Versican contributes to ligament formation of knee joints.

Versican is a large proteoglycan in the extracellular matrix. During embryonic stages, it plays a crucial role in the development of cartilage, heart, and dermis. Previously, we reported that Prx1-Vcan conditional knockout mice, lacking Vcan expression in mesenchymal condensation areas of the limb bud, show the impaired joint formation and delayed cartilage development. Here, we investigated their phenotype in adults and found that they develop swelling of the knee joint. Histologically, their newborn joint exhibited impaired formation of both anterior and posterior cruciate ligaments. Immunostaining revealed a decrease in scleraxis-positive cells in both articular cartilage and ligament of Prx1-Vcan knee joint, spotty patterns of type I collagen, and the presence of type II collagen concomitant with the absence of versican expression. These results suggest that versican expression during the perinatal period is required for cruciate ligaments' formation and that its depletion affects joint function in later ages.

Age-related changes in ACL morphology during skeletal growth and maturation are different between females and males.

Despite a well-established role of anterior cruciate ligament (ACL) anatomy on its biomechanics, little is known on how ACL anatomy develops and changes during skeletal growth. We hypothesized that ACL size and orientation will change by age during skeletal growth and maturation with different trends in males vs females. Magnetic resonance images of 269 unique knees (3-18 years old; 51% female) were used to measure ACL length, cross-sectional area, length-to-cross-sectional area ratio, and elevation angles. In both males and females, ACLs became longer, thicker, and more vertical in sagittal and coronal planes by increasing age (R2 > 0.2; P < .001 for all associations). ACL cross-sectional area-to-length ratio increased by age only in males (R2 = 0.06; P = .003). Despite similar ACL sizes between males and females at early age, adolescent males had significantly longer and thicker ACLs compared to the age-matched females (P < .05). There were no sex differences in ACL elevation angles (P > .2) except for larger coronal elevation in 7 to 10 years old females compared to age-matched males (P = .012). Observed changes in ACL cross-sectional area-to-length ratio indicate that age- and sex-dependent changes in ACL size are not homogenous. The trends seen in normalized ACL size measurements suggest that unlike ACL cross-sectional area, ACL length is primarily controlled by body size. Smaller ACLs and lower cross-sectional growth rates observed in females may be contributing factors to the higher risk of ACL injuries in females. Further investigations are required to identify the intrinsic and extrinsic factors responsible for these discrepancies.

Inhibition of microRNA-27b-3p relieves osteoarthritis pain via regulation of KDM4B-dependent DLX5.

Osteoarthritis (OA) represents a progressive degenerative disorder that predominantly affects the synovial membranes of joints. Recent studies have highlighted the significant role played by microRNAs (miRNAs) in OA development. The current study aimed to elucidate the underlying modulatory role of miR-27b-3p in the development of OA. The expression of miR-27b-3p in the OA patients and rat models post anterior cruciate ligament transection operation was measured using reverse transcription quantitative polymerase chain reaction, through which overexpressed miR-27b-3p was found in both of the samples. To further explore the miR-27b-3p functions in OA, western blot analysis, enzyme-linked immunosorbent assay, and ß-galactosidase activity assay were conducted with the results showing that knockdown of miR-27b-3p promoted expression of the osteogenic differentiation markers while inhibiting expression of the adipogenic differentiation markers, inflammatory factors, and cellular senescence of bone marrow mesenchymal stem cells (BMSCs). After that, the interactions between miR-27b-3p, lysine Demethylase 4B (KDM4B), and Distal-Less Homeobox 5 (DLX5) identified using dual-luciferase reporter gene assay and ChIP assay revealed that miR-27b-3p inhibited KDM4B and further reduced expression of DLX5. Finally, the paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) were assessed in rat models, and increased PWT and PWL were detected after miR-27b-3p silencing. In conclusion, suppression of miR-27b-3p could enhance KDM4B and DLX5 to alleviate OA pain, shedding light on a new potential therapeutic target for OA.

Developmental changes in ACLs and semitendinosus tendons dimensions according to age in children.

PURPOSE: Managing anterior cruciate ligament (ACL) injuries in skeletally immature patients remains difficult. The main aim of this study was to retrospectively compile normative data on the cross-sectional area (CSA) of the semitendinosus tendon (ST) and the diameter of the ACL in children and young adults. METHODS: Knee magnetic resonance imaging (MRI) examinations were performed for a 2-year period in 132 patients (83 female and 49 male patients). The mean age was 14.9 years (8-18 years). Measurements of the ST CSA were performed on axial views in greyscale by two independent researchers. The ACL diameter was measured as well. RESULTS: The results show the CSA of the ST was related to age, and its growth was not linear. The highest growth rate of the CSA of the ST occurred at age 12-13 at the level of the femoral growth plate and at the level of the tibial plateau. The growth of the ACL diameter was linear until 18 years of age. CONCLUSIONS: ST growth (measured in CSA increments) is almost complete at the age of 13, even though the growth is not linear. ACL growth measured in diameter increments proceeds linearly from 8 to 18 years of age. MRI is a clinically useful tool for assessing hamstring tendon grafts preoperatively. LEVEL OF EVIDENCE: Level III, diagnostic studies.

ACL Growth With Age in Pediatric Patients: An MRI Study.

BACKGROUND: There is limited knowledge of morphologic changes of the anterior cruciate ligament (ACL) during childhood. The purpose of the study is to describe normal ACL growth in pediatric patients. METHODS: We performed retrospective review of patients under 19 years of age with at least 2 serial magnetic resonance imaging (MRI) examinations of the same knee without ACL tear. The parameters measured included length of the ACL, width of the ACL in sagittal and coronal planes, physeal status, ACL-tibial inclination angle, Notch Width Index, ACL tibial attachment width and midpoint, and anterior to posterior length and height of the tibial epiphysis. Pearson correlation coefficients were calculated to determine the strength of correlation of each parameter relative to age. Growth curves were calculated for individual parameters, producing a predictive model for growth of the ACL over time. RESULTS: One hundred forty-seven patients (365 MRIs) were included. The average age at initial MRI was 12.2 years (range: 1.2 to 18.4 y). The Pearson correlation coefficient for each parameter was statistically significant relative to age. Younger patients had more oblique, anteriorly attached ACLs. Three distinct phases of growth were observed: patients age 1.5 to 5.75 years average 2.25 mm of growth per year; patients aged 6 to 11.5 average 1.46 mm of growth per year; growth slows at age 11.75, stopping by 18.5 years. The growth model for ACL sagittal width increased 0.45 mm/y from age 1.5 to 14.5 after which it plateaus, whereas coronal width increased 0.22 mm/y from age 1.5 to 18.75. CONCLUSIONS: In the pediatric patient, the ACL grows in length and width in a predictable manner until age 18. This model aids clinicians in predicting normal ACL parameters for anatomic reconstruction procedures in the skeletally immature patient. LEVEL OF EVIDENCE: Level IV.

Positive effects of platelet-rich plasma (PRP) and a Sanguisorba officinalis polysaccharide on the proliferation and differentiation of anterior cruciate ligament (ACL) fibroblasts in vitro.

Context: Sanguisorba officinalis L. (Rosaceae), a famous traditional Chinese medicine. It was recently reported that its polysaccharide could facilitate collagen production.Objectives: We investigated the mechanism by which S. officinalis polysaccharide (SOWPa) and/or platelet-rich plasma (PRP) promote regenerative potential of anterior cruciate ligament (ACL) in vitro.Materials and methods: ACL fibroblasts were treated with SOWPa (25 and 100 mg/kg), PRP, PRP + SOWPa (25 and 100 mg/kg) or vehicle alone for 24, 48, or 72 h. Cell viability, migration ability and apoptosis were evaluated by MTT, transwell and flow cytometry, respectively. Western blot analysis was performed to assess associated protein expression.Results: PRP, SOWPa (100 mg/kg) or PRP + SOWPa (100 mg/kg) treatment for 72 h significantly improved the cell viability of ACL fibroblasts from 100 ± 7.5% (control) to 156.85 ± 12.82%, 188.08 ± 15.92%, and 223.67 ± 18.82%, respectively, which was evidenced by individual decreased apoptosis rate from 31.26 ± 2.35% (control) to 20.80 ± 1.89%, 18.01 ± 1.55% and 9.33 ± 0.78%. Furthermore, the motility of ACL fibroblasts was significantly improved with increased migrated cell number per field from 5 for control to 26 for PRP, 36 for SOWPa and 44 for PRP + SOWPa, respectively. Moreover, the protein expression of differentiation markers (RUNX2, ALP, BMP2 and Col I) and TLR-4 and phosphorylated p65 (p-p65) was inhibited by the above treatment.Discussion and conclusions: Data suggested that the addition of SOWPa to PRP increased the regenerative ability of ACL fibroblasts by blocking the TLR-4/NF-κB pathway.

Tissue-specific changes in size and shape of the ligaments and tendons of the porcine knee during post-natal growth.

Prior studies have analyzed growth of musculoskeletal tissues between species or across body segments; however, little research has assessed the differences in similar tissues within a single joint. Here we studied changes in the length and cross-sectional area of four ligaments and tendons, (anterior cruciate ligament, patellar tendon, medial collateral ligament, lateral collateral ligament) in the tibiofemoral joint of female Yorkshire pigs through high-field magnetic resonance imaging throughout growth. Tissue lengths increased by 4- to 5-fold from birth to late adolescence across the tissues while tissue cross-sectional area increased by 10-20-fold. The anterior cruciate ligament and lateral collateral ligament showed allometric growth favoring change in length over change in cross-sectional area while the patellar tendon and medial collateral ligament grow in an isometric manner. Additionally, changes in the length and cross-sectional area of the anterior cruciate ligament did not increase as much as in the other ligaments and tendon of interest. Overall, these findings suggest that musculoskeletal soft tissue morphometry can vary within tissues of similar structure and within a single joint during post-natal growth.

Electrospinning of highly porous yet mechanically functional microfibrillar scaffolds at the human scale for ligament and tendon tissue engineering.

Electrospun fibers offer tremendous potential for tendon and ligament tissue engineering, yet developing porous scaffolds mimicking the size, stiffness and strength of human tissues remains a challenge. Previous studies have rolled, braided, or stacked electrospun sheets to produce three-dimensional (3D) scaffolds with tailored sizes and mechanical properties. A common limitation with such approaches is the development of low porosity scaffolds that impede cellular infiltration into the body of the implant, thereby limiting their regenerative potential. Here, we demonstrate how varying the rotational speed of the collecting mandrel during the electrospinning of poly(ε-caprolactone) (PCL) can be used to limit inter-fiber fusion (or fiber welding). Increasing the fraction of unfused fibers reduced the flexural rigidity of the electrospun sheets, which in turn allowed us to bundle the fibers into 3D scaffolds with similar dimensions to the human anterior cruciate ligament (ACL). These unfused fibers allowed for higher levels of porosity (up to 95%) that facilitated the rapid migration of mesenchymal stem cells (MSCs) into the body of the scaffolds. Mechanical testing demonstrated that the fiber-bundles possessed a Young's modulus approaching that of the native human ACL. The scaffolds were also capable of supporting the differentiation of MSCs towards either the fibrocartilage or ligament/tendon lineage. This novel electrospinning strategy could be used to produce mechanically functional, yet porous, scaffolds for a wide range of biomedical applications.

The development of the anterior cruciate ligament in the paediatric population.

PURPOSE: The aim of this study was to retrospectively compile normative data on the anterior cruciate ligament (ACL) in the paediatric population with magnetic resonance imaging, emphasizing the differences between men and women. METHODS: In this retrospective study, musculoskeletal radiologists evaluated length, area, coronal and sagittal inclination of the ACL and inclination of the intercondylar notch. A total of 253 MR examinations (130 males and 123 females between 6 and 18 years of age) were included. The association between measurements, sex and age was considered. Linear and fractional polynomial regression models were used to evaluate the relationships between measurements. RESULTS: ACL length showed significant progressive growth (p < 0.001) with age in men and women, without characterization of growth peaks. ACL area in women showed more pronounced growth up to 11 years, stabilized from 11 to 14 years and then sustained a slight reduction. In men, ACL area showed more pronounced growth up to 12 years, stabilized from 12 to 15 years and then sustained slight reduction. Coronal and sagittal inclination of the ACL showed a significant progressive increase (p < 0.001) with age in both sexes, progressively verticalizing. The intercondylar roof inclination angle showed significant progressive reduction (p < 0.001) with age in both sexes. CONCLUSION: The area of the ACL does not accompany skeletal maturation, interrupting its growth around 11-12 years. Progressive verticalization of the ACL as well as of the intercondylar notch roof in the evaluated ages was also observed. The clinical relevance of this study is that the ACL presents different angular and morphologic changes during growth in the paediatric population. Since ACL repair is now being performed on younger children, recognition of the normal developmental changes of the ACL is of utmost importance for successful ACL graft placement. LEVEL OF EVIDENCE: III.

Orientation changes in the cruciate ligaments of the knee during skeletal growth: A porcine model.

Musculoskeletal injuries in pediatric patients are on the rise, including significant increases in anterior cruciate ligament (ACL) injuries. Previous studies have found major anatomical changes during skeletal growth in the soft tissues of the knee. Specifically, the ACL and the posterior cruciate ligament (PCL) change in their relative orientation to the tibial plateau throughout growth. In order to develop age-specific treatments for ACL injuries, the purpose of this study was to characterize orientation changes in the cruciate ligaments of the Yorkshire pig, a common pre-clinical model, during skeletal growth in order to verify the applicability of this model for pediatric musculoskeletal studies. Hind limbs were isolated from female Yorkshire pigs ranging in age from newborn to late adolescence and were then imaged using high field strength magnetic resonance imaging. Orientation changes were quantified from the magnetic resonance images using image segmentation software. Statistically significant increases were found in the coronal and sagittal angles of the ACL relative to the tibial plateau during pre-adolescent growth. Additional changes were observed in the PCL angle, Blumensaat angle, intercondylar roof angle, and the aspect ratio of the intercondylar notch. Only the sagittal angle of the ACL relative to the tibial plateau experienced statistically significant changes through late adolescence. The age-dependent properties of the ACL and PCL in the female pig mirrored results found in female human patients, suggesting that the porcine model may provide a pre-clinical platform to study the cruciate ligaments during skeletal growth. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2725-2732, 2017.

Ectopic tissue engineered ligament with silk collagen scaffold for ACL regeneration: A preliminary study.

Anterior cruciate ligament (ACL) reconstruction remains a formidable clinical challenge because of the lack of vascularization and adequate cell numbers in the joint cavity. In this study, we developed a novel strategy to mimic the early stage of repair in vivo, which recapitulated extra-articular inflammatory response to facilitate the early ingrowth of blood vessels and cells. A vascularized ectopic tissue engineered ligament (ETEL) with silk collagen scaffold was developed and then transferred to reconstruct the ACL in rabbits without interruption of perfusion. At 2weeks after ACL reconstruction, more well-perfused cells and vessels were found in the regenerated ACL with ETEL, which decreased dramatically at the 4 and 12week time points with collagen deposition and maturation. ACL treated with ETEL exhibited more mature ligament structure and enhanced ligament-bone healing post-reconstructive surgery at 4 and 12weeks, as compared with the control group. In addition, the ETEL group was demonstrated to have higher modulus and stiffness than the control group significantly at 12weeks post-reconstructive surgery. In conclusion, our results demonstrated that the ETEL can provide sufficient vascularity and cellularity during the early stages of healing, and subsequently promote ACL regeneration and ligament-bone healing, suggesting its clinic use as a promising therapeutic modality. STATEMENT OF SIGNIFICANCE: Early inflammatory cell infiltration, tissue and vessels ingrowth were significantly higher in the extra-articular implanted scaffolds than theses in the joint cavity. By mimicking the early stages of wound repair, which provided extra-articular inflammatory stimulation to facilitate the early ingrowth of blood vessels and cells, a vascularized ectopic tissue engineered ligament (ETEL) with silk collagen scaffold was constructed by subcutaneous implantation for 2weeks. The fully vascularized TE ligament was then transferred to rebuild ACL without blood perfusion interruption, and was demonstrated to exhibit improved ACL regeneration, bone tunnel healing and mechanical properties.

Biodegradable Magnesium Screws Accelerate Fibrous Tissue Mineralization at the Tendon-Bone Insertion in Anterior Cruciate Ligament Reconstruction Model of Rabbit.

The incorporation of tendon graft into bone tunnel is one of the most challenging clinical issues in anterior cruciate ligament (ACL) reconstruction. As a biodegradable metal, Mg has appropriate mechanical strength and osteoinductive effects, thus may be a promising alternative to commercialized products used for graft fixation. Therefore, it was hypothesized that Mg based interference screws would promote tendon graft-bone junction healing when compared to Ti screws. Herein, we compared the effects of Mg and Ti screws on tendon graft healing in rabbits with ACL reconstruction via histological, HR-pQCT and mechanical analysis. The histological results indicated that Mg screws significantly improved the graft healing quality via promoting mineralization at the tendon graft enthesis. Besides, Mg screws significantly promoted bone formation in the peri-screw region at the early healing stage. Importantly, Mg screws exhibited excellent corrosion resistance and the degradation of Mg screws did not induce bone tunnel widening. In tensile testing, there were no significant differences in the load to failure, stress, stiffness and absorption energy between Mg and Ti groups due to the failure mode at the midsubstance. Our findings demonstrate that Mg screws can promote tendon graft healing after ACL reconstruction, implying a potential alternative to Ti screws for clinical applications.

Anterior cruciate ligament and intercondylar notch growth plateaus prior to cessation of longitudinal growth: an MRI observational study.

PURPOSE: Increasing numbers of children and adolescents are being treated for ACL tears. In order for surgeons to safely optimize treatment during ACL surgery, we must better understand ACL growth and intercondylar notch patterns in the skeletally immature knee. The aim of this study is to measure ACL and intercondylar notch volume in paediatric patients and observe how these volumes change as a function of age and gender. METHODS: Data were extracted from the picture archiving and communication systems (PACS) computer records. Sample consisted of 137 MRI knee examinations performed between January 2006 and July 2010 in patients aged 3-13. Subjects were grouped into 1-year age intervals. Patients with imaging reports including ACL tears, previous surgeries, congenital structural anomalies, or syndromes were excluded. RESULTS: Measures of ACL volume significantly increased with age (P < 0.001). A linear increase in ACL volume was observed until the age 10, with a mean increase in volume of 148 mm(3) per age group. ACL volume plateaued at 10 years, after which minimal increase in ACL volume was observed. Sex was not found to be a significant predictor of ACL volume in the multiple linear regression (P = 0.57). Similar to ACL volume, there was a significant increase in intercondylar notch volume with age with a mean increase of 835 mm(3) per age group (P < 0.0001). Intercondylar notch volume reached a plateau at age 10, after which a minimal increase in notch volume was observed in older groups. Female patients had notch volumes that were on average 892 + 259 mm(3) smaller than male patients who were in the same age group (P = 0.0006). CONCLUSION: The plateau in the growth of ACL and notch volume occurs at age 10, prior to the halt in longitudinal growth of boys and girls. Female patients have significantly smaller intercondylar notch volumes than their age-matched male counterparts, while no gender difference was seen in ACL volume. These results suggest that notch volume is an intrinsically sex-specific difference, which may contribute to the higher rate of ACL tears among females. These growth patterns are clinically relevant as it allows surgeons to better understand the anatomy, pathology, and risk factors related to ACL tears and its reconstruction. LEVEL OF EVIDENCE: Observational Study, Level IV.

Copy number variation in CEP57L1 predisposes to congenital absence of bilateral ACL and PCL ligaments.

BACKGROUND: Absence of the anterior (ACL) or posterior cruciate ligament (PCL) are rare congenital malformations that result in knee joint instability, with a prevalence of 1.7 per 100,000 live births and can be associated with other lower-limb abnormalities such as ACL agnesia and absence of the menisci of the knee. While a few cases of absence of ACL/PCL are reported in the literature, a number of large familial case series of related conditions such as ACL agnesia suggest a potential underlying monogenic etiology. We performed whole exome sequencing of a family with two individuals affected by ACL/PCL. RESULTS: We identified copy number variation (CNV) deletion impacting the exon sequences of CEP57L1, present in the affected mother and her affected daughter based on the exome sequencing data. The deletion was validated using quantitative PCR (qPCR), and the gene was confirmed to be expressed in ACL ligament tissue. Interestingly, we detected reduced expression of CEP57L1 in Epstein-Barr virus (EBV) cells from the two patients in comparison with healthy controls. Evaluation of 3D protein structure showed that the helix-binding sites of the protein remain intact with the deletion, but other functional binding sites related to microtubule attachment are missing. The specificity of the CNV deletion was confirmed by showing that it was absent in ~700 exome sequencing samples as well as in the database of genomic variations (DGV), a database containing large numbers of annotated CNVs from previous scientific reports. CONCLUSIONS: We identified a novel CNV deletion that was inherited through an autosomal dominant transmission from an affected mother to her affected daughter, both of whom suffered from the absence of the anterior and posterior cruciate ligaments of the knees.

MRI evaluation of the development of intercondylar notch width in children.

PURPOSE: The purpose of this study was to evaluate the development of intercondylar notch width in children using MRI and assesse the relationship between the cruciate ligaments and the width of the intercondylar notch during growth. METHODS: We reviewed MRIs and medical records of 76 children (age range 3.8-16.9) without derangements of the knee. Cases with knee joint instability and/or major trauma were excluded. On a standardized coronal image, measurements of the width of the intercondylar notch, knee, ACL and PCL were performed using image analysis software. The notch width index (NWI), ACL/notch, ACL/knee width, PCL/notch, and PCL/knee width were calculated. RESULTS: NWI showed statistical correlation with age. The highest values were found in the youngest children, and the lowest in the oldest group. While ACL/knee width, and PCL/knee width ratios remained proportional over time, the ACL/notch, and PCL/notch ratios increased with the age of the patient. CONCLUSION: NWI changes with age and decreases from childhood to adolescence. A relative decrease in NWI accounts for an increase in the ACL/notch and PCL/notch ratios with age. Studies about NWI in children should consider age as a cofactor for analysis.

A novel silk-based artificial ligament and tricalcium phosphate/polyether ether ketone anchor for anterior cruciate ligament reconstruction - safety and efficacy in a porcine model.

Loss of ligament graft tension in early postoperative stages following anterior cruciate ligament (ACL) reconstruction can come from a variety of factors, with slow graft integration to bone being widely viewed as a chief culprit. Toward an off-the-shelf ACL graft that can rapidly integrate to host tissue, we have developed a silk-based ACL graft combined with a tricalcium phosphate (TCP)/polyether ether ketone anchor. In the present study we tested the safety and efficacy of this concept in a porcine model, with postoperative assessments at 3months (n=10) and 6months (n=4). Biomechanical tests were performed after euthanization, with ultimate tensile strengths at 3months of ∼370N and at 6months of ∼566N - comparable to autograft and allograft performance in this animal model. Comprehensive histological observations revealed that TCP substantially enhanced silk graft to bone attachment. Interdigitation of soft and hard tissues was observed, with regenerated fibrocartilage characterizing a transitional zone from silk graft to bone that was similar to native ligament bone attachments. We conclude that both initial stability and robust long-term biological attachment were consistently achieved using the tested construct, supporting a large potential for silk-TCP combinations in the repair of the torn ACL.

MRI Anatomy of the Tibial ACL Attachment and Proximal Epiphysis in a Large Population of Skeletally Immature Knees: Reference Parameters for Planning Anatomic Physeal-Sparing ACL Reconstruction.

BACKGROUND: To aid in performing anatomic physeal-sparing anterior cruciate ligament (ACL) reconstruction, it is important for surgeons to have reference data for the native ACL attachment positions and epiphyseal anatomy in skeletally immature knees. PURPOSE: To characterize anatomic parameters of the ACL tibial insertion and proximal tibial epiphysis at magnetic resonance imaging (MRI) in a large population of skeletally immature knees. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: The ACL tibial attachment site and proximal epiphysis were examined in 570 skeletally immature knees with an intact ACL (age, 6-15 years) using 1.5-T proton density-weighted sagittal MRI; also measured were the tibial anteroposterior diameter; anterior, central, and posterior ACL attachment positions; vertical height of the epiphysis; and maximum oblique epiphyseal depth extending from the ACL tibial attachment center to the tibial tuberosity. RESULTS: In adolescents (11-15 years of age), the center of the ACL's tibial attachment was 51.5% ± 5.7% of the anteroposterior diameter of the tibia, with no significant differences between sexes or age groups (P > .05 in all cases). Mean vertical epiphyseal height was 15.9 ± 1.7 mm in the adolescent group, with significant differences between 11-year-olds (15.2 ± 1.5 mm) and 15-year-olds (16.6 ± 1.6 mm), P < .001, and between males (16.6 ± 1.5 mm) and females (14.8 ± 1.4), P < .001. Mean maximum oblique depth was 30.0 ± 5.3 mm, with a significant difference between 11-year-olds (26.7 ± 4.9 mm) and 15-year-olds (32.7 ± 5.1 mm), P < .001, and between males (29.7 ± 6.4 mm) and females (27.8 ± 5.2 mm), P < .001. The maximum oblique depth occurred at a mean angle of ~50°, and this angle did not change with age or sex. There was a significant moderate correlation (r = 0.39, P < .001) between epiphyseal vertical height and maximum oblique depth. CONCLUSION: The center of the ACL tibial attachment was consistently near 51% of the anteroposterior diameter, regardless of age or sex. The vertical depth of the tibial epiphysis was ~16 mm in adolescents. Maximum oblique depth from ACL attachment was ~30 mm, occurring at a mean angle ~50° regardless of age or sex. The normative values for tibial ACL attachment and epiphyseal anatomy presented here may be helpful in selecting candidates for surgery and in planning surgical approaches for pediatric ACL reconstruction.

Erythrocytes inhibit ligament fibroblast proliferation in a collagen scaffold.

In this work, we hypothesized that the concentration of erythrocytes in a provisional scaffold would have a significant effect on three of the major biological processes occurring in early wound healing. ACL fibroblast proliferation, collagen production, and scaffold contraction were measured in collagen gels containing fibroblasts and erythrocytes in subphysiologic (1 × 10(8) erythrocytes/ml), physiologic (1 × 10(9) erythrocytes/ml), and supraphysiologic (1 × 10(10) erythrocytes/ml) concentrations. Fibroblast-seeded gels containing only platelet-poor plasma were used as a control group. All gels were cultured for 1, 14, and 21 days. DNA, ELISA for procollagen and scaffold size measurements were used to quantify the three above parameters of wound healing. Samples with concentrations of erythryocytes lower than that in whole blood stimulated greater fibroblast proliferation and scaffold contraction than those with erythrocyte concentrations similar to that in whole blood (p < 0.027; p < 0.03). Increasing the erythrocyte concentration over that in the whole blood stimulated fibroblast collagen production (p < 0.009) and limited scaffold contraction (p < 0.031). Further work examining the role of the erythrocyte in the early provisional scaffold is warranted.

In vivo evaluation of two types of bioactive scaffold used for tendon-bone interface healing in the reconstruction of anterior cruciate ligament.

Fibrin glue combined with bone morphogenetic protein (BMP) and recombined bone xenograft (RBX), were compared to evaluate their effect on the tendon-bone interface healing. The interface of fibrin glue-BMP developed new cartilage but the new bone was thinner whereas the interface of RBX had large areas of chondrocyte-like cells, bone formation and an immature neo-enthesis structure. At 12 weeks, bone mineral density of RBX group (152 ± 52 cm(3)) and fibrin glue-BMP group (109 ± 13 cm(3)) was calculated by micro-computed tomography. The ultimate load of fibrin glue-BMP group (60 ± 18 and 51 ± 14 N) and RBX group (65 ± 21 and 57 ± 15 N) was shown by biomechanics at 6 and 12 weeks. RBX thus has an advantage on accelerating tendon-bone interface healing.

Evaluation of a hydrogel-fiber composite for ACL tissue engineering.

The anterior cruciate ligament (ACL) is necessary for normal knee stability and movement. Unfortunately the ACL is also the most frequently injured ligament of the knee with severe disruptions requiring surgical intervention. In response to this, tissue engineering has emerged as an option for ACL replacement and repair. In this study we present a novel hydrogel-fibrous scaffold as a potential option for ACL replacement. The scaffold was composed of PLLA fibers, in a previously evaluated braid-twist structure, combined with a polyethylene glycol diacrylate (PEGDA) hydrogel to improve viscoelastic properties. Both hydrogel concentration (10%, 15%, and 20%) and amount of hydrogel (soaking the fibrous scaffold in hydrogel solution or encasing the scaffold in a block of hydrogel) were evaluated. It was found that the braid-twist scaffold had a greater porosity and larger number of pores above 100 µm than braided scaffolds with the same braiding angle. After testing for their effects on swelling, fiber degradation, and protein release, as well as viscoelastic and tensile testing (when combined with fibrous scaffolds), it was found that the composite scaffold soaked in 10% hydrogel had the best chemical release and mechanical properties. The optimized structure behaved similarly to natural ligament in tension with the addition of the hydrogel decreasing the ultimate tensile stress (UTS), but the UTS was still comparable to natural ACL. In addition, cellular studies showed that the hydrogel-PLLA fiber composite supported fibroblast growth.