The fate and role of bone graft-derived cells after autologous tendon and bone transplantation into the bone tunnel

Bone Mesenchymal Stem Cells Contribute to Ligament Regeneration and Graft-Bone Healing after Anterior Cruciate Ligament Reconstruction with Silk-Collagen Scaffold

Anterior cruciate ligament (ACL) reconstruction was realized using a combination of bone mesenchymal stem cells (BMSCs) and silk–collagen scaffold, and an in vivo evaluation of this combination was performed. By combining type I collagen and degummed silk fibroin mesh, silk–collagen scaffolds were prepared to simulate ligament components. BMSCs isolated from bone marrow of rabbits were cultured for a homogenous population and seeded on the silk–collagen scaffold. In the scaffold and BMSC (S/C) group, scaffolds were seeded with BMSCs for 72 h and then rolled and used to replace the ACL in 20 rabbits. In the scaffold (S) group, scaffolds immersed only in culture medium for 72 h were used for ACL reconstruction. Specimens were collected at 4 and 16 weeks postoperatively to assess ligament regeneration and bone integration. HE and immunohistochemical staining (IHC) were performed to assess ligament regeneration in the knee cavity. To assess bone integration at the graft–bone interface, HE, Russell–Movat staining, micro-CT, and biomechanical tests were performed. After 4 weeks, vigorous cell proliferation was observed in the core part of the scaffold in the S/C group, and a quantity of fibroblast-like cells and extracellular matrix (ECM) was observed in the center part of the graft at 16 weeks after surgery. At 4 and 16 weeks postoperatively, the tenascin-C expression in the S/C group was considerably higher than that in the S group (4 w, p < 0.01; 16 w, p < 0.01). Furthermore, bone integration was better in the S/C group than in the S group, with histological observation of trabecular bone growth into the graft and more mineralized tissue formation detected by micro-CT (4 w, bone volume fraction (BV/TV), p = 0.0169, bone mineral density (BMD), p = 0.0001; 16 w, BV/TV, p = 0.1233, BMD, p = 0.0494). These results indicate that BMSCs promote ligament regeneration in the knee cavity and bone integration at the graft–bone interface. Silk–collagen scaffolds and BMSCs will likely be combined for clinical practice in the future.

Biomaterials developed for facilitating healing outcome after anterior cruciate ligament reconstruction: Efficacy, surgical protocols, and assessments using preclinical animal models

Anterior cruciate ligament (ACL) reconstruction is the recommended treatment for ACL tear in the American Academy of Orthopaedic Surgeons (AAOS) guideline. However, not a small number of cases failed because of the tunnel bone resorption, unsatisfactory bone-tendon integration, and graft degeneration. The biomaterials developed and designed for improving ACL reconstruction have been investigated for decades. According to the Food and Drug Administration (FDA) and the International Organization for Standardization (ISO) regulations, animal studies should be performed to prove the safety and bioeffect of materials before clinical trials. In this review, we first evaluated available biomaterials that can enhance the healing outcome after ACL reconstruction in animals and then discussed the animal models and assessments for testing applied materials. Furthermore, we identified the relevance and knowledge gaps between animal experimental studies and clinical expectations. Critical analyses and suggestions for future research were also provided to design the animal study connecting basic research and requirements for future clinical translation.

Capacity of muscle derived stem cells and pericytes to promote tendon graft integration and ligamentization following anterior cruciate ligament reconstruction

PURPOSE

The aim of this study is to examine the capacity of muscle tissue preserved on hamstring tendons forming candy-stripe grafts in order to improve tendon to bone ingrowth and ligamentization. We hypothesized that muscle tissue does possess a stem cell population that could enhance the healing process of the ACL graft when preserved on the tendons.

METHODS

Human samples from gracilis and semitendinosus muscles were collected during ACL surgery from ten patients and from these tissue samples human muscle-derived stem cells and tendon-derived stem cells were isolated and propagated. Both stem cell populations were in-vitro differentiated into osteogenic lineage. Alkaline phosphatase activity was determined at days zero and 14 of the osteogenic induction and von Kossa staining to assess mineralization of the cultures. Total RNA was collected from osteoblast cultures and real time quantitative PCR was performed. Western-blot for osteocalcin and collagen type I followed protein isolation. Immunofluorescence double labeling of pericytes in muscle and tendon tissue was performed.

RESULTS

Mesenchymal stem cells from muscle and tendon tissue were isolated and expanded in cell culture. More time was needed to grow the tendon derived culture compared to muscle derived culture. Muscle derived stem cells exhibited more alkaline phosphatase actvity compared to tendon derived stem cells, whereas tendon derived stem cells formed more mineralized nodules after 14 days of osteoinduction. Muscle derived stem cells exhibited higher expression levels of bone sialoprotein, and tendon derived stem cells showed higher expression of dental-matrix-protein 1 and osteocalcin. Immunofluorescent staining against pericytes indicated that they are more abundant in muscle tissue.

CONCLUSIONS

These results indicate that muscle tissue is a better source of stem cells than tendon tissue. Achievement of this study is proof that there is vast innate capacity of muscle tissue for enhancement of bone-tendon integration and ligamentization of ACL hamstring grafts and consequently muscle tissue should not be treated as waste after harvesting.

Biological enhancement of graft-tunnel healing in anterior cruciate ligament reconstruction

The sites where graft healing occurs within the bone tunnel and where the intra-articular ligamentization process takes place are the two most important sites of biological incorporation after anterior cruciate ligament (ACL) reconstruction, since they help to determine the mechanical behavior of the femur-ACL graft-tibia complex. Graft-tunnel healing is a complex process influenced by several factors, such as type of graft, preservation of remnants, bone quality, tunnel length and placement, fixation techniques and mechanical stress. In recent years, numerous experimental and clinical studies have been carried out to evaluate potential strategies designed to enhance and optimize the biological environment of the graft-tunnel interface. Modulation of inflammation, tissue engineering and gene transfer techniques have been applied in order to obtain a direct-type fibrocartilaginous insertion of the ACL graft, similar to that of native ligament, and to accelerate the healing process of tendon grafts within the bone tunnel. Although animal studies have given encouraging results, clinical studies are lacking and their results do not really support the use of the various strategies in clinical practice. Further investigations are therefore needed to optimize delivery techniques, therapeutic concentrations, maintenance of therapeutic effects over time, and to reduce the risk of undesirable effects in clinical practice.

In vivo bone tunnel remodeling in symptomatic patients after ACL reconstruction: a retrospective comparison of articular and extra-articular fixation

BACKGROUND

there is only a paucity of studies dealing with bone remodeling within the tunnels after anterior cruciate ligament (ACL) reconstruction. The objective of this study was to evaluate the influence of tendon graft type and surgical fixation technique on bone tunnel remodeling in patients with symptomatic knees after ACL reconstruction.

METHODS

in a retrospective study 99mTc-HDP bone tracer uptake (BTU) in SPECT/CT of 57 knees with symptoms of pain and/or instability after ACL reconstruction was investigated. All 57 knees were subdivided according their anatomy (femur and tibia), fixation (articular versus extra-articular fixation) and graft types into eight groups: femoral-articular versus extra-articular fixation using bone-patellar tendon-bone (BPTB) and hamstring autografts; tibial-articular versus extra-articular fixation using patellar tendon and hamstring autografts; BTU grading for each area of the localisation scheme were recorded. Tunnel diameter and length was measured in the CT scans.

RESULTS

BTU was higher for the articular fixation in the femur and for the extra-articular fixation in the tibial tunnel. Patellar tendon graft fixation showed a significantly higher BTU in the superior-lateral and posterior-central area of the tibia, meaning the areas of the tibial tunnel near the entrance into the joint. Tunnel enlargement correlated significantly with increased BTU (p<0.05).

CONCLUSION

assessment of in vivo bone tunnel remodelling in symptomatic patients after ACL reconstruction revealed different patterns of BTU with regards to graft and fixation method.