Objective: To determine the effectiveness of 'accelerated' compared to 'traditional' post-operative load bearing rehabilitation protocols following matrix-induced autologous chondrocyte implantation (MACI).Method. A randomized controlled study design was used to investigate clinical. biomechanical and radiographic assessment at 3 months post-surgery in 62 patients following MACI to the medial or lateral femoral condyle. Both rehabilitation interventions sought to protect the implant for an initial period. then incrementally increase load bearing. Under the 'accelerated' protocol, patients reached full weight bearing at 8 weeks post-surgery, compared to 11 weeks for the 'traditional' group.Results: Patients in the 'accelerated' group achieved greater 6 min walk distances and daily activity levels as measured by accelerometry (P <0.05) compared to the 'traditional' group. Furthermore, the 'accelerated' group reported significantly better improvement in knee pain at 12 weeks as indicated by the Knee Injury and Osteoarthritis Outcome Score (P <0.05), and regardless of the rehabilitation protocol employed. no patient suffered any adverse effect to the implant as assessed by magnetic resonance imaging at 3 months. Comparison of each rehabilitation group with an unaffected control group revealed a significant difference in peak knee adduction and flexion moments for the traditional group (P <0.05). However, there was no difference for accelerated patients (P > 0.05), which may demonstrate a faster return to knee loading patterns typically observed in unaffected subjects.Conclusion: The 'accelerated' load bearing approach that reduced the length of time spent ambulating on crutches resulted in reduced knee pain, improved function, no graft complications and may speed up the recovery of normal gait function. Patient follow-up to at least 24 months would be required to observe longer-term graft outcomes. (C) 2008 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.