Navicular Stress Fracture
The navicular bone of the midfoot is prone to develop bone stress injuries in all weight bearing athletes. It is especially common in track and field athletes, but can occur in any running sport. Risk factors may be intrinsic to the athlete such as biomechanical factors such as increased pronation or tight calf complex, or suboptimal bone health. Extrinsic risk factors may include poor footwear or increases in training volume.
Navicular bone stress is not diagnosed easily as it causes vague activity related medial midfoot pain. Examination may reveal biomechanical deficiency and tenderness over the dorsal aspect of the navicular bone. The tibialis anterior and posterior tendons must be assessed for injury.
Differential diagnosis includes accessory navicular bones (os supranaviculare), talonavicuar joint issues and tendinopathy to tibialis posterior or anterior tendons. This injury does may not be visible on Xray, but Increased bone oedema may be seen on MRI or increased osteoblastic activity on bone scan. A CT scan will confirm whether it is stress reaction or stress fracture (fracture line seen) and to the grade of the fracture.
Treatment involves strict immobilisation with crutches for 6-8 weeks with boot or plaster. Sometimes this is non-weight bearing. Predisposing factors need to be addressed.
At 6-8 weeks the immobilisation is removed and the navicular is examined for tenderness. If there are no signs of fracture, then gradation of exercise follows as determined by symptoms. Generally, it would take 6+ weeks back to full activity. If strict immobilisation is ignored then there may be an increased risk of delayed union and return to sport is delayed.
Surgery fixation is occasionally necessary if conservative management fails, or if there is near complete fracture or a displaced fracture