"Forgotten knee" after total knee replacement: A pragmatic study from a single-centre cohort

Area of Science:

• Orthopedic surgery
• Biomedical engineering
• Patient-reported outcomes

Background:

• Total knee replacement (TKR) outcomes are typically assessed using conventional scores, which may not fully capture patient perception.
• Some TKR patients achieve a "forgotten knee" (FK) state, feeling their prosthesis is completely natural, while others remain aware of it.
• The prevalence and factors influencing FK after TKR require further investigation.

Purpose of the Study:

• To determine the prevalence of the "forgotten knee" (FK) phenomenon after total knee replacement (TKR).
• To compare the incidence of FK with conventional clinical outcome scores.
• To assess the time course of FK acquisition post-TKR.

Main Methods:

• A prospective pragmatic cohort study enrolled patients undergoing TKR between 2001 and 2008.
• Preoperative data, including medical history and clinical measurements, were collected.
• FK was assessed using the direct question: "Do you feel the operated knee to be always normal in all everyday activities?" at follow-up visits.

Main Results:

• The study included 584 TKRs in 485 patients, with 91.6% performed for severe osteoarthritis.
• At a mean follow-up of 75.8 months, 42.9% of TKRs achieved the FK state.
• While 86.1% of TKRs had excellent Knee Society Score (KSS) outcomes, only 66.1% of those with perfect scores (KSKS=100) reported FK.

Conclusions:

• Nearly half of total knee replacement patients experience a "forgotten knee" state, indicating a natural perception of the operated limb.
• The FK phenomenon is not perfectly correlated with high scores on conventional assessment tools like the Knee Society Score.
• Achieving a "forgotten knee" is a significant indicator of successful TKR outcomes, often realized within 18 months post-surgery.