Prevalence of the fabella and its association with pain in the posterolateral corner of the knee: A cross-sectional study in a Romanian population

Abstract

The functions and clinical consequences of the fabella, a sesamoid bone found in the posterolateral aspect of the knee joint, are still a reason of intense debate in the scientific literature. Its incidence was reported to range between 20% and 87% and its presence was usually associated with the persistent pain in the posterolateral region of the knee. The aim of our study was to measure the prevalence, anatomic and clinical features of the fabella within a cross-sectional study, conducted in a Romanian orthopaedic center. Between 2015 and 2017, a consecutive series of 562 patients with knee injuries or persistent knee pain has been examined by radiographs and Magnetic Resonance Imaging and a set of anatomical and clinical parameters have been recorded. Collected data was evaluated with RadiANT DICOM Viewer and statistically analyzed with GraphPad Prism 7. The level of significance was set at P <.05. The incidence of the fabella in our study group was 16.93%, lower than previously reported for Caucasian populations. We found statistically significant differences regarding the possible association of the fabella with pain in the posterolateral corner of the knee (P = .04) and the 2 dimensions of the bone according to gender (P = .03 respectively P = .01), but the prevalence was not influenced by gender (P = .6). The anatomic characteristics could be important in differentiating this sesamoid bone from calcifications or loose bodies located in the knee joint region. Due to the high association with the posterolateral knee pain, the fabella should be recorded during knee examination as a differential diagnosis, before any surgical procedure.

Figure 1

A. Anteroposterior incidence of a radiographic film, showing the presence of fabella (arrow) behind the posterolateral femoral condyle. B. On lateral incidence the fabella (arrow) is aligned with the articular space in knee flexion. Male patient, 42 years, left knee.

Figure 2

The sagittal section of the MRI film from the same patient confirms the proximity of the fabella (arrow) to the posterolateral femoral condyle. MRI = magnetic resonance imaging.

Figure 3

Measurements of the fabella on a sagittal section of the MRI film from the left knee of a female patient, suggesting the presence of an articular facet with the posterolateral femoral condyle. MRI = magnetic resonance imaging.