Teaching Case

8-year-old male patient who presented with a history of pain in the right foot and ankle after a trivial trauma. A radiography was performed, which showed no relevant findings. After a week of pain that did not respond to analgesic medication, an ankle sprain was suspected and a MRI was requested.

Right ankle:
A patchy osseous oedema comprising the ankle, hindfoot and metatarsal bones is observed, with fluid distension of the antero-lateral recess. No soft-tissue oedema is observed.
The aforementioned findings are related to low intensity subchondral linear lesions affecting the distal tibia, the talar dome, and the posterior tuberosity of the calcaneus. There is also a high signal intensity that affects the epiphyseal plate of the distal tibia, in keeping with oedematous changes.

Left ankle:
A diffuse osseous oedema of the talus, more remarkable in its neck, is seen. Also, slight patchy signal alteration of the periphery of the calcaneus and the distal tibia is observed, consistent with oedema. No significant joint effusion is seen.

Insufficiency fractures are a subtype of stress fracture, they are commonly seen in the context of osteoporosis, hence more frequently in elderly women. [3] Nevertheless, any other process which weakens the bone structure can be a risk factor for the development of insufficiency fractures. The most common locations are found in the axial skeleton: vertebrae, sacrum, proximal femur, etc. [6]
In adults, a reduction of a 7% in bone mineral density (BMD) is associated with an increase of up to 50% of osteoporotic fractures. [5]
A decrease of up to 10% in BMD has been described in children receiving antiepileptic drugs, specifically Valproate, when compared to controls. Therefore when assessing a child under Valproate treatment who presents bone or articular pain, it is important to consider insufficiency fractures, which can be subtle or undetectable in plain films.
Chronic diseases and certain treatments may exert deletereous effects on bone health. Both restriction of the physical activity and pharmacological treatment come together as factors that can affect BMD in patients suffering epilepsy. Phenytoin and Phenobarbital have been associated to rickets and a decrease of BMD as an adverse effect of both Valproate and Carbamazepine were described during the '90s. [1, 2]

The typical presentation of an insufficiency fracture is that of progressively worsening pain in the context of a minimal trauma or no trauma at all. [6]

Conventional radiology is not useful for the diagnosis as it is initially normal in most of the cases. If performed moths after the onset of the symptoms, bone sclerosis and cortical thickening may be found in metaphyseal and epiphyseal fractures and periosteal reaction with or without formation of a callus has been described. [6] Magnetic Resonance Imaging (MRI) along with bone scan are the most sensitive tests for early diagnosis, MRI being of higher specificity not only to isolate the exact anatomic location but also to rule out alternative diagnosis such as tumours and infections. [4, 6]
The characteristic findings on MRI are low signal of the bone marrow in T1-weighted sequences and high signal, which extends into adjacent soft tissues, in fluid sensitive sequences (T2 and PD). After gadolinium-based contrast media administration, enhancement may be evident. Bone scans show intense isotope accumulation at the site of the fracture. [4, 6]

Take home message: performing an MRI is important for the diagnosis of insufficiency fractures in paediatric patients with specific bone pain who are being treated with Valproate.