Controlling Joint Instability Reduces Inflammatory Pain in Early Knee Osteoarthritis

Area of Science:

• Biomedical research
• Orthopedics
• Pain research

Background:

• Knee osteoarthritis (OA) causes joint deformity and pain, impacting physical and psychological well-being.
• Inflammatory and neuropathic pain factors in the dorsal root ganglion (DRG) contribute to chronic knee OA pain.
• The progression of pain-related factors and the effect of joint instability on pain in knee OA are not fully understood.

Purpose of the Study:

• To investigate pathological changes in pain generation during knee OA progression.
• To determine the effect of suppressing joint instability on pain reduction in knee OA.

Main Methods:

• Induction of knee OA in Wistar rats via anterior cruciate ligament transection, with a controlled abnormal movement group (CAM) and sham group.
• Assessment of joint instability, histological analysis of knee joints, and fluorescent immunohistochemistry of DRG for pain-related factors.
• Evaluation of pain behavior using behavioral tests and statistical analysis (ANOVA, Kruskal-Wallis).

Main Results:

• Knee OA induced significant joint instability and severe articular cartilage degeneration.
• Calcitonin gene-related peptide (CGRP) expression in DRG was elevated in early knee OA (4 weeks).
• No significant differences in substance P, isolectin B4, or P2X3 expression were found; neuropathic pain was not observed in advanced OA.

Conclusions:

• Calcitonin gene-related peptide (CGRP) expression in the dorsal root ganglion (DRG) contributes to inflammatory pain in early knee osteoarthritis (OA).
• Re-establishing joint stability effectively suppresses inflammatory pain in knee OA.
• Neuropathic pain, including allodynia, was not evident in the advanced stages of knee OA studied.