Synovial Fluid and Serum Inflammation Biomarkers After Autologous Matrix-Induced Chondrogenesis (AMIC) for Knee Chondral Defects

TL;DR

This study examines inflammation biomarkers in joint fluid and blood after a cartilage repair surgery called AMIC and finds that certain inflammatory markers may be linked to slower recovery.

Contribution

The study provides new insights into post-operative inflammatory profiles in synovial fluid and their potential clinical relevance in cartilage repair outcomes.

Findings

Synovial fluid IL-1β and IL-1RA increased significantly over time after AMIC surgery.

Higher IL-6 and IL-1β/IL-1RA ratio were associated with poorer clinical improvement.

Synovial fluid measurements provided more relevant information on joint biology than serum sampling.

Abstract

Background: Focal chondral and osteochondral knee defects have limited intrinsic healing capacity and may progress toward post-traumatic osteoarthritis. Early post-operative inflammatory signaling may influence clinical recovery after cartilage repair. This prospective, single-center observational cohort study aimed to characterize short-term post-operative inflammatory biomarker profiles in synovial fluid and serum after AMIC and to assess associations with patient-reported outcomes over 12 months. Methods: Fifteen patients undergoing autologous matrix-induced chondrogenesis (AMIC) for focal knee chondral/osteochondral defects were prospectively enrolled. International Knee Documentation Committee (IKDC) and Lysholm scores were recorded pre-operatively and at 6 and 12 months. Synovial fluid and serum were collected intraoperatively, at 6 and 12 weeks post-operatively. Interleukin (IL)-1β, IL-1 receptor antagonist (IL-1RA), and IL-6 were quantified using multiplex flow luminescence immunoassay, and the total synovial fluid protein level was measured. Non-parametric repeated-measures testing and Spearman’s rank correlation were applied (p < 0.05). Results: IKDC and Lysholm scores improved from (30.6 ± 9.4) to (58.8 ± 15.0) and from (57.5 ± 18.6) to (78.2 ± 14.7), respectively, exceeding established minimal clinically important difference (MCID) thresholds. Synovial fluid IL-1β and IL-1RA increased significantly over time ((p = 0.01357) and (p = 0.03953), respectively); IL-1β remained elevated, whereas IL-1RA tended to decline after 6 weeks. IL-6 levels remained low throughout. Total synovial fluid protein increased significantly (p = 0.00043). No significant correlations were observed between corresponding biomarker levels in synovial fluid and serum. Higher IL-6 and a higher IL-1β/IL-1RA ratio were associated with poorer clinical improvement (ρ = −0.80, p < 0.05 and ρ = −0.580, p < 0.05, respectively). Conclusions: AMIC was associated with a sustained intra-articular inflammatory response despite favorable 12-month outcomes. Exploratory analyses suggest that inflammatory dysregulation—particularly involving IL-6 and IL-1β/IL-1RA balance—may be linked to less favourable clinical recovery. Synovial fluid measurements provided more relevant information on local joint biology than serum sampling.

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