A simple bone cyst (SBC) is a benign bone lesion of unknown etiology. It can be differentiated from an aneurysmal bone cyst (ABC) by radiologic and histopathologic features, as well as by the absence of fusions of the USP6 gene characteristic of an ABC. In an attempt to differentiate between ABC and SBC in a recurrent bone cyst, we performed targeted RNA sequencing and found an EWSR1-NFATC2 fusion and no fusion of the USP6 gene. We subsequently analyzed additional 10 cysts, consistent with SBCs after radiologic-pathologic correlation, for the presence of an NFATC2 gene fusion, by targeted RNA sequencing, reverse-transcription polymerase chain reaction (RT-PCR) and Sanger sequencing, and fluorescent in situ hybridization. Targeted RNA sequencing showed a FUS-NFATC2 fusion in 4 of 11 SBCs and an EWSR1-NFATC2 fusion in 2 of 11 SBCs. No fusion was identified in 3 SBCs and the analysis was not successful in 2 SBCs because of the low quantity or poor quality of isolated RNA. All the 6 fusions detected by targeted RNA sequencing were confirmed by RT-PCR and Sanger sequencing, and 5 of the 6 fusions by fluorescent in situ hybridization. An additional FUS-NFATC2 fusion was identified by RT-PCR, Sanger sequencing, and fluorescent in situ hybridization in 1 of the 3 cases negative for fusions by targeted RNA sequencing. At least a large subset of SBCs represents cystic neoplasms characterized by FUS-NFATC2 or EWSR1-NFATC2 fusions, which also define a group of distinct, rare “Ewing-like” sarcomas that predominantly arise in long bones. Our results provide additional evidence of the existence of benign lesions with FUS-NFATC2 or EWSR1-NFATC2 fusions. Although they can recur locally in a nondestructive manner, their clinical course and possible relation to sarcoma with EWSR1-NFATC2 or FUS-NFATC2 fusion remains to be elucidated.
Compressive stiffness and intradiscal pressure increase with the percentage of cement fill. Fifteen per cent of cement fill was the limit beyond which no substantial increase in compressive stiffness or intradiscal pressure could be detected and is the minimum volume of cement we recommend for vertebroplasty. In the average thoracolumbar vertebra this means 4-6 ml of cement.
Seven different autologous chondrocyte implantation (ACI) grafts were used consecutively over a period of 18 years for the treatment of cartilage lesions in the knees. The aim was to evaluate this entire ACI patient series for graft-related or unrelated serious adverse events (SAE), graft failures, and to reveal potential risk factors for these incidents. The study group comprised 151 operated patients: classical periosteum-ACI (n = 45); ACI-seeded fibrin-collagen patch, fixed by either periosteum (n = 59), collagen membrane (n = 15), or fibrin glue (n = 6); ACI seeded alginate-agarose hydrogel (n = 14); and biomimetic collagen-hydroxyapatite scaffold injected with the ACI suspension (n = 12). The covariates analyzed as possible predicting factors were: age, gender, BMI, lesion depth, lesion size, lesion location, previous surgeries, and concomitant procedures. The Kaplan–Meier method for estimating survival curves, and Cox’s proportional hazards model to test for covariates, were used in the statistical analysis. The patients in this series, follow-up 10.1 (2.1–18.3) years, encountered 11% of graft-related SAE (risk factors: previous cartilage surgery, age over 40 years, BMI over 25 kg/m2, and meniscus surgery) and 10% of graft unrelated SAE (risk factors: meniscus surgery and osteotomy). None of these factors was a risk for definitive graft failure. The 10-year graft survival rate was 86%. Females had 2.8 times higher incidence of graft failures than males. There was a tendency toward higher graft failures after a previous cartilage surgery. Different ACI graft types offered safe and durable cartilage repair. Female gender, age over 40 years, increased weight, previous cartilage surgery, and meniscus loss showed increased risk for revision surgery or graft failures.
Aneurysmal bone cyst (ABC) is a benign but locally aggressive neoplasm, with a tendency for local recurrence. In contrast to other bone tumors with secondary cystic change, ABC is characterized by USP6 gene rearrangement. There is a growing list of known USP6 fusion partners, characterization of which has been enabled with the advent of next‐generation sequencing (NGS). The list of known fusion partners includes CDH11, CNBP, COL1A1, CTNNB1, EIF1, FOSL2, OMD, PAFAH1B1, RUNX2, SEC31A, SPARC, STAT3, THRAP3, and USP9X. Using NGS, we analyzed a series of 11 consecutive ABCs and identified USP6 fusions in all cases, providing further evidence that USP6 fusions are universally present in primary ABCs. We identified four novel fusion partners in five ABCs and confirmed them by RT‐PCR and Sanger sequencing, ASAP1, FAT1, SAR1A, and TNC (in two cases). Because of high sensitivity and specificity, detection of a USP6 fusion by NGS may assist in differentiating between ABC and its mimics, especially in small biopsy samples when a definite diagnosis cannot be achieved on morphological grounds alone. Further studies with a large number of cases and follow‐up are needed to determine whether different fusion partners are associated with specific clinical and pathologic features of ABCs.
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