A 35-year-old male presents to his primary care physician with pain along the bottom of his foot. The patient is a long-time runner but states that the pain has been getting worse recently. He states that when running and at rest he has a burning and aching pain along the bottom of his foot that sometimes turns to numbness. Taking time off from training does not improve his symptoms. The patient has a past medical history of surgical repair of his Achilles tendon, ACL, and medial meniscus. He is currently not taking any medications. The patient lives with his wife and they both practice a vegan lifestyle. On physical exam the patient states that he is currently not experiencing any pain in his foot but rather is experiencing numbness/tingling along the plantar surface of his foot. Strength is 5/5 and reflexes are 2+ in the lower extremities. Which of the following is the most likely diagnosis?

Common fibular nerve compression

A 48-year-old male presents to his primary care provider with a two-week history of low back pain and left leg pain. He reports that his symptoms started while he was working at his job as a construction worker. He has since experienced intermittent achy pain over his lumbar spine. He has also noticed pain radiating into his left leg and weakness in left ankle dorsiflexion. On exam, he demonstrates the following findings on strength testing of the left leg: 5/5 in knee extension, 4/5 in ankle dorsiflexion, 4/5 in great toe extension, 5/5 in ankle plantarflexion, and 5/5 in great toe flexion. The patellar reflexes are 5/5 bilaterally. He is able to toe walk but has difficulty with heel walking. Weakness in which of the following compartments of the leg is most likely causing this patient’s foot drop?

Superficial posterior compartment

A previously healthy 33-year-old woman comes to the physician because of pain and sometimes numbness in her right thigh for the past 2 months. She reports that her symptoms are worse when walking or standing and are better while sitting. Three months ago, she started going to a fitness class a couple times a week. She is 163 cm (5 ft 4 in) tall and weighs 88 kg (194 lb); BMI is 33.1 kg/m2. Her vital signs are within normal limits. Examination of the skin shows no abnormalities. Sensation to light touch is decreased over the lateral aspect of the right anterior thigh. Muscle strength is normal. Tapping the right inguinal ligament leads to increased numbness of the affected thigh. The straight leg test is negative. Which of the following is the most appropriate next step in management of this patient?

Advise patient to wear looser pants

Blood work for inflammatory markers

Lower limb cross-sections for USMLE Step 1: High-Yield Anatomy Lessons

Thigh Cross-Section - Compartment Confidential

Axial cross-section of thigh showing muscle compartments

Overview: The thigh is divided into three fascial compartments by the intermuscular septa, each with its own muscle group, nerve, and blood supply.

Compartment	Action	Muscles (Primary)	Innervation	Artery
Anterior	Extend Knee	Quadriceps, Sartorius	Femoral n.	Femoral a.
Medial	Adduct Thigh	Adductors, Gracilis	Obturator n.	Profunda Femoris a.
Posterior	Extend Hip, Flex Knee	Hamstrings	Sciatic n. (Tibial div.)	Perforating aa.

-   **Femoral Triangle:** Gateway for major neurovasculature. 📌 **NAVEL**: **N**erve, **A**rtery, **V**ein, **E**mpty Space, **L**ymphatics (Lateral to Medial).
-   **Adductor Canal:** Conducts femoral vessels to the popliteal fossa.

⭐ Dual Innervation Alert: The Adductor Magnus is a hybrid muscle, receiving signals from both the Obturator nerve (adductor part) and the Tibial division of the Sciatic nerve (hamstring part).

Leg Cross-Section - Slicing the Shank

Axial cross-section of mid-leg with muscle compartments

Anterior Compartment: Dorsiflexion & inversion/eversion.
- Muscles: Tibialis anterior, Extensor hallucis longus (EHL), Extensor digitorum longus (EDL).
- N: Deep peroneal (fibular) n.
- A: Anterior tibial a.
- 📌 Mnemonic: "The Hospitals Are Not Dirty Places" (Tibialis ant., EHL, Ant. tibial a., Deep peroneal n., EDL, Peroneus tertius).
Lateral Compartment: Eversion & plantarflexion.
- Muscles: Peroneus (fibularis) longus & brevis.
- N: Superficial peroneal (fibular) n.
Posterior Compartment: Plantarflexion & toe flexion.
- Superficial Group: Gastrocnemius, Soleus.
- Deep Group: Tibialis posterior, Flexor hallucis longus (FHL), Flexor digitorum longus (FDL).
- N: Tibial n.
- A: Posterior tibial a.

⭐ The anterior compartment is the most common site for acute compartment syndrome, often due to tibial fractures. This is a surgical emergency requiring fasciotomy to prevent muscle and nerve necrosis.

Ankle & Foot Sections - Sole Survivor

Ankle (Tarsal Tunnel): Medial malleolus to calcaneus. Contents pass deep to flexor retinaculum.
- 📌 Mnemonic: Tom, Dick, And Very Nervous Harry
- Tibialis posterior tendon
- Flexor Digitorum longus tendon
- Posterior tibial Artery, Vein, & Nerve
- Flexor Hallucis longus tendon

Ankle cross-section showing tarsal tunnel contents

Sole of the Foot (Layers): Organized into four layers, crucial for understanding plantar infections and nerve blocks.

Layer	Key Contents
1st	Abductor hallucis, Flexor digitorum brevis, Abductor digiti minimi
2nd	Quadratus plantae, Lumbricals, FDL/FHL tendons
3rd	Flexor hallucis brevis, Adductor hallucis, Flexor digiti minimi brevis
4th	Interossei (DAB/PAD), Peroneus longus tendon

High‑Yield Points - ⚡ Biggest Takeaways

Thigh compartments are defined by fascia: anterior (femoral n.), medial (obturator n.), and posterior (sciatic n.).

Femoral triangle contents (NAVEL): From lateral to medial, find the Nerve, Artery, Vein, Empty space, and Lymphatics.

The adductor canal contains the femoral artery and vein, and the saphenous nerve.

Popliteal fossa contents from superficial to deep: Tibial Nerve, Popliteal Vein, Popliteal Artery.

Injury to the common fibular nerve at the fibular neck causes foot drop.

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Lower limb cross-sections