flat foot

What causes Flat Feet?

Flat feet may be completely normal in children and young adults who have always had a fairly flat arch. This is different from a foot that previously had an arch, but has now become flat. When an arch collapses, this means that the tendon that supports the arch has stretched or snapped.

flat foot hindfoot valgus

When the arch collapses, the heel drifts outwards, and the instep touches the ground. The position of the heel can become entrenched and arthritis of the foot joints and ankle can ensue. This is a long gradual process. Initially there may be pain on the inside of the ankle over the course of the tendon. Later there will be pain on the outside of the ankle. Later still, the whole rear part of the foot is painful. Walking on uneven surfaces becomes difficult, as the foot cannot adapt. Pain may radiate up the calf.

xray x ray of flat foot

Standing on tip toes may become painful or even impossible.

If you have fallen arches, it is best to see an orthopaedic surgeon who specialises in foot and ankle surgery. You should have x-rays taken in a standing position – this is when the flattening of the foot is worst. It will also demonstrate which joints have become arthritic.

insole orthotic for flat foot

Do You Need Surgery?

Not everybody requires surgery for flat feet. It depends on how much pain they cause and how far it has progressed. The majority do not not need surgery and insoles are all that are required. They take some getting used to as they are uncomfortable for several months before you get used to them.

diseased posterior tibial tendon

How is the Surgery Performed?

There is a range of surgery performed for flat feet in adults. The surgery you have depends on how far the disease process has progressed in your tendon.

At an early stage, the tendon is very sore but it is still working. Cleaning out the sheath around the tendon can settle symptoms.

incision for flat foot surgery

When the tendon has stretched or snapped, then surgery is considered if insoles have not been successful in alleviating symptoms. This surgery involves either fusing bones in the back of your foot or breaking the heel bone and re-aligning it to support the arch of the foot and plugging a different tendon into the arch. These operations tend to work if the joint are still mobile. This surgery can take two hours.

triple fusion for flat foot
Triple Fusion

If the disease process has progressed beyond this and the joints are not mobile, then bony surgery is all that can be performed. This involves fusing three of the joints in the back of the foot – a triple fusion. The incisions are shown on the left. This re-aligns the foot, and relieves pain, but at the expense of side to side movement of the foot. This surgery often takes three hours. In order for the bones to fuse, ‘spare’ bone is taken from inside the  top end of the shin bone to fill in any spaces.

hindfoot nailing for flat foot
hindfoot nailing

If the disease has progressed even further, the ankle is arthritic as well. The only solution here is surgery and this involves inserting a metal rod up through the heel into the shin bone. This is called hindfoot nailing. This can take three hours. The bottom few inches of the fibula bone is removed to allow the joints to be fused properly.

After all bony surgery, the leg is encased in plaster of paris. You can go home 48 hours after surgery, so long as your pain is well controlled and you are mobile with crutches.

Surgery is carried out under general anaesthetic, but I also give local anaesthetic injections behind the knee or around the ankle. The injections are normally given while you are asleep for your comfort. They can give good pain relief for the first day after the operation.

Risks of Surgery

Bleeding, infection, poor bone healing, poor skin healing, injury to tendons, injury to nerves, recurrence, and a need for further surgery.

There is a small risk of blood clots in the legs or lungs (DVT and PE), and there are also risks from anaesthesia – the process of being put to sleep for your operation. If you are in plaster of paris, we can decrease the risk of DVT by using a blood thinning injection each day.

Risks of Anaesthesia

The injection behind your knee is given using an ultrasound machine to guide the needle. There is a less than 1% chance of injury to the nerve. General anaesthetic also carries risks. These risks are proportional to your general health. You will need to be assessed for your fitness for surgery and an Anaesthetist will be able to advise you on your individual risk.

plaster cast flat foot surgery
six weeks

What Happens After Surgery?


You will have had injections to numb your foot so that you are not in pain after the operation. This injection will wear off after 18-24 hours, so you must take regular painkillers so that you are not in severe pain when the injection wears off. Ibuprofen and Diclofenac should not be used for more than a few days after the operation as they can interfere with bone healing.

The pain will settle over a few weeks. You may see blood stains on the dressings. This is normal and not a cause for alarm. If blood is dripping from the dressings however, return to hospital.

aircast boot flat foot surgery
six weeks


The foot will be swollen as well as sore. You should keep the foot elevated as much as possible for the first two weeks. Keep walking down to a minimum – going to the toilet or for meals. Letting the leg hang down will cause the foot to become more swollen. Most of the swelling will settle within the first few months, but swelling can continue for up to one year.

If you are resting on your sofa, keep your foot elevated on the back rest or arm rest. If you are resting in bed, then place a few pillows under the foot to keep it elevated.


You will normally be in plaster for a total of six weeks after surgery for a flat foot. During this time, you should not weight bear on this foot. You will need crutches or a walking frame to get about.

Two weeks after the operation, you will have your plaster removed, and the stitches removed. You will then have a further plaster applied for four more weeks. After this, you will have an xray and if this is satisfactory, you will be given a removable plastic boot, in which you can put your weight through the operated foot. You will use this for a further six weeks. This can be removed for washing, performing exercises and at night.


If you are in plaster for a prolonged period, you will be at risk of developing a blood clot in your leg. You will be given injections to thin the blood to cut this risk down. These can be self-administered, even in the elderly. You can stop taking these as soon as you progress to a plastic boot.


While you are in plaster, you can perform exercises to keep the leg muscles above the knee strong, as these will become weaker as you are not weight bearing.

You can removed the plastic boot to wash, and perform exercises depending on your operation. If you have had a triple fusion, you will still be able to perform up and down movement of the ankle. If you have had a hindfoot nail, this should not be attempted.

After twelve weeks, you will be seen in the clinic and a further xray will be taken. From this time, you will start to wean yourself off the plastic boot, and have physiotherapy.


You will be unable to weight bear while in plaster. I advise that you do not return to work before the plaster is removed, especially if you are on your feet all day at work. Most people will be off work for four months as a minimum, but if you have a workplace with disabled access that allows you to use crutches and you are sitting down most of the day, you may be able to return to work while wearing the plastic boot. Remember that not everyone is the same, and some people take a longer time to recover from their surgery. Please request a sick note before you leave hospital, if you need one.

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