Histological and Histopathological Features of the Third Metacarpal/Tarsal Parasagittal Groove and Proximal Phalanx Sagittal Groove in Thoroughbred Horses with Racing History

Abstract

Information regarding the histopathology of the proximal phalanx (P1) sagittal groove in racehorses is limited. Twenty-nine cadaver limbs from nine Thoroughbred racehorses in racing/race-training underwent histological examination. Histological specimens of the third metacarpal/metatarsal (MC3/MT3) parasagittal grooves and P1 sagittal grooves were graded for histopathological findings in hyaline cartilage (HC), calcified cartilage (CC), and subchondral plate and trabecular bone (SCB/TB) regions. Histopathological grades were compared between (1) fissure and non-fissure locations observed in a previous study and (2) dorsal, middle, and palmar/plantar aspects. (1) HC, CC, and SCB/TB grades were more severe in fissure than non-fissure locations in the MC3/MT3 parasagittal groove (p < 0.001). SCB/TB grades were more severe in fissure than non-fissure locations in the P1 sagittal groove (p < 0.001). (2) HC, CC, and SCB/TB grades including SCB collapse were more severe in the palmar/plantar than the middle aspect of the MC3/MT3 parasagittal groove (p < 0.001). SCB/TB grades including SCB collapse were more severe in the dorsal and middle than the palmar/plantar aspect of the P1 sagittal groove (p < 0.001). Histopathology in the SCB/TB region including bone fatigue injury was related to fissure locations, the palmar/plantar MC3/MT3 parasagittal groove, and the dorsal P1 sagittal groove.

Keywords: articular cartilage; fissure; metacarpal/metatarsal parasagittal groove; proximal phalanx sagittal groove; subchondral bone; thoroughbred.

Figure 4

Summary of histological grades compared between fissure and non-fissure locations. HC (hyaline cartilage); CC (calcified cartilage); SCB/TB (subchondral plate and trabecular bone). (A) HC, CC, and SCB/TB histological grades were more severe in fissure (F) than non-fissure (N) locations in the third metacarpal/tarsal parasagittal groove (MC3/MT3). (B) SCB/TB histological grades were more severe in F than N locations in the proximal phalanx sagittal groove (P1). * Significant difference (p < 0.001). Circles above or below the end of the whiskers represented outliers.

Figure 5

Proportion of grades for fissure and non-fissure locations. HC (hyaline cartilage); CC (calcified cartilage); SCB/TB (subchondral plate and trabecular bone); PG (third metacarpal/metatarsal parasagittal groove); SG (proximal phalanx sagittal groove); F (fissure location); N (non-fissure location). * Significant difference (p < 0.05).

Figure 6

Summary of histological grades compared between dorsal, middle, and palmar/plantar aspects. HC (hyaline cartilage); CC (calcified cartilage); SCB/TB (subchondral plate and trabecular bone). (A) HC, CC, and SCB/TB histological grades were more severe in the palmar/plantar (P) aspect, and the HC and CC histological grades were more severe in the dorsal (D) aspect than the middle aspect (M) in the third metacarpal/tarsal parasagittal groove (MC3/MT3). (B) SCB/TB histological grades were more severe in the D and M aspects than the P aspect in the proximal phalanx sagittal groove (P1). * Significant difference (p < 0.001). Circles above or below the end of the whiskers represented outliers.

Figure 7

Proportion of grades for dorsal, middle, and palmar/plantar aspects. HC (hyaline cartilage); CC (calcified cartilage); SCB/TB (subchondral plate and trabecular bone); PG (third metacarpal/metatarsal parasagittal groove); SG (proximal phalanx sagittal groove); D (dorsal); M (middle); P (palmar/plantar). * Significant difference (p < 0.05).

Figure 1

Schematic overview of the study including histological preparation, examination, grading, and data analysis. The grouping of fissures was defined in the previously published study, where fissures were identified on both cone-beam and fan-beam computed tomography and were confirmed by histological examination [26].

Figure 2

Bone specimens from a hindlimb. From left to right: bone specimens collected from the dorsal, middle, and plantar aspects of the third metatarsal parasagittal groove (A) and proximal phalanx sagittal groove (B). The lateral side of the specimen was marked using a bandsaw. The shape of specimens from the third metacarpal bone is different from specimens from the proximal phalanx.

Figure 3

Illustration of the regions graded for histopathological changes, grouped for comparison, and outcome. Histological specimen in the box on the right demonstrated regions of hyaline cartilage (HC), calcified cartilage (CC), and subchondral plate and trabecular bone regions (SCB/TB). Histopathological grades from third metacarpal/metatarsal (MC3/MT3) and proximal phalanx (P1) were analysed separately and were compared using two approaches: (A) fissure and non-fissure locations and (B) dorsal (D), middle (M), and palmar/plantar (P) aspects. HC, CC, and SCB grades were most severe in fissure locations and the palmar/plantar aspect of the MC3/MT3 parasagittal groove. SCB grades were most severe in fissure locations and the dorsal and middle aspects of the P1 sagittal groove.