Case reveal

Findings:

• The distal interphalangeal joint capsule is moderately thickened and contains a small amount of effusion. Along the periarticular margins of the distal interphalangeal joint, midline osteophyte formation is present with joint capsule enthesopathy at the proximal navicular bone attachment.
• The middle phalanx is palmately displaced in relation to the proximal phalanx.
• The impar ligament has moderate enthesopathy at the distal phalanx insertion with resorption and mild to moderate fluid. The distal phalanx has mild dorsal distal fluid. The foot has a low heel conformation.
• The navicular bone has mild palmar T2 hyperintensity, mild synovial invagination enlargement and distal margin irregularities. 
• The navicular bursa is severely thickened with proliferation and contains decreased fluid. The joint capsule proliferation extends to the dorsal margin of the deep digital flexor tendon and palmar margin of the collateral sesamoidean ligament with unclear continuity with those structures.

• Throughout the foot, there is extensive severe injury of the deep digital flexor tendon. In the middle phalanx level, there is loss of the normal tendon architecture and severe fiber disruption and degeneration that continues distally to the navicular bone level, with remaining tendon thinning (yellow arrows). Distal to the navicular bone, the deep digital flexor tendon has mild to moderate fiber abnormalities, most prominently affecting the medial lobe there is moderate enlargement and scarring of the collateral sesamoidean ligament at the middle phalanx level. 

• The distal interphalangeal joint collateral ligaments have mild fiber abnormalities at the middle phalanx level.
• The distal phalanx collateral cartilages are mildly ossified.
• There is severe fluid in the distal phalanx palmar processes.
• Along the periarticular margins of the proximal interphalangeal joint, mild osteophyte formation is present.

Conclusions:

• Extensive, severe deep digital flexor tendon with extensive fiber disruption, thinning and degeneration
• Severe chronic navicular bursitis with probable adhesion formation 
• Moderate synovitis, mild osteoarthrosis, joint capsule enthesopathy and subluxation, distal interphalangeal joint 
• Severe palmar process fluid, mild dorsal distal fluid and mild collateral cartilage ossification, distal phalanx
• Moderate enlargement and scarring, collateral sesamoidean ligament
• Moderate insertional enthesopathy, resorption and mild to moderate fluid, impar ligament
• Mild desmopathy, distal interphalangeal joint collateral ligaments
• Mild palmar fluid, mild synovial invagination enlargement and distal margin remodeling, navicular bone
• Mild osteoarthrosis, proximal interphalangeal joint 

Radiographs (acquired prior to the MRI):

• Mild to moderate right lateral collateral sesamoidean ligament mineralization, likely representing soft tissue dystrophic mineralization.

• Mild right distal interphalangeal osteoarthrosis. 

Follow-up:

• The patient was chronically treated for a deep digital flexor tendon injury of the left front foot. Prognosis is guarded
• The patient will be managed with therapeutic shoeing and medically managed for pain. Further use for breeding is discourage to keep any extra weight off the feet.

A little bit more…

• Normal MRI anatomy of the deep digital flexor tendon: The DDFT is diffusely uniform in shape. At its insertion on the distal phalanx, it has a flattened crescent shape and becomes bilobed in shape more proximally with a greater cross-sectional area in the mid-navicular region.

• Some lesion types have a higher prevalence at various levels within the DDFT. Core lesions cane mainly found at the level of the proximal phalanx and proximal interphalangeal joint levels. In contrast, dorsal abrasions and parasagittal splits are more common at the collateral sesamoidean ligament and navicular bone levels. Overall, DDFT injuries are most frequently observed at the collateral sesamoidean ligament and navicular bone levels, followed by the DSIL and insertion levels, and are less common at the proximal interphalangeal joint and proximal phalanx levels (Dyson et al.).

• Lame horses tend to have more severe lesions, which were are reported in more locations compared to less severely affected horses. Those with lameness lasting up to six months had necrotic core lesions. (Blunden et al.).
• Distal DDFT injuries aren’t often associated with any tendon thickening. This could be due to the restrictive structures of the hoof, also possibly a source of increased pain (Murray et al.).
• Adhesions occur in the navicular bursa with the DDFT, and can be more confidently detected on high field MRI. Holowinski et al reported that discontinuity in the navicular bursa fluid signal with well-defined tissue between the DDFT and adjacent structures on high-field MR images is supportive of navicular bursa adhesion.
• Prognosis depends on the severity of the lesion. Stall rest, icing, shockwave and NSAIDs are more commonly initiated at the start of the treatment process.

References:

• Dyson S, Murray R. Magnetic resonance imaging evaluation of 264 horses with foot pain: the podotrochlear apparatus, deep digital flexor tendon and collateral ligaments of the distal interphalangeal joint. Equine veterinary journal. 2007 Jul;39(4):340-3.
• Blunden A, Murray R, Dyson S. Lesions of the deep digital flexor tendon in the digit: a correlative MRI and post mortem study in control and lame horses. Equine Veterinary Journal. 2009 Jan;41(1):25-33.
• Murray RC, Roberts BL, Schramme MC, Dyson SJ, Branch M. Quantitative evaluation of equine deep digital flexor tendon morphology using magnetic resonance imaging. Veterinary Radiology & Ultrasound. 2004 Mar;45(2):103-11.
• Lutter JD, Schneider RK, Sampson SN, Cary JA, Roberts GD, Vahl CI. Medical treatment of horses with deep digital flexor tendon injuries diagnosed with high-field-strength magnetic resonance imaging: 118 cases (2000–2010). Journal of the American Veterinary Medical Association. 2015 Dec 1;247(11):1309-18.
• Holowinski ME, Solano M, Maranda L, García‐López JM. Magnetic resonance imaging of navicular bursa adhesions. Veterinary Radiology & Ultrasound. 2012 Sep;53(5):566-72.