Predictive Factors of "Forgotten Knee" Acquisition After Total Knee Arthroplasty: Long-Term Follow-Up of a Large Prospective Cohort.

Background: In a large prospective cohort, we recently showed that only 66.1% of total knee arthroplasty (TKA) with a perfect outcome according to Knee Society Knee Score was completely forgotten in all everyday activities. The main objective of this study was to identify clinical and orthopedic factors associated with the acquisition of "forgotten knee" (FK).

Methods: Patients undergoing TKA were enrolled between January 2001 and January 2008. Preoperative medical history, anthropometric data, and clinical data were recorded, and composite scores (Knee Society Score, Lequesne) were assessed. Radiography was performed before and after surgery. At each follow-up, FK acquisition was assessed by a closed question "Does the operated knee feel always normal in all everyday activities?"

Results: We included 510 TKAs performed in 423 patients followed up for a mean of 76.6 ± 28.5 months. On multivariate analysis, depression at baseline and presence of patellar subluxation after surgery were negatively associated with FK acquisition (odds ratio [OR] = 0.28 [95% confidence interval {CI}, 0.13-0.61], P = .001; and OR = 0.31 [0.12-0.79], P = .01, respectively), whereas increased active flexion at last follow-up was positively associated (OR = 1.07 [1.03-1.10], P < .0001). In patients with a perfect outcome (Knee Society Knee Score = 100), preoperative patellar pain, and postoperative patellar subluxation were negatively associated with FK acquisition (OR = 0.41 [0.18-0.93], P = .03 and OR = 0.21 [0.05-0.90], P = .04, respectively). Gender, age, body mass index, preoperative pain and functional limitation, and patellar resurfacing were not significantly related to FK.

Conclusion: Depression and patella maltracking may be associated with lack of FK acquisition after TKA, while postoperative increase in flexion may have a positive impact.