Time Matters: Knee Cartilage Defect Expansion and High-Grade Lesion Formation while Awaiting Autologous Chondrocyte Implantation

Abstract

Objective: The objective of this study was to assess potential risk factors, including time delay until implantation, for knee cartilage defect expansion or new high-grade defect formation between biopsy and Autologous Chondrocyte Implantation (ACI) or Matrix Autologous Chondrocyte Implantation (MACI). Study design: Consecutive knee ACI and MACI cases by a single surgeon (n = 111) were reviewed. The relationship between time between biopsy and staged implantation and (1) progression in primary cartilage defect size and (2) development of a new high-grade (Outerbridge grade ≥3) cartilage defect were determined with adjustment for demographics, body mass index, smoking status, coronal alignment, initial cartilage status, and prior surgery. Results: Average size of the primary defect at time of biopsy was 4.50 cm2. Mean time to chondrocyte implantation was 155 days. Defect expansion increased 0.11 cm2 (standard error = 0.03) per month delay to implantation (P = 0.001). Independent predictors of defect expansion were male sex, smaller initial defect size, and delay to implantation (adjusted mean = 0.15 cm2 expansion per month). A total of 16.2% of patients (n = 18/111) developed a new high-grade defect. Independent predictors of a new secondary defect were Outerbridge grade 2 changes (vs. 0-1) on the surface opposing the index defect and delayed implantation (per month increase, adjusted odds ratio = 1.21, 95% confidence interval: 1.01-1.44; P = 0.036). Conclusions: Patients undergoing 2-stage cell-based cartilage restoration with either ACI or MACI demonstrated long delays between stages of surgery, placing them at risk for expanding defects and development of new high-grade cartilage defects. Patients who were male, had smaller initial defect size, and longer time between surgeries were at greater risk for defect expansion.