Table 1 MRI checklist for the assessment of patellar maltracking
Patellar maltracking: associated features | Methods of assessment (among others) | Significance |
|---|---|---|
Trochlear dysplasia | Trochlear depth, lateral trochlear inclination, trochlear facet asymmetry (evaluated on most cranial axial images showing cartilage, approximately 3 cm above the joint line) | Geometric abnormality of the trochlear groove that can result in abnormal tracking of the patella along the trochlea |
Patella alta | Insall–Salvati index, Caton–Deschamps index | Relates to a long patellar tendon. For the patella to engage with the trochlea, a higher degree of flexion than normal is needed |
Lateralization of the tibial tuberosity | Tibial tubercle–trochlear groove distance (TT–TG) | High TT–TG would exert lateral pressure on the patella during extension and, if not counteracted by vastus medialis contraction, may predispose to patellar subluxation |
Lateral patellar tilt | Patellar tilt angle, patellofemoral angle | Sensitive marker for patellar instability present in significant proportion of patients |
Lateral patellar tilt | Edema at the superolateral aspect of Hoffa’s fat pad on MRI | Sensitive marker for patellar instability present in significant proportion of patients |
Hoffa’s fat pad impingement | Edema at the superolateral aspect of Hoffa’s fat pad on MRI | Significant association with several patellar maltracking indicators |
MPFL and medial patellar retinacular injury | Best evaluated on the axial fluid-sensitive MRI sequence | Present in the majority of patellar dislocation cases |
Chondral and osteochondral damage | MRI can show discrete osteochondral defect or various degrees of patellofemoral cartilage loss (Fig. 6) | Patellar maltracking is a significant risk factor for patellofemoral OA. Patellar dislocation can result in discrete osteochondral defects at the patella or lateral femoral condyle |