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Summary: Background: The aetiology of equine metacarpal condylar fractures is not completely understood and a developmental cause has been postulated. Objectives: To investigate the subchondral bone trabecular microarchitecture of the lateral parasagittal groove and condyle in equine neonates and its adaptation with maturation and athletic activity. Study design: Ex vivo observational study. Methods: Distal metacarpi of neonates, yearlings and adult racehorses (n = 24) were harvested. Dorsal and palmar frontal histological sections, containing the lateral parasagittal groove and condyle, were studied. The sections were digitalised and subchondral trabecular bone quantity and quality parameters and trabecular orientation in the frontal plane were measured. Results: Trabecular spacing and length were greater (P = 0.004 and P = 0.0005 respectively) whereas bone fraction, trabecular number and connectivity were all lower (P = 0.0004, P = 0.0001 and P = 0.001 respectively) in the lateral parasagittal groove compared with the condyle in neonatal foals. Trabecular thickness and bone fraction increased with age in racehorses and trabecular spacing decreased. The predominant trabecular orientation had a consistent pattern in neonates and it changed with maturity and the cumulative effect of racing at all the ROIs except for the palmar lateral parasagittal groove that retained a more 'immature' pattern. Main limitations: Samples were investigated in 2D. 3D processing could have provided more information. Conclusions: Already at birth there are striking differences in the subchondral bone trabecular microarchitecture between the lateral parasagittal groove and condyle in foals. Adaptation of trabeculae is confirmed with maturity in racehorses, with the greatest adaptation measured in bone quantity parameters. The trabecular orientation had a unique and more immature orientation pattern in the lateral palmar parasagittal grooves in adult racehorses and may reflect a weaker structure at this site. [ABSTRACT FROM AUTHOR]

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: ROI 1 (0-1 mm), ROI 2 (1-3 mm) and ROI 3 (3-6 mm). Osteoclasts were counted and the bone area was measured in each ROI to calculate their density. Chondroclasts were counted in ROI 1 ., Results: Sections were studied from L and IC (n = 6) and CC sites (n = 5). Osteoclast density was significantly higher in ROI 1 when compared with ROI 3 in all groups. Although higher osteoclast density was measured in ROI 1 in the L group, no significant differences were detected when compared with control ROIs. The proportion of chondroclasts in ROI 1 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., (© 2021 EVJ Ltd.)

Background: The aetiology of equine medial femoral condyle (MFC) subchondral bone radiolucencies (SR) is unknown., Objectives: Characterise the microstructural structural features of MFC SR in juvenile Thoroughbreds with microcomputed tomography (μCT) and histology., Study Design: Cross-sectional post-mortem study., Methods: Distal femurs were collected at post-mortem. Conventional tomodensitometry was employed to scout for MFCs with and without SR lesions (SR+ and SR-, respectively). Group 1 were CT MFC SR+ and Group 2 age-matched SR- controls. Both underwent μCT and histological analysis. Group 3 CT MFC SR- foals, <6 months, were selected to search for chondronecrosis. Histological sections, processed from the lesion (Group 1) and a corresponding site in Groups 2 and 3, were assessed for chondronecrosis, fibrin, fibroplasia and osteochondral separation. Group 3 sections were surveyed for chondronecrosis alone., Results: A total of 178 femurs from 89 Thoroughbreds were harvested. Of these horses 19.1% (95% CI: 10.9%-27.3%) were CT MFC SR+ (17/23; 7.46 ± 4.36 months) and met the inclusion criteria for Group 1. Group 2 included 30 CT MFC SR- specimens (5.00 ± 2.73 months) and Group 3 had 44 CT MFC SR- s (2.68 ± 1.74 months). SR were located axially in foals <7 months of age, and centrally thereafter. All SRs had areas of thickened cartilage on histology and separation at the osteochondral junction containing fibrin (acute event) and fibroplasia (chronicity) in 73.9% (17/23; 95% CI: 56%-91.9%). In Group 1 specimens, chondronecrosis was present in 82.6% (19/23; 95% CI: 67.1%-98.1%) but four MFC SR+ had no evidence of chondronecrosis. Chondronecrosis was not detected in the Group 3 foal MFCs., Main Limitations: No longitudinal follow-up., Conclusions: The absence of chondronecrosis, pathognomic of osteochondrosis, in four MFC SR+s and in all of the CT MFC SR- foals suggests that osteochondrosis is not the cause, or the only cause, of these lesions and favours trauma as an alternate aetiological hypothesis., (© 2021 EVJ Ltd.)

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., (© 2020 EVJ Ltd.)

Reasons for Performing Study: Circumferential mural band (CMB) in the small intestine is an emerging condition in Ireland. The clinical presentation is a simple obstruction of the small intestine of unknown aetiology., Hypothesis: Horses affected with CMB in the small intestine have a good prognosis following surgical decompression into the caecum., Methods: A retrospective study was carried out and 28 cases identified from 559 colic surgeries performed over a 5.5 year period. An exploratory celiotomy was performed in every case. A simple obstruction at the mid or distal jejunum was identified caused by a CMB, which was multiple in some cases. All of the horses except 2 had undergone a regular anthelmintic programme., Results: Manual decompression of the small intestine into the caecum resulted in resolution of the simple jejunal obstruction. A constricted segment of small intestine was resected in one case, as the degree of constriction was severe. A full thickness biopsy was taken from another case. Histopathology was performed on both samples. All horses recovered from surgery and were discharged from the hospital 7-32 days post operatively. Short-term complications were observed. Survival rate was 100% at long-term follow-up. Histopathology showed inflammatory infiltration in the submucosa, muscularis and serosa with eosinophils predominating. Parasites were not detected., Conclusion and Potential Relevance: Small intestine circumferential mural bands have a good prognosis after surgical decompression of the small intestine into the caecum.

Reasons for Performing Study: Thoracic trauma occurs in newborn foals and may cause associated clinical signs; this condition remains poorly documented., Objectives: The purpose of this study was to describe the pathological features of thoracic trauma in newborn foals presented for necropsy examination between 1990 and 2000., Methods: Necropsy reports of foals with thoracic trauma from 1990-2000 were reviewed. Subject details, clinical signs, thoracic and abdominal lesions were noted and analysed statistically., Results: Sixty-seven (9%) of 760 necropsied foals had thoracic trauma. In 19 foals, fractured ribs were considered to be the cause of death (Group A). The remaining foals had fractured ribs (Group B, n = 20) or rib contusions (Group C, n = 28) that were incidental findings. Ribs 3 to 8 accounted for 86% of the traumatised bones. The most common site of injury was the costochondral junction and an area immediately above it (94%). In Group A, all but 2 foals died within the first 8 days postpartum. Haemothorax and subsequent pulmonary collapse was cited most commonly as the cause of death (53%). Diaphragmatic rupture and hernia (n = 2) also occurred., Conclusions: The focal site, consistent location and presence of lesions during the first week post partum, all suggest that thoracic trauma in newborn foals probably occurs during parturition., Potential Relevance: The description of lesions and site of occurrence of thoracic trauma in foals will increase awareness and improve the diagnosis and treatment of this life threatening condition.

The bronchoalveolar lavage (BAL) technique described produced no detectable gross or histopathological lesions. Airway fluid accumulation was observed for up to 4 h post lavage. There was good qualitative correlation between BAL cytopathological and diffuse pulmonary pathological changes. The technique provided an accurate assessment of the presence and extent of exercise induced pulmonary haemorrhage.