Microstructural features of subchondral radiolucent lesions in the medial femoral condyle of juvenile Thoroughbreds: A microcomputed tomography and histological analysis

Abstract

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.

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

“…Equine subchondral bone radiolucent lesions (SRs) or cysts are most frequently located in the cranial medial femoral condyle (MFC) 1‐3 . Survey radiographs prior to the selection of Thoroughbred yearling sales have revealed a radiographic prevalence of 3.4%‐7.8% of Thoroughbred yearlings afflicted with MFC SR 2,4,5 .…”

“…It has recently been observed that SRs in foals aged 6 months or less are first located axially in the MFC 1,2 . The youngest foal reported in the literature with histology of a naturally occurring axial MFC SR is 5 weeks of age 1 .…”

“…It has recently been observed that SRs in foals aged 6 months or less are first located axially in the MFC 1,2 . The youngest foal reported in the literature with histology of a naturally occurring axial MFC SR is 5 weeks of age 1 . The exact aetiology of spontaneous MFC SRs in juvenile horses remains unknown and there are two schools of thought: they arise secondary to a traumatic event 1 or they are a form of osteochondrosis (OC) 7,8 .…”

“…Two previous experimental studies employing surgical trauma in adult horses have reported that SRs will develop following a focal insult to the MFC 10,11 suggesting that trauma at this site can cause SR. However, the effects of trauma, either single or repeated, have not been assessed in juvenile MFCs that are structurally, biomechanically and biologically different from adult tissues 1 . In a recent study of naturally occurring SRs, osteochondral separations were identified between the cartilage and the subchondral bone at the osteochondral junction in juvenile specimens that contained fibrin (evidence of a recent microbleed) in the majority of the lesions 1 .…”

“…However, the effects of trauma, either single or repeated, have not been assessed in juvenile MFCs that are structurally, biomechanically and biologically different from adult tissues 1 . In a recent study of naturally occurring SRs, osteochondral separations were identified between the cartilage and the subchondral bone at the osteochondral junction in juvenile specimens that contained fibrin (evidence of a recent microbleed) in the majority of the lesions 1 . It could not be established if this was caused by a primary or secondary traumatic event such as instability and movement within the lesion 1 .…”