pathology. It utilises the interval between extensor digitorum communis (EDC) and extensor carpi radialis brevis (ECRB), both supplied by the posterior interosseous nerve, creating a true internervous plane. The key danger structure is the posterior interosseous nerve (PIN) within the supinator muscle belly. The critical protective manoeuvre is full forearm pronation, which displaces the PIN distally and medially away from the operative field. This approach is distinct from the more posterior Kocher approach (ECU–anconeus interval), which is safer for the PIN but provides less anterior exposure. The Kaplan approach is indicated for radial head ORIF or replacement, capitellar fixation, lateral column plating, and combined lateral and anterior elbow pathology. Extensile options proximally allow access to the capitellum and lateral supracondylar ridge; distal extension reaches the radial neck and proximal forearm. The lateral collateral ligament must be protected or repaired to prevent posterolateral rotatory instability.

Primary Indications:

• Radial head fractures requiring ORIF or replacement (Mason II-IV)
• Capitellar fractures (coronal shear, Type I and II)
• Lateral column fractures and comminution requiring plating
• Combined radial head and capitellar pathology
• Elbow arthroscopy portal placement planning
• Revision surgery for malunited radial head fractures

Why This Approach is Chosen: The Kaplan approach provides direct access to the radial head, capitellum and lateral column through an internervous plane. It is more anterior than the Kocher approach and therefore gives superior visualisation of the anterior half of the radial head and the capitellum. Full pronation protects the PIN, making the approach safe when performed correctly.

Contraindications:

• Active infection over the lateral elbow
• Severe soft tissue compromise laterally (consider staged or alternative approach)
• Isolated medial pathology (use medial approach)
• When Kocher approach is preferred for posterior pathology with lower PIN risk

Alternative Approaches:

• Kocher approach (ECU–anconeus): Safer for PIN, more posterior exposure, useful when radial head access is secondary
• Posterior (Bryan-Morrey or TRAP): For olecranon and distal humerus
• Medial (Hotchkiss): For medial column and coronoid
• Anterior (Henry): For anterior elbow and neurovascular structures

Bony Anatomy: The lateral elbow comprises the lateral epicondyle, capitellum, radial head and radial neck. The capitellum is the anterior portion of the lateral condyle and articulates with the radial head. The radial head is cylindrical and rotates within the annular ligament. The lateral column of the distal humerus extends from the lateral epicondyle proximally along the supracondylar ridge.

Muscular Layers: The lateral elbow muscles from anterior to posterior are: brachioradialis, extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB), extensor digitorum communis (EDC), extensor carpi ulnaris (ECU) and anconeus. The Kaplan interval is between ECRB and EDC. The Kocher interval is between ECU and anconeus.

Neurovascular Anatomy: The radial nerve divides into superficial radial nerve and posterior interosseous nerve (PIN) approximately 2 cm proximal to the elbow joint. The PIN enters the supinator muscle 3-4 cm distal to the lateral epicondyle. Within the supinator it courses from proximal-lateral to distal-medial. Full pronation moves the nerve distally by approximately 2 cm and medially, protecting it during radial head exposure. The radial recurrent artery and its branches are encountered in the superficial dissection and may require ligation.

Lateral Collateral Ligament Complex: The LCL complex consists of the radial collateral ligament, lateral ulnar collateral ligament (LUCL) and annular ligament. The LUCL is the primary restraint to posterolateral rotatory instability. Its origin on the lateral epicondyle must be preserved or repaired. The annular ligament encircles the radial head and maintains proximal radioulnar joint stability.

Deep Internervous Plane:

• Between: Extensor digitorum communis (posterior interosseous nerve) and extensor carpi radialis brevis (posterior interosseous nerve)
• Clinical relevance: True internervous plane - both muscles are supplied by the same nerve distal to the interval, so no muscle denervation occurs

Superficial Dissection: There is no true internervous plane superficially. The dissection passes through the subcutaneous tissue and fascia overlying the common extensor origin. The interval is identified by the difference in muscle fibre orientation: EDC fibres run more longitudinally, ECRB fibres are more oblique.

Structures at Risk in Each Layer:

Position: Supine with Arm Across Chest or on Hand Table

Pre-positioning Checklist:

• Confirm tourniquet availability (upper arm)
• Arm board or hand table positioned
• C-arm access from medial side or ceiling mount
• Radiolucent table if fluoroscopy needed
• Patient stable for supine positioning

Positioning Details:

• Supine position on radiolucent table
• Arm positioned across the chest or on a hand table with elbow flexed 90 degrees
• Tourniquet applied high on arm (sterile or non-sterile)
• Landmarks marked before incision: lateral epicondyle, radial head, olecranon tip

Alternative Positioning:

• Lateral decubitus with arm supported (less common for this approach)
• Allows combination with posterior approaches if needed

Key Bony Landmarks:

• Lateral epicondyle - palpable prominence on lateral humerus
• Radial head - palpable anterior to lateral epicondyle with forearm rotation
• Olecranon tip - posterior reference point
• Lateral supracondylar ridge - for proximal extension
• Radial neck - palpable distal to radial head

Key Soft Tissue Landmarks:

• Common extensor origin - palpable mass over lateral epicondyle
• Mobile wad - brachioradialis and ECRL anteriorly
• Anconeus - posterior triangle between olecranon and lateral epicondyle

Incision Planning:

• Longitudinal or gently curved incision from lateral epicondyle distally toward radial head and neck
• Length: 6-8 cm for standard radial head exposure
• Extend proximally along lateral supracondylar ridge for capitellar access
• Extend distally along radial border for radial neck exposure

PIN Injury Management:

• If nerve identified as damaged intra-operatively: primary repair if transected
• If neurapraxia suspected: observe, document, follow up closely
• Post-operative finger drop: urgent EMG/NCS at 3 weeks, consider exploration if no recovery by 3 months
• Tendon transfers (flexor carpi radialis to extensor digitorum communis) for permanent deficit

Proximal Extension (Lateral Column Exposure):

• Indication: Capitellar fractures, lateral column plating, distal humerus fractures
• Technique: Extend incision proximally along lateral supracondylar ridge. Elevate common extensor origin and brachioradialis anteriorly. Expose lateral column subperiosteally.
• Risk: Increased risk to radial nerve branches proximally; identify and protect

Distal Extension (Radial Neck and Shaft):

• Indication: Radial neck fractures extending into shaft, combined radial head and forearm pathology
• Technique: Extend incision distally along radial border. Partially release supinator from radius with forearm pronated. Expose radial neck and proximal shaft.
• Risk: PIN remains at risk; maintain pronation and protect nerve

Combined Approaches: For complex elbow fractures involving both medial and lateral columns, combine with medial (Hotchkiss) approach. May require staged positioning or lateral decubitus.

Intra-operative Complications:

Post-operative Complications:

Immediate Post-operative:

• Neurovascular check documenting finger and thumb extension (PIN function) and wrist extension (ECRL)
• Wound inspection
• Posterior splint or hinged elbow brace locked at 90 degrees
• Elevate limb above heart level

Range of Motion Protocol:

• Weeks 0-2: Immobilisation in splint or brace at 90 degrees
• Weeks 2-6: Begin active-assisted ROM, goal 0-120 degrees by 6 weeks
• Weeks 6-12: Progressive strengthening, full ROM
• After 12 weeks: Return to activity as tolerated

Weight Bearing:

• No weight bearing through the arm for 6 weeks if fracture fixation performed
• Early active motion encouraged to prevent stiffness

Follow-up Schedule:

• 2 weeks: Wound check, suture removal
• 6 weeks: Radiographs, assess healing, progress ROM
• 12 weeks: Radiographs, confirm union, full activity
• 6 months: Final clinical and radiographic review

DVT Prophylaxis:

• LMWH or aspirin per institutional protocol for high-risk patients
• Duration: Until mobile (minimum 2 weeks)