The most common joint injuries in professional and recreational sports participants and also in the total population are knee injuries. Arthroscopy is indicated if this modality will improve the patient outcome and potential long-term complications can be avoided. Although uncommon, complications following arthroscopy are mostly evaluated by magnetic resonance imaging (MRI). For planning further therapy strategies following postarthroscopic complications, e.g. if anterior cruciate ligament (ACL) reconstruction is required, digital radiographs and computed tomography (CT) are helpful. This article provides an overview of the different procedures for surgical treatment which are a prerequisite for the analysis of postarthroscopic images. In addition typical complications after treatment of meniscal and chondral injuries as well as after ACL reconstruction are described and typical signs in MRI, radiography and CT are explained in detail.