The midfoot is comprised of the three cuneiform bones, the cuboid and the navicular bones as well as the surrounding soft tissues. The most common cause of midfoot pain is midtarsal joint sprain after ankle injury but the most important cause of midfoot pain is a stress fracture of the navicular bone. Tendinopathy of the extensor tendons is another common cause of midfoot pain.
History
Acute onset of midfoot pain occurs with a sprain of the midtarsal joint or plantar fascia. Gradual pain is a sign of overuse injury, such as extensor tendinopathy, tibialis posterior tendinopathy or navicular stress fracture. In most conditions, pain is well localized to the site of the injury but in navicular stress fracture pain is poorly localized.
Examination
Examination involves palpation of the area of tenderness and a biomechanical examination to detect factors that predispose to injury.
Investigations
If there is a clinical suspicion of a stress fracture of the navicular or the cuneiform, an X-ray should be performed. This rarely reveals a fracture, even if one is present, but it is useful to rule out tarsal coalition (p. 660), to show bony abnormalities such as talar beaking (osteophytes at the talonavicular joint) and accessory ossicles, and to exclude bony tumors. An isotopic bone scan (with CT scan if positive) or MRI should be performed if X-ray fails to reveal a stress fracture.
Stress Fracture of the Navicular
Stress fractures of the navicular are among the most common stress fractures seen in the athlete, especially in sports that involve sprinting, jumping or hurdling. The stress fracture commonly occurs in the middle third of the navicular bone, a relatively a vascular region of the bone. Stress fractures in this region are thus susceptible to delayed union.
Causes of Navicular Stress Fracture
A combination of overuse and training errors plays a significant role in the development of navicular stress fractures. Although the exact cause of a navicular stress fracture is not known, it is believed that impingement of the navicular bone occurs between the proximal and distal tarsal bones when the muscles exert compressing and bending forces.
Symptoms of Navicular Stress Fracture
- The onset of symptoms is usually insidious, consisting of a poorly localized midfoot ache associated with activity.
- The pain typically radiates along the medial aspect of the longitudinal arch or the dorsum of the foot.
- The symptoms abate rapidly with rest.
- Examination reveals localized tenderness at the 'N-spot' located at the proximal dorsal portion of the navicular.
- If palpation confirms tenderness over the 'N-spot', the athlete should be considered to have a navicular stress fracture until proven otherwise.
Investigations
Sensitivity of X-ray in navicular stress fracture is poor. Thus, either isotopic bone scan (with CT scan if positive,) or MRI is required if clinical features suggest stress fracture. Poor positioning and scanning technique can lead to a navicular stress fracture being missed on CT scan. Appropriate views require correct angling of the CT gantry and thin (2 mm [0. 1 in.]) slices extending from the distal talus to the distal navicular.
Treatment of Navicular Stress Fracture
The treatment of a navicular stress reaction (no cortical breach) is weight-bearing rest, often in an air cast, until symptoms and signs have resolved, followed by a graduated return to activity.
- Treatment of navicular stress fracture is strict non-weight-bearing immobilization in a cast for six to eight weeks.
- At the end of this period the cast should be removed and the 'N spot' palpated for tenderness is present.
- The patient should have the cast reapplied for a further two weeks of non-weight-bearing immobilization.
- Management must be based on the clinical assessment as there is poor CT and MRI correlation with clinical union of the stress fracture.
- Often , patients with these fractures will present after a long period of pain or after a period of weight-bearing rest.
- All patients, even if they have been unsuccessfully treated with prolonged weight-bearing rest or short-term cast immobilization for a six week period.
- This method of treatment produces excellent results and may be successful even in longstanding cases.
- Some clinicians advocate surgical treatment with the insertion of a screw in cases where there is significant separation of the fracture.
- In cases of delayed or non-union, surgical internal fixation with or without bone grafting is required.
Rehabilitation and Prevention of Recurrence
Following removal of the cast, it is essential to mobilize the stiff ankle, subtalar and midtalar and midtarsal joints.
- The calf-muscles require soft tissue therapy and exercise to regain strength. These must be done before resuming running.
- Activity must be begun gradually, slowly building upto full - training over a period of six weeks.
- Predisposing factors to navicular stress fractures may include tarsal coalition, excessive pronation and restricted dorsiflexion of the ankle.
- These factors need to be corrected before resuming activity.
