Standing Magnetic Resonance Imaging Findings in the Metacarpophalangeal Region of 76 Horses and Metatarsophalangeal Region of 24 Horses

Background: Standing magnetic resonance images (MRI) of metacarpophalangeal (MCP) and metatarsophalangeal (MTP) regions are increasingly acquired but imaging findings in large case series are lacking. 

Objectives: Describe abnormalities in horses undergoing standing MRI examination with lameness localised to, and compared between, MCP/MTP regions and sport disciplines. 

Study design: Retrospective descriptive. 

Methods: Signalment and findings from MCP/MTP MRI reports at Rossdales Ltd from December 2020-January 2022 were recorded, with queries verified by image review. Inclusion-criteria: lameness localised to fetlock region. 

Results: 76 MCP and 24 MTP from 100 horses (2-19 years; racing-39, sport-43, general-purpose-18). Dorsal and palmar/plantar third metacarpal/metatarsal (McIII/ MtIII), proximal phalanx (PP), proximal sesamoid bone (PSB) injury, suspensory ligament branch (SLB) desmopathy and MCP/MTP joint abnormalities were most frequently reported. McIII abnormalities were more frequently dorsomedial (65.8%) including cortical (42.1%) and trabecular (46%) pathology, with fluid signal (26.3% cortical; 30.3% trabecular), frequent hypervascularity, cortical thickening, irregularity, and periosteal/ endosteal abnormalities. Medial MCP articulation abnormalities were more frequently reported (85.5%) than lateral (55.3%), while lateral MTP pathology (66.7%) was more frequent. Dorsoproximal PP bone injury was more frequently reported in forelimbs (72.4%) than hindlimbs (54.2%). Joint pathologies included subchondral bone thickening/sclerosis (70.8% MTP; 71.1% MCP), fluid signal (58.3% MTP; 65.8% MCP), osteophytosis (41.7% MTP; 44.7% MCP), irregularity (62.5% MTP; 48.7% MCP), distension (66.6% MTP; 39.2% MCP), chronic synovitis (62.5% MTP; 51.4% MCP) and capsulitis (45.9% MTP; 33.8% MCP). Forelimb SLB (39.4%) and PSB (38.2%) pathology occurred together in 11.8% forelimbs. SLB desmopathy was more frequent in hindlimbs (58.3%), all with PSB pathology, as was digital flexor tendon sheath pathology (hindlimbs-29.1%; forelimbs-6.5%). Bone pathology was more likely in racing/showjumping than dressage/general-purpose horses. Ligament and chronic articular abnormality were more frequent in dressage/general-purpose horses. 

Main limitations: Retrospective review. 

Conclusions: Findings indicate pathology patterns vary between forelimbs/hindlimbs and disciplines which may be useful guidance for MRI interpretation. 

Ethical animal research: Research ethics committee oversight not required by this congress: retrospective data collection. 

Informed consent: Not stated. 

Competing interests: None declared. 

Sources of funding: None.

[...]