Incidence of calcaneal apophysitis (Sever's disease) and return-to-play in adolescent athletes of a German youth soccer academy: a retrospective study of 10 years.

BACKGROUND: Calcaneal apophysitis, or Sever's disease, is the most common cause of heel pain in childhood and adolescence. It is regarded as an overuse syndrome. Studies on the incidence of calcaneal apophysitis in young athletes and their associated return-to-play time are lacking in the current literature. The aim of our current study was to identify the incidence of calcaneal apophysitis in professional youth soccer, the associated time to return-to-play, predisposing factors and their impact on time to return-to-play. METHODS: Retrospective evaluation of injury data gathered from a German youth soccer academy in the years 2009-2018. In total, 4326 injury cases in 612 players were included in the study. The diagnosis and the follow-up visits were carried out in a weekly consultation hour at the youth academy. RESULTS: During the observation period of 10 years, 22 cases of calcaneal apophysitis were detected. The incidence of calcaneal apophysitis per 100 athletes per year was found to be 0.36. The mean age of the affected athletes at the time of diagnosis was 11.8 ± 2.1 years (MW ± SD). The complaints were unilateral in 20 and bilateral in two cases. Three of the 22 detected cases of calcaneal apophysitis (13.6%) were recurrent injuries. The mean time to return-to-play of the affected athletes was 60.7 ± 64.9 days (MW ± SD). Athletes with recurrent complaints showed longer recovery time and time to return-to-play when compared to players with primary diagnosed disease. Our results could show that neither age nor body mass index at the time of diagnosis had an impact on time to return-to-play. CONCLUSIONS: This is the first study investigating the incidence of calcaneal apophysitis and the associated time to return-to-play in youth elite soccer. Calcaneal apophysitis results in substantial time loss for the athletes. Further prospective clinical studies are required to fully understand the etiology and risk factors for calcaneal apophysitis and therefore develop preventive strategies.

Detecting the Effects of the Glucocorticoid Dexamethasone on Primary Human Skeletal Muscle Cells-Differences to the Murine Cell Line.

Skeletal muscle atrophy is characterized by a decrease in muscle fiber size as a result of a decreased protein synthesis, which leads to degradation of contractile muscle fibers. It can occur after denervation and immobilization, and glucocorticoids (GCs) may also increase protein breakdown contributing to the loss of muscle mass and myofibrillar proteins. GCs are already used in vitro to induce atrophic conditions, but until now no studies with primary human skeletal muscle existed. Therefore, this study deals with the effects of the GC dexamethasone (dex) on primary human myoblasts and myotubes. After incubation with 1, 10, and 100 µM dex for 48 and 72 h, gene and protein expression analyses were performed by qPCR and Western blot. Foxo, MuRF-1, and MAFbx were significantly upregulated by dex, and there was increased gene expression of myogenic markers. However, prolonged incubation periods demonstrated no Myosin protein degradation, but an increase of MuRF-1 expression. In conclusion, applying dex did not only differently affect primary human myoblasts and myotubes, as differences were also observed when compared to murine cells. Based on our findings, studies using cell lines or animal cells should be interpreted with caution as signaling transduction and functional behavior might differ in diverse species.

Intramuscular Injection of Combined Calf Blood Compound (CFC) and Homeopathic Drug Tr14 Accelerates Muscle Regeneration In Vivo.

Skeletal muscle injuries in competitive sports cause lengthy absences of athletes from tournaments. This is of tremendous competitive and economic relevance for both the athletes and their respective clubs. Therapy for structural muscle lesions aims to promote regeneration and fast-track return-to-play. A common clinical treatment strategy for muscle injuries is the intramuscular injection of calf blood compound and the homeopathic drug, Tr14. Although the combination of these two agents was reported to reduce recovery time, the regulatory mechanism whereby this occurs remains unknown. In this in vivo study, we selected a rat model of mechanical muscle injury to investigate the effect of this combination therapy on muscle regeneration. Gene expression analysis and histological images revealed that this combined intramuscular injection for muscle lesions can enhance the expression of pro-myogenic genes and proteins and accelerate muscle regeneration. These findings are novel and depict the positive effects of calf blood compound and the homeopathic drug, Tr14, which are utilized in the field of Sports medicine.

Exposure to radial extracorporeal shockwaves induces muscle regeneration after muscle injury in a surgical rat model.

The leading cause of training interruption in sport is a muscle injury, for which the standard treatment is nonsteroidal anti-inflammatory drugs (NSAIDs). To find alternative treatments, we investigated whether the radial extracorporeal shockwave application (rESWT) could stimulate muscle regeneration. A lesion with complete rupture (grade III muscle tear) was set in the musculus rectus femoris of 12-week-old Wistar rats, and the NSAID diclofenac, rESWT, or a combined therapy were applied on day 0, 3, and 5 directly following the surgery. Rats were euthanized at 2, 4, and 7 days after surgery and the area of muscle lesion was excised for histological and gene expression analysis to determine the progress in the healing of damaged fibers and tissue regeneration. The best effect on muscle regeneration was observed in the group treated with rESWT alone. Monotherapy by diclofenac showed a smaller but still positive effect and lowest effects were detected when both therapies were applied. rESWT alone demonstrated a significant upregulation of the muscle markers MyoD and myosin. The presence of myosin gene expression indicated newly formed muscle fibers, which was confirmed by hematoxylin and eosin staining. Seven days after injury the amount of mononucleated cell decreased and regenerating fibers could be detected. This effect is most pronounced in the group treated with rESWT alone. In our study, shockwaves demonstrated the best effect on muscle regeneration. Therefore, we recommend prospective clinical studies to analyze the effect of rESWT after sports trauma to improve muscle regeneration and to shorten the rehabilitation.

Calf Blood Compound (CFC) and Homeopathic Drug Induce Differentiation of Primary Human Skeletal Muscle Cells.

The use of injections to treat structural muscle injuries is controversially discussed. In our controlled in vitro study, we investigated the biological impact of Actovegin and Traumeel alone and in combination on primary human skeletal muscle cells. Cells were characterized by immunofluorescence staining for myogenic factor 5 (Myf5) and MyoD, and cultured with or without Actovegin and / or Traumeel. The effects of these agents were assayed by cell viability and gene expression of the specific markers MyoD, Myf5, neural adhesion molecule (NCAM), and CD31. Myotube formation was determined by myosin staining. Neither Actovegin nor Traumeel showed toxic effects or influenced cell viability significantly. High volumes of Actovegin down-regulated gene expression of NCAM after 3 days but had no effect on MyoD, Myf5, and CD31 gene expression. High volumes of Traumeel inhibited MyoD gene expression after 3 days, whereas after 7 days MyoD expression was significantly up-regulated. The combination of both agents did not significantly influence cell viability or gene expression. This is the first study demonstrating that Actovegin and Traumeel potentially modulate human skeletal muscle cells. The relevance of these in vitro findings has to be highlighted in further in vivo studies.

Effects of losartan and atorvastatin on the development of early posttraumatic joint stiffness in a rat model.

BACKGROUND: After a trauma, exuberant tissue healing with fibrosis of the joint capsule can lead to posttraumatic joint stiffness (PTJS). Losartan and atorvastatin have both shown their antifibrotic effects in different organ systems. OBJECTIVE: The purpose of this study was the evaluation of the influence of losartan and atorvastatin on the early development of joint contracture. In addition to joint angles, the change in myofibroblast numbers and the distribution of bone sialoprotein (BSP) were assessed. STUDY DESIGN AND METHODS: In this randomized and blinded experimental study with 24 rats, losartan and atorvastatin were compared to a placebo. After an initial joint injury, rat knees were immobilized with a Kirschner wire. Rats received either losartan, atorvastatin or a placebo orally daily. After 14 days, joint angle measurements and histological assessments were performed. RESULTS: Losartan increased the length of the inferior joint capsule. Joint angle and other capsule length measurements did not reveal significant differences between both drugs and the placebo. At cellular level both losartan and atorvastatin reduced the total number of myofibroblasts (losartan: 191±77, atorvastatin: 98±58, placebo: 319±113 per counting field, p<0.01) and the percentage area of myofibroblasts (losartan: 2.8±1.8% [p<0.05], atorvastatin: 2.5±1.7% [p<0.01], vs control [6.4±4%], respectively). BSP was detectable in equivalent amounts in the joint capsules of all groups with only a trend toward a reduction of the BSP-stained area by atorvastatin. CONCLUSION: Both atorvastatin and losartan reduced the number of myofibroblasts in the posterior knee joint capsule of rat knees 2 weeks after trauma and losartan increased the length of the inferior joint capsule. However, these changes at the cellular level did not translate an increase in range of motion of the rats´ knee joints during early contracture development.

Evaluation of Bone Sialoprotein Coating of Three-Dimensional Printed Calcium Phosphate Scaffolds in a Calvarial Defect Model in Mice.

The bioactive coating of calcium phosphate cement (CPC) is a promising approach to enhance the bone-healing properties of bone substitutes. The purpose of this study was to evaluate whether coating CPCs with bone sialoprotein (BSP) results in increased bone formation. Forty-five female C57BL/6NRj mice with an average age of six weeks were divided into three groups. Either a BSP-coated or an uncoated three-dimensional plotted scaffold was implanted into a drilled 2.7-mm diameter calvarial defect, or the defect was left empty (control group; no CPC). Histological analyses revealed that BSP-coated scaffolds were better integrated into the local bone stock eight weeks after implantation. Bone volume/total volume (BV/TV) ratios and bone thickness at the bone⁻implant contact were analyzed via micro computed tomography (µCT) after eight weeks. BSP-coated scaffolds and uncoated CPC scaffolds increased bone thickness in comparison to the control (CPC + BSP: 691.1 ± 253.5 µm, CPC: 603.1 ± 164.4 µm, no CPC: 261.7 ± 37.8 µm, p < 0.01). Accordingly, BV/TV was enhanced in both scaffold groups (CPC + BSP: 1.3 ± 0.5%, CPC: 0.9 ± 0.5%, no CPC: 0.2 ± 0.3%, p < 0.01). The BSP coating showed a tendency towards an increased bone thickness (p = 0.18) and BV/TV (p = 0.18) in comparison to uncoated CPC scaffolds. However, a significant increase in bone formation through BSP coating was not found.

A novel rat model of stable posttraumatic joint stiffness of the knee.

BACKGROUND: Animal models of posttraumatic joint stiffness (PTJS) are helpful in understanding underlying mechanisms, which is important for developing specific treatments and prophylactic therapies. Existing rat models of PTJS in the knee failed to show that the created contracture does not resolve through subsequent remobilization. Our objective was to establish a rat model of persisting PTJS of the knee and compare it to existing models. METHODS: Thirty skeletally immature male Sprague Dawley rats underwent surgical intervention with knee hyperextension, extracartilaginous femoral condyle defect, and Kirschner (K)-wire transfixation for 4 weeks with the knee joint in 146.7° ± 7.7° of flexion (n = 10 per group, groups I-III). After K-wire removal, group I underwent joint angle measurements and group II and group III were allowed for 4 or 8 weeks of free cage activity, respectively, before joint angles were measured. Eighteen rats (n = 6 per group, groups Ic-IIIc) served as untreated control. RESULTS: Arthrogenic contracture was largest in group I (55.2°). After 4 weeks of remobilization, the contracture decreased to 25.7° in group II (p < 0.05 vs. group I), whereas 8 weeks of remobilization did not reduce the contracture significantly (group III, 26.5°, p = 0.06 vs. group I). Between 4 and 8 weeks of remobilization, no increase in extension (26.5° in group III, p = 0.99 vs. group II) was observed. Interestingly, muscles did not contribute to the development of contracture. CONCLUSION: In our new rat model of PTJS of the knee joint, we were able to create a significant joint contracture with an immobilization time of only 4 weeks after trauma. Remobilization of up to 8 weeks alone did not result in full recovery of the range of motion. This model represents a powerful tool for further investigations on prevention and treatment of PTJS. Future studies of our group will use this new model to analyze medical treatment options for PTJS.

Exposure to radial extracorporeal shock waves modulates viability and gene expression of human skeletal muscle cells: a controlled in vitro study.

BACKGROUND: Recent clinical and animal studies have shown that extracorporeal shock wave therapy has a promoting influence on the healing process of musculoskeletal disorders. However, the underlying biological effects of extracorporeal shock wave therapy on human skeletal muscle cells have not yet been investigated. METHODS: In this study, we investigated human skeletal muscle cells after exposure to radial extracorporeal shock waves in a standardized in vitro setup. Cells were isolated from muscle specimens taken from adult patients undergoing spine surgery. Primary muscle cells were exposed once or twice to radial extracorporeal shock waves in vitro with different energy flux densities. Cell viability and gene expression of the paired box protein 7 (Pax7), neural cell adhesion molecule (NCAM), and myogenic factor 5 (Myf5) and MyoD as muscle cell markers were compared to non-treated muscle cells that served as controls. RESULTS: Isolated muscle cells were positive for the hallmark protein of satellite cells, Pax7, as well as for the muscle cell markers NCAM, MyoD, and Myf5. Exposure to radial extracorporeal shock waves at low energy flux densities enhanced cell viability, whereas higher energy flux densities had no further significant impact. Gene expression analyses of muscle specific genes (Pax7, NCAM, Myf5, and MyoD) demonstrated a significant increase after single exposure to the highest EFD (4 bar, 0.19 mJ/mm2) and after double exposure with the medium EFDs (2 and 3 bar; 0.09 and 0.14 mJ/mm2, respectively). Double exposure of the highest EFD, however, results in a significant down-regulation when compared to single exposure with this EFD. CONCLUSIONS: This is the first study demonstrating that radial extracorporal shock wave therapy has the potential to modulate the biological function of human skeletal muscle cells. Based on our experimental findings, we hypothesize that radial extracorporal shock wave therapy could be a promising therapeutic modality to improve the healing process of sports-related structural muscle injuries.

Cytokine Interferon-γ suppresses the function of capsule myofibroblasts and induces cell apoptosis.

Myofibroblasts (MFs), a contractile subset of fibroblasts, play a pivotal role in physiological wound healing and in the development of many fibroconnective disorders. The complex cytokine network regulating the function of MFs in joint stiffness is still poorly understood. In this in vitro study, we investigated the effect of the cytokine Interferon-gamma (IFN-γ) on MFs isolated from human joint capsules. MFs were cultivated either in the presence of increasing concentrations of IFN-γ alone or in combination with IFN-γ neutralizing antibodies. Cell viability, cytotoxicity, apoptosis, and mRNA gene expression of the MF markers alpha-smooth muscle actin (α-SMA) and collagen type I were analyzed in MF cultures. Contraction potential was analyzed in an established collagen gel contraction assay simulating the extracellular matrix. Using immunofluorescence staining, we could verify that MFs express IFN-γ-receptor (R)-1 on their membrane. IFN-γ decreased MF viability and significantly elevated the apoptosis rate in a dose-dependent manner. IFN-γ down-regulated α-SMA and collagen type I mRNA expression which was associated with a diminished MF mediated contraction of the gel matrices. These effects were suppressed by simultaneous treatment of cells with a neutralizing IFN-γ antibody. Our experiments confirm the hypothesis that the cytokine IFN-γ is a crucial component of the regulatory network of capsule MFs. IFN-γ notably influences the ability of MFs to contract collagen matrices by suppressing α-SMA gene expression. IFN-γ is toxic for MFs in high concentrations and may negatively regulate the number of pro-fibrotic MFs during the healing process via induction of cell apoptosis. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2524-2533, 2017.

Influence of the anti-inflammatory cytokine interleukin-4 on human joint capsule myofibroblasts.

Post-traumatic joint contracture was reported to be associated with elevated numbers of contractile myofibroblasts (MFs) in the healing capsule. During the physiological healing process, the number of MFs declines; however, in fibroconnective disorders, MFs persist. The manifold interaction of the cytokines regulating the appearance and persistence of MFs in the pathogenesis of joint contracture remains to be elucidated. The objective of our current study was to analyze the impact of the anti-inflammatory cytokine interleukin (IL)-4 on functional behavior of MFs. Cells were isolated from human joint capsule specimens and challenged with three different concentrations of IL-4 with or without its neutralizing antibody. MF viability, contractile properties, and the gene expression of both alpha-smooth muscle actin (α-SMA) and collagen type I were examined. Immunofluorescence staining revealed the presence of IL-4 receptor (R)-alpha (α) on the membrane of cultured MFs. The cytokine IL-4 promoted MF viability and enhanced MF modulated contraction of collagen gels. Moreover, IL-4 intervened in gene expression by up-regulation of α-SMA and collagen type I mRNA. These effects could be specifically lowered by the neutralizing IL-4 antibody. On the basis of our findings we conclude that the anti-inflammatory cytokine IL-4 specifically regulates viability and the contractile properties of MFs via up-regulating the gene expression of α-SMA and collagen type I. IL-4 may be a helpful target in developing anti-fibrotic therapeutics for post-traumatic joint contracture in human. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1290-1298, 2017.

Inhibition of Contractile Function in Human Joint Capsule Myofibroblasts by Targeting the TGF-ß1 and PDGF Pathways.

BACKGROUND: Contractile myofibroblasts (MFs) accumulate in the joint capsules of patients suffering from posttraumatic joint stiffness. MF activation is controlled by a complex local network of growth factors and cytokines, ending in the increased production of extracellular matrix components followed by soft tissue contracture. Despite the tremendous growth of knowledge in this field, inconsistencies remain in practice and prevention. METHODS AND FINDINGS: In this in vitro study, we isolated and cultured alpha-smooth muscle actin (α-SMA) positive human joint capsule MFs from biopsy specimens and investigated the effect of profibrotic and antifibrotic agents on MF function. Both TGF-ß1 and PDGF significantly induced proliferation and increased extracellular matrix contraction in an established 3D collagen gel contraction model. Furthermore, both growth factors induced α-SMA and collagen type I gene expression in MFs. TGF-ß1 down-regulated TGF-ß1 and TGF-ß receptor (R) 1 and receptor (R) 2 gene expression, while PDGF selectively down-regulated TGF-ß receptor 2 gene expression. These effects were blocked by suramin. Interestingly, the anti-oxidant agent superoxide dismutase (SOD) blocked TGF-ß1 induced proliferation and collagen gel contraction without modulating the gene expression of α-SMA, collagen type I, TGF-ß1, TGF-ß R1 and TGF-ß R2. CONCLUSIONS: Our results provide evidence that targeting the TGF-ß1 and PDGF pathways in human joint capsule MFs affects their contractile function. TGF-ß1 may modulate MF function in the joint capsule not only via the receptor signalling pathway but also by regulating the production of profibrotic reactive oxygen species (ROS). In particular, anti-oxidant agents could offer promising options in developing strategies for the prevention and treatment of posttraumatic joint stiffness in humans.

Isolated fractures of the greater tuberosity of the proximal humerus: a long-term retrospective study of 30 patients .

BACKGROUND AND PURPOSE: The diagnosis and treatment of isolated greater tuberosity fractures of the proximal humerus is not clear-cut. We retrospectively assessed the clinical and radiographic outcome of isolated greater tuberosity fractures. PATIENTS AND METHODS: 30 patients (mean age 58 (26-85) years, 19 women) with 30 closed isolated greater tuberosity fractures were reassessed after an average follow-up time of 3 years with DASH score and Constant score. Radiographic outcome was assessed on standard plain radiographs. RESULTS: 14 of 17 patients with undisplaced or slightly displaced fractures (≤ 5 mm) were treated nonoperatively and had good clinical outcome (mean DASH score of 13, mean Constant score of 71). 8 patients with moderately displaced fractures (6-10 mm) were either treated nonoperatively (n = 4) or operatively (n = 4), with good functional results (mean DASH score of 10, mean Constant score of 72). 5 patients with major displaced fractures (> 10 mm) were all operated with good clinical results (mean DASH score of 14, mean Constant score of 69). The most common discomfort at the follow-up was an impingement syndrome of the shoulder, which occurred in both nonoperatively treated patients (n = 3) and operatively treated patients (n = 4). Only 1 nonoperatively treated patient developed a non-union. By radiography, all other fractures healed. INTERPRETATION: We found that minor to moderately displaced greater tuberosity fractures may be treated successfully without surgery.

Distal humerus hemiarthroplasty of the elbow for comminuted distal humeral fractures in the elderly patient.

BACKGROUND: The purpose of our study was to evaluate the objective and subjective outcomes, as well as the radiographic results after elbow hemiarthroplasty (HA) for comminuted distal humerus fractures in elderly patients. METHODS: Ten female patients with a mean age of 75.2 years were treated with elbow HA either for osteoporotic, comminuted distal humerus fractures (n = 8) or for early failed osteosynthesis of distal humerus fractures (n = 2). The mean follow-up period was 12.1 months. All patients were examined and evaluated using the Mayo Elbow Performance Score and the Disabilities of the Arm, Shoulder, and Hand score. Radiographic postoperative outcomes were assessed performing anteroposterior and lateral radiographs of the injured elbow. RESULTS: According to the Mayo Elbow Performance Score, nine patients achieved "good" to "excellent results" and only one patient revealed a "fair" clinical outcome. The mean Disabilities of the Arm, Shoulder, and Hand score was 11.5 (range, 0-30). The flexion of the affected elbow was 124.5° (range, 95-140°), the extension deficit was 17.5° (range, 5-30°), the pronation was 80.5° (range, 60-90°), and the supination was 79.5° (range, 50-90°). The following postoperative complications were seen: one triceps weakness, one transient ulnar nerve irritation, one superficial wound infection, and two heterotopic ossifications. None of the patients required explantation of the prosthesis. There was no evidence of loosening, radiolucency, or proximal bone resorption, whereas one patient developed progressive osteoarthritis of the proximal ulnar and radial articulation. CONCLUSIONS: Elderly patients treated with elbow HA revealed good to excellent short-term clinical outcomes. A high rate of complications occurred but most complications found were minor and reoperation rate was low. Our results must be regarded as a report on our first experience with HA. As cartilage wear is just a question of time especially in active patients, we cautiously recommend HA only for elderly and multimorbid low-demand patients.

Mid- to long-term results after bipolar radial head arthroplasty.

BACKGROUND: Radial head arthroplasty is considered the treatment of choice for unreconstructable radial head fractures in the acute fracture situation. Although short-term results in the current literature are promising, replacement of the radial head remains controversial as long-term results are still missing. We report our 8.8-year results after treatment with a bipolar radial head prosthesis by Judet. MATERIALS AND METHODS: In our department, 19 patients were treated with bipolar radial head arthroplasty between 1997 and 2001. Seventeen of these patients-14 men and 3 women-were examined retrospectively after 106 months (range, 78-139). Of these, 9 patients were treated primarily, 7 patients secondarily, and 1 because of a tumor. RESULTS: On the Mayo Elbow Performance Score, 6 patients achieved excellent results, 10 good, and one fair. The mean DASH score was 9.8 (range, 0-34). No differences were seen between primary and secondary implantation. Flexion averaged 124° (range, 110-150°), the extension deficit was 21° (range, 0-40°), pronation 64° (range, 30-90°), and supination 64° (range, 30-90°). The following complications were seen: 2 dislocations and 8 cases of degenerative changes of the capitellum, 1 with severe erosion. Signs of ulnohumeral arthrosis were found in 12 patients. No evidence of loosening, radiolucencies, or proximal bone resorption was detected. CONCLUSION: Despite major primary complications and high incidence of radiographic signs of degenerative changes after 8.8 years, mainly good clinical results were achieved with Judet's bipolar prosthesis.

New intramedullary locking nail for olecranon fracture fixation--an in vitro biomechanical comparison with tension band wiring.

BACKGROUND: The aim of this study was to determine the difference in displacement of a newly designed intramedullary olecranon fracture fixation device compared with multifilament tension band wiring after 4 cycles and 300 cycles of dynamic continuous loading. METHODS: In eight pairs of fresh-frozen cadaver ulnae, oblique olecranon fractures were created and stabilized using either newly designed intramedullary olecranon nail or multifilament tension band wiring. The specimens were then subjected to continuous dynamic loading (from 25 N to 200 N) using matched pairs of cadaveric upper extremities. The Wilcoxon test was used to determine statistical differences of the displacement in the fracture gap. RESULTS: After 4 cycles and 300 cycles, the displacement in the fracture model was significantly higher in the tension band wiring group than in the intramedullary nailing group. CONCLUSIONS: The newly designed interlocking nailing system showed higher stability in comparison with multifilament tension band wiring after continuous dynamic loading.

The effect of the pro-inflammatory cytokine tumor necrosis factor-alpha on human joint capsule myofibroblasts.

INTRODUCTION: Previous studies have shown that the number of myoblastically differentiated fibroblasts known as myofibroblasts (MFs) is significantly increased in stiff joint capsules, indicating their crucial role in the pathogenesis of post-traumatic joint stiffness. Although the mode of MFs' function has been well defined for different diseases associated with tissue fibrosis, the underlying mechanisms of their regulation in the pathogenesis of post-traumatic joint capsule contracture are largely unknown. METHODS: In this study, we examined the impact of the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) on cellular functions of human joint capsule MFs. MFs were challenged with different concentrations of TNF-alpha with or without both its specifically inactivating antibody infliximab (IFX) and cyclooxygenase-2 (COX2) inhibitor diclofenac. Cell proliferation, gene expression of both alpha-smooth muscle actin (alpha-SMA) and collagen type I, the synthesis of prostaglandin derivates E2, F1A, and F2A, as well as the ability to contract the extracellular matrix were assayed in monolayers and in a three-dimensional collagen gel contraction model. The alpha-SMA and COX2 protein expressions were evaluated by immunofluorescence staining and Western blot analysis. RESULTS: The results indicate that TNF-alpha promotes cell viability and proliferation of MFs, but significantly inhibits the contraction of the extracellular matrix in a dose-dependent manner. This effect was associated with downregulation of alpha-SMA and collagen type I by TNF-alpha application. Furthermore, we found a significant time-dependent upregulation of prostaglandin E2 synthesis upon TNF-alpha treatment. The effect of TNF-alpha on COX2-positive MFs could be specifically prevented by IFX and partially reduced by the COX2 inhibitor diclofenac. CONCLUSIONS: Our results provide evidence that TNF-alpha specifically modulates the function of MFs through regulation of prostaglandin E2 synthesis and therefore may play a crucial role in the pathogenesis of joint capsule contractures.