Recovery from synovial infection: How do the numbers stack up?

File image. © Mike Bain

Infections in the synovial fluid surrounding horse joints have the potential to end careers. So, what are the chances of a full return to work?

Researchers at Charles Sturt University in Australia have examined factors associated with the survival of horses and their return to function after synovial infections.

For their research, Danielle Crosby and her colleagues examined the medical records of all horses with synovial infections that were presented to the university’s equine hospital over a nine-year period, up until May 2017.

Of the 186 cases, 65.6%, were caused by penetrating wounds. Analysis showed that 151 of the horses had one joint structure affected, 18 had two affected, three had three structures affected, with the rest having four or more joints affected due mostly to infections carried via the blood.

Information on how each of the horses fared long-term was obtained through semi-structured telephone questionnaires, and an analysis of online race records, given that more than a third of the horses were Thoroughbreds.

Of the 186 horses, 161 of them (86.6%) were treated, and 145 of the treated horses (90.1%) survived to discharge.

Most of the affected joints were treated with synovial lavage (93.8%).

The researchers were able to get useful follow-up data on 121 of the horses, finding that 79 (65%) returned to function.

Increasing the number of days of treatment with systemic antimicrobials was associated with an increased likelihood of survival for each horse.

The overall rate of survival of horses treated for synovial infection was good, the study team reported in the journal, Frontiers in Veterinary Science.

However, the likelihood of returning to full function was lower, they said, describing a “moderate prognosis for achieving the desired use”.

Discussing their findings, the study team said the management of septic synovial structures in horses can represent a diagnostic and therapeutic challenge.

“In this study, 90.1% of horses treated for synovial infection survived to discharge and, of these, approximately two-thirds returned to function.

“We found positive association between longer systemic antimicrobial treatment duration and predicted survival,” they said. “This may reflect an increased owner commitment to treatment; however, in a previous study, 12 days or more systemic antimicrobial treatment was associated with reduced survival and post-operative performance of horses with synovial infection.”

The researchers found that horses treated with doxycycline were 2.5 times less likely to return to function.

This, they said, was likely explained by the use of this drug for infections that had proved resistant to treatment with other antimicrobial drugs, and a tendency for greater use in juvenile horses, which this and previous studies had shown are less likely to return to full function.

Increasing time in hospital, an increasing number of different antimicrobial drugs used, complications associated with treatment, and more repeat treatments with antimicrobials were linked to greater likelihood of not being able to return to function.

The authors noted that the rate of survival of horses was comparable to other studies, with improvement seen over the years due to improved diagnostic techniques allowing for more accurate identification of microorganisms and the development of endoscopic surgical techniques.

The rate of return to function for horses treated with synovial infection in this study was 65%. The rate of return to function for foals in this study (53.3%) was lower than adult horses (68.9%), and other studies have similarly reported a low return to function rates for foals of 26% and 48%.

“Collectively, these findings suggest that adult horses have improved rates of return to function compared to foals after treatment.”

This difference may be due to more complex clinical conditions in foals that are more likely to have a multi-systemic disease and multiple joint involvement.

Nearly half of the horses in the study population were used or intended to be used for racing (45.4%), and of the 58 racehorses treated, 31 (53.5%) had at least one start in a race.

After treatment for synovial infections, Standardbreds performed better than Thoroughbreds.

“This finding indicates that return to full athletic function after synovial infection is possible. Previous rates of return to racing range between 31 and 56%, similar to the findings of the current study.”

After treatment, Standardbreds performed better than Thoroughbreds.

“Although not significant in the final model, the performance data suggest an effect of breed on improved return to function.

“We speculate that Standardbreds in our population are an inherently more robust breed of horse that is more likely to perform despite secondary degenerative effects of synovial infection and they also are more likely to have a greater number of lifetime starts than Thoroughbreds, meaning there are more opportunities for performance outcomes.”

The study team comprised Crosby, Raphael Labens, Kristopher Hughes and Bryan Hilbert, all with the School of Animal and Veterinary Sciences at Charles Sturt University; and Sharon Nielsen, with Sharon Nielsen Statistical Consulting and Training.

Crosby DE, Labens R, Hughes KJ, Nielsen S and Hilbert BJ (2019) Factors Associated With Survival and Return to Function Following Synovial Infections in Horses. Front. Vet. Sci. 6:367. doi: 10.3389/fvets.2019.00367

The study, published under a Creative Commons License, can be read here

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