A 62-year-old woman presents with a small, firm, irreducible swelling in the groin below the inguinal ligament. On examination, the swelling is tender and the overlying skin is erythematous. What is the most common site of femoral hernia within the femoral sheath?

## Anatomical Sites of Femoral Hernia ### Femoral Sheath Compartments The femoral sheath is divided into three compartments by septa: | Compartment | Contents | Boundaries | Hernia Site | |-------------|----------|-----------|-------------| | **Lateral** | Femoral artery | Lateral wall of sheath | Rare | | **Middle** | Femoral vein | Between artery & vein | Uncommon | | **Medial (Femoral Canal)** | Lymph node (node of Cloquet) | Bounded by lacunar ligament medially | **Most common** | ### Why the Femoral Canal? **Key Point:** The femoral canal (medial compartment) is the **most common site** because: 1. **Widest space** — Offers the least resistance to herniation 2. **Weakest boundary** — The lacunar ligament is the medial margin; it is relatively thin and lax 3. **Anatomical funnel** — The femoral ring (entrance) is narrow, but the canal widens distally, creating a natural weak point 4. **Pressure dynamics** — Increased intra-abdominal pressure is transmitted directly into this space ### Anatomical Landmarks ```mermaid flowchart TD A["Inguinal ligament"]:::outcome B["Femoral sheath"]:::outcome C["Femoral canal<br/>(Medial compartment)"]:::action D["Lacunar ligament<br/>(Medial boundary)"]:::outcome E["Femoral artery<br/>(Lateral compartment)"]:::outcome F["Femoral vein<br/>(Middle compartment)"]:::outcome A --> B B --> C B --> E B --> F C --> D D -->|Weak point| C style C fill:#90EE90 style D fill:#FFB6C1 ``` ### Clinical Pearl **High-Yield:** Femoral hernias present **below the inguinal ligament and medial to the femoral artery**. The swelling emerges through the femoral ring (bounded by the inguinal ligament superiorly and lacunar ligament medially) into the femoral canal. The narrow femoral ring creates a **high risk of incarceration and strangulation** — up to 40–45% of femoral hernias become incarcerated, compared to 10% for inguinal hernias. ### Clinical Presentation Femoral hernias are often: - **Small and firm** (due to the narrow ring) - **Tender** (especially if incarcerated) - **Below the inguinal ligament** (key distinguishing feature from inguinal hernia) - **Medial to the femoral artery** (palpable landmark) - **More common in women** (wider pelvis, more lax ligaments) **Mnemonic: CANAL** — **C**ompartment medial, **A**natomy weak, **N**arrow ring, **A**lways at risk, **L**acunar ligament boundary.