**1. Introduction**

The stiff knee (SKN) is considered as a clinical situation that the range of motion (ROM) is less than a 50° arc of movement [1, 2]. SKN causes a variable level of functional disability, painful discomfort during scarce knee mobility, limp in the gait cycle, and hamper with activities of daily living [3]. Normal walking requires 70°–80° of ROM, stairs require 80°–90° of ROM, and squatting requires at least 130° of ROM [4].

The main causes of SKN are previous surgery on the knee, advanced primary knee ostearthritis, secondary posttraumatic ostearthrosis, reflex sympathetic dystrophy (RSD), neuromuscular disorder, sequelae of previous infection, inflammatory diseases (rheumatoid and psoriatic arthritis), arthrofibrosis, and hemofilic arthropathy. Ankylosis is more common in patients who had their knee immobilized or who are wheelchair bound. The common clinical characteristics in patients with SKN are patela baja, quadriceps contracture, intra-articular adhesions, posterior capsule contracture, poor patellar gliding, and heterotopic ossification [5, 6]. Total knee arthroplasty (TKA) in SKN is a challenging procedure. One of the goals of TKA is to improve knee mobility, including ambulatory ability in the gait [7, 8]. Other goals of TKA in patients with SKN are to relieve pain, improve the alignment to correct the knee deformity, and provide knee stability.

The most relevant factor that predicts knee mobility after TKA is preoperative range of motion [9, 10]. Young age, female sex, and obese patients are more susceptible to achieve less mobility after TKA [11, 12]. In patients with SKNs, the predominant symptom is not mechanical pain. Functional disabilities like impairments in stair climbing, unable to sit on a chair, and inability to walk a long distance are common complaints. Psychological and cosmetic harms are associated with decline in the quality life. TKA is considered a valuable option to improve functional capacity and obtain a mobile knee.
