Impingement

When a piece of soft tissue becomes trapped between two pieces of bone. The two main types of impingement are: anterior (in the front of the ankle) and posterior (in the back of the ankle).

What is it?

Impingement is when soft tissue becomes pinched between the bones in a joint. In the ankle, there are two main types of impingement: anterior (in the front of the ankle) and posterior (in the back of the ankle).

Anterior impingement is usually caused by damaged ligaments (often the result of repeated sprains). Torn or damaged ligaments become thickened and get trapped between the tibia (shin bone) and the talus (central bone in the ankle) when the foot is pulled upwards.

Repeated injuries can also cause the ankle bones to form small projections called bone spurs. These can get caught in the soft tissue between the bones when the foot is pulled upwards. This condition is also known as footballer’s ankle.

Posterior impingement is usually caused by a small bone called the os trigonum becoming trapped between the soft tissue between the tibia (shin bone) and the top of the heelbone. Ballet dancers, who go up on pointed toes regularly, are very likely to suffer from this condition.

Posterior impingement can also be the result of ankle sprains: if the ankle is unstable due to slack or torn ligaments, the heelbone and the tibia can slip and trap soft tissue in between them, causing pain when the foot is pointed downwards.

How does it feel?

Anterior impingement: pain in the front part of your ankle, which is likely to feel worse as you pull your toes up towards you. You may also experience a clicking sensation in the front of your ankle when moving your foot up and down. Your ankle may also feel weak, as though you can’t trust it to remain stable during certain activities.

Posterior impingement: pain deep in the back of the ankle. There is usually tenderness by the anklebone on the outside of the ankle. Pain is usually worse when your foot is pointed down. You may also feel a painful clicking sensation as your foot is twisted in and out.

Diagnosis

Anterior impingement: the surgeon will look for tenderness and swelling on the front of your ankle. He will check to see if the pain increases when you squat, lunge or pull your toes upwards. X-rays and scans will be taken to see if it is a bone spur that is causing the impingement.

Posterior impingement: the surgeon may inject a numbing medication into the area of the os trigonum - if the pain immediately diminishes, the problem is most likely to be posterior impingement of the os trigonum. An x-ray or scan will confirm the existence of an os trigonum.

Surgery

Anterior impingement: two small incisions are made either side of the impingement area, and using an arthroscope, the surgeon will use a small shaver to clear away thickened or inflamed tissue. If there is a bone spur on the anklebone or the shinbone, it will be removed.

You will be given an ankle splint and commence a course of physiotherapy. You should be able to return to normal activities in four to six weeks.

Posterior impingement: the Os trigonum is completely removed during minimally invasive surgery. A combination of insertions and small incisions are made in the back of the ankle and the Os trigonum is carefully removed.

If posterior impingement is the result of torn or slack ligaments, these can be repaired or tightened using arthroscopy.

After arthroscopy, you will be able to put weight on the foot almost immediately, and will be having physiotherapy twice a week. You should expect full recovery about six weeks after surgery.

After minimally invasive surgery, you will be in a splint for three weeks. Physiotherapy will be needed for the next two to three months.

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