Characteristics of Persistent Pain Composition Following Total Hip or Knee Arthroplasty: a Descriptive Study

Introduction Background: Knee and hip arthroplasties are primarily performed due to degenerative changes that typically result in pain, functional impairment, and a subsequent decline in quality of life [1]. Arthroplasty represents the definitive intervention, involving the removal of the degenerated, pain-inducing joint components and their replacement with artificial prostheses. These procedures are considered standard in orthopedic surgery, boasting high success rates and high levels of patient satisfaction [2,3,4]. Nevertheless, the surgeries are not without risks, including perioperative complications such as infection, thrombosis, and prosthetic dislocation. Additionally, the economic burden on healthcare systems is considerable, encompassing not only the costs of the surgery itself but also postoperative care and rehabilitation. Hence, it is essential that the procedure yields the desired pain-relieving and functional outcomes to justify its use. Osteoarthritis is the primary indication for arthroplasty, representing a leading cause of disability worldwide. In advanced stages of osteoarthritis, the pain profile can become multifaceted, often involving a combination of nociceptive, neuropathic, and nociplastic pain mechanisms. Nociceptive pain, stemming from joint tissue damage and inflammation, is the most prevalent form and is usually effectively managed by arthroplasty. However, the complexity of pain perception in osteoarthritis extends beyond the joint, potentially involving altered pain processing pathways within the central and peripheral nervous systems. Up to 20% of patients report significant persistent pain following arthroplasty despite uncomplicated surgery and no apparent source of pain. This could be explained by the presence of non-nociceptive pain. Neuropathic pain stem from nerve damage, while nociplastic pain is associated with altered central pain processing, leading to pain persisting even after the natural healing process [5]. Identifying the type of pain in patients with persistent post-surgical pain could have important implications for pre-surgical as well as post-surgical management.

Objective: The aim of this study is to explore the pain composition in terms of neuropathic, nociceptive and nociplastic pain in patients with persistent pain after total knee arthroplasty (TKA), total hip arthroplasty (THA), or unicompartmental knee arthroplasty (UKA).

Hypotheses: The investigators hypothesize that postoperative pain with multiple pain types is prevalent and that neuropathic and nociplastic pain is co-existent or conflated in a considerable proportion of patients. Thus, there is an increased prevalence of potential nociplastic pain among patients with a Neuropathic Pain score (DN4) reflecting 'possible neuropathic pain'.

Perspective: Correct identification of pain types has important implications for pain management pre-operatively, peri-operatively, and post-operatively. Moreover, a high proportion of patients with potential nociplastic pain could increase the focus on the link between preoperative patient characteristics and post-operative potential nociplastic pain. This would help targeting those individuals benefiting most from operation compared to non-surgical management. Although results from this post-operative population do not necessarily reflect the prevailing pre-operative pain composition, the results from the study can potentially form the basis for hypothesis testing in a pre-operative cohort.

Methods This protocol was registered before initiation of data collection.