Matrix metalloproteinase enzymes (MMPs) play a crucial role in the remodeling of articular cartilage, contributing also to osteoarthritis (OA) progression. The pericellular matrix (PCM) is a specialized space surrounding each chondrocyte, containing collagen type VI and perlecan. It acts as a transducer of biomechanical and biochemical signals for the chondrocyte. This study investigates the impact of MMP-2, -3, and -7 on the integrity and biomechanical characteristics of the PCM.

Human articular cartilage explants (n=10 patients, ethical-nr.:674/2016BO2) were incubated with activated MMP-2, -3, or -7 as well as combinations of these enzymes. The structural degradative effect on the PCM was assessed by immunolabelling of the PCM's main components: collagen type VI and perlecan. Biomechanical properties of the PCM in form of the elastic moduli (EM) were determined by means of atomic force microscopy (AFM), using a spherical cantilever tip (2.5µm).

MMPs disrupted the PCM-integrity, resulting in altered collagen type VI and perlecan structure and dispersed pericellular arrangement. A total of 3600 AFM-measurements revealed that incubation with single MMPs resulted in decreased PCM stiffness (p<0.001) when compared to the untreated group. The overall EM were reduced by ∼36% for all the 3 individual enzymes. The enzyme combinations altered the biomechanical properties at a comparable level (∼36%, p<0.001), except for MMP-2/-7 (p=0.202).

MMP-induced changes in the PCM composition have a significant impact on the biomechanical properties of the PCM, similar to those observed in early OA. Each individual MMP was shown to be highly capable of selectively degrading the PCM microenvironment. The combination of MMP-2 and -7 showed a lower potency in reducing the PCM stiffness, suggesting a possible interplay between the two enzymes. Our study showed that MMP-2, -3, and -7 play a direct role in the functional and structural remodeling of the PCM.

Acknowledgements: This work was supported by the Faculty of Medicine of the University of Tübingen (grant number.: 2650-0-0).

Purpose: With this retrospective study, the results of rotator cuff repairs in patients of 60 years and older were compared to patients younger 60.

Methods: 76 patients with an average age of 65 years (60–78 years, group A) and 167 patients younger 60 years (group B) were clinical (Constant – score) and sonographical examined after follow-up of 2 years after reconstruction of the rotator cuff.

Results: In group A, 24 one-, 37 two-, 11 three- and 4 four-tendon tears were treated and the average age and gender adjusted Constant-score was 90,4% (13–126%). 29% showed sonographical signs of a re-defect. In group B, 56 one-, 69 two-, 33 three-, and 9 four-tendon tears were treated and the average age and gender adjusted Constant-score was 81,1% (15–116%). 32% showed sonographical signs of a re-defect.

Conclusion: Both groups did not show significant differences regarding clinical results in the Constant-score size of the rotator cuff defect or occurrence of re-tears. The results in patients older 60 were even better than in younger patients, therefore the older age of the patient should not be primary reason for not repairing a symptomatic rotator cuff tear.