Isolation and characterization of connective tissue progenitor cells derived from human fracture-induced hemarthrosis in vitro.

In our search for alternative sources of connective tissue progenitor cells that can be obtained with minimal invasion, we studied human intraarticular fracture-induced hemarthrosis of the knee and attempted to isolate connective tissue progenitors from the hemarthrosis. Hemarthrosis was aspirated from the knee joints of 13 patients suffering from intraarticular osteochondral fractures of the knee. Mononuclear cells were isolated from the aspirated hemarthrosis by density gradient separation, and cultured. We were able to obtain fibroblastic adherent cells from the mononuclear cell fractions. Flow cytometry analysis after in vitro expansion on tissue culture plastic revealed that the fibroblastic cells were positive for CD29, CD44, CD105, and CD166, and negative for CD14, CD34, CD45, and CD133. These cells could differentiate in vitro into osteogenic, chondrogenic, and adipogenic cells in the presence of lineage-specific induction factors. These results demonstrate that human intraarticular fracture-induced knee hemarthrosis contains connective tissue progenitor cells with morphologic features, immunophenotypic markers, and differentiation potential that are similar to bone marrow stromal cells. This suggests that hemarthrosis, which is easy to harvest without unnecessary invasion to the patient, has possible future clinical applications such as in tissue-engineered therapies for severe osteochondral defects, posttraumatic osteoarthritis, and delayed fracture unions or nonunions.