Objective: This study aims to demonstrate the cellular composition and underlying mechanisms in subchondral bone marrow lesions (BMLs) of knee osteoarthritis (OA). Methods: BMLs were assessed by MRI Osteoarthritis Knee Score (MOAKS)≥2. Bulk RNA-sequencing (bulk-seq) and BML-specific differentially expressed genes (DEGs) analysis were performed among subchondral bone samples (including OA-BML=3, paired OA-NBML=3; non-OA=3). The hub genes of BMLs were identified by verifying in independent datasets and multiple bioinformatic analyses. To further estimate cell-type composition of subchondral bone, we utilized two newly developed deconvolution algorithms (MuSiC, MCP-counter) in transcriptomic datasets, based on signatures from open-accessed single-cell RNA sequencing (scRNA-seq). Finally, competing endogenous RNA (ceRNA) and transcription factor (TF) networks were constructed through multiple predictive databases, and validated by public non-coding RNA profiles. Results: A total of 86 BML-specific DEGs (up 79, down 7) were identified. IL11 and VCAN were identified as core hub genes. The “has-miR-424-5p/lncRNA PVT1” was determined as crucial network, targeting IL11 and VCAN, respectively. More importantly, two deconvolution algorithms produced approximate estimations of cell-type composition, and the cluster of heterotopic-chondrocyte was discovered abundant in BMLs, and positively correlated with the expression of hub genes. Conclusion: IL11 and VCAN were identified as the core hub genes of BMLs, and their molecular networks were determined as well. We profiled the characteristics of subchondral bone at single-cell level and determined that the heterotopic-chondrocyte was abundant in BMLs and was closely linked to IL11 and VCAN. Our study may provide new insights into the microenvironment and pathological molecular mechanism of BMLs, and could lead to novel therapeutic strategies.

Candida arthritis is extremely rare and also represents a major challenge of diagnosis and treatment. Here we reported a rare case of recurrent arthritis caused by Candida parapsilosis. A 56-year-old Chinese male suffered from recurrent pain and swelling in his right knee after several times of “small needle-knife” acupuncture and corticosteroid injection of the joint. Candida parapsilosis was cultured in his synovial fluid and identified by sequencing of its Internal Transcribed Spacer (ITS) gene. Here we present the radiological characteristics, arthroscopic pictures, and synovium pathology of this patient. Also, blood test and chemical analysis of his synovial fluid were listed as well as the ITS sequence of this Candida species identified. The patient underwent thorough arthroscopic debridement and then set on fluconazole 400 mg daily for 12 months. His symptoms resolved and no relapse was observed on the last follow-up. Additionally, a brief but comprehensive review of C. parapsilosis arthritis episodes from past to now were studied. With the detailed clinical information reported in this case and our literature review, we hope they would add to our knowledge of C. parapsilosis arthritis - its clinical settings, laboratory features, radiological characteristics, arthroscopic findings and experience of management.

BACKGROUND: Multiple tumor-like ectopic calcifications is a rare syndrome characterized by subcutaneous mass deposits of calcium phosphate in periarticular tissues. Although several cases of the surgical treatment of tumoral calcinosis have been reported, the present case is unique in that multiple ectopic calcifications in subcutaneous tissues were found in a hemodialysis patient who had been operated on a total of five times within a period of 1.5 years. METHODS: A hemodialysis 60-year-old male presented with multiple tumor-like ectopic calcifications bilateral in the shoulders, right buttock and right thigh. He had been operated on a total of five times within a period of 1.5 years; the operations included a subtotal parathyroidectomy with parathyroid autotransplantation in the right forearm. RESULTS: Complete excisions of the ectopic calcifications were performed in the left shoulder, right buttock and right thigh, without signs of recurrence in the same sites at follow-up. Incomplete excision of the ectopic calcification in the right shoulder resulted in recurrence in the same site, and the patient was operated on two more times 1.5 years following the initial surgery. Subtotal parathyroidectomy with parathyroid autotransplantation decreased serum levels of PTH, but the levels of serum calcium and phosphorus remained unchanged post-surgery, which appeared not to inhibit the recurrence of ectopic calcification in patients with CRF. CONCLUSIONS: If conservative therapy failed, then early and complete surgical excision may be a good therapeutic option. Highlights:

Deep learning models for Kellgren–Lawrence (KL) grading often report optimistic performance due to data leakage and fail to generalize across institutions because of domain shift. To address this reproducibility crisis, we introduce KL‐FuseNet, a multitask architecture fusing global (ConvNeXt‐Base) and local (ResNet‐50) features to predict ordinal grades, label distributions, and binary severity (KL≥2). Using strict patient‐wise stratified splits on an internal osteoarthritis initiative dataset ( n = 8260) and an independent Chinese cohort ( n = 2295), we compared zero‐shot transfer against selective fine‐tuning. KL‐FuseNet achieved robust internal agreement (quadratic Cohen's kappa [QWK]: 0.881; accuracy: 70.3%). While external zero‐shot deployment revealed a domain gap, with accuracy dropping to 66.1%, our selective fine‐tuning protocol significantly bridged this divide, boosting external accuracy to 80.0% and QWK to 0.950, with an AUC of 0.984 for clinically significant osteoarthritis (KL≥2). These results demonstrate that while KL‐FuseNet achieves state‐of‐the‐art performance under rigorous evaluation, domain‐aware adaptation is essential for clinical utility. This study establishes a reproducible pathway for deploying automated grading models across heterogeneous medical centers.