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Insufficiency fractures are a type of stress fractures that occur due to physiological stress on weakened bones. These have certain sites of predilection of which an uncommon site is fibular shaft. Isolated bilateral fibular fractures have previously only been reported twice, where the causes were repeated trauma and fatigue fracture. Insufficiency fractures of both fibula in isolation have not previously been reported. We present this case where a young patient presented with these fractures and was found to have vitamin D deficiency on subsequent investigations.
Stress fractures are typically classified into two categories – fatigue fractures caused by unusual stress on normal bones and insufficiency fractures(IF) occurring due to normal stress on abnormal or deficient bones. These have certain sites of predilection like the ribs, vertebrae, sacrum, pelvis, distal ulna, and to a lesser extent, proximal and distal tibia and fibula.
To the best of our knowledge, isolated insufficiency fractures of the both fibular bones have not been reported in the English literature and we present this unusual presentation of IF in a young patient.
2. Case report
A 22 year old female presented to the orthopaedic OPD with complains of bilateral leg pain for the past one month. Pain increased with physical activity and was partly relieved with rest. There was no history of trauma, fever, chronic illness or pain anywhere else. She was a college student and did not give any history of excessive physical activity like running, gymming or sports. On examination, there was tenderness on the outer aspects of both legs, localised slightly proximally on the left. No swelling or deformity was noted and there was no restriction of movement. No history of joint pain was given by the patient.
Radiographs of both legs revealed presence of transversely oriented undisplaced fractures in the right as well as left fibular shafts (Fig. 1). The fracture was located slightly more proximally on the left and apart from this slight difference in location, appeared very similar. No osteopenia was appreciated on the radiographs. The patient was questioned again for any remote trivial trauma but she could recall none. As vitamin D deficiency is highly prevalent in India, she was investigated for the same and found to have hypovitaminosis D with serum vitamin D levels of 13.1ng/ml. Her serum calcium was borderline low measuring 8.9mg% and parathyroid hormone levels were normal. Since no other cause for her fractures was identified, a diagnosis of osteomalacic insufficiency fractures was made and patient started on vitamin D therapy (oral cholecalciferol 60,000 IU once a week for 6 weeks) and calcium supplements along with restricted weight bearing.
Fig. 1Antero-posterior radiograph of both legs reveal almost identical transverse undisplaced fractures of proximal shafts of both fibular bones(arrows), slightly more proximal on the left. Note that the bones appear normal in density.
Insufficiency fractures(IF) or fragility fractures, occur when normal or physiological muscular activity stresses a bone that is deficient in mineral or elastic resistance.
The incidence of IF increases with age; they are more frequent in women, occur at sites that mainly contain trabecular bone, and are associated with only minimal to moderate trauma.
Although more common in the elderly, IF can also occur in the young age group suffering from underlying conditions which weaken the bone such as osteoporosis due to any cause other than ageing, chronic inflammatory diseases such as rheumatoid arthritis and corticosteroid therapy, vitamin D deficiency, hyperparathyroidism, endocrine deficiencies, chronic renal failure etc.
The fibula receives only 6.4%–16.7% of the load transmitted from the lower extremity. Thus, insufficiency fractures of the fibula are rare. These are however known to occur with a relatively increased incidence in patients with rheumatoid arthritis, most of them having an associated valgus deformity of the knee or ankle. In these cases also, isolated bilateral fibular fractures have not been reported and it is more common to find simultaneous fractures of the tibia as well.
The imaging findings in osteomalacia may include reduced bone mass, this is however not an essential feature. Looser zones are more typical of this diagnosis. These so called “pseudofractures” are actually a type of insufficiency fractures and can occur at sites of weight bearing as well as non-weight bearing bones which differentiates them from fatigue fractures.
Depending on the bone affected and timing of imaging, stress fractures can present as subtle areas of cortical lucency, periosteal reaction, callus formation, cortical thickening, obvious fracture lines or ill-defined linear sclerosis on radiographs.
Fracture line on MRI is best appreciated on T1-WI as irregular linear hypointensity. More importantly, absence of extraosseous soft tissue component can help rule out infection or tumor. Bone scans reveal increased activity at the site of the fracture.
The treatment of choice for insufficiency fractures is conservative and consists mainly of immobilisation of the affected extremity with a cast and analgesics. In some cases, internal fixation may also be required. Management of the underlying etiology is essential to prevent recurrence.
4. Learning points
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Spontaneous isolated bilateral fibular fractures are exceedingly rare.
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In cases of atraumatic fibular fractures (unilateral or bilateral), possibility of stress fractures is the top differential.
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Vitamin D deficiency being endemic in some countries such as India should be suspected in such cases.
Funding
No funding
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
References
Verma R.
Singh J.P.
Magnetic resonance imaging in stress fractures: making a correct diagnosis.
Indian Journal of Musculoskeletal Radiology.2022; 4: 49
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