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Probiotics and related microbiota-targeted interventions for knee osteoarthritis: a systematic review and meta-analysis of randomized controlled trials

This systematic review and meta-analysis of 13 randomized controlled trials suggests that probiotics and related gut microbiota-targeted interventions may produce a small, statistically significant reduction in pain intensity for patients with knee osteoarthritis, but they do not show consistent benefits for WOMAC scores or inflammatory markers, and safety conclusions remain limited by sparse data.

Original authors: Zhenning Li, Long Chen, Zehong Lin, Honghai Zhou

Published 2026-08-13

📖 6 min read🧠 Deep dive

CC BY 4.0

Original authors: Zhenning Li, Long Chen, Zehong Lin, Honghai Zhou

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine your body as a bustling, high-tech city. For years, scientists thought the pain in your knees was like a pothole in the road—a simple case of wear and tear where the cartilage cushion just wore down over time. But recently, the map of this city has been redrawn. We now know that the "traffic" inside your body isn't just about your joints; it's also about the millions of tiny, microscopic residents living in your gut. Think of your gut microbiota as a massive, diverse neighborhood of bacteria. When this neighborhood is healthy and balanced, it keeps the city's security guards (your immune system) calm and happy. But if the neighborhood gets chaotic (a state called dysbiosis), it can send out alarm signals that travel through the bloodstream, causing inflammation and pain even in places far away, like your knees. This is the "gut-joint axis," a new idea suggesting that what happens in your tummy might be shouting at your knees.

Now, imagine trying to fix a noisy city by sending in a peacekeeping force. That's what probiotics, prebiotics, and postbiotics are: they are like special reinforcements sent to the gut neighborhood to restore order. Probiotics are the living "good guys" (bacteria), prebiotics are the food that helps them grow, and postbiotics are the helpful byproducts they leave behind. The big question for doctors and patients has been: If we send these reinforcements to the gut, will they actually quiet the noise and stop the knee pain? This is the mystery that a team of researchers set out to solve by gathering every available story from the scientific world.

The Great Gut-Knee Detective Story

A team of researchers decided to play detective. Instead of running a single experiment, they went on a massive scavenger hunt, digging through libraries of medical studies (including databases in both English and Chinese) to find every single "Randomized Controlled Trial" they could. Think of these trials as the gold standard of evidence: groups of people with knee pain were split up, with one group getting the "gut reinforcements" (probiotics, prebiotics, or postbiotics) and the other group getting a fake version (a placebo) or their usual care. The goal was to see if the gut team actually made a difference.

They found 13 different studies involving 1,438 people. That's a lot of knee pain to analyze! They looked at three main things:

How much did it hurt? (Pain scores)
How well could they move? (WOMAC scores, which measure pain, stiffness, and function)
Was there less inflammation? (Levels of C-reactive protein, or CRP, in the blood)

The Big Reveal: A Small Win for Pain

Here is the most exciting part of the story: The gut reinforcements did seem to help with the pain. When the researchers added up the results, they found that people taking these gut-targeted treatments reported their pain dropping by an average of 1.06 points on a standard pain scale (where 0 is no pain and 10 is the worst pain imaginable).

To put that in perspective, if you imagine a pain scale as a ladder, these treatments helped people climb down just over one rung. It wasn't a magic cure that made the pain vanish completely, but it was a real, measurable step in the right direction. The researchers were quite confident in this specific finding because the results were consistent across the different studies, and there was no "noise" or disagreement between the data points. They call this a "small reduction," but for someone living with chronic knee pain, even a small step down the ladder can feel like a victory.

The "Maybe" Zone: Movement and Inflammation

However, the story gets a bit fuzzier when we look at the other clues. When the researchers checked if these treatments helped people move better or reduced the overall stiffness of their knees (the WOMAC scores), the results were a mixed bag. The data suggested a slight improvement, but it wasn't strong enough to be sure. It was like trying to hear a whisper in a windy room; the signal was there, but the wind (scientific uncertainty) was too loud to say for certain that the whisper was real.

Similarly, when they checked the blood for signs of inflammation (CRP levels), the gut reinforcements didn't seem to lower them significantly. This is a bit of a plot twist. You might expect that if the gut neighborhood is calmer, the whole city's inflammation should drop. But the data didn't show that. The researchers suggest that maybe the inflammation in knee osteoarthritis is more like a local fire in the joint itself, rather than a city-wide smog that can be easily cleared by gut bacteria. So, while the pain went down, the blood markers didn't necessarily follow suit.

The Safety Check: No Red Flags, But Not a Green Light Either

What about safety? Did these gut reinforcements cause any trouble? The researchers checked the "adverse event" reports. In four out of the five studies that reported on safety, nobody got sick or had bad reactions in either the treatment group or the control group. In the one study that did report events, the numbers were too small to draw a big conclusion.

The bottom line here is: We don't have a clear "danger" signal, but we also don't have a "perfectly safe" stamp of approval. The evidence is just too thin to say for sure. It's like checking the weather forecast for a tiny, isolated island; the data is too sparse to predict if a storm is coming or if it's going to be sunny forever. The researchers rated the certainty of the safety data as "very low," meaning we need more studies before we can say these treatments are definitely safe for everyone in the long run.

The Verdict

So, what's the final takeaway from this massive detective work?

The paper suggests that if you have knee osteoarthritis, trying a probiotic or a related gut treatment might help you feel a little less pain. It's not a miracle drug, and it won't fix the structural damage in your knee, but it could be a helpful sidekick to your usual treatment plan. However, don't expect it to completely fix your ability to walk or run, or to instantly lower your body's inflammation levels based on current evidence.

The researchers are very clear: this isn't a solved mystery. The "pain" clue is the strongest, but the "movement" and "safety" clues are still blurry. They are calling for bigger, better, and longer studies to see if these gut reinforcements can really become a standard part of the toolkit for fighting knee pain. Until then, the gut-joint connection remains a fascinating, promising, but still slightly mysterious path in the world of medicine.

Technical Summary: Probiotics and Related Microbiota-Targeted Interventions for Knee Osteoarthritis

Problem Statement
Knee osteoarthritis (KOA) is a prevalent chronic degenerative disorder causing pain, functional limitation, and reduced quality of life. Current management strategies primarily focus on symptom relief, with no broadly accepted disease-modifying drugs available. Emerging evidence suggests a link between gut dysbiosis, intestinal barrier dysfunction, and KOA pathophysiology via the "gut–joint axis." Mechanisms include the translocation of microbial products (e.g., lipopolysaccharide) triggering systemic and synovial inflammation, and the modulation of pain sensitization by microbial metabolites. While preclinical studies and early clinical trials suggest that probiotics, prebiotics, and postbiotics may attenuate these pathways, previous systematic reviews have been limited by small sample sizes, high heterogeneity, and a narrow focus strictly on probiotics. There is a need for a comprehensive evaluation of the broader category of gut microbiota-targeted interventions (including prebiotics and postbiotics) regarding their efficacy on pain, functional outcomes, inflammatory markers, and safety in adults with KOA.

Methodology
This study is a systematic review and meta-analysis of randomized controlled trials (RCTs) registered in PROSPERO (CRD420261391066).

Search Strategy: A systematic search was conducted across PubMed, Embase, the Cochrane Library, CNKI, Wanfang Data, and trial registries (ClinicalTrials.gov, WHO ICTRP, ChiCTR) from inception to June 5, 2026.
Eligibility Criteria: Included studies were RCTs involving adults with confirmed KOA, comparing gut microbiota-targeted interventions (probiotics, prebiotics, synbiotics, postbiotics) against placebo, usual care, or matched controls. Studies reporting pain, WOMAC scores, inflammatory markers, or safety were included.
Data Synthesis: Primary analyses prioritized baseline-adjusted between-group estimates (e.g., ANCOVA). When unavailable, mean changes from baseline were calculated. A random-effects meta-analysis using restricted maximum likelihood (REML) estimation with the Hartung–Knapp adjustment was employed to account for anticipated heterogeneity.
Statistical Rigor: Heterogeneity was assessed using Cochran's Q, $\tau^2$ , and $I^2$ . Sensitivity analyses included expanded data sources (graphical extraction), varying assumed correlation coefficients ( $r=0.3, 0.5, 0.7$ ) for estimating change-score standard deviations, and leave-one-out analyses.
Evidence Quality: The certainty of evidence was assessed using the GRADE approach.

Key Contributions

Scope Expansion: Unlike previous reviews focusing solely on probiotics, this analysis encompasses a broader spectrum of microbiota-targeted interventions, including prebiotics and postbiotics.
Methodological Precision: The study prioritizes baseline-adjusted effect estimates over simple change scores to minimize bias from baseline imbalances. It employs the Hartung–Knapp adjustment for more conservative confidence intervals in the presence of few studies.
Comprehensive Outcome Assessment: The review evaluates not only pain and function (WOMAC) but also systemic inflammatory markers (CRP/hs-CRP), exploratory mechanistic biomarkers (zonulin, 8-isoprostanes), and safety outcomes.

Results
The analysis included 14 reports representing 13 independent RCTs with 1,438 participants.

Pain Intensity: Microbiota-targeted interventions resulted in a statistically significant reduction in pain intensity compared to controls (8 studies, 662 participants; Mean Difference [MD] = −1.06, 95% CI −1.42 to −0.70; $P < 0.001$ ). Heterogeneity was negligible ( $I^2 = 0.0\%$ ). This finding remained robust in leave-one-out and sensitivity analyses.
WOMAC Scores: No statistically significant difference was found for the WOMAC total score (4 studies, 677 participants; MD = −8.05, 95% CI −19.49 to 3.39; $P = 0.111$ ). Substantial heterogeneity was observed ( $I^2 = 90.2\%$ ).
Inflammatory Markers: No significant between-group difference was found for CRP or hs-CRP levels (5 studies, 483 participants; MD = −0.42, 95% CI −1.77 to 0.94; $P = 0.439$ ), with considerable heterogeneity ( $I^2 = 96.9\%$ ).
Exploratory Outcomes: Significant improvements were observed in the Oxford Knee Score (OKS) and reductions in zonulin levels. No significant differences were found for range of motion (ROM) or 8-isoprostanes.
Safety: Five studies reported adverse events. Four studies observed zero events in both groups; only one provided an estimable relative effect. Consequently, no meta-analysis of safety was performed. The data did not show a clear signal of increased adverse events, but sparse reporting precluded firm conclusions.
Subgroup Analyses: Exploratory subgroup analyses by intervention type (probiotics vs. prebiotics) and duration (≤12 weeks vs. >12 weeks) showed no statistically significant differences in pain reduction between categories.

Significance and Claims
The authors claim that the current evidence suggests probiotics and related gut microbiota-targeted interventions may produce a small, statistically significant reduction in pain intensity in patients with KOA, supported by moderate-certainty evidence. This effect appears consistent across different intervention types and durations.

However, the paper explicitly states that:

Clinical Importance is Uncertain: The magnitude of pain reduction is modest, and it remains unclear whether it reaches a threshold of clinically important improvement or persists long-term.
Limited Functional and Anti-inflammatory Evidence: The evidence does not establish consistent benefits for overall functional status (WOMAC) or systemic inflammatory markers (CRP/hs-CRP).
Safety Uncertainty: Due to sparse event reporting and inconsistent monitoring, the certainty of evidence for safety is very low. The findings cannot confirm the safety of these interventions nor rule out rare or long-term risks.
Need for Further Research: The authors conclude that larger, adequately powered RCTs with standardized outcomes, long-term follow-up, and integrated mechanistic assessments are necessary to validate these findings and determine the optimal intervention strategies.

The study positions these interventions as potential adjunctive therapies rather than replacements for standard care, emphasizing the need for cautious interpretation until higher-quality evidence is available.

Technical Summary: Probiotics and Related Microbiota-Targeted Interventions for Knee Osteoarthritis

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