While many reviews have been performed to attempt to provide conclusive evidence regarding the outcomes of mesenchymal stem cells (MSCs) in osteoarthritis treatment, the evidence for MSC treatment in osteoarthritis remains contentious, as these reviews have been limited by the heterogeneous evidence available.
To pool the results of treatment using intra-articular injections of MSCs without any adjuvant therapies for osteoarthritis.
Systematic review and meta-analysis.
The review was conducted in accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. All clinical trials of level 1 or 2 evidence that reported clinical outcomes of patients with osteoarthritis of the knees treated using intra-articular injections of MSCs without any adjuvant therapies were included.
A total of 19 studies with 440 knees were included. All studies reported an improvement in the outcomes after intervention. The standardized mean differences (SMDs) for the visual analog scale (VAS) for pain at rest and upon exertion were -1.48 (95% CI, -1.85 to -1.11) and -2.25 (95% CI, -2.64 to -1.85), respectively. The SMDs for the total Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and total Knee injury and Osteoarthritis Outcome Score were -1.19 (95% CI, -1.53 to -0.84) and 0.88 (95% CI, 0.66-1.10), respectively. Only the source of MSCs and whether the MSCs were cultured or uncultured were clinically important and statistically significant moderators of the treatment outcome. The use of bone marrow MSCs reduced the VAS for pain by 1.50 (95% CI, 0.04-2.96; 
Intra-articular injections of MSCs without any adjuvant therapies improves pain and function for osteoarthritis. Significantly better outcomes were obtained with the use of bone marrow MSCs as compared with adipose MSCs and with the use of cultured MSCs as opposed to uncultured MSCs.