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

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.

LEVEL OF EVIDENCE: III, retrospective comparative study.