Tarsal tunnel syndrome is the ankle’s version of carpal tunnel: the posterior tibial nerve compressed where it passes through a tunnel with a bony floor and a fibrous roof. Dr. Gisele J. Girault teaches all three tunnels on the same principle — a relatively superficial nerve, a roof of ligament or retinaculum, and a syndrome that develops when the space inside gets smaller.
What separates tarsal tunnel from its upper-limb equivalents is not the mechanism but the results. Girault is candid about it: “I do find greater success with carpal tunnel and cubital tunnel as opposed to with tarsal tunnel.” Understanding why is most of what makes the diagnosis useful.
This reference covers the anatomy, who develops it, how it is distinguished from plantar fasciitis, what the nerve study contributes, and the injection approach. It sits under our clinical reference to joint and extremity injection.
The tarsal tunnel: floor, roof and contents
Dr. Robert Stall describes the structure precisely. The tibial nerve enters the tunnel posterior to the medial malleolus. The tunnel is formed by a bony floor and a connective tissue roof: the floor is a concave surface made by the medial aspect of the tibia, talus and calcaneus; the roof is the flexor retinaculum, which spans obliquely between the medial malleolus and the medial tubercle of the calcaneus.
Girault notes what travels through it alongside the nerve — the artery and the vein — which is relevant both to why fluid states compress it and to what a needle must avoid.
The nerve itself is a major one. Stall describes the tibial nerve as one of the two terminal branches of the sciatic nerve, carrying axons from the L4 to S3 spinal nerves and providing motor and sensory innervation to most of the posterior leg and foot. Within the tunnel it divides into the medial and lateral plantar nerves, and it gives rise to the medial calcaneal nerve supplying the plantar surface of the heel — which is why heel pain can be part of the picture.
Three entrapment sites, not one
Stall teaches that the tibial nerve has more than one vulnerable point along its course, and a patient who fails treatment at the ankle may have been compressed higher up.
- The soleus hiatus — in the midline of the calf, approximately four finger-breadths below the popliteal crease, in the tendon of the soleus muscle
- The “high tarsal tunnel” — a few centimetres proximal to the medial malleolus, a friction point between the tendon of the soleus and the flexor hallucis longus. Stall flags that this is a colloquial term which does not appear in formal anatomical literature, so it will not be found described that way in a textbook
- The tarsal tunnel proper — at the medial ankle, beneath the flexor retinaculum
Even within the tunnel itself, one point is often not enough. Stall teaches palpating both proximal and distal to the flexor retinaculum, because entrapment points can occur on either side of it, and both may need treating for the best clinical result.
Who develops tarsal tunnel syndrome
Girault’s three populations all narrow the tunnel from the inside rather than injuring it from the outside.
Diabetes. The commonest association in her practice, and the one that complicates treatment most.
Obesity. A consistent finding in the patients she sees with the diagnosis.
Lower extremity oedema. Any cause of swelling in the legs. As she puts it, patients “can develop tarsal tunnel just because the tunnel has gotten narrowed because of all the fluid” they are carrying — the same mechanism that produces carpal tunnel symptoms in pregnancy.
Oedema is worth noticing because it is often treatable in itself. A tunnel narrowed by fluid can be widened by addressing the fluid.
Tarsal tunnel or plantar fasciitis: the distinguishing feature
These two are confused constantly, and Girault explains why: the pain and symptoms “tend to be in a very similar distribution.”
Tarsal tunnel pain sits around the medial malleolus of the ankle and runs down along the plantar surface — overlapping substantially with where plantar fasciitis is felt.
Her separating finding is numbness: “with tarsal tunnel, you tend to see more numbness. With plantar fasciitis, you usually don’t see numbness. So that might be one distinction.”
That is the single most practical differentiator available at the bedside, because it follows directly from the mechanism. A compressed nerve produces sensory symptoms; an inflamed and degenerated fascia produces pain on load. The fascial diagnosis is covered in plantar fasciitis injection.
Forefoot pain pointing to one interspace with a palpable nodule is a different problem again — see Morton’s neuroma.
What the nerve conduction study contributes
Girault notes that EMG and nerve conduction testing can confirm tarsal tunnel in the same way it confirms carpal and cubital tunnel.
Jim Lewis R. NCS.T, CNCT puts the tibial nerve in perspective in his course — among the conditions the tibial nerve is tested for, tarsal tunnel is effectively the one. The study records at the medial malleolus, with the navicular bone as the palpable landmark.
The refinement he describes matters where the diagnosis is uncertain. Because the tibial nerve splits into the medial and lateral plantar nerves at this level, recordings can be taken over the abductor hallucis and over the abductor digiti minimi in the foot and compared, separating the two branches rather than treating the nerve as a single unit.
One caution applies with force here. In a diabetic patient, a background peripheral neuropathy makes a superimposed focal compression harder to identify — the slowing gets attributed to the neuropathy and the treatable component at the tunnel goes unrecognised. The same problem in the hand is discussed in carpal tunnel electrodiagnostic testing.
Injection technique and realistic expectations
Girault positions the patient supine with the foot rotated outward, exposing the medial ankle, and palpates the medial malleolus to orient.
The approach is deliberately shallow. She is explicit that she is not trying to pass under the retinaculum — the needle goes in at roughly 45 degrees, just beneath the skin, targeting the area posterior to the flexor retinaculum and the flexor tendon. The volume is about one to one and a half cc of a 50/50 steroid and lidocaine mixture. The inflammatory component she is treating is usually in the retinaculum itself, often from overuse.
Two rules apply absolutely: do not hit the nerve, and do not inject into the tendons.
Her honesty about results is the most useful part of the teaching. Relief is common but less reliable than at the wrist or elbow, and the reason is usually the company the diagnosis keeps: “a lot of times with tarsal tunnel, there’s also a component of diabetic neuropathy involved, which can be very difficult to treat.” She describes inheriting many of these patients from podiatry, after the non-injection options have been exhausted.
Where the neuropathic component dominates, the treatment shifts from the tunnel to the whole foot — Girault blocks the five nerves of the ankle for diabetic peripheral neuropathy rather than injecting a single focal target.
For clinicians
Medial ankle injection places a needle beside a nerve, an artery and a vein in a confined space, and is learned on live anatomy with supervision. This reference carries no needle depths or trajectories for that reason. Empire teaches the foot and ankle injections and the ankle block across the pain management academy.
Learn blocks with your hands, not from a page
Empire’s Pain Management Training (THE Pain Show) is accredited for 25.25 AMA PRA Category 1 Credits™, jointly provided by AKH, Inc, and Empire Medical Training. For narrower peripheral work, Joint, Extremity and Non-Spinal Injection Training carries 6.75 credits for the complete in-person hybrid program, and Advanced Musculoskeletal Ultrasound Guided Injections builds the guidance skills above.
Explore THE Pain Show
Claim Your Prize!