Equinus is arguably the most common deformity of the foot and ankle that no one talks about. Equinus is not only a contributing factor in a number of foot- and ankle-related pathologies such as plantar fasciitis and hammertoe deformities, but also has an effect on other areas higher up in the body—i.e., the knees, hips, and back.
What is Equinus Deformity, and How Does It Affect Me?
Equinus is defined as limitation of ankle joint dorsiflexion (upward movement of the ankle) (1). Classically, ten degrees of ankle dorsiflexion is required for normal walking (2). If you have less than ten degrees, then you have either bony or muscular equinus (1).
Bony equinus is when extra pieces of bone around the ankle (either from the talus or tibia bone) block the normal motion of the joint. This equinus allows very little ankle motion, and the motion usually stops abruptly (1).
Muscular equinus is due to tightness of the gastrocnemius and soleus muscles, which make up the Achilles tendon. The Achilles tendon is the longest tendon in the body. It is located at the back of the leg and ends at the back of the heel bone.
If these muscles are tight, they will want to pull the ankle joint down (plantarflexion), opposing the ankle dorsiflexory motion during walking. An extreme example of muscular equinus can be seen in individuals with neuromuscular diseases such as cerebral palsy (1).
What Causes Equinus Deformity?
Equinus deformity can contribute to certain foot and ankle injuries. It is usually not seen as a single deformity.
For example, plantar fasciitis (which is defined as inflammation or damage of the plantar fascia, a band of tissue that runs underneath the foot) has an attachment to the heel bone, much like the Achilles tendon (gastrocnemius-soleus complex)(3).
Because of this common attachment, any stretching of one will cause the other to stretch also. So when the tight ankle joint tries to walk “normally,” and the gastrocnemius-soleus complex is stretched, the plantar fascia is also stretched, leading to possible tears in the fascia.
Hammertoe deformities can also be caused by equinus (1). If a tight ankle joint has difficulty achieving the normal ten degrees of ankle movement, it will recruit all the muscles it can to lift the ankle up (dorsiflex).
One of these muscles, located on the top of the foot, is attached to the toes. As this muscle works hard to lift the ankle joint, the toes also lift up, causing the hammertoe deformities.
What Are the Effects of Equinus Deformity?
Equinus can also have detrimental effects on other areas of the body. For example, the limited range of ankle-joint motion can increase pressure on the knees (knee flexion and genu recurvatum), since most of the body weight is shifted forward (1).
The lower back can be affected also due to body malalignment, causing lower back pain (lumbar lordosis) (1).
What Are the Treatment Options for Equinus Deformity?
Treatment depends on whether the equinus deformity is bony or muscular. Bony equinus can be treated conservatively by physical therapy, orthotics, anti-inflammatory medication, and cortisone injections, but the only way to increase range of motion is by surgical removal of the bony obstruction(s) (1).
Muscular equinus can be treated conservatively with a heel lift, which will reduce the strain on the gastrocnemius-soleus. There is also complex orthotic therapy and stretching using a brace or splint, or simple “calf wall stretches.”
It is preferable to use these treatments in conjunction with one another; as the gastrocnemius-soleus complex becomes more flexible, the heel lift and orthotics can be adjusted. In severe cases there is a surgical option for muscular equinus. This involves surgical lengthening of the Achilles tendon.
Questions to Ask Your Doctor
- Do I have equinus deformity? What kind?
- How did it happen?
- What are my treatment options?
- Is surgery necessary for treatment?
- How can I prevent equinus from happening?
- Has equinus caused other problems with my feet and ankles?