Acquired adult flatfoot deformity (AAFD) is a progressive flattening of the arch of the foot that occurs as the posterior tibial tendon wears down. It has many other names such as posterior tibial tendon dysfunction, posterior tibial tendon insufficiency and dorsolateral peritalar subluxation. This problem may progress from early stages with pain along the posterior tibial tendon to advanced deformity and arthritis throughout the hindfoot (back of the foot) and ankle.

A Lisfranc injury involves the joints and/or the ligaments of the middle of the foot. The Lisfranc ligament is a ligament of the foot that runs between two bones called the medial cuneiform and the second metatarsal. The name comes from French surgeon Jacques Lisfranc de St. Martin (1790-1847), who was the first physician to describe injuries to this ligament.

There are a variety of causes for this injury such as a car accident, sports injury, or a simple slip and fall. Sometimes the injury can be mistaken for a foot sprain when X-rays do not show any broken bones. Delaying treatment can sometimes lead to more significant problems. The key for the treatment of a Lisfranc injury is proper diagnosis.

Tendons connect muscles to bones and stretch across joints, enabling you to bend those joints. One of the most important tendons in the lower leg is the posterior tibial tendon. This tendon starts in the calf, stretches down behind the inside of the ankle, and attaches to bones in the middle of the foot. 

The posterior tibial tendon helps hold up your arch and provides support as you step off on your toes when walking. If this tendon becomes inflamed, overstretched, or torn, you may experience pain on the inner ankle and gradually lose the inner arch on the bottom of your foot, leading to flatfoot. 

Rheumatoid arthritis (RA) is a systemic disease that attacks multiple joints throughout the body. About 90 percent of people with RA eventually develop symptoms related to the foot or ankle. Usually symptoms appear in the toes and forefeet first, then in the middle and back of the foot, and finally in the ankles. Other inflammatory types of arthritis that affect the foot and ankle include gout, ankylosing spondylitis, psoriatic arthritis, and Reiter's syndrome.

The exact cause of RA is unknown but there are several theories. Some people may be more likely to develop RA because of their genes. However, it usually takes a chemical or environmental trigger to activate the disease. In RA, the body's immune system turns against itself. Instead of protecting the joints, the body produces substances that attack and inflame the joints.

A stress fracture is a small crack in a bone. These fractures most often are a result of overuse and can occur with an increase in activity. Stress fractures most commonly occur in the weight­bearing bones of the legs. When a bone is subjected to a new stress, such as a new exercise routine, it may not be prepared for the increased workload, and as a result, may develop a stress fracture.