Differences in third metacarpal trabecular microarchitecture between the parasagittal groove and condyle at birth and in adult racehorses

Elastic Modulus and Its Relation to Apparent Mineral Density in Juvenile Equine Bones of the Lower Limb

Density-modulus relationships are necessary to develop finite element models of bones that may be used to evaluate local tissue response to different physical activities. It is unknown if juvenile equine trabecular bone may be described by the same density-modulus as adult equine bone, and how the density-modulus relationship varies with anatomical location and loading direction. To answer these questions, trabecular bone cores from the third metacarpal (MC3) and proximal phalanx (P1) bones of juvenile horses (age <1 yr) were machined in the longitudinal (n = 134) and transverse (n = 90) directions and mechanically tested in compression. Elastic modulus was related to apparent computed tomography density of each sample using power law regressions. We found that density-modulus relationships for juvenile equine trabecular bone were significantly different for each anatomical location (MC3 versus P1) and orientation (longitudinal versus transverse). Use of the incorrect density-modulus relationship resulted in increased root mean squared percent error of the modulus prediction by 8-17%. When our juvenile density-modulus relationship was compared to one of an equivalent location in adult horses, the adult relationship resulted in an approximately 80% increase in error of the modulus prediction. Moving forward, more accurate models of young bone can be developed and used to evaluate potential exercise regimens designed to encourage bone adaptation.

Imaging and Gross Pathological Appearance of Changes in the Parasagittal Grooves of Thoroughbred Racehorses

Simple Summary

Early detection of racehorses at risk of stress fracture is key to reducing the number of horses with catastrophic fractures while racing. Bone changes are often visible in the limbs of Thoroughbred racehorses in work, particularly in the fetlock region. However, it is currently unknown whether some of these changes indicate an impending fracture or are a healthy adaptation to high-speed exercise. This study looks at imaging and gross changes in a specific area (parasagittal grooves (PSGs) of the cannon bone) and the utility of X-ray, computed tomography (CT) and magnetic resonance imaging (MRI) to detect the changes. All fetlock joints were assessed from twenty horses that died during racing or training, including horses with and without fetlock fracture. Overall, X-ray was poor for detecting PSG changes. Some PSG changes on CT and MRI were common in Thoroughbred racehorses and possibly represent normal bone adaptation when seen in clinical cases. However, certain CT and MRI findings were more prevalent in horses with a fracture, possibly indicating microdamage accumulation and increased risk of fracture. Bilateral advanced imaging is recommended in clinical cases of suspected fetlock pathology.

Abstract

(1) Background: Parasagittal groove (PSG) changes are often present on advanced imaging of racing Thoroughbred fetlocks and have been suggested to indicate increased fracture risk. Currently, there is limited evidence differentiating the imaging appearance of prodromal changes in horses at risk of fracture from horses with normal adaptive modelling in response to galloping. This study aims to investigate imaging and gross PSG findings in racing Thoroughbreds and the comparative utility of different imaging modalities to detect PSG changes. (2) Methods: Cadaver limbs were collected from twenty deceased racing/training Thoroughbreds. All fetlocks of each horse were examined with radiography, low-field magnetic resonance imaging (MRI), computed tomography (CT), contrast arthrography and gross pathology. (3) Results: Horses with fetlock fracture were more likely to have lateromedial PSG sclerosis asymmetry and/or lateral PSG lysis. PSG lysis was not readily detected using MRI. PSG subchondral bone defects were difficult to differentiate from cartilage defects on MRI and were not associated with fractures. The clinical relevance of PSG STIR hyperintensity remains unclear. Overall, radiography was poor for detecting PSG changes. (4) Conclusions: Some PSG changes in Thoroughbred racehorses are common; however, certain findings are more prevalent in horses with fractures, possibly indicating microdamage accumulation. Bilateral advanced imaging is recommended in racehorses with suspected fetlock pathology.

Osteoclast density is not increased in bone adjacent to radiolucencies (cysts) in juvenile equine medial femoral condyles

BACKGROUND

There is a knowledge gap about how equine MFC subchondral radiolucencies (SR) arise and evolve. Osteoclasts are believed to have a role but have not been studied in situ.

OBJECTIVES

To measure and compare osteoclast density and the percentage of chondroclasts in healthy and MFC SR specimens from juvenile Thoroughbreds.

STUDY DESIGN

Cadaveric study.

METHODS

Medial femoral condyles (MFC) from a tissue bank of equine stifles were studied. Inclusion criteria were MFCs (≤8 months old) with a computed tomography SR lesion and histological focal failure of endochondral ossification (L group). Contralateral, lesion-free, MFCs were a control group (CC). Osteochondral slabs were cut through the lesion (L), a healthy site immediately caudal to the lesion, (internal control; IC) and the contralateral, site-matched controls (CC). Histological sections were immunostained with Cathepsin K for osteoclast counting. Osteoclasts in contact with the growth cartilage (chondroclasts) were also counted. The sections were segmented into regions of interest (ROI) at different depths in the subchondral bone: ROI₁ (0-1 mm), ROI₂ (1-3 mm) and ROI₃ (3-6 mm). Osteoclasts were counted and the bone area was measured in each ROI to calculate their density. Chondroclasts were counted in ROI₁ .

RESULTS

Sections were studied from L and IC (n = 6) and CC sites (n = 5). Osteoclast density was significantly higher in ROI₁ when compared with ROI₃ in all groups. Although higher osteoclast density was measured in ROI₁ in the L group, no significant differences were detected when compared with control ROIs. The proportion of chondroclasts in ROI₁ was lower in the L sections when compared with controls but no significant differences were detected.

MAIN LIMITATIONS

Limited sample size.

CONCLUSIONS

Osteoclasts are important actors in MFC subchondral bone development, digesting both growth cartilage (chondroclasts) and bone, but the pathophysiology of early MFC SRs cannot be explained solely by an increased osteoclast presence in the subchondral bone.

Validation of standing cone beam computed tomography for diagnosing subchondral fetlock pathology in the Thoroughbred racehorse

BACKGROUND

Subchondral bone pathology is common in Thoroughbred racehorses and believed to precede more serious injury. Early identification of pathology is critical to allow for intervention.

OBJECTIVES

To determine interobserver variability of fetlock subchondral bone lesions using cone beam and fan beam computed tomography (CBCT, FBCT) and to validate a robotics-controlled CBCT to identify fetlock subchondral bone pathology in the Thoroughbred racehorse.

STUDY DESIGN

Prospective cohort study.

METHODS

FBCT and CBCT images were acquired of 25 metacarpo-/metatarsophalangeal joints of Thoroughbred racehorses. Images were analysed for subchondral bone lesions commonly identified in Thoroughbred fetlocks by an imaging specialist and surgery specialist. Interobserver and intermodality equivalence were determined with a Pearson correlation analysis and Bland-Altman equivalence test.

RESULTS

Interobserver FBCT correlation was significant (P < .05) for 19 of 25 variables (Pearson R mean 0.77). Concordance was significant for all 25 variables (Bland Altman average difference 0.28 ± 0.21 mm). Interobserver CBCT correlation was significant for 21 of 25 variables (Pearson R mean 0.73). Concordance was significant for all variables (Bland Altman average difference 0.07 ± 1.90 mm). Intermodality (FBCT vs CBCT) correlation and concordance was significant for all variables as interpreted by the radiologist (Pearson R mean of 0.72, Bland Altman average difference 0.21 ± 0.47 mm). Intermodality correlation was significant for 19 of 25 variables as interpreted by the surgeon (Pearson R mean of 0.72). Concordance was significant for all variables (Bland Altman average difference 0.49 ± 0.52 mm).

MAIN LIMITATIONS

Neither FBCT nor CBCT images were compared with other imaging modalities/histopathology; limited number of cases included; inconsistent agreement of small lesions in specific categories.

CONCLUSIONS

Standing CBCT is a valid diagnostic modality to identify subchondral bone lesions in Thoroughbred fetlocks. This technology may provide valuable information regarding the development and progression of fetlock pathology and yield insight into predisposing factors leading to more severe pathology.

Abundant osteoclasts in the subchondral bone of the juvenile Thoroughbred metacarpus suggest an important role in joint maturation

BACKGROUND

The administration of bisphosphonate medications, which target osteoclastic-bone remodelling, to juvenile and adult racehorses is a matter of debate owing to concerns that these molecules remain bound to the bone-mineralised matrix and may interfere with subsequent bone growth, adaptation to exercise and healing of bone microdamage in equine athletes. Osteoclasts participate in endochondral ossification, subchondral bone remodelling and bone repair. There is a knowledge gap on the role of equine osteoclast biology in the growth and maturation of joint surfaces and this information is important to inform judicious bisphosphonate use.

OBJECTIVES

Measure and compare the osteoclast density in the subchondral bone of Thoroughbred (TB) distal third metacarpi (McIII) at different sites, varying depths from the articular surface and with age (0-84 months).

STUDY DESIGN

Ex vivo cadaveric study.

METHODS

McIIIs from foals, yearlings and adults were collected, fixed in formaldehyde and stored at 4°C. Sections were cut from the lateral hemi-metacarpus, stained and scored for cartilage degeneration. Osteoclasts were counted on immunohistochemically (Cathepsin K) stained sections. Osteoclast density was compared in regions of interest (ROIs-the sagittal ridge, axial and abaxial condyle) and also at two depths (0-3 mm and 3-6 mm) into the subchondral bone below the osteochondral junction.

RESULTS

The osteoclast density was consistently highest in the subchondral cortical bone plate (0-3 mm) when compared with the deeper trabecular bone in all age groups. Furthermore, the osteoclast density was significantly higher in juvenile Thoroughbreds (foals and yearlings) within both sites in the subchondral bone when compared with adults.

MAIN LIMITATIONS

The number of specimens available for study was restricted.

CONCLUSIONS

Osteoclasts are important in normal McIII epiphyseal and articular surface maturation and have a propensity to localise at the osteochondral junction and subchondral cortical bone plate zone in juvenile Thoroughbreds.