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Connect Tissue Res. 2019 Mar;60(2):95-106. doi: 10.1080/03008207.2018.1455670. Epub 2018 Apr 12.

Critical-sized cartilage defects in the equine carpus.

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a Department of Orthopaedics and Traumatology , University of Helsinki , Helsinki , Finland.
b Research Unit of Medical Imaging, Physics and Technology , University of Oulu , Oulu , Finland.
c Medical Research Center , University of Oulu and Oulu University Hospital , Oulu , Finland.
d Department of Applied Physics , University of Eastern Finland , Kuopio , Finland.
e Institute of Biomedicine , University of Eastern Finland , Kuopio , Finland.
f Department of Equine Sciences , Utrecht University , Utrecht , The Netherlands.
g SIB Labs , University of Eastern Finland , Kuopio , Finland.
h Section of Veterinary Clinical Sciences , School of Veterinary Medicine, University College Dublin , Dublin , Ireland.
i Department of Orthopaedics and Traumatology , Helsinki University Hospital , Helsinki , Finland.



The horse joint, due to its similarity with the human joint, is the ultimate model for translational articular cartilage repair studies. This study was designed to determine the critical size of cartilage defects in the equine carpus and serve as a benchmark for the evaluation of new cartilage treatment options.


Circular full-thickness cartilage defects with a diameter of 2, 4, and 8 mm were created in the left middle carpal joint and similar osteochondral (3.5 mm in depth) defects in the right middle carpal joint of 5 horses. Spontaneously formed repair tissue was examined macroscopically, with MR and µCT imaging, polarized light microscopy, standard histology, and immunohistochemistry at 12 months.


Filling of 2 mm chondral defects was good (77.8 ± 8.5%), but proteoglycan depletion was evident in Safranin-O staining and gadolinium-enhanced MRI (T1Gd). Larger chondral defects showed poor filling (50.6 ± 2.7% in 4 mm and 31.9 ± 7.3% in 8 mm defects). Lesion filling in 2, 4, and 8 mm osteochondral defects was 82.3 ± 3.0%, 68.0 ± 4.6% and 70.8 ± 15.4%, respectively. Type II collagen staining was seen in 9/15 osteochondral defects but only in 1/15 chondral defects. Subchondral bone pathologies were evident in 14/15 osteochondral samples but only in 5/15 chondral samples. Although osteochondral lesions showed better neotissue quality than chondral lesions, the overall repair was deemed unsatisfactory because of the subchondral bone pathologies.


We recommend classifying 4 mm as critical osteochondral lesion size and 2 mm as critical chondral lesion size for cartilage repair research in the equine carpal joint model.


Animal model; cartilage repair; critical-sized defect; preclinical research; spontaneous repair

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