Mosaicplasty application with hexagonal graft system and comparison of standard cylindrical graft system in calf knee model (A biomechanical study)

The treatment of cartilage injuries has a significant place in orthopedic surgery. Several methods are used in treatment, but each treatment modality has its own limitations. Till today, any method that can treat the hyaline cartilage tissue completely has not been developed yet. Mosaicplasty is one of the treatment methods used in reconstruction of the cartilage defects. Good results can be obtained especially in accompanying injuries to subchondral bone. In mosaicplasty technique, cylindrical grafts are used. However, there can be some problems due to the presence of complications like creating potential dead-space between grafts, insufficient covering of the defected area, graft collapse, absence of graft union, postoperative hemarthrosis, arthrofibrosis, formation of subchondral fracture and cyst, graft cartilage necrosis, donor-site morbidity. In our study, we aimed to increase graft stability and fill potential dead-spaces by applying hexagon grafts (honeycomb model) instead of standard cylindrical graft in mosaicplasty, because of having the best occupying area and volume geometry characteristics in the nature. In order to prepare hexagon grafts, hexagon graft receivers and tunnel-openning tubes were prepared. 24 fresh left femoral condylar region including both condyles of 200-400-kg- calves having no macroscopic cartilage injuries and of which soft tissues are cleaned are used in the study. Samples are divided into three groups so that each group has eight femoral condyles. 1st Group; one cylindrical and one hexagon graft 15 mm deep were taken from lateral anterior articular surface and medial anterior articular surface of trochlea. Cylindrical graft was applied to medial condyle load bearing area and hexagon graft was applied to lateral condyle load bearing area in each femur. 2nd Group: three cylindrical and hexagon grafts 15 mm deep were taken from the lateral anterior articular surface and medial anterior articular surface of trochlea. Cylindrical grafts were applied to medial condyle load bearing area and hexagon grafts were applied to lateral condyle load bearing area in each femur. 3rd group: a 5-mm-deep hexagon graft and a 20-mm-deep hexagon graft were taken from the lateral anterior articular surface and medial anterior articular surface of trochlea. 5-mm-deep hexagon graft was applied to medial condyle load bearing area and 20-mm-deep hexagon graft was applied to lateral condyle load bearing area in each femur. Grafts in each group were taken from non weight-bearing area of the lateral anterior articular surface and medial anterior articular surface of trochlea. 9-mm-diameter cylindrical grafts taken from non weight-bearing area were applied press-fit to 8 mm cylindrical tunnels. Similarly, 9-mm-diametar hexagon grafts taken from non weight-bearing area were applied press-fit to 8 mm hexagon tunnels. Screw hooks of 5 mm depth and 2 mm in diameter were applied in the center of grafts manually after opening the entry point with a 2 mm Kirshner wire. Afterwards they were subjected to pull out test at the rate of 20 mm/min at computer assisted Shimadzu AG-15 test device. 3 evaluations were done in this study. 1st evaluation: Pull out data of single cylindrical and single hexagon grafts in the 1st group was compared. Pull out data of triple cylindrical and triple hexagon grafts in the 2nd group was compared. Pull out data of the single 5-mm-deep hexagon and single 20-mm-deep hexagon grafts in the 3rd group was compared. Pull out data of 15-mm-deep single cylindrical graft in the 1st group and 5 mm deep single hexagon grafts was compared. 2nd evaluation: Cylindrical and hexagon grafts in the 1st and 2nd groups were compared by calculating the friction fields. The influence of the friction fields on the stability was researched. 3rd evaluation: Surface area (cartilage surface) of the cylindrical and hexagon grafts in the 1st and 2nd groups, the covering rate of the defected area was calculated by estimating their volumes. Pull out powers of the 15-mm-deep cylindrical graft (n: 8) and single 15-mm-deep hexagon graft (n: 8) in the 1st group (Table 8) were different. But it was statistically insignificant (p>0, 05). Pull out power between the 15-mm-deep triple cylindrical graft and 15-mm-deep triple hexagon graft in the 2nd group was different in favor of triple hexagon grafts and it was statistically significant (p<0,05). Although the pull out powers of the 5-mm-deep single hexagon graft (n: 8) and single 20-mm-deep hexagon graft (n: 8) in the 3rd group were different, it was statistically insignificant (p>0, 05). No statistical significances were found (p>0, 05) between the pull out power of 15-mm-deep single cylindrical grafts (n: 8) in the 1st group and 5-mm-deep single hexagon grafts (n: 8) in the 3rd group. It was calculated that there was a difference between the friction field, surface area and volume of the grafts. It was demonstrated that hexagon grafts had more friction field and they could also cover more surface area. In conclusion, based on biomechanical results, it can be stated that graft geometry, especially in multiple graft applications (according to pull out test), is one of the factors that influences the stability and that hexagon grafts are more stable in multiple applications in comparison to cylindrical grafts and they can cover larger defected area. Another advantage of the hexagon grafts is that they can be applied shorterly. Keywords: mosaicplasty, hyaline cartilage, cartilage treatment, autologous osteochondral graft transfer