Posteromedial rotatory instability of the elbow

1. High-Yield Summary

• The Triad of Varus Posteromedial Rotatory Instability (VPMRI): Posteromedial rotatory instability of the elbow represents a severe, complex injury pattern defined by an osseoligamentous triad: a fracture of the anteromedial facet of the coronoid process (AMF), avulsion or complete rupture of the lateral collateral ligament (LCL) complex (primarily the lateral ulnar collateral ligament [LUCL]), and an intact radial head. The posterior bundle of the medial collateral ligament (pMCL) is frequently disrupted, while the anterior bundle (aMCL) is compromised when fracture lines extend through the sublime tubercle.
• Pathognomonic Biomechanical Vector: In sharp contrast to posterolateral rotatory instability (valgus, axial load, and supination), PMRI results from an axial load applied to the flexed or extended elbow coupled with an adduction/varus moment and an internal rotation torque of the forearm relative to the humerus. The sharp medial trochlea drives as a coronal shear wedge directly into the unsupported, cantilevered anteromedial facet of the coronoid process.
• The Deceptive Plain Radiograph and the “Drop Sign”: Following the traumatic event, spontaneous reduction of the elbow joint commonly occurs, rendering initial emergency department radiographs deceptively benign or misdiagnosed as an inconsequential coronoid tip sprain. A subtle widening of the ulnohumeral joint space greater than 4 mm on a non-weight-bearing true lateral radiograph (the pathognomonic “Drop Sign”) or subtle medial joint space narrowing indicates uncontained posterior subluxation and persistent rotatory instability.
• Mandatory Thin-Slice 3D Computed Tomography: Plain radiographs consistently underestimate the true depth, surface area, and comminution of anteromedial facet fractures. High-resolution thin-slice (sub-millimeter) computed tomography (CT) with 2D coronal, sagittal, and 3D volume-rendered reconstructions (employing digital subtraction of the distal humerus) is mandatory for all coronoid fractures to classify the lesion under the O’Driscoll system and map the coronal shear plane.
• Dual-Column Surgical Restoration Paradigm: Nonoperative management of displaced or unstable PMRI inevitably precipitates rapid, severe medial joint overload, recurrent subluxation, and rapid post-traumatic ulnohumeral osteoarthritis within months. Durable operative reconstruction requires rigid medial buttress plate fixation of the anteromedial facet (to resist coronal shear forces; independent lag screws alone uniformly fail) combined with anatomic repair or reconstruction of the lateral collateral ligament complex to eliminate varus and posteromedial rotatory laxity.

2. Anatomy

Osseous Geometry of the Greater Sigmoid Notch and Anteromedial Facet

The greater sigmoid notch (trochlear notch) of the proximal ulna provides the fundamental osseous constraint of the ulnohumeral articulation. Formed by the olecranon posteriorly and the coronoid process anteriorly, the notch possesses an arc of approximately 180 degrees that conforms tightly to the spool-shaped humeral trochlea. A central longitudinal sagittal guiding ridge divides the greater sigmoid notch into medial and lateral articular facets, corresponding to the asymmetric medial and lateral flanges of the humeral trochlea.

The coronoid process acts as the critical anterior and rotatory buttress of the elbow. Morphologically, the coronoid can be partitioned into three distinct anatomical regions: the central tip, the anterolateral facet, and the anteromedial facet (AMF). The anteromedial facet represents a unique structural entity that projects medially and anteriorly beyond the longitudinal cortical axis of the ulnar diaphysis. While the central tip and lateral coronoid are structurally buttressed by the dense anterior ulnar cortex, the anteromedial facet hangs over the medial metaphysis as a cantilevered shelf, lacking direct cortical support beneath its articular surface. This structural asymmetry renders the anteromedial facet extraordinarily susceptible to shear failure when subjected to axial and varus loads.

Situated on the posteroinferior margin of the anteromedial facet is the sublime tubercle (tuberculum coronoideum). Located approximately 3 to 5 mm distal to the articular margin, the sublime tubercle serves as the anatomic footprint for the anterior bundle of the medial collateral ligament (aMCL). Fracture lines traversing the anteromedial facet that exit through or distal to the sublime tubercle inherently disrupt the primary soft-tissue restraint to valgus stress, converting an asymmetric rotatory instability into a circumferential, multidirectional disruption.

Medial and Lateral Collateral Ligamentous Architecture

Elbow stability relies on a balanced synergy between primary osseous constraints and secondary capsuloligamentous stabilizers across both columns:

• Lateral Collateral Ligament (LCL) Complex: Composed of the Lateral Ulnar Collateral Ligament (LUCL), the Radial Collateral Ligament (RCL), the Annular Ligament (AL), and the Accessory Lateral Collateral Ligament (ALCL). The LUCL originates from the isometric center of curvature of the capitellum on the lateral epicondyle, arches superficial to the annular ligament and posterior to the radial neck, and inserts definitively onto the crista supinatoris of the ulna. The LUCL is the primary static constraint resisting posterolateral and posteromedial rotatory translation of the proximal radioulnar unit. In PMRI, the lateral complex is torn or avulsed from the lateral humeral epicondyle as the elbow opens under varus load.
• Medial Collateral Ligament (MCL) Complex: Composed of the anterior bundle (aMCL), posterior bundle (pMCL), and transverse ligament (Cooper’s ligament). The aMCL originates from the anteroinferior aspect of the medial epicondyle and inserts onto the sublime tubercle; it provides the primary static restraint against valgus stress between 20 and 120 degrees of flexion. The pMCL is a fan-shaped thickening of the posteroinferior capsule inserting along the medial margin of the olecranon; it tightens in flexion beyond 60 degrees and serves as the primary soft-tissue restraint against internal rotation and posteromedial rotatory subluxation. In PMRI, the pMCL is routinely ruptured or avulsed, whereas the aMCL remains intact unless the fracture involves the sublime tubercle (O’Driscoll Type II Subtype 3).
• Anterior and Posterior Joint Capsule: The anterior capsule inserts 5 mm distal to the coronoid tip and reinforces anterior stability in extension. The posterior capsule resists excessive internal rotation and hyperflexion. In PMRI, the posterior capsule is stripped or torn in continuity with the posterior bundle of the MCL.
• Dynamic Muscular Stabilizers: The flexor-pronator muscle mass (pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis, and flexor carpi ulnaris) originates from the medial epicondyle and provides active dynamic resistance to valgus and varus displacement. On the lateral side, the common extensor mass and anconeus act as dynamic buttresses against rotatory and varus displacement.

Surgical Internervous Planes: Medial and Lateral Corridors

Reconstruction of posteromedial rotatory instability requires dual-column surgical access utilizing distinct anatomical internervous corridors:

• Flexor Carpi Ulnaris (FCU) Split Approach (Medial): Developed directly between the humeral and ulnar heads of the FCU. Although both heads are innervated by the ulnar nerve, careful intermuscular dissection distal to the cubital tunnel allows direct perpendicular exposure of the anteromedial coronoid facet and sublime tubercle while retracting the anterior flexor mass anteriorly. This approach offers optimal visualization for placing low-profile buttress plates along the medial articular margin.
• Over-the-Top Approach (Hotchkiss, Medial): Exploits the interval between the pronator teres (innervated by the median nerve) and the flexor carpi radialis (median nerve), or elevates the flexor-pronator mass anteriorly from the medial epicondylar ridge. This corridor provides broad visualization of the anterior coronoid and anterior capsule but requires more retraction around the median nerve and brachial artery.
• Taylor-Scham Interval (Medial): Subperiosteal elevation of the flexor-pronator origin and FCU off the subcutaneous border of the proximal ulna from posterior to anterior, preserving the anterior soft-tissue sleeve.
• Kocher Interval (Lateral): Developed between the anconeus muscle posteriorly (innervated by a dedicated radial nerve branch originating proximal to the elbow) and the extensor carpi ulnaris (ECU) muscle anteriorly (innervated distally by the posterior interosseous nerve [PIN]). This internervous plane preserves muscular innervation, exposing the lateral epicondylar origin of the LCL complex, the capitellum, and the crista supinatoris.

Neurovascular Danger Zones

Meticulous respect for adjacent neurovascular structures is paramount during operative stabilization:

• Ulnar Nerve: Courses through the retroepicondylar groove and passes between the two heads of the FCU within the cubital tunnel, directly adjacent to the sublime tubercle and the posterior bundle of the MCL. The ulnar nerve is highly vulnerable to traction injury during fracture exposure, direct compression from medial retractors, and mechanical impingement by prominent buttress plate hardware or screw tips. Formal identification, neurolysis, and subcutaneous anterior transposition or protected in situ release are mandatory during medial exposure.
• Median Nerve and Brachial Artery: Traverse anterior to the brachialis muscle within the antecubital fossa. Placement of deep anterior Hohmann retractors over the anterior coronoid margin without maintaining direct bone contact can crush or lacerate the neurovascular bundle. Retractors must be placed subperiosteally directly against the anterior coronoid cortex.
• Posterior Interosseous Nerve (PIN): The deep motor branch of the radial nerve winds around the radial neck before piercing the supinator muscle at the arcade of Frohse, approximately 20 to 30 mm distal to the radiocapitellar joint. During lateral exposure, keeping the forearm in full pronation translates the PIN up to 10 mm anteriorly and medially away from the posterolateral joint capsule, establishing a safe surgical margin.
• Medial Antebrachial Cutaneous Nerve (MACN): Branches of the MACN cross the medial joint line anterior to the medial epicondyle. Laceration or entrapment produces painful medial elbow neuromas or dysesthesias along the ulnar border of the forearm.

3. Pathogenesis

Biomechanical Kinematics of Varus Posteromedial Rotatory Instability

Posteromedial rotatory instability is characterized by a specific three-dimensional kinematic failure mechanism distinct from all other forms of elbow trauma. The injury sequence is initiated by a fall onto an outstretched hand with the elbow loaded in extension or early flexion (between 10 and 30 degrees). The forearm is subjected to a tri-axial force vector consisting of:

• Axial Compression: Drives the humeral articular surface distally into the trochlear notch of the ulna.
• Varus Moment (Adduction): Tilts the forearm medially relative to the humerus, opening the lateral radiocapitellar and ulnohumeral joint spaces.
• Internal Rotation Torque: Rotates the forearm bones internally beneath the distal humerus, forcing the steep medial flange of the humeral trochlea against the anteromedial facet of the coronoid process.

As the medial trochlear condyle impacts the unsupported, cantilevered anteromedial facet, the bone fails under pure coronal shear stress. The resulting fracture plane is typically oblique, propagating from anteromedial to posterolateral across the articular surface of the coronoid. Once the anteromedial bony buttress shears off, the medial trochlea loses its anterior and medial containment, allowing the proximal ulna to subluxate posteromedially.

The Two-Column Sequential Failure Cascade

The progression of soft-tissue and osseous destruction follows an unyielding biomechanical cascade:

• Stage 1 (Coronal Shear Fracture): The medial trochlea fractures the anteromedial facet of the coronoid process (O’Driscoll Type II). The size of the sheared fragment varies from a thin rim (Subtype 1) to a substantial fragment involving the coronoid tip (Subtype 2) or extending into the sublime tubercle (Subtype 3).
• Stage 2 (Lateral Column Distraction): Continued varus opening moments generate immense tensile strain across the lateral capsuloligamentous structures. The lateral collateral ligament complex, predominantly the lateral ulnar collateral ligament (LUCL) and radial collateral ligament (RCL), ruptures interstitially or avulses completely from its lateral humeral epicondylar footprint.
• Stage 3 (Posterior Capsule and pMCL Disruption): As the ulna displaces posteromedially, the posterior capsule and the posterior bundle of the medial collateral ligament (pMCL) are stripped from the medial olecranon and posterior humerus.
• Stage 4 (Global Circumferential Disruption): If the coronal shear fracture extends through the sublime tubercle, the anterior bundle of the MCL (aMCL) is detached with the osseous fragment. The elbow is rendered globally unstable, with profound laxity under both varus and valgus stress vectors.

Osseous Contrast: Radial Head Preservation

A fundamental biomechanical distinction between PMRI and posterolateral rotatory instability (or the terrible triad) lies in the state of the radial head. In terrible triad injuries, valgus loading compresses the radial head forcefully against the capitellum, causing radial head fracture, while tension across the anterior capsule avulses the transverse coronoid tip. In contrast, during PMRI, the varus moment distracts the lateral column, completely unloading the radiocapitellar articulation while concentrating 100% of the axial compressive force onto the medial ulnohumeral joint. Consequently, the radial head is structurally preserved and intact in classic PMRI. Recognizing an intact radial head in the presence of an elbow dislocation or coronoid fracture should immediately alert the clinician to a varus posteromedial rotatory mechanism.

4. Natural History

Epidemiology and Patient Demographics

Posteromedial rotatory instability accounts for approximately 10% to 15% of all coronoid fractures and represents an underdiagnosed subset of traumatic elbow injuries. The epidemiology exhibits a bimodal age distribution:

• Young Athletic Cohort (Ages 18 to 40): Typically sustained during high-energy trauma, contact sports, gymnastics, skateboarding, or motor vehicle collisions involving high axial loading on an extended upper extremity.
• Older Adult Cohort (Ages 50 to 75+): Frequently sustained during low-energy ground-level falls onto an outstretched hand. In this population, age-related trabecular osteopenia diminishes the shear strength of the cantilevered anteromedial facet, allowing coronal shear fractures to occur with minimal torsional energy. Females represent a slight majority in the older demographic.

The Catastrophic Natural History of the Missed PMRI

The natural history of an undiagnosed or conservatively managed displaced anteromedial facet fracture is uniformly catastrophic. Because the elbow frequently self-reduces, patients are often discharged from emergency departments with a diagnosis of an uncomplicated elbow sprain or an “insignificant” small coronoid flake fracture. However, the loss of the anteromedial facet eliminates the medial buttress resisting internal rotation and varus displacement. With active elbow motion, the medial humeral trochlea subluxates posteromedially off the greater sigmoid notch into the osseous defect.

This persistent subluxation concentrates extreme contact pressures onto the remaining articular cartilage of the medial trochlea and ulnohumeral groove. Progressive full-thickness chondral loss, joint space collapse, severe synovitis, and extensive osteophyte formation develop with alarming rapidity, often within 3 to 12 months following injury. Seminal clinical series have demonstrated that nonoperative treatment or inadequate fixation of displaced anteromedial facet fractures leads directly to rapid, end-stage post-traumatic ulnohumeral osteoarthritis, chronic debilitating pain, severe flexion contractures, and secondary ulnar neuropathy requiring complex salvage procedures.

Prognosis with Early Anatomic Reconstruction

Conversely, when PMRI is recognized acutely and managed with anatomical medial buttress plating and lateral collateral ligament reconstruction, the prognosis is favorable. Rigid internal fixation achieves bony union rates exceeding 92% to 95%, restores concentric ulnohumeral joint tracking, normalizes contact pressure distributions across the trochlea, and prevents the onset of rapid arthrosis. Most patients regain a functional arc of motion (exceeding 100 degrees of flexion-extension) and achieve high patient-reported outcome scores.

5. Clinical Presentation

Patient History and Symptom Inquiry

Evaluation begins with a detailed traumatic history. Clinicians must specifically inquire about:

• Exact Trauma Vector: A fall onto the outstretched hand with the elbow extended or slightly flexed, accompanied by an immediate sensation of the elbow shifting inward or “popping out.”
• Mechanical Instability Symptoms: In subacute or chronic presentations, patients describe subjective clicking, painful clunking, or an apprehension of the joint “giving way” when bearing axial weight on the extended arm, such as pushing up from a seated position in a chair or performing a push-up.
• Localization of Pain: Intense pain localized to both the medial and lateral aspects of the elbow (dual-column pain), reflecting the medial coronoid shear fracture and the lateral ligamentous disruption.
• Neurologic Complaints: Paresthesias, numbness, or burning sensations radiating into the small and ring fingers, indicative of acute traction or compression of the ulnar nerve within the cubital tunnel.

Physical Examination and Provocative Maneuvers

Physical examination in the acute setting reveals significant circumferential swelling and characteristic “dual-column” ecchymosis overlying both the medial epicondyle/cubital tunnel and the lateral Kocher interval. Point tenderness is exquisitely localized over the anteromedial coronoid (distal and anterior to the medial epicondyle) and over the lateral epicondylar isometric point. In awake patients, severe muscle spasm and guarding often preclude full provocative stress testing; however, when tolerated or performed under regional anesthesia or general sedation, specific provocative maneuvers confirm the diagnosis:

6. Imaging and Diagnostic Studies

Plain Radiography: The Benchmark Views and Pathognomonic Signs

Initial imaging must comprise a standardized elbow radiographic series: true anteroposterior (AP), true lateral (with the shoulder abducted 90 degrees and the cassette strictly parallel to the humeral condyles), and bilateral 45-degree internal and external oblique projections.

• The “Drop Sign”: On the true lateral radiograph, the normal ulnohumeral joint demonstrates a concentric, parallel radiolucent arc of 1 to 2 mm between the trochlea and olecranon. A widening of the ulnohumeral joint space greater than 4 mm with the arm resting in a sling or splint (the pathognomonic Drop Sign) signifies uncontained posterior subluxation and gross capsular and ligamentous disruption.
• Loss of Parallel Ulnohumeral Joint Lines: Incongruity between the curvature of the medial trochlea and the coronoid base, producing a wedge-shaped widening of the joint space.
• The Coronoid “Double-Line” or Fleck Sign: On the AP view, the anteromedial facet fracture appears as a subtle linear cortical step-off or double shadow superimposed on the medial ulnar border, often misinterpreted as a minor avulsion fragment.
• Lateral Joint Space Widening: Asymmetrical opening of the radiocapitellar joint on the AP view reflecting complete rupture of the lateral collateral ligament complex under varus resting tension.

Computed Tomography: Thin-Slice Multiplanar and 3D Volume Rendering

Computed tomography (CT) is the definitive gold standard for evaluating PMRI and is mandatory for all patients with suspected coronoid fractures. Standard radiographs fail to visualize the true extent of anteromedial facet fractures in over 60% of cases. Scanning protocols must utilize thin slices (0.5 to 1.0 mm) with dedicated multiplanar reformations and 3D volume-rendered reconstructions:

• Axial Cuts: Essential for mapping the coronal shear fracture line, determining the percentage of the anteromedial facet articular surface involved, and evaluating whether the fracture extends into the lesser sigmoid notch or crista supinatoris.
• Coronal Cuts: Quantify the depth and vertical height of the fractured fragment and definitively establish whether the fracture line exits through or distal to the sublime tubercle (distinguishing O’Driscoll Subtype 1/2 from Subtype 3).
• Sagittal Cuts: Assess the integrity of the coronoid tip and olecranon articular arc, confirming that the central and lateral coronoid remain intact.
• 3D CT with Digital Subtraction of the Distal Humerus: The single most valuable imaging tool for surgical planning. Digitally removing the distal humerus provides an unobstructed, “en face” view of the greater sigmoid notch, allowing precise measurement of fragment dimensions, assessment of articular comminution, and planning of buttress plate placement.

Magnetic Resonance Imaging (MRI)

While CT is superior for osseous mapping, MRI serves a complementary role in subacute presentations or when occult ligamentous injury is suspected. High-resolution coronal and axial fat-suppressed T2-weighted or proton-density sequences accurately assess:

• Lateral Collateral Ligament Complex: Confirms proximal avulsion of the LUCL and RCL from the lateral epicondylar footprint (present in over 90% of PMRI cases) versus midsubstance tearing.
• Medial Collateral Ligament Complex: Differentiates between isolated tears of the posterior bundle (pMCL) and complete rupture or avulsion of the anterior bundle (aMCL).
• Chondral Shear Lesions: Identifies impaction fractures or full-thickness osteochondral delamination on the medial trochlea resulting from the initial shear impact.

7. Classification

The O’Driscoll Classification of Coronoid Fractures

The O’Driscoll classification system is the universally accepted, anatomically validated system that directly correlates fracture morphology with the underlying biomechanical mechanism and dictates surgical management. In contrast to the historical Regan-Morrey classification (which only evaluated coronoid height on lateral radiographs and failed to recognize anteromedial facet fractures), the O’Driscoll system explicitly classifies anteromedial facet fractures as Type II:

Biomechanical Relevance of O’Driscoll Subtypes

The distinction between O’Driscoll Type II Subtypes 1, 2, and 3 is fundamental to surgical decision-making. In Subtypes 1 and 2, the sublime tubercle remains intact, meaning the anterior bundle of the MCL remains attached to the stable distal ulnar shaft; primary instability is driven by varus stress and posteromedial rotatory translation, which is corrected once the AMF is buttressed and the LCL is repaired. In Subtype 3, however, the fracture cleaves off the sublime tubercle, detaching the primary valgus stabilizer. Consequently, Subtype 3 injuries present with severe bidirectional (varus and valgus) instability. Plating must extend sufficiently posteroinferiorly along the medial ulna to secure the sublime tubercle, and any residual aMCL laxity must be directly addressed with suture anchors.

8. Treatment

Medical / Nonoperative Management

Nonoperative management has an exceedingly narrow, highly restricted role in PMRI and must never be considered the primary standard of care for displaced injuries. It is strictly reserved for patients meeting all of the following stringent criteria:

• Truly non-displaced fracture of the anteromedial facet (articular step-off and gap strictly less than 1.0 mm on thin-slice CT).
• O’Driscoll Type II Subtype 1 morphology (small rim fragment sparing the tip and sublime tubercle).
• Complete absence of ulnohumeral subluxation or “Drop Sign” on all radiographic views.
• Demonstrated concentric joint stability throughout a dynamic fluoroscopic arc of motion under anesthesia (or severe medical contraindications precluding any surgical intervention).

When pursued, nonoperative treatment requires immobilization of the elbow in 90 degrees of flexion with the forearm in FULL PRONATION (which tightens the medial soft-tissue sleeve and seats the radial head against the capitellum, offloading the anteromedial facet) for 7 to 10 days in a rigid posterior splint. Active-assisted motion in an articulated hinged elbow brace with an extension block at 30 degrees is then initiated, maintaining forearm pronation during extension. Mandatory weekly true lateral radiographs are performed for the first 4 weeks; if even 1.0 mm of displacement, articular step-off, or ulnohumeral subluxation develops, nonoperative treatment has failed, and immediate operative conversion is indicated.

Operative Management: Dual-Column Reconstruction

The definitive management of PMRI is operative reconstruction. The overarching “Goals of Surgery” are fourfold:

• Restore the anterior and medial articular buttress of the ulnohumeral joint to resist coronal shear forces.
• Anatomically repair or reconstruct the lateral collateral ligament complex (LUCL) to eliminate varus opening and rotatory subluxation.
• Assess and restore medial collateral ligament integrity (particularly if the sublime tubercle is fractured).
• Achieve concentric, stable ulnohumeral tracking through a full functional arc of motion (30 to 130 degrees) without subluxation.

Step 1: Patient Positioning and Setup: The patient is positioned supine with the operative arm supported on a radiolucent arm board, allowing simultaneous or sequential access to both the medial and lateral columns. A sterile pneumatic tourniquet is applied high on the arm.

Step 2: Medial Approach and Ulnar Nerve Protection: A curved medial skin incision is made centered between the medial epicondyle and the olecranon tip. The ulnar nerve is identified proximal to the cubital tunnel, carefully mobilized with vessel loops, and unroofed through the arcade of Struthers, retroepicondylar groove, and between the two heads of the FCU. Motor branches to the FCU are preserved. An anterior subcutaneous or subfascial transposition is performed at the conclusion of the case, or the nerve is protected in situ with an overlying soft-tissue sling.

Step 3: Exposure and Rigid Buttress Plating of the Anteromedial Facet: The interval between the two heads of the FCU is split to expose the anteromedial coronoid and sublime tubercle. The capsule is opened longitudinally along the articular margin. The fracture hematoma is evacuated, and the coronal shear fragment is identified. Reduction is achieved under direct articular visualization using a small dental pick or ball-spiked pusher. Independent lag screws alone are strictly prohibited, as coronal shear vectors consistently cause screw cutout and catastrophic fragment displacement. A low-profile, pre-contoured 1.5 mm, 2.0 mm, or 2.4 mm coronoid buttress plate (or mini-fragment T-plate/L-plate) is contoured to fit precisely along the medial cortical margin of the coronoid base beneath the joint capsule. The plate acts as a true anti-glide buttress, counteracting the inferior and posterior displacement vector of the medial trochlea. For small rim fragments (Subtype 1), the plate is under-contoured to compress the rim, or high-tensile suture anchors are placed into the subchondral bone to create a lasso fixation construct over the fragment.

Step 4: Lateral Exposure and Anatomic LUCL Repair: Attention is directed to the lateral column. A standard Kocher approach is developed between the anconeus and ECU. The common extensor origin and capsule are evaluated. In over 90% of PMRI cases, the LCL/LUCL is avulsed directly from the lateral humeral epicondyle. The footprint at the isometric center of curvature of the capitellum is decorticated. Two 2.8 mm or 3.5 mm high-strength suture anchors are inserted into the isometric point, or transosseous bone tunnels are drilled through the epicondyle. The avulsed LUCL and capsule are secured with locking Krakow or Bunnell sutures. Crucially, the sutures are tensioned and tied with the elbow at 30 to 40 degrees of flexion with the forearm locked in FULL PRONATION.

Step 5: Assessment of Sublime Tubercle and aMCL: In O’Driscoll Type II Subtype 3 fractures, the sublime tubercle fragment is incorporated into the medial buttress plate. Following medial and lateral fixation, the elbow is stressed in valgus. If residual valgus laxity or medial joint opening is observed, the aMCL is repaired directly with suture anchors to the medial epicondyle or sublime tubercle.

Step 6: Dynamic Fluoroscopic Assessment & External Fixator Indications: Tourniquet is released, and the elbow is put through a dynamic arc of flexion and extension under live fluoroscopy. If concentric reduction is maintained from 0 to 130 degrees without a drop sign or subluxation, primary reconstruction is complete. If persistent subluxation occurs when extending beyond 40 degrees of flexion (due to extreme comminution, severe osteopenia, or massive soft-tissue disruption), a hinged external fixator is placed spanning the elbow, centered strictly on the axis of rotation of the capitellum, locked in 90 degrees for 2 weeks, and then unlocked for passive motion.

Indications & Contraindications

Surgical thresholds are defined by explicit anatomical and biomechanical criteria:

Absolute Operative Indications

• Articular Step-off: Any anteromedial coronoid facet fracture with articular displacement or step-off greater than or equal to 1.5 mm.
• Ulnohumeral Subluxation: Any coronoid fracture accompanied by radiographically evident ulnohumeral subluxation or a positive Drop Sign (greater than 4 mm joint widening).
• Sublime Tubercle Involvement: All O’Driscoll Type II Subtype 3 fractures involving the sublime tubercle and aMCL footprint.
• Gross Rotatory Instability: Anteromedial facet fractures with documented complete disruption of the lateral collateral ligament complex.
• Secondary Displacement: Failure of conservative management manifested by early loss of reduction or persistent rotatory instability.

Contraindications to Reconstruction

• Stable Non-Displaced Fractures: Truly non-displaced (less than 1.0 mm) stable Subtype 1 fractures in compliant patients demonstrating complete stability on dynamic fluoroscopy.
• Active Sepsis: Active superficial or deep joint sepsis.
• Severe Medical Comorbidity: Severe medical comorbidities rendering the patient unfit for general anesthesia or regional block.
• Pre-Existing Advanced Arthrosis: Advanced pre-existing ulnohumeral osteoarthritis where joint preservation is futile and salvage arthroplasty or arthrodesis is indicated.

9. Outcome

Validated Patient-Reported Outcome Measures (PROMs)

Surgical stabilization of PMRI yielding concentric, stable joint reduction produces substantial improvements in validated patient-reported outcomes. In contemporary clinical series and systematic reviews, patients treated acutely with anatomical medial buttress plating and LCL repair achieve mean Mayo Elbow Performance Scores (MEPS) ranging from 86 to 94 points, corresponding to good-to-excellent clinical ratings in over 85% of cases. Disabilities of the Arm, Shoulder, and Hand (DASH) and QuickDASH scores average between 12 and 18 points at final follow-up, reflecting minimal residual disability in activities of daily living.

Functional Range of Motion and Biomechanical Restoration

Restoration of a functional elbow arc of motion (defined by Morrey as 30 degrees of extension to 130 degrees of flexion, with 50 degrees of pronation and 50 degrees of supination) is achievable in the vast majority of patients undergoing timely reconstruction:

• Mean Flexion-Extension Arc: Averages 115 to 125 degrees postoperatively. Patients typically maintain a mild residual extension deficit of 10 to 15 degrees, which is clinically well tolerated and does not impair functional reach.
• Forearm Rotation Arc: Pronation and supination are remarkably well preserved, with a mean rotational arc exceeding 140 to 150 degrees, provided that the proximal radioulnar joint was not violated and the LUCL was tensioned in proper pronation.
• Bony Union Rates: Anatomic buttress plate fixation of the anteromedial facet achieves primary osseous union in 92% to 98% of cases, with nonunion rarely encountered when rigid plate fixation is utilized.

Long-Term Joint Survivorship and Secondary Arthroplasty Rates

The long-term joint survivorship of PMRI is directly governed by the timeliness and quality of initial surgical stabilization. Landmark long-term studies demonstrate that when anatomical buttress fixation and LCL repair are executed within 2 to 3 weeks of injury, radiographic progression to moderate or severe post-traumatic osteoarthritis is limited to less than 15% to 20% of patients over a 5- to 10-year period. Conversely, when surgery is delayed beyond 4 to 6 weeks or when the fracture is inadequately stabilized with independent screws, over 70% of patients develop rapid, severe post-traumatic osteoarthritis, with many requiring salvage interposition arthroplasty or total elbow arthroplasty within 5 years of the index trauma.

10. Complications

Due to the complex dual-column exposure, adjacent neurovascular structures, and severe articular shear forces, PMRI carries a substantial complication profile that must be proactively anticipated and managed:

11. Pearls and Pitfalls

Master Surgical Pearls

• Preoperative 3D CT Digital Subtraction Mapping: Always request 3D CT reconstructions with digital subtraction of the distal humerus before entering the operating room. Viewing the coronoid process “en face” without humeral superposition reveals the exact obliquity of the coronal shear line, identifies occult articular comminution, and dictates the precise pre-contouring of the medial buttress plate.
• The Medial Buttress Anti-Glide Principle: Never rely on independent lag screws or headless compression screws to fix anteromedial facet fractures. The biomechanical vector in PMRI is a coronal shear force driven by the medial humeral trochlea; screws placed perpendicular to the fracture line experience cantilever bending loads and rapidly cut out of osteopenic bone. A low-profile plate must be contoured as an anti-glide buttress resting against the medial cortex of the coronoid base, capturing the fragment beneath its shoulder and resisting shear displacement.
• Routine Ulnar Nerve Anterior Subcutaneous Transposition: The ulnar nerve resides directly over the medial buttress plate bed and the sublime tubercle. Routine mobilization and anterior subcutaneous transposition not only removes the nerve from the zone of hardware irritation and scar entrapment but also provides wide, relaxed surgical visualization of the anteromedial coronoid without the need for aggressive traction on the nerve.
• LCL Isometric Tensioning in Complete Pronation: When reconstructing or repairing the avulsed lateral collateral ligament complex, the assistant must lock the forearm in complete, maximum PRONATION with the elbow flexed at 30 to 40 degrees. Pronation rotates the radial head into close congruity with the lesser sigmoid notch and tensions the medial soft-tissue sleeve, ensuring that the reconstructed LUCL is not over-tightened in external rotation.
• Live Fluoroscopic Stability Arc Verification: Prior to wound closure, cycle the elbow through a complete flexion-extension arc under live fluoroscopy. Observe the ulnohumeral joint space throughout the range of motion. If widening or ulnohumeral subluxation is detected as the elbow extends past 40 degrees, the joint remains unstable; perform immediate re-tensioning of the lateral complex or place a hinged external fixator.

Critical Diagnostic and Operative Pitfalls

• The “Benign Sprain” Diagnostic Trap: The most disastrous pitfall in elbow traumatology is misdiagnosing a spontaneously reduced PMRI as a simple elbow sprain based on seemingly normal or minimally displaced plain radiographs. Any coronoid fracture, regardless of size, must be treated as complex instability until proven otherwise with thin-slice CT.
• Misidentifying the Injury as an Isolated LCL or Radial Head Pathology: In PMRI, clinical swelling and tenderness are often more prominent laterally due to the LCL tear, while the radial head is intact. Clinicians who focus exclusively on the lateral pain may perform an isolated lateral ligament repair while neglecting the fractured anteromedial facet, leading to rapid failure of the lateral repair and progressive medial joint destruction.
• Neglecting the Sublime Tubercle and aMCL Insertion: Failing to recognize that the fracture line extends through the sublime tubercle (O’Driscoll Type II Subtype 3) leaves the anterior bundle of the MCL incompetent. Stabilizing the anteromedial facet while ignoring the sublime tubercle converts the joint from posteromedial instability to severe valgus instability. The plate must capture the sublime tubercle, and the aMCL must be refixed.
• Overlooking the “Drop Sign” on Post-Reduction Radiographs: Discharging a patient whose lateral radiograph exhibits a ulnohumeral joint space greater than 4 mm (the Drop Sign) guarantees persistent subluxation, rapid cartilage erosion, and irreversible arthrosis. Any persistent drop sign demands immediate surgical exploration.
• Prolonged Postoperative Immobilization: Immobilizing the elbow in a cast for more than 10 to 14 days leads to crippling arthrofibrosis and permanent flexion contractures. Rigid dual-column internal fixation must provide sufficient mechanical stability to permit active-assisted motion within the first postoperative week.

12. Controversy

Buttress Plating vs. Suture Anchor / Suture Lasso for Small AMF Rim Fractures (<2 mm Subtype 1)

Substantial debate persists regarding the optimal fixation method for small, marginal anteromedial rim fractures (O’Driscoll Type II Subtype 1) involving less than 2 mm of articular bone. Rigid buttress plating of very small, comminuted rim fragments can be technically demanding and risks fragment fragmentation during screw insertion. Proponents of suture anchor or transosseous suture lasso fixation argue that passing heavy non-absorbable sutures through the anterior capsule and over the osseous rim effectively buttresses small fragments with minimal surgical trauma and hardware profile. Conversely, biomechanical purists contend that suture constructs lack sufficient rigidity to resist coronal shear forces during dynamic loading, advocating for micro-fragment plates (1.5 mm) or spring plates with under-contoured prongs to ensure true rigid anti-glide buttressing.

Routine vs. Selective Anterior Transposition of the Ulnar Nerve

While all surgeons agree on the necessity of mobilizing and protecting the ulnar nerve during medial coronoid exposure, consensus is lacking regarding whether the nerve should be routinely transposed anteriorly or returned to the cubital tunnel in situ. Advocates of routine subcutaneous anterior transposition emphasize that the nerve bed is directly compromised by medial buttress hardware, scar formation, and local hematoma, and that transposition minimizes the risk of late symptomatic ulnar neuropathy. Skeptics argue that extensive anterior transposition requires extensive circumferential devascularization of the ulnar nerve, potentially precipitating ischemic neuropathy, and maintain that protected in situ release with a fascial flap is associated with lower overall neurological complication rates if plate hardware is kept low-profile.

Mandatory vs. Selective Repair of the Anterior Bundle of the MCL

In O’Driscoll Type II Subtypes 1 and 2 fractures, the sublime tubercle remains attached to the intact ulnar shaft, but the anterior bundle of the MCL may sustain partial-thickness interstitial strain or micro-avulsion. Some authors advocate for routine surgical inspection and suture anchor augmentation of the aMCL in all PMRI cases to maximize medial stability. However, comparative biomechanical and clinical investigations demonstrate that when the anteromedial facet is anatomically buttressed and the lateral collateral ligament complex is rigidly reconstructed, the intact aMCL provides adequate valgus stability, rendering routine MCL exploration and repair unnecessary unless gross valgus laxity is demonstrated intraoperatively.

Hinged External Fixation: Primary Prophylactic Adjunct vs. Staged Bail-Out

The threshold for applying an articulated hinged external fixator remains a topic of active clinical discussion. Certain trauma surgeons recommend the routine application of a hinged external fixator in all PMRI cases involving severe comminution or delayed presentation (greater than 3 weeks), arguing that the fixator completely offloads the fragile medial buttress plate and reconstructed LCL, permitting aggressive early motion while guaranteeing concentric joint reduction. Others reserve the external fixator strictly as a salvage bail-out when intraoperative fluoroscopy demonstrates persistent ulnohumeral subluxation or drop sign beyond 40 degrees of extension despite anatomical dual-column fixation, citing concerns over pin-site infections, radial nerve injury during lateral pin placement, and prolonged operative time.

13. Evidence-Based Synthesis

Modern clinical decision-making is grounded in high-quality randomized controlled trials and prospective registry analyses, corroborated by seminal biomechanical and anatomical descriptions.

14. References

• Doornberg JN, Ring DC. Fracture of the anteromedial facet of the coronoid process. J Bone Joint Surg Am. 2006. doi:10.2106/00004623-200610000-00014 [Level IV: Clinical Case Series / Cohort Study]
• Pollock JW, Brownhill J, Ferreira L et al. The effect of anteromedial facet fractures of the coronoid and lateral collateral ligament injury on elbow stability and kinematics. J Bone Joint Surg Am. 2009. doi:10.2106/JBJS.H.00222 [Level IV: Clinical Case Series / Cohort Study]
• Lanzerath F, Hackl M, Wegmann K et al. The treatment of anteromedial coronoid facet fractures: a systematic review. J Shoulder Elbow Surg. 2021. doi:10.1016/j.jse.2020.09.008 [Level I: Systematic Review / Meta-Analysis]
• Zwerus EL, Somford MP, Maissan F et al. Physical examination of the elbow, what is the evidence? A systematic literature review. Br J Sports Med. 2018. doi:10.1136/bjsports-2016-096712 [Level I: Systematic Review / Meta-Analysis]
• Badre A. Understanding Varus Posteromedial Instability: Biomechanics, Injury Patterns, and Achieving Successful Stability. Hand Clin. 2025. doi:10.1016/j.hcl.2025.06.004 [Level IV: Clinical Case Series / Cohort Study]

15. Master Class Pro-Tip

The most common and devastating failure mode in managing posteromedial rotatory instability is attempting to secure the sheared anteromedial facet with independent lag screws alone while ignoring the lateral column. The anteromedial facet fails under coronal shear stress; independent screws placed across this fracture plane lack buttress resistance, and the downward thrust of the medial trochlea inevitably shears the fragment off the screws, resulting in fixation collapse and rapid articular destruction. You must utilize a low-profile 1.5 mm or 2.0 mm pre-contoured buttress plate placed directly along the medial cortical margin of the coronoid base beneath the joint capsule, acting as an uncompromising anti-glide stop. Furthermore, never close the medial side without formally exposing and repairing the lateral collateral ligament complex through a Kocher interval. When securing the avulsed LUCL to its isometric center on the lateral epicondyle, the assistant must lock the forearm in maximum PRONATION at 30 to 40 degrees of flexion. Pronation rotates the radial head into the lesser sigmoid notch, tightens the medial soft-tissue sleeve, and closes the lateral rotatory gap. If you fail to buttress the medial shear or fail to tension the lateral complex in pronation, the joint will subluxate, and the patient will face catastrophic ulnohumeral osteoarthritis within twelve months.

Master Class Surgical Pearl: Coronal Shear Restoration and Dual-Column Balancing