To the authors' knowledge, this is the first report of simultaneous atraumatic bilateral neck of femur fracture occurring in a patient with significant background of chronic glucocorticoid usage. In particular, undisplaced neck of femur fracture in the contralateral hip was incidentally detected on magnetic resonance imaging – despite the absence of pain, trauma or concerning radiographic features. This case highlights two important points: first, clinicians should have an index of suspicion for bilateral fracture incidence in patients with long-term glucocorticoid usage; second, in cases of chronic glucocorticoid usage with known unilateral fragility hip fracture, magnetic resonance imaging should be considered to rule out contralateral radiograph-negative hip fracture even in the absence of symptoms.

Presence of simultaneous bilateral neck of femur fractures following low-velocity injury or without antecedent trauma should raise suspicion of an underlying systemic etiology. Amongst the limited reports of such cases in existing literature, possible contributing factors include severe osteoporosis, hypophosphatemic rickets disease, renal osteodystrophy and anti-epileptic usage. Arisumi et al. reported a case of a 33-year-old gentleman with severe osteoporosis and vitamin-D deficiency who developed simultaneous bilateral neck of femur fractures without antecedent trauma [4], while Uzun et al. reported a case of a 26-year-old lady with significant history of autosomal recessive hypophosphatemic rickets disease with similar atraumatic presentation during the postpartum period [1]. John et al. reported three cases of end-stage renal disease with renal osteodystrophy with simultaneous bilateral neck of femur fractures after episodes of grand mal convulsions [2]. Sadiq et al. reported a case of low-energy simultaneous bilateral neck of femur fractures in a 50-year-old epileptic patient on long-term phenytoin who fell from bed [3].

Considering that our patient's bone mineral density was in the osteopenic range, our case demonstrates that chronic glucocorticoid usage may be an independent risk factor for simultaneous bilateral neck of femur fractures even without severe osteoporosis. The incidence of fragility fractures may be predisposed by glucocorticoid usage through several mechanisms: suppressed osteoblastic activity, reduced intestinal and renal calcium absorption and/or increased calcium excretion [5]. The net effect is inhibition of bone formation, as well as increased bone resorption (resulting from secondary hyperparathyroidism) [5]. These alterations in bone physiology may similarly explain the incidence of delayed union or non-union of surgically-treated hip fractures in patients with chronic glucocorticoid usage, and the proposed use of anabolic drugs such as teriparatide in such patients to facilitate osteoblastic activation [6].

Importantly, clinicians should be aware that both short-term high glucocorticoid exposure, as well as high cumulative glucocorticoid exposure over time, predispose incidence of hip fracture. In a population-based study using the Danish National Health Service data, consisting of 81,342 patients, Amiche et al. demonstrated that the risk of hip fractures was independently increased by both high daily prednisolone dose (i.e., exceeding 15mg per day) (adjusted odds ratio (OR) 2.50 (2.19-2.85)) and high cumulative prednisolone dose (i.e., exceeding 1g) (adjusted OR 1.64 (1.54-1.74)) [7]. This risk was further compounded when the prednisolone regime consisted of both a high daily and cumulative dose (adjusted OR 2.94 (2.52-3.42)).

While current clinical practice recommends the use of magnetic resonance imaging to rule out occult fractures in symptomatic patients with predisposing comorbidities, the diagnostic approach to asymptomatic patients – with or without known unilateral fragility fracture – is unclear. This in turn highlights a gap in current literature on the prevalence of asymptomatic, radiograph-negative hip fractures in patients with predisposing factors: while studies examining the magnetic resonance imaging results of asymptomatic hips exist, the majority of such research focuses on the prevalence of acetabular cartilage loss and labral tears in athletes [8] or avascular necrosis in patients with risk factors such as systemic lupus erythematosus [9]. Future research addressing this specific gap in knowledge will be necessary in determining whether there is utility in routine magnetic resonance imaging to rule out asymptomatic, radiograph-negative hip fractures in patients with risk factors, when balanced against the cost and availability of magnetic resonance imaging capabilities. Our case provides an example where the aforementioned change in clinical approach would have significant clinical utility. Importantly, failure to pick up these occult fractures will lead to debilitating consequences downstream, including fracture displacement with or without trauma, readmission for further treatment, subsequent secondary surgical-related risks and resetting a patient’s rehabilitation post-surgery.