Background <p>Osteoarthritis (OA) is a chronic degenerative joint disease affecting millions of people mainly aged over 65. OA leads to progressive damage across joint components, including bone degeneration with osteophyte formation, cartilage erosion, synovitis, and meniscal deterioration. Early OA treatments focus on symptom management, but advanced knee OA often requires alternative approaches. Regenerative medicine, such as tissue engineering, offers promising solutions. Mesenchymal stem cell (MSC) intra-articular injections have gained popularity for OA management. Autologous sources, such as bone marrow aspirate concentrate (BMAC) and adipose-derived stem cells (ADSCs), are widely used.</p> Objective <p>This study compared the therapeutic efficacy of single BMAC and ADSC injections in knee OA patients, focusing on MSC quantity and quality in harvested tissues. To support this, hematological studies analyzed and quantified CD34+ cells in adipose and bone marrow samples.</p> Methods <p>60 patients diagnosed with symptomatic degenerative knee OA were enrolled. Patients under 50 received BMAC injections, while those over 50 received ADSC injections. Follow-ups were conducted at baseline(t0), 1 month (t1), 3 months (t2), and 6 months (t3) using the Visual Analog Scale (VAS), WOMAC score, Kellgren–Lawrence classification, and range of motion (ROM). Bone marrow and adipose samples were harvested and processed to quantify viable MSCs. Mononuclear cells were isolated using density gradient centrifugation, and CD34+ cells were subsequently enriched through magnetic separation using column-based processing. Cultured MSCs were counted weekly to evaluate proliferation.</p> Results <p>Both groups showed significant clinical improvements in VAS, WOMAC, and ROM scores (<i>p</i> &lt; 0.01). No statistically significant correlation was observed between MSC quantity and treatment efficacy (<i>p</i> ≥ 0.01). MSC cultures succeeded in 32 aspirates: 30 from bone marrow and 2 from adipose tissue, with cell counts ≥ 0.35 × 10⁵ cells/mL.</p> Conclusions <p>At 6 months, both BMAC and ADSC treatments resulted in significant clinical improvements (<i>p</i> &lt; 0.01), with no significant differences between groups (<i>p</i> ≥ 0.01). Our findings indicated that bone marrow samples generally yielded higher MSC counts and showed slightly faster recovery rates among BMAC-treated patients, but with no substantial differences at the 6&#xa0;month mark. MSC efficacy may depend on factors beyond cell quantity. Further studies with extended follow-ups are required.</p> Graphical abstract <p></p>