Secondary Valgus Stabilizer | Mason Classification | Rule of 3
MASON CLASSIFICATION
Critical Must-Knows
- Secondary valgus stabilizer - critical if MCL is torn
- Mechanical block needs aspiration to confirm (remove pain)
- Safe Zone (90-110 degrees) for hardware placement to avoid impingement
- Essex-Lopresti - always check DRUJ/wrist for tenderness
- Terrible Triad = Radial Head + Coronoid + Dislocation
Clinical Pearls
- "Aspirate hemarthrosis + inject L.A. to assess true ROM
- "Fat pad sign may be the only radiological sign
- "Excision contraindicated if forearm instability (check wrist!)
- "Use bare metal stems for replacement (cemented or press-fit)
Clinical Imaging
Imaging Gallery
Exam Essentials
Rule of Threes
Fractures often come in threes (Terrible Triad):
- Radial Head Fracture
- Coronoid Fracture
- Elbow Dislocation (LCL injury) Always look for the other two!
The 'Safe Zone'
90-110 degree arc of the radial head that does not articulate with the proximal radioulnar joint.
- Safe for plate/screw prominent heads
- Determine intra-operatively using reference marks
Don't Miss Essex-Lopresti
Longitudinal Radioulnar Dissociation.
- Radial Head Fracture
- Interosseous Membrane (IOM) tear
- DRUJ Dislocation Exam Trap: Always document "Non-tender DRUJ" or get wrist X-rays.
Surgical Threshold
Mechanical Block is the primary indication for Type II.
- Must aspirate hematoma and inject local anaesthetic first
- If block resolves then Non-operative
- If block persists then Surgery
Quick Decision Guide
| Mason Type | Key Feature | Stability | Treatment |
|---|---|---|---|
| Type I | Non-displaced (less than 2mm) | Stable | Sling for comfort, Early ROM (start within 1 week) |
| Type II | Displaced greater than 2mm | Usually Stable | ORIF if mechanical block, otherwise conservative |
| Type III | Comminuted | Variable | ORIF (if less than 3 fragments) OR Replacement (if more than 3 fragments) |
| Type IV | + Dislocation | Unstable | Reduce, Fix/Replace Head, Repair LCL, Fix Coronoid |
BLOCKIndications for Surgery
| B | Block to motion Mechanical block after LA injection |
| L | Loose bodies Intra-articular fragments |
| O | Open fracture Requires washout/fixation |
| C | Complex instability Type IV (Terrible Triad) or Essex-Lopresti |
| K | Kill greater than 2mm displacement? Controversial - displacement alone not absolute indication |
| B | Block to motion Mechanical block after LA injection | C | Complex instability Type IV (Terrible Triad) or Essex-Lopresti |
| L | Loose bodies Intra-articular fragments | K | Kill greater than 2mm displacement? Controversial - displacement alone not absolute indication |
| O | Open fracture Requires washout/fixation |
Hook:If there's a BLOCK, you need to unlocking it (Surgery).
RCDTerrible Triad Components
| R | Radial Head Fracture Usually Type III/IV |
| C | Coronoid Fracture Usually Type I/II (Regan-Morrey) |
| D | Dislocation (LCL) Posterolateral dislocation |
| R | Radial Head Fracture Usually Type III/IV |
| C | Coronoid Fracture Usually Type I/II (Regan-Morrey) |
| D | Dislocation (LCL) Posterolateral dislocation |
Hook:RCD - Reality Check Required (It's worse than it looks)
MCEAssociated Injuries
| M | MCL Injury Assess valgus stability |
| C | Coronoid/Capitellum Associated fractures |
| E | Essex-Lopresti DRUJ injury + IOM tear |
| M | MCL Injury Assess valgus stability |
| C | Coronoid/Capitellum Associated fractures |
| E | Essex-Lopresti DRUJ injury + IOM tear |
Hook:MCE - Must Check Everything (Wrist, Medial side, CT)
Overview and Epidemiology
Mechanism of Injury
FOOSH (Fall on Outstretched Hand):
- Axial load + Valgus force leads to Radial Head impacting Capitellum.
- Pronation: Anterolateral fragment (most common).
- Extension: Posterior dislocation.
Demographics
- Most common adult elbow fracture (around 33% of elbow fractures, around 4% of all fractures)
- Median age around 43 years; no consistent sex predominance in population data
- Female fractures tend to be lower-energy (falls); male fractures younger and higher-energy
- Consider osteoporosis assessment in older patients with low-energy injury
Biomechanics
- Primary stabilizer: Radiocapitellar contact (60% load transfer)
- Secondary valgus stabilizer: Resists valgus if MCL is incompetent. Contributes 30% to valgus stability.
- Longitudinal stability: Prevents proximal migration of radius
The Secondary Stabilizer Concept
The radial head is a secondary stabilizer to valgus stress. If the MCL (primary stabilizer) is intact, the radial head is less critical for stability. If the MCL is torn (e.g., Mason IV), the radial head becomes critical to prevent valgus instability. Thus, excision is contraindicated in Mason IV or Essex-Lopresti.
Anatomy and Pathophysiology
Anatomical Structures
| Structure | Significance | Surgical Relevance |
|---|---|---|
| Safe Zone | 90-110° non-articulating arc | Place plates/screws here to avoid PRUJ impingement |
| LCL Complex | Lateral stabilizers | Often torn in Type IV - repair after head fixation |
| Posterior Interosseous Nerve (PIN) | Motor nerve to extensors | At risk during Kocher approach (pronate to protect) |
| Blood Supply | Radial recurrent artery | Retrograde flow - risk of AVN/Non-union in neck fractures |
Finding the Safe Zone
Intra-operatively, the Safe Zone can be identified by using reference marks:
- Radial Styloid (Lateral) corresponds to midpoint of safe zone in some citations, but unreliable.
- Lister's Tubercle alignment? Best Method: Mark the radial head in full pronation and supination relative to the sigmoid notch. The area that does not articulate with the lesser sigmoid notch of the ulna is the safe zone. Roughly corresponds to the lateral aspect of the head when forearm is in neutral.
The Kocher Interval
- The interval is between Anconeus (Radial N) and ECU (PIN).
- It is safe distally but the PIN crosses the radial neck proximally within the supinator.
- Pronation moves the PIN anteriorly, away from the surgical field, making the dissection safer.
Kaplan Interval
- Between ECU and EDC.
- Better access to anterolateral coronoid and anterior capsule.
- Higher risk to PIN and LCL if extended proximally.
- Often preferred for Terrible Triad injuries to access coronoid.
Classification Systems
Mason Classification (Modified by Broberg & Morrey)
| Type | Description | Stability | Treatment |
|---|---|---|---|
| Type I | Non-displaced (less than 2mm), no block | Stable | Conservative |
| Type II | Displaced greater than 2mm, partial head | Usually Stable | ORIF if block/large fragment |
| Type III | Comminuted entire head | Variable | Replacement (or ORIF if simple) |
| Type IV | Fracture + Ulnohumeral Dislocation (Terrible Triad likely) | Unstable | Surgery (usually Replacement + LCL repair) |
This classification is simple but guides surgical decision making effectively.
Clinical Assessment
History
- Mechanism: Fall on outstretched hand.
- Pain: Lateral elbow pain, worse with pronation/supination.
- Mechanical Sx: Locking or clicking (loose bodies).
- Wrist pain: Ask specifically! (Essex-Lopresti).
Examination
- Tenderness: Radial head, LCL origin, DRUJ (wrist).
- ROM: Assess flexion/extension and pro/supination.
- Mechanical Block: Hard stop vs pain inhibition.
- Stability: Valgus stress (MCL), Pivot shift (LCL).
The Aspiration Test
Pain inhibition can mimic a mechanical block.
- Aseptically aspirate hematoma from the 'soft spot'.
- Inject 5-10ml of Local Anaesthetic (Lignocaine/Marcaine).
- Re-examine ROM. Result: If full ROM returns = Type I (No block). If block persists = Type II (Mechanical Block) leads to Surgery.
Differential Diagnosis of Acute Lateral Elbow Pain after a Fall
| Condition | Discriminating Features | Key Investigation |
|---|---|---|
| Radial head fracture | Lateral tenderness, painful/blocked rotation, positive fat pad sign | AP/lateral + radiocapitellar view; CT if complex |
| Capitellum fracture (Hahn-Steinthal) | Anterior pain, double-arc sign on lateral, block to flexion | CT (often radiographically subtle) |
| Lateral collateral ligament injury / PLRI | Apprehension, positive pivot-shift, recurrent giving way | Examination under anaesthesia; MRI |
| Essex-Lopresti lesion | Radial head fracture PLUS wrist/DRUJ pain, proximal radial migration | Wrist radiographs, DRUJ stress, compare ulnar variance |
| Simple elbow dislocation (reduced) | Gross swelling, prior deformity, concentric reduction on film | Post-reduction radiographs; assess for fracture |
| Occult/non-displaced fracture | Effusion (fat pad sign) without visible fracture line | Repeat film at 7-10 days or CT/MRI |
Investigations
Imaging Protocol
AP, Lateral, Radiocapitellar (Greenspan) views.
- Look for: Cortical disruption, step-off, fat pad sign (sail sign).
- Check DRUJ context.
Indicated for:
- Comminuted fractures (Type III)
- Associated coronoid fractures
- Dislocation/Subluxation
- Surgical planning (ORIF vs Replacement)
Only for subtle ligamentous injury or occult fractures if CT equivocal. Mostly clinical diagnosis for ligaments.
Radiocapitellar View
The Radiocapitellar (Greenspan) View is taken with the beam angled 45 degrees to the shoulder. It profiles the radial head without overlap from the coronoid/ulna, making it excellent for detecting subtle fractures.
Management Algorithm
Indication: Type I, Type II without block
Protocol:
- Sling for comfort (max 3-5 days).
- Early Active ROM immediately as pain allows.
- Resolution of hematoma allows movement.
- X-ray at 1 week to check displacement.
Outcomes: Excellent (90-95%). Stiffness is main risk if immobilized too long.
Surgical Technique
ORIF Principles
- Approach: Kocher (between Anconeus and ECU) or Kaplan (between ECU and EDC).
- Protection: Pronate forearm to protect PIN (moves it medially away from field).
- Reduction: K-wires for temporary hold.
- Fixation: Mini-fragment screws (2.0/2.4mm) or Headless Compression Screws.
- Plate Position: Must be in Safe Zone (lateral aspect in neutral rotation).
- Check: Range of motion intra-op. Impingement?
Ensure anatomic reduction to prevent arthritis.
Kocher Interval
The Kocher Interval is between the Anconeus (Radial n.) and ECU (PIN). It is the true internervous plane? Actually, both are supplied by Radial nerve branches, but the plane is safe distally. Pronation moves the PIN anteriorly and away from the radial neck, increasing the safe zone for dissection.
Complications
Complications Management
| Complication | Incidence | Prevention/Management |
|---|---|---|
| Stiffness | 15-20% | Early ROM! Avoid prolonged immobilization (greater than 1 week). |
| Heterotopic Ossification | 5-10% | Gentle tissue handling. Indomethacin/Radiation if high risk. |
| PIN Palsy | 1-3% | Pronate during exposure. Retract gently anteriorly. |
| Implant Failure/Loosening | 5% | Safe zone placement. Avoid overstuffing replacement. |
| Proximal Radial Migration | Variable | Occurs after Excision if IOM incompetent (Essex-Lopresti). |
Postoperative Care
Rehab Protocol
Splint/Sling for comfort. Elevate. Start active ROM as soon as block/pain allows (usually Day 3-5). If LCL repaired: Elbow hinge brace needed.
Active Flexion/Extension, Pro/Supination. Avoid passive stretching (HO risk). Wean sling.
Start strengthening once union evident (ORIF) or soft tissue healed (Arthroplasty).
Full activity. Contact sports depend on fracture healing.
Outcomes
Prognostic Factors
| Factor | Impact | Explanation |
|---|---|---|
| Mason Type | High | Type I/II do better than Type III/IV |
| Associated Injuries | Critical | Dislocation or Coronoid fracture worsens prognosis significantly |
| Time to ROM | High | Early mobilization is key to preventing stiffness |
| Workers Comp | Moderate | Poorer subjective outcomes reported |
Replacement vs Excision
In a stable elbow with an intact MCL and interosseous membrane, pooled meta-analysis data show excision and replacement give similar Mayo Elbow Performance Scores and complication rates, with a slightly better arc after excision. Replacement is favoured where stability is needed (terrible triad, Essex-Lopresti) and in younger patients (long-term arthritis concern). Excision is reserved for low-demand, stable elbows.
Controversies & Areas of Uncertainty
The 'greater than 3 fragments' rule
Traditional teaching mandates arthroplasty once a head has more than 3 fragments. Recent series (Walsh 2022) show selected comminuted heads fixed by experienced surgeons achieve comparable QuickDASH/Broberg-Morrey scores. The fragment count is a guide, not an absolute.
Excision vs replacement
Despite widespread enthusiasm for arthroplasty, meta-analysis shows no clear superiority over excision in a stable, isolated Mason III elbow. Cost, implant availability and patient age drive the decision more than functional score.
Displacement threshold for surgery
The historical 2 mm step-off as a surgical trigger is not evidence-based; a true mechanical block (confirmed after aspiration/local anaesthetic) is the more reliable indication. Many displaced Mason II fractures do well non-operatively.
Routine MCL repair in terrible triad
Whether to repair the MCL after LCL repair and bony fixation is debated. Most protocols achieve stability with LCL repair alone; MCL repair or a hinged external fixator is reserved for residual instability tested intra-operatively.
Evidence Base
Standard Surgical Protocol for the Terrible Triad
- 36 consecutive elbow dislocations with radial head AND coronoid fractures treated with a sequential protocol (fix/replace radial head, fix coronoid, repair LCL +/- MCL +/- hinged external fixator).
- At mean 34 months: flexion-extension arc averaged 112 degrees, forearm rotation 136 degrees; mean Mayo Elbow Performance Score 88.
- Concentric stability restored in 34 of 36 elbows; 8 patients required reoperation.
Safe Zone Anatomy for Internal Fixation
- Cadaveric dissection defined an approximately 110-degree non-articulating arc of the radial head/neck safe for hardware.
- Provided reproducible intra-operative reference marks (neutral, full supination, full pronation) to localise the zone from a lateral approach.
- Hardware outside this zone risks impingement on the lesser sigmoid notch and loss of forearm rotation.
Early Mobilization in Simple Radial Head Fractures
- 180 patients with simple radial head fractures randomised to immediate mobilization, sling for 2 days then mobilization, or cast for 7 days.
- Both early-mobilization groups had better range of motion, strength and function than 7-day immobilization; benefit greatest in displaced fractures.
- A 48-hour delay before mobilization reduced early pain without compromising outcome; over 4 mm displacement or over 30 degrees angulation predicted worse results.
Failure Mechanisms of Metal Radial Head Replacement
- 44 patients (47 elbows) undergoing removal of a failed metallic radial head implant analysed.
- Most common reason for revision was painful loosening (31 elbows); stiffness, instability and over-lengthening (11 elbows) were also frequent.
- Degenerative change was present in all but one elbow; instability was not seen with bipolar implants.
Exam Viva Scenarios
Use these scenarios to practise clinical reasoning and management decisions
Scenario 1: Mason II Management
"A 35-year-old carpenter presents with a radial head fracture after a fall. X-ray shows a Type II fracture with 3mm displacement. He has limited pronation. Talk me through your management."
Scenario 2: Terrible Triad
"You are called to ED for a 40-year-old female with an unstable elbow after reduction of a dislocation. X-ray shows a comminuted radial head fracture and a coronoid tip fracture. How do you manage this?"
Scenario 3: Essex-Lopresti
"A patient with a comminuted radial head fracture also complains of severe wrist pain. X-rays of the wrist show ulnar positive variance. What is the diagnosis and management implication?"
MCQ Practice Points
Safe Zone
Q: What describes the 'Safe Zone' for radial head fixation? A: A 90-110 degree arc on the lateral aspect (in neutral) that does not articulate with the ulna. Hardware here avoids impingement.
Kocher Approach Nerve Risk
Q: Which nerve is most at risk during the Kocher approach to the radial head? A: Posterior Interosseous Nerve (PIN). It winds around the radial neck within the supinator. Pronation moves it anteriorly and safely away.
Valgus Stability
Q: The radial head is the secondary stabilizer against which force? A: Valgus force. The MCL is primary. Radial head is critical only if MCL is deficient.
Mason IV Treatment
Q: What is the treatment for a Mason IV fracture (Dislocation + Fracture)? A: Surgery. Requires reduction, stabilization of the head (Fix or Replace), and usually LCL repair. Excision is contraindicated due to instability.
Aspiration Test
Q: What is the purpose of aspirating a radial head fracture hematoma? A: To relieve pain and mechanical block caused by fluid pressure, allowing assessment of true mechanical block vs pain inhibition. Distinguishes surgical vs non-surgical Type II.
Guidelines, Registries & Global Practice
Global Epidemiology
- Around 33% of elbow fractures; around 1.7-5.4 per 10,000 per year in population studies.
- Median age around 43 years with no consistent sex predominance (Duckworth/Court-Brown cohort).
- Bimodal pattern: younger high-energy injuries vs older low-energy falls (osteoporosis subset).
- Roughly one third have associated injuries (coronoid, LCL, MCL, capitellum, DRUJ).
Society Guidance (Consensus)
- AO Foundation / AOTrauma: Mason-Johnston framework; ORIF for reconstructable, arthroplasty for unreconstructable, preserve the head when the elbow/forearm is unstable.
- BOA / BSSH (UK): Early mobilization for stable fractures; CT for complex patterns; specialist referral for instability.
- AAOS (US): No isolated radial-head-specific clinical practice guideline; management follows fracture-pattern and stability principles.
- EFORT / European consensus: Endorses safe-zone fixation and avoidance of over-stuffing in arthroplasty.
High- vs Limited-Resource Practice Variation
| Element | High-Resource Setting | Limited-Resource Setting |
|---|---|---|
| Imaging | CT routine for Mason III/IV and associated injuries | Plain films +/- radiocapitellar view; CT selectively |
| Unreconstructable head | Modular metal radial head arthroplasty | Radial head excision if elbow/forearm stable (cost/availability) |
| Terrible triad | Implant-based fixation + LCL anchors +/- hinged ex-fix | Suture/transosseous LCL repair; longer cast if implants scarce |
| Rehabilitation | Early supervised therapy | Self-directed early active motion programmes |
Registry Note
Unlike hip and knee arthroplasty, radial head replacement is not robustly captured by national joint registries (NJR, AJRR, AOANJRR, SHAR), so the evidence base rests on institutional series and meta-analyses rather than registry survivorship. Quote this if asked why implant-survival data for radial head prostheses are weaker than for hip/knee.
RADIAL HEAD FRACTURES
Clinical summary
Classification (Mason)
- •Type I: Non-displaced (less than 2mm)
- •Type II: Displaced partial head
- •Type III: Comminuted
- •Type IV: Associated Dislocation
Key Concepts
- •Secondary Valgus Stabilizer
- •Safe Zone (110° arc)
- •Aspiration Test for Block
- •Terrible Triad (Head + Coronoid + D/L)
Surgery Indications
- •Mechanical Block (Type II)
- •Open Fracture
- •Type III/IV (Instability)
- •Essex-Lopresti Association
Treatment Options
- •Type I: Early ROM (less than 1 wk)
- •Type II: ORIF (Headless screws)
- •Type III: Replacement (Metal)
- •Excison: ONLY if stable (Rare)
Complications
- •Stiffness (Most common)
- •PIN Nerve Palsy
- •HO (Heterotopic Ossification)
- •Implant Loosening