Case 3 | Left Foot Pain (2 Weeks): Peripheral Nerve Entrapment in the Context of Obesity and Prolonged Standing

1. Case Background

The patient is a 30-year-old Chinese female, working as a chef, with a body weight of 95 kg.

She presented with left foot pain lasting for approximately two weeks.

Pain characteristics:

• Pain occurs during walking and is intermittent

• One episode of significant exacerbation, during which she was unable to move for approximately two hours

• Pain is not constant

• No clear history of ankle sprain, fall, or direct trauma

On the surface, this appears to be a common presentation of “foot pain.” However, the pain pattern does not fully match typical ankle sprain or simple local soft-tissue strain, warranting further analysis.

2. Four-Level Thinking Analysis

🔵 Level 1 | Symptom Level – What are the symptoms?

At the symptom level, the presentation seems straightforward:

• Pain localized to the left foot

• Pain related to walking

• Short duration of symptoms

At this level, it is most easily categorized as:

• Local foot strain, gout, or small joint inflammation

• Ankle or soft tissue problem, ankle instability

However, in Four-Level Thinking, Level 1 focuses on recording phenomena rather than drawing conclusions, leaving room for deeper analysis.

🟡 Level 2 | Functional / Neurological Level – How does the pain behave?

Further examination revealed several key findings:

• Hyperalgesia in the painful area

• Subjective abnormal sensations described by the patient (e.g., “feels thick,” “feels different from normal”)

• Severe, sharp pain that does not resemble simple pressure pain or muscle strain

These features suggest:
👉 The pain is more consistent with neurological dysfunction, rather than a primary muscle or joint problem.

At this level, diagnostic thinking shifts from “structural pain” to neuropathic pain.

🟠 Level 3 | Structural / Mechanism Level – Which structure is responsible?

After excluding restricted ankle joint motion and obvious joint pathology, and based on neurological localization:

• Sensory disturbance and pain were mainly distributed over the distal lower leg and dorsum of the foot

• Marked tenderness was noted at Xuanzhong (GB39)

• Ankle muscle strength was symmetrical bilaterally, making common peroneal nerve involvement unlikely

Considering nerve distribution and physical findings, the diagnosis gradually focused on:

Superficial peroneal nerve entrapment

Palpation over common entrapment sites of the superficial peroneal nerve reproduced localized pain, completing the symptom–structure verification loop.

🔴 Level 4 | Background / Load Level – Why did this problem occur in this person?

This is the most critical level in this case.

The patient is approximately 175 cm tall and weighs about 95 kg, which is clearly above the ideal weight range.
She works as a chef and stands for approximately 8–12 hours per day, placing her lower limbs under sustained load.

Under this background, several important biomechanical factors are present:

• Excess body weight significantly increases continuous load on the lower limbs

• Prolonged standing maintains the lateral lower-leg fascia in a state of chronic high tension

• The sliding space of the nerve within the fascial tunnel becomes progressively restricted

Under the combined load of obesity and prolonged standing, even without obvious trauma, the following can occur:

• Chronic mechanical irritation of peripheral nerves

• Gradual accumulation of neural tension

• Final manifestation as localized foot pain

Therefore, the superficial peroneal nerve entrapment in this case is not an incidental event, but the result of:

Obesity and occupational prolonged standing
→ lower-limb biomechanical imbalance
→ peripheral nerve entrapment

This represents a complete causal chain.

3. Treatment Strategy

The treatment objective was clear:
To relieve mechanical entrapment of the superficial peroneal nerve within the fascial tunnel, while reducing ongoing load.

Treatment strategies included:

• Releasing fascia and soft tissues around the nerve entrapment area

• Reducing continuous mechanical irritation to the nerve

• Emphasizing lifestyle-level adjustments, especially:

  • Avoiding prolonged uninterrupted standing

  • Optimizing work–rest cycles

  • Weight management as a core long-term intervention

The focus of treatment was not short-term pain suppression, but changing the conditions under which the nerve is chronically overloaded.

4. Clinical Insight

The key of Four-Level Thinking is not identifying “where the nerve is trapped,”
but understanding “why this person developed entrapment at this site.”

In this case, if one stops at the structural diagnosis of “superficial peroneal nerve entrapment” and ignores the patient’s body weight and occupational standing load, recurrence is likely.
Only by placing obesity and long-term load at the core of the etiological framework does diagnosis and intervention become complete.