Computed tomography identifies the proximodorsomedial subchondral bone of equine central tarsal bones as a predilection site for sclerosis, demineralisation and associated fractures.

This study used CT scans of horses’ hocks to map where bone hardening, bone loss, and cracks occur in the central tarsal bone. It found the top-front-inside (proximodorsomedial) bone just under the cartilage is the main hotspot, where hardening is closely linked to areas of bone loss and fractures.

What the researchers set out to understand

• Determine where, within the equine central tarsal bone (CTB), structural changes are most likely to occur on computed tomography (CT).
• Characterize the types of changes—sclerosis (bone hardening), demineralisation (bone loss/lucency), cyst-like lesions, and fissures/fractures—and assess how they relate to each other.
• Address a gap in the literature beyond well-known slab and dorsomedial–plantarolateral fracture patterns by mapping lesion distribution across predefined CTB regions.

Why this matters

• The CTB is a key load-bearing bone in the horse’s hock (tarsus), articulating proximally with the talus and distally with the third tarsal bone, and medially/laterally with adjacent tarsals.
• Subchondral bone (the layer just beneath joint cartilage) adapts to load; excessive or repetitive stress can lead to sclerosis, focal bone loss, microcracks, and ultimately fractures.
• Identifying a consistent “predilection site” helps clinicians target imaging review, improve early detection, and refine management to prevent progression.

Study design and methods

• Design: Retrospective case series.
• Population: 94 clinical tarsi evaluated with CT (both standing and recumbent studies included), reflecting a heterogeneous but warmblood-oriented case mix.
• Assessment: CTBs were divided into 8 anatomical regions spanning proximal vs distal subchondral bone and dorsomedial/dorsolateral/plantaromedial/plantarolateral quadrants.
• Recorded variables: Degree of sclerosis (none to severe), presence of demineralisation (lucencies), cyst-like lesions, and fissures/fractures, with precise regional mapping.
• Analysis: Associations between sclerosis grade and lesion prevalence were tested; orientations of fissures/fractures were classified.

Key findings

• High prevalence of substantial sclerosis:
  • 85 of 94 tarsi showed at least one region of moderate-to-severe sclerosis.
  • About 90% of those sclerosis changes involved the dorsomedial region, especially proximally beneath the articular surface.
• Lesions cluster where sclerosis is greatest:
  • At the dorsomedial site, higher sclerosis grades were significantly associated with more lesions (p=0.04).
• Demineralisation focuses proximally and dorsomedially:
  • Of 32 demineralising lesions, 21 were in the proximal subchondral bone dorsomedially.
• Fissures and fractures follow a characteristic orientation and often co-exist with demineralisation:
  • 24 CTBs had fissures/fractures; 19 of 24 ran dorsomedial to plantarolateral.
  • Of those 19, 17 were associated with demineralisation, suggesting fatigue-related progression.
  • Five fissures/fractures with different configurations lacked associated demineralisation, consistent with more acute or distinct mechanisms.
• Cyst-like lesions favor the distal subchondral bone and the medial side:
  • 27 cyst-like lesions were identified; 21 of 27 were distal, and nearly half (13 of 27) were medial.

How to interpret these results

• The proximodorsomedial subchondral plate of the CTB is a biomechanical hotspot:
  • Concentrated loading at the top-front-inside surface likely drives adaptive sclerosis.
  • Adjacent focal bone loss (demineralisation) and typical dorsomedial–plantarolateral fissures are consistent with stress redistribution and fatigue microdamage.
• Link between sclerosis and damage:
  • Where bone is most sclerotic, lesions are more frequent, implying that load-induced remodeling can precede or accompany structural failure.
• Different fracture phenotypes, different pathways:
  • Fractures without nearby demineralisation may reflect acute high-impact events rather than chronic fatigue.
• Distal, medial cyst-like lesions:
  • These likely relate to distal intertarsal joint loading and early degenerative changes, separate from the proximal dorsomedial fatigue pattern.

Clinical and imaging implications

• Targeted scrutiny:
  • Carefully examine the dorsomedial proximal subchondral bone of the CTB on CT and radiographs.
  • Look for a combination of features: a dense sclerotic band, adjacent small lucencies, and fine linear defects oriented dorsomedial–plantarolateral.
• Radiography tips:
  • Use dorsomedial–plantarolateral obliques and high-detail views to improve sensitivity for the typical fracture orientation.
• Risk staging and monitoring:
  • Moderate-to-severe sclerosis at this site with emerging demineralisation may signal increased risk of fissure/fracture progression.
  • Serial imaging can track remodeling or healing, particularly in performance horses with hock soreness.
• Differential considerations:
  • Distal cyst-like changes may indicate developing distal intertarsal osteoarthritis and warrant separate assessment and management.

Strengths and limitations

• Strengths:
  • Large CT dataset for a single small tarsal bone across clinical cases.
  • Systematic regional mapping enables practical, site-specific interpretation.
• Limitations:
  • Retrospective design limits control over imaging protocols and case selection.
  • Warmblood-oriented, heterogeneous sample reduces generalisability across breeds and disciplines.
  • No clinical outcome correlation or histological confirmation to validate lesion biology.
  • Standing vs recumbent CT variability and potential artifacts were not deeply explored.

How this advances prior knowledge

• Extends the understanding of CTB pathology beyond classic slab and dorsomedial–plantarolateral fractures by:
  • Pinpointing the proximodorsomedial subchondral plate as the dominant site for sclerosis and linked demineralisation.
  • Demonstrating a strong spatial and mechanistic association between sclerosis, bone loss, and fissuring.

Future directions

• Prospective studies correlating CT findings with lameness, performance, and outcomes to determine prognostic value.
• Biomechanical and finite element modeling to quantify load distribution and identify thresholds for damage at the dorsomedial proximal plate.
• Histopathology to validate whether “cyst-like” lesions represent true subchondral cysts, channels, or resorption cavities.
• Standardized CT protocols (standing vs recumbent) and dose/reconstruction parameters optimized for subchondral assessment.

Practical takeaways

• The proximodorsomedial proximal subchondral bone of the central tarsal bone is the prime hotspot for pathology.
• Moderate-to-severe sclerosis at this site increases the likelihood of adjacent demineralisation and dorsomedial–plantarolateral fissures/fractures.
• Distal, medial cyst-like lesions are common but appear to represent a different process, likely linked to distal joint loading.
• Both CT and carefully chosen radiographic views should prioritise this region to improve early detection and risk assessment.