Approximately 30% of Patients Undergoing Knee Cartilage Biopsy Subsequently Undergo Matrix-Induced Autologous Chondrocyte Implantation at a Mean 4.3-Year Follow-Up.

PURPOSE: To evaluate implantation rates, time to implantation, and predictors of implantation following matrix-induced autologous chondrocyte implantation (MACI) biopsy for knee chondral defects. METHODS: Patients undergoing MACI biopsy or implantation for symptomatic knee chondral defects from 2017 to 2024 at a single institution were reviewed. At a minimum 1-year follow-up, the decision to proceed with implantation, recurrent symptoms, complications, and reoperations were assessed. Kaplan-Meier analysis estimated time to implantation, and multivariable logistic regression identified predictors of MACI implantation. RESULTS: A total of 208 knees in 202 patients (mean age 28.0 ± 10.9 years, range 11-59) underwent MACI biopsy for 243 chondral defects (patella [38%], femoral condyle [34%], and trochlea [26%]). At a mean follow-up of 4.3 years (range 1.0-8.3), 64 knees (31%) proceeded to second-stage MACI implantation. Among 144 knees not implanted, 87 (60%) reported symptom improvement, and 26 (18%) had persistent symptoms. The remaining 22% did not undergo implantation due to another cartilage procedure, insurance denial, or pending scheduling. Patients who underwent biopsy at the home institution had a shorter time from biopsy to implantation compared with those biopsied at outside institutions (6.1 vs 13.1 months, P = .001). Median time to implantation was 9.4 months (95% confidence level: 7.2-12.2) for home biopsies. Lower body mass index was associated with progression to implantation after adjusting for covariates (odds ratios 0.92, P = .019). Patients implanted within 4 months had larger chondral defects (4.0 vs 3.0 cm2, P = .045). At a mean 4.1-year follow-up, 6 patients (8%) experienced postoperative complications, including 3 (4%) who required revision chondroplasty. CONCLUSIONS: MACI biopsy for knee chondral defects resulted in approximately one-third of patients proceeding to MACI implantation, at a median of 9.4 months after biopsy. Lower body mass index was associated with higher likelihood of progression to implantation, larger chondral defects with earlier implantation, and among patients who did not proceed to implantation, approximately 60% reported symptom improvement following concomitant chondroplasty at the time of biopsy. LEVEL OF EVIDENCE: Level IV, retrospective case series.