Mayo Classification — Olecranon Fractures

Overview — Olecranon Fractures

Olecranon fractures are intra-articular fractures of the proximal ulna involving the trochlear notch — the articular surface that engages the humeral trochlea in the humeroulnar joint. They account for approximately 10% of all elbow fractures and occur in a bimodal distribution: younger patients from high-energy trauma (direct fall onto the elbow, road traffic accidents) and elderly patients from low-energy falls onto an extended elbow. The olecranon is the site of the triceps tendon insertion — the main elbow extensor — making olecranon fractures functionally significant (loss of active elbow extension if the extensor mechanism is disrupted). The Mayo classification (Morrey, modified by Chadha 2014) grades olecranon fractures by stability (displacement + comminution) and directly guides management from non-operative treatment to tension band wiring to plate fixation.

Anatomy: the olecranon forms the posterior aspect of the proximal ulna and the posterior wall of the trochlear notch; the trochlear notch is the semilunar articular surface of the ulna that grips the humeral trochlea; the olecranon tip is the most prominent posterior elbow structure (the `funny bone`); the triceps tendon inserts onto the posterior surface of the olecranon; the ulnar nerve passes through the cubital tunnel immediately posterior to the medial epicondyle and immediately medial to the olecranon — it must be identified and protected in olecranon surgery; the olecranon bursa overlies the olecranon tip (olecranon bursitis from direct impact can mimic a fracture clinically)
The `stress riser` problem: the olecranon fracture has a unique problem — the tension band wire (TBW), the most commonly used fixation, undergoes progressive failure over time; the TBW works well for simple transverse fractures but fails for comminuted and oblique patterns; the K-wires of the TBW commonly migrate proximally (through the triceps tendon or superficially under the skin), requiring removal in up to 50–70% of patients; this is the most common complication of olecranon TBW and is a classic examination topic

Mayo Classification (Morrey)

Mayo Type	Stability	Displacement	Comminution	Description	Management
Type I — Stable	STABLE — the forearm does not sublux relative to the humerus	<2 mm displacement	A = non-comminuted; B = comminuted	An undisplaced or minimally displaced (<2 mm) olecranon fracture; the forearm is stable (no subluxation or dislocation of the ulna relative to the humerus); the extensor mechanism may be intact (the patient can perform a straight-leg raise of the elbow against gravity); the periosteum and anterior capsule are intact	Non-operative — above-elbow plaster/splint with the elbow in 60–90° of flexion; 3 weeks immobilisation; then progressive mobilisation; repeat X-ray at 1 week to confirm no displacement; non-operative is appropriate only if the extensor mechanism is intact (patient can extend the elbow against gravity) and the fracture is truly undisplaced on stress X-ray
Type II — Stable + Displaced	STABLE — the forearm is stable	>2 mm displacement	A = non-comminuted; B = comminuted	A displaced olecranon fracture (>2 mm step-off) without instability of the forearm; the humeroulnar joint is stable (the forearm does not sublux); the extensor mechanism is disrupted by the displacement; the triceps pulls the proximal olecranon fragment proximally; the IIA (non-comminuted, transverse) is the classic tension band wiring indication; IIB has comminution that precludes tension band wiring	Type IIA (non-comminuted): TENSION BAND WIRING (TBW) — the standard treatment; 2 parallel K-wires through the olecranon (one in the medullary canal + one in the lateral cortex OR two intramedullary) + a figure-of-eight tension band wire encircling the K-wires anteriorly and through the triceps tendon; the TBW converts the tensile extensor pull into compression at the articular surface; Type IIB (comminuted): PLATE FIXATION (3.5 mm LCP or reconstruction plate applied to the posterior surface of the olecranon/proximal ulna) — TBW fails in comminuted fractures because the comminuted fragments do not support the wire configuration; a plate bridges the comminuted zone
Type III — Unstable + Displaced	UNSTABLE — the forearm is subluxed or dislocated relative to the humerus	Significant displacement	A = non-comminuted; B = comminuted	A displaced olecranon fracture WITH associated forearm instability — the humeroulnar joint is disrupted; the forearm subluxes or dislocates from the humerus; this occurs because the coronoid and the medial/lateral collateral ligaments are also disrupted; Type IIIA may be a `trans-olecranon fracture-dislocation` (a complex injury where the forearm bones dislocate anteriorly while the olecranon fracture is present — the opposite of a posterior dislocation); the key distinction from Type II is the FOREARM INSTABILITY — test by checking the humeroulnar joint relationship on fluoroscopy	PLATE FIXATION is always required for Type III; TBW is INSUFFICIENT for unstable fractures (cannot control the forearm instability); a posterior ulnar plate (3.5 mm LCP) is applied from the proximal olecranon to the ulnar shaft, spanning the entire fracture zone; associated coronoid fracture, radial head fracture, and ligamentous injuries must be addressed (the terrible triad protocol if applicable); hinged external fixator may be added if instability persists after fixation

Tension Band Wiring vs Plate Fixation

Feature	Tension Band Wiring (TBW)	Plate Fixation
Indication	Mayo Type IIA (displaced, non-comminuted, stable); simple transverse fracture pattern; the classic olecranon TBW indication	Mayo Type IIB (comminuted) and ALL Type III (unstable); oblique fractures; fractures with proximal ulnar involvement; trans-olecranon fracture-dislocations
Principle	Converts tensile extensor force into articular surface compression (same principle as patellar TBW); dynamic fixation — compression increases with elbow flexion	Provides rigid angular-stable fixation across the fracture; resists bending, shear, and torsional forces; bridges comminuted zones; controls forearm instability
Complication	K-wire MIGRATION (most common — 50–70% of patients; K-wires back out proximally through the triceps or subcutaneously); prominence → skin irritation → planned removal at 12 months after union	Plate prominence (the posterior ulnar surface has minimal soft tissue coverage — the plate is palpable and may cause pain and skin breakdown); wound healing complications; stiffness from extensive dissection
Hardware removal	Planned removal in 50–70% (K-wire migration); removal under LA in clinic or GA	Elective removal if symptomatic; the plate is thick and palpable posteriorly; some surgeons routinely offer removal at 12–18 months; modern low-profile plates reduce this complication

Exam Pearls

Mayo classification: I (stable, <2 mm — non-op); II (stable, >2 mm — IIA non-comminuted = TBW; IIB comminuted = plate); III (unstable — always plate); A = non-comminuted, B = comminuted
TBW indication: Mayo Type IIA only (displaced, non-comminuted, stable, transverse pattern); TBW fails for comminuted, oblique, and unstable fractures
K-wire migration: the most common complication of TBW; proximal K-wire migration through the triceps = pain and prominence; occurs in 50–70% of patients; planned removal at 12 months; warn patients pre-operatively
Type III (unstable): always plate; associated with trans-olecranon fracture-dislocation (anterior dislocation of the forearm in the context of olecranon fracture); the terrible triad protocol applies if coronoid + radial head are also fractured
Ulnar nerve: runs in the cubital tunnel posterior to the medial epicondyle; immediately adjacent to the olecranon surgical field; must be identified and protected during posterior elbow approaches; ulnar nerve neuropathy is a complication of olecranon fixation if the nerve is not protected
Excision of the proximal olecranon fragment: in elderly osteoporotic patients with a comminuted Mayo IIB fracture where ORIF is technically not feasible, excision of the proximal fragment + triceps advancement (re-attachment of the triceps to the residual olecranon/proximal ulna) is an alternative; contraindicated if >50% of the trochlear notch is involved (creates elbow instability)
Articular congruency: the goal of all olecranon fixation is to restore the articular surface of the trochlear notch to <2 mm step-off; articular incongruency leads to post-traumatic humeroulnar arthritis; this is particularly important in Type III trans-olecranon fracture-dislocations where the entire trochlear notch may be involved

Mayo Classification — Olecranon Fractures

References

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