What imaging characteristics are suggestive of malignancy in patients with femoral neck fractures? A look at calcar impaction lesions.

Introduction: Femoral heads are often sent for histological analysis when malignancy is suspected following a neck of femur (NOF) fracture. Anecdotally, a commonly seen lytic appearance on plain radiographs prompts suspicion of malignancy but does not correlate with histology results.

Aim: To evaluate the radiographic patterns of NOF fractures deemed suspicious for malignancy, and correlate those patterns with their subsequent histology results.

Methods: We performed a retrospective study of all NOF fracture patients who had femoral head histopathological analysis (N =376), across five hospitals in Yorkshire, over three years (2017-2019). Included were patients whose radiographs were deemed suspicious for malignancy by their clinicians (N = 79). All radiographs were evaluated, and their patterns categorized. Chi-Square test was used to analyse the relationship between each radiographic pattern and histology outcome (benign vs malignant disease). A p - value < 0.05 was deemed statistically significant.

Results: 79 eligible patients were identified, comprising 51 females and 28 males, with a mean age of 77 years. Radiographic patterns most associated with malignancy were 'multiple sclerotic lesions' (9 patients, 7 malignant, p < 0.01), and 'single lytic central neck lesion' (8 patients, 6 malignant, p = 0.01). 26 patients had an eccentric lesion with lytic appearance in the superolateral aspect of the femoral head/neck, all of which were benign (p < 0.01).

Conclusion: Being familiar with radiographic patterns of disease will help clinicians decide when to investigate a femoral head for malignancy. We identified a discrete pseudopathological pattern that commonly prompts clinicians to investigate for malignancy. We named this the 'calcar impaction lesion' as we posit that this 'lytic' appearance is due to mechanical impaction of osteoporotic bone during injury. Recognizing this pattern can save time and resources by avoiding unnecessary investigations.