Defining the lateral and accessory views of the patella: an anatomic and radiographic study with implications for fracture treatment.

OBJECTIVE: The majority of orthopaedic surgeons rely on a lateral fluoroscopic image to assess reduction during patella fracture osteosynthesis. However, a comprehensive radiographic description of the lateral view of the patella has not been performed previously, and no accessory views to better visualize specific anatomic features have been developed. The purpose of this study was to provide a detailed anatomic description of all radiographic features of the true lateral of the patella, describe reproducible accessory views for assessing specific features of the patella, and demonstrate their utility in a fracture model.

METHODS: Twelve cadaver knee specimens free of patellofemoral pathology were used, and imaging was performed using standard C-arm fluoroscopy. For each specimen, a true lateral radiographic projection of the patella was obtained and distinct features were noted. Next, an arthrotomy was made and steel wire was contoured and fixed to various anatomic regions of the patella so as to obliterate the radiographic densities on the true lateral projection, thus confirming their anatomic correlation. Ideal views of the lateral and medial facets themselves were determined using radiographic markers and varying amounts of internal or external rotation of the specimen. Last, a transverse osteotomy was created in each patella and the ability of the true lateral and accessory views to detect malreduction was assessed.

RESULTS: The true lateral projection of the patella was obtained with the limb in neutral alignment. Constant radiographic features of the lateral view of the patella include the articular tangent, a secondary articular density of variable length, and a dorsal cortical density. The articular tangent was produced by the central ridge between the medial and lateral facets in all specimens. The secondary articular density was created by a confluence of the edge of the lateral and edge of the medial facets in 5 patellas, a confluence of the edge of the lateral facet and the intersection of the odd and medial facets in 6 patellas, and the edge of the lateral facet alone in 1 patella. The edge of the lateral facet gave a constant contribution to the appearance of the secondary articular density in all cases. A distinct accessory view of the tangent of the lateral facet could be seen with an average of 17 degrees of patella external rotation (range, 12-35 degrees), and the tangent of the medial facet with an average of 26.5 degrees of internal rotation (range, 15-45 degrees). These accessory views were better able to visualize malreduction than the single lateral projection in a fracture model in all specimens.

CONCLUSIONS: Described here is a comprehensive description of the true lateral radiographic view of the patella and accessory views. These views can be used in the evaluation of minimally displaced patella fractures if a computerized tomography is not desired to better assess the true amount of displacement and when assessing intraoperative reduction during patella fracture osteosynthesis.