Outcomes of Autologous Chondrocyte Implantation in the Knee following Failed Microfracture

OBJECTIVES: Marrow stimulation techniques such as drilling or microfracture are first-line treatment options for symptomatic cartilage defects of the knee. For young patients who have failed microfracture, cartilage restoration techniques such as autologous chondrocyte implantation (ACI), OATS, and osteochondral allograft and are frequently employed. Nevertheless, there a few reports in the literature evaluating the results of ACI following failed microfracture and those available suggest inferior outcomes compared to primary ACI. This study was performed to evaluate the clinical outcomes of autologous chondrocyte implantation (ACI) following failed microfracture in the knee and compare these outcomes to those of primary ACI. METHODS: Patients were identified who underwent autologous chondrocyte implantation for symptomatic chondral lesions of the knee refractory to previous microfracture. Postoperative data were collected using several subjective scoring systems (Noyes, Tegner, Lysholm, IKDC, KOOS, SF12). An age-matched cohort of 103 patients who underwent primary ACI of the knee was used as a control group. Statistics were performed in a paired manner using a Student’s t-test for ordinal data and chi-square test for categorical data. RESULTS: Ninety-two patients met the inclusion criteria. The average patient age was 30.1 years (range, 14-49 years) at the time of ACI. The average duration from microfracture to ACI was 21.2 months (range, 1-88 months). ACI was performed in the tibiofemoral compartment in 42 patients, the patellofemoral compartments in 38 patients, and in both in 12 patients. The primary lesion treated with ACI involved the MFC in 38 patients, the trochlea in 25 patients, the patella in 19 patients, and the LFC in 10 patients. The lesions averaged 467mm3 in the trochlea, 445mm3 in the LFC, 265mm3 in the patella, and 295mm3 in the patella. Nineteen patients underwent concurrent ACI to multiple lesions. Thirty-one patients underwent concomitant patellar anteromedialization, 9 patients underwent meniscal allograft, and 6 underwent realignment ostetomies (5 HTO, 1 DFO). Follow-up was available on 84 of 92 patients (91%) at an average length of follow-up of 47 months (range, 24-102 months). The control group of patients was well matched with regard to age, gender, BMI, workers compensation status, and preoperative subjective scores. Failure, defined by need for further cartilage restoration or knee arthroplasty, occurred in 8 patients (3 osteochondral allograft, 3 TKA, 1 revision ACI, 1 Denovo NT). Seventeen additional patients underwent reoperation for intra-articular debridement. There was no difference between the failure rate (8.7% v. 2.9%, p=0.21) or reoperation rate (27.2% v. 27.2%, p=0.98) in the study and control groups. For the study group, significant improvements were witnessed postoperatively for all measured questionairre parameters. No significant differences were witnessed between the study and control groups (p>0.05) with regard to any of the postoperative subjective parameters (Figure). CONCLUSION: In patients with discrete articular cartilage lesions of the knee and history of failed microfracture, ACI may render favorable clinical outcomes comparable to primary ACI. While other series have demonstrated inferior results following previous microfracture, our series suggests that in appropriately selected patients ACI may be used successfully as a second line treatment following failed microfracture.