Primary Autologous Chondrocyte Implantation of the Knee Versus Autologous Chondrocyte Implantation After Failed Marrow Stimulation: A Systematic Review

Background: Marrow stimulation (MST) surgery, which includes microfracture, subchondral drilling, and abrasion arthroplasty, and autologous chondrocyte implantation (ACI) are 2 surgical options to treat articular cartilage lesions in the knee joint. Recent studies have suggested worse outcomes when ACI is used after failed MST. Purpose: To investigate the failure rates and clinical outcomes of primary knee ACI versus ACI after failed MST surgery (secondary ACI). Study Design: Systematic review. Methods: A systematic review was performed by searching the PubMed, Embase, and Cochrane Library databases to identify studies evaluating clinical outcomes of patients undergoing primary versus secondary ACI of the knee joint. The search terms used were as follows: “knee” AND (“autologous chondrocyte implantation” OR “osteochondral allograft”) AND (microfracture OR “marrow stimulation”). Patients undergoing primary ACI (group A) were compared with those undergoing secondary ACI (group B) based on treatment failure rates and patient-reported outcomes (PROs). Results: Seven studies (2 level 2 studies, 5 level 3 studies) were identified and met inclusion criteria, including a total of 1335 patients (group A: n = 838; group B: n = 497). The average patient age in all studies was 34.2 years, and the average lesion size was 5.43 cm2. Treatment failure occurred in 14.0% of patients in group A and 27.6% of patients in group B ( P < .00001). Four studies reported PROs. One study found significantly better Subjective International Knee Documentation Committee scores ( P = .011), visual analog scale (VAS) pain scores ( P = .028), and VAS function scores ( P = .005) in group A. Another study found significantly better Knee injury and Osteoarthritis Outcome Score (KOOS) Pain scores ( P = .034), KOOS Activities of Daily Living scores ( P = .024), VAS pain scores ( P = .014), and VAS function scores ( P = .032) in group A. Two studies found no significant difference in PROs between groups A and B ( P < .05). Conclusion: Patient-reported improvement can be expected in patients undergoing primary or secondary ACI of the knee joint. Patients undergoing secondary ACI have a significantly higher risk of treatment failure and may have worse subjective outcomes compared with patients undergoing primary ACI.