431: Subtyping Pain�Embodiment Relationship and Postoperative Pain Course After Knee Arthroplasty

Topic: Clinical Science
Subtopic: Pain category (ICD-11), Acute postsurgical pain, Psychology, Assessment and Measurement of Pain/Nociception, Physiotherapy

Background and Aims: The acute pain course after knee replacement (KR) may serve as an indicator of persistent postoperative pain (1). Moreover, distorted embodiment (e.g., “my knee was not part of my body”) is thought to interact with postoperative pain (2)(3). Therefore, this study aimed to identify subtypes in the dynamic interaction between postoperative pain and distorted embodiment, and to clarify their contribution to the course of pain.

Methods: Sixty-two KR patients were assessed daily from postoperative day 1 to ≥21. Rest pain and walking pain were measured using NRS. Concurrently, embodiment measures (ownership and agency) were assessed using 7-point Likert scales. Time-series data were analyzed using psychological network analysis (4). Bridge expected influence (BEI) was computed for each node in the temporal network (5). The metrics of pain-to-embodiment and embodiment-to-pain influence were calculated by summing BEI within pain and embodiment domains for hierarchical clustering. Pain courses over postoperative days 1–21 were summarized as linear slopes and compared between subtypes using Bayesian linear regression.

Results: Hierarchical clustering identified five subtypes: C1 (n=39, 62.9%), weak or negligible pain–embodiment interaction; C2 (n=3, 4.8%), strong pain–embodiment interaction associated with improvement in both domains; C3 (n=13, 21.0%), weak-to-moderate interaction associated with improvement; C4 (n=4, 6.5%), pain was weakly associated with changes in embodiment, whereas embodiment was associated with pain improvement; and C5 (n=3, 4.8%), pain was associated with embodiment improvement, whereas embodiment was associated with pain worsening. Bayesian linear regression showed that rest and walking pain slopes in C2 were less steep than those in the other subtypes, with differences supported by posterior credible intervals.

Conclusions: These findings suggest that stronger pain–embodiment interactions after KR may be associated with delayed postoperative pain improvement. Even when such interactions are simultaneously associated with improvements in pain and embodiment during the postoperative acute phase, they may be related to poorer long-term outcomes. In addition, in approximately 60% of patients after KR, interactions between pain and embodiment were weak or negligible. This suggests that, to better understand mechanisms underlying the postoperative pain course, more comprehensive investigations including not only embodiment but also other factors are needed.

References: 1) Chapman CR, Donaldson GW, Davis JJ, Bradshaw DH. Improving individual measurement of postoperative pain: the pain trajectory. J Pain. 2011; 12: 257-262.
2) Hirakawa Y, Hara M, Fujiwara A, Hanada H, Morioka S. The relationship among psychological factors, neglect-like symptoms and postoperative pain after total knee arthroplasty. Pain Res Manag. 2014; 19: 251-256.
3) Hiyama Y, Wada O, Nakakita S, Mizuno K. Joint awareness after total knee arthroplasty is affected by pain and quadriceps strength. Orthop Traumatol Surg Res. 2016; 102: 435-439.
4) Epskamp S, Waldorp LJ, Mõttus R, Borsboom D. The Gaussian Graphical Model in Cross-Sectional and Time-Series Data. Multivariate Behav Res. 2018; 53: 453-480.
5) Jones PJ, Ma R, McNally RJ. Bridge Centrality: A Network Approach to Understanding Comorbidity. Multivariate Behav Res. 2021; 56: 353-367.

Presenting Author: Tomoya Tanaka
Submitting Author: Tomoya Tanaka

Senior Author: Shu Morioka

IASP 2026 Global Year theme of Neuropathic Pain: No

• Masayuki Koga: PT, MSc - Department of rehabilitation, Kawanishi City Medical Center/ Department of Neurorehabilitation, Graduate School of Health Sciences, Kio University
• Kazuki Hayashida: PT, PhD - Wakayama Faculty of Health Care Sciences, Takarazuka University of Medical and Health Care/ Neurorehabilitation Research Center, Kio University
• Hayato Shigetoh: PT, PhD - Faculty of Health Sciences, Kyoto Tachibana University/ Neurorehabilitation Research Center, Kio University
• Ren Fujii: PT, PhD - Musashigaoka Clinical Research Center, Medical Corporation Tanakakai, Musashigaoka Hospital/ Neurorehabilitation Research Center, Kio University
• Masahiro Ubuyashiki: PT - Department of Rehabilitation, Fukuchiyama City Hospital/ Department of Neurorehabilitation, Graduate School of Health Sciences, Kio University
• koji Nakanishi: PT, MSc - department of rehabilitation, Yasaka Hospital
• Takuya Wada: PT - Department of Rehabilitation, Saiseikai Shiga Hospital
• Hironori Tanaka: PT - Department of Rehabilitation, Fukuchiyama City Hospital
• Shu Morioka: PT, PhD - Department of Neurorehabilitation, Graduate School of Health Sciences, Kio University/ Neurorehabilitation Research Center, Kio University