Final flexion mobility after a total knee arthroplasty is an important factor in patient comfort. Some patients gain in flexion mobility, others do not. Is it possible to identify the clinical factors related to the patient that predicted the final gain in flexion? Materials and methods: A multicenter retrospective study directed by the Societe francaise de la hanche etdu genou (SFHG) was conducted on 1601 cases of total knee arthroplasty that had presented no complications and a minimal follow-up of 2 years. The gain in flexion was assessed by the difference between the preoperative and the final range of flexion. The range of the gain in flexion was tested based on eight factors: age, gender, etiology, body mass index, frontal deformity, preoperative flexum deformity and four levels of preoperative mobility: < 90 degrees, 90 degrees - 109 degrees, 110 degrees - 129 degrees, and >= 130 degrees. Results: A mean gain in flexion of 8.4 degrees +/- 14 degrees was found for the overall series. In 66% of cases, we found an increase of flexion and in 19% a loss of flexion. In cases with BMI higher than 35, varus deformity with an HKA angle < 166 degrees, or flessum greater than 5 degrees, the gain in flexion was significantly higher. A significantly different gain in flexion (P < 0.0001) was found in the four levels of preoperative flexion: the greatest gain in flexion was found in the ``<90 degrees'' group, then this gain was less in the next two groups, to become a significant decrease in the ``>= 130 degrees'' group. A decrease in flexion was noted in 51% of the cases in the latter group. Other factors such as age, sex, and etiology had no influence on the gain in flexion. Discussion: After TKA, a gain in flexion was often noted. The amount of gain depended on the preoperative range of flexion: the lower this level was, the more flexion increased. The presence of a varus deformity, morbid obesity, or flessum was associated with greater gain in flexion, even if the final flexion was lower than the mean flexion in the overall population. The search for these factors made it possible to predict a gain in flexion and discuss this with the patient. (C) 2015 Elsevier Masson SAS. All rights reserved.