Does subchondral bone of the equine proximal phalanx adapt to race training?

Abstract

Sagittal fractures of the first phalanx are a common, potentially catastrophic injury in racehorses. These fractures are often linked to an acute, one time, biomechanical event; however, recent evidence implies that chronic exposure to stress can lead to the accumulation of bony changes that affect the structural integrity of the bone and increase the likelihood of fracture. The aim of the study was to compare variations of two common metrics of bone adaptation - subchondral bone density and thickness across the proximal articular surface of the first phalanx in Thoroughbred horses that (1) raced but never experienced a first phalanx fracture (Raced Control); (2) raced and had experienced fracture of the contralateral first phalanx (Contralateral to Fracture); (3) had never raced or experienced a first phalanx fracture (Unraced Control). A total of 22 first phalangeal bones were sampled post-mortem and imaged using micro-computed tomography calibrated for mineral density measures. Measurements of volumetric subchondral bone mineral density and thickness were taken from images at five sites from medial to lateral, in three coronal planes (25, 50 and 75% dorsal-palmar). At each of the 15 sites, measurements were repeated and averaged across 10 adjacent micro-computed tomography slices of bone, spanning 0.75 mm. The magnitude and variance of these measurements were compared between sites and between cohorts with non-parametric statistical tests. Across the proximal osteochondral surface of the first phalanx, the pattern of subchondral bone volumetric bone mineral density and thickness varied with each coronal section studied. The subchondral bone thickness was greater for the central and dorsal coronal sections, compared with the palmar section. For the race-fit groups (Raced Control and Contralateral to Fracture), the highest volumetric bone mineral density was in the central sagittal groove. The volumetric bone mineral density was significantly greater in the sagittal groove in the central coronal section in the raced than the unraced group. The Contralateral to Fracture group demonstrated significantly greater variance of volumetric bone mineral density compared with the Raced Control and Unraced Control (P < 0.0001), with no difference in variance noted between the Raced Control and Unraced Control groups. There was a small (R rank = 0.3) but significant correlation between subchondral bone volumetric bone mineral density and thickness in the Contralateral to Fracture group (P = 0.005). The findings demonstrate that differences exist in subchondral bone volumetric bone mineral density and thickness across the proximal osteochondral surface of the equine first phalanx in horses with different training histories. The findings also demonstrate that the subchondral bone of the sagittal groove of the equine first phalanx adapts to race-training in the race-fit groups (Raced Control and Contralateral to Fracture) with an increase in volumetric bone mineral density relative to unraced controls. Within the race-trained ...

Conservative versus surgical treatment of 21 sports horses with osseous trauma in the proximal phalangeal sagittal groove diagnosed by low‐field MRI

“…Traditionally, etiology of sagittal fracture of PP has been attributed to a monotonic event; 12 however, recently, repetitive trauma to the region has also been suggested as a contributory factor. 1,2,15 Authors have reported that horses with high water signal in the sagittal groove of the PP have mainly a chronic history of lameness (5/8 horses) 1 ; however, in this study, acute onset of lameness occurred in 14 of 21 horses. The difference in onset may reflect more rapid presentation and diagnosis of this injury in our population of horses, or it could represent different aetiologies.…”

Bone marrow oedema-type signal in the proximal phalanx of Thoroughbred racehorses

“…As proposed in the study, there is a growing recognition that stress-related pathology can be associated with the development of sagittal P1 fracture. More recently, this theory has been supported by a study using microcomputed tomography, which indicated that chronic exposure to stress could lead to excessive or inappropriate modeling or remodeling of the subchondral bone (SCB), characterized by variance in SCB volumetric mineral density observed in the contralateral limbs of P1 fractured cases [10]. These evidence may imply that avoidance of the progression to complete fracture could be possible by awareness of the clinical features and utilization of appropriate imaging modalities, such as sMRI.…”

“…It has been suggested that thickening of the trabeculae of MC3/MT3 could lead to a decrease in biomechanical integrity, and ultimately, increased fracture risk [20]. Noble et al proposed that maladaptation of P1 SCB to exercise, which was characterized by variance in SCB volumetric mineral density, may provide an alternate explanation to the one-time biomechanical event theory for sagittal fracture of P1 [10]. In the current study, special stains that can directly evaluate modeling and remodeling of the bone were not performed.…”

Arthroscopic evaluation of the metacarpophalangeal and metatarsophalangeal joints in horses with parasagittal fractures of the proximal phalanx

“…However, these theories are not necessarily mutually exclusive. Evaluation of the radiographic evidence for prodromal changes within the proximal phalanx in horses sustaining parasagittal fractures, 6 finite element modelling of the equine proximal phalanx 22 and evaluation of subchondral bone density and thickness across the proximal articular surface 23 using micro‐computed tomography have attempted to address some of these theories. Loss of active support from the soft tissues surrounding the fetlock joint, for example, the superficial and deep digital flexor tendons, has been suggested as a causative factor in overload of the suspensory apparatus and subsequent hyperextension of the fetlock joint.…”