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.

Functional outcomes and synovial fluid (SF) cytokine concentrations in response to platelet-rich plasma (PRP) or stromal vascular fraction (SVF) post-treatments following open wedge high tibial osteotomy (HTO) in 20 patients with knee osteoarthritis (OA) were examined. Six weeks after surgery, the knees of 10 patients were injected with autologous PRP (PRP subgroup), while another 10 patients were injected with autologous SVF (SVF subgroup) and monitored for 1.5 years. Pain assessment (VAS score) and functional activity (KOOS, KSS, Outerbridge, and Koshino scores) were applied. PRP subgroup performed better compared with the SVF subgroup according to KOOS, KSS, and VAS scores, while the SVF subgroup demonstrated better results according to Outerbridge and Koshino testing and produced more pronounced cartilage regeneration in the medial condyle and slowed down cartilage destruction in its lateral counterpart. SF was collected before and one week after PRP or SVF injections and tested for concentrations of 41 cytokines (Multiplex Assay). In the PRP subgroup, a significant decrease in IL-6 and CXCL10 synovial concentrations was accompanied by an increase in IL-15, sCD40L, and PDGF-AB/BB amounts. The SVF subgroup demonstrated a significant decrease in synovial TNFα, FLT-3L, MIP-1β, RANTES, and VEGF concentrations while SF concentrations of MCP-1 and FGF2 increased. Both post-treatments have a potential for increased tissue regeneration, presumably due to the downregulation of inflammation and augmentation of synovial growth factor concentrations.

Deforming osteoarthritis (OA) of the knee is a progressive disease associated with pain and compromised function of the joint. Typical biomechanical modifications in the gait of subjects with medial knee OA are characterized by decreased gait speed and overload on the affected limb. The borderline stage for conservative versus surgical management is Grade II OA. The aim of this research was to study preoperatively the specific features of gait, knee, and hip function in patients with Grade II medial OA. We examined 26 patients with Grade II unilateral gonarthritis with varus deformity and 20 healthy adults. Biomechanical parameters of gait were recorded using an inertial sensor system. The gait cycle (GC) slightly increased both for the affected and for the intact limb. The hip joint movements showed significant symmetrical reduction in the first flexion amplitude, as well as a symmetrical delay in full hip extension at the end of the stance phase. In the knee, the first flexion amplitude was significantly reduced on the affected side compared to healthy control. The extension amplitude in the single support phase was significantly increased in both the affected and the intact lower limbs. The swing amplitude was significantly reduced on the affected side. On the affected side, the changes were more pronounced, both in incidence and in severity. The affected knee showed a syndrome of three reduced amplitudes. In patients, walking is characterized by several groups of symptoms: those of unloading of the affected limb, those of limiting the load on the affected joint and the musculoskeletal system as a whole, and those of gait harmonization. The symptoms of unloading the affected side and those of harmonization are the common symptoms of adaptation, typical for several pathological conditions with a relatively preserved function. The intensity of the observed symptoms can help assess changes in the subject’s functional condition over time and during the treatment.

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.