Incidence and radiological characteristics of fabellae in an Asian population.
BACKGROUND
The fabella, a sesamoid bone sometimes found in the lateral head of the gastrocnemius muscle, often articulates directly with the lateral femoral condyle. This study aimed to determine the incidence of fabellae in an Asian population and to characterise the radiological features of the fabella.


METHODS
Electronic radiographs and magnetic resonance imaging films of 80 consecutive patients who underwent knee arthroscopy between May 2005 and October 2009 were reviewed to determine the presence and characteristics of the fabella.


RESULTS
The incidence of fabellae was 31.25% in our study cohort. The median length, thickness, width and distance of the fabella from the lateral femoral condyle were 7.06 mm, 4.89 mm, 6.12 mm and 33.19 mm, respectively. The fabella was consistently bony and located in the lateral head of the gastrocnemius, with 52% of the fabellae having an articulating facet. Fabellae in men were found to be larger than in women, although the difference was not statistically significant. The presence of an articulating groove was associated with increased size of the fabella, but not with the distance between the fabella and its insertion onto the lateral head of the gastrocnemius.


CONCLUSIONS
The incidence of fabellae in our population was lower than that in regional studies. They were consistently bony and not all had articulating grooves on the lateral femoral condyle. We found that the larger the fabella, the higher the chances of it having an articulating groove. By defining the radiological characteristics of the fabella, we provide objective parameters to help differentiate the fabella from other loose bodies or calcifications in the knee.
Department of Orthopaedic Surgery, Singapore General Hospital, Outram Road, Singapore 169609. bobchew_79@hotmail.com.
Chee Ping
CP
Chew
Kong Hwee
KH
Lee
Joyce Suang Bee
JS
Koh
Tet Sen
TS
Howe
D000293:Adolescent; D000328:Adult; D001182:Arthroscopy; D001208:Asia; D015331:Cohort Studies; D005260:Female; D006801:Humans; D015994:Incidence; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000473:pathology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging* / Q000473:pathology; D011859:Radiography; D012716:Sesamoid Bones / Q000000981:diagnostic imaging* / Q000473:pathology; D012737:Sex Factors; D055815:Young Adult