**7.4.1 Second-look arthroscopy with chondral core biopsy**

During the second-look procedures, a chondral core biopsy specimen was procured. This was performed arthroscopically with a 5.5 mm sterilized BioCorkscrew anchor driver (Arthrex, Naples, FL). Typically, a 2 mm diameter specimen of cartilage together with a core of bone up to 1 cm in length is obtained (Fig 15).

Arthroscopically, the regenerated articular cartilage appeared smooth and had excellent integration with the surrounding native cartilage without any delamination or hypertrophy. The exception was case 2, in which the drill holes over the lateral patellofemoral joint were too far apart with resultant tufts of cartilage seen between areas devoid of regenerated cartilage (Fig 16).

Fig. 15. Solid articular cartilage core biopsy with a 2 mm diameter including the underlying subchondral bone.

Articular Cartilage Regeneration with Stem Cells 149

Histologic samples were stained as follows: hematoxylin-eosin (H&E) stain was used to visualize overall morphology, Safranin-O was used to highlight proteoglycans, immunohistochemistry staining with anti–collagen type I mouse Ab I-8H5 stain (catalog No. CP 17; Calbiochem Merck, Darmstadt, Germany) was used to highlight collagen type I, and immunohistochemistry staining with anti–collagen type II mouse monoclonal antibody Ab 3 (clone 6B3) (catalog No. MAB8887; Millipore, Billerica, MA) was used to highlight collagen type II. Optimal dilution and predigestion with pepsin were determined by the investigator with the protocol being saved by use of software of an automated immunohistochemical slide preparation system (Ventana Benchmark; Ventana

Cases 1 and 2 with gross grade IV kissing lesions are presented with multiple biopsy specimens and histologic analyses after second-look arthroscopy. Cases 3, 4, and 5 are

**Case 1**: Biopsy was performed 22 months after the initial surgery in a 49-year-old woman with a varus deformity who underwent debridement, subchondral drilling, and an open

Fig. 17. Progressive serial weight-bearing radiographs of Case 1 with high tibial osteotomy.

Approximately 80% of the weight-bearing medial compartment had grade III and IV lesions. Weight-bearing radiographs at 8 and 18 months showed reappearance of the medial femorotibial joint space. Second-look arthroscopy of the regenerated cartilage showed a stable, smooth surface with no delamination. On probing, the regenerated cartilage had the same consistency as the surrounding normal cartilage. The second-look images and biopsy

Immunohistochemistry staining was performed to assess the collagen type I and type II content of the biopsy specimens. Specimens from the medial femoral condyle and medial tibial plateau showed the presence of collagen type I confined to the superficial layer. Collagen type II was present throughout the deeper layers. These are features of hyaline cartilage as opposed to fibrocartilage (Fig 18). Fig 19 shows a higher magnification of the

**7.4.2 Histology** 

Medical Systems, Tucson, AZ).

patients with smaller isolated lesions.

wedge high tibial osteotomy with Tomofix fixation (Fig 17).

Notice re-appearance of the medial articulation.

histological sections from the medial tibial plateau.

specimens are included in Fig 18.

Fig. 16. 34-year-old female from Fig 22. Second-look arthroscopy from the lateral patella facet and lateral trochlear showed tufts of cartilage forming at each individual drill hole. Upon histological stains, notice the red staining with Safranin-O representing proteoglycans and the brown staining of collagen type II diffuse throughout the regenerated tissue. Collagen type I stain is minimal and localized near the superficial layers.
