What is the recommended injection site and technique for a tarsal tunnel injection?

Tarsal Tunnel Injection Site and Technique

The recommended injection site for tarsal tunnel syndrome is posterior to the medial malleolus, with the foot positioned in neutral position to maximize tarsal tunnel compartment volume and minimize pressure on the posterior tibial nerve.

Anatomical Considerations

The tarsal tunnel is a fibro-osseous tunnel located on the medial side of the ankle, beneath the flexor retinaculum. This tunnel contains:

• Posterior tibial nerve and its branches (medial plantar, lateral plantar, and calcaneal branches)
• Posterior tibial vessels
• Tendons of the tibialis posterior, flexor digitorum longus, and flexor hallucis longus muscles

Optimal Injection Site Selection

When selecting the injection site for tarsal tunnel syndrome:

• Location: Target the area posterior to the medial malleolus where the posterior tibial nerve passes through the tarsal tunnel
• Site preparation:
  • Select a site free from veins, lesions, heavy hair, bruises, scars, and muscle ridges 1
  • Clean the site with antiseptic swab using circular motion from center to outside 1
  • Allow site to dry thoroughly before administering injection 1

Proper Foot Positioning

Research demonstrates that foot positioning significantly affects tarsal tunnel compartment volume:

• Neutral position: Provides maximum tarsal tunnel volume (21.5 ± 0.9 cm³) 2
• Eversion: Decreases volume to 18.0 ± 0.9 cm³ 2
• Inversion: Decreases volume to 20.3 ± 1.0 cm³ 2

Therefore, maintaining the foot in neutral position during injection maximizes compartment volume and minimizes pressure on the nerve, potentially improving injection efficacy 2.

Injection Technique

1. Patient positioning:

   • Place the patient in a supine or lateral position with the affected foot accessible
   • Position the foot in neutral alignment (not everted or inverted) 2

2. Needle insertion:

   • Use a 25-27 gauge needle
   • Rest the ankle on a firm, well-lit surface 1
   • Stretch the skin slightly 1
   • Insert the needle posterior to the medial malleolus at a 45-60° angle
   • Advance the needle until positioned near (but not into) the posterior tibial nerve

3. Medication administration:

   • Inject the medication slowly
   • Typical injectates include corticosteroids to reduce edema and inflammation 3
   • Remove the needle without pressing the area 1
   • If blood or fluid is present, blot site lightly with gauze or cotton ball 1

Clinical Considerations

• Diagnostic value: Positive response to injection may help confirm the diagnosis of tarsal tunnel syndrome
• Therapeutic benefit: Corticosteroid injections into the tarsal tunnel can reduce edema and provide symptomatic relief 3
• Caution: Avoid direct injection into the nerve to prevent nerve damage
• Follow-up: Evaluate response to injection to guide further management decisions

Common Pitfalls to Avoid

1. Incorrect foot positioning: Eversion or inversion decreases tarsal tunnel volume and may increase pressure on the nerve 2
2. Improper needle placement: Too deep insertion risks nerve damage
3. Failure to identify anatomical variations: Accessory muscles or space-occupying lesions may alter the anatomy 4
4. Inadequate aseptic technique: Increases infection risk
5. Multiple repeated injections: May cause tissue atrophy or nerve damage

Remember that while injections may provide temporary relief, they are often part of conservative management. If symptoms persist despite conservative measures including injections, surgical decompression may be necessary, with success rates varying from 44% to 96% 3.