Summary:. Hamstring tendons (HT) represent a widely used autograft for ACL reconstruction. Harvesting, processing and pretensioning procedures together with the time out of the joint could theoretically hamper tendon cells (TCs) viability. The authors hypothesize that HT cells are not impaired at the end of the surgical procedures and their tenogenic phenotype may be strongly improved by exposure to PEMF. Methods. Remnants of semitendinosus and gracilis tendons were collected at the end of the surgical procedures before skin closure from 15 healthy donors who underwent ACL reconstruction with autologous hamstring tendons. To isolate TCs, the tendon was minced and digested with 0.3 % type I collagenase and the nucleated cells were plated at a density 5x10E3 cells/cm2 and cultured in chamber slides in differentiation medium composed of DMEM + 5ng/ml basic fibroblast growth factor (b-FGF) for 7, 14, 21 days. The following cell cultures were set up:. -. TCs cultured with differentiation medium + exposure to PEMF 8 h/day (PEMF generator system IGEA, intensity of magnetic field = 1.5 mT, frequency = 75 Hz). -. TCs cultured with differentiation medium without exposure to PEMF. At day 0, day 7, day 14 and day 21, immunofluorescence analysis was performed to evaluate the expression of collagen type I, collagen type VI, scleraxis and PCNA (proliferative marker). Subsequently, tendon explant cultures were set up to verify, at day 21, explant viability and the expression of collagen type I, collagen type VI, beta-catenin and PCNA. Results. The TCs from the tendon fragments at the end of the ACL reconstruction were alive and they expressed markers of proliferation and tendon phenotype at the end of the culture periods. The TCs in the presence PEMF 8h/day showed greater production of collagen type I, collagen type VI and scleraxis than that of TCs cultured without PEMF (p<0,05): the expression of this markers increased from 7 to 21 days of culture. The expression of PCNA, in the presence of PEMF stimulus, was significantly lower (p<0,05) than that of TCs cultured without PEMF. A similar behavior was surprisingly observed in tendon explant cultures. Conclusions. Hamstring tendons used for ACL reconstruction are not simple autologous tenoconductive scaffold but are a biologic structure rich in progenitor cells that show tenogenic behavior. Their tenogenic phenotype may be strongly improved by exposure to PEMF. In a future clinical perspective, the postoperative use of PEMF could be used to enhance the ligamentization processes of autologous hamstring tendons, when used as autografts for ACL reconstructions

Introduction and Objective. The rupture of the anterior cruciate ligament is a common sports injury and surgical reconstruction is often required to restore full function of the knee. Hamstring tendons are usually used as autografts. In addition to knee pain and stiffness, infections are feared complications after surgery. Incubation of the autograft in a vancomycin solution until implantation reduced the infection rate by about ten-fold. Recent studies showed no negative effect of vancomycin on the biomechanical properties of porcine tendons. A negative effect of high vancomycin concentrations on chondrocytes and osteoblast is reported, but the effect on tendon and tenocytes is not known. Materials and Methods. Rat Achilles tendons or isolated tenocytes were incubated with an increasing concentration of vancomycin (0 – 10 mg). Tendons were incubated for 0 – 40 minutes, while tenoyctes were incubated for 20 minutes followed by culturing for up to 7 days. Cell viability was assessed with PrestoBlue Assay and live/dead stain. The potential effect of vancomycin on the expression of tendon specific genes and extracellular matrix (ECM) genes was quantified. Possible structural changes of the tendon are analyzed. Results. Incubation of the tendons or tenocytes with 5 mg vancomycin for 20 minutes (clinical use) had no negative effects on the cell viability in the tendons or the isolated tenocytes, while incubation with the toxic control (ethanol) significantly reduced cell viability. Even twice the concentration and a longer incubation time had no negative effect on the cells in the tendons or the isolated cells. Vancyomycin did not affect the expression of Col1a1, Col3a1, and the tenocyte markers mohawk, scleraxis and tenomodulin. Conclusions. The results showed that clinical practice of wrapping the autograft in vancomycin did not impair the tenocyte viability. The expression of collagens and tenocyte markers was also not affected, neither in the incubated tendons nor in the isolated cells. This indicates that vancomycin had no effect on cell phenotype and the formation of the extracellular matrix, which, in addition to cell viability, is important for the performance of the autograft

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

Alarmins- also referred to as damage associated molecular patterns (DAMPS)- are endogenous molecules mobilized in response to tissue damage known to activate the innate immune system and regulate tissue repair and remodelling. The molecular mechanisms that regulate inflammatory and remodelling pathways in tendinopathy are largely unknown therefore identifying early immune effectors is essential to understanding the pathology. S100A8 and S100A9 are low molecular weight calcium binding proteins primarily released by activated phagocytes in an inflammatory setting and also secreted as a heterodimeric complex that exhibits cytokine like functions. Based on our previous investigations we sought evidence of S100A8/A9 expression in human tendinopathy and thereafter, to explore mechanisms whereby S100 proteins may regulate inflammatory mediators and matrix regulation in human tenocytes. Torn supraspinatus tendon (established pathology) and matched intact subscapularis tendon (representing ‘early pathology’) biopsies were collected from patients undergoing arthroscopic shoulder surgery. Control samples of subscapularis tendon were collected from patients undergoing arthroscopic stabilisation surgery. S100A8/A9 expression was analysed at transcript and protein level using quantitative RT-PCR and immunohistochemistry, respectively. Primary human tenocytes were cultured from hamstring tendon tissue obtained during hamstring tendon ACL reconstruction. The in vitro effect of recombinant human S100 A8/A9 on primary human tenocytes was measured using quantitative RT-PCR and ELISA. Immunohistochemistry of tendinopathic tissues demonstrated the presence of S100 A8/A9 in diseased tissues compared to control tissue. In addition, early pathological diseased tissue indicated greater S100A9 expression compared with established diseased pathology. These findings were reflected by data obtained at transcript level from diseased tissues. Recombinant human S100A8, A9 and A8/A9 complex led to significant increase in expression of inflammatory mediators, including IL-6 in vitro. Further analysis via quantitative RT-PCR demonstrated recombinant S100A8, A9 and A8/A9 complex treatment on tenocytes, in vitro, had no direct effect on the expression of genes involved in matrix remodelling. The presence of S100A8 and S100A9 in early tendinopathic lesions suggests expression is upregulated in response to cellular damage. S100A8 and S100A9 are endogenous ligands of Toll-like receptors (TLRs) and receptor for advanced glycation end products (RAGE). These receptors have known regulatory effects on immune mediated cytokine production. We propose S100A8 and S100A9 as active alarmins in the early stages of tendinopathy and thus targeting of its downstream signalling may offer novel therapeutic approaches in the management of human tendon disorders

The objective was to seek evidence of hypoxia in early human tendinopathy and thereafter, to explore mechanisms whereby tissue hypoxia may regulate apoptosis, inflammatory mediators and matrix regulation in human tenocytes. Fifteen torn supraspinatus tendon (established pathology) and matched intact subscapularis tendon (representing ‘early pathology’) biopsies were collected from patients undergoing arthroscopic shoulder surgery. Control samples of subscapularis tendon were collected from 10 patients undergoing arthroscopic stabilisation surgery. Markers of hypoxia were quantified by immunohistochemical methods. Human tendon-derived primary cells were derived from hamstring tendon tissue obtained during hamstring tendon ACL reconstruction. The impact of hypoxia upon tenocyte biology ex vivo was measured using quantitative RT-PCR, multiplex cytokine assays, apoptotic proteomic profiling, immunohistochemistry and annexin V FACS staining. Increased expression of HIF 1a, Bcl-2 and clusterin (hypoxic and apoptotic markers) was detected in subscapularis tendon samples compared to both matched torn samples and non matched control samples (p<0.01). Hypoxic tenocytes exhibited increased production of proinflammatory cytokines (p<0.001), altered matrix regulation (p<0.01) with increased production of Collagen type III operating through a MAPK dependent pathway. Finally, hypoxia increased expression of several mediators of apoptosis and thereby promoted tenocyte apoptosis. Hypoxia promotes expression of proinflammatory cytokines, key apoptotic mediators and drives matrix component synthesis towards a collagen type III profile by human tenocytes. We propose hypoxic cell injury as a critical pathophysiological mechanism in early tendinopathy offering novel therapeutic opportunities in the management of tendon disorders

Conventional non-steroidal anti-inflammatory drugs (NSAIDs) and newer specific cyclo-oxygenase-2 (cox-2) inhibitors are commonly used in musculoskeletal trauma and orthopaedic surgery to reduce the inflammatory response and pain. These drugs have been reported to impair bone metabolism. In reconstruction of the anterior cruciate ligament the hamstring tendons are mainly used as the graft of choice, and a prerequisite for good results is healing of the tendons in the bone tunnel. Many of these patients are routinely given NSAIDs or cox-2 inhibitors, although no studies have elucidated the effects of these drugs on tendon healing in the bone tunnel. In our study 60 female Wistar rats were randomly allocated into three groups of 20. One received parecoxib, one indometacin and one acted as a control. In all the rats the tendo-Achillis was released proximally from the calf muscles. It was then pulled through a drill hole in the distal tibia and sutured anteriorly. The rats were given parecoxib, indometacin or saline intraperitoneally twice daily for seven days. After 14 days the tendon/bone-tunnel interface was subjected to mechanical testing. Significantly lower maximum pull-out strength (p < 0.001), energy absorption (p < 0.001) and stiffness (p = 0.035) were found in rats given parecoxib and indometacin compared with the control group, most pronounced with parecoxib

Introduction. The exact mechanisms leading to tendinopathies and tendon ruptures remain poorly understood while their occurrence is clearly associated with exercise. Overloading is thought to be a major factor contributing to the development of tendon pathologies. However, as animal studies have shown, heavy loading alone won't cause tendinopathies. It has been speculated, that malfunctioning adaptation or healing processes might be involved, triggering tendon tissue degeneration. By analysing the expression of the entirety of degrading enzymes (degradome) in pathological and non-pathological, strained and non-strained tendon tissue, the aim of this study was to identify common or opposite patterns in gene regulation. This approach may generate new targets for future studies. Materials and Methods. RNA was extracted from different tendon tissues: normal (n=7), tendinopathic (n=4) and ruptured (n=4) Achilles tendon; normal (n=4) and tendinopathic (n=4) posterior tibialis tendon; normal hamstrings tendon with or without subjection to static strain (n=4). The RNA was reverse transcribed, then pooled per group The expression of 538 protease genes was analysed using Taqman low-density array quantitative RT-PCR. To be considered relevant, changes had to be at least 4fold and measurable at a level below 36 Cts. Results. In general, there was little common regulation when exercised was compared with pathological tissue. The expression of PAMR1 and TNFαIP3 was upregulated with exercise (169-fold and 78-fold), Achilles tendinopathy (9724-fold and 7-fold) and Achilles tendon rupture (1809-fold and 10-fold), while DDI1, PSMB11 and PSH2 which were down-regulated with exercise were upregulated with Achilles pathology. Discussion. The newly found targets may deliver insights into the initiation and progression of tendon pathologies: PAMR1, a regeneration associated muscle protease which has been shown to be downregulated in Duchenne muscular dystrophy and upregulated in regenerating muscle fibers, might also be involved in tendon regeneration; TNFαIP3, which negatively regulates the NF-κB/pro-inflammatory pathway, could have anti-inflammatory function in tendon regeneration. PSMB11 and PSH2 are for the first time shown to be expressed in tendon and regulated in tendon pathology. Using this approach we were able to generate new targets and to add information on function, regulation and expression sites of recently identified proteins

Introduction. Tendon healing begins with inflammation and results in an incomplete repair with fibrosis, culminating in tendon pathology along with tissue degeneration. Inflammatory mediators regulate the expression of growth factors, and members of the TGFβ superfamily including BMPs have been suggested to play a key role in the development of fibrosis. In established tendon diseases where inflammation and reparative processes persists, the cellular phenotype of tendon cells has been implied to undergo a transformation from that of normal tissue. This study investigates the inflammation-driven mechanisms of tendon pathology using an in vitro tendon cell model. We hypothesized that cells from diseased tendons will exhibit dysregulation of TGFβ superfamily members in response to inflammatory mediators when compared to cells derived from healthy tendons. Materials and Methods. Diseased human tendon cells were isolated from patients with large to massive rotator cuff tears (n=4). Cells isolated from healthy human hamstring tendons served as control tissue (n=5). Cells were treated with human recombinant IL-1β (5ng/ml), oncostatin M (10ng/ml), IL-6 (10ng/ml), IL-10 (10ng/ml) in serum-free medium, or serum-free medium alone (control) for 24 hours. Cell viability was monitored by Alamar Blue assay, and expression of TGFB1, TGFBR1, TGFBR2, CTGF, BMP2 and BMP7 were quantified by quantitative reverse transcription polymerase chain reaction (RT-QPCR). Results. Cytokine stimulation did not significantly influence cell viability in either group. In diseased cells, IL-1β induced a 4.9-fold increase in BMP2 compared to control cells (p=0.032). There were no significant changes in the expression of other TGFβ superfamily genes after stimulation with other cytokines. CTGF was significantly increased in diseased compared to healthy cells following IL-1β stimulation (p=0.0295). No other genes showed differential regulation by inflammatory cytokines between diseased and healthy cells. Discussion. This work suggests that BMP-2, a growth factor related to cell differentiation, is dysregulated with IL-1β stimulation and plays a key role in the development of tendon diseases. Differences in IL-1β-induced CTGF expression suggests increased responsiveness of diseased cells to this cytokine. BMP-2 could be an important growth factor in the development of tendon diseases and further investigation of its role in chronic inflamed tissue is warranted

Introduction. Tendinopathies are debilitating and painful conditions. They are believed to result from repetitive overuse, which can create micro-damage that accumulates over time, and initiates a catabolic cell response. The aetiology of tendinopathy remains poorly understood, therefore the ideal treatment remains unclear. However, current data support the use of eccentric exercise as an effective treatment. In a previous study, we have shown that eccentric loading generates perturbations in the tendon at 10Hz, which is not present during other less effective loading regimes. Consequently, we hypothesis that 10Hz loading initiates an increased anabolic response in tenocytes, that can promote tendon repair. Materials and Methods. Human tenocytes from healthy hamstring tendons and tendinopathic Achilles tendons were derived by collagenase digest and outgrowth respectively. Tenocytes were seeded into 3D collagen gels. The gels were fixed in custom-made chambers and placed in an incubator for 24hrs whilst gene expression stabilised. After 24hrs, cyclic uniaxial strain at 1% ± 1% was applied to the cells, at either 1Hz (n=4) or 10Hz (n=4) using a Bose loading system. After 15 minutes of cyclic strain, the samples were maintained in chambers under 1% static strain for 24 hrs after which gene expression was characterised using RT-PCR. Results. In healthy cells, data showed an increase in expression of all analysed genes after loading (MMP1, MMP2, MMP13, COL1A1, COL3A1, COL5A1, ADAMTS5, IL6, IL8 and TIMP3). Furthermore, the increase in gene expression was larger in the higher frequency loading group, across all genes. Tendinopathic cells showed a more varied response, with upregulation of MMP1, MMP13, COL3A1, ADAMTS5, IL6 and IL8, and downregulation of COL1A1 and COL5A1. Once again, all changes were more pronounced in the higher frequency loading group. Discussion. These preliminary data suggest increased matrix turnover as a result of loading, particularly with high frequency loading in healthy tenocytes, whilst the profile of tendinopathic cells, may indicate an early healing response, where collagen type III is preferentially unregulated relative to types I and V. High frequency loading elicited a more pronounced cellular response, perhaps correlating with the improved repair seen with eccentric loading in vivo

Summary Statement. ACL reconstruction using a quadriceps tendon autograft was quantitatively evaluated using a robotic testing system. Biomechanical results on joint stability and graft function support its use as an alternative to the hamstrings. Introduction. Recently, a number of surgeons have chosen the quadriceps tendon (QT) autograft as an alternative autograft over the hamstrings tendon for ACL reconstruction because its bone-to-bone healing on one side, large size, and preservation of lateral and rotatory knee function could lead to fewer post-operative complications. However, there have been little or no biomechanical studies that quantitatively evaluate knee function after reconstruction using a QT autograft. Therefore, the objective of this study was to assess the function of a reconstructed knee with a QT autograft and compare the results with a quadrupled semitendinosus and gracilis (QSTG) tendon autograft on the same knee. Methods. Ten human cadaveric knees (57.4 ± 4.2 years of age) were tested using a robotic/UFS testing system in 4 knee states: intact, ACL-deficient, and after ACL reconstruction with both QT and QSTG autografts. Reconstructions were performed in randomised order using posterolateral femoral tunnel placement. The knee kinematics in each state were measured at 5 flexion angles (full extension, 15°, 30°, 60°, and 90°) under 3 externally applied loading conditions: (1) 134 N anterior tibial load (ATL), (2) 134 N ATL with 200 N axial compression, and combined rotatory (CR) load of 10 Nm valgus and 5 Nm internal tibial torque (at 15° and 30°). Based on the established procedure, knee kinematics and in-situ forces were obtained using the principle of superposition. A repeated measures ANOVA was used to compare anterior tibial translation (ATT) and in-situ forces between the knee states at each flexion angle, with a Bonferroni post-hoc analysis. Results. Under the ATL, the ATT was found to be restored to within 1.1 mm of the intact knee for both reconstructions (P > 0.05). The in-situ forces in the grafts were also not significantly different from those in the intact ACL except in deep flexion (P < 0.05 at 90° for both grafts). With added axial compression, both reconstructions could still restore the ATT to within 2.4 mm of the intact joint at all flexion angles, and the in-situ forces in both grafts were within 25 N of the intact ACL at 15°, 30°, and 60° (P > 0.05). Under the CR load, knee kinematics and in-situ forces in the grafts were not significantly different from the intact ACL at any tested angle (P > 0.05). Further, no significant differences could be detected between the reconstructions under any experimental condition (P > 0.05). Discussion/Conclusion. ACL reconstruction with a QT autograft was found to restore knee function close to levels of the intact knee and similar to those reconstructed with a QSTG autograft. These results support clinical findings suggesting the QT autograft as a viable alternative for ACL reconstruction

Introduction. Regular, repeated stretching increases joint range of movement (RoM), however the physiology underlying this is not well understood. The traditional view is that increased flexibility after stretching is due to an increase in muscle length or stiffness whereas recent research suggests that increased flexibility is due to modification of tolerance to stretching discomfort/pain. If the pain tolerance theory is correct the same degree of micro-damage to muscle fibres should be demonstrable at the end of RoM before and after a period of stretch training. We hypothesise that increased RoM following a 3 weeks hamstrings static stretching exercise programme may partly be due to adaptive changes in the muscle/tendon tissue. Materials and Methods. Knee angle and torque were recorded in healthy male subjects (n=18) during a maximum knee extension to sensation of pain. Muscle soreness (pain, creatine kinase activity, isometric active torque, RoM) was assessed before knee extension, and 24 and 48 hours after maximum stretch. An exercise group (n=10) was given a daily home hamstring stretching programme and reassessed after 3 weeks and compared to a control group (n=8). At reassessment each subject's hamstring muscles were stretched to the same maximum knee extension joint angle as determined on the first testing occasion. After 24 hours, a reassessment of maximum knee extension angle was made. Results. At the start of the study RoM was 71.3 ± 10.0 degrees and there was no significant difference between groups. After 3 weeks stretching RoM increased significantly (p=0.01) by 9 degrees; the control group showed no change. Stiffness did not differ for either group. Pain score and RoM were the most sensitive markers of muscle damage and were significantly changed 24 and 48 hours after the initial stretch to end of range, (p<0.005) and (p=0.004) respectively. Discussion. The results show that a 3 week stretching programme causes muscle adaptation resulting in an increase in the extensibility of the hamstring muscle/tendon unit but no change in stiffness. The lack of evidence of muscle damage suggests that participants in the stretching group are likely to have undergone a physical change/adaptation rather than simply an increase in pain threshold

Objectives

Regenerative medicine is an emerging field aimed at the repair and regeneration of various tissues. To this end, cytokines (CKs), growth factors (GFs), and stem/progenitor cells have been applied in this field. However, obtaining and preparing these candidates requires invasive, costly, and time-consuming procedures. We hypothesised that skeletal muscle could be a favorable candidate tissue for the concept of a point-of-care approach. The purpose of this study was to characterize and confirm the biological potential of skeletal muscle supernatant for use in regenerative medicine.

Objectives

We aimed to examine the characteristics of deep venous flow in the leg in a cast and the effects of a wearable neuromuscular stimulator (geko; FirstKind Ltd) and also to explore the participants’ tolerance of the stimulator.

Objectives

The purpose of this study was to evaluate chronological changes in the collagen-type composition at tendon–bone interface during tendon–bone healing and to clarify the continuity between Sharpey-like fibres and inner fibres of the tendon.

The purpose of this anatomical study was to explore the morphological variations of the semitendinosus and gracilis tendons in length and cross-section and the statistical relationship between length, cross-section, and body height.

We studied the legs of 93 humans in 136 cadavers. In 43 specimens (46.2%) it was possible to harvest the tendons from both legs.

We found considerable differences in the length and cross-section of the semitendinosus and the gracilis tendons with a significant correlation between the two. A correlation between the length of the femur, reflecting height, and the length of the tendons was only observed in specimens harvested from women. The reason for this gender difference was unclear. Additionally, there was a correlation between the cross-sectional area of the tendons and the length of the femur. Surgeons should be aware of the possibility of encountering insufficient length of tendon when undertaking reconstructive surgery as a result of anatomical variations between patients.

We have investigated whether cells derived from haemarthrosis caused by injury to the anterior cruciate ligament could differentiate into the osteoblast lineage in vitro. Haemarthroses associated with anterior cruciate ligament injuries were aspirated and cultured. After treatment with β-glycerophosphate, ascorbic acid and dexamethasone or 1,25 (OH)₂D₃, a significant increase in the activity of alkaline phosphatase was observed. Matrix mineralisation was demonstrated after 28 days and mRNA levels in osteoblast-related genes were enhanced.

Our results suggest that the haemarthrosis induced by injury to the anterior cruciate ligament contains osteoprogenitor cells and is a potential alternative source for cell-based treatment in such injury.