In this retrospective study we aimed to analyse the risk factors for complications after different methods of distal interphalangeal arthrodesis in the hand. Forty-four per cent were treated with K-wire/cerclage fixation, 46% with X-fuse® implants (Stryker GmbH, Selzach, Switzerland) and 10% with headless compression screws (HBS®-screw, KLS Martin Group, Tuttlingen, Germany). The median follow-up was 16 weeks (range 6–224). The overall complication incidence was 44% (minor complications 29% and major 15%). The logistic regression showed that osteoarthritis, revisional arthrodesis and smoking had a negative impact on the total complication incidence. A Cox-regression analysis showed that HBS®-screw arthrodesis was associated with a significantly lower incidence of major complications compared with K-wire/cerclage and X-Fuse®-arthrodesis. Revisional arthrodesis was five times more frequently connected with major complications than primary surgery. Smokers were three times more likely to experience major complications than non-smokers. We conclude that arthrodesis of the distal interphalangeal joint often leads to complications. Risk factors must be kept in mind. Level of evidence: III

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Background: Synovial sarcoma (SS) is a malignant soft tissue tumor of mesenchymal origin that frequently occurs in young adults. Translocation of the SYT gene on chromosome 18 to the SSX genes on chromosome X leads to the formation of oncogenic fusion genes, which lead to initiation and proliferation of tumor cells. The detection and quantification of circulating tumor DNA (ctDNA) can serve as a non-invasive method for diagnostics of local or distant tumor recurrence, which could improve survival rates due to early detection. Methods: We developed a subtype-specific targeted next-generation sequencing (NGS) approach specifically targeting SS t(X;18)(p11;q11), which fuses SS18 (SYT) in chromosome 18 to SSX1 or SSX2 in chromosome x, and recurrent point mutations. In addition, patient-specific panels were designed from tumor exome sequencing. Both approaches were used to quantify ctDNA in patients’ plasma. Results: The subtype-specific assay allowed detection of somatic mutations from 25/25 tumors with a mean of 1.68 targetable mutations. The minimal limit of detection was determined at a variant allele frequency of 0.05%. Analysis of 29 plasma samples from 15 tumor patients identified breakpoint ctDNA in 6 patients (sensitivity: 40%, specificity 100%). The addition of more mutations further increased assay sensitivity. Quantification of ctDNA in plasma samples (n = 11) from one patient collected over 3 years, with a patient-specific panel based on tumor exome sequencing, correlated with the clinical course, response to treatment and tumor volume. Conclusions: Targeted NGS allows for highly sensitive tumor profiling and non-invasive detection of ctDNA in SS patients, enabling non-invasive monitoring of tumor dynamics.

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