Grafted tendon healing in tibial tunnel is inferior to healing in femoral tunnel after anterior cruciate ligament reconstruction: a histomorphometric study in rabbits

Engineering a functional ACL reconstruction graft containing a triphasic enthesis-like structure in bone tunnel for the enhancement of graft-to-bone integration

Background

Anterior cruciate ligament (ACL) rupture is a common sports injury, which causes knee instability and abnormal joint kinematics. The current ACL graft was single-phasic, and not convenient for the formation of enthesis-like tissue in the bone tunnel, resulting in poor integration of graft-to-bone.

Methods

A band-shaped acellular tendon (BAT) was prepared as the core component of the ACL reconstruction graft at first, while sleeve-shaped acellular cartilage (SAC) or sleeve-shaped acellular bone (SAB) was fabricated using a vacuum aspiration system (VAS)-based decellularization protocol. The biocompatibility of the three acellular matrixes was evaluated. Furthermore, a collagen-binding peptide (CBP) derived from the A3 domain of von Willebrand factor was respectively fused into the N-terminal of GDF7, TGFβ3, or BMP2 to synthesize three recombinant growth factors capable of binding collagen (named C-GDF7, C-TGFβ3, or C-BMP2), which were respectively tethered to the BAT, SAC or SAB for improving their inducibilities in stem cell differentiation. An in-vitro experiment was performed to evaluate theirs osteogenic, chondrogenic, and tenogenic inducibilities. Then, C-TGFβ3-tethering SAC (C-TGFβ3@SAC) and C-BMP2-tethering SAB (C-BMP2@SAB) were sequentially surrounded at the bone tunnel part of C-GDF7-tethering BAT (C-GDF7@BAT), thus a sleeve-shaped acellular graft with a triphasic enthesis-like structure in bone tunnel part (named tissue-engineered graft, TE graft) was engineered. Lastly, a canine ACL reconstruction model was used to evaluate the in-vivo performance of this TE graft in enhancing graft-to-bone integration.

Results

The BAT, SAC, and SAB well preserved the structure and components of native tendon, cartilage, and bone, showing good biocompatibility. C-GDF7, C-TGFβ3, or C-BMP2 showed a stronger binding ability to BAT, SAC, and SAB. The C-GDF7@BAT, C-TGFβ3@SAC, or C-BMP2@SAB was a controlled delivery system for the scaffold-specific release of GDF7, TGFβ3, and BMP2, thus showing superior tenogenic, chondrogenic, or osteogenic inducibility, respectively. Using a canine ACL reconstruction model, abundant newly-formed bone and connective collagen fibers could be observed at the integration site between TE graft and bone tunnel at postoperative 16 weeks. Meanwhile, the failure load of the reconstructed ACL by TE graft was significantly higher than that of the autograft.

Conclusion

The TE graft could be used to reconstruct ruptured ACL and augment graft-to-bone integration, thus demonstrating high potential for clinical translation in ACL reconstruction.

Translational potential of this article

The findings of the study indicated that the TE graft could be a novel graft for ACL reconstruction with the ability to augment graft-to-bone integration, which may provide a foundation for future clinical application.

The hydroxyapatite modified 3D printed poly L-lactic acid porous screw in reconstruction of anterior cruciate ligament of rabbit knee joint: a histological and biomechanical study

BACKGROUND

3D printing technology has become a research hotspot in the field of scientific research because of its personalized customization, maneuverability and the ability to achieve multiple material fabrications. The focus of this study is to use 3D printing technology to customize personalized poly L-lactic acid (PLLA) porous screws in orthopedic plants and to explore its effect on tendon-bone healing after anterior cruciate ligament (ACL) reconstruction.

METHODS

Preparation of PLLA porous screws with good orthogonal pore structure by 3D printer. The hydroxyapatite (HA) was adsorbed on porous screws by electrostatic layer-by-layer self-assembly (ELSA) technology, and PLLA-HA porous screws were prepared. The surface and spatial morphology of the modified screws were observed by scanning electron microscopy (SEM). The porosity of porous screw was measured by liquid displacement method. Thirty New Zealand male white rabbits were divided into two groups according to simple randomization. Autologous tendon was used for right ACL reconstruction, and porous screws were inserted into the femoral tunnel to fix the transplanted tendon. PLLA group was fixed with porous screws, PLLA-HA group was fixed with HA modified porous screws. At 6 weeks and 12 weeks after surgery, 5 animals in each group were sacrificed randomly for histological examination. The remaining 5 animals in each group underwent Micro-CT and biomechanical tests.

RESULTS

The pores of PLLA porous screws prepared by 3D printer were uniformly distributed and connected with each other, which meet the experimental requirements. HA was evenly distributed in the porous screw by ELSA technique. Histology showed that compared with PLLA group, mature bone trabeculae were integrated with grafted tendons in PLLA-HA group. Micro-CT showed that the bone formation index of PLLA-HA group was better than that of PLLA group. The new bone was uniformly distributed in the bone tunnel along the screw channel. Biomechanical experiments showed that the failure load and stiffness of PLLA-HA group were significantly higher than those of PLLA group.

CONCLUSIONS

The 3D printed PLLA porous screw modified by HA can not only fix the grafted tendons, but also increase the inductivity of bone, promote bone growth in the bone tunnel and promote bone integration at the tendon-bone interface. The PLLA-HA porous screw is likely to be used in clinic in the future.

Influence of the Tibial Tunnel Angle and Posterior Tibial Slope on "Killer Turn" during Posterior Cruciate Ligament Reconstruction: A Three-Dimensional Finite Element Analysis

This study aimed to evaluate the influence of various posterior tibial slopes (PTSs) and tibial tunnel angles (TTAs) on "killer turn" in posterior cruciate ligament (PCL) reconstruction by using three-dimensional finite element analysis (FEA). The study models were created using computed tomography images of a healthy young Asian male. Using SolidWorks, PCL grafts and tibial bone tunnels at different tibial drilling angles (30°, 45°, 60°) were developed. Anterior opening wedge high tibial osteotomy (aOW-HTO) was performed to evaluate the influence of the PTS (+8°, +4°, native, -4°, -8°). An FEA was performed utilizing the ANSYS software program. In the same PTS model, the peak of the equivalent Von Mises stress in PCL grafts decreased as the angle of the TTA increased. In the same TTA model, the peak of the Von Mises in PCL grafts decreased as the PTS angle increased. The "high-contact stress area" (contact stress greater than 10 MPa) was diminished when the TTA and PTS were increased. aOW-HTO was used to steepen the PTS, and a larger TTA may reduce the stress at the "killer turn" during PCL reconstruction. In conclusion, the study findings suggest that using aOW-HTO to steepen the PTS and a larger TTA may reduce the stress at the "killer turn" during PCL reconstruction. The usefulness and safety of this surgical procedure need to be evaluated in future clinical studies.

Bioactive Decellularized Tendon-Derived Stem Cell Sheet for Promoting Graft Healing After Anterior Cruciate Ligament Reconstruction

BACKGROUND

Stem cell sheets provide a scaffold-free option for the promotion of graft healing after anterior cruciate ligament reconstruction (ACLR). However, cell viability, stability, and potential uncontrolled actions create challenges for clinical translation. The decellularization of cell sheets may overcome these problems as studies have shown that the natural extracellular matrix of stem cells is bioactive and can promote tissue repair.

HYPOTHESIS

The decellularized tendon-derived stem cell (dTDSC) sheet can promote graft healing after ACLR.

STUDY DESIGN

Controlled laboratory study.

METHODS

An optimized decellularization protocol was developed to decellularize the TDSC sheets. A total of 64 Sprague-Dawley rats underwent ACLR with or without the dTDSC sheet wrapping the tendon graft (n = 32/group). At 2 and 6 weeks after surgery, graft healing was assessed by micro-computed tomography, histology, and biomechanical testing. The accumulation of iNOS⁺ and CD206⁺ cells and the expression of metalloproteinase 1 (MMP-1), MMP-13, and tissue inhibitor of metalloprotease 1 (TIMP-1) were assessed by immunohistochemistry.

RESULTS

The decellularization was successful, with the removal of 98.4% nucleic acid while preserving the collagenous proteins and bioactive factors. The expression of bone morphogenetic protein 2 (BMP-2) and VEGF in the dTDSC sheet was comparable with the TDSC sheet (P > .05). Micro-computed tomography showed significantly more tunnel bone formation in the dTDSC sheet group. The dTDSC sheet group demonstrated better graft osteointegration and higher integrity of graft midsubstance with significantly higher ultimate failure load (16.58 ± 7.24 vs 8.93 ± 2.45 N; P = .002) and stiffness (11.97 ± 5.21 vs 6.73 ± 2.20 N/mm; P = .027). Significantly fewer iNOS⁺ cells but more CD206⁺ cells, as well as lower MMP-1 and MMP-13 but higher TIMP-1 expression, were detected at the tendon-bone interface and graft midsubstance in the dTDSC sheet group.

CONCLUSION

An optimized decellularization protocol for producing bioactive dTDSC sheets was developed. Wrapping tendon graft with a dTDSC sheet promoted graft healing after ACLR, likely via enhancing bone formation and angiogenesis by BMP-2 and VEGF, modulating macrophage polarization and MMP/TIMP expression, and physically protecting the tendon graft.

CLINICAL RELEVANCE

dTDSC sheets alleviate the quality control and safety concerns of cell transplantation and can be used as a cell-free alternative for the promotion of graft healing in ACLR.

Distinct inflammatory macrophage populations sequentially infiltrate bone‐to‐tendon interface tissue after ACL reconstruction surgery in mice

Macrophages are important for repair of injured tissues, but their role in healing after surgical repair of musculoskeletal tissues is not well understood. We used single‐cell RNA sequencing (RNA‐seq), flow cytometry, and transcriptomics to characterize functional phenotypes of macrophages in a mouse anterior cruciate ligament reconstruction (ACLR) model that involves bone injury followed by a healing phase of bone and fibrovascular interface tissue formation that results in bone‐to‐tendon attachment. We identified a novel “surgery‐induced” highly inflammatory CD9+ IL1+ macrophage population that expresses neutrophil‐related genes, peaks 1 day after surgery, and slowly resolves while transitioning to a more homeostatic phenotype. In contrast, CX3CR1+ CCR2+ macrophages accumulated more slowly and unexpectedly expressed an interferon signature, which can suppress bone formation. Deletion of Ccr2 resulted in an increased amount of bone in the surgical bone tunnel at the tendon interface, suggestive of improved healing. The “surgery‐induced macrophages” identify a new cell type in the early phase of inflammation related to bone injury, which in other tissues is dominated by blood‐derived neutrophils. The complex patterns of macrophage and inflammatory pathway activation after ACLR set the stage for developing therapeutic strategies to target specific cell populations and inflammatory pathways to improve surgical outcomes. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

The Permissive Safe Angle of the Tibial Tunnel in Transtibial Posterior Cruciate Ligament Reconstruction: A Three-Dimensional Simulation Study

Objective

To determine the permissive safe angle (PSA) of the tibial tunnel in transtibial posterior cruciate ligament (PCL) reconstruction based on a three‐dimensional (3D) simulation study.

Methods

This was a computer simulation study of transtibial PCL reconstruction using 3D knee models. CT images of 90 normal knee joints from 2017 to 2020 were collected in this study, and 3D knee models were established based on CT data. The tunnel approaches were subdivided into the anterior 1/3 of the anteromedial tibia (T1), middle 1/2 of the anteromedial tibia (T2), the tibial crest (T3), anterior 1/3 of the anterolateral tibia (T4), middle 1/2 of the anterolateral tibia (T5). Five tibial tunnels (T1–T5) were simulated on the 3D knee models. The PSAs, in different tibial tunnel approaches were measured, and subgroup analyses of sex, age and height were also carried out.

Results

The mean PSAs of the tibial tunnels with 5 different approaches (T1–T5) were 58.49° ± 6.82°, 61.14° ± 6.69°, 56.12° ± 7.53°, 52.01° ± 8.89° and 49.90° ± 10.53°, respectively. The differences of the mean PSAs between the anteromedial and anterolateral approaches were significant (P < 0.05). However, there was no significant difference of the mean PSA value between the two anteromedial tibial tunnel approaches (T1–T2) (P > 0.05), as well as between the two anterolateral tibial tunnel approaches (T4–T5). The patient's anthropomorphic characteristics of sex, age, and height were not associated with the PSAs.

Conclusions

The PSA varied with the anteromedial, tibial crest and anterolateral approaches for transtibial PCL reconstruction, and surgeons should limit the PCL drill guide by referring to the specific PSA for different surgical approaches.

Tackling the Challenges of Graft Healing After Anterior Cruciate Ligament Reconstruction-Thinking From the Endpoint

Anterior cruciate ligament (ACL) tear is common in sports and accidents, and accounts for over 50% of all knee injuries. ACL reconstruction (ACLR) is commonly indicated to restore the knee stability, prevent anterior–posterior translation, and reduce the risk of developing post-traumatic osteoarthritis. However, the outcome of biological graft healing is not satisfactory with graft failure after ACLR. Tendon graft-to-bone tunnel healing and graft mid-substance remodeling are two key challenges of biological graft healing after ACLR. Mounting evidence supports excessive inflammation due to ACL injury and ACLR, and tendon graft-to-bone tunnel motion negatively influences these two key processes. To tackle the problem of biological graft healing, we believe that an inductive approach should be adopted, starting from the endpoint that we expected after ACLR, even though the results may not be achievable at present, followed by developing clinically practical strategies to achieve this ultimate goal. We believe that mineralization of tunnel graft and ligamentization of graft mid-substance to restore the ultrastructure and anatomy of the original ACL are the ultimate targets of ACLR. Hence, strategies that are osteoinductive, angiogenic, or anti-inflammatory should drive graft healing toward the targets. This paper reviews pre-clinical and clinical literature supporting this claim and the role of inflammation in negatively influencing graft healing. The practical considerations when developing a biological therapy to promote ACLR for future clinical translation are also discussed.

The bone microstructure from anterior cruciate ligament footprints is similar after ligament reconstruction and does not affect long-term outcomes

PURPOSE

The purpose of this study was to assess the quality of the bone tissue microstructure from the footprints of the anterior cruciate ligament (ACL) and its impact on late follow-up outcomes in patients who undergo anterior cruciate ligament reconstruction (ACLR).

METHODS

The records of 26 patients diagnosed with a completely torn ACL who underwent ACLR were collected. During the surgery performed using the Felmet method, bone blocks from the native ACL footprints were collected. The primary measurements of the bone microstructure were made using a microtomographic scanner. In late follow-up examinations, a GNRB arthrometer was used.

RESULTS

There was no significant difference in the bone microstructure assessed using micro-CT histomorphometric data according to the blood test results, plain radiographs, age or anthropometric data. There was no difference in the bone volume/total volume ratio or trabecular thickness in the area of the native ACL footprints. Routine preoperative examinations were not relevant to the quality of the bone microstructure. The elapsed time from an ACL injury to surgery had no relevance to the results of arthrometry.

CONCLUSION

The similarities in the microstructure of bone blocks from ACL footprints from the femur and tibia allow the variable use of these blocks to stabilize grafts in the Felmet method. The bone microstructure is not dependent on the time from injury to surgery. Histomorphometric values of the structure of the femoral and tibial ACL footprints have no impact on the long-term stability of the operated knee joint.

TRIAL REGISTRATION

The approval of the Bioethics Committee of the Silesian Medical Chamber in Katowice, Poland (resolution 16/2014) was given for this research.

LEVEL OF EVIDENCE

II.

[The killer turn in the posterior cruciate ligament reconstruction: mechanism and improvement]

OBJECTIVE

To summarize the research progress of killer turn in posterior cruciate ligament (PCL) reconstruction.

METHODS

The literature related to the killer turn in PCL reconstruction in recent years was searched and summarized.

RESULTS

The recent studies show that the killer turn is considered to be the most critical cause of graft relaxation after PCL reconstruction. In clinic, this effect can be reduced by changing the fixation mode of bone tunnel, changing the orientation of bone tunnel, squeezing screw fixation, retaining the remnant, and grinding the bone at the exit of bone tunnel. But there is still a lack of long-term follow-up.

CONCLUSION

There are still a lot of controversies on the improved strategies of the killer turn. More detailed basic researches focusing on biomechanics to further explore the mechanism of the reconstructed graft abrasion are needed.

Biomechanical, histologic, and molecular characteristics of graft-tunnel healing in a murine modified ACL reconstruction model

Purpose

The purpose of our study was to introduce and validate a metal-free, reproducible and reliable mouse model of anterior cruciate ligament (ACL) reconstruction (ACLR) surgery as an effective tool for a better understanding of molecular mechanisms of graft-tunnel healing after ACLR.

Methods

A total of 150 C57BL/6 mice were randomly allocated into five Groups: Group 1 (mice with intact ACL), Group 2–4 (mice underwent modified ACLR surgery and sacrificed 1-, 2-, and 4-weeks after surgery), and Group 5 (mice underwent unmodified ACLR surgery and sacrificed 4 weeks after surgery). Micro-computed tomography (CT), biomechanical histological as well as immunohistochemical (IHC) analyses were performed to characterize the modified ACLR.

Results

Micro-CT analysis demonstrated there is a non-significant increase in BV/TV and BMD of the bone tunnel during the tendon-to-bone healing following ACLR. Biomechanical tests showed that the mean load-to-failure forces of Group 3 and 4 are equal to 31.7% and 46.0% of that in Group 1, while the stiffness was 33.1% and 57.2% of that of Group 1, respectively. And no obvious difference in biomechanical parameters was found between Group 4 and 5. Histological analysis demonstrated that formation of fibrovascular tissue in the tibial tunnel and aperture in Groups 4 and 5 and direct junction appeared between tendon graft and tunnel both in Groups 4 and 5. IHC results showed that there are gradually enhanced expression of Patched1, Smoothened and Gli2 concomitant with decreased Gli3 protein in the tendon-bone interface during the tendon-bone healing process.

Conclusion

We introduced a metal-free, reproducible and reliable mouse model of ACLR compared to the unmodified ACLR procedure, and characterized the expression pattern of key molecules in Ihh signaling during the graft healing process.

The translational potential of this article

In the present study we introduced and validated, for the first time, a metal-free, reproducible and reliable ACLR mouse model, which could be used to investigate the detailed molecular mechanisms of graft-tunnel healing after ACLR. We also explored new strategies to promote the healing of tendon-to-bone integration.

Anterior Cruciate Ligament Reconstruction in a Rabbit Model Using a Decellularized Allogenic Semitendinous Tendon Combined with Autologous Bone Marrow-Derived Mesenchymal Stem Cells

As a regular adoptable material for anterior cruciate ligament (ACL) reconstruction, free tendon allograft exhibits unsatisfactory outcomes, such as retarded ligamentization and tendon–bone integration. The application of bone marrow‐derived mesenchymal stem cells (BMSCs), as well as a decellularized free tendon allograft developed by our group, was proven to be effective in improving ACL reconstruction results. This study aimed to investigate the efficacy and feasibility of decellularized allogenic semitendinous tendon (ST) combined with autologous BMSCs used as a substitute to free tendon allograft in a rabbit model. This study finally shows that the decellularized allogenic ST combined with autologous BMSCs could significantly improve ACL reconstruction results compared with allograft. stem cells translational medicine2019;8:971&982

Evaluation of the theoretical optimal angle of the tibial tunnel in transtibial anatomic posterior cruciate ligament reconstruction by computed tomography

Background

“Killer turn” effect is a critical explanation for the recurrent posterior laxity following transtibial posterior cruciate ligament (PCL) reconstruction, which affected by the angle of the tibial tunnel. Meanwhile, excessive tunnel angle would have an adverse impact on the healing of tendon to bone. The purpose was to evaluate the theoretical optimal angle of the tibial tunnel in transtibial anatomic PCL reconstruction.

Methods

The measurements were performed on CT sagittal plane, including the thickness of cancellous bone (L1), the theoretical optimal angle of the tibial tunnel (TOA, which was measured between tibial plateau and the extension cord connecting the center of PCL insertion site with a point 5 mm superior from marrow cavity vertex), L2 - the distance from anterior tunnel aperture to anterior end of tibial plateau, L3 - the distance from anterior tunnel aperture to tibial tuberosity (lowest edge of patellar ligament attachment).

Results

The value of TOA and L3 were 35.4 ± 7.9 ° and 26.8 ± 11.4 mm, respectively. L1 and L2 were higher in males than females (L1, P = 0.002; L2, P = 0.046). Regarding age, L1, TOA, L2 and L3 were higher in the 46–60 years group than 31–45 years group (P = 0.02, P = 0.001, P = 0.038, P = 0.032, respectively). With regard to height, L1 was lower in group I - < 1.66 m than group II - 1.66 to 1.75 m and group III - > 1.75 m (I v II, P = 0.015, I v III, P = 0.026). L2 was also lower in group I than group II and group III (I v II, P = 0.026, I v III, P = 0.006). TOA and L3 showed no significant differences among sex and height groups (P > 0.05).

Conclusions

TOA (35.4 ° ± 7.9 °) and L3 (26.8 ± 11.4 mm) could be used as a reference for ideal tibial tunnel placement in transtibial anatomic PCL reconstruction, so as to prevent recurrent PCL laxity and ensure good graft healing. However, further clinical validation is needed.

Does the graft-tunnel friction influence knee joint kinematics and biomechanics after anterior cruciate ligament reconstruction? A finite element study

Graft tissues within bone tunnels remain mobile for a long time after anterior cruciate ligament (ACL) reconstruction. However, whether the graft-tunnel friction affects the finite element (FE) simulation of the ACL reconstruction is still unclear. Four friction coefficients (from 0 to 0.3) were simulated in the ACL-reconstructed joint model as well as two loading levels of anterior tibial drawer. The graft-tunnel friction did not affect joint kinematics and the maximal principal strain of the graft. By contrast, both the relative graft-tunnel motion and equivalent strain for the bone tunnels were altered, which corresponded to different processes of graft-tunnel integration and bone remodeling, respectively. It implies that the graft-tunnel friction should be defined properly for studying the graft-tunnel integration or bone remodeling after ACL reconstruction using numerical simulation.

MRI-based tendon bone healing is related to the clinical functional scores at the first year after anterior cruciate ligament reconstruction with hamstring tendon autograft

PURPOSE

The correlation between tendon bone healing and clinical functional scores after anterior cruciate ligament reconstruction (ACLR) using four-stranded hamstring tendon autograft has rarely being reported. The purpose of this study was to determine the correlation between magnetic resonance imaging (MRI)-based tendon bone healing and clinical functional scores after ACLR using hamstring tendon.

METHODS

Thirty-eight patients with ACLR using four-stranded hamstring tendon autograft were included in this prospective study in the authors' hospital from 2013 to 2014. All patients were performed Tegner, Lysholm, International Knee Documentation Committee (IKDC) subjective scores, KT-1000 and MRI examinations in 3, 6, 12 months after the operation, respectively. According to MRI, the healing degree of tendon bone was divided into five grades, and the healing degree of the tendon at different time points was evaluated. Moreover, the correlations between the clinical scores and tendon bone healing level at 12 months after the operation were determined.

RESULTS

The Tegner, Lysholm, and IKDC scores of all patients were gradually improved over time after ACLR, and the degree of tendon bone healing was gradually increased. Moreover, there were significantly positive correlations between the level of tendon bone healing and the clinical functional scores at 12 months after the operation.

CONCLUSION

The clinical functional scores and the degree of tendon bone healing were gradually improved over time after ACLR. Moreover, there were significant positive correlations between the level of tendon bone healing and clinical functional scores of knee joint at the first year after the operation.

LEVEL OF EVIDENCE

III.

Acceleration of tendon-bone healing of anterior cruciate ligament graft using intermittent negative pressure in rabbits

Background

The purpose of this study was to test effects of negative pressure on tendon–bone healing after reconstruction of anterior cruciate ligament (ACL) in rabbits.

Methods

Hind legs of 24 New Zealand White rabbits were randomly selected as negative pressure group and the contralateral hind legs as control. Reconstruction of the ACL was done. Joints of the negative pressure side were placed with drainage tubes connecting the micro-negative pressure aspirator. Control side was placed with ordinary drainage tubes. Drainage tubes on both sides were removed at the same time 5 days after operation. After 6 weeks, joint fluid was drawn to detect the expression levels of interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α); at the same time, femur–ligament–tibia complex was obtained to determine tendon graft tension and to observe the histomorphology, blood vessels of the tendon–bone interface, and expression of vascular endothelial growth factor (VEGF).

Results

The maximum load breakage of tendon graft was significantly greater in the negative pressure group than in the control group (P < 0.05). Histological studies of the tendon–bone interface found that there was more new bone formation containing chondroid cells and aligned connective tissue in the negative pressure group than in the control group. Expression of VEGF was higher in the negative pressure group than in the control group (P < 0.01). Content of IL-1β and TNF-α in synovial fluid is lower in the negative pressure group than in the control group (P < 0.01).

Conclusions

Intermittent negative pressure plays an active role in tendon–bone healing and creeping substitution of ACL reconstruction in the rabbits.

Allograft integration in a rabbit transgenic model for anterior cruciate ligament reconstruction

BACKGROUND

Tissue engineering strategies include both cell-based and cell homing therapies. Ligamentous tissues are highly specialized and constitute vital components of the musculoskeletal system. Their damage causes significant morbidity and loss in function.

HYPOTHESIS

The aim of this study is to analyze tendinous graft integration, cell repopulation and ligamentization by using GFP+/- allografts in GFP+/- transgenic New Zealand white (NZW) rabbits.

MATERIAL AND METHODS

Graft implantation was designed to closely mimic anterior cruciate ligament (ACL) repair surgery. Allografts were implanted in 8 NZW rabbits and assessed at 5 days, 3 weeks and 6 weeks through: (1) arthroCT imaging, (2) morphological analysis of the transplanted allograft, (3) histological analysis, (4) collagen type I immunochemistry, and (5) GFP cell tracking. Collagen remodeling was appreciated at 3 and 6 weeks.

RESULTS

Graft repopulation with host cells, chondrocyte-like cells at the tendon-bone interface and graft corticalization in the bone tunnels were noticed at 3 weeks. By contrast we noticed a central necrosis aspect in the allografts intra-articularly at 6 weeks with a cell migration towards the graft edge near the synovium.

DISCUSSION

Our study has served to gain a better understanding of tendinous allograft bone integration, ligamentization and allograft repopulation. We believe that both cell-based therapies and cell homing therapies are beneficial in ligament tissue engineering. Future studies may elucidate whether cell repopulation occurs with pre-differentiated or progenitor cells. We believe that both cell-based therapies and cell homing therapies are beneficial in ligament tissue engineering.

LEVEL OF EVIDENCE

Level V (animal study).

Efficacy evaluation for the treatment of subcapital femoral neck fracture in young adults by capsulotomy reduction and closed reduction

BACKGROUND

Subcapital femoral neck fracture in young adults has many complications, and the incidence is increasing year-by-year. The selection of the proper operation method to avoid them is an ambiguous matter. This study aimed to evaluate the treatment effect of subcapital femoral neck fracture by the capsulotomy and internal fixation with iliac bone grafting or closed reduction and internal fixation in young adults.

METHODS

From March 2003 to February 2010, 65 young patients with subcapital femoral neck fractures were treated, including 39 males and 26 females with average age of 34.5 years (range, 19-50 years); 29 cases of the left side and 36 cases of the right side. They were randomly divided into Group A with 34 cases treated by closed reduction and internal fixation and Group B with 31 cases treated by the capsulotomy and internal fixation with iliac bone grafting. The two groups had no significant differences in sex, age, body mass index and preoperative Harris Hip Score. The observation criteria involved the length of the incision, blood loss, operation time, nonunion rate, avascular necrosis of the femoral head (ANFH) rate and Harris Hip Score.

RESULTS

Four of 65 patients were lost follow-up, and the follow-up rate was 93.8%, the average follow-up time was 38.7 months (range, 33-47 months). In Group A, the incision length was 5.1 ± 2.2 cm, blood loss was 84.0 ± 13.2 ml, and operation time was 52.9 ± 10.2 min. In Group B, the incision length was 15.4 ± 4.6 cm, blood loss was 396.0 ± 21.3 ml, and operation time was 116.5 ± 15.3 min. Nonunion occurred in 8 patients (25.2%) in Group A and 1 patient (3.3%) in Group B. ANFH occurred in 9 patients (29.1%) in Group A and 2 patients (6.7%) in Group B. Postoperative Harris Hip Score was 89.0 ± 5.6 in Group A and 95.0 ± 4.5 in Group B. The above index of two groups was considered statistically significant (P < 0.05).

CONCLUSIONS

Capsulotomy and internal fixation with iliac bone grafting can improve fracture healing, reduce ANFH in young adults. It is a safe and effective operation for subcapital femoral neck fracture.

Grafted tendon healing in femoral and tibial tunnels after anterior cruciate ligament reconstruction

PURPOSE

To evaluate tendon-to-bone healing after anterior cruciate ligament (ACL) reconstruction in the fibrous interzone (FIZ) of the femoral and tibial tunnels using magnetic resonance imaging (MRI).

METHODS

Five men and 5 women (mean age, 29 years) underwent arthroscopic ACL reconstruction by a single surgeon, using the semitendinosus and gracilis tendon. The tendon-to-bone healing in the FIZ was evaluated using sagittal and coronal MRI at 1, 3, 6, 9, 12, and 24 weeks, with the knee flexed at 60º and the tendon graft straight in both images. The signal intensity of the FIZ was visually assessed by comparing it with anatomic landmarks in the same patient's knee, and classified into 4 grades. It was grade 3 when similar to that of the patellar tendon, grade 2 when similar to that of skeletal muscle, grade 1 when greater than that of muscle but less than that of joint fluid, and grade 0 when similar to that of joint fluid. At 24 weeks, subjective and objective functional outcomes were evaluated using the Lysholm score and the International Knee Documentation Committee score.

RESULTS

At 24 weeks, no patient had knee laxity. All patients had an International Knee Documentation Committee score of A, and their mean Lysholm score was 98.5. In the femoral tunnel, the FIZ did not change during the first 9 weeks (in particular the anterior part), but healing occurred rapidly thereafter. In the tibial tunnel, the FIZ healed over time in all locations, and healing was complete in the lateral and posterior parts at 12 weeks, and in all locations at 24 weeks. The mean signal intensity grade was significantly higher in the tibial than femoral FIZ at 3 to 12 weeks (p<0.01).

CONCLUSION

After ACL reconstruction, the tendon-to- bone healing in the FIZ of the tibial tunnel was faster than that of the femoral tunnel.

Effect of muscle preserved on tendon graft on intra-articular healing in anterior cruciate ligament reconstruction

PURPOSE

The aim of this study was to determine the impact on intra-articular healing of muscle tissue retained on tendon grafts used for anterior cruciate ligament (ACL) reconstruction.

METHODS

In an animal study on 40 New Zealand rabbits, a semi-tendon/semi-muscle graft (SSG) and a total tendon graft (TTG) were individually harvested from the Achilles tendons in each animal. After transecting the ACLs in both knees of each rabbit, SSG and TTG were randomly used on bilateral sides of the knee for ACL reconstruction. After 2, 4, and 8 weeks, functional scoring, gross observations, and histological evaluations of the repaired knees were performed (each time point; n = 10). Biomechanical testing was conducted on remaining animals at 8 weeks (n = 10).

RESULTS

At 2, 4, and 8 weeks after surgery, there were no statistically significant differences in functional scores between the SSG group and TTG group (n.s.). As healing progressed, skeletal muscle on the SSG was gradually absorbed with a corresponding decrease in graft diameter, compared to TTG, at each time point (P < 0.001). However, healing and incorporation of the intra-articular graft in the SSG were more apparent than those in the TTG, based on histology. The vascularity and cellularity in the center of the sample were significantly greater in the SSG group than the TTG group at all the time points (P < 0.01). At 8 weeks, the SSG group's ultimate failure load, yield load, and elongation at failure were significantly less than for the TTG group (P < 0.01). There were no significant differences in stiffness between the two groups with biomechanical testing (n.s.).

CONCLUSION

Results of this study indicate that muscle left on tendon grafts promotes intra-articular healing and remodeling of the graft in a rabbit model. However, excessive amounts of retained skeletal muscle weaken tendon graft's strength for ACL reconstruction. Preserving small amounts of muscle on tendon grafts is feasible for improving the biological success of ACL reconstruction in humans.

Evaluation of the potential application of three different biomaterials combined with bone morphological proteins for enhancing tendon-bone integration

INTRODUCTION

Secure tendon-bone integration is crucial for successful anterior cruciate ligament (ACL) reconstruction. Previous studies have applied different types of biomaterial or biomaterial combined with bone-growth factors to enhance tendon-bone integration. However, which approach is better remains controversial. This comparison evaluation could help identify a suitable composite biomaterial for osteointegration of grafted tendon.

MATERIALS AND METHODS

Three different composite biomaterials mixed with bone morphological proteins (BMPs) were fabricated. The in vitro study investigates cell metabolism, osteogenic gene expression and the growth behaviour of bone marrow stromal cells (BMSCs) on fibrin glue-BMPs (FGB), calcium phosphate cement-BMPs (CPCB) and recombined bone xenograft (RBX), which are commercially, clinically available biomaterials. Meanwhile, the changes in the physical, morphological and mechanical properties between the three composites and the original biomaterials were also observed. The in vivo study mainly examined the osteogenic ability of the three composites through rat ectopic testing.

RESULTS

The porosity structure of three biomaterials was improved after being combined with BMPs powder for SEM observation, and the setting times of the injectable composites were not significantly delayed. More importantly, there were no significant decreases in compressive strength between the three composite biomaterials and the original biomaterials. The highest proliferation rate of BMSCs was found in the RBX group, followed by the CPCB and FGB groups. BMSCs seeded onto an RBX showed the highest alkaline phosphatase (ALPase) activity and gene expression of collagen I (P < 0.05). Histological examination showed endochondral new bone formation in the specimens of all groups, but the ALPase activity of newly formed tissue in the RBX group showed the highest level (P < 0.01).

CONCLUSION

Our results indicate that RBX seems to be a very good choice for accelerating tendon-bone integration, and CPCB also has a large potential ability to be used. However, these two composites still need to be modified, and we postulate that a combination of them would be more favourable for tendon osteointegration after ACL reconstruction than either composite used alone.

Evaluation with contrast-enhanced magnetic resonance imaging of the anterior cruciate ligament graft during its healing process: a two-year prospective study

OBJECTIVE

The aim of this study was to evaluate, with contrast-enhanced-magnetic resonance imaging (MRI), the changing imaging appearance of an anterior cruciate ligament (ACL) graft during the revascularization phase by quantitatively assessing the morphological and signal intensity changes taking place at its cross-sectional surface over time.

MATERIALS AND METHODS

Fifty patients underwent contrast-enhanced-MRI on the third postoperative day and at a mean of 6, 12, and 24 months time interval after surgery. Proton-density images were obtained to evaluate morphological and signal intensity characteristics. Oblique-axial T1-weighted images obtained before and after intravenous gadolinium administration were used for quantitative analysis. Enhancement index (EI: signal-to-noise quotient(after gadolinium)÷signal-to-noise quotient(before gadolinium)) and cross-sectional area (CSA) were calculated for two regions of interest: the transplanted graft and its surrounding hypervascular tissue, and at three distinct graft sites (intra-articular, intraosseous tibial tunnel, and intraosseous juxta screw sites). Comparisons of EI and CSA at every site and time interval were performed using analysis of variance.

RESULTS

A variable MRI appearance of the graft during the different time intervals was attributed to the varying amount of the hypervascular tissue gradually surrounding the graft. Graft EI and peripheral tissue CSA progress in a parallel, time- and site-related pattern along the graft course. The initial heterogeneity with intermediate signal intensity at the intra-articular graft site reflected intense revascularization. A slower revascularization progress was noticed at the other two intraosseously enclosed sites.

CONCLUSION

During the healing process the amount of revascularization tissue influences the MR imaging characteristics of the graft according to the examined site and the time interval after surgery. By 2 years postoperatively, revascularization completion coincides with the homogeneously low signal intensity of the graft, closely resembling native ACL.

Inhibitory effect of synovial fluid on tendon-to-bone healing: an experimental study in rabbits

PURPOSE

The purpose of this study was to explore the effects of joint synovial fluid on tendon-to-bone healing in intra-articular ligament reconstruction of the knee.

METHODS

We divided 40 female New Zealand white rabbits into 4 groups randomly, with 10 animals in each group. Transfer of the semitendinosus tendon to the tibial bone tunnel was performed to create tendon-to-bone healing models. An intra-articular bone tunnel (IBT) was used on the left side and an extra-articular bone tunnel (EBT) on the right. Histologic evaluation was performed at 2, 4, and 8 weeks after the operation and biomechanical testing at 8 weeks.

RESULTS

On the basis of fibroblast proliferation, collagen fiber density, collagen fiber orientation, and tendon-to-bone connection, histologic scores were significantly lower in the IBT group than in the EBT group at 2, 4, and 8 weeks. Cell counts per high-power field at the tendon-bone interface were significantly lower in the IBT group than in the EBT group at 2 and 4 weeks. In addition, biomechanical testing showed that the IBT group was significantly inferior to the EBT group in terms of ultimate failure load, yield load, and stiffness. There was also a significant difference between the 2 groups in failure mode.

CONCLUSIONS

Joint synovial fluid appeared to have an inhibitory effect on tendon-to-bone healing in rabbits at an early stage.

CLINICAL RELEVANCE

Our findings imply that prevention of infiltration of joint synovial fluid into the bone tunnel might be beneficial in improving the clinical outcome of cruciate ligament reconstruction of the knee.

Prevalence and influence of tibial tunnel widening after isolated anterior cruciate ligament reconstruction using patella-bone-tendon-bone-graft: long-term follow-up

The aim of the present study was to evaluate incidence, degree and impact of tibial tunnel widening (TW) on patient-reported long-term clinical outcome, knee joint stability and prevalence of osteoarthritis (OA) after isolated anterior cruciate ligament (ACL) reconstruction. On average, 13.5 years after ACL reconstruction via patella-bone-tendon-bone autograft, 73 patients have been re-evaluated. Inclusion criteria consisted of an isolated anterior cruciate ligament rupture and reconstruction, a minimum of 10-year follow-up and no previous anterior cruciate ligament repair or associated intra-articular lesions. Clinical evaluation was performed via the International Knee Documentation Committee (IKDC) score and the Tegner and Lysholm scores. Instrumental anterior laxity testing was carried out with the KT-1000™ arthrometer. The degree of degenerative changes and the prevalence of osteoarthritis were assessed with the Kellgren-Lawrence score. Tibial tunnel enlargement was radiographically evaluated on both antero-posterior and lateral views under establishment of 4 degrees of tibial tunnel widening by measuring the actual tunnel diameters in mm on the sclerotic margins of the inserted tunnels on 3 different points (T1-T3). Afterwards, a conversion of the absolute values in mm into a 4 staged ratio, based on the comparison to the results of the initial drill-width, should provide a better quantification and statistical analysis. Evaluation was performed postoperatively as well as on 2 year follow-up and 13 years after ACL reconstruction. Minimum follow-up was 10 years. 75% of patients were graded A or B according to IKDC score. The mean Lysholm score was 90.2±4.8 (25-100). Radiological assessment on long-term follow-up showed in 45% a grade I, in 24% a grade II, in 17% a grade III and in additional 12% a grade IV enlargement of the tibial tunnel. No evident progression of TW was found in comparison to the 2 year results. Radiological evaluation revealed degenerative changes in sense of a grade II OA in 54% of patients. Prevalence of a grade III or grade IV OA was found in 20%. Correlation analysis showed no significant relationship between the amount of tibial tunnel enlargement (P>0.05), long-term clinical results, anterior joint laxity or prevalence of osteoarthritis. Tunnel widening remains a radiological phenomenon which is most commonly observed within the short to midterm intervals after anterior cruciate ligament reconstruction and subsequently stabilises on mid and long- term follow-up. It does not adversely affect long-term clinical outcome and stability. Furthermore, tunnel widening doesn't constitute an increasing prevalence of osteoarthritis.

Crimp frequency is strongly correlated to myofibroblast density in the human anterior cruciate ligament and its autologous tendon grafts

PURPOSE

Collagen crimp is essential for maintaining viscoelastic properties of normal ligament and tendon tissue. The actin isoform α-smooth muscle actin (ASMA) has been identified in fibroblastic cells of these tissues. These highly differentiated cells, so-called myofibroblasts may transmit tensile forces to the extracellular matrix, thus it has been suggested that they are responsible for the wrinkling of the extracellular matrix and the formation of crimp. During anterior cruciate ligament (ACL) graft remodeling, crimp formation plays an integral role. Thus, it was our purpose to determine the relationship between myofibroblast density and crimp frequency in human tendon graft tissue and the ACL.

METHODS

Different tendon grafts and ACLs were harvested from young human multi-organ donors immediately after death. Myofibroblasts were immunostained with a monoclonal antibody, and histomorphometry was performed using a digital imaging system. Crimp length was measured, and data were correlated.

RESULTS

All tendons and ACLs showed a significant correlation of myofibroblast density and crimp frequency (R(2) 0.81-0.43). The strongest correlation was found for the patellar tendon, the poorest for the gracilis tendon. There is also evidence that the phenotype respectively the shape of myofibroblasts might be responsible for different stages of crimp formation.

CONCLUSION

With the present investigation, we found that myofibroblasts might be involved in crimp formation and should be viewed as an integral part of normal tendon and ligament tissue. Furthermore, the shape of myofibroblasts may further indicate the contractile potency of the extracellular matrix, thus presenting a dynamic and variable crimp rather than a static situation. This study is an experimental study. In terms of clinical relevance all the mentioned tendons can be used as auto- or allografts for ACL reconstruction, nevertheless their microscopic structure and cellular population have yet not been adequately investigated and compared.

Research in orthopaedics from China has thrived over the last decade: a bibliometric analysis of publication activity

INTRODUCTION

Over the past decades, there have been great advances in orthopaedics in China. The purpose of this study was to investigate the orthopaedic research output in the three Chinese-speaking regions - the Mainland (ML), Hong Kong (HK), and Taiwan (TW).

HYPOTHESIS

We hypothesized that there was a positive trend in China orthopaedic research during the past decade and this regardless of the Chinese-speaking regions of origin.

MATERIALS AND METHODS

Forty-nine orthopaedic journals were retrieved from the PubMed database and Science Citation Index Expanded. Articles from ML, TW, and HK in 2000 to 2009 were identified. The total number of articles, clinical trials, randomized controlled trials (RCTs), impact factors (IF), citations, and articles published in the top 10 orthopaedic journals were analyzed.

RESULTS

A total of 1878 published articles in 2000 to 2009 were broken down as follows: ML (607), TW (865), and HK (406). There was a significant increase in published articles for ML and TW from 2000 to 2009. The number of published articles from ML exceeded the total sum of articles from TW and HK in 2009. The accumulated IF of articles from TW (1751.91) was higher than that from ML (1054.67) and HK (708.25). TW had the highest average IF (2.025), followed by ML (1.902) and HK (1.862). The total citations of published articles in 2000 to 2009 from TW (4759) were higher than those for HK (2276) and ML (1751). The highest average citation of each article was from HK (5.784), followed by TW (5.720) and ML (3.051). TW published 339 articles in 10 high-impact journals, whereas ML and HK published 267 and 154 articles, respectively.

DISCUSSION

Chinese researchers in the field of orthopaedics have been more and more active in the global orthopaedic community during the past 10 years. ML seems to have caught up to HK and TW in respect to research output.

A watertight construct in arthroscopic rotator cuff repair

BACKGROUND

It is unknown which type of rotator cuff repair technique best isolates the healing zone interface from the synovial fluid environment. The purpose of this study was to determine the leakage area and pattern onto the rotator cuff footprint after 3 different rotator cuff repairs.

MATERIALS AND METHODS

Six fresh frozen cadaveric glenohumeral joints in each of 3 groups were injected with gelatin to a pressure of 103 mm Hg (∼2 psi) after 1 of 3 different rotator cuff repairs of a supraspinatus tear: (1) single-row repair (SR), (2) knotless transosseous equivalent repair (KTE), and (3) traditional transosseous equivalent repair (TTE), which uses medial tied knots. Specimens were cycled in external rotation and abduction and were cooled to allow the gelatin to solidify. The supraspinatus was dissected off the footprint and photographs were taken. Scion Image (Frederick, MD, USA) was used to quantify the area.

RESULTS

The average area of leakage was 1.09 cm(2) for the SR and 1.15 cm(2) for the KTE. The TTE did not demonstrate any leakage. The pattern of leakage for the KTE was medial and central on the footprint, whereas the SR demonstrated leakage up to the tied knots. The difference in the area of leakage in the SR and KTE compared with the TTE was statistically significant. There was no difference in area of leakage between the SR and KTE.

CONCLUSION

A transosseous equivalent repair technique best prevents leakage onto the rotator cuff footprint compared with single-row and knotless repairs.

Effect of varying the length of soft-tissue grafts in the tibial tunnel in a canine anterior cruciate ligament reconstruction model

PURPOSE

To investigate the effect of graft length within the bone tunnel on tendon-bone healing at an early stage after anterior cruciate ligament (ACL) reconstruction using Achilles tendon autograft in a canine model.

METHODS

We divided 40 adult dogs into 4 groups (n = 10 per group). Each dog underwent ACL reconstruction with Achilles tendon autograft in both knees. In groups I, II, III, and IV, the graft length within the tibia tunnel was 5 mm, 10 mm, 15 mm, and 20 mm, respectively. Five dogs in each group were killed 6 and 12 weeks postoperatively, with 3 knees used for histologic observation and 7 knees for mechanical testing.

RESULTS

Six weeks after surgery, the histologic scores in group I were lower than those in the other groups (P < .01) and those in group II were lower than those in group III and group IV (P < .01). However, there was no difference between group III and group IV (P > .05). At 12 weeks, there were no significant differences in histologic scores between groups (P > .05). The biomechanical test at 6 weeks showed that the mean graft pullout strength improved from group I to group IV. Except between groups III and IV (P = .142), there was a significant difference in the pullout strength among other groups. At week 12, the failure points were in the midsubstance of most specimens and more tibial-side graft pullout was found in group I than in the other groups (P < .001).

CONCLUSIONS

The histologic maturity and biomechanical strength of the tendon-bone junction after ACL reconstruction in dogs will be delayed at an early stage if the graft length in the bone tunnel is less than 15 mm.

CLINICAL RELEVANCE

There is a minimal acceptable amount of intratunnel tendon graft to allow satisfactory early tendon-bone healing, and attempts to save tendon graft length that lower the amount of intratunnel graft below a minimum of 15 mm should be avoided.

Anterior cruciate ligament reconstruction using quadriceps tendon autograft for adolescents with open physes- a technical note

Background

One major concern in the treatment of ACL lesions in children and adolescents with open physes is the risk of iatrogenic damage to the physes and a possibly resulting growth disturbance.

Purpose

The primary purpose of this article is to describe our technique of a transphyseal ACL reconstruction using quadriceps tendon-bone autograft in children and adolescents with open growth plates. The secondary aim is to report our early results in terms of postoperative growth disturbances which are considered to be a major concern in this challenging group of patients. It was our hypothesis that with our proposed technique no significant growth disturbances would occur.

Methods

From January 1997 to December 2007 49 consecutive children and adolescents with open growth plates were treated for a torn ACL using the aforementioned surgical technique. The patients (28 males and 21 females) with a median age at surgery of 13 (range 8-15) years were retrospectively evaluated. Outcome measures were follow-up radiographs (weight-bearing long leg radiographs of the injured and uninjured knee, anteroposterior and lateral views, a tangential view of the patella and a tunnel view of the injured knee) and follow-up notes (6 weeks, 3, 6, 12 months and until closing of physes) for occurrence of any tibial and/or femoral growth changes.

Results: All of the 49 patients had a sufficient clinical and radiological follow-up (minimum 5 years, rate 100%). 48 cases did not show any clinical and radiological growth disturbance. One case of growth disturbance in a 10.5 years old girl was observed. She developed a progressive valgus-flexion deformity which was attributed to a malplacement of the autograft bone block within the femoral posterolateral epiphyseal plate leading to an early localized growth stop. None of the patients were reoperated due to ACL graft failure. Five of the patients underwent revision ACL surgery due to another adequate sports trauma after the growth-stop. The tibial fixation screw had to be removed under local anaesthesia in 10 patients.

Conclusions

The described ACL reconstruction technique represents a promising alternative to previously described procedures in the treatment of children and adolescents with open growth plates. Using quadriceps tendon future graft availability is not compromised, as the most frequently used autograft-source, ipsilateral hamstring tendons, remains untouched.

Biology and augmentation of tendon-bone insertion repair

Surgical reattachment of tendon and bone such as in rotator cuff repair, patellar-patella tendon repair and anterior cruciate ligament (ACL) reconstruction often fails due to the failure of regeneration of the specialized tissue ("enthesis") which connects tendon to bone. Tendon-to-bone healing taking place between inhomogenous tissues is a slow process compared to healing within homogenous tissue, such as tendon to tendon or bone to bone healing. Therefore special attention must be paid to augment tendon to bone insertion (TBI) healing. Apart from surgical fixation, biological and biophysical interventions have been studied aiming at regeneration of TBI healing complex, especially the regeneration of interpositioned fibrocartilage and new bone at the healing junction. This paper described the biology and the factors influencing TBI healing using patella-patellar tendon (PPT) healing and tendon graft to bone tunnel healing in ACL reconstruction as examples. Recent development in the improvement of TBI healing and directions for future studies were also reviewed and discussed.