Chronic Pain after Bone Fracture: Current Insights into Molecular Mechanisms and Therapeutic Strategies

The Impact of Lesser Trochanter Displacement on Hip Flexor Strength Recovery in Patients With Trochanteric Fracture

INTRODUCTION

Trochanteric fractures (TFs) are common in older individuals and are expected to increase with Japan's aging population. These fractures often result in poor long-term outcomes, such as decreased independent walking and reduced hospital discharge rates. A significant aspect of TF involves displacement of the lesser trochanter (LT), which can weaken hip flexor muscles and potentially affect the recovery of activities of daily living (ADLs), including walking. Previous research has shown conflicting results regarding the effect of lesser trochanteric displacement on hip function and walking ability. This study aimed to determine whether displacement of the LT affects the recovery of hip flexor strength and walking ability at discharge in patients with TF.

METHODS

This prospective cohort study included 29 patients with TF admitted to a rehabilitation hospital between April 2023 and June 2024. The patients were classified into two groups: the LT displacement and the non-LT (NLT) displacement groups. Muscle strength (hip flexion, abduction, and knee extension) was measured using a handheld dynamometer. Walking ability assessments included gait speed, timed up-and-go test (TUG), 6-minute walk test (6 MWT), and functional ambulation category (FAC). Cognitive function was evaluated using the Hasegawa Dementia Rating Scale-Revised (HDS-R). Statistical analyses included repeated-measures analysis of variance (ANOVA) for muscle strength comparisons over time, with adjustments for violations of sphericity using the Greenhouse-Geisser correction.

RESULTS

There were no significant differences between the LT and NLT groups in terms of demographic characteristics such as age, sex, or cognitive function. Repeated-measures ANOVA revealed a significant difference in hip flexor strength on the injured side between the groups, with the LT group showing persistent weakness until discharge. Significant improvements were noted in hip abduction and knee extension strength on the injured side, although no group differences were observed. Post-hoc analysis indicated significant strength improvements over time, particularly between admission and discharge, for most muscle groups, except for hip flexor strength in the LT group.

CONCLUSION

Lesser trochanteric displacement in patients with TF resulted in a specific decline in hip flexor strength on the injured side, which persisted until discharge. However, no significant impact on walking ability was observed, likely because of compensatory mechanisms involving other muscles.

Clinical Effectiveness of Bee Venom Acupuncture for Bone Fractures and Potential Mechanisms: A Narrative Overview

Bee venom acupuncture, a type of herbal acupuncture, combines the pharmacological actions of bioactive compounds from bee venom with the mechanical stimulation of meridian points. Bee venom acupuncture is gaining popularity, particularly in the Republic of Korea, primarily for pain relief of various conditions. This study aimed to summarize and evaluate the available evidence on the use of bee venom acupuncture for recovery after bone fractures. Electronic literature searches for experimental studies and clinical trials were conducted using the PubMed, China Academic Journals (CAJ), and OASIS databases. The search revealed 31 studies, of which six met our criteria. These studies demonstrated that bee venom acupuncture can be effective in treating bone fractures, suggesting a promising area for future research. However, evidence supporting its efficacy in this context is limited. Rigorous trials with large sample sizes and robust designs are needed to clarify the role of bee venom acupuncture for these indications. In addition, future studies should explore the optimal dosage and concentration of bee venom acupuncture.

Modeling neuropathic pain in a dish

The study of pain mechanisms has advanced significantly with the development of innovative in vitro models. This chapter explores those already used in or potentially useful for neuropathic pain research, emphasizing the complementary roles of animal and human cellular models to enhance translational success. Traditional animal models have provided foundational insights into the neurobiology of pain and remain invaluable for understanding complex pain pathways. However, integrating human cellular models addresses the need for better replication of human nociceptors. The chapter details methodologies for culturing rodent and human primary sensory neurons, including isolation and culture techniques, advantages, and limitations. It highlights the application of these models in neuropathic pain research, such as identifying pain-associated receptors and ion channels. Recent advancements in using induced pluripotent stem cell (iPSC)-derived sensory neurons are also discussed. Finally, the chapter explores advanced in vitro models, including 2D co-cultures and 3D organoids, and their implications for studying neuropathic pain. These models offer significant advantages for drug screening and ethical research practices, providing a more accurate representation of human pain pathways and paving the way for innovative therapeutic strategies. Despite challenges such as limited access to viable human tissue and variability between samples, these in vitro models, alongside traditional animal models, are indispensable for advancing our understanding of neuropathic pain and developing effective treatments.

Spinal Caspase-6 Contributes to Intrathecal Morphine-induced Acute Itch and Contact Dermatitis-induced Chronic Itch Through Regulating the Phosphorylation of Protein Kinase Mζ in Mice

Patients receiving neuraxial treatment with morphine for pain relief often experience a distressing pruritus. Neuroinflammation-mediated plasticity of sensory synapses in the spinal cord is critical for the development of pain and itch. Caspase-6, as an intracellular cysteine protease, is capable of inducing central nociceptive sensitization through regulating synaptic transmission and plasticity. Given the tight interaction between protein kinase Mζ (PKMζ) and excitatory synaptic plasticity, this pre-clinical study investigates whether caspase-6 contributes to morphine-induced itch and chronic itch via PKMζ. Intrathecal morphine and contact dermatitis were used to cause pruritus in mice. Morphine antinociception, itch-induced scratching behaviors, spinal activity of caspase-6, and phosphorylation of PKMζ and ERK were examined. Caspase-6 inhibitor Z-VEID-FMK, exogenous caspase-6 and PKMζ inhibitor ZIP were utilized to reveal the mechanisms and prevention of itch. Herein, we report that morphine induces significant scratching behaviors, which is accompanied by an increase in spinal caspase-6 cleavage and PKMζ phosphorylation (but not expression). Intrathecal injection of Z-VEID-FMK drastically reduces morphine-induced scratch bouts and spinal phosphorylation of PKMζ, without abolishing morphine analgesia. Moreover, intrathecal strategies of ZIP dose-dependently reduce morphine-induced itch-like behaviors. Spinal phosphorylation of ERK following neuraxial morphine is down-regulated by ZIP therapy. Recombinant caspase-6 directly exhibits scratching behaviors and spinal phosphorylation of ERK, which is compensated by PKMζ inhibition. Also, spinal inhibition of caspase-6 and PKMζ reduces the generation and maintenance of dermatitis-induced chronic itch. Together, these findings demonstrate that spinal caspase-6 modulation of PKMζ phosphorylation is important in the development of morphine-induced itch and dermatitis-induced itch in mice.

Exploring the terminological validity of 'chronic pain' nursing diagnosis: A retrospective descriptive study using nursing diaries

AIM

The aim of this study is to generate empirical evidence, drawing from clinical records, with the goal of elevating the level of evidence supporting the nursing diagnosis (ND) of 'chronic pain'.

BACKGROUND

Chronic pain is a prevalent condition that affects all age groups. Patients often feel disbelieved about their pain perception, leading to adverse psychological effects, difficulty accessing healthcare and poor rehabilitation outcomes.

DESIGN

Retrospective descriptive study. Standards for Reporting Diagnostic Accuracy Studies guidelines were followed in this study.

METHODS

Data were extracted from Electronic Health Records (EHR) of patients admitted to the University Hospital of Perugia, Italy, between March 2016 and December 2022. The study sample comprised individuals without a specific medical diagnosis or high-risk population. Out of 1,048,565 EHR, 43,341 clinical-nursing diaries with the keyword 'pain' were identified, from which 283 clinical-nursing notes were selected based on a keyword-based retrieval technique and diagnostic definition for further analysis.

RESULTS

Our study findings support the diagnostic descriptors of the 'chronic pain' ND in clinical-nursing diaries. We observed the presence of 9 out of 11 defining characteristics, 7 out of 10 related factors, 4 out of 8 at-risk populations and 11 out of 17 associated conditions.

CONCLUSIONS

The study validated diagnostic criteria for chronic pain and proposed 'haematological pathology' as a new associated condition. The findings were presented to the Diagnosis Development Committee of NANDA-International for further review. However, limitations of the study prompted the need for further analysis using natural language processing and artificial neural network techniques. As a result, a new research direction using artificial intelligence (AI) tools was initiated.

RELEVANCE TO CLINICAL PRACTICE

The study validates diagnostic descriptors for chronic pain and proposes future directions in semantic analysis and AI tools, aiming to enhance clinical practice and decision-making in nursing care.

PATIENT OR PUBLIC CONTRIBUTION

No patient or public contribution.

Glabridin Therapy Reduces Chronic Allodynia, Spinal Microgliosis, and Dendritic Spine Generation by Inhibiting Fractalkine-CX3CR1 Signaling in a Mouse Model of Tibial Fractures

Patients undergoing bone fractures frequently suffer from irritating chronic pain after orthopedic repairs. Chemokine-mediated interactions between neurons and microglia are important steps for neuroinflammation and excitatory synaptic plasticity during the spinal transmission of pathological pain. Recently, glabridin, the main bioactive component of licorice, has been shown to exhibit anti-nociceptive and neuroprotective properties for inflammatory pain. This present study evaluated the therapeutic potential of glabridin and its analgesic mechanisms using a mouse model of tibial fracture-associated chronic pain. Repetitive injections of glabridin were delivered spinally daily for 4 continuous days from days 3 to 6 after the fractures. Herein, we discovered that repeated administrations of glabridin (10 and 50 μg, but not 1 μg) could prevent prolonged cold allodynia and mechanical allodynia following bone fractures. A single intrathecal intervention with glabridin (50 μg) relieved an existing chronic allodynia two weeks following the fracture surgeries. Systemic therapies with glabridin (intraperitoneal; 50 mg kg^-1) were protective against long-lasting allodynia caused by fractures. Furthermore, glabridin restricted the fracture-caused spinal overexpressions of the chemokine fractalkine and its receptor CX3CR1, as well as the elevated number of microglial cells and dendritic spines. Strikingly, glabridin induced the inhibition of pain behaviors, microgliosis, and spine generation, which were abolished with the co-administration of exogenous fractalkine. Meanwhile, the exogenous fractalkine-evoked acute pain was compensated after microglia inhibition. Additionally, spinal neutralization of fractalkine/CX3CR1 signaling alleviated the intensity of postoperative allodynia after tibial fractures. These key findings identify that glabridin therapies confer protection against inducing and sustaining fracture-elicited chronic allodynia by suppressing fractalkine/CX3CR1-dependent spinal microgliosis and spine morphogenesis, suggesting that glabridin is a promising candidate in the translational development of chronic fracture pain control.

Hydrogen-Rich Saline Attenuates Chronic Allodynia after Bone Fractures via Reducing Spinal CXCL1/CXCR2-Mediated Iron Accumulation in Mice

PURPOSE

Neuroinflammation often initiates iron overload in the pathogenesis of neurological disorders. Chemokine-driven neuroinflammation is required for central sensitization and chronic allodynia following fractures, but specific molecular modulations are elusive. This present study explored whether hydrogen-rich saline, as one potent anti-inflammatory pharmaceutical, could alleviate fracture-caused allodynia by suppressing chemokine CXCL1 expression and iron overload.

METHODS

A mouse model of tibial fracture with intramedullary pinning was employed for establishing chronic allodynia. Three applications of hydrogen-rich saline (1, 5 or 10 mL/kg) were administrated intraperitoneally on a daily basis from days 4 to 6 following fractures. Spinal CXCL1 and its receptor CXCR2 levels, transferrin receptor 1 (TfR1) expression and iron concentration were examined. Recombinant CXCL1, a selective CXCR2 antagonist and an iron chelator were used for verification of mechanisms.

RESULTS

Repetitive injections of hydrogen-rich saline (5 and 10 mL/kg but not 1 mL/kg) prevent fracture-caused mechanical allodynia and cold allodynia in a dose-dependent manner. Single exposure to hydrogen-rich saline (10 mL/kg) on day 14 after orthopedic surgeries controls the established persistent fracture allodynia. Furthermore, hydrogen-rich saline therapy reduces spinal CXCL1/CXCR2 over-expression and TfR1-mediated iron accumulation in fracture mice. Spinal CXCR2 antagonism impairs allodynia and iron overload following fracture surgery. Intrathecal delivery of recombinant CXCL1 induces acute allodynia and spinal iron overload, which is reversed by hydrogen-rich saline. Moreover, iron chelation alleviates exogenous CXCL1-induced acute pain behaviors.

CONCLUSIONS

These findings identify that hydrogen-rich saline confers protection against fracture-caused chronic allodynia via spinal down-modulation of CXCL1-dependent TfR1-mediated iron accumulation in mice.

Sensory Neuron-Specific Deletion of Tropomyosin Receptor Kinase A (TrkA) in Mice Abolishes Osteoarthritis (OA) Pain via NGF/TrkA Intervention of Peripheral Sensitization

Tropomyosin receptor kinase A (TrkA/NTRK1) is a high-affinity receptor for nerve growth factor (NGF), a potent pain mediator. NGF/TrkA signaling elevates synovial sensory neuronal distributions in the joints and causes osteoarthritis (OA) pain. We investigated the mechanisms of pain transmission as to whether peripheral sensory neurons are linked to the cellular plasticity in the dorsal root ganglia (DRG) and are critical for OA hyperalgesia. Sensory neuron-specific deletion of TrkA was achieved by tamoxifen injection in 4-week-old TrkA^fl/fl;Na_V1.8^CreERT2 (Ntrk1 ^fl/fl;Scn10a^CreERT2) mice. OA was induced by partial medial meniscectomy (PMM) in 12-week-old mice, and OA-pain-related behavior was analyzed for 12 weeks followed by comprehensive histopathological examinations. OA-associated joint pain was markedly improved without cartilage protection in sensory-neuron-specific conditional TrkA knock-out (cKO) mice. Alleviated hyperalgesia was associated with suppression of the NGF/TrkA pathway and reduced angiogenesis in fibroblast-like synovial cells. Elevated pain transmitters in the DRG of OA-induced mice were significantly diminished in sensory-neuron-specific TrkA cKO and global TrkA cKO mice. Spinal glial activity and brain-derived neurotropic factor (BDNF) were significantly increased in OA-induced mice but were substantially eliminated by sensory-neuron-specific deletion. Our results suggest that augmentation of NGF/TrkA signaling in the joint synovium and the peripheral sensory neurons facilitate pro-nociception and centralized pain sensitization.