17/04/2025
Prevalence, clinical predictors, and mechanisms of resorption in lumbar disc herniation (LDH) 💡: a systematic review
👉 Lumbar disc herniation (LDH) is characterized as the rupture of fibrous annulus of the intervertebral disc, resulting in herniation or prolapse of nucleus pulposus (NP), which compresses and inflames spinal nerves and cauda equina nerve roots and thus causes clinical symptoms (https://pubmed.ncbi.nlm.nih.gov/23484826/).
👉 Most of the symptoms of LDH can be relieved by conservative treatment that can shrink the herniated portion and thus reduce compression (https://pubmed.ncbi.nlm.nih.gov/24630494/).
📘 In a new systematic review, Xie and colleagues (https://pubmed.ncbi.nlm.nih.gov/39944739/) tried to uncover the following three questions:
1️⃣ What is the percentage of spontaneous resorption in the conservative management of LDH?
2️⃣ How do we predict that spontaneous resorption may occur in LDH patients?
3️⃣ What are the molecular mechanisms of NP spontaneous resorption in LDH patients?
1️⃣ Prevalence of Resorption:
▶️ The authors found that the overall incidence of NP resorption was 76.6%, and the incidence of resorption was higher in ruptured disc herniations than in inclusive disc herniations. The incidence of resorption differed significantly between countries. The resorption process occurred mainly within 3-6 months of conservative treatment. These data are based on 31 studies were included, including 2,199 patients who received conservative treatment.
2️⃣ Clinical Predictors of Resorption:
▶️ Predictors include NP size, inflammatory response, prolapse extent, and imaging features like the percentage of edge-enhancing areas and posterior longitudinal ligament (PLL) rupture on enhanced MRI.
▶️ Larger herniations ((https://pubmed.ncbi.nlm.nih.gov/36243388/), and those with disrupted PLL showed higher resorption rates, likely due to greater exposure to epidural vasculature (https://pubmed.ncbi.nlm.nih.gov/36722839/
▶️ The "bull’s-eye sign" on enhanced MRI (indicating neovascularization and inflammation) strongly predicts resorption (https://pmc.ncbi.nlm.nih.gov/articles/PMC11165499/).
▶️ Modic changes and cartilage endplate involvement were associated with lower resorption likelihood, potentially increasing recurrence risk.
3️⃣ Mechanisms of Resorption:
💡 Four main mechanisms were identified (s. illustration):
1. Inflammatory Response: Pro-inflammatory cytokines (e.g., TNF-α, IL-1β) trigger matrix degradation and immune cell recruitment.
2. Neovascularization: New blood vessel formation at herniation sites facilitates immune access and resorption.
3. Macrophage Infiltration: M1 macrophages drive inflammation and phagocytosis, while M2 macrophages promote tissue repair and anti-inflammatory effects.
4. Matrix Protease Activation: Matrix metalloproteinases (MMP-3, MMP-7) degrade NP tissue, aiding resorption.
▶️ The autoimmune response is triggered when NP is exposed to the epidural space, disrupting the blood-NP barrier.
💡 Discussion and Implications:
✅ Conservative treatment is preferred for LDH, with resorption being a key indicator of success, but NSAIDs are suspected to hinder this process by suppressing inflammation critical for resorption (https://pubmed.ncbi.nlm.nih.gov/38099946/).
✅ The review suggests that modulating macrophage activity (M1/M2 balance) and exploring autophagic pathways could enhance resorption.
✅ Imaging advancements, particularly MRI, are vital for predicting and monitoring resorption.
⭕ Limitations include the low quality of included studies, reliance on imaging for diagnosis, and limited follow-up data, which may affect result reliability.
