Deep Digital Flexor Tendon Lesions: What the Research Says
Evidence from 25 peer-reviewed studies
What Professionals Should Know
- •Palmar foot pain involves multiple structures beyond the navicular bone alone—assess DSIL, navicular bursa, and DDFT as part of a functional unit in lame horses
- •Not all navicular bone changes correlate with lameness; focal medullary lesions dorsal to FFC lesions appear most clinically relevant
- •Adaptive changes occur in navicular apparatuses of all horses; identifying which lesions cause pain and dysfunction should guide targeted treatment rather than treating all structural changes identically
- •MR imaging reliably represents tissue damage in the equine foot and can be confidently used to diagnose moderate-to-severe lesions of the deep digital flexor tendon, collateral sesamoidean ligament, and navicular bursa
- •Interpret dorsal and proximal navicular bone findings on MR with caution, as agreement with actual tissue pathology is poor and may not reflect true disease severity
- •MR signal changes in foot structures correlate with specific histopathologic processes, validating its use as a diagnostic tool but emphasizing the importance of considering anatomic location and lesion severity when making clinical decisions
- •Navicular bursoscopy may improve short-term lameness despite MRI showing bursal proliferation and worsening appearance—manage client expectations about imaging vs. clinical recovery.
- •Poor return-to-work rates (29%) suggest bursoscopy alone is insufficient; multimodal treatment of concurrent foot lesions (DDFT, navicular bone, ligaments) should be considered.
- •Post-operative rehabilitation protocols may be critical to functional recovery even when imaging appears to worsen—prioritize structured rehabilitation rather than relying on imaging resolution.
- •Distal border fragments should be considered clinically significant especially when large or concurrent with other lesions; radiographic findings must be interpreted alongside clinical signs as imaging doesn't always correlate with soft tissue pathology
- •Intensive exercise and training stress are key drivers of navicular bone deterioration through disrupted bone remodeling; managing workload appropriately is critical for prevention and management of navicular disease
- •Synovial invaginations and nutrient foramina changes may indicate circulatory disturbances and abnormal bone turnover—consider vascular and metabolic factors when managing horses with navicular pathology, not just mechanical factors
- •Radiographic measurements can reliably predict the presence and type of soft tissue lesions in the foot—use this to guide advanced imaging decisions and treatment planning
- •Long-toed conformation is a significant risk factor for navicular bone pathology; address toe length in remedial farriery protocols
- •Specific radiographic parameters (palmar angle, phalanx angles, navicular bone dimensions) should prompt investigation of particular structures on MRI rather than generic foot imaging
- •Ultrasound alone may miss manica flexoria tears—consider additional diagnostic imaging (contrast radiography) and intrathecal analgesia blocks when clinical signs suggest DFTS pathology but ultrasound is inconclusive
- •Intrathecal analgesia can help localize DFTS problems and guide decisions between conservative and surgical management
- •Multi-modal diagnostic approach improves diagnostic confidence for complex digital flexor tendon sheath cases
- •Suspect caudal distal radial osteochondromata in young Thoroughbred racehorses with forelimb lameness; imaging findings may be subtle without ultrasonography
- •Always evaluate the deep digital flexor tendon in these cases as concurrent lesions significantly impact prognosis and treatment planning
- •Appropriate identification and management of associated soft tissue injury is critical for return to racing
- •If standard MRI is inconclusive about adhesions in the navicular bursa, MR bursography with controlled distension can provide diagnostic clarity for horses with palmar heel pain
- •Adhesions in the navicular bursa may not be visible on conventional MRI and require contrast distension to be reliably detected
- •This advanced imaging technique can guide treatment decisions in cases where conventional diagnostics cannot rule out bursal adhesions as a pain source
- •Standing MR imaging should be used for suspected palmar navicular erosions as radiography often appears normal or equivocal and delays diagnosis
- •Deep palmar navicular erosions carry a poor prognosis—44% of cases resulted in euthanasia and only one horse returned to work, supporting early diagnosis of shallow lesions to allow therapeutic intervention
- •Sudden onset lameness with positive MR findings on the palmar navicular aspect warrants careful prognosis discussion with owners regarding likelihood of return to performance
- •Navicular bursoscopy should be considered in lame horses with foot pain localised to the navicular region, as it identifies lesions missed by standard imaging (CT/MRI)
- •Expect to find DDFT tears in nearly all cases of clinical navicular bursa disease, and cartilage damage in approximately one-third of cases
- •Bursoscopy enables minimally invasive treatment, with good prognosis: ~73% of followed horses returned to soundness and pre-injury performance
- •Transcuneal ultrasound is a reliable diagnostic tool for evaluating navicular syndrome—use it to identify bursal inflammation, DDFT changes, and impar ligament involvement that correlate with clinical caudal heel lameness
- •Normal measurements alone don't diagnose navicular disease; focus on subjective findings like bursitis, mineralization patterns, and cortical bone changes visible on ultrasound
- •This imaging approach helps differentiate navicular syndrome components, allowing more targeted management and prognosis discussions with owners
- •MR imaging reliably identifies DDFT pathology in navicular syndrome, particularly lesions at the distal sesamoid level, supporting its use for diagnostic confirmation before treatment decisions
- •Distal sesamoid bone marrow changes are consistent findings in navicular disease and may indicate the extent of degenerative changes affecting prognosis
- •Understanding the correlation between MR signal patterns and specific histologic lesions (edema, necrosis, cyst formation) helps interpret clinical MR images and explain lameness severity
- •Collateral ligament desmitis of the DIP joint should be considered in cases of foot lameness, particularly when lameness worsens in circles; ultrasound can miss lesions so MRI is recommended for definitive diagnosis
- •Response to palmar digital analgesia (87% improvement) suggests the collateral ligaments of the DIP joint are major pain sources in foot lameness, so careful assessment of this region is warranted
- •Concurrent soft tissue injuries are common (61% of cases), so imaging should evaluate the entire palmar/plantar foot structures including DDFT, navicular region, and distal sesamoidean ligaments
- •MRI provides superior diagnostic capability for equine foot lameness compared to traditional imaging methods when soft tissue and cartilage pathology is suspected
- •This technology offers a non-invasive diagnostic tool that can identify lesions missed by radiography, scintigraphy, and ultrasound, potentially improving clinical outcomes
- •Early adoption of MRI imaging in equine practice may enhance diagnostic accuracy and treatment planning for chronic or refractory foot lameness cases
- •If navicular syndrome is suspected but radiographs appear normal or inconsistent with clinical signs, CT or MRI can reveal significant pathology not visible on conventional radiography and guide more targeted therapeutic decisions
- •CT provides superior bony detail while MRI excels at soft tissue visualization; consider requesting CT for osseous assessment and MRI for tendon and ligament evaluation of the navicular region
- •Radiographic changes alone should not be used to rule out navicular syndrome; advocate for advanced imaging when clinical signs persist despite normal or equivocal radiographic findings
- •MRI should be integrated into your diagnostic approach for horses with foot pain and suspected DDFT injury to enable accurate diagnosis and prognosis assessment
- •Serial MRI imaging during rehabilitation is essential for monitoring lesion progression and guiding return-to-work decisions in DDFT cases
- •When MRI is unavailable, ultrasound and computed tomography can provide complementary diagnostic information, though MRI remains the gold standard for soft tissue characterization
- •MRI findings of hyperintense lesions on the dorsal DDFT border within the navicular bursa are reliable indicators for surgical intervention via bursoscopy
- •While bursoscopy allows direct visualization and removal of synovial masses, prognosis remains cautious—manage owner expectations accordingly
- •Correlation between imaging and endoscopic findings is good, so bursoscopy can be confidently recommended when MRI shows these lesions
- •If intra-articular corticosteroid injection to the navicular bursa is necessary, triamcinolone acetonide may be a safer choice than methylprednisolone based on lower cell toxicity in laboratory conditions
- •Methylprednisolone's rapid cytotoxic effects suggest particular caution with this agent near sensitive soft tissues like the DDFT and navicular fibrocartilage
- •These are laboratory findings in isolated tissue; clinical outcomes may differ—discuss risks/benefits with your veterinarian before injection decisions
- •Advanced imaging (MRI and CT) should be considered complementary to ultrasound for complex flexor tendon cases, particularly when determining prognosis and return-to-work timelines.
- •Understanding 'magic angle' artefacts in MRI is essential to avoid misinterpretation of deep digital flexor tendon lesions.
- •Newer imaging protocols including contrast-enhanced MRI and emerging techniques may improve early detection of tendon pathology before clinical signs become apparent.
- •MRI-guided injection of DDFT lesions within the hoof is technically feasible and achieves high accuracy, offering a new option for therapeutic injection of difficult-to-access distal tendon lesions
- •Distal injection locations (adjacent to navicular bone) show higher success rates than proximal locations, which should inform injection targeting strategy
- •This technique could enable standing patients to receive intralesional biologic therapeutics for DDFT healing without general anesthesia, though cadaver validation limits current clinical applicability
- •Understanding that navicular disease results from mechanical stress mismanagement at the enthesis can guide farrier and veterinary management toward reducing compressive loading through trimming, shoeing, and movement modifications.
- •The navicular apparatus functions as a sophisticated pulley system; shoeing and trimming changes that alter foot angle or loading distribution directly affect force dissipation at the enthesis and disease risk.
- •Recognition of the bursa and fat pad's protective roles suggests that interventions preserving fluid dynamics and reducing pressure spikes (e.g., appropriate shoe design, controlled exercise) may help prevent or manage navicular pathology.
- •Do not rely solely on radiographs to diagnose or rule out navicular syndrome; advanced imaging (MRI/CT) may be necessary when clinical signs suggest navicular disease but radiographs are inconclusive
- •Navicular syndrome diagnosis requires integration of history, physical examination, lameness evaluation, and diagnostic anesthesia alongside imaging—no single test is definitive
- •Consider structures beyond the traditional navicular complex (bone, bursa, DDFT) when investigating chronic forelimb lameness, as newer imaging reveals additional pathologic involvement
- •Understanding the comparative strengths of CT, CECT, and standing LFMRI helps practitioners select the most appropriate imaging modality for specific foot pathology types
- •Standing LFMRI offers a non-invasive alternative to traditional imaging without requiring general anesthesia, but clinicians need to know when each modality has superior diagnostic capability
- •Knowledge of imaging limitations prevents missed diagnoses and guides whether additional or alternative imaging is warranted in equine foot lameness cases
- •Choose LFMRI when soft tissue detail (tendon and ligament quality) is the priority; choose CT when bony detail of the phalanges is critical for diagnosis
- •CT and LFMRI are complementary rather than interchangeable—consider both modalities or select based on the suspected pathology location
- •Contrast enhancement on CT may obscure DDFT detail, so standard CT may be preferable when DDFT evaluation is the clinical question
- •MRI findings in foot cases can be interpreted with greater confidence when understanding the underlying histopathological changes they represent
- •MRI appears capable of detecting different disease stages in DDFT and navicular bone, potentially improving prognosis and treatment planning
- •Further research is still needed to fully understand the causes and progression of foot lameness—use MRI findings alongside clinical assessment, not as definitive standalone diagnosis
Key Research Findings
Significant histological differences between lame and control horses in navicular bone medulla, flexor aspect, proximal/distal borders, DSIL insertion, and navicular bursa (p<0.05)
Pathological abnormalities in lame horses involved not only navicular bone but also DSIL and navicular bursa as a complex
No significant differences found in collateral sesamoidean ligaments, dorsal navicular bone, distal phalanx articular cartilage, or DIP joint collateral ligament lesions between groups
Navicular bone medullary abnormalities were generally found only dorsal to lesions of the flexor fibrocartilage complex
MR signal alterations directly correlated with histologic tissue-level changes including structural damage, fibroplasia, fibrocartilaginous metaplasia, hemosiderosis, osteonecrosis, and cortical defects
MR imaging demonstrated high sensitivity and specificity for detecting moderate-to-severe lesions in most structures, with particularly high specificity for DDFT, CSL, and navicular bursa pathology
Agreement between MR and histologic grading ranged from good (navicular bursa, DDFT, navicular bone medulla, CSL) to poor (dorsal and proximal navicular bone aspects)
MR imaging was sensitive for abnormalities in all structures except the dorsal aspect of the navicular bone, indicating variable clinical utility by anatomic location
All 7 horses (10 limbs) developed proliferative bursal tissue following navicular bursoscopy despite surgical debridement.
Almost all horses improved to resolved lameness at recheck MRI despite worsening navicular bursa appearance and relatively unchanged concurrent lesions.
Only 2 of 7 horses (29%) returned to their previous level of work, indicating poor long-term functional outcomes.
Navicular syndrome was confirmed as multifactorial with concurrent lesions in multiple foot structures affecting all treated limbs.
Distal border of navicular bone undergoes elongation and sharpening due to pressure from deep digital flexor tendon and adaptive bone remodeling, with fragment formation linked to both mechanical stress and entheseophyte development
Pathological changes occur most frequently in the distal border (85% of cases), DDFT (91%), flexor surface (78.4%), and navicular spongiosa (76%), with 90% of horses with chronic palmar pain showing mild to severe distal border lesions
Increased physical activity induces pathological changes including increased vascular foramina, irregular DDFT attachment margins, spongiosa sclerosis, microcrack accumulation, and altered trabecular architecture
Evidence Base
Histopathology in horses with chronic palmar foot pain and age-matched controls. Part 1: Navicular bone and related structures.
Blunden, Dyson, Murray et al. (2006) — Equine veterinary journal
How does magnetic resonance imaging represent histologic findings in the equine digit?
Murray, Blunden, Schramme et al. (2006) — Veterinary radiology & ultrasound : the official journal of the American College of Veterinary Radiology and the International Veterinary Radiology Association
Magnetic resonance imaging changes of the navicular bursa following navicular bursoscopy in seven horses
Hoaglund E. L., Barrett M. F. (2021) — Equine Veterinary Education
Insight into the pathomorphology of the distal border of the equine navicular bone
M. Frątczak, J. Włodarek, H. Frąckowiak et al. (2017) — Acta Veterinaria Brno
Correlation of radiographic measurements of structures of the equine foot with lesions detected on magnetic resonance imaging.
de Zani, Polidori, di Giancamillo et al. (2016) — Equine veterinary journal
The use of intrathecal analgesia and contrast radiography as preoperative diagnostic methods for digital flexor tendon sheath pathology.
Fiske-Jackson A R, Barker W H J, Eliashar E et al. (2013) — Equine veterinary journal
Clinical, radiological and ultrasonographic features, treatment and outcome in 22 horses with caudal distal radial osteochondromata.
Wright I M, Minshall G J (2012) — Equine veterinary journal
Positive contrast magnetic resonance bursography for assessment of the navicular bursa and surrounding soft tissues.
Maher, Werpy, Goodrich et al. (2011) — Veterinary radiology & ultrasound : the official journal of the American College of Veterinary Radiology and the International Veterinary Radiology Association
Deep erosions of the palmar aspect of the navicular bone diagnosed by standing magnetic resonance imaging.
Sherlock, Mair, Blunden (2009) — Equine veterinary journal
Endoscopic assessment and treatment of lesions of the deep digital flexor tendon in the navicular bursae of 20 lame horses.
Smith, Wright, Smith (2007) — Equine veterinary journal
Assessment of the ultrasonographic characteristics of the podotrochlear apparatus in clinically normal horses and horses with navicular syndrome.
Grewal, McClure, Booth et al. (2005) — Journal of the American Veterinary Medical Association
Magnetic resonance imaging findings in the equine deep digital flexor tendon and distal sesamoid bone in advanced navicular disease--an ex vivo study.
Busoni, Heimann, Trenteseaux et al. (2005) — Veterinary radiology & ultrasound : the official journal of the American College of Veterinary Radiology and the International Veterinary Radiology Association
Collateral desmitis of the distal interphalangeal joint in 18 horses (2001-2002).
Dyson S J, Murray R, Schramme M et al. (2004) — Equine veterinary journal
Magnetic resonance imaging of the equine foot: 15 horses.
Dyson S, Murray R, Schramme M et al. (2003) — Equine veterinary journal
Use of radiography, computed tomography and magnetic resonance imaging for evaluation of navicular syndrome in the horse.
Widmer, Buckwalter, Fessler et al. (2000) — Veterinary radiology & ultrasound : the official journal of the American College of Veterinary Radiology and the International Veterinary Radiology Association
Magnetic resonance imaging for diagnosing and managing deep digital flexor tendinopathy in equine athletes: Insights, advances and future directions.
Scharf Alexandra, Acutt Elizabeth, Bills Kathryn et al. (2025) — Equine veterinary journal
Presence and size of synovial masses within the navicular bursa correlate well between magnetic resonance imaging and bursoscopy and have a guarded prognosis.
Giorio Maria Elisabetta, Graham Robyn J, Berner Dagmar et al. (2024) — Equine veterinary journal
Ex vivo effects of corticosteroids on equine deep digital flexor and navicular fibrocartilage explant cell viability.
S. Sullivan, S. Cole, M. Stewart et al. (2021) — American journal of veterinary research
Equine flexor tendon imaging part 2: Current status and future directions in advanced diagnostic imaging, with focus on the deep digital flexor tendon.
Ehrle Anna, Lilge Svenja, Clegg Peter D et al. (2021) — Veterinary journal (London, England : 1997)
Accuracy of open magnetic resonance imaging for guiding injection of the equine deep digital flexor tendon within the hoof.
Groom, White, Adams et al. (2018) — Veterinary radiology & ultrasound : the official journal of the American College of Veterinary Radiology and the International Veterinary Radiology Association
Show 5 more references
Human Achilles and Equine Navicular Apparatus: A Structural and Functional Comparison of Two Premier Enthesis Organs
M. Osborn, U. Blas-Machado, E. Uhl (2016) — The FASEB Journal
Navicular syndrome in equine patients anatomy, causes, and diagnosis.
Waguespack, Hanson (2013) — Compendium (Yardley, PA)
Comparisons of computed tomography, contrast-enhanced computed tomography and standing low-field magnetic resonance imaging in horses with lameness localised to the foot. Part 2: Lesion identification.
Vallance S A, Bell R J W, Spriet M et al. (2012) — Equine veterinary journal
Comparisons of computed tomography, contrast enhanced computed tomography and standing low-field magnetic resonance imaging in horses with lameness localised to the foot. Part 1: anatomic visualisation scores.
Vallance S A, Bell R J W, Spriet M et al. (2012) — Equine veterinary journal
Relationship between histopathological lesions and magnetic resonance imaging (MRI) in diseases of the foot of the horse
Schramme Michaël (2012) — Bulletin de l'Académie Vétérinaire de France