**2. Stiffness**

Normal knee range of motion (ROM) ranges from 0 to 140 degrees, while achievement of postoperative ROM from 0 to 110 degrees can be defined as success TKA [4]. In general, a minimum of 90 degrees of knee flexion is required for functional recovery in daily activities, as 83 degrees of knee flexion is required for going up and down stairs and 93 degrees for sitting, which were demonstrated by a biomechanical study [5, 6]. Stiffness after TKA has variable incidence, ranging from 1.3 to 5.3 percent, but some literature proposed up to 60 percent of patients who suffered from stiff TKA [7]. These variables may cause by a variety of definitions as there was absolutely no consensus on degrees of knee flexion limitation defined as stiff TKA. The standardized definition by the TKA Complications Workgroup of The Knee Society described that limitation of ROM as reported by the patient with physical examination showed extension restriction to 15 degrees short of full extension or flexion less than 90 degrees were defined as stiffness. However, this definition could not be applicable if the preoperative arc of motion is less than 75 degrees [3].
