Predicting chronic postsurgical pain: current evidence and a novel program to develop predictive biomarker signatures

Effect of Different Doses of Esketamine on Postoperative Recovery in Patients Undergoing Gynecologic Laparoscopic Surgery, a Randomized, Double-Blind, Single-Center Clinical Study

Purpose

This study aimed to explore the effect of preoperative different doses of esketamine on postoperative recovery in patients undergoing gynecologic laparoscopic surgery.

Methods

A total of 99 women scheduled for gynecologic laparoscopic surgery under general anesthesia were enrolled and randomized. Three minutes before surgical incision, patients in the three groups were intravenously administered 0.25 mg/kg esketamine, 0.5 mg/kg esketamine, and an equivalent dose of saline, respectively. The primary outcome was the Quality of Recovery-15 (QoR-15) score assessed on 1 day (pod1), 3 days (pod3), and 7 days postoperatively (pod7). Secondary outcomes encompassed the VAS score, MAP, HR, frequency of rescue analgesia and length of hospital stay.

Results

Compared with group C, QoR-15 score was significantly improved in group E1 and E2 on pod1, while the rest VAS score was significantly decreased at 6h postoperatively (F =19.164, P < 0.001; F = 6.059, P = 0.034). On pod1, the VAS scores at rest and movement in group E2 were significantly lower than those in group C (P = 0.007, P = 0.038). There was a significant decrease in resting VAS scores in the E2 group compared with group C on pod3 (P = 0.021). Compared with group C, the QoR-15 score in group E2 increased on pod7 (P = 0.008), but there was no clinical difference. There was no significant difference in MAP and HR among the three groups at each time point (F = 0.758, P = 0.471; F = 0.232, P = 0.794). There was a significant difference in the number of postoperative rescue analgesia among the three groups (P = 0. 023).

Conclusion

Preoperative single small dose of esketamine can improve the quality of recovery 24h after gynecologic laparoscopic surgery patients, decrease the number of rescue analgesia, and may contribute to the rapid recovery of patients. And 0.5 mg/kg esketamine seems to be better.

Chronic postsurgical pain after cardiac surgery: A narrative review

Chronic postsurgical pain (CPSP) is a prevalent and debilitating sequela of cardiac surgery, exerting a profound impact on patients' quality of life, functional recovery, and healthcare systems. Its pathophysiology includes complex mechanisms, including peripheral and central sensitization, neuroplastic alterations, and inflammatory pathways, influenced by demographic, psychological, and perioperative factors. Inadequate management of acute pain is a critical contributor to its development. This review examines the etiology of CPSP, presents key risk factors, and critically evaluates pharmacological and nonpharmacological interventions. Particular attention is devoted to the role of regional anesthesia techniques and emerging preventive and therapeutic strategies, highlighting the necessity of multidisciplinary, evidence-informed approaches to address this persistent clinical challenge.

Outcome Indicators for Evaluating Interventions by Advanced Practice Nurses Specialising in Acute Pain: A Scoping Review

AIM

To identify outcome indicators to evaluate interventions delivered by advanced practice nurses specialising in acute pain as reported in the scientific literature.

DESIGN

Scoping review.

DATA SOURCES

Three databases (PubMed, Scopus and CINAHL) were systematically searched in December 2023 to identify studies published between 1996 and 2023.

REVIEW METHODS

Search results were managed through the Rayyan platform. Two review authors independently performed data selection and extraction, and a third reviewer resolved conflicts.

RESULTS

The search identified 1263 studies. After screening titles and abstracts, 14 full-text studies were selected for data extraction and analysis. These studies encompassed a variety of designs, including randomised controlled trials, cohort studies and observational studies. The outcome indicators used to evaluate advanced practice nurses' interventions in acute pain management were examined across three key dimensions: study population and setting, intervention and model of acute pain nurse care and quality-of-care assessment. The specific outcome indicators identified included 'pain score', 'side effects', 'analgesia prescription', 'non-pharmacological interventions', 'nurses' pain management knowledge', 'patient/parent education' and 'APN contact'.

CONCLUSION

This review underscores the growing and evolving role of advanced practice nurses (APNs) in acute pain management, highlighting the diversity of care models and interventions implemented across clinical settings. Key outcome indicators, such as 'pain score', 'side effects' and 'nursing staff's understanding of pain management', were identified, with certain indicators, like 'APN contact' and 'non-pharmacological interventions', more closely linked to the nurse-led approach.

IMPLICATIONS FOR THE PROFESSION

This scoping review underscores the importance of developing and evaluating outcome indicators to enhance the assessment of interventions provided by advanced practice nurses in acute pain management. While consensus on specific indicators has not yet been reached, this review highlights the need for further research to refine and standardise these indicators, thereby contributing to more uniform and comparative evaluations of care.

IMPACT

The identified outcome indicators can inform the evaluation of APN interventions in acute pain management, supporting efforts to optimise and standardise care. Further implementation and assessment of these indicators will be essential to enhance the quality and effectiveness of patient care.

REPORTING METHOD

The PRISMA extension for Scoping Review guidelines was used.

PATIENT OR PUBLIC CONTRIBUTION

No patient or public contribution.

The Role of Biomarkers in Acute Pain: A Narrative Review

Acute pain, a critical aspect of patient care, presents a challenge due to its subjective nature and complex biological underpinnings. Biomarkers for acute pain promise a paradigm shift in how pain is perceived, diagnosed, and managed. The study of genetic, inflammatory, and neurotransmission markers associated with pain experience may hold the key for the development of personalized and effective pain management strategies. This narrative review explores the neurobiological pathways of acute pain, encompassing inflammatory responses and neurotransmission mechanisms. It synthesizes current research on the identification and clinical application of biomarkers, emphasizing their potential to enhance diagnostic precision, treatment effectiveness, and risk prediction. We underscore the promising role of acute pain biomarkers in identifying patients at risk for developing acute and potentially chronic pain, predicting patients' response to pharmacological interventions, and aiding in the development of novel therapeutic and pain preventive strategies. The evolving landscape of biomarker research not only deepens our understanding of pain mechanisms but also lays the foundation for more tailored and patient-specific healthcare interventions.

Predicting Individual Pain Sensitivity Using a Novel Cortical Biomarker Signature

Importance

Biomarkers would greatly assist decision-making in the diagnosis, prevention, and treatment of chronic pain.

Objective

To undertake analytical validation of a sensorimotor cortical biomarker signature for pain consisting of 2 measures: sensorimotor peak alpha frequency (PAF) and corticomotor excitability (CME).

Design, Setting, and Participants

This cohort study at a single center (Neuroscience Research Australia) recruited participants from November 2020 to October 2022 through notices placed online and at universities across Australia. Participants were healthy adults aged 18 to 44 years with no history of chronic pain or a neurological or psychiatric condition. Participants experienced a model of prolonged temporomandibular pain with outcomes collected over 30 days. Electroencephalography to assess PAF and transcranial magnetic stimulation (TMS) to assess CME were recorded on days 0, 2, and 5. Pain was assessed twice daily from days 1 through 30.

Exposure

Participants received an injection of nerve growth factor (NGF) to the right masseter muscle on days 0 and 2 to induce prolonged temporomandibular pain lasting up to 4 weeks.

Main Outcomes and Measures

The predictive accuracy of the PAF/CME biomarker signature was determined using a nested control-test scheme: machine learning models were run on a training set (n = 100), where PAF and CME were predictors and pain sensitivity was the outcome. The winning classifier was assessed on a test set (n = 50) comparing the predicted pain labels against the true labels.

Results

Among the final sample of 150 participants, 66 were female and 84 were male; the mean (SD) age was 25.1 (6.2) years. The winning classifier was logistic regression, with an outstanding area under the curve (AUC = 1.00). The locked model assessed on the test set had excellent performance (AUC = 0.88; 95% CI, 0.78-0.99). Results were reproduced across a range of methodological parameters. Moreover, inclusion of sex and pain catastrophizing as covariates did not improve model performance, suggesting the model including biomarkers only was more robust. PAF and CME biomarkers showed good to excellent test-retest reliability.

Conclusions and Relevance

This study provides evidence for a sensorimotor cortical biomarker signature for pain sensitivity. The combination of accuracy, reproducibility, and reliability suggests the PAF/CME biomarker signature has substantial potential for clinical translation, including predicting the transition from acute to chronic pain.

Evidence for regional anesthesia in preventing chronic postsurgical pain

Chronic postsurgical pain (CPSP) is a common adverse outcome following surgical procedures. Despite ongoing research, the risk factors and effective strategies for mitigating CPSP remain uncertain. Regional anesthesia is a potentially beneficial yet debated intervention for mitigating the risk of CPSP. This review will delve into the mechanistic aspects of regional anesthesia and critically assess the current literature to provide a thorough understanding of its role and effectiveness. The incidence and severity of CPSP are linked to nerve damage, neuroplastic changes and immunological responses. Although numerous mechanisms contributing to CPSP have been identified, translational research is sparse, and findings are often inconsistent. Evidence suggests that regional anesthetic techniques could have a role in reducing CPSP risk across various clinical scenarios. Techniques studied include wound infiltration, peripheral nerve blocks, fascial plane blocks, thoracic paravertebral blocks and epidural anesthesia. Current data indicate that epidural anesthesia might decrease CPSP risk following thoracotomy, wound infiltration may be effective after major breast surgery and cesarean delivery, and serratus anterior plane block or pectoralis/interpectoral plane blocks might be beneficial in breast surgery. However, the existing evidence is limited and marked by several constraints especially the multifactorial causes, underscoring the need for further research in this area.

Chronic postsurgical pain and transitional pain services: a narrative review highlighting European perspectives

BACKGROUND/IMPORTANCE

Chronic postsurgical pain (CPSP) is a significant, often debilitating outcome of surgery, impacting patients' quality of life and placing a substantial burden on healthcare systems worldwide. CPSP (pain persisting for more than 3 months postsurgery) leads to both physical and psychological distress. Recognized as a distinct chronic pain entity in International Classification of Diseases, 11th Revision, CPSP enables better reporting and improved management strategies. Despite advancements in surgical care, CPSP remains prevalent, affecting 5%-85% of patients, with higher rates following thoracotomies, amputations, mastectomies and joint replacements.

OBJECTIVE

The acute to chronic pain transition involves complex interactions between peripheral and central mechanisms, with central sensitization playing a key role. Identifying high-risk patients is crucial for prevention, with factors such as surgical type, nerve injury, neuropathic elements in acute postoperative pain, and psychosocial conditions being significant contributors.

EVIDENCE REVIEW

Current pain management strategies, including multimodal therapy and regional anesthesia, show limited effectiveness in preventing CPSP. Neuromodulation interventions, though promising, are not yet established as preventive modalities.

FINDINGS

Transitional pain services (TPSs) offer a comprehensive, multidisciplinary approach to managing CPSP and reducing opioid dependence, addressing both physical and psychosocial aspects of functional recovery. While promising results have been seen in Canada and Finland, TPSs are not yet widely implemented in Europe. There is also growing interest in pain biomarkers, through initiatives such as the A2CPS program, aiming to improve CPSP prediction and develop targeted interventions.

CONCLUSIONS

Future research should focus on large-scale studies integrating various factors to facilitate CPSP prediction, refine prevention strategies and reduce its long-term impact.

Innovations in acute and chronic pain biomarkers: enhancing diagnosis and personalized therapy

Pain affects millions worldwide, posing significant challenges in diagnosis and treatment. Despite advances in understanding pain mechanisms, there remains a critical need for validated biomarkers to enhance diagnosis, prognostication, and personalized therapy. This review synthesizes recent advancements in identifying and validating acute and chronic pain biomarkers, including imaging, molecular, sensory, and neurophysiological approaches. We emphasize the emergence of composite, multimodal strategies that integrate psychosocial factors to improve the precision and applicability of biomarkers in chronic pain management. Neuroimaging techniques like MRI and positron emission tomography provide insights into structural and functional abnormalities related to pain, while electrophysiological methods like electroencepholography and magnetoencepholography assess dysfunctional processing in the pain neuroaxis. Molecular biomarkers, including cytokines, proteomics, and metabolites, offer diagnostic and prognostic potential, though extensive validation is needed. Integrating these biomarkers with psychosocial factors into clinical practice can revolutionize pain management by enabling personalized treatment strategies, improving patient outcomes, and potentially reducing healthcare costs. Future directions include the development of composite biomarker signatures, advances in artificial intelligence, and biomarker signature integration into clinical decision support systems. Rigorous validation and standardization efforts are also necessary to ensure these biomarkers are clinically useful. Large-scale collaborative research will be vital to driving progress in this field and implementing these biomarkers in clinical practice. This comprehensive review highlights the potential of biomarkers to transform acute and chronic pain management, offering hope for improved diagnosis, treatment personalization, and patient outcomes.

Gray matter volume of limbic brain structures during the development of chronic back pain: a longitudinal cohort study

ABSTRACT

This study set out to investigate in a population-based longitudinal cohort, whether chronification of back pain (BP) is related to structural gray matter changes in corticolimbic brain structures. Gray matter volume (GMV) was measured in participants with chronic BP (CBP, n = 168) and controls without chronic pain (n = 323) at 2 time points with an interval of 7 years (baseline t1, follow-up t2). Over this time period, participants with CBP showed an increase of GMV in the left ventral striatum, whereas controls showed a decrease. By contrast, participants with CBP had a GMV decrease in the left parahippocampal gyrus. Within the CBP group, pain duration was negatively associated with GMV in the left caudate. Those with emerging CBP had less GMV in the right entorhinal area, right amygdala, and left medial frontal cortex. Additional variables differing between those who had BP at t1 and later developed CBP or not were pain intensity, body mass index, and depression score. In sum, these findings are in accordance with the notion that limbic brain properties are both predisposing risk factors and drivers of brain reorganization during the development of CBP.

What has brain diffusion magnetic resonance imaging taught us about chronic primary pain: a narrative review

ABSTRACT

Chronic pain is a pervasive and debilitating condition with increasing implications for public health, affecting millions of individuals worldwide. Despite its high prevalence, the underlying neural mechanisms and pathophysiology remain only partly understood. Since its introduction 35 years ago, brain diffusion magnetic resonance imaging (MRI) has emerged as a powerful tool to investigate changes in white matter microstructure and connectivity associated with chronic pain. This review synthesizes findings from 58 articles that constitute the current research landscape, covering methods and key discoveries. We discuss the evidence supporting the role of altered white matter microstructure and connectivity in chronic primary pain conditions, highlighting the importance of studying multiple chronic pain syndromes to identify common neurobiological pathways. We also explore the prospective clinical utility of diffusion MRI, such as its role in identifying diagnostic, prognostic, and therapeutic biomarkers. Furthermore, we address shortcomings and challenges associated with brain diffusion MRI in chronic primary pain studies, emphasizing the need for the harmonization of data acquisition and analysis methods. We conclude by highlighting emerging approaches and prospective avenues in the field that may provide new insights into the pathophysiology of chronic pain and potential new therapeutic targets. Because of the limited current body of research and unidentified targeted therapeutic strategies, we are forced to conclude that further research is required. However, we believe that brain diffusion MRI presents a promising opportunity for enhancing our understanding of chronic pain and improving clinical outcomes.

Structural and functional connectivity coupling as an imaging marker for bone metastasis pain in lung cancer patients

BACKGROUND

Cancer pain is a common symptom in patients with malignant tumors and associated with poor prognosis and a high risk of death. Structural connectivity (SC) and functional connectivity (FC) couplings have not yet been explored in lung cancer patients with bone metastasis pain.

METHODS

In total, 51 patients with lung cancer without bone metastasis pain (BMP-), 52 patients with lung cancer with bone metastasis pain (BMP+), and 28 healthy controls (HC) were prospectively enrolled in our study. Firstly, SC-FC couplings were measured and analyzed at global, regional, and modular levels. Subsequently, individualized SC-FC coupling networks were constructed based on the Euclidean distance metric. In addition, the convolutional neural network (CNN) model was selected to analyze and classify three groups based on individualized networks.

RESULTS

The coupling analysis demonstrated that weaker SC-FC couplings related to lung cancer itself were present at various levels, including global, regional, inter-network, and intra-network couplings. Notably, hyper-couplings related to bone metastasis pain were present in several brain regions, mainly involving the default mode network, frontoparietal network, salience network, and limbic system. Significant positive correlations were observed between regional coupling in the right amygdala and the numeric rating scale scores in BMP+. Moreover, CNN model built on individualized networks exhibited relatively great classification performance.

CONCLUSION

Alterations in SC-FC coupling patterns may play a crucial role in the development and modulation of bone metastasis pain. Understanding these changes could provide valuable insights into the neural mechanisms underlying cancer pain.

Do cytokines play a role in the transition from acute to chronic musculoskeletal pain?

Musculoskeletal pain has a high prevalence of transition to chronic pain and/or persistence as chronic pain for years or even a lifetime. Possible mechanisms for the development of such pain states are often reflected in inflammatory or neuropathic processes involving, among others, cytokines and other molecules. Since biologics such as blockers of TNF or IL-6 can attenuate inflammation and pain in a subset of patients with rheumatoid arthritis, the question arises to what extent cytokines are involved in the generation of pain in human musculoskeletal diseases. In numerous experimental non-human studies, cytokines have been shown to alter neuronal sensitivity in the peripheral and central nociceptive systems. In this review, we addressed the involvement of cytokines in postoperative pain, complex regional pain syndrome, rheumatoid arthritis, osteoarthritis, temporomandibular joint disease, low back pain and fibromyalgia using PubMed searches including meta-analyses of data. There is evidence that certain pro- and anti-inflammatory cytokines are regulated in all of these diseases, often in both acute and chronic disease states. However, within these data, we found a great deal of heterogeneity in the association between cytokine levels and pain. Neutralization of cytokines showed antinociceptive effects in subgroups of patients with chronic pain (e.g., in a proportion of patients with rheumatoid arthritis), but failed to reduce chronic pain in other diseases (e.g., osteoarthritis). More systematic studies are needed to unravel the pathogenic role of cytokines in human musculoskeletal pain, taking into account the disease process and the mechanisms of pain initiation and maintenance.

The Role of Cortisol and Dehydroepiandrosterone in Obesity, Pain, and Aging

Obesity, chronic pain, and aging are prevalent global challenges with profound implications for health and well-being. Central to these processes are adrenal hormones, particularly cortisol and dehydroepiandrosterone (DHEA), along with its sulfated form (DHEAS). Cortisol, essential for stress adaptation, can have adverse effects on pain perception and aging when dysregulated, while DHEA/S possess properties that may mitigate these effects. This review explores the roles of cortisol and DHEA/S in the contexts of obesity, acute and chronic pain, aging, and age-related diseases. We examine the hormonal balance, specifically the cortisol-to-DHEA ratio (CDR), as a key marker of stress system functionality and its impact on pain sensitivity, neurodegeneration, and physical decline. Elevated CDR and decreased DHEA/S levels are associated with worsened outcomes, including increased frailty, immune dysfunction, and the progression of age-related conditions such as osteoporosis and Alzheimer's disease. This review synthesizes the current literature to highlight the complex interplay between these hormones and their broader implications for health. It aims to provide insights into potential future therapies to improve pain management and promote healthy weight and aging. By investigating these mechanisms, this work contributes to a deeper understanding of the physiological intersections between pain, aging, and the endocrine system.

Neuroimage Signature in Post-Stroke Pain: A Systematic Review

INTRODUCTION

Central Post-Stroke Pain (CPSP) is a debilitating condition with a significant prevalence in stroke survivors. Set apart by its refractory to treatment neuropathic pain, it appears to arise from lesions in the spino-thalamo-cortical pathways, particularly in the thalamus. Despite advances in neuroimaging techniques, the pathophysiology of CPSP remains poorly understood, with limited diagnostic criteria and therapeutic approaches.

OBJECTIVE

This systematic review aims to identify neuroimaging markers associated with CPSP, establish correlations between brain lesions and CPSP development, and explore the utility of neuroimaging techniques for diagnosis and prognosis. Secondary objectives involve establishing a link between CPSP and secondary brain area lesions and what type of pain patients with CPSP are more likely to experience.

METHODS

A systematic review was conducted following PRISMA guidelines. Relevant articles were sourced from PubMed, Embase, and Web of Science, using a predefined search strategy targeting CPSP and neuroimaging studies (MRI, PET, SPECT). Studies involving adult CPSP patients with post-stroke neuroimaging were included. Data from 14 studies was analyzed, focusing on lesion locations, neuroimaging findings, and functional connectivity. Risk of bias was assessed using the QUADAS-2 tool.

RESULTS

Key findings highlighted the association of CPSP with lesions in the ventral posterolateral and the ventral medial nuclei of the thalamus, spinothalamic pathway, and cortical areas like the insula and operculum. Functional connectivity studies highlighted the role of disrupted neural networks in pain perception. Limitations in the reviewed studies included small sample sizes, selection bias, and heterogeneity in study designs.

CONCLUSIONS

Neuroimaging findings confirm the significance of thalamic and spinothalamic pathway lesions in CPSP pathophysiology. Despite these insights, gaps in research underline the need for larger, multicenter trials to identify reliable biomarkers for diagnosis and therapeutic targets. Advanced neuroimaging combined with machine learning could be the key to understanding and managing CPSP.

Development and validation of a prediction model for chronic post-surgical pain risk: a single-center prospective study of video-assisted thoracoscopic lung cancer surgery

BACKGROUND

Chronic post-surgical pain (CPSP) is a common complication following video-assisted thoracoscopic surgery (VATS) that significantly impacts the quality of life of patients. Although multiple risk factors have been identified, no systematically validated prediction model exists to guide clinical decision-making.

OBJECTIVES

This study aimed to develop and validate a risk prediction model for CPSP in patients undergoing VATS for lung cancer.

METHODS

This prospective cohort study included clinical data from 400 patients with non-small cell lung cancer who underwent VATS from June 2022 to June 2023. Patients were randomly assigned to a training cohort and an internal test cohort and assessed for sleep quality, psychological status, and pain levels. A nomogram prediction model was established based on variables significantly associated with CPSP in the training cohort. The model was internally validated in the internal test cohort to evaluate its discrimination, calibration, and clinical utility.

RESULTS

Independent risk factors for CPSP included female gender, severe acute pain post-surgery, lymph node dissection, and cold pain sensation, while paravertebral nerve block was identified as a protective factor. The AUC values were 0.878 in training cohort and 0.805 in internal test cohort, respectively, indicating that the model performed well in identifying patients at risk for CPSP. The calibration curves in both cohorts showed a good fit, indicating that the model's predictions were reliable. And the DCA curve showed that using our model to guide decisions resulted in a higher net benefit compared to a strategy of not screening or treating all patients.

CONCLUSION

An effective risk prediction model for CPSP was successfully developed and validated in this study. This model can aid physicians in conducting more accurate assessments of CPSP risk in patients prior to surgery and in offering personalized strategies for managing CPSP.

CLINICAL REGISTRATION NUMBER

Registration website: https://www.chictr.org.cn/ . Registration date: 2022/5/21.

REGISTRATION NUMBER

ChiCTR2200060196.

Temporal summation of pain in sickle cell disease: comparison of adolescents and young adults with chronic vs. infrequent pain

OBJECTIVE

This study examined the role of central sensitization in the experience of pain among adolescents and young adults with the most severe genotypes of sickle cell disease (SCD). We hypothesized that adolescents and young adults with chronic SCD pain would demonstrate a higher perceptual response to repeated stimulation of identical intensity (i.e., temporal summation of pain, TSP) compared to counterparts with infrequent pain. We also examined psychological risk factors that can impact pain sensitivity.

METHODS

Patients ages 12-21 years, diagnosed with SCD type Hb SS or Hb S Beta0Thalasemia, who reported infrequent pain (≤2 pain days/month; n = 25) or met AAPT criteria for chronic SCD pain (n = 25) were enrolled. Patients were age- and sex-matched, with similar proportions receiving chronic blood transfusion and hydroxyurea. Patients completed static quantitative sensory testing (QST) and dynamic TSP testing to assess pain sensitivity. Patients and a caregiver completed demographic and psychological measures (depression, anxiety, pain interference, pain catastrophizing).

RESULTS

Simple slope analysis revealed differentially elevated heat TSP among adolescents and young adults with chronic SCD pain (b = 3.14, p = .002) but not those with infrequent pain (b = 0.45, p = .61). Faster habituation was further observed for those with chronic compared to infrequent pain. Adolescents and young adults with chronic pain reported more frequent depression, anxiety, and pain interference symptoms; however, psychological symptoms and pain catastrophizing were not associated with QST or TSP (ps >.17).

CONCLUSION

Current results demonstrate that a well-established, prognostic, QST risk marker (i.e., TSP) may distinguish chronic from infrequent pain subgroups of adolescents and young adults with SCD.

Opioid Use Following Spine Surgery in Ambulatory Surgical Centers Versus Hospital Outpatient Departments

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

To assess the association between undergoing spine surgery in an ambulatory surgical center (ASC) vs a hospital outpatient department (HOPD) and (a) perioperative opioid prescription patterns and (b) prolonged opioid use.

METHODS

Data from the Merative MarketScan Database included patients aged 18-64 who underwent single-level or multilevel anterior cervical discectomy and fusion (ACDF) or lumbar decompression between January 2017 and June 2021. Primary outcomes included receipt of a perioperative opioid prescription, perioperative oral morphine milligram equivalents (MMEs), and prolonged opioid use (defined as opioid prescription 91-180 days post-surgery). Secondary outcomes included the number of perioperative opioid prescriptions filled (single/multiple) and type of initial perioperative opioid filled (potent/weak). Analysis of prolonged opioid use was limited to opioid-naive patients. Propensity score matching (1 ASC to 3 HOPD cases) and logistic regression models were used for analysis.

RESULTS

The study included 11,654 ACDF and 26,486 lumbar decompression patients. For ACDF, ASCs had higher odds of an initial potent opioid prescription (OR = 1.18, 95% CI 1.08-1.30, P < .001) and higher total adjusted mean MMEs (+21.14, 95% CI 3.08-39.20, P = .02). For lumbar decompression, ASCs had increased odds of an initial potent opioid (OR = 1.23, 95% CI 1.16-1.30, P < .001) but lower odds of multiple opioid prescriptions (OR = 0.90, 95% CI 0.85-0.96, P < .001). There was no significant association between the surgery setting and prolonged opioid use.

CONCLUSION

Differences in perioperative opioid prescribing were observed between ASCs and HOPDs, but there was no increase in prolonged opioid use in ASCs. Further research is needed to optimize postoperative pain management in different outpatient settings.

A novel cortical biomarker signature predicts individual pain sensitivity

Importance

Biomarkers would greatly assist decision making in the diagnosis, prevention and treatment of chronic pain.

Objective

The present study aimed to undertake analytical validation of a sensorimotor cortical biomarker signature for pain consisting of two measures: sensorimotor peak alpha frequency (PAF) and corticomotor excitability (CME).

Design

In this cohort study (recruitment period: November 2020-October 2022), participants experienced a model of prolonged temporomandibular pain with outcomes collected over 30 days. Electroencephalography (EEG) to assess PAF and transcranial magnetic stimulation (TMS) to assess CME were recorded on Days 0, 2 and 5. Pain was assessed twice daily from Days 1-30.

Setting

Data collection occurred at a single centre: Neuroscience Research Australia.

Participants

We enrolled 159 healthy participants (through notices placed online and at universities across Australia), aged 18-44 with no history of chronic pain, neurological or psychiatric condition. 150 participants completed the protocol.

Exposure

Participants received an injection of nerve growth factor (NGF) to the right masseter muscle on Days 0 and 2 to induce prolonged temporomandibular pain lasting up to 4 weeks.

Main Outcomes and Measures

We determined the predictive accuracy of the PAF/CME biomarker signature using a nested control-test scheme: machine learning models were run on a training set (n = 100), where PAF and CME were predictors and pain sensitivity was the outcome. The winning classifier was assessed on a test set (n = 50) comparing the predicted pain labels against the true labels.

Results

The final sample consisted of 66 females and 84 males with a mean age of 25.1 ± 6.2. The winning classifier was logistic regression, with an outstanding area under the curve (AUC=1.00). The locked model assessed on the test set had excellent performance (AUC=0.88[0.78-0.99]). Results were reproduced across a range of methodological parameters. Moreover, inclusion of sex and pain catastrophizing as covariates did not improve model performance, suggesting the model including biomarkers only was more robust. PAF and CME biomarkers showed good-excellent test-retest reliability.

Conclusions and Relevance

This study provides evidence for a sensorimotor cortical biomarker signature for pain sensitivity. The combination of accuracy, reproducibility, and reliability, suggests the PAF/CME biomarker signature has substantial potential for clinical translation, including predicting the transition from acute to chronic pain.

Addressing gaps in pain research from an integrated whole person perspective

ABSTRACT

While our understanding of pain is rapidly growing, some areas of pain research are lagging behind. This article discusses two current and inter-related gaps in knowledge that are in need of addressing: first, the connections between "brain" and "body" components of pain; and second, the process of endogenous pain resolution. Historical reasons for these research gaps are discussed and solutions are outlined based on an integrative, whole person research approach. These include comprehensive mapping of the mechanosensory and nociceptive innervation of deep tissues; developing objective, non-invasive measurements to quantify the metabolic, structural and mechanical components of the peripheral tissue environment; integrating our understanding of pain pathophysiology, across whole organs and whole body, as well as across bio-psycho-social domains; and understanding the interplay of nervous system and peripheral tissue mechanisms that promote the endogenous resolution of pain and prevent its acute-to-chronic transition. Current NIH-led efforts in these areas are outlined, including several studies within the NIH HEAL (or Help End Addition Long Term) initiative and the National Center for Complementary and Integrative Health's strategic priorities in whole person research.

Fast 3D fMRI acquisition with high spatial resolutions over a reduced FOV

PURPOSE

To develop and demonstrate a fast 3D fMRI acquisition technique with high spatial resolution over a reduced FOV, named k-t 3D reduced FOV imaging (3D-rFOVI).

METHODS

Based on 3D gradient-echo EPI, k-t 3D-rFOVI used a 2D RF pulse to reduce the FOV in the in-plane phase-encoding direction, boosting spatial resolution without increasing echo train length. For image acceleration, full sampling was applied in the central k-space region along the through-slab direction (kz) for all time frames, while randomized undersampling was used in outer kz regions at different time frames. Images were acquired at 3T and reconstructed using a method based on partial separability. fMRI detection sensitivity of k-t 3D-rFOVI was quantitively analyzed with simulation data. Human visual fMRI experiments were performed to evaluate k-t 3D-rFOVI and compare it with a commercial multiband EPI sequence.

RESULTS

The simulation data showed that k-t 3D-rFOVI can detect 100% of fMRI activations with an acceleration factor (R) of 2 and ˜80% with R = 6. In the human fMRI data acquired with 1.5-mm spatial resolution and 800-ms volume TR (TRvol), k-t 3D-rFOVI with R = 4 detected 46% more activated voxels in the visual cortex than the multiband EPI. Additional fMRI experiments showed that k-t 3D-rFOVI can achieve TRvol of 480 ms with R = 6, while reliably detecting visual activation.

CONCLUSIONS

k-t 3D-rFOVI can simultaneously achieve a high spatial resolution (1.5-mm isotropically) and short TRvol (480-ms) at 3T. It offers a robust acquisition technique for fast fMRI studies over a focused brain volume.

Perioperative Analgesic Interventions for Reduction of Persistent Postsurgical Pain After Total Hip and Knee Arthroplasty: A Systematic Review and Meta-analysis

BACKGROUND

High pain levels immediately after surgery have been associated with persistent postsurgical pain. Still, it is uncertain if analgesic treatment of immediate postsurgical pain prevents the development of persistent postsurgical pain.

METHODS

We searched MEDLINE, CENTRAL, and Embase up to September 12, 2023, for randomized controlled trials investigating perioperative analgesic interventions and with reported pain levels 3 to 24 months after total hip or knee arthroplasty in patients with osteoarthritis. The primary outcome was pain score 3 to 24 months after surgery, assessed at rest and during movement separately. Two authors independently screened, extracted data, and assessed risk of bias using the Cochrane Risk of Bias 2 tool. We conducted meta-analyses and tested their robustness with trial sequential analyses and worst-best and best-worst case analyses.

RESULTS

We included 49 trials with 68 intervention arms. All but 4 trials were at high risk of bias for the primary outcome. Moreover, the included trials were heterogeneous in terms of exclusion criteria, baseline pain severity, and which cointerventions the participants were offered. For pain at rest, no interventions demonstrated a statistically significant difference between intervention and control. For pain during movement, perioperative treatment with duloxetine (7 trials with 641 participants) reduced pain scores at 3 to 24 months after surgery (mean difference -4.9 mm [95% confidence interval {CI}, -6.5 to -3.4] on the 0-100 visual analog scale) compared to placebo. This difference was lower than our predefined threshold for clinical importance of 10 mm.

CONCLUSIONS

We found no perioperative analgesic interventions that reduced pain 3 to 24 months after total hip or knee arthroplasty for osteoarthritis. The literature on perioperative analgesia focused little on potential long-term effects. We encourage the assessment of long-term pain outcomes.

Transitional pain services updates and a novel service for the obstetric population

PURPOSE OF REVIEW

This paper is an update of the publications on Transitional Pain Services and explores the viability of a dedicated transitional pain service for women.

RECENT FINDINGS

We address common pain pathologies establishing referral criteria, pathways, and effective strategies to decrease chronification of pain during pregnancy.

SUMMARY

This review highlights the importance establishing transitional pain service models at every institution and in particular in obstetric population as pain is normalized by Society during pregnancy.

A multichannel electrophysiological approach to noninvasively and precisely record human spinal cord activity

The spinal cord is of fundamental importance for integrative processing in brain-body communication, yet routine noninvasive recordings in humans are hindered by vast methodological challenges. Here, we overcome these challenges by developing an easy-to-use electrophysiological approach based on high-density multichannel spinal recordings combined with multivariate spatial-filtering analyses. These advances enable a spatiotemporal characterization of spinal cord responses and demonstrate a sensitivity that permits assessing even single-trial responses. To furthermore enable the study of integrative processing along the neural processing hierarchy in somatosensation, we expand this approach by simultaneous peripheral, spinal, and cortical recordings and provide direct evidence that bottom-up integrative processing occurs already within the spinal cord and thus after the first synaptic relay in the central nervous system. Finally, we demonstrate the versatility of this approach by providing noninvasive recordings of nociceptive spinal cord responses during heat-pain stimulation. Beyond establishing a new window on human spinal cord function at millisecond timescale, this work provides the foundation to study brain-body communication in its entirety in health and disease.

Targeting the soluble epoxide hydrolase pathway as a novel therapeutic approach for the treatment of pain

Chronic pain is a major burden and the complexities of chronic pain pathophysiology, including both peripheral and central sensitisation mechanisms, involves multiple cell types (neuronal, immune, neuroimmune, and vascular) which substantially complicates the development of new effective analgesic treatments. The epoxy fatty acids (EpFAs), including the epoxyeicosatrienoic acids (EETs), are derived from the metabolism of polyunsaturated fatty acids (PUFAs) via the cytochrome P450 enzymatic pathway and act to shut-down inflammatory signalling and provide analgesia. The EpFAs are rapidly metabolised by the enzyme soluble epoxide hydrolase (sEH) into their corresponding diol metabolites, which recent studies suggest are pro-inflammatory and pro-nociceptive. This review discusses clinical and mechanistic evidence for targeting the sEH pathway for the treatment of pain.

The endocannabinoid system as a therapeutic target in neuropathic pain: a review

INTRODUCTION

This review highlights the critical role of the endocannabinoid system (ECS) in regulating neuropathic pain and explores the therapeutic potential of cannabinoids. Understanding the mechanisms of the ECS, including its receptors, endogenous ligands, and enzymatic routes, can lead to innovative treatments for chronic pain, offering more effective therapies for neuropathic conditions. This review bridges the gap between preclinical studies and clinical applications by emphasizing ECS modulation for better pain management outcomes.

AREAS COVERED

A review mapped the existing literature on neuropathic pain and the effects of modulating the ECS using natural and synthetic cannabinoids. This analysis examined ECS components and their alterations in neuropathic pain, highlighting the peripheral, spinal, and supraspinal mechanisms. This review aimed to provide a thorough understanding of the therapeutic potential of cannabinoids in the management of neuropathic pain.

EXPERT OPINION

Advances in cannabinoid research have shown significant potential for the management of chronic neuropathic pain. The study emphasizes the need for high-quality clinical trials and collaborative efforts among researchers, clinicians, and regulatory bodies to ensure safe and effective integration of cannabinoids into pain management protocols. Understanding the mechanisms and optimizing cannabinoid formulations and delivery methods are crucial for enhancing therapeutic outcomes.

Tear Proteins Altered in Patients with Persistent Eye Pain after Refractive Surgery: Biomarker Candidate Discovery

Some patients develop persistent eye pain after refractive surgery, but factors that cause or sustain pain are unknown. We tested whether tear proteins of patients with pain 3 months after surgery differ from those of patients without pain. Patients undergoing refractive surgery (laser in situ keratomileusis or photorefractive keratectomy ) were recruited from 2 clinics, and tears were collected 3 months after surgery. Participants rated their eye pain using a numerical rating scale (NRS, 0-10; no pain-worst pain) at baseline, 1 day, and 3 months after surgery. Using tandem mass tag proteomic analysis, we examined tears from patients with pain [NRS ≥ 3 at 3 months (n = 16)] and patients with no pain [NRS ≤ 1 at 3 months (n = 32)] after surgery. A subset of proteins (83 of 2748 detected, 3.0%) were associated with pain 3 months after surgery. High-dimensional statistical models showed that the magnitude of differential expression was not the only important factor in classifying tear samples from pain patients. Models utilizing 3 or 4 proteins had better classification performance than single proteins and represented differences in both directions (higher or lower in pain). Thus, patterns of protein differences may serve as biomarkers of postsurgical eye pain as well as potential therapeutic targets.

Reliability of task-based fMRI in the dorsal horn of the human spinal cord

The application of functional magnetic resonance imaging (fMRI) to the human spinal cord is still a relatively small field of research and faces many challenges. Here we aimed to probe the limitations of task-based spinal fMRI at 3T by investigating the reliability of spinal cord blood oxygen level dependent (BOLD) responses to repeated nociceptive stimulation across two consecutive days in 40 healthy volunteers. We assessed the test-retest reliability of subjective ratings, autonomic responses, and spinal cord BOLD responses to short heat pain stimuli (1s duration) using the intraclass correlation coefficient (ICC). At the group level, we observed robust autonomic responses as well as spatially specific spinal cord BOLD responses at the expected location, but no spatial overlap in BOLD response patterns across days. While autonomic indicators of pain processing showed good-to-excellent reliability, both β-estimates and z-scores of task-related BOLD responses showed poor reliability across days in the target region (gray matter of the ipsilateral dorsal horn). When taking into account the sensitivity of gradient-echo echo planar imaging (GE-EPI) to draining vein signals by including the venous plexus in the analysis, we observed BOLD responses with fair reliability across days. Taken together, these results demonstrate that heat pain stimuli as short as one second are able to evoke a robust and spatially specific BOLD response, which is however strongly variable within participants across time, resulting in low reliability in the dorsal horn gray matter. Further improvements in data acquisition and analysis techniques are thus necessary before event-related spinal cord fMRI as used here can be reliably employed in longitudinal designs or clinical settings.

Deciphering nociplastic pain: clinical features, risk factors and potential mechanisms

Nociplastic pain is a mechanistic term used to describe pain that arises or is sustained by altered nociception, despite the absence of tissue damage. Although nociplastic pain has distinct pathophysiology from nociceptive and neuropathic pain, these pain mechanisms often coincide within individuals, which contributes to the intractability of chronic pain. Key symptoms of nociplastic pain include pain in multiple body regions, fatigue, sleep disturbances, cognitive dysfunction, depression and anxiety. Individuals with nociplastic pain are often diffusely tender - indicative of hyperalgesia and/or allodynia - and are often more sensitive than others to non-painful sensory stimuli such as lights, odours and noises. This Review summarizes the risk factors, clinical presentation and treatment of nociplastic pain, and describes how alterations in brain function and structure, immune processing and peripheral factors might contribute to the nociplastic pain phenotype. This article concludes with a discussion of two proposed subtypes of nociplastic pain that reflect distinct neurobiological features and treatment responsivity.

Chronic Postsurgical Pain in Children and Adolescents: A Call for Action

Chronic postsurgical pain (CPSP) affects a significant proportion of children and adolescents after major surgery and is a detriment to both short- and long-term recovery outcomes. While clinical characteristics and psychosocial risk factors for developing CPSP in children and adults are well established in the literature, there has been little progress on the prevention and management of CPSP after pediatric surgery. Limited evidence to support current pharmacologic approaches suggests a fundamentally new paradigm must be considered by clinicians to both conceptualize and address this adverse complication. This narrative review provides a comprehensive evaluation of both the known and emerging mechanisms that support our current understanding of CPSP. Additionally, we discuss the importance of optimizing perioperative analgesic strategies to mitigate CPSP based on individual patient risks. We highlight the importance of postoperative pain trajectories to identify those most at risk for developing CPSP, the early referral to multi-disciplinary pain clinics for comprehensive evaluation and treatment of CPSP, and additional work needed to differentiate CPSP characteristics from other chronic pain syndromes in children. Finally, we recognize ongoing challenges associated with the universal implementation of available knowledge about pediatric CPSP into practically useful care plans for clinicians.

The Effect of Everyday-Life Social Contact on Pain

Pain is a biopsychosocial phenomenon, resulting from the interplay between physiological and psychological processes and social factors. Given that humans constantly interact with others, the effect of social factors is particularly relevant. Documenting the significance of the social modulation of pain, an increasing number of studies have investigated the effect of social contact on subjective pain intensity and pain-related physiological changes. While evidence suggests that social contact can alleviate pain, contradictory findings indicate an increase in pain intensity and a deterioration of pain coping strategies. This evidence primarily stems from studies examining the effect of social contact on pain within highly controlled laboratory conditions. Moreover, pain assessments often rely on one-time subjective reports of average pain intensity across a predefined period. Ecological momentary assessments (EMAs) can circumvent these problems, as they can capture diverse aspects of behavior and experiences multiple times a day, in real time, with high resolution, and within naturalistic and ecologically valid settings. These multiple measures allow for the examination of fluctuations of pain symptoms throughout the day in relation to affective, cognitive, behavioral, and social factors. In this opinion paper, we review the current state and future relevance of EMA-based social pain research in daily life. Specifically, we examine whether everyday-life social support reduces or enhances pain. The first part of the paper provides a comprehensive overview of the use of EMA in pain research and summarizes the main findings. The review of the relatively limited number of existing EMA studies shows that the association between pain and social contact in everyday life depends on numerous factors, including pain syndromes, temporal dynamics, the nature of social interactions, and characteristics of the interaction partners. In line with laboratory research, there is evidence that everyday-life social contact can alleviate, but also intensify pain, depending on the type of social support. Everyday-life emotional support seems to reduce pain, while extensive solicitous support was found to have opposite effects. Moreover, positive short-term effects of social support can be overshadowed by other symptoms such as fatigue. Overall, gathering and integrating experiences from a patient's social environment can offer valuable insights. These insights can help interpret dynamics in pain intensity and accompanying symptoms such as depression or fatigue. We conclude that factors determining the reducing versus enhancing effects of social contact on pain need to be investigated more thoroughly. We advocate EMA as the assessment method of the future and highlight open questions that should be addressed in future EMA studies on pain and the potential of ecological momentary interventions for pain treatment.

Mechanisms and Preventative Strategies for Persistent Pain following Knee and Hip Joint Replacement Surgery: A Narrative Review

Chronic postsurgical pain (CPSP) following total knee arthroplasty (TKA) and total hip arthroplasty (THA) is a prevalent complication of joint replacement surgery which has the potential to decrease patient satisfaction, increase financial burden, and lead to long-term disability. The identification of risk factors for CPSP following TKA and THA is challenging but essential for targeted preventative therapy. Recent meta-analyses and individual studies highlight associations between elevated state anxiety, depression scores, preoperative pain, diabetes, sleep disturbances, and various other factors with an increased risk of CPSP, with differences observed in prevalence between TKA and THA. While the etiology of CPSP is not fully understood, several factors such as chronic inflammation and preoperative central sensitization have been identified. Other potential mechanisms include genetic factors (e.g., catechol-O-methyltransferase (COMT) and potassium inwardly rectifying channel subfamily J member 6 (KCNJ6) genes), lipid markers, and psychological risk factors (anxiety and depression). With regards to therapeutics and prevention, multimodal pharmacological analgesia, emphasizing nonopioid analgesics like acetaminophen and non-steroidal anti-inflammatory drugs (NSAIDs), has gained prominence over epidural analgesia. Nerve blocks and local infiltrative anesthesia have shown mixed results in preventing CPSP. Ketamine, an N-methyl-D-aspartate (NMDA)-receptor antagonist, exhibits antihyperalgesic properties, but its efficacy in reducing CPSP is inconclusive. Lidocaine, an amide-type local anesthetic, shows tentative positive effects on CPSP. Selective serotonin reuptake inhibitors (SSRIs) and serotonin norepinephrine reuptake inhibitors (SNRIs) have mixed results, while gabapentinoids, like gabapentin and pregabalin, present hopeful data but require further research, especially in the context of TKA and THA, to justify their use for CPSP prevention.

Broadening the Scope of Resilience in Chronic Pain: Methods, Social Context, and Development

PURPOSE OF REVIEW

A wellspring of new research has offered varying models of resilience in chronic pain populations; however, resilience is a multifaceted and occasionally nebulous construct. The current review explores definitional and methodological issues in existing observational and clinical studies and offers new directions for future studies of pain resilience.

RECENT FINDINGS

Definitions of pain resilience have historically relied heavily upon self-report and from relatively narrow scientific domains (e.g., positive psychology) and in narrow demographic groups (i.e., Caucasian, affluent, or highly educated adults). Meta-analytic and systematic reviews have noted moderate overall quality of resilience-focused assessment and treatment in chronic pain, which may be attributable to these narrow definitions. Integration of research from affiliated fields (developmental models, neuroimaging, research on historically underrepresented groups, trauma psychology) has the potential to enrich current models of pain resilience and ultimately improve the empirical and clinical utility of resilience models in chronic pain.

Personalized assessment and management of non-specific low back pain

BACKGROUND AND OBJECTIVE

Low back pain (LBP), and in particular non-specific low back pain (NSLBP), which accounts for approximately 90% of LBP, is the leading cause of years lived with disability worldwide. In clinical trials, LBP is often poorly categorized into 'specific' versus 'non-specific' and 'acute' versus 'chronic' pain. However, a better understanding of the underlying pain mechanisms might improve study results and reduce the number of NSLBP patients.

DATABASES AND DATA TREATMENT

Narrative review.

RESULTS

NSLBP is a multi-dimensional, biopsychosocial condition that requires all contributing dimensions to be assessed and prioritized. Thereby, the assessment of the contribution of nociceptive, neuropathic and nociplastic pain mechanisms forms the basis for personalized management. In addition, psychosocial (e.g. anxiety, catastrophizing) and contextual factors (e.g. work situation) as well as comorbidities need to be assessed and individually weighted. Personalized treatment of NSLBP further requires individually choosing treatment modalities, for example, exercising, patient education, cognitive-behavioural advice, pharmacotherapy, as well as tailoring treatment within these modalities, for example, the delivery of tailored psychological interventions or exercise programs. As the main pain mechanism and psychosocial factors may vary over time, re-assessment is necessary and treatment success should ideally be assessed quantitatively and qualitatively.

CONCLUSIONS

The identification of the main contributing pain mechanism and the integration of the patients' view on their condition, including beliefs, preferences, concerns and expectations, are key in the personalized clinical management of NSLBP. In research, particular importance should be placed on accurate characterization of patients and on including outcomes relevant to the individual patient.

SIGNIFICANCE STATEMENT

Here, a comprehensive review of the challenges associated with the diagnostic label 'non-specific low back pain' is given. It outlines what is lacking in current treatment guidelines and it is summarized what is currently known with respect to individual phenotyping. It becomes clear that more research on clinically meaningful subgroups is needed to best tailor treatment approaches.

Redefining sensitization could be a sensitive issue

Commentary on: van den Broeke EN, Crombez G, Vlaeyen JWS. Reconceptualizing sensitization in pain: back to basics. PAIN Reports 2024;9:e1125.

Prognostic models for chronic postsurgical pain-Current developments, trends, and challenges

PURPOSE OF REVIEW

Prognostic models for chronic postsurgical pain (CPSP) aim to predict the likelihood for development and severity of CPSP in individual patients undergoing surgical procedures. Such models might provide valuable information for healthcare providers, allowing them to identify patients at higher risk and implement targeted interventions to prevent or manage CPSP effectively. This review discusses the latest developments of prognostic models for CPSP, their challenges, limitations, and future directions.

RECENT FINDINGS

Numerous studies have been conducted aiming to develop prognostic models for CPSP using various perioperative factors. These include patient-related factors like demographic variables, preexisting pain conditions, psychosocial aspects, procedure-specific characteristics, perioperative analgesic strategies, postoperative complications and, as indicated most recently, biomarkers. Model generation, however, varies and performance and accuracy differ between prognostic models for several reasons and validation of models is rather scarce.

SUMMARY

Precise methodology of prognostic model development needs advancements in the field of CPSP. Development of more accurate, validated and refined models in large-scale cohorts is needed to improve reliability and applicability in clinical practice and validation studies are necessary to further refine and improve the performance of prognostic models for CPSP.