Why Radiographic Findings Must Match the Horse

This interpretation framework reflects referral-level radiological assessment used in equine lameness practice, including case review, second-opinion reporting, and longitudinal follow-up of sport horses.

Reviewed against current reference standards and updated to reflect contemporary equine diagnostic imaging for veterinarians practice.

The horse is lame and lameness is abolished by palmar digital nerve blocks. You’ve acquired what you think is a good set of radiographs but you are unable to detect any radiological abnormality.

You went back and blocked the navicular bursa and the lameness improved.

So what now?

Or maybe it’s the opposite. There are many radiographic abnormalities – multiple large and variably shaped synovial invaginations; some increase in opacity of the spongiosa; questionable irregularity of the palmar margin of the palmar compact bone.

But the horse is sound and competing, without any history of medication and without any special pads or shoes.

This is where clinical-radiographic correlation matters. A radiographic finding only becomes meaningful when it is interpreted alongside the horse’s history, clinical examination and response to diagnostic analgesia.

The navicular bone cannot be considered in isolation, and radiographic abnormalities involving it do not automatically identify the source of pain.

Radiographs are not definitive. They’re a tool. And like any tool, their value depends on their quality and how they’re used.

Now it’s time to bring them together and ask the bigger question:

Does what I see on the screen match the horse in front of me? That’s the question every good lameness equine veterinarian learns to ask. Because when it doesn’t – the radiograph isn’t wrong. It’s just not the whole story.

What Equine Radiographs Can and Cannot Tell You

Radiographs are central to the diagnostic workup of palmar foot pain, but they are not definitive. They show structural change, not the source of pain itself.

The anatomy is complex, so a structural abnormality should always be interpreted in the context of the structures around it and the clinical findings.

The navicular bone cannot be considered in isolation. It forms part of the podotrochlear apparatus, contributes to the distal interphalangeal joint, and is closely related to the deep digital flexor tendon.

What radiographs can show

A well-positioned set of navicular radiographs can highlight:

• Synovial invaginations
• Alterations of shape of the navicular bone
• Palmar compact bone irregularity
• Alterations of opacity of the spongiosa
• Entheseophyte formation
• Some distal border fragments
• A bipartite or tripartite navicular bone
• Some fractures

What radiographs may not show

But what they can’t show is just as important:

• Early osseous pathology
• Bone marrow oedema, fibrosis or necrosis
• Injury to related soft tissues such as the DDFT, collateral sesamoidean ligament or distal sesamoidean impar ligament
• Navicular bursa pathology

These limitations are not necessarily due to poor technique. They reflect the inherent limitations of radiography as an imaging modality, particularly for early osseous change and soft tissue pathology.

If the clinical findings remain unexplained by radiography, MRI may be appropriate to investigate osseous and soft tissue pathology that cannot be identified radiographically, if it is available and within the client’s budget.

If MRI is not feasible, response to medication of the navicular bursa and/or the distal interphalangeal joint may provide additional clinical information in selected cases.

That is why interpretation must begin with the horse, not the image. If the radiographic findings do not fit the clinical picture, go back to the history, clinical examination, diagnostic analgesia and the quality and completeness of the imaging before deciding what significance to place on what you see.

How to Decide Whether a Radiographic Finding Is Clinically Significant

When the radiographic findings and the clinical picture do not appear to agree, the next step is not to force the image to explain the lameness.

Instead, go back to the horse. Consider the history, clinical examination, response to diagnostic analgesia and the quality and completeness of the radiographic examination before deciding whether a radiographic finding is likely to be clinically relevant.

The following clinical findings may help you decide how much significance to place on a normal, borderline or abnormal radiographic examination:

1. Does the lameness appear to localise to the palmar aspect of the foot?

• Bilateral low-grade forelimb lameness
• Worse on hard ground or tight circles
• May not improve with farriery or rest

If these signs persist, do not dismiss them simply because the radiographs appear unremarkable. The source of pain may involve structures or changes that are not detectable radiographically.

Low-field MRI also has limitations, and not all pain is necessarily associated with a detectable structural abnormality.

Palmar digital nerve blocks are not specific to the palmar aspect of the foot and may also desensitise structures more proximally.

2. What does the response to diagnostic analgesia tell you?

A positive response to analgesia of the navicular bursa can provide useful localisation information, but it does not necessarily identify the navicular bone as the primary source of pain.

Closely related soft tissue structures may also contribute, and more than one structure can be involved.

A radiographic examination without detectable abnormalities therefore does not exclude clinically significant pathology.

3. Could hoof conformation be contributing to the clinical picture?

• Long toe, low heel
• Broken-back hoof-pastern axis
• Mediolateral imbalance

Hoof conformation and balance may alter loading of the podotrochlear apparatus, the distal interphalangeal joint and associated soft tissues.

These structures include the deep digital flexor tendon, structures associated with the ungular cartilages and the attachments to the distal phalanx.

4. Does the history fit the radiographic findings?

• Intermittent lameness
• Poor performance without overt lameness but an insidious shortening of step length
• Discomfort that returns despite rest and corrective shoeing

These findings may still be clinically important even when radiographic abnormalities are absent or equivocal.

The important point is not to make the radiograph fit the diagnosis. It is to decide whether the imaging findings make sense when considered alongside the horse’s history, examination and response to diagnostic analgesia.

Common Mistakes When Interpreting Equine Radiographs

Interpretation errors can occur when a radiographic finding is considered in isolation, without enough weight being given to image quality, the clinical examination, diagnostic analgesia and the horse’s history.

Here are the most common mistakes, and what they can cost the horse, the client, and the veterinarian.

1. Was the radiographic examination technically adequate?

The lateromedial projection is essential, but it must be acquired without obliquity to be of diagnostic value.

The entire radiograph should also be assessed systematically. Consider the thickness and opacity of the palmar compact bone, whether there is proximal or distal extension, whether a distal fragment or proximal entheseophyte is present, and whether there are changes involving the distal interphalangeal joint or distal phalanx.

2. Were enough high-quality views obtained?

A limited number of projections may not provide enough information to assess the navicular bone and surrounding structures adequately.

For a complete radiographic assessment, image quality, positioning and the range of projections all matter. Avoid declaring the navicular bone normal or abnormal on the basis of an incomplete examination.

3. Could the radiographic finding be incidental?

It is easy to focus on an enlarged synovial invagination, focal increased opacity or a small entheseophyte and assume that it explains the clinical problem.

In a sound horse, some radiographic abnormalities may not be clinically relevant at that time.

Conversely, clinically important pain may still be present when radiographs are unremarkable.

4. Are you communicating the uncertainty clearly?

Radiographs can create a false sense of certainty if they are used to provide a definitive answer when the clinical picture remains unresolved.

It can be more appropriate to explain that the radiographs do not identify a clear cause of pain, that radiography has limitations, and that further investigation or a second opinion may be appropriate.

5. Do you need to reassess or image further?

Radiographs provide information from one point in time. If the clinical picture changes, remains unresolved or does not fit the original interpretation, reassessment may be warranted.

That may include repeating the clinical examination, reviewing the existing images, obtaining additional radiographic projections, considering ultrasonography or other imaging modalities, or seeking a second opinion.

Foot balance and farriery should also remain part of the clinical assessment where relevant.

When the Radiographic Findings and the Horse Don’t Match

These cases demonstrate why radiographic findings need to be interpreted alongside the clinical examination, diagnostic analgesia and the horse’s history.

Case 1: Radiographs Look Normal. The Horse Is Not.

Horse: 10-year-old Warmblood gelding, dressage
History: Subtle, bilateral forelimb lameness. Worse in circles and on hard surfaces.
Diagnostic blocks: Positive response to navicular bursa analgesia
Radiographs:

• Normal palmar compact bone margins
• No significant increased opacity of the spongiosa
• Symmetrical, well-defined synovial invaginations

Follow-up: MRI revealed dorsal fibrillation of the DDFT in the region of the navicular bone and mild increased signal intensity in the spongiosa of the navicular bone, possibly consistent with bone edema.

Outcome: Treated appropriately and returned to work with hoof care and a controlled rehabilitation program.

The radiographs did not identify everything that was contributing to the clinical picture.

Case 2: The Films Look Alarming. The Horse Isn’t Lame.

Horse: 12-year-old show jumper, competing sound
History: No lameness, consistent performance at 1.20m level
Radiographs:

• Generalised increased radiopacity of the spongiosa of the navicular bone. Multiple large synovial invaginations restricted to the distal horizontal border of the navicular bone.
• Mild flattening of the palmar margin of the palmar compact bone, lateral to the sagittal ridge

Clinical examination: Normal gait under all circumstances (in hand, on the lunge and ridden), well trimmed and shod; no pads; conventional open shoes; no response to hoof testers.

Outcome: Passed prepurchase examination with radiographic findings noted but not considered currently clinically relevant, but with a caveat that progression may occur. Follow-up 18 months later: still sound.

The radiographic abnormalities were present, but they did not correspond with clinical lameness at that time.

Case 3: The Grey Zone

Horse: 9-year-old eventer
History: Mild intermittent left forelimb lameness
Blocks: Improved from grade 2/8 lameness to grade 1/8 after palmar digital nerve blocks; sound after palmar blocks at the level of the base of the proximal sesamoid bones
Farriery history:  Mediolateral foot imbalance; trimming and shoeing interval six weeks
Radiographs:

• Six variably sized and shaped synovial invaginations along the distal horizontal border of the navicular bone and an additional radiolucent area at the junction of the horizontal and medial sloping border
• Small rounded mineralised opacity distal to the distal medial aspect of the navicular bone

Approach:  Hoof balance addressed. Trimming and shoeing interval reduced to 5 weeks. Lameness resolved within 4 weeks with no further intervention.

In this case, the radiographic findings were only one part of the clinical picture.

How to Apply This in Your Next Lameness Workup

Radiographs matter, but they do not tell the whole story. The navicular bone cannot be considered in isolation, and a radiographic abnormality should not automatically be assumed to explain the horse’s lameness.

When you are working through your next case, keep these principles in mind:

• Do not assume that unremarkable radiographs mean there is no source of pain. Radiography has limitations, and clinically important pathology may not always be detectable radiographically.
• Correlate the imaging findings with the clinical examination. Consider the history, lameness examination and response to diagnostic analgesia alongside what you see on the radiographs.
• Make sure the radiographic examination is adequate. Image quality, positioning and appropriate projections all influence what you can identify and how confidently you can interpret it.
• Do not overinterpret abnormalities in a sound horse. A radiographic finding may be present without being clinically relevant at that time.
• Look at the whole horse. Hoof balance, farriery, performance history and the findings from the clinical examination all contribute to your interpretation.
• Be comfortable with uncertainty. If the clinical and radiographic findings do not agree, reconsider the examination, review the images, obtain additional information where appropriate or seek a second opinion.

The goal is not to find a radiographic abnormality and make the horse fit it. It is to determine whether the imaging findings make sense in the context of the horse in front of you.

If you want to strengthen your approach to equine lameness investigation, image interpretation and clinical decision-making, you can explore our equine lameness continuing education.

Final Thoughts

The navicular bone is not always the source of pain in a horse with palmar foot pain. Radiographs can provide valuable information, but they should not be interpreted in isolation.

The most useful question is not simply, “What abnormality can I see?” It is, “Does this finding fit the horse in front of me?”

That means bringing the radiographs back to the history, clinical examination, diagnostic analgesia and the quality of the imaging before deciding how much clinical significance to place on a finding.

When those pieces do not agree, the answer is not to force certainty. It is to reassess the case, consider what the imaging modality may have missed and decide whether further investigation or a second opinion is warranted.

The principles outlined here reflect teaching and case-based reasoning used in advanced lameness education, including material taught by Dr Sue Dyson in referral and postgraduate clinical settings.