Background/Objectives: Osteonecrosis of the femoral head (ONFH) is a common condition in hip surgery, which is characterized by the death of bone cells due to disruption of the blood supply and ultimately irreversible destruction of the hip joint. As a result of the COVID-19 pandemic, a significant increase in the incidence of ONFH has been identified. To better understand the pathogenesis of ONFH in the context of COVID-19, our research aimed to determine pathomorphological changes in articular tissues specific to post-COVID-19 ONFH. Methods: Using morphological, morphometric, and statistical methods, the femoral heads after hip arthroplasty were retrospectively studied in patients with post-COVID-19 ONFH (n = 41) compared to a non-COVID-19 group of patients (n = 47). Results: Our results revealed that the key morphofunctional biomarkers of post-COVID-19 ONFH were clusters of mast cells, extensive areas of fibrosis, numerous arterial and venous thrombi, and giant cell granulomas. The potential relationship of those morphological features with the action of the SARS-CoV-2 coronavirus was discussed. Conclusions: Mast cells have been proposed as the leading players that may trigger the main molecular and cellular mechanisms in the development of post-COVID-19 ONFH and can be considered a diagnostic sign of the disease.

This pilot study examined the long-term structural changes in the osteochondral unit of 20 patients with knee osteoarthritis (KOA) who underwent high tibial osteotomy (HTO) and received post-treatment with either platelet-rich plasma (PRP) or stromal vascular fraction (SVF). Ten patients were injected with autologous PRP (PRP subgroup), while another ten patients received autologous SVF (SVF subgroup) six weeks after surgery and were monitored for 18 months. Histological samples of bone and cartilage (2 mm in diameter and 2 cm long) were taken from tibial and femoral sites during surgery and 18-month post-HTO, and morphometric analyses were conducted using Mega-Morf12 software. Both post-treatment resulted in an increase in articular cartilage height at both sites (p < 0.001 in the tibia and femur), indicating positive outcomes. Significant improvements in subchondral and trabecular bone architecture were also observed, with SVF injection showing higher reparative capacity in terms of bone volume (p < 0.001 for the tibia and p = 0.004 for the femur), subchondral bone height (p < 0.001 for the tibia and p = 0.014 for the femur), trabecular bone volume (p < 0.001 for the femur), and intertrabecular space (p = 0.009 for the tibia and p = 0.007 for the femur). This pilot study, for the first time, demonstrates that HTO surgery combined with PRP and SVF post-treatments can lead to significant enhancements in knee articular cartilage and bone architecture in KOA patients, with SVF showing higher regenerative potential. These findings may contribute to improving treatment strategies for better clinical outcomes in HTO therapy for patients with KOA.

Intra-articular hyaluronan injections represent a widely used and generally safe therapeutic approach for knee osteoarthritis (OA). However, the side effects of this treatment remain insufficiently studied. Acute post-injection reactions, particularly those arising from an improper technique resulting in the deposition of the therapeutic agent into joint tissues, are well-documented. In contrast, chronic hyaluronan-induced inflammatory responses have received scant attention in the scientific literature. The aim of this study is to characterize for the first time the morphological patterns of chronic granulomatous inflammation induced by exogenous hyaluronan (e-HA) in osteoarthritic knees, focusing on three distinct tissue reactions: synovitis, adipositis, and osteomyelitis. Using a three-case series approach and morphological analysis, we identified e-HA penetration pathways; described associated foreign body responses in the synovial, adipose, and bone tissues of the joints; and emphasized the clinical relevance of these underreported adverse effects. These observations highlight an understudied phenomenon—an active conflict between e-HA and joint tissues that recognize it as a foreign body. The prevalence, clinical significance, and prognostic implications of this phenomenon require further investigation.

Osteophytes (OPs) are a diagnostic hallmark of osteoarthritis (OA). However, the mechanisms underlying their initiation and their relationship with early subchondral bone changes remain poorly understood. Existing research primarily relies on animal models and late-stage OA tissue, leaving the initial morphological events leading to OP formation unclear. Background/Objectives: This study aimed to identify early changes in the subchondral bone as a key trigger for OP initiation in human OA through a comprehensive histological analysis of the subchondral area, including its peripheral regions. Methods: We conducted an extensive histological examination of full-section human tibial plateaus, including load-bearing and non-load-bearing compartments, obtained from patients with early and late stages of OA. Results: Our data demonstrate that subchondral bone changes, including osteoporosis, osteosclerosis, and microcracks, begin at the pre-chondropathic stage alongside microscopically intact cartilage. We identified a previously undescribed zone on the vertical wall of the tibial condyle (the VEPLS zone), characterized by reduced calcium content in the cortical plate and the persistence of embryonic cartilage, making it morphologically vulnerable. The first event in OP formation is microcracks in the cortical angle and the adjacent subchondral trabecula. These injuries initiate reparative osteogenesis, which, under continuous traumatic load (presumably shear forces due to joint instability), becomes insufficient, leading to cortical angle protrusion and OP formation. OP growth is accompanied by the deformation of the VEPLS zone cortical plate, causing vascular impairment and exacerbating bone weakness. Conclusions: Based on our findings, we propose the concept of tissue micro-instability. This concept posits that osteophytosis results from chronic microcracks and failed bone regeneration in vulnerable subchondral structures, induced by joint instability. We define an OP as a pathological outgrowth arising from this tissue micro-instability. Our study highlights the critical role of the peripheral subchondral area, particularly the VEPLS zone, in OA pathogenesis.