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An ongoing rotating detonation rocket engine program is investigating the influence of combustor annulus radii on RDRE operating characteristics with flat-faced impinging injectors. To facilitate the isolation of all but the radius of curvature effects in the experiments, the annular gap was kept constant at 5 mm in combustors having either 25-mm or 51-mm outer diameter. The mixing processes were kept similar by utilizing injectors with the same net injector-to-annular gap area ratio (AR = 0.11), same radial separation distance of the orifices, and same center-of-gap impingement distance from the front-end wall. The wave dynamics, plenum pressure, and axial pressure profiles in these RDREs were compared over the mass flux and equivalence ratio ranges of 80 - 400 kg/s/m 2 and 0.26 - 2.6, respectively, with gaseous methane–oxygen propellant. Experiments showed that stable one-wave operation would occur in the 25-mm RDRE at most mass fluxes where stable two-wave operation was established in the 51-mm RDRE. Stable one-wave operation with a single counter-rotating wave was maintained in the 51-mm RDRE at mass fluxes of 240 kg/s/m 2 and below. Under these fueling conditions in the 25-mm RDRE, a counter-rotating wave also appeared while it operated with a single dominant wave. The wave spin speeds were typically 20–40% less than the Chapman–Jouguet detonation speed of the propellant and depended only on mass flux and wave number rather than the annulus diameter. [ABSTRACT FROM AUTHOR]

Purpose: Ligaments are frequently damaged in sports activities and trauma, and severe ligament injury can lead to joint instability and osteoarthritis. In this study, we aimed to regenerate the medial collateral ligament (MCL) using an absorbable stent-shaped poly-L-lactic acid (PLLA) scaffold in a rabbit model to examine the biocompatibility and mechanical properties.Methods: Twenty-three Japanese white rabbits were used in this study. MCL defects were surgically created in the knee joints and then reconstructed using stent-shaped PLLA scaffolds. As controls, flexor digitorum longus (FDL) tendons were implanted into the contralateral knees. Seven rabbits were sacrificed at three time points, conducted four, eight and 16 weeks after the operation. The regenerated tissues were histologically evaluated using fibre alignment scoring, morphology of fibroblast scoring and immunohistochemical analysis of types I and III collagen. The regenerated tissues were also biomechanically evaluated by measuring the ultimate failure load and stiffness.Results: At four weeks post-operation, spindle-shaped cells were observed on the inside of the scaffolds. At eight weeks, maturation of the regenerated tissues and collagen fibre alignment parallel to the ligaments was observed. At 16 weeks, the fibre alignment had become denser. The fibre alignment and morphology of fibroblast scores significantly increased in a time-dependent manner. Expression of type I collagen was more strongly observed in the scaffold group at eight and 16 weeks post-operation than at four weeks. Type III collagen was also observed at four, eight and 16 weeks post-operation. A thin layer of fibrocartilage was observed at the ligament-bone junction at eight and 16 weeks. The ultimate failure load of the scaffold group was 46.7 ± 20.7 N, 66.5 ± 11.0 N and 74.3 ± 11.5 N at four, eight and 16 weeks post-operation, respectively. There was no statistical difference between the normal MCL and the scaffold group at 16 weeks post-operation.Conclusions: The stent-shaped PLLA scaffold allowed for MCL regeneration with type I collagen expression and fibrocartilage formation and resulted in sufficient mechanical function. [ABSTRACT FROM AUTHOR]

Purpose: ADVANCE Medial-Pivot (MP) (Wright Medical Technology, Arlington, TN, USA) total knee arthroplasty (TKA) was developed to replicate normal tibiofemoral knee joint kinematics, allowing medial-pivot knee motion. The design concept of the prosthesis is unique; therefore, the influence on the patellofemoral knee joint remains unclear at present. The purpose of this study was to determine the in vivo patellofemoral kinematics with ADVANCE MP TKA and compare them with the pre-operative conditions.Methods: ADVANCE MP TKA was performed in ten subjects with osteoarthritis (OA). At before and one month after surgery, lateral radiographs with weight-bearing at maximum extension, 30, 60 and 90° were taken, and patella flexion angle (PF), tibiopatellar angle (TP) and estimated patellofemoral contact point (PC) were evaluated, according to a previously reported method.Results: In PF and TP, there was no statistically significant change between pre-operative and postoperative values. Pre-operative PC reached its peak at 90°; however, its peak was at 60° at one month after surgery. Postoperative PC at maximum extension was significantly higher compared to before surgery.Conclusions: The results in this study indicated that ADVANCE MP TKA changed patellofemoral joint kinematics compared to before surgery. Early postoperative evaluation is the limitation of this study; however, we consider that the results in this study might be one of the keys to resolving the kinematic features of this prosthesis, helping clinicians to comprehend this prosthesis. [ABSTRACT FROM AUTHOR]

Purpose: A procedure using an interspinous process spacer (IPS) was recently developed for the treatment of posture-dependent lumbar spinal-canal stenosis (LSS) patients. We developed a novel IPS which can be inserted with simpler procedures and removed percutaneously. The objectives of this study were: (1) to evaluate the feasibility and safety of this novel technique, and (2) to assess the effectiveness of this spacer in terms of preventing an increase of epidural pressure in lumbar extension using a porcine model.Methods: Eight young pigs were used. Under general anesthesia and image guidance, the spacers were inserted. Three months after operation, MR images were taken and all spacers were removed. Blood samples were obtained before and 1, 3, 7 days after surgery. After killing the animals, the lumbar spines were observed macroscopically. Another six animals were used. Under general anesthesia and image guidance, a flexible pressure transducer was inserted into the epidural space and epidural pressure was measured in neutral and at maximum extension with and without spacer insertion.Results: Percutaneous insertion and removal of the spacer was successful for all animals through small skin incisions. MR images showed minimal damage to the muscle. No significant up-regulation of Interleukin-6 (IL-6) and CRP was detected. Macroscopic observation of the lumbar spine 3 months after the operation revealed that the area of the interspinous process contacting with the inserted spacer showed some bone erosion/remodeling. Insertion of the spacer did not affect the epidural pressure in neutral but significantly prevented an increase of epidural pressure in lumber extension.Conclusions: This study demonstrated that the percutaneous insertion and removal of a novel IPS was feasible and safe using a simple technique. Furthermore, this procedure can be recognized as minimally invasive surgery from the viewpoint of skin incision, short insertion track, inflammatory mediators, and muscle damage. Improvements should be attempted in future studies using softer or more elastic materials for the spacer to lessen bone erosion/remodeling at contacting area of the inserted spacer. [ABSTRACT FROM AUTHOR]

Purpose: This is a randomised controlled trial to examine whether intra-articular injection of tranexamic acid (TXA) decreases blood loss, as well as reducing leg swelling after total knee arthroplasty (TKA).Methods: We performed 100 TKA in osteoarthritis patients. At closure, a total of 2,000 mg/20 ml TXA was injected into the knee joint through a closed suction drain (TXA group). For the control group, the same volume of physiological saline was injected. The pre-operative condition of the patients, post-operative haemoglobin (Hb) levels, discharge volumes from drain, D-dimer and needs for transfusion were compared between these two groups. Furthermore, leg diameters (thigh, suprapatellar portion and calf girth) were measured pre- and post-operatively to investigate whether TXA has an influence on leg swelling after surgery.Results: The results revealed that post-operative decrease in Hb level was significantly reduced in the TXA group. Furthermore, knee joint swelling after operation was significantly suppressed in the TXA group compared to the control group.Conclusions: The results revealed intra-articular administration of TXA decreased not only blood loss, but also knee joint swelling after TKA. [ABSTRACT FROM AUTHOR]

Only a few cases of double-layered meniscus have been described in the English literature. We report two cases of bilateral double-layered lateral meniscus, where an additional semicircular meniscus was observed over the normal lateral meniscus. One of the patients exhibited a bucket-handle tear with a double-layered meniscus. To our knowledge, this abnormality is extremely rare and the incidence of double layered meniscus with bucket-handle tear has not been previously reported. [ABSTRACT FROM AUTHOR]

Graft tunnel placement is the factor with most influence on the outcome of double-bundle anterior cruciate ligament (ACL) reconstruction. However the final decision for the graft location has to be decided subjectively under arthroscopy, and can be misplaced due to the effect of the knee flexion angle. The displacement of the estimated placement by surgeons from the ACL anatomical attachment is due to the knee's differing knee flexion angle. Eight cadaveric knees and an electromagnetic position recording system were employed. After digitizing the anatomical location of AM and PL bundle center, four experienced surgeons estimated the graft placement repeatedly at 70 degrees , 90 degrees and 110 degrees of knee flexion. The displacements between these two positions were calculated and analyzed separately in antero-posterior and disto-proximal directions. The displacements of the estimated AM bundle placements were 4.7 +/- 3.4 mm at 70 degrees , 4.3 +/- 2.2 mm at 90 degrees , and 6.0 +/- 2.6 mm at 110 degrees , while those of the PL bundle were 4.0 +/- 2.2 mm at 70 degrees , 3.4 +/- 1.9 mm at 90 degrees , and 4.2 +/- 2.5 mm at 110 degrees . The best results were obtained at 90 degrees of knee flexion. Additionally, the estimated placements for both AM and PL bundle were located more distally as the flexion angle increased. Our results imply that the knee should be set at 90 degrees when determining the graft placement in double-bundle reconstruction to prevent misplacement of the graft usually in a disto-proximal direction. [ABSTRACT FROM AUTHOR]

We have made three types of poly (DL-lactide-co-glycolide) (PLG) scaffolds (porosity: scaffold I 80 +/- 0.9%, II 85 +/- 0.8%, III 92 +/- 0.7%; compression module determined with 10% strain: scaffold I 0.26 MPa, II 0.091 MPa, III 0.0047 MPa). Osteochondral defects made in the femoral condyle of rabbits were treated with these scaffolds and the possibilities of cartilage repair were investigated histologically. At post-operative weeks 6 and 12, histological scores in the groups of scaffolds II and III were significantly higher than the score in the group of scaffold I. Scaffolds II and III, which have higher porosity than scaffold I, allow better migration of bone marrow cells and better replacement of the scaffold with bone and cartilage than scaffold I. This study suggests that higher porosity allowing bone marrow cells to migrate to the scaffold is important in repairing osteochondral defects. [ABSTRACT FROM AUTHOR]

RNA interference (RNAi) technology has recently emerged as an important biological strategy for gene silencing. Previously, the efficacies of RNAi in cultured nucleus pulposus cells in vitro have been reported. However, RNAi in the disc in vivo has never been reported. Therefore, the aims of the present study were to establish a method for RNAi in the disc in vivo and to evaluate the applicability of this technique for endogenous genes in the intervertebral discs using Fas Ligand (FasL) as a representative endogenous gene. To evaluate the efficacy of RNAi in vivo, two reporter luciferase plasmids (Firefly and Renilla) were used. These plasmids and unmodified short interference RNA (siRNA) duplex for targeting Firefly luciferase were co-transfected into coccygeal intervertebral disc of Sprague-Dawley rats in vivo using the ultrasound gene transfer technique. To evaluate the RNAi of the endogenous gene in vivo, siRNAs targeting rat FasL were transfected with the same technique. Non-specific siRNA was used as the negative control. The discs receiving no siRNAs were used as the control. The inhibitory effect of Firefly luciferase against Renilla luciferase was obtained using the results of dual-luciferase assay. Down-regulation of endogenous FasL was calculated by the data from real-time PCR. Our results showed that siRNA for Firefly luciferase can dramatically down-regulate the Firefly luciferase gene expression in vivo compared with Renilla luciferase. The inhibitory effects were maintained for at least 24 weeks and at 24 weeks post transfection, the inhibitory rate was 80% compared with the control group. Furthermore, the siRNA co-transfection group inhibited endogenous FasL expression by 53% compared with the control group. The present study demonstrates long-term down-regulation mediated by unmodified siRNA is possible not only for the exogenous reporter gene, but also for endogenous FasL expression in rat discs in vivo. This application of RNAi might be promising as a local therapy for disc degeneration and associated disorders by down-regulating some of the genes that are harmful for the normal physiology of the disc and may cause disc degeneration. [ABSTRACT FROM AUTHOR]

Disc degeneration is deeply associated with many spinal disorders and thus has a significant clinical impact on society. The currently available surgical treatment often necessitates removing a pathological disc and spinal fusion. However, it is also well known that these surgical treatments have many potential problems including invasion and cost. Therefore, biological approaches for regenerating these pathological discs have received much attention. Gene therapy is one of these biological approaches. Gene therapy involves the transfer of genes to cells so the recipient cells express these genes and thereby synthesize the RNA and protein they encode in a continuous fashion. One of the significant advantages of gene therapy is that we can expect a lasting duration of biological effect which is potentially beneficial for most disc degeneration associated disorders, as they are, by nature, chronic conditions. Originally, gene therapy was mediated by viral vectors, but recent technological progress has enabled us to opt for non-virus-mediated gene therapy for the disc. Furthermore, the development of the RNA interference technique has enabled us to down-regulate a specific gene expression in the disc opening the door for a new generation of intradiscal gene therapy. [ABSTRACT FROM AUTHOR]

The purpose of this study was to clarify the change in the cross-sectional area (CSA) of a patellar tendon graft after anterior cruciate ligament (ACL) reconstruction, and its relationship with postoperative knee laxity. Forty patients (25 men and 15 women) were included in this study. Intraoperative CSA measurements were performed with an instrumented areamicrometer, while a magnetic resonance imaging (MRI) evaluation was utilized for the assessment postoperatively. For intraoperative measurement, the average CSA of a 10-mm wide patellar tendon graft was 32.3 ± 7.0 mm2, while the average CSA measured at follow-up (mean: 14.8 months) was 48.8 mm2, showing a significant mean increase ratio of 49.4%. This value corresponded to 115% of the native ACL. The average CSA measured in 30 patients at 6 months was 49.7 mm2, almost equal to the value at the final follow-up (49.8 mm2) in the same patient group. Among potentially influential factors, postoperative notch width (available space for the ACL graft) had significant correlation with the CSA of the graft at follow-up. Finally, both intra- and postoperative CSA values did not correlate with postoperative knee laxity, indicating that a bigger graft does not guarantee a better laxity. [ABSTRACT FROM AUTHOR]

It was recently reported that plasma levels of adrenomedullin (AM), identified as a vasorelaxant peptide, are significantly higher in rheumatoid arthritis (RA) patients than in osteoarthritis (OA) patients. The objective of the present study was to elucidate AM production in synovial cells from patients with RA. Adrenomedullin mRNA was detected in cultured synovial cells from RA patients by reverse transcription polymerase chain reaction (RT-PCR). Immunohistochemical analysis demonstrated the presence of AM in synovial cells from RA patients. In addition, we investigated AM levels in knee joint fluids from RA and OA patients. Those from RA patients were elevated approximately threefold over those of OA patients. In this study, we demonstrated for the first time AM expression in synovial cells from RA patients and high levels of AM production in RA joint fluid. [ABSTRACT FROM AUTHOR]

: We present a case of tuberculous greater trochanteric bursitis occurring 51 years after tuberculous nephritis in a 71-year-old man. Radiographs of the affected hip revealed focal osteolysis of the greater trochanter and calcification in the surrounding soft tissues. Contrast-enhanced CT scans and MRI revealed that the enlarged bursa extended into the femoral intermuscular spaces. Bacterial culture of the biopsied bursa grew Mycobacterium tuberculosis. Total excision of the infected bursa, combined with antituberculous therapy, was curative. Tuberculosis of the greater trochanteric bursa should be included in the differential diagnosis of chronic hip pain. New tuberculous musculoskeletal lesions can occur elsewhere in the body many years after primary tuberculous lesions have healed. [ABSTRACT FROM AUTHOR]

Objective: To evaluate the ability of contrast-enhanced three-dimensional (3D) helical computed tomography (CT) to image soft tissue tumors in the extremities.Design and Patients: Forty-five consecutive patients with soft tissue tumors in the extremities were examined (mean age 46.2 years; 24 females, 21 males). Twenty-five patients had benign lesions and 20 had malignant lesions. All the patients underwent contrast-enhanced 3DCT scanning and magnetic resonance (MR) imaging preoperatively. All patients were surgically treated. Spiral CT scanning was performed with intravenous contrast enhancement. 3D reconstruction images were produced after thresholding, using Active-Windows (version 2.0, General Electric, Milwaukee, WI) software. 3DCT findings were compared in a masked fashion with the MR imaging and surgical findings regarding bone and major vessel invasion by the tumors.Results: Forty-four of 45 tumors were satisfactorily imaged for the interpretation of their size, location and relationship to the skeleton and major vessels. One malignant tumor was judged on 3DCT to invade the major vessel, but the vessel proved to be normal at surgery.Conclusions: Contrast-enhanced 3D helical CT can be used for the evaluation of soft tissue tumors in the extremities, for preoperative surgical planning. [ABSTRACT FROM AUTHOR]

Two cases of malignant lesions are reported, both of which arose secondary to an originally benign giant cell tumor (GCT) of bone. The first case was a typical benign GCT, which occurred in the left proximal tibia of a 31-year-old woman. The tumor was treated by curettage and bone grafting. However, it recurred twice during 15 years of follow-up. The second recurrence showed that the lesion histologically had turned into malignant fibrous histiocytoma. The second case also started as an initially benign GCT that arose in the left distal femur of a 41-year-old man. The patient underwent curettage and bone grafting. The lesion recurred 13 years postoperatively. The histological appearance of the recurrent tumor showed it to be an osteogenic sarcoma. In both patients, radiation and never been given. Malignant transformation has rarely been reported in patients with GCT of bone who have not received radiation treatment. [ABSTRACT FROM AUTHOR]

Copyright of International Orthopaedics is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of International Orthopaedics is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study was designed to examine localization of the growth factors in the autogenous patellar tendon graft used to reconstruct the anterior cruciate ligament (ACL) in the canine model. Among the various growth factors, basic fibroblast growth factor, transforming growth factor-beta1, and platelet-derived growth factor were selected for analysis as potential factors that regulate graft remodeling processes. In the control patellar tendon and the ACL only basic fibroblast growth factor was positively stained. In the reconstructed graft increased levels of staining for all the three factors were observed in the early postoperative period, reaching the greatest expression 3 weeks after implantation. Thereafter immunoreactivity of these growth factors decreased and returned to the preoperative levels, which were similar to that of the control ACL 12 weeks postoperatively. This rapid reduction in the level of their localization indicates that once the extrinsic cells are infiltrated to the graft and revascularization completed, these growth factors may have less significance for subsequent remodeling. [ABSTRACT FROM AUTHOR]

Copyright of International Orthopaedics is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The purpose of this study was to analyze the validity of the newly designed functional ability test (FAT) for the normal population and patients with deficiency of the anterior cruciate ligament (ACL). The FAT consists of four tests: the figure-of-eight hop, the up-down hop, the side hop, and the single hop. Sixty control subjects and 50 patients with unilateral ACL deficiency were tested. In the control group, the values measured were significantly different between males and females in all of the tests. On the other hand, when left/right difference values were compared, no significant difference was found between males and females in any of the tests. More than 95% of control group exhibited symmetrical function in each part of the FAT, whereas in the ACL-deficient group, the percentage of patients who showed abnormal symmetry was 68% in the figure-of-eight hop, 58% in the up-down hop, 44% in the side hop, and 42% in the single hop. The percentage of ACL-deficient patients with functional asymmetry in at least one of the four tests was 82%. The FAT was found to be useful in evaluating lower limb function in ACL-deficient patients. [ABSTRACT FROM AUTHOR]

The effect of basic fibroblast growth factor (bFGF) on the healing of partial anterior cruciate ligament (ACL) lacerations was investigated in 17 adult mongrel canines. The defect was created in the midsubstance of both ACLs using a biopsy punch. In the bFGF group, a bFGF-impregnated pellet was sutured to the infrapatellar fat pad close to the defect. In the control group, the same pellet without bFGF was used. The healing process was evaluated macroscopically and histologically at 1, 3, 6, and 24 weeks postoperatively. In the bFGF group, a pannus-like tissue which contained abundant blood vessels extended into the defect from the adjacent synovial tissue in the early postoperative phase. Histological examination of the tissue which filled the defect revealed initial remodeling processes with a decreased number of cells and better orientation of the collagen fibers at 6-24 weeks. On the other hand, in the control group, poor healing processes were observed at each examination period. This study demonstrated that the application of a bFGF-impregnated pellet may enhance the healing potential of a partially injured ACL. Enhanced neovascularization and the formation of granulation tissue induced by bFGF early in the healing process accounted for the increased healing response. [ABSTRACT FROM AUTHOR]

Twentyfour meniscal allotransplantations were conducted in 12 adult mongrel dogs. The medial meniscus was replaced using a deep-frozen meniscal allograft. The junction between the meniscus and capsule was treated in one of the three ways. In the control group, the meniscus was sutured only to the adjacent capsular tissue (group C). In the second group, fibrin glue was injected at the junction (group F), and in the third group, fibrin glue and endothelial cell growth factor (ECGF) were injected at the juncture between the transplanted meniscus and the adjacent capsule before the meniscus was sutured (group FE). Histological observation was performed to investigate the effect of fibrin glue and ECGF on the healing process of transplants at various intervals of 1, 4, 8 and 12 weeks. No immunological response was noted in any of the knees. The healing of the transplanted meniscus was first observed at the peripheral attachment. Also, the pannus-like tissue extended from the synovium to the surface of the meniscus. The healing rate in each group at 1 week and 12 weeks was 22% and 77% in group C, 52% and 80% in group F, and 64% and 80% in group FE, respectively. At 4 and 8 weeks, early cellular repopulation was found in group FE and the area which contained new cells was larger than the acellular central core at 8 weeks. However, there was no difference among the three groups at 12 weeks.(ABSTRACT TRUNCATED AT 250 WORDS) [ABSTRACT FROM AUTHOR]

Microfibrillar collagen hemostat (Avitene) is an absorbable topical hemostatic agent prepared from purified bovine corium collagen. A 65-year-old woman presented with left buttock and lower extremity radicular pain. The patient underwent a disc excision in which Avitene was used to control venous bleeding from the epidural space. Leg pain decreased postoperatively, but she developed radicular pain when she started walking 3 days after the operation. Magnetic resonance imaging (MRI) performed post-operatively showed there was a mass lesion located between the dural sac and L5 nerve root. The lesion exhibited high signal intensity on T1-weighted images and higher signal intensity at the rim of the mass on T2-weighted images. A second operation performed 10 days later revealed that the nerve root was adherent to an extradural granulomatous mass associated with Avitene. Macroscopically, the resected mass was found to be composed mainly of microfibrillar collagen hemostat materials. Hemostat agents may produce a clinically symptomatic, radiologically apparent mass lesion. When considering a mass lesion arising after spine surgery, the differential diagnosis should include foreign body granuloma along with recurrent disc herniation and peridural scar formation. [ABSTRACT FROM AUTHOR]

The authors describe the MR features of a case of microgeodic phalangeal syndrome in a 9-year-old boy. Roentgenograms showed multiple small areas of osteolysis in the middle phalanx of the right index finger. T1-weighted MR images showed lesions with diffuse low signal intensity not only in this phalanx but also in other phalanges. These lesions exhibited high signal intensity on T2-weighted images. Contrast-enhanced T1-weighted images showed a wide non-enhancing area in the middle phalanx of the index finger. [ABSTRACT FROM AUTHOR]

We report on a rare case of an intraosseous hemangioma involving the proximal tibia in a 70-year-old man. Radiographically, the lesion was a well-defined osteolytic lesion with marginal sclerosis. The CT images demonstrated a well-defined osteolytic lesion with partial cortical breakthrough. T1-weighted MR images showed a hypointense lesion, while T2-weighted images revealed hyperintense areas, with internal, hypointense septa. Gadolinium-enhanced T1-weighted images showed lattice-like enhancement of the lesion. [ABSTRACT FROM AUTHOR]

Melanoma is an interesting tumor, showing the appearance of metastasis without any trace of its primary lesion. To report a very rare case of malignant melanoma in the sacrum with unknown primary origin. The authors present a case of a 52-year-old man who was admitted with increasing lower back, left buttock, and left lower extremity pain, and dysuria. Plain radiograph, computed tomography scan, and magnetic resonance imaging revealed a destructive lesion in the sacrum and left ilium, which infiltrated the spinal canal and sacroiliac joint. The tumor cells were immunoreactive for HMB-45. The pathological diagnosis was malignant melanoma. No obvious primary malignant melanoma was detected on the skin surface, on the oral or anal mucosa, or in the fundus oculi. Following radiotherapy and chemotherapy, the severe buttock pain disappeared and the patient was able to walk without impediment. However the patient died nine months after initial diagnosis. Malignant melanoma in the sacrum with an unknown primary site, showing S1 radiculopathy is reported for the first time. The melanoma could have been a metastatic tumor of the sacrum, although the primary site was not detected. The incidence of primary melanoma is increasing faster than any other cancer. Thus treatment of patients with spinal metastasis of melanoma is an important challenge for orthopedic surgeons. [ABSTRACT FROM AUTHOR]