A 32-year-old male carpenter from Delhi presents with a 3-day history of progressive swelling and severe pain in his right palm, particularly in the thenar region. He recalls a puncture wound from a rusty nail over the thenar eminence 4 days ago. On examination, the thenar eminence is tense, erythematous, and warm. There is severe pain on passive abduction of the thumb. Flexion of the thumb is weak and painful. Which anatomical space is most likely involved in this infection?

Explanation

## Clinical Presentation Analysis **Key Point:** The thenar space is a potential space between the adductor pollicis (posteriorly) and the flexor pollicis brevis and opponens pollicis (anteriorly). Infection in this space presents with swelling and tenderness over the thenar eminence, pain on passive thumb abduction, and weakness of thumb flexion. ## Anatomical Considerations | Feature | Thenar Space | Central Palmar Space | Hypothenar Space | |---------|--------------|----------------------|-----------------| | **Boundaries** | Adductor pollicis (post), FPB + OPP (ant) | Between flexor tendons, lumbrical fascia | Hypothenar muscles | | **Clinical sign** | Pain on thumb abduction | Swelling of entire palm | Swelling over hypothenar eminence | | **Thumb involvement** | Thumb flexion weak/painful | Fingers 2–5 affected | Spared | | **Entry point** | Thenar eminence puncture | Central palm puncture | Hypothenar eminence puncture | ## Why This Is Thenar Space Infection 1. **Anatomical entry:** Puncture wound directly over thenar eminence → direct inoculation into thenar space 2. **Clinical signs:** Pain on passive thumb abduction is pathognomonic — abduction stretches the adductor pollicis, which forms the posterior boundary of the thenar space 3. **Motor deficit:** Weakness of thumb flexion indicates involvement of flexor pollicis longus (FPL) tendon, which runs through the thenar space 4. **Localized swelling:** Thenar eminence swelling, not diffuse palmar swelling **Clinical Pearl:** Thenar space infections can track proximally into the forearm via the carpal tunnel and along the FPL sheath (radial bursa), leading to serious forearm cellulitis if untreated. Early drainage is essential. **High-Yield:** The **"pain on passive abduction of thumb"** is the cardinal clinical sign that distinguishes thenar space infection from other palmar space infections.