Terrible Triad of the Elbow — Pattern (Not Graded)

The `terrible triad` of the elbow is a devastating injury complex characterised by three simultaneous injuries: posterior elbow dislocation, fracture of the radial head, and fracture of the coronoid process. It was named by Hotchkiss in 1996 because of its notoriously poor outcomes with simple closed management — instability, stiffness, and post-traumatic arthritis were the rule rather than the exception when these injuries were treated conservatively. The triad is caused by a fall onto an outstretched hand (FOOSH) with the forearm in supination and the elbow in semi-flexion, generating a posterolateral rotatory mechanism. The key to successful management is understanding the anatomy of elbow stability and reconstructing all injured components in a systematic sequence. Modern surgical management with anatomical fixation has transformed outcomes.

• The three-injury combination: (1) Posterior elbow dislocation — the ulna dislocates posterolaterally relative to the distal humerus (the most common elbow dislocation direction in adults — posterolateral rotatory instability mechanism); (2) Radial head fracture — the radial head fractures as it impacts the capitellum during the dislocation; classified by the Mason classification (Type I — undisplaced; Type II — partial articular displaced; Type III — comminuted; Type IV — with dislocation); (3) Coronoid fracture — the coronoid process of the ulna is avulsed or sheared off during the dislocation; classified by the Regan-Morrey classification (Type I — tip; Type II — <50% height; Type III — >50% height) or the O`Driscoll classification (by coronoid facet and tip/anteromedial/basal subtypes)
• Epidemiology: peak incidence in adults aged 30–60 years; bimodal distribution; young adults from high-energy trauma (sports, falls); older adults from low-energy FOOSH (osteoporotic); it is important to distinguish from simple elbow dislocation (no associated fractures) and from the transolecranon fracture-dislocation (a distinct pattern with anterior dislocation)

• Morrey`s concentric circle model (Hotchkiss 1996): elbow stability is provided by concentric rings of soft tissue and bony stabilisers from the outer ring inward: Outer ring — the lateral collateral ligament complex (LCL — specifically the lateral ulnar collateral ligament, LUCL) and the medial collateral ligament (MCL — anterior band is the primary medial stabiliser); these are the first structures to fail in elbow dislocation; Middle ring — the anterior joint capsule and other capsular structures; Inner ring — the bony constraints: the coronoid process (most important bony stabiliser against posterior translation — even a small coronoid fracture removing >10% of the coronoid height destabilises the elbow); the radial head (acts as a secondary stabiliser for the lateral column and also stabilises the forearm in axial loading — particularly when the MCL is injured); the olecranon (stabilises the posterior aspect); the distal humerus articular surface (trochlea and capitellum)
• The O`Driscoll sequential injury pattern: terrible triad occurs through a predictable sequence of soft tissue and bony failures; Stage 1 = LUCL ruptures (the first structure to fail in posterolateral rotatory instability — PLRI); Stage 2 = anterior and posterior capsule ruptures; Stage 3A = MCL ruptures without bone injury; Stage 3B = MCL rupture + coronoid fracture + radial head fracture = the terrible triad; the sequence explains why all three components must be assessed and repaired to restore stability
• The coronoid is the keystone: the coronoid process of the ulna is the single most important bony stabiliser of the elbow; it resists posterior translation of the ulna relative to the humerus; a Type III coronoid fracture (involving >50% of the coronoid height) creates profound instability that is very difficult to reconstruct; even a small Type I coronoid tip fracture in the context of the terrible triad must be fixed (the capsule and ligaments attached to the coronoid tip are critical for stability); the coronoid is described as having a `tip` and an `anteromedial facet` — anteromedial facet fractures are a distinct and underappreciated cause of rotatory instability

• Plain X-ray: AP and lateral elbow X-rays; the dislocation and both fractures should be identifiable; on the lateral view: the radial head is displaced posteriorly; the coronoid fracture tip may be visible as a small fragment anteriorly (the `teardrop fragment`); the distal humerus alignment is disrupted; post-reduction X-rays are essential to confirm concentric reduction and to re-assess fracture displacement; always check the radiocapitellar line to confirm radial head reduction after dislocation reduction
• CT scan: mandatory for all terrible triad injuries; CT characterises: (1) the exact morphology of the coronoid fracture (O`Driscoll subtype — is it a pure tip fracture, or does it involve the anteromedial facet?); (2) the radial head fracture pattern (Mason classification — is fixation possible or is replacement required?); (3) associated injuries (olecranon fracture, distal humerus fracture); (4) the extent of ligamentous avulsion bony fragments; (5) presence of intra-articular loose bodies; 3D CT reconstruction is particularly helpful for surgical planning

Surgical management of the terrible triad follows a systematic sequence — repairing structures in a specific order ensures that stability is tested at each stage and that the correct amount of reconstruction is performed. The principle is `repair from the inside out` — beginning with the deepest, most critical stabilisers and progressing to the superficial.

• Elbow stiffness: the most common complication even after anatomical repair; the elbow is intrinsically prone to post-traumatic stiffness due to its tight capsule; early motion (within 2 weeks of surgery) is the most important factor in preventing stiffness; the goal is to begin active-assisted ROM within 1–2 weeks; contracture release (open or arthroscopic) may be required at 6–12 months if a significant flexion contracture persists (>30° of lost motion that is functionally limiting)
• Recurrent instability: if repair is inadequate or if the elbow is mobilised too early, recurrent dislocation or subluxation may occur; the most vulnerable position is extension + supination (the PLRI position); rehabilitation braces that block the last 30° of extension are used in the first 4–6 weeks
• Post-traumatic osteoarthritis: the combined bony and soft tissue injury creates a high-risk environment for cartilage damage and progressive OA; most patients develop some degree of OA over 10–20 years; total elbow arthroplasty (TEA) is the ultimate salvage for end-stage OA
• Heterotopic ossification (HO): peri-elbow HO is common after elbow dislocation with associated fractures; prophylaxis with indomethacin or single-fraction radiotherapy is used in high-risk cases (delayed surgery, repeat manipulation, associated head injury); established HO is excised at 12–18 months (once the bone scan shows quiescent activity)

• Terrible triad: 3 injuries = posterior elbow dislocation + radial head fracture + coronoid fracture; FOOSH with supination + semi-flexion; posterolateral rotatory mechanism (Hotchkiss 1996)
• Concentric circle stability model: outer = MCL/LCL (LUCL is the critical lateral ligament); middle = capsule; inner = coronoid (most important bony stabiliser) + radial head (lateral column) + olecranon; ALL must be assessed and repaired
• Coronoid classification: Regan-Morrey (Type I tip, Type II <50%, Type III >50%); O`Driscoll (adds anteromedial facet subtype); even Type I tip must be repaired in terrible triad (anterior capsule attachment = critical); Type III = profound instability
• Radial head: NEVER excise without replacement in terrible triad (elbow will collapse medially without radial head support in MCL-deficient elbow); Mason III → radial head arthroplasty; Mason II → ORIF in `safe zone` (posterolateral 90° arc)
• Surgical sequence: coronoid (Step 1 — most important) → radial head (Step 2) → LUCL repair (Step 3) → MCL if still unstable (Step 4) → hinged ex-fix if still unstable (Step 5); `inside-out` repair sequence
• LUCL: lateral ulnar collateral ligament; primary constraint vs PLRI; avulsed from lateral epicondyle; repaired with suture anchor to lateral epicondyle in pronation; reconstruction with graft if tissue inadequate
• Hinged external fixator: last resort; maintains concentric reduction while allowing early motion; axis of rotation centred on the elbow axis (co-axial with the trochleo-capitellum); removed at 6–8 weeks; prevents recurrent dislocation during healing
• CT mandatory: characterises coronoid subtype (especially anteromedial facet — missed on plain X-ray); radial head fixability; loose bodies; surgical plan; 3D reconstruction for complex cases