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

What it exposes. The Kaplan approach gives direct lateral access to the radial head, the capitellum and the lateral column of the distal humerus through a true internervous plane. It is the workhorse exposure for radial head ORIF and replacement, capitellar fixation and lateral column plating. Why this approach. The Kaplan interval is more anterior than the Kocher approach, so it gives superior visualisation of the anterior half of the radial head and of the capitellum. Because both muscles of the interval are supplied by the posterior interosseous nerve distal to the plane, dissection here denervates neither muscle. Full pronation protects the PIN, making the approach safe when the technique is respected. Radial head fractures account for about 33 percent of all elbow fractures, and anatomic reduction of the capitellar articular surface demands the anterior exposure this approach provides. 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 Contraindications and cautions: - Active infection over the lateral elbow
• Severe soft tissue compromise laterally (consider staged or alternative approach)
• Isolated medial pathology (use a medial approach)
• When posterior pathology is primary and a lower-PIN-risk Kocher exposure suffices Kaplan versus the alternatives. The Kaplan interval is the high-yield exam distinction — know how it differs from Kocher and when each lateral/medial route is preferred.

Position and landmarks. Supine on a radiolucent table, the arm across the chest or on a hand table with the elbow flexed 90 degrees. A high upper-arm tourniquet is applied; C-arm access is from the medial side or a ceiling mount. Before incision, mark the lateral epicondyle, the radial head (palpated anterior to the epicondyle during forearm rotation), the olecranon tip and the lateral supracondylar ridge (the line of proximal extension). The common extensor origin and the mobile wad (brachioradialis and ECRL) are the key soft-tissue landmarks. A standard radial-head exposure uses a 6–8 cm longitudinal or gently curved incision from the lateral epicondyle distally toward the radial neck.

Work down through the layers on the lateral side, developing the EDC–ECRB interval, pronating to protect the PIN, and entering the joint anterior to the lateral collateral ligament.

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Structures at risk, by layer

Post-operative complications

PIN injury — recognition and management. PIN injury in lateral elbow approaches ranges from 2 to 10 percent depending on technique and fracture complexity; the Kaplan interval carries a higher theoretical risk than Kocher because it is more anterior, but with proper pronation the risk is comparable. Most injuries are neurapraxia recovering within 3–6 months; permanent finger drop occurs in less than 1 percent. Intra-operatively, a transected nerve is primarily repaired. Post-operative finger drop is worked up with EMG/NCS at 3 weeks (allowing Wallerian degeneration to declare axonal injury); if there is no clinical or EMG recovery by 3 months, explore the nerve. A permanent deficit is managed with tendon transfers (flexor carpi radialis to extensor digitorum communis, palmaris longus to EPL). Always exclude a correctable cause first — tight dressing or compartment syndrome. Extensile options. Extend proximally along the lateral supracondylar ridge, elevating the common extensor origin and brachioradialis anteriorly, to expose the capitellum and lateral column for capitellar fractures and lateral column plating (watch for radial nerve branches proximally). Extend distally along the radial border, partially releasing the supinator from the radius with the forearm pronated, to reach the radial neck and proximal shaft (the PIN remains at risk — maintain pronation). For complex bicondylar injuries, the Kaplan approach can be combined with a medial (Hotchkiss) approach, sometimes requiring lateral decubitus or staged positioning. Closure and aftercare. Copious irrigation and meticulous haemostasis of the radial recurrent branches. Repair the annular ligament and LCL (if divided) with absorbable and transosseous/anchor fixation respectively; close the fascia over the common extensors loosely and approximate skin over a posterior splint or hinged brace locked at 90 degrees. Rehabilitation: immobilise at 90 degrees for 0–2 weeks, begin active-assisted ROM aiming for 0–120 degrees by 6 weeks, progressive strengthening 6–12 weeks, and return to activity after 12 weeks; no weight bearing through the arm for 6 weeks after fracture fixation. Follow up radiographs at 2, 6 and 12 weeks, with a final review at 6 months.

• Radial head ORIF — the principal operation: reduce split fragments with pointed clamps, provisional K-wires, then 1.5 mm or 2.0 mm countersunk or headless screws; a buttress or locking radial head plate for comminution. Check forearm rotation under direct vision and fluoroscopy to ensure no mechanical block.
• Radial head replacement — for comminuted Mason III/IV fractures not amenable to fixation: measure diameter and height accurately, insert with the forearm pronated, and repair the annular ligament around the prosthetic neck.
• Capitellar fixation — reduce the coronal shear fragment anatomically and fix with headless compression screws inserted anterior-to-posterior, countersunk beneath the articular surface; add a lateral column plate for lateral column comminution.
• Lateral column plating — via the proximal extension along the supracondylar ridge for distal humerus fractures involving the lateral column.
• Elbow arthroscopy portal placement planning and exposure for combined radial head and capitellar pathology.