Arthrogenic lameness of the fetlock: synovial fluid markers of inflammation and cartilage turnover in relation to clinical joint pain.
BACKGROUND
Joint pain is one of the most common causes of lameness in the horse but its pathogenesis is poorly understood.


OBJECTIVE
To investigate which synovial fluid markers may be related to the presence of clinically detectable joint pain in the horse.


METHODS
Concentrations of structural (CPII, C2C, GAG) and inflammatory markers (PGE2, LTB4, CysLTs, bradykinin and substance P) were measured in fetlock joint fluid from 22 horses in which lameness was localised to the fetlock region by perineural anaesthesia. Levels of these markers were then compared in horses that responded (n = 15) to those that did not (n = 7) to subsequent intra-articular anaesthesia (IAA).


RESULTS
Of all markers analysed, only substance P levels were significantly higher (P = 0.0358) in synovial fluid of horses that showed a positive response to IAA compared to those with a negative response to IAA. Notably, while PGE2 levels were found to be elevated in all 22 lame horses compared to sound controls (P = 0.0025), they were not related to the response to IAA.


CONCLUSIONS
While levels of PGE2 are elevated in synovial fluid of lame horses that respond to perineural anaesthesia, only substance P is related to joint pain as detected by the response to intra-articular anaesthesia.


CONCLUSIONS
Substance P is associated with clinically detectable joint pain in the horse. Elevated levels of PGE2 in fetlock-lame horses, regardless of their response to IAA, indicate that either this mediator does not reflect intra-articular pain or that IAA might have limitations in differentiating between intra- and peri-articular sources of pain. Either way, a negative response to IAA may not exclude intra-articular pathology.
de Grauw
J C
JC
Department of Equine Sciences, Faculty of Veterinary Medicine, Utrecht University, The Netherlands.
van de Lest
C H A
CH
van Weeren
R
R
Brommer
H
H
Brama
P A J
PA
D000818:Animals; D018771:Arthralgia / Q000175:diagnosis / Q000378:metabolism / Q000662:veterinary*; D015415:Biomarkers / Q000032:analysis; D001842:Bone and Bones / Q000378:metabolism; D002356:Cartilage / Q000378:metabolism; D016022:Case-Control Studies; D015237:Dinoprost / Q000032:analysis; D005260:Female; D006734:Horse Diseases / Q000175:diagnosis* / Q000378:metabolism; D006736:Horses; D007794:Lameness, Animal / Q000175:diagnosis* / Q000378:metabolism; D008297:Male; D009407:Nerve Block / Q000662:veterinary; D013373:Substance P / Q000032:analysis*; D013582:Synovial Fluid / Q000737:chemistry*; D013640:Tarsal Joints / Q000473:pathology*
D015415:Biomarkers; D013373:Substance P; D015237:Dinoprost