Imaging in Patellofemoral Instability

Abstract

Imaging in the setting of patellofemoral (PF) instability should begin with an adequate radiographic series including frontal, lateral, and axial projections. Potential predisposing factors such as trochlear or patellar dysplasias and patellar position should be assessed. Further evaluation with cross-sectional imaging by CT and MRI is helpful in providing measurements such as the tibial tuberosity-trochlear groove (TT-TG) distance and for soft tissue evaluation. MRI also allows for evaluation of sequela of recent or prior translational events of the PF joint, e.g., bone marrow contusions, location of disruption of the medial retinaculum and medial PF ligament (MPFL), extent of fractures, and the presence of osteochondral injury and fragments. The normal postoperative appearance after PF procedures requires knowledge of the normal pre-procedure anatomy and the surgical techniques performed on a particular patient. Proximal soft tissue realignment procedures include medial capsular plication, MPFL repair and reconstruction, lateral release, and trochleoplasty. Distal realignment procedures include a tibial tubercle osteotomy. Lastly, in the setting of chondral injury, various procedures may be performed for cartilage restoration, including pinning, chondral regeneration (e.g., autologous cartilage implantation), or osteochondral plugs.