Mason classification of radial head fractures (also searched with possessive/alternate eponym spelling where applicable, ICD-10: S52.12) is the universally accepted orthopedic and trauma staging system used to categorize radial head fractures based on fracture displacement, comminution, and the presence of a mechanical block to forearm rotation^{1, 7}. Originally proposed by Dr. J. Mark Mason in 1954 and subsequently modified by Hotchkiss and other hand and upper extremity specialists, this classification stratifies injuries to guide clinical decision-making between conservative non-operative treatment and surgical intervention, such as open reduction and internal fixation (ORIF) or prosthetic radial head replacement^{1, 3, 6}. Radial head fractures represent the most common bony injury of the adult elbow, accounting for approximately one-third of all elbow fractures and nearly twenty percent of all acute elbow trauma presentations following a fall onto an outstretched hand^{2, 3, 5}. Precise clinical staging utilizing the Mason framework ensures optimal restoration of radiocapitellar joint congruity, preservation of secondary valgus and longitudinal stability, and mitigation of long-term complications such as post-traumatic stiffness and osteoarthritis^{1, 4}.

Etiology & Risk Factors

• Mechanism of Injury: The overwhelming majority of radial head fractures occur via indirect trauma resulting from an axial load transmitted up the forearm during a fall onto an outstretched hand (FOOSH) with the elbow in partial flexion and the forearm in pronation^{3, 6}.
• High-Energy Trauma: High-velocity motor vehicle collisions or falls from significant heights impart substantial axial and valgus vectors, frequently resulting in complex, comminuted Mason Type III fractures accompanied by dislocation or multi-ligamentous disruption^{4, 7}.
• Concomitant Soft-Tissue & Bony Injuries: Radial head fractures rarely occur in isolation when associated with high-energy forces. Common pathological associations include tears of the lateral ulnar collateral ligament (LUCL) complex, medial ulnar collateral ligament (MCL) rupture, coronoid process fractures, distal radioulnar joint (DRUJ) disruption (Essex-Lopresti lesion), and posterolateral rotatory instability (PLRI)^{1, 4}.
• Demographic Risk Factors: Peak incidence occurs in adults aged thirty to sixty years, with a higher prevalence in females, largely attributable to age-related reductions in bone mineral density and increasing rates of osteoporotic fragility fractures³. Participation in high-impact contact sports or occupational hazards involving heavy machinery further elevates injury susceptibility³.

Pathophysiology

The radial head functions as a critical biomechanical stabilizer within the upper extremity, transmitting approximately sixty percent of axial load across the radiocapitellar joint while serving as a secondary static restraint to valgus stress and a primary contributor to longitudinal forearm rotation stability^{1, 3}. When an axial compressive force is applied across the forearm, the proximal radial head impacts the convex capitellum of the distal humerus. The specific vector of force, magnitude of impact, and degree of forearm rotation at the moment of impact dictate the resulting structural failure pattern. Low-energy shear forces produce undisplaced split or marginal rim fractures (Mason Type I), whereas higher energy impacts drive the radial head against the capitellum, causing multi-fragmentary articular depression, cortical comminution, and displacement (Mason Types II and III)^{1, 6}. Intra-articular fracture extension disrupts the smooth hyaline cartilage architecture, precipitating rapid intra-articular bleeding and acute hemarthrosis within the constrained synovial capsule of the elbow joint. This capsular distention provokes severe pain, protective muscle spasm, and mechanical impingement if displaced bone fragments protrude beyond the radial rim. Furthermore, concurrent disruption of the annular ligament and interosseous membrane compromises load-sharing across the forearm, predisposing the radius to proximal migration and chronic wrist or elbow instability if unaddressed^{1, 4}.

Clinical Presentation & Classic Clinical Signs

• History & Cardinal Symptoms: Patients typically present following acute trauma, reporting immediate lateral elbow pain, localized swelling, and an inability to fully extend the elbow or rotate the forearm. A clear history of a fall onto an outstretched hand or high-impact axial loading is universally elicited^{3, 6}.
• Physical Examination & Named Clinical Signs:
  • Inspection & Posture: The affected arm is typically held in protective flexion (approximately thirty to forty-five degrees) supported by the contralateral hand. Diffuse swelling and ecchymosis surrounding the lateral elbow and antecubital fossa are frequently observed³.
  • Palpation & The Radial Head Tenderness Sign: Exquisite focal point tenderness is elicited directly over the radial head, situated approximately one to two centimeters distal to the lateral epicondyle. Passive rotation of the forearm causes the radial head to rotate beneath the examiner's palpating thumb, eliciting sharp, reproducible pain^{1, 3}.
  • Mechanical Block to Motion: A hard or springy mechanical block encountered during passive or active pronation and supination strongly indicates displaced intra-articular fragments or loose bodies entrapped within the radiocapitellar articulation^{1, 2}.
  • Ligamentous & Neurovascular Testing: Valgus stress testing of the elbow evaluates medial collateral ligament integrity. Posterolateral rotatory drawer testing assesses rotational stability. Distal neurovascular examination must meticulously evaluate the posterior interosseous nerve (PIN), a branch of the radial nerve vulnerable to traction or direct contusion as it traverses the arcade of Froshse near the radial neck³.

Diagnostic Workup & Interpretation (Laboratory, Imaging & ECG/Pathology)

Staging, Classification & Clinical Scoring Systems

Differential Diagnosis

Management & Treatment Protocol

• Initial Stabilization & Resuscitation: Immediate management in the acute setting involves immobilization of the elbow joint in a posterior long-arm splint with the elbow flexed at ninety degrees and the forearm in neutral rotation to minimize soft-tissue tension. Ice application and extremity elevation are instituted immediately to mitigate edema. Baseline neurovascular status must be documented prior to and following immobilization^{3, 6}.
• First-Line Medical / Pharmacological Therapy:
  • Analgesia: Paracetamol (acetaminophen) administered at 1,000 mg PO every six hours PRN (maximum 4,000 mg per twenty-four-hour period) combined with non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen 400 to 600 mg PO every eight hours with food (or celecoxib 200 mg PO daily) to control acute inflammatory pain and provide prophylaxis against heterotopic ossification.
  • Adjunctive Opioids: For severe acute trauma or post-operative pain, short-acting opioid analgesics (e.g., oxycodone 5 mg PO every four to six hours PRN) are prescribed strictly for the initial forty-eight to seventy-two hours post-injury.
• Surgical / Interventional Indications:
  • Mason Type I Protocols: Non-operative management is standard. Diagnostic and therapeutic aspiration of the radiocapitellar joint under sterile technique using 5 to 10 mL of 1% lidocaine evacuates the hematoma, relieves intracapsular pressure, reduces pain, and allows immediate initiation of active range-of-motion exercises within forty-eight to seventy-two hours^{1, 6}.
  • Mason Type II Protocols: Indicated for fractures with greater than 2 mm displacement or those exhibiting a mechanical block to pronation/supination. Open reduction and internal fixation (ORIF) is performed using headless compression screws countersunk beneath the articular surface. Hardware must be placed meticulously within the "safe zone"—the 110-degree arc of the radial head that does not articulate with the lesser sigmoid notch of the ulna during forearm rotation (extending between the radial styloid and Lister's tubercle equivalents when oriented)^{1, 2}.
  • Mason Type III Protocols: Indicated for severely comminuted, non-reconstructable fractures and fractures associated with elbow instability, Essex-Lopresti lesions, or medial collateral ligament tears. Modular titanium radial head arthroplasty is performed to restore exact radiocapitellar height, provide valgus and longitudinal stability, and enable early postoperative mobilization. Concomitant repair or reconstruction of torn lateral and medial collateral ligament complexes is routinely executed^{1, 4, 7}.

Complications & Prognosis

• Acute & Chronic Complications:
  • Post-Traumatic Joint Stiffness: The most frequent complication following radial head fractures, characterized by loss of full extension and flexion contractures resulting from capsular fibrosis, prolonged immobilization, or heterotopic ossification. Managed via aggressive physical therapy, dynamic splinting, and occasionally arthroscopic or open arthrolysis^{1, 3}.
  • Heterotopic Ossification (HO): Ectopic bone formation within the peri-articular soft tissues and joint capsule. Prophylactic low-dose oral NSAIDs (e.g., indomethacin) or single-fraction radiation therapy are administered in high-risk polytrauma or surgical cohorts¹.
  • Post-Traumatic Osteoarthritis: Secondary degenerative joint disease arising from initial cartilage damage, articular step-off, or joint incongruity.
  • Hardware Failure & Overstuffing: Screw loosening, implant breakage, or oversizing of a radial head prosthesis ("overstuffing"), which increases radiocapitellar joint pressure, induces capitellar cartilage wear, and restricts elbow motion^{1, 7}.
  • Neurovascular Injury: Iatrogenic or traumatic neuropraxia of the posterior interosseous nerve (PIN) during lateral surgical approaches³.
• Prognosis: The prognosis for undisplaced Mason Type I fractures managed conservatively with early functional rehabilitation is excellent, yielding full recovery of motion and strength in the vast majority of patients. Displaced and comminuted Mason Types II and III treated with anatomical internal fixation or contemporary modular radial head arthroplasty achieve good-to-excellent functional outcomes and high Mayo Elbow Performance Scores, provided rigid fixation and stable soft-tissue reconstruction are achieved^{1, 4}.