## 2 Materials and Methods
### Surgical Techniques and Rehabilitation Protocols  
Arthroscopic mosaicplasty was performed in one step using the Autogenous Osteochondral Grafting System (Smith & Nephew, London, UK) surgical instrumentation, as previously described [20]. In brief, damaged cartilaginous and fibrous tissue was excised, and the lesion was then measured for size and location. Recipient 15 mm deep holes were made perpendicular to the cartilage surface. After preparing the defect area, osteochondral grafts were harvested. The donor site was preferentially the superolateral ridge of the femoral condyle, whereas the superomedial ridge was used only when four grafts were necessary. Tubular chisels were used to harvest the graft and then, with a smooth cannula, the grafts were delivered into the defect. One plug was used in 4 patients, 2 plugs in 9 patients, 3 plugs in 5 patients, and 4 plugs in 2 patients. The stability of the plugs was tested by cyclic bending of the knee while grafts were visualized. Arthroscopic MACT was performed in two steps as previously described [21]. In brief, the first procedure consisted of an arthroscopic biopsy of healthy cartilage, sent for chondrocyte cell culture and subsequent seeding onto a hyaluronic acid-based scaffold (Hyaff 11, Fidia Advanced Biopolymers Laboratories, Padova, Italy) to obtain the bioengineered tissue Hyalograft C (Fidia Advanced Biopolymers Laboratories, Padova, Italy). After 6 weeks, the second step was performed, and the bioengineered tissue was arthroscopically implanted through cannulated devices. Because of the physical adhesive characteristics of the graft, no fibrin glue or sutures were used to fix the implant. Under arthroscopic control, the stability of implanted patches was evaluated during cyclic bending of the knee. Postoperative rehabilitation protocols were comparable for both treatments. Postoperative management focused on early mobilization to facilitate faster resolution of swelling, promote healing and joint nutrition, and prevent adhesions. Passive knee range of motion (ROM) exercises on a continuous passive motion (CPM) machine (0\({}^{\circ}\)-30\({}^{\circ}\)) and static quadriceps exercises were started few days after surgery. Usually, 90\({}^{\circ}\) of knee flexion was reached within 4 weeks and full ROM within 8 weeks after surgery. Toe-touch ambulation with crutches and braces in full extension was allowed the third or fourth week and was usually completed within 6 to 8 weeks after surgery. Progressive \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Baseline Characteristics** & **Mosaicplasty** & **MACT** & **Comparison** \\ \hline Patients, n (Men/Women) & 20 (15/5) & 23 (18/5) & NS \\ Age, y mean (SD) & 28.7 (7.3) & 29.1 (5.9) & NS \\ BMI, mean (SD) & 23.4 (2.6) & 24.0 (2.4) & NS \\ Sport activity, n (\%) & & & \\ _Non-competitive level_ & 11 (55.0\%) & 12 (52.2\%) & NS \\ _Competitive level_ & 9 (45.0\%) & 11 (47.8\%) & \\ Etiology, n (\%) & & & \\ _Traumatic_ & 5 (25.0\%) & 12 (52.2\%) & NS \\ _Degenerative_ & 15 (75.0\%) & 11 (47.8\%) & \\ Combined surgery, n (\%) & 15 (75.0\%) & 15 (65.2\%) & \\ _ACL reconstruction_, \(n\) & 9 (45.0\%) & 12 (52.2\%) & NS \\ _Meniscal treatment_, \(n\) & 11 (55.0\%) & 10 (43.5\%) & \\ Previous surgery, \% & 8 (40.0\%) & 11 (47.8\%) & \\ _ACL reconstruction_, \(n\) & 4 (20.0\%) & 3 (13.0\%) & \\ _Meniscal treatment_, \(n\) & 3 (15.0\%) & 4 (17.4\%) & NS \\ Cartilage treatment, n & 1 (5.0\%) & 4 (17.4\%) & \\ Defect size, cm\({}^{2}\) (SD) & 2.0 (0.6) & 2.0 (0.6) & NS \\ Location, n (\%) & & & \\ _Medial Femoral Condyle_ & 12 (60.0\%) & 12 (52.2\%) & NS \\ _Lateral Femoral Condyle_ & 8 (40.0\%) & 11 (47.8\%) & \\ \hline \hline \end{tabular} Statistical analysis showed no significant differences between the two groups. ACL, anterior cruciate ligament; BMI, body mass index; MACT, matrix-assisted autologous chondrocyte transplantation; NS, not significant; SD, standard deviation; y, years.  
\end{table} 
Table 1: Comparison of patient and lesion characteristics in the two groups.