Summary

This study aims to determine how the M1:M2 monocyte ratio in cBMA affects clinical outcomes after foot and ankle procedures.

Abstract

Introduction

Concentrated bone marrow aspirate (cBMA) is a biological adjuvant used during orthopedic surgery procedures to enhance tissue repair and modulate inflammation by delivering cells and signalling factors within a scaffold. Although previous studies have investigated both the pro- and anti-inflammatory cytokines within cBMA, little work has been completed determining how cBMA cellular populations impact patient outcomes. Monocytes are one such cell type found within cBMA with the capability to exist on a spectrum between pro-inflammatory M1 and anti-inflammatory M2 populations. The global ratio of M1:M2 monocytes increases in pro-inflammatory diseases. This study aims to determine how the M1:M2 monocyte ratio in cBMA affects clinical outcomes after foot and ankle procedures. We hypothesized that patients who produced an “anti-inflammatory” cBMA with a lower M1:M2 monocyte ratio at the time of injection would have improved clinical outcomes.

Methods

The study proposal was reviewed and approved by an Institutional Review Board. Patients aged 18-85 years old undergoing a foot and ankle procedure with cBMA injection were offered enrolment into this study. Patients with a history of inflammatory disorders, corticosteroid use, cancer, and previous injections in the past year were excluded. Samples of peripheral blood (PB), bone marrow aspirate (BMA), and cBMA were collected during the procedure. The samples were analyzed by automated cell counting and multicolor fluorescence activated cell sorting with specific antibodies recognizing monocytes (CD14+CD16+) and the M1 (CD86+) and M2 (CD163+CD206+) populations within that monocyte population. Cytokine concentrations within the samples were evaluated with ELISA. Clinical outcomes were assessed with Patient-Reported Outcomes Measurement Information System (PROMIS) Global-10 and Foot and Ankle Outcome Score (FAOS) questionnaires on the day of the procedure, at the 3-month, 6-month, and 1-year follow-up visits.

Results

Currently, 38 patients have been enrolled in the study. The mean age was 49.3 years (range 18-84 years). cBMA had a mean fold increase of 5.3±5.5 for all leukocytes, 7.0±6.0 for monocytes, 9.2±9.4 for lymphocytes, 3.4±4.0 for neutrophils, and 10.7±14.0 for platelets when compared to BMA. No significant differences in M1 monocyte levels were found between PB, BMA, and cBMA (p>0.5). M2 monocytes were significantly more prevalent in PB than in BMA (p=0.0008) and cBMA (p=0.0027). The ratio of M1:M2 monocytes across all subjects trended higher in cBMA compared to PB (p=0.18). The patient had a significant effect on M1 (p=0.0093), and M2 (p<0.0001) levels, as well as M1:M2 ratio (p<0.0001) in PB, BMA, and cBMA. ELISA results and patient outcome comparisons are pending full enrolment of all planned subjects into the study.

Discussion And Conclusion

Both the cells and cytokines found within cBMA are important for generating its site-directed effects. cBMA preparation enriches multiple leukocyte populations involved in inflammation modulation including M1 and M2 monocytes. Due to the overabundance of adjuvant therapeutic options, predicting responders and non-responders to any given treatment is necessary to provide high-quality patient care at reduced costs. The results of this study will enable orthopedic surgeons to evaluate the quality of a cBMA preparation and determine which patients should receive cBMA versus an alternative therapy.