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1、Normal radiographs of the knee with anteroposterior(a),lateral(b),and axial(c)biew demonstrate normal patellar position and morphology.The anteroposterior projection(a)is useful for evaluting the femur and proximal tibia,femoral and tibial plateaus.The lateral projection is useful for evaluating pat
2、ellar height,patellofemoral compartment,suprapatellar recess(SR),quadriceps tendon(QT),patellar tendon(PT).The axial view of the patella helps in assessment of the shape of the patella,note media(MF)and lateral(LF)patellar facets and median ridge(MR).Also note normal and rough anterior patellar cort
3、ex(blue arrow).,Sagittal proton density(a)and axial fat-suppressed T2-weighted(b)MR images of a normal knee.Note the low signal patellar(PT)and quadriceps(QT)tendons and the thick,homogeneous-appearing patellar cartillage(red arrows).Note the lateral and media retinacula,passive stabilizers of the p
4、atella.,In 1941,Wiberg classified patellar shape into three different morphologies:Type I(a)demonstrates roughly symmetric and equal-sized,concave medial(MF)and lateral(LF)patellar facets.Type II(b)shows a medial facet that is slightly smaller than the lateral facet and a concave lateral facet.Type
5、III(c)also shows a smaller and more vertically oriented medial patellar facet,which is associated with maltracking disorders 18.,5-year-old male with hereditary osteo-onychodysplasia(nail-patella syndrome).AP(a),later(b),and axial(c)views of the knee demonstrate complete absence of the bilateral pat
6、ellar ossification centers.,Anteroposterior and axial radiographs(a)show bilateral,well-corticated ossified fragments in the superolateral aspect of the patellas(arrows).Coronal and axial T2-weighted fat-suppressed MR image(b)show the well-corticated ossified fragment.Note the normal bone marrow sig
7、nal and cartilage across the synchondrisis,The well-corticated nature of the fragment and lack of abnormal marrow signal help to differentiate this entity from a patellar fracture.,Anteroposterior,lateral,and axial radiographs(s)show a lucent,round lesion with well-defined margins at the superolater
8、al aspect of the patella(arrows).Sagittal proton density and axial T2-weighted fat-suppressed MR images(b)show a focal subchondral osseous defect with intact-appearing overlying cartilage;the cartilage is thickened,and fills the defect.There is normal bone marrow signal and smooth,homogeneous signal
9、 of the articular cartilage.,Congenital patella alta is an anatomic risk factor for patellofemoral instability.The insall-Salvati index is the ratio of the length of the patella(PL)to the patellar tendon(PT).The normal value is between 1.0 and 1.2,with increased values indicating patella alta and de
10、creased value indicating patella baja.Lateral radiograph(a)at approximately 30 degrees of knee flxion shows a noemally placed patella,with Insall-Salvati index of 1.1.Lateral radiograph(b)of an 8-year-old male shows patella alta,with Insall-Salvati index measuring 1.8.Axial T2-weighted tubro spin ec
11、ho MR image(c)form this same patient shows finding of a lateral patellar dislocation.There is bone marrow edema of the medial aspect of the patella(arrow)and disruption of the medial patellar retinaculum(asterisk).This patient had a history of recurrent dislocations,likely due to his congenital pate
12、lla alta.,Anteroposterior(a)and lateral(b)radiographs of a 15-year-old female patient with cingenital right-sided patella baja.,Lateral radiographs of a patient one year following total knee arthroplasty demonstrates patella baja.The patellar tendon is scarred to the upper tibia(arrow).,Patella baja
13、 may also be seen in association with neuromuscular diseases.Fromtal(c)and lateral(d)radiographs in this patient with a history of polio show marked patella baja.Also nite that the bine are osteopenic and gracile and that there is a paucity of soft tissues,in keeping with the patients history of pol
14、io.,Trochlear dysplasia is among the most significant anstomic factors contributing to patellar maltracking Lateral radiograph(a)depicts one sign,the crossing sign,in which the line of the deepest aspect of the trochlear groove crosses over the antenor aspect of the femoral condyles(arrow).Sagittal
15、proton density image(b)depicts another hnding of trochlear dysplasia.The ventral trochlear prominence(vtp)has been detined as the distance between the line paralleling the ventral cortical surface of the distal femur and the most anterior point of the femoral trochlear floor.In this image is seen a
16、step-like deformity at the intertace of the anterior femoral cortex and trochiea with a vte measuring 9 mm,consistent with trochlear dysplasia.Axial T2-weighted fat-suppressed image(c)shows a congenitaly dysplastic trochlea with a markedly shallow trochiear depth(arrow),consistent with trochlear dys
17、olbsia Addisanally noted is marked asymmetry of the medial(MF)and lateral(LF)trochlear facets.A lateral to medalfemoral facet.rano ot greater than 1.75 is generally considered diagrosnc for trochlear dysplasia.In this case the ratio measures23.representing another tinding of trochlear doplasia,Troch
18、lear depth assessed on axial T2-weighted fat-suppressed images.A line is first drawn parallel to the posterior temoral condies(A).Lines drawn perpendicular to this indicate the anteroposterior dimensions of the lateral(B)and medial(C)trochlear facets and of the deepest portion of the lemoral trochle
19、a(D)Calculate trochlear depth with the equaion(BC/2)-D.Trochlear depth of 3 mm or less indicates trochlear dysplasia.image(a)shows a normal trochlear depth,image(b)shows a dysplasnc trochlea with marked flattening,The distance from the tibial tubercle to the trochilear groove is measured on axial MR
20、 images.A distance of 20 mm indicates considerable lateralization and is almost always associated with patellar instability.Axial MR images in the top row(a)show a normal tibial-tubercle groove distance(blue double-headed arrow).Images in the second row(b)show markedly lateral position of the tibial
21、 tubercle in relation to the trochlear groove(blue double-headed arrow).,30-vear old female former long distance runner presents with progressively increasing knee pain for 3 years,now sugnihcantly limiting her actinty Lateral radiograph(a)shows subchondral sclerosis(blue arrow)of the patela.Sagitta
22、l proton density(b),sagittal T2-weighted fat-suppressed(cl,and anial T2-weighted fat-suppressed(d)images show muitifocal areas of full-thickness cartilage fissuring along the patelitlafwhite arrows).with subjacent areas of marrow edema(red arrows)and subcortical cystic change.Note the normal carhlag
23、e elsewhere.,15-year-old male patient with knee pain.Lateral(a)and axial(b)radiographs show irregularity and a defect along the patellar apex(arrows).Sagittal proton density(c)and axial T2-weighted fat-suppressed(d)images show an osteochondral lesion in the mid patella at the apex with bone marrow e
24、dema(asterisk).Sagittal proton density image(e)from MRI performed 6 years latershows interval resolution of the lesion.,13-year-old female presenting with knee pain.Sagittal proton density(a),sagittal fat suppressed proton density(b),and axial fat-saturated proton density(c)MR images show an osteoch
25、ondritis dissecans lesion.There is surrounding high signal(black arrows)with small cystic change and focal cartilage defect.Sagittal proton density image(d)from four months later,following arthroscopic lesion repair,shows a well:incorporated bone graft.,16-year-old male with a history of acute lymph
26、oblastic leukemia(now in remissionl,diabetes melitus,and obesity.Anteroposterior(a),lateral(b),and axial(c)radiographs show a lucent area in the central posterior region of the right patella,with a halo of sclerosis.Sagital proton density(d),and coronal(e)and acial(f)T2 weighted fat-suppressed image
27、s demonstrate a lesion of intermediate and low signal intensity,surounded bya peripheral margin of low signal intensity Dark areas represent bone infarcts.,Axial radiograph(a)showing slight lateral subluxation of patella with corticated body along the medial patellar facet(arrow),stigmata of disloca
28、tion.,Axial radiograph(b)in a different patient shows normal alignment.Note the mild heterogeneity involving lateral aspect of the lateral femoral condyle(white arrow)and the subtle depression in the articular surface of the medial patellar facet(blue arrow,findings reflective of a recent patellar d
29、islocation.,Coronal fat-suppressed proton density(c)and axial fat-suppressed T2-weighted(d,elimages demonstrate bone marrow contusions along the medial patellar facet(white arrow)and the lateral aspect of the lateral femoral condyle(blue arrow).There is a partial tear of the medial patellar retinacu
30、lum(asterisk),and there is a moderate sized joint effusion with a fluid-fluid level(red arrow)representing hemarthrosis.These findings are typical for lateral patellar dislocation.,Anteroposterior(a)and lateral(b)radiographs in a patiernt presenting with a direct fall onto the patella showa comminut
31、ed fracture of the patella,with 8 mm of distraction at the mid bone.,Three images of a 12-year-old male following a fall who presented with anterior knee pain,swelling,and decreased ambulation.Lateral radiograph(a)shows a minimally displaced fracture of the interior patelia(arrow)with thickening of
32、the patellar tendon and a small knee joint effusion.Sagirtal proton density image(b)shows a tracture at the inferior pole of the patella(arrow)with edema of the patellar tendon.Axtial T2-weighted fat-suppressed image(c)shows edema at the inferior pole.,34-vear-old male presenting with persistent ant
33、erior right knee pain,associated with knee swelling.locking,and buckling.Sagittal proton density(a)and sagittal(b)and axial(c)T2-weighted fat-suppressed images were obtained showing severe thickening of the proximal patellar tendon and increased signal(arrows),consistent with severe tendinopathy of
34、the proximal patellar tendon.,44-year-old male former professional basketball player with chronic knee pain.Lateral radiograph(d)shows diffuse thickening and heterogeneity of the patellar tendon(arrow),with a small mature calcification within the proximal aspect,findings representing chronic tendino
35、pathy.,38year-old male following injury to his left knee while playing softball;reports feeling a tearing sensation.Lateral radiograph(a)shows soft issue prominence along the inftrapatellar tencon(astersk)and a subtle transverse lucenm in the inferior pateltla(white arrow).There is patella alta Sagi
36、ftal proton density(b)and sagirtal T2-weighted fat-suppressed(c)MR images show a complete tear of the patellar tendon at the inferior-most aspect of the patela(arrowsl.with retraction inferiorly.There is prominent patella alta.,Active 13-year-old male presenting with ongoing left knee pain.Lateral r
37、adiograph(a)shows a small fragment of bone adjacent to lower portion of left patella(arrow)and mild infrapatellar edema.MR sagittal T2-weighted(b)and coronal fat-suppressed proton density(c)images show fragmentation of the inferior patella and mild tendinosis at the patellar insertion of the patella
38、 tendon(arrow).,50-year-old patient with chronic anterior knee pain.Lateral radiograph(d)and sagittal proton density MR(e）image show abnormal morphology of the inferior patellar pole with adjacent mature calcification,consistent with chronic sequelae of Sinding-Larsen-Johansson syndrome.,Lateral(a)and axial(b)radiographs show significant soft tissue swelling anterior to the patella(arrows).Sagittal T2-weighted(c)and axial T2-weighted fat-suppressed(d)images show an oval-shaped fluid signal structure anterior to the patella representing the fluid-filled prepatellar bursa(asterisk).,
