Radiography: Radiograms are the most useful imaging modality in the majority of cases, with complications of a patellar fracture frequently identified radiographically. Anteroposterior (AP), lateral, and tangential or Merchant views should be featured in a radiographic examination for patellar fractures. In evaluating the trabecular pattern of the patella, comminution, and separation of fracture fragments, lateral views may be useful. In the assessment of vertical fractures and differentiating a fracture from a partitioned patella, tangential views are useful. Patella fractures may be obscured by AP radiographs. Radiology reports should note any distance over 3 mm between fragments of fractured patellar, as this may indicate increased incidence of posttraumatic degenerative arthritis and malunion. The identification of an osteochondral fracture is also crucial, as a loose body may occur if a fragment that contains cartilage, subchondral bone, and trabecular bone is displaced. In transverse fracture, it is important to evaluate the fragment displacement. Osteochondral fragments are best demonstrated on the lateral view; usually it is possible to identify the presence of an effusion and a high-riding patella. Radiographs are less useful than other modalities (e.g., MRI) in characterizing any cartilaginous injury associated with an osteochondral patellar fracture and can define fractures not otherwise detectable by radiographic examination. Sleeve fractures are located in the coronal plane of the patella, and are difficult to diagnose with radiographs. Differentiating between acute fractures from a partitioned patella may pose challenges on radiographs. The features of bipartite patella include even, corticated, opposing margins, best seen in the tangential projection. Comparison of two knees may be useful.

CT: CT is useful particularly when a suspected fracture cannot be seen on radiographs and for osteochondral injuries. If the CT scan results are normal, then a fracture can be excluded. The use of CT scanning can prevent delays in treatment and identify the location of fragments and the position of any intra-articular loose bodies. CT scanning has limited usefulness in evaluating soft tissue and bone marrow injury, and an MRI should be considered. CT scans may be better than MRIs in identifying loose bodies. CT scans are obtained with the patient in the supine position and with 15° of external rotation of feet pressed against a footrest at 90°. A complete exam comprises three scans with the knee resting, extended quadriceps contracted, and with a flexion of the knee of 15° with a relaxed leg. Multiplanar reconstruction should be done to better localize the displaced fragments. CT cannot determine the age of fractures because it may remain evident for up to 24 months.