Shortening of patellar tendon after total knee arthroplasty (TKA) was previously reported by several studies. Its etiology still remains controversial. Patellar tendon shortening, a direct cause of patella baja, has a dramatic negative impact in terms of clinical outcomes after TKA. Main objective of this study is to assess the feasibility of utilizing a different technique with Ultrasound that is easy to use, cost-effective and able to eliminate the problem of differential magnification occurring in other techniques which count on standard x-rays and to establish the correlation between clinical outcomes and changes in patellar tendon length and thickness after TKA. The study was designed as prospective cohort and, after a minimum of 4-year-follow up period, 47 knees of 24 patients who had undergone primary TKA without patellar resurfacing were included in the study. All patients were scored with Kujala and HSS scores and all patellar tendons were evaluated with USG regarding their length and thickness. We used conventional grey-scale ultrasound imaging (US) to determine any changes in patellar tendon morphology. All cases were evaluated by the same radiologist. The patellar tendon was examined with the knee in 30° flexion. The flexion angle helped to stretch the extensor mechanism and avoid anisotropy (concavity) of the patellar tendon. The transducer was placed along the long axis of the tendon. The patellar tendon was initially examined in the longitudinal plane in order to measure the total length. Then, total length was divided into three parts and sagittal thickness was calculated at the proximal, median, and distal thirds of the patellar tendon. Both the length and thickness of the tendon were measured before surgery and at the 4th year of follow-up. Of the 47 knees that were included in our study, the mean pre-operative and postoperative length of the patellar tendon was 40.78±6.15 mm and 35.93±4.52 mm. Our results suggested significant shortening of the patellar tendon after primary TKA surgery (p<0.05). Intergroup analysis suggested that reduced sagittal thickness in the proximal third of the tendon was more strongly correlated with an increase in functional outcomes (p<0.05). Our results suggested no significant difference in clinical outcome scores between patients with increased or decreased length of the patellar tendon after TKA (p>0.05). We suggest that determining morphologic changes in sagittal thickness as well as length is important in explaining some of the ambiguous causes of anterior knee pain and impaired clinical outcomes after TKA. More accurate documentation of morphologic changes in the patellar tendon after TKA will certainly help to develop new techniques by surgeons or avoid some existing routines that may harm the tendon. USG is a feasible method for evaluating patellar tendon morphology after TKA but more future studies are needed

An understanding of the remodelling of tendon is crucial for the development of scientific methods of treatment and rehabilitation. This study tested the hypothesis that tendon adapts structurally in response to changes in functional loading. A novel model allowed manipulation of the mechanical environment of the patellar tendon in the presence of normal joint movement via the application of an adjustable external fixator mechanism between the patella and the tibia in sheep, while avoiding exposure of the patellar tendon itself. Stress shielding caused a significant reduction in the structural and material properties of stiffness (79%), ultimate load (69%), energy absorbed (61%), elastic modulus (76%) and ultimate stress (72%) of the tendon compared with controls. Compared with the material properties the structural properties exhibited better recovery after re-stressing with stiffness 97%, ultimate load 92%, energy absorbed 96%, elastic modulus 79% and ultimate stress 80%. The cross-sectional area of the re-stressed tendons was significantly greater than that of stress-shielded tendons. The remodelling phenomena exhibited in this study are consistent with a putative feedback mechanism under strain control. This study provides a basis from which to explore the interactions of tendon remodelling and mechanical environment

We compared the biological characteristics of extrinsic fibroblasts infiltrating the patellar tendon with those of normal, intrinsic fibroblasts in the normal tendon in vitro. Infiltrative fibroblasts were isolated from the patellar tendons of rabbits six weeks after an in situ freeze-thaw treatment which killed the intrinsic fibroblasts. These intrinsic cells were also isolated from the patellar tendons of rabbits which had not been so treated. Proliferation and invasive migration into the patellar tendon was significantly slower for infiltrative fibroblasts than for normal tendon fibroblasts. Flow-cytometric analysis indicated that expression of α5β1 integrin at the cell surface was significantly lower in infiltrative fibroblasts than in normal tendon fibroblasts. The findings suggest that cellular proliferation and invasive migration of fibroblasts into the patellar tendon after necrosis are inferior to those of the normal fibroblasts. The inferior intrinsic properties of infiltrative fibroblasts may contribute to a slow remodelling process in the grafted tendon after ligament reconstruction

In order to clarify the role of cytokines in the remodelling of the grafted tendon for ligament reconstruction we compared the responses to interleukin (IL)-1β, platelet-derived growth factor (PDGF)-BB and transforming growth factor (TGF)-β1 of extrinsic fibroblasts infiltrating the frozen-thawed patellar tendon in rats with that of the normal tendon fibroblasts, in regard to the gene expression of matrix metalloproteinase (MMP)-13, using Northern blot analysis. We also examined, immunohistologically, the local expression of IL-1β, PDGF-BB, and TGF-β1 in fibroblasts infiltrating the frozen-thawed patellar tendon. Northern blot analysis showed that fibroblasts derived from the patellar tendon six weeks after the freeze-thaw procedure in situ showed less response to IL-1β than normal tendon fibroblasts with respect to MMP-13 mRNA gene expression. The immunohistological findings revealed that IL-1β was over-expressed in extrinsic fibroblasts which infiltrated the patellar tendon two and six weeks after the freeze-thaw procedure in situ, but neither PDGF-BB nor TGF-β1 was over-expressed in these extrinsic fibroblasts. Our findings indicated that IL-1β had a close relationship to matrix remodelling of the grafted tendon for ligament reconstruction, in addition to the commencement of inflammation during the tissue-healing process

We performed a biomechanical and histological study to clarify the effect of stress enhancement on the in situ frozen-thawed patellar tendon of the rabbit as a tendon autograft model. We used 48 Japanese White rabbits divided into three groups. In group 1, the patellar tendon underwent in situ freeze-thaw treatment with liquid nitrogen to kill intrinsic fibroblasts. In group 2, after similar treatment, the medial and lateral portions were resected so that the cross-sectional area was reduced by a third. In group 3, after treatment, the cross-sectional area was reduced by a half. In groups 2 and 3, the stress in the tendon was calculated theoretically to be 150% and 200% of the physiological stress during locomotion. Eight rabbits in each group were killed at three and six weeks, respectively. At three weeks, the mean values for the tensile strength of groups 2 and 3 were 113.7% and 75.7% of that of group 1, and at six weeks 101.2% and 57.4%, respectively. The tensile strength in group 3 was significantly lower than that in groups 1 and 2. The histological findings in group 2 were similar to those in group 1, although an acellular area appeared to be wider in the core portion compared with group 1 at each period. In group 3, the collagen bundles of the tendon were less organised than those of groups 1 and 2. Our findings showed that stress enhancement affects the remodelling of the frozen-thawed patellar tendon and that excessively high stress reduces the mechanical properties of the tendon. This indicates that high stress on the patellar tendon autograft should be avoided during ligament reconstruction

Obesity decreases patellar tendon stiffness in females but not males Introduction Patellar tendon (PT) injuries are frequent due to excessive mechanical loading during strenuous physical activity. PT injury incidence is higher in females and obese individuals. The reason behind higher tendon injury incidence in females and obese individuals might be structural changes in tendons such as stiffness or elasticity. Tendon stiffness can recently be quantified using shear wave elastography (SWE). We aimed to examine the stiffness of PT in healthy sedentary participants using this new technology. This prospective study was carried out with 58 (34 female, 24 male) healthy sedentary participants between the ages of 18–44 years (27.5±7.7 years). Body mass and body fat percentage were measured with the Bioelectrical Impedance method using Tanita BC-418 MA Segmental Body Composition Analyser (Tanita Corporation, Tokyo, Japan). Participants were subsequently categorized into ‘normal-weight’ (BMI < 23 kg/m2) and ‘obese’ (BMI>27.5 kg/m2). SWE of the PT was measured with the ACUSON S3000 (Siemens Medical Solution, Mountain Wiew, CA, USA) ultrasound device using the Siemens 9L4 (4–9 MHz) linear-array probe with the Virtual Touch Imaging Quantification® method. The measurement was performed by placing the US probe longitudinally on patellar tendon with knee flexed at 30°. The region between about 1 cm distal of patellar bone-tendon junction and 1 cm proximal of bone-tendon junction of tibia was used for PT stiffness measurement (Figure 1). Average of three successive measurements at 10 sec intervals was recorded as PT stiffness. PT stiffness was quantified with MATLAB Version 2015 (Mathworks, Massachusetts, USA) by converting colour data into numbers. PT stiffness, in males, in females, in normal males, in obese males, in normal females, and in obese females was 8.6±1.0 m/sec, 7.4±1.1 m/sec, 8.6±1.1 m/sec, 8.5±1.0 m/sec, 7.9±0.9 m/sec, and 6.2±0.9 m/sec, respectively. Average body fat percentage in males, in females, in normal males, in obese males, in normal females, and in obese females was 20.1±7.4 kg/m2, 30.1±8.1 kg/m2, 15.4±5.2 kg/m2, 24.7±4.6 kg/m2, 25.6±5.5 kg/m2, and 38.1±5.0 kg/m2, respectively. Males PT stiffness was higher when compared to that of females (p=0.000). PT stiffness was similar in obese and normal males (p=0.962) but obese females had lower PT stiffness compared to normal females (p=0.001). PT stiffness of females was lower than males and obesity decreased PT stiffness in females but not in males. The possible explanation of lower PT stiffness in females might be due to their higher estrogen levels that lead to a decrease in estradiol level and collagen synthesis. Lower tendon stiffness in obese females might be metabolic effects due to the increased adipose tissue that contains proteins such as adipokinome, chemerin, lipocalin 2, serum amyloid A3 and adiponectin. These proteins lead to disturbance of tendon homeostasis and decreased collagen content. Altered tendon homeostasis and decreased collagen content may lead to a decrease in tendon stiffness. Decreased PT stiffness in especially in obese women might be associated with increased risk of PT injury

Abstract. Objectives. The need for gender specific knee arthroplasty is debated. This research aimed to establish whether gender differences in patellar tendon moment arm (PTMA), a composite measure that characterises function of both the patellofemoral and tibiofemoral joints, are a consequence of knee size or other variation. Methods. PTMA about the instantaneous helical axis was calculated from positional data acquired using optical tracking. First, data post-processing was optimised, comparing four smoothing techniques (raw, Butterworth filtered, generalised cross-validation cubic spline interpolated and combined filtered/interpolated) using a fabricated knee. Then PTMA was measured during open-chain extension for N=24 (11 female) fresh-frozen cadaveric knees, with physiologically based loading and extension rates (420°/s) applied. Gender differences in PTMA were assessed before and after accounting for knee size with epicondylar width. Results. Combined smoothing enabled sub-mm accuracy (root-mean-squared (RMS) error 0.16mm, max error 0.47mm), whereas large errors were measured for raw (RMS 3.61mm, max 23.71mm), filtered-only (RMS 1.19mm, max 7.38mm) and interpolated-only (RMS 0.68mm, max 1.80mm) techniques. Before scaling, average PTMA throughout knee flexion was 46mm and mean, maximum, and minimum absolute values of PTMA were larger in males (mean differences >8mm, p<0.001), as were the PTMAs at terminal extension and flexion, and the change in PTMA from peak to terminal extension (differences >4mm, p<0.05). After scaling, the PTMA in deep flexion and the change in PTMA from peak to terminal extension were still larger in male knees (differences >2mm, p<0.05). The flexion angle of peak PTMA, unaffected by scaling, was closer to terminal extension for female knee (female 15°, male 29°, p<0.05). Conclusion. Gender differences in PTMA were identified both before and after accounting for knee size, with implications for gender-specific arthroplasty and musculoskeletal models. The developed measurement framework could also be applied in vivo for accurate measurement of the PTMA. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

This investigation of elite male collegiate basketball players aims to determine 1) the change in 3D dynamic functional variables across a single season and 2) correlate cross-season changes in functional variables with changes in clinical and quantitative ultrasound measures. Eleven male college basketball players (mean age 19, range 18–21 years) from a single team underwent baseline patellar tendon shear wave (SW) elastography and dynamic function at the start of the season (Visit1) and at a late-season time point (Visit2). Players reported their VISA-P scores every two weeks across their 24-week season. Each athlete performed a box-ground-box jump five times while 3D lower extremity kinematic and kinetic variables were collected. Functional measures included for landing (LAND) and take-off (TOFF) phases: knee valgus angle, valgus torque, and peak limb force. Knee valgus angular impulse and ground contact time were also measured. Paired t-tests and Pearson correlation coefficients (r) compared Visit1 and Visit2 variables and assessed the strength of linear dependency, respectively. The mean change in VISA-P score was 15.18 (+/-8.55). No functional variables were different across the season. Clinical, quantitative ultrasound and functional variables were moderately correlated with take-off valgus moment, landing force, take-off force and contact time. Other correlations were low (< 0.4). Our analyses have shown moderate correlations between important clinical, quantitative imaging and function measurements. These correlations reflect the changes that occur between relevant time points and which relate internal structure and external function

Abstract

Cryopreserved patellar tendon allografts are often recommended for reconstruction of anterior cruciate ligaments (ACLs) because living donor fibroblasts are thought to promote repair. Animal studies, however, indicate that ligaments regenerate from recipient rather than donor cells. If applicable to man, these observations suggest that allograft cell viability is unimportant. We therefore used short tandem repeat analysis with polymerase chain reaction (PCR) amplification to determine the source of cells in nine human ACLs reconstructed with cryopreserved patellar tendon allografts. PCR amplification of donor and recipient DNA obtained before operation and DNA from the graft obtained two to ten months after transplantation revealed the genotype of cells and showed only recipient cells in the graft area. Rather than preserve the viability of donor cells, a technique is required which will facilitate the introduction of recipient cells into patellar tendon allografts.

Patellar tendinosis (PT) is common and can result in prolonged disability, especially in jumping athletes. Recently developed ultra-short-echo (UTE) MRI sequences allow for quantitative evaluation of tendon biostructure with T2* relaxometry. This study evaluated the relationships between changes over time (COT) in quantitative T2*-metrics, qualitative PT grades, and patient reported symptoms within 10 male basketball players from a single collegiate basketball team. All subjects completed weekly VISA-P symptomology questionnaires over the basketball season. Bilateral 3-Tesla MRIs (GE Healthcare) were obtained at pre- and post-season study visits. High-resolution, PD-weighted, FSE sequences were used to qualitatively grade PT. Quantitative T2*-metrics were evaluated using high-resolution, 3D, multi-echo, UTE-MRI sequences. Bilinear exponential fits of SI to corresponding echo time were used to calculate T2*-metrics. All qualitative and quantitative evaluations were region specific (proximal, middle, distal). Linear mixed effects models assessed associations of side and region with T2*-metrics. Spearman correlations evaluated relationships between outcome measures. Within and between study visits, significant side-to-side differences in T2*-metrics were found and were significantly impacted by leg dominance (p<0.05). Pre-season T2*-metrics correlated with COT in T2*-metrics, COT in T2*-metrics correlated with COT in qualitative PT grades, and post-season T2*-metrics correlated with max changes in VISA-P scores (ρ≥0.64). Quantitative T2*-metrics can detect PT and may be capable of predicting the onset of pathology. T2*-metrics could benefit the clinical management of PT: it is sensitive to changes in pathologic severity over time, and therefore can serve as a quantitative metric to guide treatment and evaluate intervention efficacy.

This study of collegiate basketball players evaluated change over time (COT) in ultrasound shear wave (SW) elastography metrics across the basketball season, and correlated to morphologic changes on conventional ultrasound imaging, and VISA-P scores. In eleven male collegiate basketball players (mean age 19, age range 18–21), patella tendon (PT) ultrasound and SW elastography of both knees were performed at pre-season and post-season time points, and players reported their VISA-P scores throughout the season. Patella tendinopathy grade and SW metrics were correlated to VISA-P scores using Spearman correlation coefficients. Paired t-test was used to assess differences in mean SW metrics at pre-and post-season timepoints, accounting for leg dominance. 6 of 11 players (54.5%) had baseline patella tendinopathy on ultrasound progressing in 4 players. The mean change in VISA-P score was 15.18 (+/−8.55). No significant correlation was seen between ultrasound grades of tendinopathy and VISA-P. Pre-season SW velocities did not significantly correlate with baseline VISA-P scores. Post-season SW values and SW COT demonstrated strong correlation with change in VISA-P score in dominant and non-dominant knees. Although not statistically significant, there was a trend towards higher SW velocity for tendinopathy in both dominant and non-dominant knees at both study visits. SW metrics of the PT correlated to change in VISA-P scores in the dominant and non-dominant knees, whereas conventional ultrasound grades of patella tendinopathy did not. There was a trend towards higher SW velocities in patella tendinopathy which may indicate detection of change in intrinsic tissue stiffness.

Tendons are characterised by an inferior healing capacity when compared to other tissues, ultimately resulting in the formation of a pathologically altered extracellular matrix structure. Although our understanding of the underlying causes for the development and progression of tendinopathies remains incomplete, mounting evidence indicates a coordinated interplay between tendon-resident cells and the ECM is critical. Our recent results demonstrate that the matricellular protein SPARC (Secreted protein acidic and rich in cysteine) is essential for regulating tendon tissue homeostasis and maturation by modulating the tissue mechanical properties and aiding in collagen fibrillogenesis [1,2]. Consequently, we speculate that SPARC may also be relevant for tendon healing. In a rat patellar tendon window defect model, we investigated whether the administration of recombinant SPARC protein can modulate tendon healing. Besides the increased mRNA expression of collagen type 1 and the downregulation of collagen type 3, a robust increase in the expression of pro-regenerative fibroblast markers in the repair tissue after a single treatment with rSPARC protein was observed. Additionally, pro-fibrotic markers were significantly decreased by the administration of rSPARC. Determination of structural characteristics was also assessed, indicating that the ECM structure can be improved by the application of rSPARC protein. Therefore, we believe that SPARC plays an important role for tendon healing and the application of recombinant SPARC to tendon defects has great potential to improve functional tendon repair

Tendons display poor intrinsic healing properties and are difficult to treat[1]. Prior in vitro studies[2] have shown that, by targeting the Activin A receptor with magnetic nanoparticles (MNPs), it is possible to remotely induce the tenogenic differentiation of human adipose stem cells (hASCs). In this study, we investigated the tenogenic regenerative potential of remotely-activated MNPs-labelled hASCs in an in vivo rat model. We consider the potential for magnetic controlled nanoparticle mediated tendon repair strategies. hASCs were labelled with 250 nm MNPs functionalized with anti-Activin Receptor IIA antibody. Using a rapid curing fibrin gel as delivery method, the MNPs-labelled cells were delivered into a Ø2 mm rat patellar tendon defect. The receptor was then remotely stimulated by exposing the rats to a variable magnetic gradient (1.28T), using a customised magnetic box. The stimulation was performed 1 hour/day, 3 days/week up to 8 weeks. Tenogenesis, iron deposition and collagen alignment were assessed by histological staining and IHC. Inflammation mediators levels were assessed by ELISA and IHC. The presence of human cells in tendons after 4 and 8 weeks was assessed by FISH analysis. Histological staining showed a more organised collagen arrangement in animals treated with MNPs-labelled cells compared to the controls. IHC showed positive expression of tenomodulin and scleraxis in the experimental groups. Immunostaining for CD45 and CD163 did not detect leukocytes locally, which is consistent with the non-significant levels of the inflammatory cytokines analysis performed on plasma. While no iron deposition was detected in the main organs or in plasma, the FISH analysis showed the presence of human donor cells in rat tendons even after 8 weeks from surgery. Our approach demonstrates in vivo proof of concept for remote control stem cell tendon repair which could ultimately provide injectable solutions for future treatment. We are grateful for ERC Advanced Grant support ERC No.789119, ERC CoG MagTendon No.772817 and FCT grant 2020.01157.CEECIND

Tissue engineering and regenerative medicine (TERM) hold the promise to provide therapies for injured tendons despite the challenging cues of tendon niche and the lack of specific factors to guide regeneration. The emerging potential of magnetic responsiveness and magnetic nanoparticles (MNPs) functionalities offers new perspectives to tackle TERM challenges. Moreover, pulsed electromagnetic field (PEMF) is FDA approved for orthopaedics with potential to control inflammation upon injury. We previously demonstrated that magnetic cell-sheets assisted by PEMF trigger the inflammation resolution by modulating cytokine-enriched environments [1]. To further understand the potential of magnetically assisted living patches, we have recently conducted in vivo studies using a rat patellar defect model. After labeling of human adipose stem cells with iron oxide MNPs for 16h, magCSs were cultured up to 3 days in α-MEM medium under non-magnetic or PEMF conditions. MagCSs were evaluated by immunocytochemistry, and real time RT-PCR for tendon markers. Cell metabolic activity was also assessed by MTS and ECM proteins quantified by Sirius Red/Fast Green. The MagCSs effect in ameliorating healing was assessed after implantation in window defects created in the patellar tendon of rats. PEMF was externally applied (3mT, 70Hz) 3d/week for 1h (magnetotherapy). After 4 and 8w, tendons were histologically characterized for immune-detection of tendon and inflammatory markers, and for Perls van Gieson and HE stains. Blood and detoxification organs were screened for inflammatory mediators and biodistribution of MNPs, respectively. In vitro results suggest that PEMF stimulates cellular metabolic activity, influences protein synthesis and the deposition of collagen and non-collagenous proteins is significantly increased compared to non-magnetic conditions. No adverse reactions, as infection or swelling, were observed after surgery or during follow-up. After 8w, magCSs remained at the implantation site and no MNPs were detected on detoxification organs. Plasma levels of IL1α, β, IL6 and TNFα assessed by multiplex assay were below detectable values (<12.5pg/ml). Thus, the combination of cell sheets and magnetic technologies hold promise for the development of living tendon substitutes. Acknowledgement to ERC-COG MagTendon772817, H2020 Achilles 810850, FCT - 2020.01157.CEECIND

We developed an in vivo model of the attachment of a patellar tendon to a metal implant to simulate the reconstruction of an extensor mechanism after replacement of the proximal tibia. In 24 ewes, the patellar tendon was attached to a hydroxyapatite (HA)-coated titanium prosthesis. In 12, the interface was augmented with autograft containing cancellous bone and marrow. In the remaining ewes, the interface was not grafted. Kinematic gait analysis showed nearly normal function of the joint by 12 weeks. Force-plate assessment showed a significant increase in functional weight-bearing in the grafted animals (p = 0.043). The tendon-implant interface showed that without graft, encapsulation of fibrous tissue occurred. With autograft, a developing tendon-bone-HA-implant interface was observed at six weeks and by 12 weeks a layered tendon-fibrocartilage-bone interface was seen which was similar to a direct-type enthesis. With stable mechanical fixation, an appropriate bioactive surface and biological augmentation the development of a functional tendon-implant interface can be achieved

We report an unusual case of knee disease where calcific tendonitis occurring in both quadriceps and patellar tendon simultaneously in the same knee. A 47 year old female presented to orthopaedics outpatient clinic with acute onset of swelling and knee pain with no history of trauma. She was found to have a moderate effusion of the knee joint with mild tenderness over the mid quadriceps tendon. Active flexion of the knee joint was painful with a range of motion between 0-90 degrees. She is otherwise healthy with no past medical history. Plain radiographs and Magnetic Resonance Imaging (MRI) Scan revealed calcification of both tendons. Calcific tendonitis is classically found in the supraspinatus tendon of the shoulder. In addition, it has been described in other areas of the body such as the wrist, thigh, hip, knee and ankle. This condition usually occurs in the quadriceps or patellar tendons separately and rarely affecting both tendons in the same knee simultaneously. The patients condition improved significantly with physiotherapy, anti-inflammatory medications and ultrasound therapy. Calcific tendinitis of both quadriceps and patellar tendon is a very rare cause of knee pain. Most of the time it is treated conservatively with non-steroidal anti-inflammatory drugs and ultrasound therapy and some times steroid injection. However; patient may require surgical intervention especially in refractory cases to resolve the condition

Introduction and Objective. Anterior cruciate ligament reconstruction (ACLR) with tendon autografts is the “gold standard” technique for surgical treatment of ACL injuries. Common tendon graft choices include patellar tendon (PT), semitendinosus/gracilis “hamstring” tendon (HT), or quadriceps tendon (QT). Healing of the graft after ACLR may be affected by graft type since the tissue is subjected to mechanical stresses during post-operative rehabilitation that play important roles in graft integration, remodeling and maturation. Abnormal mechanical loading can result in high inflammatory and degradative processes and altered extracellular matrix (ECM) synthesis and remodeling, potentially modifying tissue structure, composition, and function. Because of the importance of load and ligamentization for tendon autografts, this study was designed to compare the differential inflammatory and degradative metabolic responses to loading by three tendon types commonly used for autograft ACL reconstruction. Materials and Methods. With IRB approval (IRB # 2009879) and informed patient consent, portions of 9 QT, 7 PT and 6 HT were recovered at the time of standard of care ACLR surgeries. Tissues were minced and digested in 0.2 mg/ml collagenase solution for two hours and were then cultured in 10% FBS at 5% CO. 2. , 37°C, and 95% humidity. Once confluent, cells were plated in Collagen Type I-coated BioFlex® plates (1 × 10. 5. cells/well) and cultured for 2 days prior to the application of strain. Then, media was changed to supplemented DMEM with 2% FBS for the application of strain. Fibroblasts were subjected to continuous mechanical stimulation (2-s strain and 10-s relaxation at a 0.5 Hz frequency) at three different elongation strains (mechanical stress deprivation-0%, physiologic strain-4%, and supraphysiological strain-10%). 9. for 6 days using the Flexcell FX-4000T strain system. Media was tested for inflammatory biomarkers (PGE2, IL-8, Gro-α, and MCP-1) and degradation biomarkers (GAG content, MMP-1, MMP-2, MMP-3, TIMP-1, and TIMP-2). Significant (p<0.05) difference between graft sources were assessed with Kruskal-Wallis test and post-hoc analysis. Results are reported as median± interquartile range (IQR). Results. Differences in Inflammation-Related Biomarker Production (Figure 1): The production of PGE2 was significantly lower by HT fibroblasts compared to both QT and PT fibroblasts at all timepoints and strain levels. The production of Gro-α was significantly lower by HT fibroblasts compared to QT at all time points and strain levels, and significantly lower than PT on day 3 at 0% strain, and all strain levels on day 6. The production of IL-8 by PT fibroblasts was significantly lower than QT and HT fibroblast on day 3 at 10% strain. Differences in Degradation-Related Biomarker Production (Figure 2): The production of GAG by HT fibroblasts was significantly higher compared to both QT and PT fibroblasts on day 6 at 0% strain. The production of MMP-1 by the QT fibroblasts was significantly higher compared to HT fibroblasts on day 3 of culture at all strain levels, and in the 0% and 10% strain levels on day 6 of culture. The production of MMP-1 by the QT fibroblasts was significantly higher compared to PT fibroblasts at in the 0% and 4% strain groups on day 3 of culture. The production of TIMP-1 by the HT fibroblasts was significantly lower compared to PT fibroblasts on day 3 of culture. Conclusions. The results of this study identify potentially clinically relevant difference in the metabolic responses of tendon graft fibroblasts to strain, suggesting a lower inflammatory response by hamstring tendon fibroblasts and higher degradative response by quadriceps tendon fibroblasts. These responses may influence ACL autograft healing as well as inflammatory mediators of pain in the knee after reconstruction, which may have implications regarding graft choice and design of postoperative rehabilitation protocols for optimizing outcomes for patients undergoing ACL reconstruction. For any figures or tables, please contact the authors directly

Summary. Our results prove that Demineralised Cortical Bone (DCB) can be used as biological tendon graft substitute, combined with correct surgical technique and the use of suture bone anchor early mobilisation can be achieved. Introduction. Surgical repair of tendon injuries aims to restore length, mechanical strength and function. In severe injuries with loss of tendon substance a tendon graft or a substitute is usually used to restore functional length. This is usually associated with donor site morbidity, host tissue reactions and lack of remodelling of the synthetic substitutes which may result in suboptimal outcome. In this study we hypothesise that DCB present in biological tendon environment with early mobilisation and appropriate tension will result in remodelling of the DCB into ligament tissue rather that ossification of the DCB at traditional expected. Our preparatory cadaveric study (abstract submitted to CORS 2013) showed that the repair model used in this animal study has sufficient mechanical strength needed for this animal study. Methods. 6 mature female sheep undergone surgical resection of the distal 1 cm of the right patellar tendon and osteotomy of patellar tendon attachment at the tibial tuberosity under general anaesthesia. Repair was done using DCB with 2 suture bone anchor. Animals were allowed immediate mobilisation after surgery and were sacrificed at 12 weeks. The force passing through the operated and non-operated legs was assessed preoperatively and at week 3, week 6, week 9 and week 12 bay walking the animals over a force plate. Radiographs were taken immediately after euthanasia, the Patella-Tendon-tibia constructs were retrieved and pQCT scan was done. Histological analysis included tenocytes and chondrocytes cell counts, semi-quantitative scoring of the neo-enthesis and polarised microscopy. Result. In this study, none of the retrieved specimens showed any evidence of ossification of the DCB as proved by the pQCT analysis. One animal failed to show satisfactory progress after week 3, X-rays showed patella alta, on specimen retrieval no damage to the DCB was found, sutures and stitches were intact and no evidence of anchor pullout was found. Force plate analysis of the other 5 animals showed satisfactory progression over time with 44% functional weight bearing at week 3 progressing to 79% at week 12. There was full range of movement of the stifle joint after 12 weeks. Histological analysis proved formation of neo-enthesis with evidence of cellulisation, vascularisation and remodelling of the collagen leading to ligamentisation of the DCB. Discussion. Surgical reconstruction of damaged tendons is technically challenging, patellar tendon injuries presents even more challenging situation as it involves weight bearing joint. It is generally accepted that a period of immobilisation with passive range of movement exercises and protected weight bearing for up to 6 weeks post operatively is usually advised. Some surgeons use offloading metal wire to protect the repair for 6 weeks involving second surgical procedure to remove the wire. Demineralised bone is usually used in orthopaedics to utilise its osteogenic properties as bone graft substitute and to enhance osteogenesis in load bearing situations. In our study we explored a potential new use of the demineralised bone as tendon graft substitute, it acts as collagen scaffold allowing host cells to remodel its fibres into ligament like structure

We examined the mechanical properties of Vicryl (polyglactin 910) mesh in vitro and assessed its use in vivo as a novel biomaterial to attach tendon to a hydroxyapatite-coated metal implant, the interface of which was augmented with autogenous bone and marrow graft. This was compared with tendon re-attachment using a compressive clamp device in an identical animal model. Two- and four-ply sleeves of Vicryl mesh tested to failure under tension reached 5.13% and 28.35% of the normal ovine patellar tendon, respectively. Four-ply sleeves supported gait in an ovine model with 67.05% weight-bearing through the operated limb at 12 weeks, without evidence of mechanical failure. Mesh fibres were visible at six weeks but had been completely resorbed by 12 weeks, with no evidence of chronic inflammation. The tendon-implant neoenthesis was predominantly an indirect type, with tendon attached to the bone-hydroxyapatite surface by perforating collagen fibres