Impact of chronicity of injury on the proportion of mesenchymal stromal cells derived from anterior cruciate ligaments.

Background aims. The graft-healing potential of mesenchymal stromal cells (MSCs) derived from the remnants of ruptured anterior cruciate ligaments (ACLs) after ACL reconstruction may depend on the chronicity of the injury. The aim of this study was to assess the quantitative and phenotypic differences between MSCs isolated from ACL remnants in patients with (sub) acute and chronic tearing. Methods. Torn ACL remnants were harvested during ACL reconstruction from 41 patients, 24 with (sub)acute ACL (<6 months from injury to surgery) and 17 with chronic ACL (time interval >6 months) tears. MSCs isolated from these samples were assessed for quantitative and phenotypic differences, and the correlation between the proportion of MSCs and the chronicity of ACL tear was evaluated. Results. At passage 0, the mean proportion of MSCs (CD34-, CD44+, CD90+ and CD105+) was higher in (sub)acute than in chronic ACL tear samples (20.69% ± 7.82% versus 9.85% ± 8.01 %, P < 0.001). At passages 1 and 2, however, MSC proportions did not differ significantly in the two groups. Time interval showed a negative correlation with MSC proportion only at passage 0 (r = -0.505, P < 0.001). The optimal cutoff value for time from injury to surgery yielding <10% freshly isolated ACL-MSCs, a percentage expected to have low tissue healing potential, was 23.5 months. Conclusions. The proportion of freshly isolated MSCs was higher in samples from patients with (sub) acute tearing than in chronic ACL tearing and negatively correlated with the time interval between trauma and surgery. [ABSTRACT FROM AUTHOR]