Flatfeet can be a difficult problem for many adults. Many people will experience some form of adult-acquired flatfoot in their lifetime, some of which may become very painful and problematic. An important point to make about adult-acquired flatfoot, however, is that not all flatfeet are pathological. Only flatfeet that cause significant pain and discomfort should be considered problematic.
Adult-acquired flatfoot has many different causes, the most common of which being either a weakness or dysfunction of the posterior tibial muscle and/or tendon. Posterior tibial tendon dysfunction (PTTD) is a common etiology of flatfeet in the adult.
The Tibialis Posterior muscle originates in the deep posterior compartment of the leg muscles, and courses down into the foot. The tendon inserts mainly into the navicular bone, but also into the midtarsal bones and the calcaneus. This expansive insertion of the tendon helps to support the arch of the foot. The tibialis posterior acts to re-supinate the subtalar joint during gait. In other words, when the foot is pronating, the tibialis posterior acts to oppose this action. When the tibialis posterior is weakened or the tendon becomes elongated, this action is lost. Thus, the foot remains in a pronated position through the gait cycle. This, in turn, may lead to a pathological flatfoot.
Symptoms of PTTD/adult-acquired flatfoot include pain in the instep, or medial arch of the foot. There may also be pain the medial ankle, as well as the lateral (outside) of the foot. One of the classic tests for PTTD is to have the patient perform single-leg heel raises. By going on the tip-toes of one foot, the tibialis posterior is tested for strength. The normal foot will show the heel inverting, or turning inward. Someone with later stages of PTTD will have a heel that does not invert. There may also be difficulty in performing this test, particularly when it is repeated several times in a row.
PTTD and adult-acquired flatfoot are evaluated by the physician using both the history and physical exam, as well as several imaging techniques. An x-ray is typically taken to rule out other causes of pain, such as fracture, dislocation, infection, and other problems that may be evident on x-ray. Beyond plain films, and MRI may be taken to evaluate the posterior tibial tendon. Distinction is made between a tendon that is effected only by inflammation along the synovium (the fluid sheath that helps it move smoothly), partial tears in the tendon, and complete ruptures of the tendon. The findings of an MRI may guide the treatment and will help in surgical planning in particular.
Treatment of PTTD and adult-acquired flatfoot is dependent upon the stage of the disease. The condition was first classified by Johnson and Strom, and the added onto by Myerson. There are four stages of PTTD, the details of which are beyond the scope of this article. Essentially, stage I and II are still flexible stages, meaning that a functional foot is still attainable. Stage III and IV are rigid deformities, where a functional foot is no longer attainable, and accommodation of the deformity is the goal of treatment.
Non-operative treatment for stage I and II includes immobilization in either a cast or boot for 4-6 weeks, followed by some type of orthotic device. Depending on the severity of the deformity, a foot orthotic may be sufficient. However, many people will require an ankle-foot orthosis (AFO) for sufficient functional improvement. Stage III and IV PTTD will not tolerate a functional device, as the foot and ankle are in a rigid position. Therefore, these patients will require an accommodative device, which will allow them to walk with a decreased amount of pain.
Operative treatment is ideally done for stage I and II PTTD to address adult-acquired flatfoot. Surgery for this condition focuses on realigning the foot to be in a more functional position, and will often restore power and function to the posterior tibial tendon. This may be done with a combination of soft tissue and bony procedures, including tendon transfers, fusions of the joints in the first ray, and osteotomy of the calcaneus. Stage III and IV, because they involve more rigid deformities of the foot and ankle, will typically require fusion of involved and painful joints. This means that the joint will no longer move, but the pain at this joint will be decreased due to a lack of movement.
As you can see, the approach to adult-acquired flatfoot is multi-faceted, and requires a thorough evaluation. The foot and ankle surgeon addressing the situation should recognize all of the factors involved, and the patient should recognize the inherent risks and benefits associated with both conservative treatment and reconstructive surgery for adult-acquired flatfoot.
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