Summary

The results of this study demonstrates that ACI is a procedure that preserves the native knee with long-term graft survival of 74.4% and maintenance of functional improvements in 51.2% of patients at 20 years following treatment for isolated femoral condyle articular cartilage lesions

Abstract

Introduction

There has been an accumulation of high-level evidence demonstrating good clinical outcomes for the use of Autologous Chondrocyte Implantation (ACI) in articular cartilage repair in the knee over the short and mid-term. Long-term evidence, however, remains limited. The aim of this study is to report the long-term outcomes and identify predictors of success and failure following ACI for isolated femoral condyle articular cartilage defects in the knee.

Methods

Study participants consisted of a cohort of patients treated with ACI for unipolar isolated defects of the femoral condyle. Patients were identified from the inhouse prospectively maintained ACI database. Each patient underwent a 2-stage procedure to reconstruct a chondral lesion using expanded chondrocytes (Oscell, Oswestry, UK). Kaplan-Meier survival analysis was performed, and clinical outcome was determined using the modified Lysholm score. Mixed multilevel modelling was used to identify predictive factors.

Results

The study population consisted of 29 males and 12 females with a mean age of 36.6 years (SD 8.95, range 18-52). All patients had a single chondral defect of the distal femur with 30 lesions on the medial femoral condyle (MFC) and 11 on the lateral femoral condyle (LFC). The median defect area was 4.38cm^2 ([IQR], 2.3-6.0) with the largest defect measuring 13.5cm^2. The mean number of cells implanted was 3.01 x 10^6 cells/cm^2. The average follow-up time was 11 years (SD 5.03) with a maximum follow-up of 20 years post-ACI. The mean pre-operative Lysholm score was 42.9 (SD 17.3, 11-74). Improvement in clinical outcome scores were found to peak at year 7 with a mean score of 61.0 (SE 3.31). The biggest increase in Lysholm score was achieved in the first year with a mean increase of 16.7 (SE 4.10, p<0.05). Mean Lysholm scores at 15 and 20 years post-ACI were 59.7 and 57.1 respectively. Functional improvement was maintained in 65.7% (95% CI, 52%-83%) at 10 years and 51.2% (95% CI, 35%-75%) at 20 years. Mixed multilevel modelling identified an inverse relationship between total number of cells implanted and Lysholm score. For every extra 1 million cells implanted, the Lysholm score at 12 months decreased by 3.9 (95% CI, 0.7-7.1). Eight patients (19.5%) were considered to have failed with a conversion to total knee arthroplasty at a mean time of 8.1 years (SD 3.15) following ACI. Survival at 20 years was 74.4% (95% CO, 60%-91%) with maintenance of the native knee for which treatment was initially sought.

Conclusions

ACI is a procedure that preserves the native knee with long-term graft survival of 74.4% and maintenance of functional improvements in 51.2% of patients at 20 years. In addition, the total number of cells implanted rather than cell seeding density influenced the clinical outcome of patients in this study, with increasing cell number having a negative effect on clinical outcome.