Microcomputed tomography and histology of a fragmented medial coronoid process in a 20-week-old golden retriever

Correlation between histopathologic, arthroscopic, and magnetic resonance imaging findings in dogs with medial coronoid disease

OBJECTIVE

To describe the magnetic resonance imaging (MRI), arthroscopic, and histopathologic changes in dogs with medial coronoid disease and to identify potential relationships between these findings.

STUDY DESIGN

Retrospective case series.

SAMPLE POPULATION

Twenty-five diseased medial coronoid processes (MCP) were collected from 19 dogs with a confirmed diagnosis of medial coronoid disease that were surgically treated by subtotal coronoid ostectomy. A reference group of normal MCP was collected from 9 dogs euthanatized for reasons unrelated to elbow disease.

METHODS

MCP specimens were evaluated by MRI using a novel grading scheme (all dogs), arthroscopy using a modified Outerbridge scheme (affected dogs only) and histopathology (all dogs).

RESULTS

The common histopathologic findings were subchondral microfractures, subchondral microfractures continuous with cartilaginous fissures, moderate to severe hypercellularity of the marrow space, trabecular bone necrosis, and articular cartilage degeneration. The severity of cartilage disease in the MCP was moderate to severe in most specimens, even in cases with minimal arthroscopic pathology. Three distinct patterns of bone marrow lesion (BML) were identified adjacent to the MCP, but there was no correlation between BML pattern and either histopathologic or arthroscopic findings. There was moderate correlation between modified Outerbridge scores and MRI scores. No correlation was identified between the histopathologic changes and either MRI or arthroscopic scores.

CONCLUSION

There was no significant correlation between the clinical scores and histopathologic changes. Ongoing improvements in the resolution of noninvasive imaging techniques will likely improve description and understanding of the MCP disease in dogs.

Transection of vessels in epiphyseal cartilage canals leads to osteochondrosis and osteochondrosis dissecans in the femoro-patellar joint of foals; a potential model of juvenile osteochondritis dissecans

OBJECTIVE

To transect blood vessels within epiphyseal cartilage canals and observe whether this resulted in ischaemic chondronecrosis, an associated focal delay in enchondral ossification [osteochondrosis (OC)] and pathological cartilage fracture [osteochondrosis dissecans (OCD)] in the distal femur of foals, with potential translational value to the pathogenesis of juvenile osteochondritis dissecans (JOCD) in children.

METHOD

Ten Norwegian Fjord Pony foals were operated at the age of 13-15 days. Two vessels supplying the epiphyseal growth cartilage of the lateral trochlear ridge of the left distal femur were transected in each foal. Follow-up examination was carried out from 1 to 49 days post-operatively and included plain radiography, macroscopic and histological examination.

RESULTS

Transection of blood vessels within epiphyseal cartilage canals resulted in necrosis of vessels and chondrocytes, i.e., ischaemic chondronecrosis, in foals. Areas of ischaemic chondronecrosis were associated with a focal delay in enchondral ossification (OC) in foals examined 21 days or more after transection, and pathological cartilage fracture (OCD) in one foal examined 42 days after transection.

CONCLUSION

The ischaemic hypothesis for the pathogenesis of OC has been reproduced experimentally in foals. There are several similarities between OCD in animals and JOCD in children. It should be investigated whether JOCD also occurs due to a focal failure in the cartilage canal blood supply, followed by ischaemic chondronecrosis.

Micro-computed tomography of early lesions of osteochondrosis in the tarsus of foals

INTRODUCTION

Osteochondrosis (OC) is an important developmental orthopedic disease of human and equine patients. The disease is defined as a focal disturbance in enchondral ossification. In horses, the disturbance can occur secondary to failure of the blood supply to growth cartilage. Diagnosis of the early, subclinical stages that can clarify the etiology is currently confined to cross-sectional histological examination. The potential for micro-computed tomography (micro-CT) with angiography to detect early lesions of OC has not yet been investigated.

MATERIALS AND METHODS

Nine Standardbred foals bred from parents with OC of the tarso-crural joint were sacrificed at weekly intervals from birth to 7 weeks of age. Permanent barium angiograms were created within one hind limb post mortem, and samples collected from two predilection sites for OC within the tarso-crural joint of the perfused hind limb. The resulting 18 sample blocks were scanned with a custom-built micro-CT equipment set-up, and analyzed as 2D slices and 3D volume rendered models before sectioning for conventional histological examination.

RESULTS

Histological examination identified eight early lesions in seven locations within six joints from the nine foals. Micro-CT with angiography was able to detect seven lesions in the same sites as histological examination. Lesions consisted of non-perfused foci within growth cartilage. No perfused vessels exited from subchondral bone deep to any lesion. Six of the seven lesions were associated with focal defects in the subchondral bone plate. Evidence of ongoing ossification was seen in three out of the seven lesions and included one separate center of ossification.

CONCLUSION

Micro-CT was a useful technique for examination of early lesions of OC. The results of micro-CT were compatible with failure of cartilage canal vessels at the point where they cross the ossification front. Resultant areas of ischemic chondronecrosis were associated with focal delay in enchondral ossification as visualized in 3D volume rendered models. Micro-CT combined with histology clarified the role of different forms of ossification in the secondary repair responses to lesions.

Cartilage canals in the medial coronoid process of young Golden Retrievers

The aim of the study was to establish the location of cartilage canals in the medial coronoid process (MCP) of the ulna of young Golden Retrievers, a breed that is predisposed to fractures of the medial coronoid process (FMCP). To determine whether the presence of cartilage canals could be associated with the predilection site of FMCP, the right elbows of nine young Golden Retrievers (aged 4, 6, 8, 10, 13, 16, 18, 22 and 24 weeks) were dissected and, with no prior decalcification, the formaldehyde-fixed MCPs were embedded in methylmethacrylate. The entire MCPs were serially sectioned in the frontal plane from cranial to caudal and the sections (5 microm) were routinely stained. Between the ages of 5 and 10 weeks, three main cartilage canals were visible--medial, central and lateral. All originated from the periosteum of the distal parts of the MCP and ended proximally under the articular cartilage. Branches of the main canals were seen more cranially and caudally. At the age of 13 weeks, the central canal was absent, and the remaining canals showed a smaller diameter. From 16 weeks onwards, no cartilage canals were seen. No direct relationship could be established between the predilection site of FMCP (lateral part of the MCP) and the presence/absence of cartilage canals, since both medial and lateral canals disappeared at the same age. Further research is needed to elucidate the pathogenesis of FMCP.

Cartilage gene expression correlates with radiographic severity of canine elbow osteoarthritis

The relationship between radiographic measures of severity of osteoarthritis (OA) and changes in gene expression in joints are not well characterised. In this study, the expression of 11 candidate genes was characterised by quantitative reverse transcriptase polymerase chain reaction in normal and OA cartilage and bone from the elbows of dogs with fragmented coronoid disease. The levels of expression of type I collagen alpha2 chain (COL1A2), type III collagen alpha1 chain (COL3A1), lumican (LUM), matrix metalloproteinase-2 (MMP2), -9 (MMP9) and -13 (MMP13) genes were increased and the expression of tissue inhibitor of metalloproteinase-2 (TIMP2) and cathepsin D (CTSD) genes were decreased in OA cartilage relative to normal cartilage. All differences correlated with radiographic measures of severity of OA. Levels of expression of COL1A2, MMP2, MMP9, MMP13 and TIMP1 were increased, whereas expression of TIMP2 was decreased in OA bone relative to normal bone. Cartilage gene expression may be correlated with the radiographic severity of OA.

Histomorphometry of Fragmented Medial Coronoid Process in Dogs: A Comparison of Affected and Normal Coronoid Processes

OBJECTIVE

To determine if fatigue microdamage is associated with fragmented medial coronoid process (FMCP).

STUDY DESIGN

Prospective study.

ANIMALS

Thirty-eight dogs were admitted for subtotal coronoid ostectomy as treatment for FMCP. Surgical specimens of medial coronoid process (MCP) were retrieved from treated dogs. Normal MCP were collected from 5 age- and breed-matched dogs and 2 age-matched research beagles that were euthanatized for reasons other than elbow disease.

METHODS

MCP specimens from affected elbows were classified into 4 groups based on disease severity. Specimens were bulk-stained for microdamage using 1% basic fuchsin, embedded in polymethylmethacrylate and sectioned at 130 microm. Specimens were evaluated using epifluorescent microscopy (425-440 excitation, 475 nm barrier filter) for diffuse damage (D.DX), osteocyte loss, and porosity. Cartilage thickness was evaluated using bright field microscopy. Qualitative observations were also made.

RESULTS

MCP specimens from affected elbows had increased D.Dx, increased osteocyte loss, and greater porosity than normal groups. Specimens classified as severe FMCP (Classes 3, 4) had the most fatigue microdamage. Some Class 1 specimens, defined as having no visible fissuring of the articular cartilage (AC), had large microcracks in trabecular bone.

CONCLUSIONS

Accumulation of subchondral fatigue microdamage, is associated with MCP fragmentation. Fissuring occurs in the subchondral bone before gross fibrillation of articular cartilage develops.

CLINICAL RELEVANCE

Accumulation of fatigue microdamage in the MCP is important in the pathogenesis of FMCP. The underlying cause of this microdamage accumulation must be identified before treatment plans that will prevent further osteoarthritis of the elbow joint can be designed.