Central osteophytes develop in cartilage with abnormal structure and composition: data from the Osteoarthritis Initiative cohort

Micro-computed tomography reveals high-density mineralised protrusions and microstructural lesions in equine stifle joint articular cartilage

BACKGROUND

Stifle osteoarthritis (OA) lesions are most common in the medial femorotibial (MFT) compartment. Their characterisation and mapping will inform equine veterinarians towards an accurate diagnosis of OA.

OBJECTIVES

Investigate and map micro-CT (μCT) changes in the hyaline articular cartilage (HAC) in the medial femoral condyle (MFC) and medial tibial plateau (MTP).

STUDY DESIGN

Ex vivo cadaveric.

METHODS

Stifles (n = 7 OA and 17 control [CO]) were retrieved from a tissue bank. The MFC and MFT were imaged with μCT. Regions of interest (ROIs) were cranial (MFCcr; MTPcr) and caudal (MFCca; MTPca) sites. In each ROI, μCT images were scored for HAC fibrillation, surface mineralisation and for the presence of high-density mineralised protrusions (HDMP). The lesions were mapped, and site-matched histology was performed.

RESULTS

The microstructure of healthy and abnormal HAC was discernible on μCT images and confirmed with histology. HAC fibrillation was more prevalent (p = 0.019) in the MFCcr of the OA group (n = 7/7, 100%) when compared with the CO group (n = 7/17, 41%). Score 1 HAC surface mineralisation was more prevalent (p = 0.038) in the OA MFCca (n = 4/7, 57%) when compared with the CO group (n = 2/17, 12%). HDMP were heterogenous and hyperdense mineralised material protruding into the HAC and were more frequent (p = 0.033) in MFCs (n = 12/24, 50%) compared with MTPs (n = 5/24, 20%). Score 3 HDMPs were also more prevalent (p = 0.003) in the MFCcr (n = 7/24, 29%) compared with MFCca (n = 0/24, 0%) and in MFCs (n = 7/24, 29%) compared with MTPs (n = 3/24, 12.5%) (p = 0.046).

MAIN LIMITATIONS

Clinical history was not available for all specimens.

CONCLUSIONS

Equine HDMP and HAC surface mineralisation are imaged for the first time in the MFT joint. HAC fibrillation and erosion and HDMP are more frequent in the cranial aspect of the MFC. μCT images of OA in equine stifle joints provide a novel perspective of lesions and improve understanding of OA.

Osteochondral Abnormalities on Three-Dimensional Ultrashort Echo Time MRI Scans Are Associated with Knee Cartilage Degradation

Background The calcified cartilage layer and subchondral bone plate (SBP) contribute to osteoarthritis development. Three-dimensional (3D) ultrashort echo-time (UTE) MRI can help to evaluate calcified cartilage and SBP in various stages of cartilage degradation. Purpose To compare calcified cartilage and SBP abnormalities using 3D UTE MRI with cartilage degradation and osteochondral junction (OCJ) abnormalities observed at proton-density fast spin-echo with fat suppression (PDFS) MRI. Materials and Methods Between April 2018 and March 2019, 143 participants were prospectively enrolled in this study and underwent routine knee MRI with an additional sagittal 3D UTE MRI examination for chronic knee pain. The MRI scans were retrospectively analyzed by two musculoskeletal radiologists independently and at consensus. Cartilage degradation grades and OCJ abnormalities were evaluated at PDFS MRI. Calcified cartilage and SBP abnormalities were assessed at 3D UTE MRI by considering the location of cartilage degradation. The relationship between cartilage degradation grade and abnormalities of calcified cartilage and SBP was assessed using Spearman rank correlation analysis. The association between OCJ abnormalities on PDFS MRI scans and calcified cartilage and SBP abnormalities was analyzed using logistic regression models. Results In total, 143 knees (71 right and 72 left knees) from 143 participants (mean age, 50.8 years ± 17.6 [SD]; 72 male and 71 female participants) were analyzed. On 3D UTE MRI scans, calcified cartilage defects showed a moderate positive correlation with the cartilage degradation grade (ρ = 0.49-0.52; P < .001). Calcified cartilage thinning (ρ = 0.2-0.3; P < .001), SBP irregular thickening (ρ = 0.3-0.35; P < .001), and defects (ρ = 0.34-0.42; P < .001) exhibited a weak positive correlation with the cartilage degradation grade. OCJ abnormalities depicted at PDFS MRI were associated with calcified cartilage and SBP abnormalities (P < .05). Conclusion Calcified cartilage layer and SBP abnormalities at 3D UTE MRI were associated with cartilage degradation and OCJ abnormalities depicted at PDFS MRI. © RSNA, 2024 Supplemental material is available for this article.

Unusual lesions seen in the caudals of the hadrosaur, Edmontosaurus annectens

The study of pathologies in the fossil record allows for unique insights into the physiology, immunology, biomechanics, and daily life history of extinct organisms. This is especially important in organisms that have body structures dissimilar to those of extant organisms as well as transitional groups whose extant relatives may have very dissimilar physiologies. Comparisons between modern groups and their fossil ancestors are further complicated by the fact that fossil groups may have experienced unique biomechanical stresses as well as possessing a mixture of anatomical features seen in their related extant groups. In this study, we present lesions in the caudal vertebrae of the hadrosaur, Edmontosaurus annectens from the Ruth Mason Dinosaur Quarry of South Dakota, which exhibit unique morphologies. X-ray microtomography was performed on the most extreme example of this morphology to allow for both a detailed and more accurate diagnosis of the pathologic condition as well as virtual conservation of the specimen. Based on the location, the overall morphology of the lesion, and the relative "normal" appearance of the internal microstructure, the most probable cause is postulated as long-term biomechanical stresses exerted on this section of the tail by both lateral and dorsoventral motions of the tail. This deduction was based on a process of elimination for a variety of known osteological conditions; however, future work is needed to determine the nature of the stresses and why this condition has not been recorded in more hadrosaurian specimens.

Interpretation of Cartilage Damage at Routine Clinical MRI: How to Match Arthroscopic Findings

This review is intended to aid in the interpretation of damage to the articular cartilage at routine clinical MRI to improve clinical management. Relevant facets of the histologic and biochemical characteristics and clinical management of cartilage are discussed, as is MRI physics. Characterization of damage to the articular cartilage with MRI demands a detailed understanding of the normal and damaged appearance of the osteochondral unit in the context of different sequence parameters. Understanding the location of the subchondral bone plate is key to determining the depth of the cartilage lesion. Defining the bone plate at MRI is challenging because of the anisotropic fibrous organization of articular cartilage, which is susceptible to the "magic angle" phenomenon and chemical shift artifacts at the interface with the fat-containing medullary cavity. These artifacts may cause overestimation of the thickness of the subchondral bone plate and, therefore, overestimation of the depth of a cartilage lesion. In areas of normal cartilage morphology, isolated hyperintense and hypointense lesions often represent degeneration of cartilage at arthroscopy. Changes in the subchondral bone marrow at MRI also increase the likelihood that cartilage damage will be visualized at arthroscopy, even when a morphologic lesion cannot be resolved, and larger subchondral lesions are associated with higher grades at arthroscopy. The clinical significance of other secondary features of cartilage damage are also reviewed, including osteophytes, intra-articular bodies, and synovitis. Online supplemental material is available for this article. Work of the U.S. Government published under an exclusive license with the RSNA.

High-Density Mineralized Protrusions and Central Osteophytes: Associated Osteochondral Junction Abnormalities in Osteoarthritis

The aim of this study was to determine the association between high-density mineralized protrusions (HDMPs) and central osteophytes (COs), and describe the varying appearance of these lesions using advanced clinical imaging and a novel histological protocol. Seventeen consecutive patients with clinically advanced knee osteoarthritis undergoing knee arthroplasty were included. Surgical tissues containing the osteochondral region were investigated using computed tomography (CT); a subset was evaluated using confocal microscopy with fluorescence. Tissues from seven subjects (41.2%) contained HDMPs, and tissues from seven subjects (41.2%) contained COs. A significant association between HDMPs and COs was present (p = 0.003), with 6 subjects (35.2%) demonstrating both lesions. In total, 30 HDMPs were found, most commonly at the posterior medial femoral condyle (13/30, 43%), and 19 COs were found, most commonly at the trochlea (5/19, 26.3%). The HDMPs had high vascularity at their bases in cartilaginous areas (14/20, 70%), while the surrounding areas had elevated levels of long vascular channels penetrating beyond the zone of calcified cartilage (p = 0.012) compared to HDMP-free areas. Both COs and HDMPs had noticeable bone-resorbing osteoclasts amassing at the osteochondral junction and in vascular channels entering cartilage. In conclusion, HDMPs and COs are associated lesions in patients with advanced knee osteoarthritis, sharing similar histologic features, including increased vascularization and metabolic bone activity at the osteochondral junction. Future studies are needed to determine the relationship of these lesions with osteoarthritis progression and symptomatology.