Navicular stress fractures are uncommon but serious injuries, characterized by a chronic midfoot ache. The cause is a repetitive chronic load to the midfoot, often from dynamic sporting-type activities. A Navicular stress fracture is difficult to diagnose as it may not be seen on regular x-rays. Treatment involves a period of prolonged non-weight-bearing. Navicular stress fractures that are not healing may require surgery to stablize the fracture with one or more screws.
Patients who develop navicular stress fractures will present with a chronic mid-foot ache. Although anyone can get a navicular stress fracture, the most common presentation is in the athlete. The injury may begin after a series of repetitive loading episodes. However, unlike a typical stress fracture of the metatarsals (which are much more common), these loading episodes tend to be more dynamic. Some examples include the lead foot of an active golfer, a middle distance runner, or any college or professional athlete performing dynamic repetitive activities.
The symptoms are often generalized to the mid-foot. The relatively nonspecific location of the symptoms makes this condition difficult to diagnose. Pain may be with athletic activities only, but some patients might even have a limp while walking.
Physical examination will demonstrate a generalized tenderness around the top of the mid-foot. An astute physician may be able to localize the tenderness to the top of the navicular bone. Certainly, attempts to hop or rise up on the toes of the affected foot will be painful. There is some suggestion that patients with slightly higher arch feet, as well as patients with a relatively long second toe and second metatarsal, may have an increased risk of developing navicular stress fractures. These two situations may increase the concentration of force into the navicular, particularly in patients doing activities that involve them getting up on their, toes such as sprinting and jumping. But most commonly, the person with a navicular stress fracture has a normally-aligned foot.
X-rays are often read as normal. Sometimes a subtle fracture line can be identified. In more advanced cases, or in cases where there is degeneration of the talonavicular joint, x-rays will be abnormal.
Diagnosis can be made with an MRI, a CT scan, or a bone scan. An MRI or a CT scan will allow the fracture orientation to be identified. In addition, those studies will allow determination of whether the fracture is complete or incomplete.
Navicular stress fractures can be difficult to treat due to the relative lack of blood supply to the navicular (a good blood supply is needed for healing of any bone injury), and the fairly extensive force that this bone absorbs in both normal walking and in sporting type activities.
Good results have been reported when treating undisplaced navicular stress fractures with treatment involving casting, and a period of non-weightbearing of 6 weeks. Success rates of 85-90% have been reported with this treatment method. Many doctors will also recommend the use of a bone stimulator, which is designed to encourage bone healing. However, there is no clear evidence that the stimulator improves the time to healing.
However, if the patient is allowed to walk on the cast, the rate of healing may fall as low as 25%. It is common to require three, four, or more months to make a full recovery from an undisplaced navicular stress fracture, and it may be a season-ending injury for an athlete. Furthermore, patients who have developed a navicular stress fracture are at risk for having a recurrent fracture, as the underlying biomechanics are usually unchanged even after the fracture has healed.
Surgery may be recommended for some patients, especially if an initial period of non-operative treatment is not successful. Surgery may include drilling across the fracture, placement of one or more screws, and possibly the addition of a bone graft to improve healing. Surgery usually results in successful healing, but a period of rest and non-weightbearing is required after surgery, and overall recovery time is still prolonged.
In rare cases, a navicular fracture may go on to displace. Non-operative treatment is no longer appropriate; a surgeon needs to reduce the fracture (set it in exact position), hold it in place with screws, and possibly add a bone graft.
The most obvious and concerning potential problem with non-operative treatment is persistence of the fracture. If the fracture is not showing signs of healing, then surgery should be considered.
In rare cases, the navicular bone can collapse. This is probably not the end point of a stress fracture, but may be part of a more complex and rare disease. Collapse compromises function of the hindfoot joints, and is difficult to manage.
If a navicular fracture heals in poor alignment, arthritis of the associated joint (the talonavicular joint) will set in, with pain and stiffness. Surgery to fuse the talonavicular joint can alleviate much of the midfoot pain associated with talonavicular arthritis. However, it is associated with a fairly prolonged recovery time of six or more weeks of non-weightbearing. In addition, it increases the stiffness of the midfoot.