Common cell based strategies for treating bone defects require time-consuming and expensive isolation and expansion of autologous cells. We developed a novel expedited technology creating gene activated muscle grafts. We hypothesized that BMP-2 activated muscle grafts provide healing capabilities comparable to autologous bone grafting, the clinical gold standard.

Two male, syngeneic Fischer 344 rats served as tissue donors. Muscle tissue was harvested from hind limbs and incubated with an adenoviral vector carrying the cDNA encoding BMP-2. Bone tissue was harvested from the iliac crest. Segmental bone defects were created in the right femora of 12 rats and were filled with either BMP-2 activated muscle tissue or bone grafts. After 8 weeks, femora were evaluated by radiographs, microCT, and biomechanical tests.

BMP-2 activated muscle grafts and autologous bone grafts resulted in complete mineralization and healing, as documented by radiographs and microCT. Bone volume in the muscle graft defects (33+/-12mm3) was similar to autologous bone graft defects (39+/-5mm3). Torque at failure of the two groups was statistically indistinguishable (240+/-115 Nmm vs. 232+/-108Nmm).

In previous experiments we demonstrated that the large segmental defect model in this study will not heal with either empty defects or non-activated muscle grafts. Our findings therefore demonstrate that BMP-2 gene activation of muscle tissue effectively stimulates defect healing similar to autologous bone grafts.

Over the last 10 years ACI (Autologous Chondrocyte Implantation) has become an important surgical technique for treating large cartilage defects. The original method has been improved by using cell seeded scaffolds for implantation. The aim of our prospective study was to evaluate the efficiency of a matrix based ACI (MACI) with a collagen type I scaffold for repairing large cartilage defects of the knee. We present the clinical and radiological results of 22 pts. one year after collagen scaffold based ACI.

Out of 39 pts. treated with ACI for cartilage defects of the knee 22 had reached the one year follow up. We documented preoperatively and postoperatively (3, 6 and 12 months) the clinical situation with the IKDC Knee Examination Form. MRI scans were evaluated at all time points.

41% of the pts. were female, 59% male. The average age was 33 yrs. (min:15; max:49), the average BMI 25,4 (min:19; max:36). One third of the cartilage defects were localized retropatellar, the remaining on the medial or lateral femoral condyle. The average defect size was 5.7 cm2. In about 75% of the cases an additional surgical procedure was performed (ACL-reconstruction, lateral release, meniscal surgery). One major complication (a deep wound infection) occured. The IKDC score improved over time during follow up significantly. Patients with retropatellar defects have a poorer outcome compared to femoral defects. The MRI showed an improvement of the implanted scaffold over time as well.

The present study confirms the benefits of MACI in young patients with large cartilage defects of the knee. The matrix based ACI is a surgically less demanding technique then the traditional ACI. We expect a good long term outcome from MACI comparable to that of traditional ACI.