In this, one of three articles that focus on exercise and your joints, we review the anatomy of the ankle. We also describe some simple movements that can help you increase joint function and decrease the possibility of bleeds.

Let's take a closer look at the structure of the ankle. While the foot adapts to uneven surfaces and absorbs stresses from the ground, it is the ankle that distributes those forces to the lower leg and the rest of the body. To do this, the foot-ankle area actually employs several joints. The two joints that are most commonly affected in PWHs are the main ankle joint, or talocrural joint, and the subtalar joint. The talocrural joint is where the tibia, the inner long leg bone, meets the fibula (the smaller long leg bone) and the talus (bottom bone). This joint is surrounded by two important muscles: the dorsiflexors, located in the front of the lower leg or shin, which control the ability of the foot to move upward; and the plantarflexors, or calf muscles, which enable the foot to extend downward. It is at this joint that most injuries occur.

The subtalar joint is where the talus and calcaneus (heel bone) meet. This joint is surrounded by the invertor muscles, which control the ability of the foot to move inward, and the evertors, which enable the foot to move outward.

During a spontaneous bleeding episode, blood accumulates in the main ankle joint causing the entire ankle area to swell and resulting in a series of effects on the foot and ankle. First this type of swelling moves the ankle joint into a resting position in which the foot is slightly plantarflexed, or dropped downward. Once the foot is swollen and in a resting position, it is difficult to regain upward mobility into dorsiflexion. However, to walk properly your foot requires some upward movement. As a result, the ankle tries to compensate for this decrease in upward mobility by increasing the mobility at the subtalar joint. This causes a lowered arch, and the ankle and foot becomes less stable. Also, when the foot is less stable the ligaments - ropes of tissue that link the foot bones together - become overstretched and inflamed. This abnormal and excessive stretching on the foot and ankle can increase the tendency to sprain the ankle.

To prevent such a cycle of bleeding, swelling, injury and joint destruction, it is important to regularly exercise the muscles around the foot and ankle with strengthening and mobility exercises. Strong muscles protect the joint and decrease the chance of injury. Adequate joint mobility is also crucial in protecting the joint. In addition, strong muscles and adequate joint mobility prevent lowering of the foot's arch.

You should consider wearing foot orthotics if your arches have already dropped somewhat because of repeated joint bleeds. These are semi-rigid devices put in a shoe to help keep the foot in a neutral position that enables the ankle to function optimally. In addition, anyone with haemophilia should always wear supportive shoes to protect his ankles. For those who participate in sports, especially children who play basketball or similar high-impact activities, high-top sneakers, which provide more stability to the ankle, are a must. Of course, non-impact activities like swimming that put little stress on the ankle are highly recommended.

The following exercises are designed to build range of motion and strength of muscles around the ankle. To increase the strengthening component, simply add small weights to your range-of-motion movements. If your ankle and foot motion is normal, you should exercise once or twice a day to maintain strength. If you are already experiencing some limitations in your ankle and foot function, it is essential that you exercise as often as possible. When you have a bleed, exercise as soon as the bleeding is under control to help you regain mobility and increase stability at the ankle joint.

Theresa Kelly is the assistant chief physical therapist in the Department of Rehabilitation Medicine at the New York Hospital/Cornell Medical Centre.

June Zimmerman is a writer and specialises in medicine and healthcare.