Chronic Pain and Stiffness After Total Knee Arthroplasty: A Comprehensive, Phenotype-Based Review of Mechanisms, Diagnosis and Management

Background/Objectives: Total knee arthroplasty (TKA) relieves pain and restores function for most patients with end-stage knee disease; yet, a clinically important minority are left with persistent pain, stiffness or both despite well-fixed, well-aligned implants. These “hidden failures” are poorly captured by implant survivorship but drive disability, dissatisfaction and disproportionate cost—stiff knees incur roughly 1.5–7.5 times the two-year treatment costs of non-stiff knees. This review integrates three usually separate studies within one phenotype-based framework. Methods: A structured comprehensive narrative review and thematic synthesis was undertaken; PubMed/MEDLINE, Web of Science and Google Scholar were searched between 30 October 2025 and 1 May 2026, identifying 467 records, of which 239 met the eligibility criteria and informed the synthesis. Results: Clinically meaningful chronic pain affects roughly 10–30% of recipients and stiffness approximately 1–7%, with high-impact chronic pain persisting in about one-in-five and neuropathic features in a third to a half of those affected. Contemporary dissatisfaction estimates appear closer to 7–14% than the historical “one-in-five” paradigm, with persistent pain and stiffness the dominant drivers of residual dissatisfaction. Symptoms arise from interacting mechanical, fibrotic, infective, neuropathic, central and psychosocial mechanisms. Six practical phenotypes are proposed—pain-dominant with preserved motion, stiffness-dominant, combined stiff-and-painful, neuropathic-dominant, centrally sensitized, and arthrofibrosis with true mechanical block—and diagnosis, prevention and management are organized around them, spanning risk stratification, surgical technique, manipulation under anesthesia (mean gains ~30–47°, ~6% failure), arthrolysis, revision and multidisciplinary pain care. Conclusions: Chronic pain and stiffness are the quiet arithmetic of arthroplasty success—rare on the survivorship curve, common in the clinic. Matching treatment to phenotype and reserving the operating theater for a knee with a mechanical fault to fix rather than a nervous system to calm, offers the clearest path from a technically successful operation to a genuinely successful recovery.