A 36 yearold lady presentswithleftknee painafterslippingonice.She now hassevere knee pain
withmildswelling,andisunable toweightbear.Triage nurseshave givenhercodeineand
paracetamol,butexaminationisstill difficultdue topain.She isverytender alongthe jointline
particularlymedially,andcannotflex orextendherknee.She issentforanXray:
Lateral knee X-ray
AP knee X-ray
1. What doesthe X-rayshow?
2. Can yousee a fracture?
3. Doesshe needfurtherimaging?
The lateral knee x-rayshowsalipohaemarthrosis.Whenthereisanintraarticularfracture,fat and
bloodcan fromthe bone marrow intothe joint.The fat islessdense thanblood,soitforms2 layers.
Lipohaemarthrosesoccurinapproximately40% of all intraarticularfracturesof the knee,andare
usuallydue toa minimallydisplacedtibialplateaufracture.
2. There is no fracture seenonthe APor lateral Xray. Lipohaemarthrosismaybe the onlysignof
3. CT is indicated to further evaluate. In this patient, a CT left knee showed a minimally displaced
medial tibial platueau fracture. She was reviewed by Orthopaedics, who advised her to wear a
zimmer splint and not to weightbear. She was discharged home with appropriate analgesia and
follow up with the Orthopaedic Consultant in fracture clinc.
A 40 yearold man fell off hisbicycle andlandedonleftelbow.He gotstraightback upand cycled
home.Overthe followingdayhe hadgraduallyincreasingpain andswellingof hiselbow.On
examination,there wasasmall jointeffusion,nobonytenderness andlimitedflexion to45 degrees.
1. What do the X-raysshow?
2. What isthe treatment?
1. The lateral X-rayshowsa displacedanteriorfatpadand a visible posteriorfatpad.The APX-ray
showsa haemarthrosisandan intraarticularradial headfracture.
Thisis the fat padsign.Fat pads are intra-articularbutextra-synovial.Whenthere isajointeffusion
or haemarthrosis,the fatpadsare displaced.Onanormal Xray,the anteriorfatpad can be visible,
howeveradisplacedanteriorfatpad,the “SAILsign”,isabnormal and can indicate anoccultfrature.
A visible posteriorfatpadis alwaysabnormal.Inadults, the commonestfracture causingthe fatpad
signisa radial headfracture.Inchildren itisusuallyasupracondylarfracture.
Elbowjointeffusioncausingdisplacementof anteriorfatpadand visible posteriorfatpad.
2. This radial headfracture isnon displaced,andtherefore will heal wellwith immobilisation.He was
dischargedhome ina sling andadvisedtonotuse hisarm, withOrthopaedicfollowupinfracture
If there is displacementof the fracture fragment,the fragmentneedstobe reducedandfixatedwith
a plate or screwsintheatres.Thisisimportantto reduce the riskof stiffness,reducedfunction,