A 35-year-old woman with a Monteggia fracture (proximal radius fracture with anterior radial head dislocation) is compared to a 40-year-old man with a Galeazzi fracture (distal radius fracture with dorsal ulnar head dislocation). Which radiological finding is the most reliable way to differentiate these two injuries on anteroposterior and lateral forearm radiographs?

Explanation

## Radiological Differentiation of Monteggia and Galeazzi ### The Radial Head–Capitellum Line **Key Point:** On the lateral radiograph, the radial head must always align with the capitellum of the humerus. In Monteggia, the radial head is displaced *anteriorly* (out of alignment with capitellum). In Galeazzi, the radial head remains in normal alignment with the capitellum because the dislocation is at the distal radioulnar joint (DRUJ), not the proximal radioulnar joint. ### Comparison Table: Radiological Features | Radiological Finding | Monteggia | Galeazzi | |----------------------|-----------|----------| | **Radial head–capitellum alignment (lateral view)** | **Disrupted** (anterior dislocation) | **Preserved** | | **Fracture location** | Proximal/middle radius | Distal radius | | **DRUJ on lateral view** | Normal | **Disrupted** (dorsal ulnar head) | | **Radial bow** | May be preserved or lost | **Severely disrupted** | | **Key discriminator** | Proximal radioulnar joint pathology | Distal radioulnar joint pathology | ### Why This Feature Discriminates **High-Yield:** The radial head–capitellum alignment is the **most reliable single radiological sign** because: 1. It is visible on a single lateral view 2. It directly reflects the location of the dislocation (proximal vs. distal) 3. It is reproducible and objective ### Clinical Pearl **Clinical Pearl:** A mnemonic for remembering the anatomy: "The radial head must always point to the capitellum." If it doesn't on the lateral view, you have a proximal radioulnar joint problem (Monteggia). If the radial head is in place but the distal radioulnar joint is disrupted, you have Galeazzi. ### Mnemonic **Mnemonic:** **RHC** = **R**adial **H**ead–**C**apitellum line. If disrupted on lateral view → Monteggia (proximal pathology). If preserved → Galeazzi (distal pathology). [cite:Rockwood & Green's Fractures in Adults 9e Ch 42]