I get asked this a lot in clinic when it comes to ankle pain that does not finish settling after a sprain. A patient walks in 8 to 12 weeks after a typical inversion sprain. They did the textbook things. Rest, ice, compression, elevation. They worked through the standard sprain rehabilitation programme. The swelling has gone, the bruising has faded, and on flat ground the ankle behaves itself. But the moment they walk on grass, sand, or step off a kerb, the lateral ankle protests. The ankle feels weak, sometimes unsteady, and there is a small spot just in front of the bony bump on the outside of the ankle that aches with direct pressure. The rehab they have been told to keep doing is not changing anything.
If that sounds like your situation, the question worth asking is whether you are dealing with ankle instability at all. The pattern fits sinus tarsi syndrome, a small inflamed tunnel just below the bony bump on the outside of the ankle that does not feature in any of the standard ankle sprain rehab programmes. It is a different problem from a chronic ankle sprain, and the management plan it needs is different too.
I see this every now and then in clinic, and that is because it is often missed in the first few months after a sprain. The lateral ankle is taken up with so much sprain rehabilitation work that everyone, including the patient, assumes more rehab will eventually fix it. So here is how I help my patients tell the two apart, in the order they usually ask the questions.
First, why would my "unstable" ankle not actually be unstable?
When you stand on uneven ground, your brain has to know where your ankle is in space. That sense of position comes from sensory nerve endings in the joints and ligaments around the ankle. The sinus tarsi, the small tunnel just below the outer ankle bone, is packed with those nerve endings. It is genuinely one of the most sensory-rich spots in the lower limb.
When an inversion ankle sprain damages the tissues in the sinus tarsi, the sensory feedback going up to your brain gets disrupted. Your brain stops getting a clear reading of where your ankle actually is in space. And the brain interprets that uncertainty as instability. The ankle is not structurally lax. The ligament is testing fine. But the feeling is one of weakness and a wobble, particularly on uneven ground where the sensory feedback is most useful.
In fact, that is the first thing I explain to my patients when we get to this point in the consult: an ankle can feel unstable without being structurally lax. The sensation is real. The mechanism is just not the ligament.
Where should the pain actually be sitting?
Pull up the side of your foot and look at the outside of your ankle. There is the bony bump (the lateral malleolus) about halfway up the lateral side. About 1 to 2 fingers below that bump, slightly toward the front of the foot, is a soft little dimple. Press into it firmly with your thumb. If your familiar ankle pain reproduces from that pressure, you are in sinus tarsi territory.
Compare that to a chronic ankle sprain or lateral ligament problem. Chronic sprain pain sits over the ligament itself, which lives just below and slightly behind the bony bump. It is a different exact location, but only by a finger's width. The difference is small but the diagnoses are not.
The single most useful clinical sign I rely on is the dimple pressure test. If pressing into the dimple reproduces the patient's pain, sinus tarsi syndrome moves up the differential and a chronic sprain moves down.
What movements should be hurting me?
Sinus tarsi syndrome flares on uneven ground. Patients tell me their pain worsens on grass, beach sand, cambered footpaths, and stepping off kerbs. The reason is the subtalar joint, which sits beneath the ankle joint and works much harder on uneven ground. Loading the subtalar joint loads the sinus tarsi, and the pain follows.
Compare that to a true chronic ankle sprain, which presents with episodes of the ankle actually giving way. You will land funny, your ankle will roll, and you will have to catch yourself. Sinus tarsi syndrome does not really do that. It feels wobbly but does not actually give way.
That is a useful pattern to test against your own experience. If you have actually rolled the ankle since the original sprain, chronic ankle sprain is more likely. If the ankle has not actually rolled but feels like it might at any moment on uneven ground, sinus tarsi syndrome moves up.
What about the time pattern?
A regular acute ankle sprain has a relatively predictable recovery curve. The acute swelling settles in the first 2 to 4 weeks, the bruising fades by 6 weeks, and most patients are running pain-free by 8 weeks with mild residual stiffness at worst. By 12 weeks, almost all of the sprain-related symptoms should be gone.
If your sprain is past the 12-week mark and the lateral ankle still aches in the way I described above, that delay is the first red flag. It says: something specific is maintaining this pain, and more of the same rehab is not going to fix it. The 8 to 12 week window is where I expect to see sinus tarsi syndrome patients walking through the door, often after they have already tried another round of ankle rehab with no change.
Why isn't more rehab making it better?
The standard ankle sprain rehab targets the lateral ligaments. The work is calf raises, single-leg balance, peroneal strengthening, and progressive sport-specific drills. It is good rehab for a lateral ligament injury. The problem is that sinus tarsi syndrome is not a ligament injury.
What sinus tarsi syndrome actually needs is three things, in this order. First, offloading the subtalar joint so the inflammation in the tunnel can settle. That usually means custom orthotics built from a full biomechanical assessment, not off-the-shelf insoles. Second, proprioception work that targets the disrupted sensory feedback specifically, not the generic balance work prescribed for any ankle sprain. Third, where the inflammation has chronified, focused shockwave therapy to stimulate healing in the tissues of the tunnel itself.
So the rehab is not failing because you are doing it badly. It is failing because it was never designed for the problem you actually have.
Okay, what would you do this week if you were me?
If the pattern above sounds like your situation, the working diagnosis is sinus tarsi syndrome. The next step is not more ankle rehab. It is a thorough clinical reassessment that specifically tests the sinus tarsi: palpation of the dimple, subtalar joint testing, and a full biomechanical evaluation of how your foot is loading.
The management plan changes accordingly. You need a custom orthotic prescription that controls the subtalar position, a sinus tarsi-specific rehab programme that includes proprioception retraining, and where appropriate, focused shockwave therapy to settle the chronic inflammation in the tunnel. Most patients respond well over 3 to 6 months when the diagnosis is made early.
Where this is missed for too long, the disrupted sensory feedback compounds. You end up favouring the ankle, walking differently, and producing secondary problems further up the chain such as a sore knee or hip on the same side.
If your lateral ankle is not finishing healing the way it should, book a consultation with any of our podiatrists in Singapore at any of our three locations. The earlier the diagnosis lands, the faster the dimple settles.
