The prevalence, morphology and topography of fabella in knee joints in the Polish population and its association with size of patella

Purpose The fabella is a sesamoid bone located posterior to the lateral femoral epicondyle within the gastrocnemius muscle. While commonly present in mammals, its prevalence in humans remains unclear, with reported rates ranging from 3% to 87%. Fabella is more frequently observed in Asian and Australian populations but is rare in European and American populations. Although often asymptomatic, it can sometimes cause knee pain, known as "fabella syndrome," and may contribute to neurological symptoms when in proximity to the common fibular nerve. Given the limited awareness of fabella’s presence, this study aims to assess its prevalence and anatomical characteristics to aid in the differential diagnosis of knee pain. Methods A retrospective analysis was conducted on 500 knee radiographs from 383 patients experiencing knee pain. Data collected included patient age and sex, fabella presence and dimensions, fabella location (distances to surrounding bony structures), patella dimensions, and patellotibial ligament length. Results Fabella was detected in 31 females (14.76%) and 29 males (25.66%). Among the examined knees, fabella was present in 40 (12.82%) of female and 39 (20.74%) of male knees. The mean fabella length was 8.85 mm (SD = 2.59), and thickness was 5.63 mm (SD = 1.88), with no significant sex differences. No correlation was found between fabella size and patella dimensions. Notably, patients with fabella were older on average, and bilateral fabellae were significantly larger than unilateral cases (p < 0.05). Conclusion Fabella is a relatively common anatomical variant in Central European populations, present in one in six women and one in four men. Its increased prevalence in older individuals suggests a potential age-related development. A comprehensive understanding of fabella anatomy may aid clinicians in diagnosing and managing unexplained knee pain, particularly in elderly patients.