- Extensive fluid signal intensity is seen tracking along the junction between the keratinized and laminar tissue on the solar aspect of the foot affecting the frog on midline and extending into the lateral sulcus. At the solar margin of the laminar tissue in the lateral sulcus, a fluid-filled tract is seen extending through the digital cushion, deep digital flexor tendon and navicular bursa, terminating at the navicular bone (green arrows).
- A wide, complete parasagittal split (yellow arrow) in the lateral lobe of the deep digital flexor tendon bordered by extensive moderate fiber abnormalities with associated lobe enlargement and extension of the navicular bursa through the split. The deep digital flexor tendon lateral lobe split is continuous with the previously described fluid-filled tract.
- The navicular bursa is distended with fluid and there is extensive moderate synovial membrane thickening (pink arrows).
- On the navicular bone flexor surface, lateral to the sagittal ridge, there is a focal angular defect in the bone with a linear region of decreased density in the underlying compact bone (blue arrows). This finding is located at the termination of the tract. There is extensive moderate fluid in the navicular bone. In addition, there is diffuse contrast enhancement of the navicular bursa synovial membrane, the adjacent subcutaneous tissues and the tract margins.
- Extensive moderate fluid is also seen in the solar aspect of the distal phalanx with multifocal mild to moderate fluid and prominent vascular pattern in the middle phalanx. On post-contrast images, there is enhancement of the navicular bone, affecting the trabecular bone as well as a focal region of compact bone loss on the flexor surface. There is also enhancement in the trabecular bone of the solar aspect of the distal phalanx and multiple focal regions in the middle phalanx.
- The distal interphalangeal joint contains a mild to moderate amount of effusion.
Summary:
- Fluid-filled tract within the plantar soft tissues, extending from the lateral sulcus of the frog, with extensive solar fluid accumulation
- Complete deep digital flexor tendon parasagittal split with extensive moderate fiber abnormalities/enlargement
- Severe navicular bursitis
- Focal navicular bone flexor surface defect with decreased compact bone density, and extensive moderate fluid
- Extensive moderate fluid, distal phalanx
- Mild to moderate multifocal fluid and prominent vascular pattern, middle phalanx,
- Mild to moderate synovitis, distal interphalangeal joint
Conclusions:
- The findings on this study are consistent with a penetrating solar injury which extends through the digital cushion, deep digital flexor tendon, navicular bursa and terminates on the navicular bone flexor surface with associated abnormalities in all of these structures. Septic navicular bursitis is considered likely. Concurrent septic synovitis of the distal interphalangeal is also a possibility.
Follow-up:
- Euthanasia was elected.
- FINAL ANATOMIC DIAGNOSES
- Synovitis, suppurative, subacute, locally-extensive, moderate, distal interphalangeal joint of the left hind limb,
- Tendonitis, cellulitis and edema, subacute, locally-extensive, moderate, deep digital flexor and common digital extensor tendons, sheaths and fascia at the level of the middle phalanx
- COMMENTS: Gross examination revealed abscesses within and surrounding the distal interphalangeal joint on the left hind leg. The soft tissues associated with the distal aspect of the middle phalanx were also edematous and mildly thickened. There was no gross evidence of arthritis or osteomyelitis noted within the affected regions.
A little bit more…
- Penetrating injuries to the sole and frog of a horse’s hoof are common and can be serious or even life-threatening. The treatment and prognosis depend significantly on the structures involved, as determined by the injury’s location, direction, and depth (de Heer et al., Schiavo et al.).
- Solar penetrating injuries can be particularly severe if they affect critical structures such as the navicular bursa, navicular bone, distal phalanx, distal sesamoid impar ligament (DSIL), deep digital flexor tendon (DDFT), digital flexor tendon sheath (DFTS), and distal interphalangeal (DIP) joint (de Heer et al.).
- To evaluate the extent of these injuries, diagnostic imaging including plain radiography, +/- placement of a sterile metal probe within puncture wound, and contrast radiography techniques such as arthrography, bursography, and fistulography, may be considered. However, these methods can sometimes be inconclusive, especially when it comes to assessing soft tissue damage within the hoof. The DDFT, which is frequently affected by solar penetration, cannot be imaged in detail using these modalities (de Heer et al., Schiavo et al.).
- Important synovial structures at risk from penetrating injuries, such as the DIP joint, DFTS, and navicular bursa, can be further investigated using synoviocentesis and synovial fluid analyses. Diagnostic ultrasonography of the DDFT using a transcuneal approach offers a restricted field of view. Since only the mid portion of the DDFT can be visualized, lesions located on the lateral or medial lobes remain undetected. Additionally, positioning the transducer perpendicular to the DDFT is not feasible, leading to the frequent oversight of subtle tendon lesions (de Heer et al.).
- MRI offers the best soft tissue contrast for the evaluation of solar penetrating injuries (Schiavo et al.).
- The prognosis and treatment of penetrating foot injuries depend on the structures involved. In a recent study by Schiavo et al. including 11 horses with penetrating injuries, the following outcomes were noted:
- Six horses (60%) had an excellent outcome, returning to full athletic function.
- Five horses (40%) were sound but had not yet resumed full work by the conclusion of the study.The median time to return to full work was 6 months for those with an excellent outcome and 8 months for those that were sound but not yet in full work.
- Comparison with Previous Studies (Steckel et al., Findley et al., Richardson et al.):
- Previous studies have shown varying degrees of success, with return to soundness rates ranging from 30% to 63% for different types of penetrating injuries.
- The absence of synovial sepsis significantly improves the prognosis for horses with DDFT injuries.
- For superficial solar puncture wounds, local debridement of the draining tract is often sufficient and can usually be performed on a standing horse. However, if a synovial structure such as the DIP joint, navicular bursa, or DFTS is involved, arthroscopic lavage under general anesthesia is recommended. In cases of severe DDFT necrosis, with or without involvement of the navicular bursa, a more invasive approach known as the street-nail procedure is recommended. This procedure involves radical excision of the penetrating tract and fenestration of the DDFT, with or without lavage of the navicular bursa. These surgical interventions are typically combined with systemic administration of antimicrobial drugs and the application of bandages to ensure proper healing and prevent infection (de Heer et al., O’Neill et al.).
References:
- De Heer N, Compagnie E, Ter Braake F. Penetrating solar wounds to the foot: benefit of MRI in treatment decisions. Vlaams Diergeneeskundig Tijdschrift. 2015 Feb 27;84(1).
- Schiavo S, Cillán‐García E, Elce Y, Liuti T, Taylor SE. Horses with solar foot penetration, deep digital flexor tendon injury, and absence of concurrent synovial sepsis can have a positive outcome. Veterinary Radiology & Ultrasound. 2018 Nov;59(6):697-704.
- O’Neill H, O’Meara B. Diagnosis and treatment of penetrating injuries of the hoof in horses. In Practice. 2010 Dec;32(10):484-90.
- Steckel RR, Fessler JF, Huston LC. Deep puncture wounds of the equine hoof: a review of 50 cases.
- Findley, JA, Pinchbeck, GL, Milner, PI et al. Outcome of horses with synovial structure involvement following solar foot penetrations in four UK veterinary hospitals: 95 cases. Equine Vet J. 2014;46:352–357.
- Richardson, GL, O’Brien, TR, Pascoe, JR Meagher, DM. Puncture wounds of the navicular bursa in 38 horses, a retrospective study. Vet Surg. 1986;15:156–160
