In this study, we present three-dimensional computed tomography (CT) scan image findings of a case with congenital total absence of the quadriceps muscle and patella and partial absence of the sartorius muscle, which caused fixed flexion contracture of the knee joint. Physical examination, radiography, three-dimensional CT scan, and chromosome analysis of the patient were done. On physical examination, the knee joint was at 85 degree fixed flexion contracture. Radiographic views demonstrated soft tissue defects around left femur. Chromosome analysis was normal. CT scan showed total absence of the quadriceps femoris muscle and patella. Congenital absence of the extensor mechanism and patella are very rare anomalies. This case differed from other patellar aplasia or dysplasia syndromes with the presence of fixed flexion knee contracture and aplasia of the extensor mechanism.