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OBJECTIVE To verify the existence of intertransverse joints (ITJs) in young foals. ANIMALS 11 warmblood foals. PROCEDURES Postmortem examination of the lumbar area in foals < 200 days old using CT, MRI, dissection, and histomorphology. Data were analyzed with descriptive statistics. RESULTS Age of foals varied between 1 and 200 days (median, 11 days). Ten foals had 6 lumbar (L) vertebrae, and 1 foal had 5. All 11 foals, irrespective of age, had ITJs between the first sacral and last lumbar vertebrae and between the last and second-to-last lumbar vertebrae. In 6 foals (all with 6 L vertebrae), ITJs also existed between the fourth and fifth L vertebra. One foal, also with 6 L vertebrae, additionally had a unilateral (right) ITJ between the transverse processes of the third and fourth L vertebra. Based on CT, width of ITJs was seemingly greater in young (< 1 month old) foals because of the incomplete ossification of the transverse processes. The ITJs were confirmed and further characterized by MRI, dissection, and histomorphology. CLINICAL RELEVANCE ITJs already exist in very young warmblood foals and are present at birth. During the first months of life, these juvenile ITJs develop similarly to other synovial joints with increasing ossification and concomitant decrease of thickness of the cartilage layer. Knowledge of the presence of these ITJs in young animals is clinically relevant, as they should be recognized as nonpathologic when for instance a young foal is presented for presumed arthropathy and examined with advanced imaging techniques.

BackgroundAllogenic mesenchymal stem cell (MSC) secretome is a novel intra-articular therapeutic that has shown promise in in vitro and small animal models and warrants further investigation.ObjectivesTo investigate if intra-articular allogenic MSC-secretome has anti-inflammatory effects using an equine model of joint inflammation.Study DesignRandomized positively and negatively controlled experimental study.MethodIn phase 1, joint inflammation was induced bilaterally in radiocarpal joints of eight horses by injecting 0.25 ng lipopolysaccharide (LPS). After 2 h, the secretome of INFy and TNFα stimulated allogeneic equine MSCs was injected in one randomly assigned joint, while the contralateral joint was injected with medium (negative control). Clinical parameters (composite welfare scores, joint effusion, joint circumference) were recorded, and synovial fluid samples were analyzed for biomarkers (total protein, WBCC; eicosanoid mediators, CCL2; TNFα; MMP; GAGs; C2C; CPII) at fixed post-injection hours (PIH 0, 8, 24, 72, and 168 h). The effects of time and treatment on clinical and synovial fluid parameters and the presence of time-treatment interactions were evaluated. For phase 2, allogeneic MSC-secretome vs. allogeneic equine MSCs (positive control) was tested using a similar methodology.ResultsIn phase 1, the joint circumference was significantly (p < 0.05) lower in the MSC-secretome treated group compared to the medium control group at PIH 24, and significantly higher peak synovial GAG values were noted at PIH 24 (p < 0.001). In phase 2, no significant differences were noted between the treatment effects of MSC-secretome and MSCs.Main LimitationsThis study is a controlled experimental study and therefore cannot fully reflect natural joint disease. In phase 2, two therapeutics are directly compared and there is no negative control.ConclusionsIn this model of joint inflammation, intra-articular MSC-secretome injection had some clinical anti-inflammatory effects. An effect on cartilage metabolism, evident as a rise in GAG levels was also noted, although it is unclear whether this could be considered a beneficial or detrimental effect. When directly comparing MSC-secretome to MSCs in this model results were comparable, indicating that MSC-secretome could be a viable off-the-shelf alternative to MSC treatment.

Aortic rupture in horses is a rare condition. Although it is relatively common in the Friesian breed, only limited histopathologic information is available. Twenty Friesian horses (1–10 years old) were diagnosed with aortic rupture by postmortem examination. Ruptured aortic walls were analyzed with histology and immunohistochemistry. Based on the histologic and immunohistochemical findings, these cases were divided into 3 groups: acute ( n = 4, 20%), subacute ( n = 8, 40%), and chronic ( n = 8, 40%). Features common to samples from horses in all groups included accumulation of mucoid material; disorganization and fragmentation of the elastic laminae; aortic medial smooth muscle hypertrophy; and medial necrosis of varying degrees, ranging from mild and patchy in the acute cases to severe midzonal necrosis in the chronic cases. Inflammation, most likely secondary to medial necrosis, varied from predominantly neutrophilic infiltrates in the media and periadventitial tissue in the acute group to the presence of mainly hemosiderophages in the periadventitial tissue in the chronic group. Medial fibrosis with aberrant collagen morphology was seen in the subacute group and, more commonly, in the chronic group. Only minimal changes were seen in the aortic vasa vasorum. Smooth muscle hypertrophy and accumulation of mucoid material were not related to the age of the lesions. The findings of this study suggest that a connective tissue disorder affecting elastin or collagen in the aortic media is potentially the underlying cause of aortic rupture in Friesian horses.

SummaryObjective: Even though equine multi-limb tendinopathy models have been reported, it is unknown if fore- and hindlimb tendon healing behave similarly. The aim of this study was to compare the healing process of surgically induced superficial digital flexor tendon (SDFT) core lesions of fore- and hindlimbs in horses.Methods: Tendon core lesions were surgically induced in the SDFT of both fore- and hindlimbs in eight horses. One randomly assigned forelimb and one randomly assigned hindlimb were injected with saline one and two weeks post-surgery. The healing process was monitored clinically and ultrasonographically. After 24 weeks, the tendons were harvested and biochemical, biomechanical and histological parameters were evaluated.Results: Twenty-four weeks post-surgery, the forelimb SDFT lesions had a significantly higher colour Doppler ultrasound vascularization score (p = 0.02) and glycosaminoglycan concentration (p = 0.04) and a significantly lower hydroxylysylpyridinoline content (p = 0.03).Clinical relevance: Our results indicate that fore- and hindlimb SDFT surgically induced lesions exhibit significant differences in several important parameters of tendon healing 24 weeks post-surgery. These differences create significant challenges in using all four limbs and accurately interpreting the results that one might generate. Therefore these findings do not support the use of four-limb models for study of tendon injury until the reasons for these differences are much better understood.