One of the most common causes for a flat foot in the adult is a rupture of the posterior tibial tendon. The posterior tibial tendon (along with other supportive ligaments) is responsible for maintaining the arch of the foot. This tendon passes behind the ankle and winds around one of the bones inside the ankle called the medial malleolus.
There are certain individuals who seem to be prone to developing a rupture of the posterior tibial tendon. These include women who are overweight and those people who have a flat foot that has been present since early adulthood or even childhood. In these individuals the posterior tibial tendon may be prone to stretch out and tear. As the tendon tears, its supportive function is lost.
Once the foot begins to flatten, other structures including supportive ligaments on the inside of foot begin to stretch and tear and the foot becomes very flat. Frequently, the patient will note pain which begins on the inside of the foot, just behind the ankle. This is due to inflammation of the tendon, which is also associated with partial rupture or tearing of the tendon.
One of two things will happen to the foot at this stage. Either the foot remains mobile and flexible or it will start to become stiff. If the condition deteriorates further, the flattening of the foot is associated with stiffening of the joints of the back of the foot. This will limit the inward and outward movement of the foot (inversion and eversion).
The stiffer the foot, the more difficult it becomes to treat the condition. For this reason it is important to initiate treatment as early as possible once the diagnosis of a rupture of the posterior tibial tendon is made.
Symptoms of a posterior tibial tendon rupture include:
• Inward rolling of the foot
• Flattening of the foot
Diagnosis of a posterior tibial tendon rupture can be made by a foot and ankle specialist during a physical exam of the foot. X-rays, MRIs or CT scans may be taken to view the bone, tendons and muscles to help confirm a posterior tibial tendon rupture diagnosis.
Treatment for a posterior tibial tendon rupture begins with support of the foot. This is done with shoe modifications, orthotic arch support and, at times, a brace that is custom molded to the ankle. The problem with this deformity is that once the foot becomes flat, there is very little that can stop it from flattening out further.
This occurs as one stands, since the weight of the body and the mechanical effect of this weight push the foot out further. However, provided the foot can be maintained in a reasonably straight position, there is never any urgency to perform any reconstructive surgery. Ultimately, the decision to perform surgery for a posterior tibial tendon rupture depends on the patient’s symptoms.
There are certain flat foot deformities in which the foot is so very flat it is not in the patient’s best interest to have orthotic arch support treatment. In these individuals the foot is so deformed and under so much stress, severe ankle arthritis develops.
Surgical treatment for the adult’s flat foot deformity is divided into three different types:
• Tendons are repaired or transferred
• Bones are cut or realigned
• Joints are fused together
It is always preferable to avoid a fusion (called arthrodesis) of the foot if possible, since stiffness of the foot is never ideal. The extent of the deformity is the key factor in the decision.
For the flat foot where the tendon is ruptured but there is not significant deformity, a tendon is usually transferred to replace the torn posterior tibial tendon. It is not possible to repair the torn posterior tibial tendon, since it will quickly stretch out and tear again. The tendon transfer uses a tendon which lies behind the back of the ankle, but which is not a critical tendon, and can be easily used without causing loss of foot function.
The tendon transfer is combined with a cut on the heel bone (called a calcaneal osteotomy). The heel bone needs to be shifted to add support to the tendon transfer on the inside of the ankle. This operation is now one of the most common operations performed around the world to correct this condition.
When the deformity gets a little worse, bone cuts or osteotomies must be added to reshape the foot. In some of these, a bone graft has to be used to elongate different parts of the foot. Mercy’s surgeons provide the option of graft bone used from the bone bank rather than using the patient’s bone.
The use of bone from the bone bank significantly reduces the risks of taking the patient’s own bone from the pelvis. After the bone is cut, the bone graft is shaped and then inserted to reshape the arch and contour of the foot.
For the severe flat foot deformity, the foot becomes quite stiff and a tendon transfer and bone cut is no longer enough to correct the deformity. The foot has to be reshaped and realigned and the joints fused together with screws to maintain the corrected position.
Although the foot is somewhat stiff, the up and down movement of the foot is fully maintained. The inward and outward (inversion and eversion) movement is lost.