FIG. 1.

Histological sections depicting interindividual and intraindividual variability of spontaneous osteochondral repair following a unilateral or bilateral study design. Representative safranin O-stained histological sections reflect the larger variability of spontaneous osteochondral repair for the unilateral experimental design compared with the bilateral design, resulting in increased sample size requirements when only one joint per animal is evaluated. In particular, the important histological parameters of matrix staining and subchondral bone reconstitution as well as the total score value¹⁰ vary more between different animals (unilateral design; images A and B) than between different joints of the same animal (bilateral design; images C and D; Table 3). Most single parameters of osteochondral repair, including matrix staining and subchondral bone reconstitution, as well as the overall histological score, were improved for the unilateral design compared with bilaterally operated animals (Table 2). The sections illustrated were taken from the defects having a histological rating equal to the mean score for its respective experimental group. Photomicrographs were obtained using standardized photographic parameters, including light intensity. Black triangles indicate defect margins. Scale bar: 1.0 mm. Color images available online at www.liebertpub.com/tec