Case Study: Ankle Pain Misdiagnosis – Sural Nerve Entrapment Mimicking Achilles Tendinopathy

Our Patient

Our patient is a 42 year-old male recreational runner complaining of posterior heel pain. His symptoms – pain during running and stair climbing, tenderness upon palpation, and early morning stiffness – had persisted for the past 8 months. He had a history of running overload.

The Challenge

The patient had sought treatment at another clinic, with no satisfactory results. Based on reported symptoms and MRI results, he had been diagnosed with mid-portion Achilles tendinopathy, and treated with conservative care,

His treatment protocol included:

• 6 sessions of shockwave therapy directed at the Achilles tendon
• TECAR radiofrequency therapy
• Physical therapy, including progressive eccentric loading of the Achilles – a standard protocol for Achilles tendinopathy

Despite treatment, his symptoms persisted, and even worsened slightly after shockwave therapy.

Our Diagnostic Process

During the clinical exam, we questioned the patient to obtain more details about the quality and distribution of his pain. He described the pain as “burning and sharp,” and radiating toward the lateral foot. The foot was hypersensitive to pressure from socks and footwear, and he reported nighttime discomfort. An inverted ankle stretch worsened his pain symptoms.

A focused physical exam revealed:

• A mildly thickened Achilles tendon.
• Absence of central tenderness, but marked tenderness 1-2 cm lateral to the tendon.
• Positive Tinel sign – a diagnostic test for nerve compression – posterior to the lateral malleolus (the knob-like bone on the outside of the ankle).
• Sensitivity to light touch.
• Pain reproduced by tension applied to the sural nerve.

At this point we suspected sural nerve entrapment.

Diagnostic ultrasonography confirmed our suspicions:

• Focal enlargement at the lateral ankle.
• Hypoechoic fascicles, with loss or normal crispness.
• Mild perineural edema.
• Symptoms reproduced with sonopalpation.
• Pain reproduced with dynamic inversion and dorsiflexion.

The sural nerve appeared to be entrapped at the fascial crossing, posterior to the lateral malleolus, with symptoms mimicking Achilles tendinopathy.

Our Treatment Protocol

To release the nerve and restore gliding, we performed an ultrasound-guided hydrodissection procedure. We positioned the needle superior to the nerve and injected a 5% dextrose solution (D5W), with a small amount of hyaluronic acid. The procedure successfully released the nerve, resulting in immediate pain relief.

Results

The patient saw a 70% improvement within 48 hours, and reported 90-100% pain resolution at the 2-week follow-up. He was able to return to a progressive running program, and was completely asymptomatic at the 3-month follow-up.

Discussion

Prior to visiting our clinic the patient had sought treatment elsewhere, where he received shockwave and radiofrequency therapy, and physical therapy. Due to misdiagnosis, the shockwaves were directed at the Achilles tendon, and not the nerve, failing to provide relief. Radiofrequency therapy provided minor temporary relief, but was ineffective in decompressing the nerve. During physical therapy, the eccentric loading protocol increased tension on the nerve, exacerbating irritation.

Rather than proceeding with the initial diagnosis, we took a closer look at the pain quality and location, and used dynamic ultrasonography to uncover the true pathology – an entrapped sural nerve.

Key Takeaways

Doctors are often quick to diagnose posterior heel pain as Achilles tendinopathy, and in this case, abnormal MRI results — which are common in asymptomatic runners — contributed to the misdiagnosis. When the problem is neural entrapment, treatment directed at the tendon is bound to fail.

In our case, proper and thorough diagnosis backed by dynamic ultrasonography led to appropriate and successful treatment, with a single injection completely resolving the patient’s condition.