Having an accessory navicular bone, also known as a Kidner foot, is a type of enlarged or extra bone located on the navicular tuberosity of the inner midfoot. An accessory bone is generally asymptomatic in the beginning but can often cause pain and difficulty fitting into a shoe especially when the bony prominence rubs against the shoe. This is commonly seen in those with a flexible flatfoot and those who are more prone to having trauma to the area of the posterior tibial tendon, which attaches to navicular tuberosity.
Other than a bony prominence to the inside of the midfoot, your doctor or podiatrist will clinically find that the prominence is also tender to touch and that you may have pain with walking or physical activity. Your doctor will obtain a history of any acute injuries and will conduct a foot-related physical exam as well as order foot x-rays to accurately diagnose an accessory navicular bone. Plain radiographs are necessary to help rule out a navicular fracture and to classify one out the three types of accessory navicular: Type 1 is where the accessory bone is within the posterior tibial tendon, Type 2 is an accessory bone is connected by cartilage to the navicular, and Type 3 is enlarged navicular tuberosity.
Your podiatrist may recommend conservative treatments such as a change in shoe gear, activity modification, and offloading pads to help alleviate the pain. When conservative measures have failed to manage the condition, an outpatient surgery called the Kidner procedure may be done to trim off the extra accessory navicular bone. In addition, it may be necessary to also surgically reattach the posterior tibial tendon to the navicular, which would require a longer recovery process.
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