The Statistical Fragility of Marrow Stimulation for Cartilage Defects of the Knee: A Systematic Review of Randomized Controlled Trials

OBJECTIVE

Marrow stimulation is used to address knee cartilage defects. In this study, we used the fragility index (FI), reverse fragility index (rFI), and fragility quotient (FQ) to evaluate statistical fragility of outcomes reported in randomized controlled trials (RCTs) evaluating marrow stimulation.

DESIGN

PubMed, Embase, and MEDLINE were queried for recent RCTs (January 1, 2010-September 5, 2023) assessing marrow stimulation for cartilage defects of the knee. The FI and rFI were calculated as the number of outcome event reversals required to alter statistical significance for significant and nonsignificant outcomes, respectively. The FQ was determined by dividing the FI by the study sample size.

RESULTS

Across 155 total outcomes from 21 RCTs, the median FI was 3 (interquartile range [IQR], 2-5), with an associated median FQ of 0.067 (IQR, 0.033-0.010). Thirty-two outcomes were statistically significant, with a median FI of 2 (IQR, 1-3.25) and FQ of 0.050 (IQR, 0.025-0.069). Ten of the 32 (31.3%) outcomes reported as statistically significant had an FI of 1. In total, 123 outcomes were nonsignificant, with a median rFI of 3 (IQR, 2-5). Studies assessing stem cell augments were the most fragile, with a median FI of 2. In 55.5% of outcomes, the number of patients lost to follow-up was greater than or equal to the FI.

CONCLUSION

Statistical findings in RCTs evaluating marrow stimulation for cartilage defects of the knee are statistically fragile. We recommend combined reporting of P-values with FI and FQ metrics to aid in the interpretation of clinical findings in comparative trials assessing cartilage restoration.

Circadian variation in the release of small extracellular vesicles can be normalized by vesicle number or TSG101

Numerous candidate biomarkers in urine extracellular vesicles (EVs) have been described for kidney diseases, but none are yet in clinical use, possibly due to a lack of proper normalization. Proper normalization corrects for normal biological variation in urine flow rate or concentration, which can vary by over one order of magnitude. Here, we observed inter- and intra-animal variation in urine excretion rates of small EVs (<200 nm in diameter) in healthy rats as a series of six 4-h fractions. To visualize intra-animal variation, we normalized a small EV excretion rate to a peak excretion rate, revealing a circadian pattern for each rat. This circadian pattern was distinct from urine volume, urine albumin, urine creatinine, and urine albumin-to-creatinine ratio. Furthermore, urine small EV excretion was not significantly altered by sex, food/water deprivation, or ischemic acute kidney injury. Urine excretion of the exosomal/small EV marker protein tumor susceptibility gene 101 (TSG101) displayed a similar circadian pattern to urine small EV excretion; both measurements were highly correlated (R² = 0.85), with an average stoichiometry of 10.0 molecules of TSG101/vesicle in healthy rats. The observed stoichiometry of TSG101/vesicle in rat urine translated to human spot urine samples (10.2 molecules/vesicle) and cultured kidney-derived cell lines (human embryonic kidney-293 and normal rat kidney 52E cells). Small EV number and its surrogate, TSG101 protein, can normalize for circadian variation when testing candidate biomarkers in small EVs. Just as creatinine has emerged as the customary normalization factor for liquid-phase urine biomarkers, vesicle number and its surrogate, molecules of exosome/small EV-associated TSG101, should be considered as viable, normalizing factors for small EV biomarkers.