TRAP (Triceps-Reflecting Anconeus Pedicle) Approach to the Elbow

What it exposes. The TRAP (Triceps-Reflecting Anconeus Pedicle) approach, described by O'Driscoll (Mayo Clinic), gives direct posterior access to both columns of the distal humerus, the olecranon fossa and the articular block. It is the workhorse extensile exposure for intra-articular bicolumnar distal humeral fractures, distal humeral non-union and mal-union reconstruction, and selected complex and revision total elbow arthroplasty. Why this approach exists. Bicolumnar distal humeral fractures (AO/OTA 13C, including low T and Y patterns) require access to both the medial and lateral columns and to the articular surface through the olecranon fossa. The classic answer, an olecranon osteotomy, buys that exposure at the cost of an osteotomy that may fail to unite and hardware that is often symptomatic. The TRAP delivers comparable bilateral exposure by mobilising the triceps together with the anconeus as a single distally-based pedicle, leaving the extensor mechanism attached to the olecranon throughout. Because the anconeus blood supply is preserved, the reflected sleeve remains viable and heals back reliably, and because the triceps is never detached, triceps insufficiency is uncommon and closure needs no tendon-to-bone repair. Primary indications. - Intra-articular bicolumnar distal humeral fractures (AO/OTA 13C, including low T and Y patterns) where both columns must be visualised and fixed

• Distal humeral non-union and mal-union requiring extensile take-down, decompression and reconstruction
• Complex and revision total elbow arthroplasty where wide posterior exposure of both columns is needed
• Stiff or ankylosed elbow requiring an extensile posterior release when the extensor mechanism must be preserved
• Selected reconstruction after tumour resection or post-traumatic deformity of the distal humerus Contraindications and relative limitations. - Compromised posterior soft tissues or open wounds over the planned incision
• Active sepsis around the elbow
• A fracture pattern whose articular comminution is so severe that an olecranon osteotomy is genuinely required for visualisation (a relative, surgeon-judgement decision)
• A need for continuous intra-operative elbow flexion and extension to assess the prosthesis, for which a Bryan-Morrey triceps-sparing approach may be preferable Alternative posterior approaches. The TRAP is one of five principal posterior exposures, and choosing among them is driven by the fracture pattern and the planned procedure rather than by geography.

Position and landmarks. The classic position is lateral decubitus with the affected side uppermost, the arm supported over a padded bolster and draped free so the elbow can be flexed, extended and rotated to reach both columns through a single incision. Prone gives equivalent access; supine with the arm across the chest is possible but less convenient for bilateral column work. Pad all pressure points (dependent arm, shoulder, greater trochanter, lateral malleolus), place an axillary roll to protect the brachial plexus, apply a proximal-arm tourniquet if a bloodless field is desired, and confirm image-intensifier access from the opposite side. The key landmarks are the olecranon (central prominence at the apex of the incision), the medial epicondyle (medial column; ulnar nerve behind it), the lateral epicondyle (lateral column; extensor-supinator origin), and the small triangular anconeus just distal-lateral to the olecranon — the keystone of the pedicle. The incision is a posterior midline cut curved around the olecranon tip, slightly onto the lateral side, long enough to expose both epicondyles and the proximal ulna, avoiding a scar directly over the tender olecranon tip and bursa.

The TRAP does not exploit one classical internervous plane. It uses two intervals and then elevates the triceps off bone, raising the entire triceps-anconeus sleeve as one continuous pedicle attached distally at the olecranon. Work from the ulnar nerve on the medial side and the Kocher interval on the lateral side, then unify the two into the distally-based pedicle.

Anatomy underpinning the exposure

Bony anatomy. The distal humerus is conceptualised as two columns (medial and lateral) linked by a tie-arch that carries the trochlea centrally and the capitellum laterally, with the olecranon fossa posteriorly and the coronoid fossa anteriorly. The medial column is shorter and ends more distally than the lateral column. The olecranon fossa is the key posterior landmark: clearing it of tissue is what restores extension and exposes the articular block. Muscular layers. | Layer | Muscle | Nerve Supply | Role in the Approach | |-------|--------|--------------|----------------------| | Posterior arm | Triceps (all heads) | Radial nerve | Elevated off the humerus as the dominant component of the pedicle | | Posterior forearm (proximal) | Anconeus | Radial nerve | Mobilised with the triceps; the keystone of the distally-based pedicle | | Lateral forearm | Extensor carpi ulnaris | Radial nerve (posterior interosseous) | The lateral boundary of the Kocher interval | | Medial forearm | Flexor carpi ulnaris | Ulnar nerve | Medial boundary; the ulnar nerve runs between its two heads | Neurovascular anatomy. | Structure | Course | Clinical Significance | |-----------|--------|----------------------| | Ulnar nerve | Posterior to the medial epicondyle, through the cubital tunnel, between the heads of FCU | Most important danger structure — must be identified and protected | | Radial nerve | Spiral groove posteriorly, pierces the lateral intermuscular septum roughly 10 cm proximal to the lateral epicondyle | At risk with proximal extension onto the lateral column | | Posterior antebrachial cutaneous nerve | Subcutaneous, crosses the lateral elbow | Skin-flap neuroma risk | | Medial antebrachial cutaneous nerve | Subcutaneous on the medial side | Skin-flap neuroma risk; nerve to the olecranon area | | Anconeus vascular pedicle | Branches of profunda brachii (middle collateral artery) and the interosseous recurrent artery | Preserved — keeps the reflected pedicle viable |

Structures at risk, by layer.

Extensile options. The dissection can be extended proximally along the posterior humeral shaft for more diaphyseal exposure — the limit is the radial nerve, which crosses the spiral groove posteriorly and pierces the lateral intermuscular septum roughly 10 cm proximal to the lateral epicondyle; stay strictly subperiosteal, and if a long proximal extension is needed, identify and protect the radial nerve. Exposure continues distally onto the proximal ulna, but because the anconeus remains attached to the pedicle, extensive distal extension onto the ulna is limited unless the anconeus is further mobilised — the approach is therefore principally a distal-humeral and elbow exposure rather than a forearm exposure. Closure. Because the triceps remained attached to the olecranon throughout, there is no tendon-to-bone repair of the extensor mechanism. The elevated triceps is returned to its anatomic position and reapproximated to the posterior humeral periosteum and the fascial sleeve; the Kocher interval (anconeus to extensor carpi ulnaris) is repaired and the medial fascia is reconstituted. Decide on the ulnar nerve: leave it in situ in a well-decompressed tunnel, or transpose it anteriorly (subcutaneous) if it was transposed, if it is unstable, or if hardware lies directly beneath it. Place a drain, close the subcutaneous layer and skin, and apply a well-padded splint with the elbow in extension or slight flexion. Preserved extensor-mechanism continuity means a lower risk of postoperative triceps insufficiency than approaches that detach the triceps, and reliable healing because the anconeus pedicle keeps the reflected tissue vascularised.

• ORIF of bicolumnar distal humeral fractures — the principal operation done through this exposure: dual column plating (orthogonal or parallel), with direct articular reduction through the fossa.
• Non-union and mal-union reconstruction — take-down, bone graft and revision fixation.
• Complex and revision total elbow arthroplasty — wide posterior exposure with the extensor mechanism preserved.
• Release of a stiff or ankylosed elbow — capsulectomy with the pedicle reflected.
• Selected tumour and reconstruction surgery of the distal humerus.

The TRAP (Triceps-Reflecting Anconeus Pedicle) approach, described by O'Driscoll, is a posterior extensile exposure of the distal humerus and elbow. Through a posterior midline incision curved around the olecranon, the surgeon identifies and protects the ulnar nerve (the single most important danger structure), then develops the lateral Kocher interval (between the anconeus and the extensor carpi ulnaris) and the medial interval (between the triceps and the medial intermuscular septum). The triceps and anconeus are then elevated together as a single, distally-based pedicle that stays attached to the olecranon, exposing both columns and the olecranon fossa without an olecranon osteotomy. The anconeus blood supply (branches of the profunda brachii, principally the middle collateral artery, and the interosseous recurrent artery) is preserved, keeping the reflected extensor mechanism viable. Because the triceps is never detached from the olecranon, closure requires no tendon-to-bone repair, and triceps insufficiency is uncommon.

Guidelines, Registries & Global Practice

Surgical approaches to the distal humerus are taught to a convergent standard across the examination systems. The choice among the posterior approaches (olecranon osteotomy, triceps-splitting, Bryan-Morrey, paratricipital and TRAP) is driven by fracture pattern, the planned procedure and surgeon preference, not by geography. Side-by-side principles (where guidance converges): | Body | Position on distal humerus exposure | |------|-------------------------------------| | AO Foundation | Anatomic articular reconstruction and stable column fixation are the goals; the approach must provide sufficient exposure to achieve both, and the extensor mechanism should be respected | | BOA / BOAST | Soft-tissue-friendly surgery, staged management where the soft envelope is compromised, and dual-column fixation for bicolumnar injuries | | AAOS / OTA | Both-column visualisation and rigid fixation; olecranon osteotomy remains an option where articular visualisation demands it, with extensor-mechanism-sparing alternatives increasingly favoured | Practical considerations. In high-resource settings, pre-operative CT with three-dimensional reconstruction is standard for planning column-specific fixation, and a full armamentarium of approaches and pre-contoured plates is available. In resource-limited settings the same principles of bilateral column fixation are achieved with the surgeon's preferred extensile approach and available implants; the TRAP is attractive here precisely because it needs no osteotomy-specific fixation hardware. Consent (globally applicable). Discuss ulnar nerve injury (the principal neurological risk of any posterior elbow approach), infection, stiffness and heterotopic ossification, and the possibility of reoperation. No country-specific billing or reimbursement item numbers are relevant.