Inflammasome Activation in the Hip Synovium of Rapidly Destructive Coxopathy Patients and Its Relationship with the Development of Synovitis and Bone Loss.

Rapidly destructive coxopathy (RDC), a rare disease of unknown etiology, is characterized by the rapid destruction of the hip joint. In the current study, the potential involvement of inflammasome signaling in the progression of RDC was investigated. Histopathologic changes and the gene expression of inflammasome activation markers in hip synovial tissues collected from patients with RDC were evaluated and compared with those of osteoarthritis and osteonecrosis of the femoral head patients. The synovial tissues of patients with RDC exhibited remarkable increases in the number of infiltrated macrophages and osteoclasts, and the expression of inflammasome activation markers was also increased compared with those of osteoarthritis and osteonecrosis of the femoral head patients. To further understand the histopathologic changes in the joint, a co-culture model of macrophages and synoviocytes that mimicked the joint environment was developed. Remarkably, the gene expression levels of NLRP3, GSDMD, IL1B, TNFA, ADMTS4, ADMTS5, MMP3, MMP9, and RANKL were significantly elevated in the synoviocytes that were co-cultured with activated THP-1 macrophages, suggesting the association between synovitis and inflammasome activation. Consistent with these findings, osteoclast precursor cells that were co-cultured with stimulated synoviocytes exhibited an increased number of tartrate-resistant acid phosphatase-positive cells, compared with cells that were co-cultured with non-stimulated synoviocytes. These findings suggest that the activation of inflammasome signaling in the synovium results in an increase in local inflammation and osteoclastogenesis, thus leading to the rapid bone destruction in RDC.

IL4 stimulated macrophages promote axon regeneration after peripheral nerve injury by secreting uPA to stimulate uPAR upregulated in injured axons.

Accumulating evidences suggest that M2 macrophages are involved with repair processes in the nervous system. However, whether M2 macrophages can promote axon regeneration by directly stimulating axons nor its precise molecular mechanism remains elusive. Here, the current study demonstrated that typical M2 macrophages, which were generated by IL4 simulation, had the capacity to stimulate axonal growth by their direct effect on axons and that the graft of IL4 stimulated macrophages into the region of Wallerian degeneration enhanced axon regeneration and improved functional recovery after PNI. Importantly, uPA (urokinase plasminogen activator)-uPA receptor (uPAR) was identified as the central axis underlying the axon regeneration effect of IL4 stimulated macrophages. IL4 stimulated macrophages secreted uPA, and its inhibition abolished their axon regeneration effect. Injured but not intact axons expressed uPAR to be sensitive to uPA. These results unveil a cellular and molecular mechanism underlying the macrophage related axon regeneration and provide a basis of a novel therapy for PNI.

Interplay between Inflammation and Pathological Bone Resorption: Insights into Recent Mechanisms and Pathways in Related Diseases for Future Perspectives.

Bone is a mineralized and elastic connective tissue that provides fundamental functions in the human body, including mechanical support to the muscles and joints, protection of vital organs and storage of minerals. Bone is a metabolically active organ that undergoes continuous remodeling processes to maintain its architecture, shape, and function throughout life. One of the most important medical discoveries of recent decades has been that the immune system is involved in bone remodeling. Indeed, chronic inflammation has been recognized as the most significant factor influencing bone homeostasis, causing a shift in the bone remodeling process toward pathological bone resorption. Bone osteolytic diseases typified by excessive bone resorption account for one of the greatest causes of disability worldwide, with significant economic and public health burdens. From this perspective, we discuss the recent findings and discoveries highlighting the cellular and molecular mechanisms that regulate this process in the bone microenvironment, in addition to the current therapeutic strategies for the treatment of osteolytic bone diseases.

"Half-folded" pedicled scapular bone flap for nonunion after humeral neck fracture: A case report.

Treatment of a nonunion of the proximal humerus remains a challenge because of the small proximal fragment and poor central cancellous bone stock of the humeral head. In this report, we describe our experience using a "half-folded" pedicled scapular bone flap with an anatomical locking plate to treat an atrophic nonunion of the proximal humerus in a 64-year-old right-handed woman. The patient had fallen and experienced a common humeral neck fracture 2.5 years previously. During the operation, we elevated the pedicled scapular bone flap, which measured 8.0 cm long and 1.5 cm wide, with a vascular pedicle about 10 cm long. We modified the bone flap to the half-folded type to fill the massive bone cavity in the humeral head. The proximal tip of the flap was divided into two segments while keeping the ventral soft tissue intact. The grafted bone bridging between the head and shaft of the humerus was rigidly fixed with a plate and screw. The operated shoulder was fixed with a sling and a chest belt for 3 weeks, after which the patient began active motion exercises of the shoulder joint. The flap survived without serious donor site morbidity, and good bone healing was obtained about 3.5 months after surgery. The patient was able to use the shoulder comfortably in daily activity without any serious donor site morbidity at 16 months after the surgery. This procedure may be effective in treating nonunion of the proximal humerus with a massive bone cavity in the humeral head.

Dynamic transcriptome analysis of osteal macrophages identifies distinct subset with senescence features in experimental osteoporosis.

Given the potential fundamental function of osteal macrophages in bone pathophysiology, we study here their precise function in experimental osteoporosis. Gene profiling of osteal macrophages from ovariectomized mice demonstrated the upregulation of genes that were involved in oxidative stress, cell senescence and apoptotic process. A scRNA-seq analysis revealed that osteal macrophages were heterogenously clustered into 6 subsets that expressed proliferative, inflammatory, anti-inflammatory and efferocytosis gene signatures. Importantly, postmenopausal mice exhibited a 20-fold increase in subset-3 that showed a typical gene signature of cell senescence and inflammation. These findings suggest that the decreased production of estrogen due to postmenopause altered the osteal macrophages subsets, resulting in a shift toward cell senescence and inflammatory conditions in the bone microenvironment. Furthermore, adoptive macrophage transfer onto calvarial bone was performed and mice that received oxidative-stressed macrophages exhibited greater osteolytic lesions than control macrophages, suggesting the role of these cells in development of inflammaging in bone microenvironment. Consistently, depletion of senescent cells and oxidative-stressed macrophages subset alleviated the excessive bone loss in postmenopausal mice. Our data provided a new insight into the pathogenesis of osteoporosis and sheds light on a new therapeutic approach for the treatment/prevention of postmenopausal osteoporosis.

miR181a/b-1 controls osteocyte metabolism and mechanical properties independently of bone morphology.

Bone derives its ability to resist fracture from bone mass and quality concurrently; however, many questions about the molecular mechanisms controlling bone quality remain unanswered, limiting the development of diagnostics and therapeutics. Despite the increasing evidence on the importance of miR181a/b-1 in bone homeostasis and disease, whether and how osteocyte-intrinsic miR181a/b-1 controls bone quality remains elusive. Osteocyte-intrinsic deletion of miR181a/b-1 in osteocytes in vivo resulted in compromised overall bone mechanical behavior in both sexes, although the parameters affected by miR181a/b-1 varied distinctly based on sex. Furthermore, impaired fracture resistance in both sexes was unexplained by cortical bone morphology, which was altered in female mice and intact in male mice with miR181a/b-1-deficient osteocytes. The role of miR181a/b-1 in the regulation of osteocyte metabolism was apparent in bioenergetic testing of miR181a/b-1-deficient OCY454 osteocyte-like cells and transcriptomic analysis of cortical bone from mice with osteocyte-intrinsic ablation of miR181a/b-1. Altogether, this study demonstrates the control of osteocyte bioenergetics and the sexually dimorphic regulation of cortical bone morphology and mechanical properties by miR181a/b-1, hinting at the role of osteocyte metabolism in the regulation of mechanical behavior.

Noncanonical Pyroptosis Triggered by Macrophage-Derived Extracellular Vesicles in Chondrocytes Leading to Cartilage Catabolism in Osteoarthritis.

OBJECTIVE: The severity of osteoarthritis (OA) and cartilage degeneration is highly correlated with the development of synovitis, which is mediated by the activity of inflammatory macrophages. A better understanding of intercellular communication between inflammatory macrophages and chondrocytes should aid in the discovery of novel therapeutic targets. We undertook this study to explore the pathologic role of inflammatory macrophage extracellular vesicles (EVs) in cartilage degeneration. METHODS: Macrophages were stimulated by treatment with bacterial lipopolysaccharides to mimic the state of inflammatory macrophages, and the resulting EVs were harvested for chondrocyte stimulation in vitro and for intraarticular injection in a mouse model. The stimulated chondrocytes were further subjected to RNA-sequencing analysis and other functional assays. The action of caspase 11 was disrupted in vitro using a specific small interfering RNA or wedelolactone, and in experimental murine OA models by intraarticular injection of wedelolactone. RESULTS: Stimulated chondrocytes exhibited a significant elevation in the expression of chondrocyte catabolic factors. Consistent with these results, RNA-sequencing analyses of stimulated chondrocytes indicated that up-regulated genes were mainly categorized into apoptotic process and tumor necrosis factor signaling pathways, which suggests the induction of apoptotic process. Moreover, these chondrocytes exhibited a significant elevation in the expression of pyroptosis-related molecules that were correlated with the expression of chondrocyte catabolic factors. The disruption of caspase 11 significantly alleviated pyroptotic and catabolic processes in stimulated chondrocytes and pathologic changes in collagenase-induced and joint instability-induced OA models. CONCLUSION: Our results provide new insight into the pathologic mechanisms of OA and suggest that noncanonical pyroptosis in chondrocytes represents an attractive therapeutic target for treatment.

Low-Grade Inflammation in the Pathogenesis of Osteoarthritis: Cellular and Molecular Mechanisms and Strategies for Future Therapeutic Intervention.

Osteoarthritis (OA) is a musculoskeletal disease characterized by cartilage degeneration and stiffness, with chronic pain in the affected joint. It has been proposed that OA progression is associated with the development of low-grade inflammation (LGI) in the joint. In support of this principle, LGI is now recognized as the major contributor to the pathogenesis of obesity, aging, and metabolic syndromes, which have been documented as among the most significant risk factors for developing OA. These discoveries have led to a new definition of the disease, and OA has recently been recognized as a low-grade inflammatory disease of the joint. Damage-associated molecular patterns (DAMPs)/alarmin molecules, the major cellular components that facilitate the interplay between cells in the cartilage and synovium, activate various molecular pathways involved in the initiation and maintenance of LGI in the joint, which, in turn, drives OA progression. A better understanding of the pathological mechanisms initiated by LGI in the joint represents a decisive step toward discovering therapeutic strategies for the treatment of OA. Recent findings and discoveries regarding the involvement of LGI mediated by DAMPs in OA pathogenesis are discussed. Modulating communication between cells in the joint to decrease inflammation represents an attractive approach for the treatment of OA.

Evaluation of biological responses to micro-particles derived from a double network hydrogel.

Double network hydrogels (DN gels) composed of poly (2-acrylamido-2-methyl propanesulfonic acid) (PAMPS) as the brittle first network and poly (N,N-dimethylacrylamide) (PDMA) as the ductile second network have been proven to be a substitute biomaterial for cartilage, with promising biocompatibility and low toxicity, when they are used as bulk materials. For their further applications as articular cartilages, it is essential to understand the biological reactions and adverse events that might be initiated by wear particles derived from these materials. In this study, we used DN gel micro-particles of sizes 4 µm and 10 µm generated by the grinding method to mimic wearing debris of DN gels. The biological responses to particles were then evaluated in a macrophage-cultured system and an inflammatory osteolysis murine model. Our results demonstrated that DN gel particles have the ability to activate macrophages and promote the expression of Tnf-α, both in vitro and in vivo. Furthermore, the implantation of these particles onto calvarial bone triggered local inflammation and bone loss in a mouse model. Our data reveal that the potential foreign body responses to the generated particles from artificial cartilage should receive more attention in artificial cartilage engineering with the goal of developing a safer biocompatible substitute.

Determination of optimal concentration of vitamin E in polyethylene liners for producing minimal biological response to prosthetic wear debris.

The introduction of vitamin E-blended ultra-high molecular weight polyethylene (VE-UHMWPE) for use in prosthetic components of hip implants has resulted in the production of implants that have excellent mechanical properties and substantially less adverse cellular responses. Given the importance of a biological response to wear in the survival of a prosthesis, we generated wear debris from UHMWPE that had been prepared with different concentrations of vitamin E of 0.1, 0.3, 0.5, and 1% and evaluated their biological reaction in vitro and in vivo. All types of VE-UHMWPE debris promoted a significantly lower expression of Tnf-α in murine peritoneal macrophages than that induced by conventional UHMWPE debris. However, levels of Tnf-α were not significantly different among the macrophages that were stimulated with VE-UHMWPE wear at the concentrations tested. The ability of wear debris to induce inflammatory osteolysis was assessed in a mouse calvarial osteolysis model. The expressions of Tnf-α, Il-6, and Rankl in granulomatous tissue formed around the wear debris were significantly reduced in mice that had been implanted with 0.3%VE-UHMWPE debris as compared to the corresponding values for mice that had been implanted with UHMWPE debris. Consistent with this finding, 0.3%VE-UHMWPE debris showed the lowest osteolytic activity, as evidenced by the reduced bone resorption area, the degree of infiltration of inflammatory cells and the TRAP staining area. Our results suggested that a 0.3% vitamin E concentration is the most appropriate concentration for use in prosthetic components with a reduced adverse cellular response for prolonging the life-span of the implant.

Inhibitory role of Annexin A1 in pathological bone resorption and therapeutic implications in periprosthetic osteolysis.

There is currently no therapy available for periprosthetic osteolysis, the most common cause of arthroplasty failure. Here, the role of AnxA1 in periprosthetic osteolysis and potential therapeutics were investigated. Reducing the expression of AnxA1 in calvarial tissue was found to be associated with increased osteolytic lesions and the osteolytic lesions induced by debris implantation were more severe in AnxA1-defecient mice than in wild-type mice. AnxA1 inhibits the differentiation of osteoclasts through suppressing NFκB signaling and promoting the PPAR-γ pathway. Administration of N-terminal-AnxA1 (Ac2-26 peptide) onto calvariae significantly reduced osteolytic lesions triggered by wear debris. These therapeutic effects were abrogated in mice that had received the PPAR-γ antagonist, suggesting that the AnxA1/PPAR-γ axis has an inhibitory role in osteolysis. The administration of Ac2-26 suppressed osteolysis induced by TNF-α and RANKL injections in mice. These findings indicate that AnxA1 is a potential therapeutic agent for the treatment of periprosthetic osteolysis.

Targeting thymidine phosphorylase as a potential therapy for bone loss associated with periprosthetic osteolysis.

Macrophages are generally thought to play a key role in the pathogenesis of aseptic loosening through initiating periprosthetic inflammation and pathological bone resorption. The aim of this study was to identify macrophage-derived factors that promote osteoclast differentiation and periprosthetic bone destruction. To achieve this, we examined the effects of 12 macrophage-derived factors that were identified by RNA-seq analysis of stimulated macrophages on osteoclast differentiation. Surprisingly, thymidine phosphorylase (TYMP) was found to trigger significant number of osteoclasts that exhibited resorbing activities on dentine slices. Functionally, TYMP knockdown reduced the number of osteoclasts in macrophages that had been stimulated with polyethylene debris. TYMP were detected in serum and synovial tissues of patients that had been diagnosed with aseptic loosening. Moreover, the administration of TYMP onto calvariae of mice induced pathological bone resorption that was accompanied by an excessive infiltration of inflammatory cells and osteoclasts. The RNA-seq for TYMP-induced-osteoclasts was then performed in an effort to understand action mode of TYMP. TYMP stimulation appeared to activate the tyrosine kinase FYN signaling associated with osteoclast formation. Oral administration of saracatinib, a FYN kinase inhibitor, significantly suppressed formation of bone osteolytic lesions in a polyethylene debris-induced osteolysis model. Our findings highlight a novel molecular target for therapeutic intervention in periprosthetic osteolysis.

Flightless I is a catabolic factor of chondrocytes that promotes hypertrophy and cartilage degeneration in osteoarthritis.

Synovial macrophages that are activated by cartilage fragments initiate synovitis, a condition that promotes hypertrophic changes in chondrocytes leading to cartilage degeneration in OA. In this study, we analyzed the molecular response of chondrocytes under condition of this type of stimulation to identify a molecular therapeutic target. Stimulated macrophages promoted hypertrophic changes in chondrocytes resulting in production of matrix-degrading enzymes of cartilage. Among the top-upregulated genes, FliI was found to be released from activated chondrocytes and exerted autocrine/paracrine effects on chondrocytes leading to an increase in expression of catabolic and hypertrophic factors. Silencing FliI in stimulated cells significantly reduced expression of catabolic and hypertrophic factors in cocultured chondrocytes. Our further results demonstrated that the FliI-TLR4-ERK1/2 axis is involved in the hypertrophic signaling of chondrocytes and catabolism of cartilage. Our findings provide a new insight into the pathogenesis of OA and identify a potentially new molecular target for diagnostics and therapeutics.

Cardiotrophin Like Cytokine Factor 1 (CLCF1) alleviates bone loss in osteoporosis mouse models by suppressing osteoclast differentiation through activating interferon signaling and repressing the nuclear factor-κB signaling pathway.

A growing body of evidence suggests that immune factors that regulate osteoclast differentiation and bone resorption might be promising therapeutic agents for the treatment of osteoporosis. The expression of CLCF1, an immune cell-derived molecule, has been reported to be reduced in patients with postmenopausal osteoporosis. This suggests that it may be involved in bone remodeling. Thus, we explored the functional role of CLCF1 in osteoclastogenesis and bone loss associated with osteoporosis. Surprisingly, the administration of recombinant CLCF1 repressed excessive bone loss in ovariectomized mice and prevented RANKL-induced bone loss in calvarial mouse model. Likewise, the addition of recombinant CLCF1 to RANKL-stimulated monocytes resulted in a significant suppression in the number of differentiated osteoclasts with small resorption areas being observed on dentine slices in vitro. At the same dosage, CLCF1 did not exhibit any detectable negative effects on the differentiation of osteoblasts. Mechanistically, the inhibition of osteoclast differentiation by the CLCF1 treatment appears to be related to the activation of interferon signaling (IFN) and the suppression of the NF-κB signaling pathway. Interestingly, the expression of the main components of IFN-signaling namely, STAT1 and IRF1, was detected in macrophages as early as 1 h after stimulation with CLCF1. Consistent with these results, the blockade of STAT1 in macrophages abolished the inhibitory effect of CLCF1 on osteoclast differentiation in vitro. These collective findings point to a novel immunoregulatory function of CLCF1 in bone remodeling and highlight it as a potentially useful therapeutic agent for the treatment of osteoporosis.

Transcriptional profiling of murine macrophages stimulated with cartilage fragments revealed a strategy for treatment of progressive osteoarthritis.

Accumulating evidence suggests that synovitis is associated with osteoarthritic process. Macrophages play principal role in development of synovitis. Our earlier study suggests that interaction between cartilage fragments and macrophages exacerbates osteoarthritic process. However, molecular mechanisms by which cartilage fragments trigger cellular responses remain to be investigated. Therefore, the current study aims at analyzing molecular response of macrophages to cartilage fragments. To this end, we analyzed the transcriptional profiling of murine macrophages exposed to cartilage fragments by RNA sequencing. A total 153 genes were differentially upregulated, and 105 genes were down-regulated in response to cartilage fragments. Bioinformatic analysis revealed that the most significantly enriched terms of the upregulated genes included scavenger receptor activity, integrin binding activity, TNF signaling, and toll-like receptor signaling. To further confirm our results, immunohistochemical staining was performed to detected regulated molecules in synovial tissues of OA patients. In consistence with RNA-seq results, MARCO, TLR2 and ITGα5 were mainly detected in the intima lining layer of synovial tissues. Moreover, blockade of TLR2 or ITGα5 but not Marco using specific antibody significantly reduced production of TNF-α in stimulated macrophages by cartilage fragments. Our data suggested that blocking TLR2 or ITGα5 might be promising therapeutic strategy for treating progressive osteoarthritis.

Blockade of XCL1/Lymphotactin Ameliorates Severity of Periprosthetic Osteolysis Triggered by Polyethylene-Particles.

Periprosthetic osteolysis induced by orthopedic implant-wear particles continues to be the leading cause of arthroplasty failure in majority of patients. Release of the wear debris results in a chronic local inflammatory response typified by the recruitment of immune cells, including macrophages. The cellular mediators derived from activated macrophages favor the osteoclast-bone resorbing activity resulting in bone loss at the site of implant and loosening of the prosthetic components. Emerging evidence suggests that chemokines and their receptors are involved in the progression of periprosthetic osteolysis associated with aseptic implant loosening. In the current study, we investigated the potential role of chemokine C-motif-ligand-1 (XCL1) in the pathogenesis of inflammatory osteolysis induced by wear particles. Expressions of XCL1 and its receptor XCR1 were evident in synovial fluids and tissues surrounding hip-implants of patients undergoing revision total hip arthroplasty. Furthermore, murine calvarial osteolysis model induced by ultra-high molecular weight polyethylene (UHMWPE) particles was used to study the role of XCL1 in the development of inflammatory osteolysis. Mice received single injection of recombinant XCL1 onto the calvariae after implantation of particles exhibited significantly greater osteolytic lesions than the control mice. In contrast, blockade of XCL1 by neutralizing antibody significantly reduced bone erosion and the number of bone-resorbing mature osteoclasts induced by UHMWPE particles. In consistence with the results, transplantation of XCL1-soaked sponge onto calvariae caused osteolytic lesions coincident with excessive infiltration of inflammatory cells and osteoclasts. These results suggested that XCL1 might be involved in the development of periprosthetic osteolysis through promoting infiltration of inflammatory cells and bone resorbing-osteoclasts. Our further results demonstrated that supplementing recombinant XCL1 to cultured human monocytes stimulated with the receptor activator of nuclear factor kappa-B ligand (RANKL) promoted osteoclastogenesis and the osteoclast-bone resorbing activity. Moreover, recombinant XCL1 promoted the expression of inflammatory and osteoclastogenic factors, including IL-6, IL-8, and RANKL in human differentiated osteoblasts. Together, these results suggested the potential role of XCL1 in the pathogenesis of periprosthetic osteolysis and aseptic loosening. Our data broaden knowledge of the pathogenesis of aseptic prosthesis loosening and highlight a novel molecular target for therapeutic intervention.

Identification of IL-27 as potent regulator of inflammatory osteolysis associated with vitamin E-blended ultra-high molecular weight polyethylene debris of orthopedic implants.

Vitamin E-blended ultra-high molecular weight polyethylene (VE-UHMWPE) is a newly introduced material for prosthetic components that has proven a better mechanical performance with lesser adverse cellular responses than conventional polyethylene in experimental animal models. However, the mechanisms by which VE-UHMWPE particles trigger a reduced osteolytic activity are unclear and remain to be investigated. Therefore, the current study aims at exploring a possible anti-osteolytic mechanism associated with VE-UHMWPE particles. Transcriptional profiling and bioinformatic analyses of human macrophages stimulated by VE-UHMWPE particles revealed a distinct transcriptional program from macrophages stimulated with UHMWPE particles. Out of the up-regulated genes, IL-27 was found to be significantly elevated in macrophages cultured with VE-UHMWPE particles as compared to these with UHMWPE particles (p = 0.0084). Furthermore, we studied the potential anti-osteolytic function of IL-27 in osteolysis murine model. Interestingly, administration of recombinant IL-27 onto calvariae significantly alleviated osteolytic lesions triggered by UHMWPE particles (p = 0.0002). Likewise, IL-27 inhibited differentiation of osteoclasts (p = 0.0116) and reduced inflammatory response (p < 0.0001) elicited by conventional UHMWPE particles in vitro. This is the first study demonstrating the involvement of IL-27 in macrophage response to VE-UHMWPE particles and its regulatory role in osteolysis. Our data highlight a novel therapeutic agent for treatment of inflammatory osteolysis induced by polyethylene debris. STATEMENT OF SIGNIFICANCE: Aseptic loosening due to inflammatory osteolysis remains the major cause of arthroplasty failure and represents a substantial economic burden worldwide. Ideal approach to prevent this failure should be directed to minimize inflammatory response triggered by wear particles at the site of implant. Understanding the mechanism by which VE-UHMWPE particles triggers lesser cellular responses and reduced osteolysis as compared to conventional UHMWPE particles may aid in discovery of regulatory factors. In the current study, we reported that IL-27 is a potent regulator of inflammatory osteolysis involved in the reduced biologic activities and osteolytic potentials associated with VE-UHMWPE particles. Initiating the production IL-27 in vivo after total joint arthroplasties might be a novel strategy to prolong the life-spam of implant.

Failed Reconstruction of the Extensor Pollicis Longus in a Patient with a Major Variation of the Extensor Indicis Proprius Tendon: A Case Report.

Tendon transfer with extensor indicis proprius (EIP) has been performed widely for reconstructing ruptures of the extensor pollicis longus because of its simplicity and clinical outcome. We experienced a rerupture of the extensor pollicis longus restored by incorrect tendon transfer because of a major unrecognized variation in the anatomy of the EIP. Surgeons should perform such transfer with a detailed knowledge of the possible anatomical variations to avoid such serious complications.