KNEE Bone marrow mesenchymal stem cells in a hyaluronan scaffold for treatment of an osteochondral defect in a rabbit model S. Løken Æ R. B. Jakobsen Æ A. A ˚ røen Æ S. Heir Æ A. Shahdadfar Æ J. E. Brinchmann Æ L. Engebretsen Æ F. P. Reinholt Received: 30 October 2007 / Accepted: 6 May 2008 / Published online: 1 July 2008 Ó Springer-Verlag 2008 Abstract The purpose of this study was to evaluate the efficiency of using mesenchymal stem cells (MSC) in a hyaluronan scaffold for repair of an osteochondral defect in rabbit knee. Bone marrow was harvested from the posterior iliac crest in 11 New Zealand White rabbits. MSC were isolated and cultured in autologous serum for 28 days and transferred to a hyaluronan scaffold 24 h prior to implan- tation. A 4 mm diameter and 1.5 mm deep defect was created in the medial femoral condyle of both knees and the scaffold with MSC was implanted in one knee while an empty scaffold was implanted in the contra-lateral knee. After 24 weeks the rabbits were killed and histological sections were subjected to semiquantitative and quantita- tive evaluation by observers blinded regarding treatment modality. High degree of filling was obtained, but there was no statistically significant difference between the two treatments. However, there was a tendency for a better quality of repair in the MSC treated knees. No hypertrophy was observed by either method. MSC in a hyaluronan scaffold may be a promising treatment approach, but fur- ther studies are needed to determine the best combination of scaffold and cells. Keywords Mesenchymal stem cells Á Autologous transplantation Á Articular cartilage Á Hyaluronic acid Á Tissue engineering Á Surgery Á Knee Á Rabbits Introduction Focal cartilage and osteochondral injuries are common [1] and injured articular cartilage has limited capacity for complete spontaneous healing. With the aim of increasing the healing potential, autologous chondrocyte implantation (ACI) was introduced, and the first clinical results using this approach in treatment of human knees were published in 1994 [5]. In this so-called first generation chondrocyte implantation procedure, the defect is covered by a perios- teum flap sutured to the rim of the defect and the chondrocytes as a cell suspension are implanted under the flap. The second generation chondrocyte implantation procedure involves the use of autologous chondrocytes implanted in scaffolds [4, 29]. With both first and second generation approaches the chondrocytes are harvested from the joint and then expanded in vitro. In this process the cells dedifferentiate and lose their ability to produce S. Løken (&) Á A. A ˚ røen Á L. Engebretsen Orthopaedic Centre, Ulleva ˚l University Hospital and Medical School, 0407 Oslo, Norway e-mail: s-loek@online.no S. Løken Á A. A ˚ røen Á S. Heir Institute of Surgical Research, University of Oslo, Rikshospitalet Medical Centre, 0027 Oslo, Norway S. Løken Á A. A ˚ røen Á S. Heir Á L. Engebretsen Oslo Sports Trauma Research Center, Norwegian University of Sport and Physical Education, 0806 Oslo, Norway R. B. Jakobsen Á A. Shahdadfar Á J. E. Brinchmann Institute of Immunology, University of Oslo, Rikshospitalet Medical Centre, 0027 Oslo, Norway S. Heir Martina Hansens Hospital, 1306 Baerum, Norway F. P. Reinholt Institute of Pathology, University of Oslo, Rikshospitalet Medical Centre, 0027 Oslo, Norway F. P. Reinholt The Pathology Clinic, Rikshospitalet Medical Centre, 0027 Oslo, Norway 123 Knee Surg Sports Traumatol Arthrosc (2008) 16:896–903 DOI 10.1007/s00167-008-0566-2