64 Part I Chapter 3 Abstract This review summarizes the role of SPECT/CT in patients with a painful postoperative knee and describes typical diagnostic criteria in these patients. Pain after knee surgery is common and is influenced by the underlying pathology, the type of surgery, and the patient. Knee joint-preserving surgery includes osteotomy, ligament reconstruction, meniscus surgery and cartilage repair procedures, often used in combination. Knee arthroplasty procedures consist of unicondylar, patellofemoral and primary or revision total knee prosthesis. In patients with pain after knee joint preserving surgery, MRI remains the reference standard. After ligament reconstruction, CT can evaluate postoperative tunnel positioning and bone SPECT/ CT can contribute by assessing overloading or biodegradation problems. After meniscal or cartilage surgery SPECT/CT can be particularly helpful to identify compartment overloading or nonhealing chondral or osteochondral lesions as cause of pain. SPECT/CT arthrography can assess cartilage damage at an early stage due to altered biomechanical forces. After corrective osteotomy of the knee SPECT/CT can reveal complications such as overloading, non-union or patellofemoral problems. After arthroplasty, conventional radiographs lack both sensitivity to detect aseptic loosening and specificity in differentiating aseptic from infectious loosening. Secondly, hardware-induced artefacts still hamper CT and MRI, despite improving and increasingly available metal artefact reduction techniques. Bone scintigraphy is a proven useful adjunct to conventional radiography and MRI to reveal the pain generator and is less hampered by artefacts from metallic implants compared to CT and MRI. Nevertheless, the optimal imaging strategy in evaluating complications after knee arthroplasty is still a matter of debate. Although the evidence on the use of bone-SPECT/CT is still limited, it is growing steadily. In particular, recent data on specific uptake patterns in tibial and femoral zones after TKA and the impact of integrating biomechanics into the assessment of SPECT/CT appear promising, but more research is needed.