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UF Health University of Florida
Veterinary Diagnostic Imaging College of Veterinary Medicine
LA Radiology Overview

Case reveal

Survey radiographs:

  • At the level of the lateral collateral fossa of the distal phalanx, there is a focal, medium-sized, poorly defined region of decreased mineral opacity (arrowheads).
  • Along the dorsolateral aspect of the distal limb, just proximal to the coronary band, the soft tissues are moderately thickened.
  • Along the distal border of the distal phalanx, the vascular channels are mildly to moderately widened, most notably along the medial quarter of the distal phalanx.

Arthrogram:

  • Positive contrast media fills the distal interphalangeal joint.
  • A well-defined, linear region of positive contrast media extends laterally at the level of the distal interphalangeal joint, into the adjacent soft tissues of the lateral aspect of the foot (green arrowheads).
  • The region of the lateral fossa of the distal phalanx contains positive contrast media. This contrast is located where the lateral collateral ligament of the distal interphalangeal joint should be present. In addition, a linear well-defined region of positive contrast media extends through the tissues at the level of the lateral collateral cartilage.  
  • Multiple linear regions of contrast media extend proximally along the palmar margins of the distal limb, to the level of the fetlock, representing lymphatic drainage (blue arrows).

Conclusions:

  • Lateral extension of the distal interphalangeal joint capsule and synovial fluid, beyond the level of the lateral collateral ligament and ungual cartilage of the distal interphalangeal joint, right fore.
  • Moderate resorption of the lateral collateral fossa of the distal phalanx, right fore.
  • Moderate soft tissue thickening of the dorsolateral aspect of the distal phalanx, right fore.
  • Mild to moderate distal phalanx remodeling secondary to chronic compressive trauma, right fore.

These radiographic findings are compatible with severe injury(tear) to the lateral collateral ligament and the lateral cartilage of the distal interphalangeal joint.

Magnetic resonance imaging

  • Complete tear of the lateral collateral ligament of the distal phalanx and mild associated hemorrhage and focal moderate bone resorption, right fore.
  • Complete lateral collateral cartilage tear, and moderate chondrosesamoidean desmopathy, right fore.
  • Mild to moderate, multifocal partial thickness articular cartilage defects, distal interphalangeal joint, right fore.
  • Moderate proliferative synovitis, distal interphalangeal joint, right fore.
There is complete fiber disruption of the lateral collateral ligament of the distal interphalangeal joint at the level of the distal phalanx. There is focal moderate bone loss of the lateral fossa bordered by sclerosis at the insertion of the lateral collateral ligament of the distal interphalangeal joint. In the region of the lateral collateral ligament, there is a severe amount of disorganized tissue. In the lateral collateral cartilage of the distal phalanx, immediately palmar to the lateral chondrosesamoidean ligament, there is a complete, transverse split. The chondrosesamoidean
 ligament and medial collateral sesamoidean ligament are moderately thickened. A focal portion of the distal interphalangeal joint capsule and a mild amount of synovial fluid extend through the fiber disruption in the lateral collateral ligament and in the split in the lateral collateral cartilage, into the adjacent subcutaneous tissues of the lateral aspect of the digit. 

Ultrasound:

Note marked thickening and heterogeneity of the lateral collateral ligament in comparison to the contralateral side.

Follow-up:

  • The patient was given a guarded prognosis. Surgery in this region is not an option. Stall rest was recommended. Plasma right protein (or other biologics) injections were also recommended to help with the healing process. To aid with stabilization of the joint, coaptation was advised.

A little bit more…

  • Collateral ligament (CL) injuries of the distal interphalangeal joint (DIPJ) are recognized as a significant cause of equine foot lameness. These ligaments, located dorsomedially and dorsolaterally, play a critical role in stabilizing the DIPJ during locomotion. Injury may result from non-physiologic motion, hoof imbalance, angular limb deformities, or abrupt maneuvers on uneven terrain. Diagnosis and management of CL desmopathy have evolved with advances in imaging, particularly magnetic resonance imaging (MRI), which is the gold standard for evaluating these deep-seated structures.

Diagnostic imaging

  • Radiography remains a first-line imaging tool but has limited sensitivity for soft tissue injuries. It may reveal enthesophyte formation or avulsion fragments in chronic or severe cases, but up to two-thirds of horses with DIPJ-associated lameness show no radiographic abnormalities (Zubrod et al., 2005). Radiographs are more useful when osseous involvement is suspected, such as bone resorption at ligament insertion.
Arthrography of the distal interphalangeal joint is a poorly described technique for the diagnosis of collateral ligament tears, but is sporadically mentioned in the literature (example above from a study by Pauwels et al.)
  • Ultrasonography can visualize the proximal portion of the CLs through the coronary band, but its utility is constrained by the hoof capsule and operator experience. Beasley et al. (2019) found that over 56% of CL lesions were located distal to the coronary band, making them inaccessible to ultrasound. False negatives are common, and ultrasonography may miss significant pathology, especially in the distal ligament or when periligamentous edema is present.
  • Magnetic Resonance Imaging (MRI) offers superior soft tissue contrast and multiplanar capabilities, allowing comprehensive evaluation of the CLs from origin to insertion. Both high-field and low-field MRI systems have demonstrated efficacy in detecting ligament enlargement, fiber disruption, and associated osseous changes. Zubrod et al. (2005) and Gutierrez-Nibeyro et al. (2008) emphasized the value of STIR and T2-weighted sequences for identifying fluid accumulation indicative of inflammation or injury. MRI also enables detection of concurrent pathology, such as deep digital flexor tendon lesions or navicular bone changes, which may contribute to lameness.
  • In Beasley et al.’s (2019) retrospective study of 28 horses, 48 CL lesions were identified, with a predominance in the medial ligament. Lesions were graded based on signal intensity, shape distortion, and margin definition. Notably, osseous changes were present in 44% of cases, primarily at the ligament insertion. Despite the severity of some lesions, 24 of 28 horses returned to work, and no significant correlation was found between lesion grade or location and time to recovery.

Prognosis and Treatment

  • Treatment strategies vary depending on lesion severity and concurrent findings. Conservative management typically includes stall rest followed by a structured rehabilitation program. Horses with mild to moderate desmopathy may benefit from turnout and gradual return to exercise. More severe cases, especially those with avulsion fragments or joint effusion, may require extended rest, corrective shoeing, and intra-articular medication.
  • Adjunct therapies such as extracorporeal shock wave therapy, casting, and intralesional injections (e.g., urinary bladder matrix) have been used with mixed outcomes. Gutierrez-Nibeyro et al. (2008) reported that 60% of horses returned to their previous level of exercise following rest and rehabilitation, with recovery times ranging from 8 to 68 weeks. Horses with persistent lameness or advanced joint degeneration may have a guarded prognosis and could be retired from athletic use.
  • MRI follow-up studies have shown that resolution of hyperintense signal and normalization of ligament size correlate with clinical improvement. However, persistent signal changes may be observed and reflect fibrosis or chronic remodeling.

References:

  • Pauwels, Frederik, et al. “Contrast enhanced computed tomography findings in 105 horse distal extremities.” Journal of Equine Veterinary Science 104 (2021): 103704.
  • Dyson, Sue J., et al. “Collateral desmitis of the distal interphalangeal joint in 18 horses (2001–2002).” Equine veterinary journal 36.2 (2004): 160-166.
  • Dyson, S., and R. Murray. “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 journal39.4 (2007): 340-343.
  • Zubrod, Chad J., et al. “Injury of the collateral ligaments of the distal interphalangeal joint diagnosed by magnetic resonance.” Veterinary Radiology & Ultrasound 46.1 (2005): 11-16.
  • Dyson, S., T. Blunden, and R. Murray. “The collateral ligaments of the distal interphalangeal joint: magnetic resonance imaging and post mortem observations in 25 lame and 12 control horses.” Equine Veterinary Journal 40.6 (2008): 538-544.
  • Gutierrez‐Nibeyro, Santiago D., et al. “Magnetic resonance imaging findings of desmopathy of the collateral ligaments of the equine distal interphalangeal joint.” Veterinary Radiology & Ultrasound 50.1 (2009): 21-31.
  • Beasley, B., et al. “Magnetic resonance imaging characterisation of lesions within the collateral ligaments of the distal interphalangeal joint–28 cases.” Equine Veterinary Education 32 (2020): 11-17.
  • Evrard, Laurence, et al. “Ultrasonography of the collateral ligaments of the distal interphalangeal joint in horses: technique and reference images.” Journal of equine veterinary science 32.9 (2012): 584-589.