# Proof: Cracking your knuckles regularly causes arthritis later in life.

- **Generated**: 2026-03-28
- **Verdict**: DISPROVED (with unverified citations)
- **Audit trail**: [proof_audit.md](proof_audit.md) | [proof.py](proof.py)

## Key Findings

- **4 out of 4** independent authoritative sources explicitly reject a causal link between habitual knuckle cracking and arthritis.
- A peer-reviewed study of 215 participants (Deweber et al. 2011) found osteoarthritis prevalence was **similar** among crackers (18.1%) and non-crackers (21.5%), with no statistically significant difference.
- A study of 300 patients (Castellanos & Axelrod 1990) found "no increased preponderance of arthritis of the hand" in habitual knuckle crackers.
- **No peer-reviewed study was found** that supports a causal link between knuckle cracking and arthritis.

## Claim Interpretation

**Natural language claim**: "Cracking your knuckles regularly causes arthritis later in life."

**Formal interpretation**: This claim asserts a causal relationship between habitual knuckle cracking and the development of arthritis (specifically osteoarthritis of the hand). To disprove, we require at least 3 independent authoritative sources — peer-reviewed studies and major medical institutions — that explicitly find no such causal relationship. The threshold of 3 is appropriate given the abundance of published research on this topic. This is a disproof by scientific consensus: the `proof_direction` is "disprove", meaning verified sources that reject the claim count toward the threshold.

## Evidence Summary

| ID | Fact | Verified |
|----|------|----------|
| B1 | Harvard Health: no arthritis risk from knuckle cracking | Yes |
| B2 | Deweber et al. 2011 (JABFM): no association between KC and hand OA | Partial (aggressive normalization fragment match) |
| B3 | Castellanos & Axelrod 1990 (PMC): no increased arthritis in crackers | Yes |
| B4 | Johns Hopkins Arthritis Center: no evidence KC causes arthritis | Yes |
| A1 | Verified source count | Computed: 4 independent sources confirmed (all 4 citations countable) |

## Proof Logic

The proof follows a disproof-by-consensus approach. Four independent authoritative sources were consulted, each addressing whether habitual knuckle cracking causes arthritis:

1. **Harvard Health Publishing** (B1) directly states that knuckle cracking "probably won't raise your risk for arthritis," based on several studies comparing arthritis rates.

2. **Deweber et al. 2011** (B2), published in the Journal of the American Board of Family Medicine, conducted a retrospective case-control study of 215 participants (135 with hand osteoarthritis, 80 controls). They found that "a history of habitual KC does not seem to be a risk factor for hand OA," with OA prevalence at 18.1% among crackers vs 21.5% among non-crackers.

3. **Castellanos & Axelrod 1990** (B3), published in the Annals of the Rheumatic Diseases, studied 300 patients and found "no increased preponderance of arthritis of the hand in either group" — though they did note reduced grip strength and hand swelling in habitual crackers.

4. **Johns Hopkins Arthritis Center** (B4) states unequivocally: "There is no evidence that cracking knuckles causes any damage such as arthritis in the joints."

All 4 sources were countable (verified or partial), exceeding the threshold of 3 required for disproof (A1). Since all 4 independently agree that knuckle cracking does not cause arthritis, the claim is disproved by scientific consensus.

## Counter-Evidence Search

Three adversarial checks were performed to search for evidence supporting the claim:

1. **Peer-reviewed studies supporting a causal link**: Searched PubMed and Google Scholar — no study was found establishing a causal link between knuckle cracking and arthritis.

2. **Grip strength loss as arthritis precursor**: The Castellanos 1990 study found reduced grip strength in crackers but explicitly ruled out an arthritis association. Grip strength loss is a functional effect, not evidence of arthritis.

3. **Cavitation mechanism causing cartilage damage**: The biomechanical literature on knuckle cracking (gas bubble formation in synovial fluid) shows no evidence that this process damages articular cartilage or leads to degenerative joint changes.

## Conclusion

**DISPROVED (with unverified citations)**: The claim that cracking your knuckles regularly causes arthritis is disproved by scientific consensus. All 4 independent sources — including 2 peer-reviewed studies and 2 major medical institutions — explicitly find no causal relationship between habitual knuckle cracking and arthritis.

The "with unverified citations" qualifier applies because one citation (B2, JABFM) was verified only via aggressive normalization (fragment match), not full quote verification. This is likely due to the journal page's HTML rendering. However, the disproof does not depend solely on B2: the remaining 3 sources (B1, B3, B4) are all fully verified and independently sufficient to meet the threshold of 3.

Note: 2 citation(s) come from unclassified or low-credibility tier sources (B2: jabfm.org tier 2, B4: hopkinsarthritis.org tier 2). Both are well-known medical institutions (JABFM is a peer-reviewed medical journal; Johns Hopkins is a top-tier research hospital). The tier 2 classification reflects domain-level heuristics, not actual source quality.

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Generated by [proof-engine](https://github.com/yaniv-golan/proof-engine) v0.10.0 on 2026-03-28.
