Risk assessment for condylar stress fracture in elite racing Thoroughbreds using standing computed tomography-based virtual mechanical testing.

Abstract

<h4>Background</h4>Condylar stress fracture of the third metacarpal bone (MC3) is a common catastrophic injury in Thoroughbred racehorses and is associated with parasagittal groove (PSG) subchondral osteolysis. Standing computed tomography (sCT) imaging enables sensitive identification of this fatigue-induced early subchondral bone injury (SBI), but there is no objective method for identifying racehorses at heightened risk of condylar stress fracture.<h4>Objectives</h4>To estimate PSG first principal strain in elite Thoroughbred racehorses that have undergone subjective risk assessment using sCT fetlock screening.<h4>Study design</h4>Retrospective clinical study.<h4>Methods</h4>We used fetlock sCT images from nine thoracic limbs from seven Thoroughbred racehorses. A tuned, validated, 3D finite element (FE) analysis was used as a virtual mechanical test to estimate PSG first principal strain in the distal MC3 from these joints. Virtual mechanical testing results were compared with a subjective clinical imaging risk assessment using a screening approach by Racing Victoria.<h4>Results</h4>MC3 condyles with PSG SBI consistently and significantly displayed increased levels of first principal strain throughout the PSG. We found focal strain concentrations associated with the SBI location compared to condyles with no evidence of PSG SBI. Diagnosis of SBI with PSG focal osteolysis, FE-predicted strain elevation, and clinical imaging risk assessment were concordant with R² = 0.62.<h4>Main limitations</h4>The sample size was small, and our virtual mechanical testing protocol does not account for whole-joint physiology.<h4>Conclusions</h4>Risk assessment through sCT screening is an established approach to injury prevention in racing Thoroughbreds. Concordance of a current clinical imaging risk assessment approach by Racing Victoria with objective FE analysis of principal strain in sites of PSG SBI in the present study suggests 3D FE analysis using a validated pipeline has potential as a new approach for routine assessment of risk of MC3 condylar stress fracture in Thoroughbred racehorses once computational pipeline automation yields a clinically relevant analysis time.