Qu, Jin

Background: Low-intensity pulsed ultrasound (LIPUS), as a safe biophysiotherapy, can enhance bone-tendon (B-T) healing in vivo and induce osteogenic or chondrogenic differentiation of mesenchymal stromal cells in vitro. This study aimed to determine whether LIPUS can improve the efficacy of transplanted mesenchymal stromal cells on B-T healing. Hypothesis: LIPUS can induce lineage-specific differentiation of transplanted adipose-derived stromal cells (ASCs) at the B-T healing site, thus resulting in superior healing quality when compared with LIPUS or ASCs alone. Study Design: Controlled laboratory study. Methods: A total of 112 mature rabbits with partial patellectomy in the hindlimb were randomly assigned into mock sonication without ASCs (control), ultrasonication without ASCs (LIPUS), mock sonication with ASCs (ASCs), and ultrasonication with ASCs (LIPUS + ASCs). The treatment time of the mock sonication or ultrasonication was 20 minutes per day. Autologous ASCs were transplanted to the healing site by fibrin glue during the operation, and LIPUS was delivered daily starting at postoperative day 3 until euthanasia. The patella–patellar tendon junctions were postoperatively harvested at 8 and 16 weeks for radiological, histological, and mechanical evaluations. Additionally, 9 animals were used for ASC tracking with mCherry protein. Results: Radiologically, there was more new bone formation and remodeling in the LIPUS + ASCs group as compared with the other groups. Synchrotron radiation micro–computed tomography showed that the LIPUS + ASCs group significantly increased bone volume fraction, trabecular thickness, and trabecular number at the healing site as compared with the other groups at postoperative 8 weeks ( P < .05 for all). Histologically, immunohistochemical staining confirmed that the transplanted mCherry-ASCs can differentiate into osteoblasts and fibrochondrocytic-like cells. Meanwhile, as compared with the other groups, the LIPUS + ASCs group showed more formation and maturity of the fibrocartilage layer and new bone at postoperative weeks 8 and 16 ( P < .05 for all). Biomechanically, the LIPUS + ASCs group showed significantly higher failure load and stiffness versus the other groups at postoperative weeks 8 and 16 ( P < .05 for all). Conclusion: Autologous ASC transplantation stimulated with LIPUS can result in superior B-T healing quality when compared with LIPUS or ASCs alone. Clinical Relevance: This study demonstrates the effectiveness of using ASC transplantation stimulated with LIPUS for B-T healing and provides a foundation for future clinical studies.

ABSTRACTThe purpose of the current study was to develop a novel technology to enhance tendon‐to‐bone interface healing by trypsinizing and mineralizing (TM) an intrasynovial tendon allograft in a rabbit bone tunnel model. Eight rabbit flexor digitorum profundus (FDP) tendons were used to optimize the trypsinization process. An additional 24 FDP tendons were stratified into control and TM groups; in each group, 4 tendons were used for in vitro evaluation of TM and 8 were transplanted into proximal tibial bone tunnels in rabbits. The samples were evaluated histologically and with mechanical testing at postoperative week 8. Maximum failure strength and linear stiffness were not significantly different between the control and TM tendons. A thin fibrous band of scar tissue formed at the graft‐to‐bone interface in the control group. However, only the TM group showed obvious new bone formation inside the tendon graft and a visible fibrocartilage layer at the bone tunnel entrance. This study is the first to explore effects of TM on the intrasynovial allograft healing to a bone tunnel. TM showed beneficial effects on chondrogenesis, osteogenesis, and integration of the intrasynovial tendon graft, but mechanical strength was the same as the control tendons in this short‐term in vivo study. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:468–474, 2015.

AbstractTendon‐to‐bone integration is a great challenge for tendon or ligament reconstruction regardless of use of autograft or allograft tendons. We mineralized the tendon, thus transforming the tendon‐to‐bone into a “bone‐to‐bone” interface for healing. Sixty dog flexor digitorum profundus (FDP) tendons were divided randomly into five groups: (1) normal FDP tendon, (2) CaP (non‐extraction and mineralization without fetuin), (3) CaPEXT (Extraction by Na2HPO4 and mineralization without fetuin), (4) CaPFetuin (non‐extraction and mineralization with fetuin), and (5) CaPEXTFetuin (extraction and mineralization with fetuin). The calcium and phosphate content significantly increased in tendons treated with combination of extraction and fetuin compared to the other treatments. Histology also revealed a dense mineral deposition throughout the tendon outer layers and penetrated into the tendon to a depth of 200 µm in a graded manner. Compressive moduli were significantly lower in the four mineralized groups compared with normal control group. No significant differences in maximum failure strength or stiffness were found in the suture pull‐out test among all groups. Mineralization of tendon alters the interface from tendon to bone into mineralized tendon to bone, which may facilitate tendon‐to‐bone junction healing following tendon or ligament reconstruction. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31:1713–1719, 2013