Assessing Recovery in Total Knee Arthroplasty: A critical narrative review of Muscle Mass, Strength, Physical Performance and Patient Reported Outcome Measures. (Preprint)

<sec> <title>BACKGROUND</title> Total Knee Arthroplasty (TKA) is the primary treatment for advanced knee osteoarthritis. Despite its clinical success and favourable Patient-Reported Outcome Measures (PROMs), approximately 20–30% of patients continue to experience persistent functional limitations and muscle weakness. This highlights the need for a comprehensive evaluation of recovery parameters beyond pain and Range of Motion (ROM). Given the wide range of methods available for assessing TKA outcomes, clinicians often select tools based on personal preference and understanding, which may affect accuracy and consistency; for example, the Knee Injury and Osteoarthritis Outcome Score (KOOS) may overestimate function compared to gait analysis studies. </sec> <sec> <title>OBJECTIVE</title> The aim of this study was to conduct a narrative review focusing on the utility, strengths and limitations of different outcome measures used in routine orthopaedic practice to optimise post-TKA evaluation. </sec> <sec> <title>METHODS</title> A literature search was conducted in February 2025 across two databases (PubMed and Web of Science). Eligible studies included original research articles, systematic reviews, and meta-analyses, that focused on validated measures used to evaluate TKA. Case reports, conference abstracts, and studies focused exclusively on surgical techniques were excluded. Themes were identified across studies to structure the results according to types of assessments and clinical applicability. </sec> <sec> <title>RESULTS</title> A total of 6,831 studies were retrieved and screened in this review, with four themes emerging around muscle mass, strength, performance and PROMs. The Oxford Knee Score (OKS) is favoured for its ease of use and minimal ceiling effects. Broader tools like KOOS and Western Ontario and McMaster Universities Osteoarthritis (WOMAC) provide detailed insights but are less practical clinically. For muscle strength, the Portable Fixed Dynamometer (PFD) showed high reliability and comparability to Isokinetic Dynamometry. Dual-energy X-ray Absorptiometry (DXA) remains the gold standard for assessing muscle mass, while Bioelectrical Impedance Analysis (BIA) offers a practical alternative. The Five-Repetition Sit-to-Stand (5R-STS) test effectively evaluates lower limb power and speed. </sec> <sec> <title>CONCLUSIONS</title> Clinicians should integrate both objective (muscle mass, strength, performance) and subjective (PROMs) measures to improve TKA recovery assessment. This multidimensional approach not only enhances the accuracy of patient evaluation but also supports the development of tailored rehabilitation strategies that address individual deficits and optimise functional outcomes. </sec>