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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 evalu
2、ating patellar 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
3、 anterior patellar cortex (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 reti
4、nacula, passive stabilizers of the patella.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 la
5、teral facet and a concave lateral facet.Type 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
6、 knee demonstrate complete absence of the bilateral patellar 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
7、-corticated ossified fragment. Note the normal bone marrow signal 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
8、a lucent, round lesion with well-defined margins at the superolateral 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 th
9、e defect. There is normal bone marrow signal and smooth, homogeneous signal 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 va
10、lue is between 1.0 and 1.2, with increased values indicating patella alta and decreased 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 sho
11、ws patella alta, with Insall-Salvati index measuring 1.8. Axial T2-weighted tubro spin echo 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 (a
12、sterisk). This patient had a history of recurrent dislocations, likely due to his congenital patella 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 arthroplas
13、ty demonstrates patella baja. The patellar tendon is scarred to the upper tibia (arrow).Patella baja 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 oste
14、openic and gracile and that there is a paucity of soft tissues, in keeping with the patients history of polio.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 deep
15、est aspect of the trochlear groove crosses over the antenor aspect of the femoral condyles (arrow).Sagittal 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
16、surface of the distal femur and the most anterior point of the femoral trochlear floor.In this image is seen a 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 dysolbsia Addisanally noted is marked asymmetry of the medial (MF) and lateral (LF) troc
