Radiographic Identification of Osseous Cyst- Like Lesions in the Distal Phalanx in 22 Lame Thoroughbred Horses Managed Conservatively and Their Racing Performance

Abstract

Reasons for performing study: To investigate the racing performance of Thoroughbred horses with osseous cyst-like lesions (OCLLs) in the distal phalanx causing lameness and treated conservatively.Objectives: To assess horses' ability to race and perform after radiographic identification of OCLL in the distal phalanx of Thoroughbred horses with lameness at the time of detection and undergoing conservative treatment.Study Design: Retrospective case control study.Methods: The clinical database of one equine clinic was reviewed in a 10-year period for Thoroughbreds showing lameness localized to the foot and a radiographic diagnosis of OCLL in the distal phalanx. Sex, age at time of detection of the OCLL, degree of lameness, affected limb, and treatment were recorded. Successful performance of horses was assessed by racing at least once after detection of the OCLL and maximum racing performance rating (RPR). Radiographic features such as size, location, sclerotic rim of the OCLL and irregularity of the articular surface of the distal phalanx were compared to successful performance using univariable statistical analysis. Successful performance of horses with OCLL was compared to a control group of maternal siblings by parametric testing.Results: Twenty-two horses met the inclusion criteria. Thirteen horses raced after the detection of OCLLs. Eight did not race, one case had not yet reached racing age, resulting in 62% (13/21) of racing age racing at least once. The number of successfully performing horses with an OCCL was significantly lower compared to their maternal siblings [p = 0.03, Odds ratio (OR) = 0.30]. If horses with OCLL in the distal phalanx raced, their RPR was similar to their maternal siblings. No significant association was found between radiographic features of OCLLs and successful performance, but OCLLs in the left forelimb carried a more favorable outcome for racing (p = 0.02, OR = 2.33 95%CI 1.27, 4.27) compared to OCLLs in any other limb.Conclusions: Horses with lameness and an OCLL in the distal phalanx managed conservatively are less likely to race when compared to their maternal siblings. If horses with OCLLs in the distal phalanx are able to race, their performance, measured as RPR, was comparable to their maternal siblings. Due to the small numbers in this study the results should be interpreted carefully.

A case‐control study of the morphological measurements of equine distal interphalangeal joints affected by osseous cyst‐like lesions

“…2017a; Peter et al . 2018), OCLLs were most commonly located in the centre of the articular surface of the distal phalanx. In our study, 81% of OCLLs of the distal phalanx were located in the central third of the articular surface in the mediolateral plane, with 14% medial and 5% lateral.…”

“…This distribution is similar to that reported by Peter et al . (2018) who identified 73% of OCLLs of the distal phalanx in the central third of the articular surface, with 18% medial and 9% lateral in 22 Thoroughbred horses with OCLLs diagnosed by radiography. It is not clear whether the more abaxially located OCLLs have a different pathogenesis from those axially located OCLLs.…”

“…In our study, all OCLLs of the distal phalanx were located either centrally or palmarly/plantarly in the dorsopalmar/plantar plane, again agreeing with the results of Peter et al . (2018). All 9 (100%) of the OCLLs identified in the distal condyle of the middle phalanx were located in the central third of the articular surface in the dorsal‐palmar/plantar plane.…”

“…2017b; Peter et al . 2018). Such indentations may occur independently or in association with deeper subchondral/trabecular bone lesions.…”

“…These lesions have been reported in the DIP joint and are most commonly located at the articular surface of the distal phalanx (Petterrson and Sevelius 1968;Wagner et al 1982;Verschooten and DeMoor 1982;Dyson 1991;Story and Bramlage 2004;Dyson et al 2005;Mair and Sherlock 2008;Sherlock and Mair 2011;Butler et al 2017a). The size and morphology of OCLLs affecting the DIP joint are variable, and small lesions described as 'depressions' or 'indentations' of the subchondral bone of the articular surface of the distal phalanx have been reported (Sherlock and Mair 2011;Butler et al 2017b;Peter et al 2018). Such indentations may occur independently or in association with deeper subchondral/trabecular bone lesions.…”