Coronoid & Terrible Triad Injuries
1) Overview
• Coronoid process fractures are frequently associated with elbow instability following trauma, and they are particularly important in fracture–dislocation patterns.
• The coronoid serves as the anterior buttress of the ulnohumeral joint, limiting posterior translation/rotation, and it is one of the principal osseous contributors to elbow stability.
• The terrible triad classically consists of:
Elbow dislocation (most commonly posterior/posterolateral),
Radial head/neck fracture,
Coronoid fracture,
and it is almost always accompanied by injury to the lateral collateral ligament (LCL) complex.
• The central problem after these injuries is the “instability + stiffness” combination: inadequate stability leads to recurrent subluxation/dislocation, whereas early/prolonged immobilization leads to significant loss of motion.
• The core treatment goal is balancing stable reconstruction with early motion.
2) Epidemiology
• Coronoid fractures are relatively uncommon. However, their clinical impact is substantial in elbow fracture–dislocation patterns.
• In adults, elbow dislocations are the second most common major joint dislocation after the shoulder and account for approximately 10–25% of all elbow injuries.
• In complex dislocations (fracture–dislocations), associated lesions are common (radial head, coronoid, etc.), and combinations such as the terrible triad carry a high risk of complications.
3) Etiology – Mechanism
• The most common mechanism is a fall on an outstretched hand (FOOSH) with axial loading across the elbow plus a valgus force and forearm rotation (particularly external rotation).
• In contemporary descriptions, the terrible triad is typically considered a valgus–external rotation injury pattern (posterior dislocation + radial head fracture + a coronoid fracture component—often a tip fracture, though morphology may vary).
• Soft-tissue injury often follows a lateral-to-medial progression: LUCL/LCL complex → capsule → MCL bundles (Horii circle). This trajectory helps explain different instability patterns arising from the same traumatic event.
• The combination of an anteromedial coronoid facet fracture and an LCL tear may indicate the varus posteromedial instability spectrum (it can be clinically confused with terrible triad, but biomechanics and surgical strategy differ).
4) Diagnosis – Physical Examination – Imaging
Clinical evaluation
• In the acute setting, the elbow is typically swollen, deformed, and very painful; the patient cannot actively move it, and the range of motion is markedly limited.
• A neurovascular examination is mandatory for every elbow dislocation/fracture–dislocation (particularly for ulnar nerve symptoms; in delayed cases, compartment risk should be considered).
• Post-reduction stability must be tested; forearm rotation can influence stability depending on the injured collateral side (clinically, pronation may increase stability with LCL insufficiency, and supination may increase stability with MCL insufficiency).
Imaging
• First-line: AP and lateral radiographs; obtain oblique views when an associated fracture is suspected.
• Critical for surgical planning: CT (multiplanar and/or 3D), especially in comminuted coronoid/radial head fractures, to define the fracture pattern.
• MRI may assist with ligament/soft-tissue assessment; in acute complex cases, decision-making is most often based on osseous injury patterns and overall stability.
5) Classifications
Coronoid fractures
• Regan–Morrey (by fragment size):
o Type I: tip fracture
o Type II: partial coronoid height involvement
o Type III: basal/large fragment
(This system is simple and widely used; however, CT often reveals more informative sub-patterns.)
• O’Driscoll (by anatomic location):
o Type I: tip fractures
o Type II: anteromedial facet (critical for VPM instability)
o Type III: basal fractures
Terrible triad
• There is no single “official” classification; in practice, key determinants of treatment are:
o reconstructability of the radial head fracture,
o coronoid fragment type (tip vs AMF vs basal),
o degree of post-reduction instability and associated ligament insufficiency.
6) Treatment
• A stable elbow + early controlled motion: the main surgical objective is to restore enough stability to allow early motion and thereby reduce postoperative stiffness.
A) Nonoperative treatment
• In isolated, minimally displaced coronoid fractures, short immobilization followed by early ROM can be considered if the elbow is stable.
• Especially in isolated tip fractures (small/minimally displaced fragments), nonoperative management may be chosen; however, the decision must be stability-based.
• In simple dislocations, if stability is adequate, early motion after 7–10 days in a posterior splint is recommended; when a brace is used, follow-up/treatment often continues for approximately 4 weeks.
B) Surgical indications
• Persistent instability (tendency to subluxate/dislocate after reduction)
• Complex dislocation / terrible triad pattern
• Displaced coronoid fracture or a coronoid fracture that compromises elbow stability
• Need for reconstruction of the radial head fracture (ORIF or replacement)
C) Surgical technique – “restoring stability”
1. Approach and planning
• CT is highly valuable for clarifying the fracture pattern and establishing an appropriate surgical plan.
• The “foundations” of reconstruction: restoring osseous stabilizers (radial head + coronoid) plus repair of the LCL complex, with MCL repair when needed.
2. Sequence of reconstruction
• In multi-fragment fracture–dislocations, the recommended approach is to fix the “deepest” fracture first:
coronoid → olecranon (if present) → radial head → collateral ligaments.
• The aim is to rebuild the bone–ligament components that allow the elbow to function like a “stable hinge.”
• A commonly used strategy specific to the terrible triad is:
radial head ORIF/arthroplasty + coronoid fixation + LCL repair, with MCL reconstruction if required.
3. Coronoid fixation – “according to fragment type”
• Screws/mini-plate: when the fragment is reconstructible and comminution is limited.
• Transosseous tunnels + fixation together with the anterior capsule: a practical method to enhance stability in comminuted tip-type fractures.
• In terrible triad injuries with small coronoid fragments, “lasso suture” techniques are commonly used; cannulated screw fixation is an alternative.
4. Radial head: ORIF or replacement?
• In terrible triad treatment, fixation or replacement of the radial head is often an indispensable component for elbow stability.
5. Ligament repair
• In terrible triad injuries, LCL repair is one of the essential/key steps.
• If instability persists despite this reconstruction, MCL repair/reconstruction becomes relevant.
6. If persistent instability remains
• If stability still cannot be achieved, options such as a static/hinged external fixator, ulnohumeral pinning, or an “internal hinge” may be considered.
7) Complications
• Elbow stiffness (among the most common and functionally most disabling complications)
• Heterotopic ossification
• Recurrent instability / subclinical microinstability (particularly long-term)
• Post-traumatic osteoarthritis (a long-term issue; PTOA may remain a substantial burden even when outcomes improve)
• Neurovascular problems (especially ulnar nerve)
• Infection, malunion/nonunion, implant-related problems (particularly in complex reconstructions)
UCL / LCL Injuries (Elbow Collateral Ligament Injuries)
1) Overview
• The principal static soft-tissue stabilizers of the elbow are the medial and lateral collateral ligament complexes; injury to these structures can result in clinical instability.
• The UCL (MCL) complex consists of anterior, posterior, and transverse bundles; the anterior bundle is the most critical component resisting valgus stress.
• The LCL complex includes the radial collateral ligament, annular ligament, LUCL, and the accessory LCL; the LUCL is a key determinant of posterolateral rotatory instability (PLRI).
• Clinically, the direction/pattern of instability (valgus vs varus/rotatory) drives the diagnostic and treatment pathway.
2) Epidemiology
• In adults, elbow dislocations are the second most common major joint dislocation after the shoulder and represent approximately 10–25% of elbow injuries; ligament injury can accompany even “simple” dislocations.
• UCL injuries are more prominent in overhead/throwing sports (especially baseball); partial tears may be managed nonoperatively, whereas full-thickness or chronic tears often require reconstruction.
• LUCL/PLRI is commonly considered a ligamentous injury pattern associated with traumatic elbow dislocation.
3) Etiology – Mechanism
UCL (valgus instability)
• The main mechanism is microtrauma from repetitive valgus stress; valgus load increases particularly during the late cocking / early acceleration phases of throwing.
• Acute traumatic valgus instability may also occur; disruption of the anterior bundle of the MCL in acute trauma is accepted as a potential cause of valgus instability.
LCL/LUCL (PLRI)
• The typical PLRI mechanism is forearm supination + axial loading + valgus (posterolateral) stress + elbow extension, leading to progressive insufficiency of the lateral collateral complex and anterior capsule.
• Elbow instability can be conceptualized as a lateral-to-medial progression of soft-tissue disruption after trauma (Horii circle).
• Iatrogenic LUCL injury (during open/arthroscopic procedures around the lateral elbow) is also part of the PLRI etiology.
4) Diagnosis – Physical Examination – Imaging
Clinical history
• UCL: medial elbow pain, reduced throwing performance (velocity/control), sometimes ulnar nerve irritation; valgus extension overload and flexor–pronator pathology should be considered in the differential diagnosis.
• PLRI/LUCL: lateral pain, clicking/“clunk,” and a sense of “giving way,” particularly near extension and during supination-loaded activities (chair-rise/push-up).
Physical examination
• Suspected UCL: valgus stress test + milking maneuver + moving valgus stress test (provokes pain/apprehension through a functional arc).
• Suspected PLRI: lateral pivot shift (often more evident under anesthesia), chair-rise and tabletop relocation tests; the pivot shift mechanism and the LUCL’s role in controlling it are clinically important.
Imaging
• Initial: AP and lateral radiographs (to avoid missing associated fracture/dislocation patterns).
• UCL: diagnosis is typically made with physical examination plus MRI (MRA when needed).
• PLRI: radiographs may show an isolated dislocation or a dislocation with an associated radial head/coronoid tip fracture; when instability is suspected, dynamic assessment (fluoroscopy) becomes valuable. If clinical suspicion is high but examination is limited by pain, EUA/dynamic fluoroscopy can aid diagnosis.
• MRI is important for demonstrating the rupture level and distinguishing partial vs full-thickness tears.
5) Classifications
• By instability direction: valgus, varus, anterior, posterolateral rotatory, etc. (in practice, a pattern-based approach guides diagnosis and treatment).
• By chronicity: acute, chronic, recurrent.
• By degree of disruption (Horii circle / 3 stages): elbow instability may be conceptualized in three stages—early posterolateral subluxation, then incomplete, and finally complete dislocation.
• Practical clinical classification for UCL: partial vs full-thickness; acute avulsion vs chronic attenuation (key for treatment selection).
6) Treatment / Surgical Indications / Techniques
General principle
• The goal is to achieve a stable joint and plan early controlled motion in a manner consistent with the instability pattern; prolonged immobilization increases the risk of stiffness.
UCL (MCL) injuries
Nonoperative treatment (first-line; “default” for most cases)
• In most patients: rest + physical therapy; surgery is generally reserved for high-level overhead throwers/professional athletes.
• Nonoperative management typically includes up to ~6 weeks away from sport, functional exercises, and strengthening. Injection-based approaches (especially steroids) should be considered cautiously given potential risks of ligament weakening/rupture and heterogeneous results in the literature.
Surgical indications
• High-demand overhead athlete with persistent symptoms/objective valgus instability despite an appropriate nonoperative program.
• Acute full-thickness rupture or chronic full-thickness tears (especially in competitive athletes).
Techniques
• Primary repair for selected acute proximal/distal avulsions; graft reconstruction is commonly used for chronic/full-thickness tears.
LCL/LUCL – PLRI
Nonoperative treatment
• If there is no associated fracture and post-reduction stability is adequate: short immobilization + early ROM; however, if PLRI symptoms recur, nonoperative failure is possible.
Surgical indications
• Persistent post-reduction instability, functional giving-way/insecurity, recurrent PLRI episodes, and the presence of associated fractures/instability patterns.
Techniques
• Acute LUCL/LCL repair when tissue quality is suitable (most commonly to the humeral origin at the lateral epicondyle).
• LUCL reconstruction for chronic symptomatic PLRI (using a tendon graft; the goal is to restore isometry and rotatory stability).
7) Complications
• Persistent instability (recurrent valgus instability or PLRI; recurrent subluxation/“giving way” episodes).
• Elbow stiffness (especially after trauma/dislocation; a key complication shaping rehabilitation strategy).
• Ulnar nerve symptoms (may accompany UCL pathology; can also be seen after trauma).
• Post-traumatic arthritis and chronic pain; iatrogenic lateral instability (after lateral procedures).
• Ulnar neuritis / valgus extension overload spectrum that may accompany UCL pathology (can influence clinical course and return-to-play planning).