2007 Radiology Exam - Musculoskeletal Case 2

Information Provided to Candidate

• Trakehner
• 13 years old
• Female
• Lame left tarsus – 2 weeks

State the radiographic findings.

• What is your assessment of these findings?
• Are further imaging studies needed? If so, what are they and why? If no, why not?

See images below. Click to enlarge.

Findings Expected from Candidate

• The candidate was presented with 4 standard views of an equine tarsus (laser printed Eklin digital). There is soft tissue swelling primarily over the calcaneous and a small soft tissue defect over the plantar aspect of the calcaneous, most apparent on the lateral view. There is a subtle cortical irregularity and focal bone loss over the plantaromedial aspect of the calcaneous, apparent on the dorsomedial – plantarolateral oblique view as well as faintly visible on the dorsoplantar view.
• Given these changes, candidates were expected to ask for a plantaroproximal to plantarodistal oblique view (calcaneous skyline). Swelling of plantar soft tissues and a focal cortical lysis on the medial aspect of the calcaneous is readily visible on this view.

Conclusion Expected from the Candidate

• The most likely diagnosis is osteomyelitis of the plantaromedial aspect of the calcaneous with associated soft tissue swelling, also likely infection of the calcanean bursa.
• A sonographic exam would assist in assessment of the calcanean bursa and plantar soft tissues and a fistulogram may also allow confirmation of disruption to the calcaneal bursa.

Summary of Overall Candidate Performance

• Many candidates performed poorly on this case. The plantar swelling was noted by almost all candidates but the area of bone lysis on the medial aspect was often missed, as was the small soft tissue defect indicating the presence of a wound. Most candidates failed to ask for a plantaroproximal-plantarodistal oblique view of the calcaneous – this view should be considered a routine part of the evaluation of a horse with swelling in the calcaneal region.
• When given the skyline view, the candidates were able to identify the area of lysis on the medial aspect of the calcaneous, both in the skyline view and, retrospectively, in the dorsomedial-plantarolateral oblique view. Most of the candidates then made a correct diagnosis but several attributed the bone change to resorption caused by pressure necrosis secondary to soft tissue injury, not infection.

Followup:
An ultrasound exam of the region showed involvement of the superficial digital flexor tendon and severe distension of the calcaneal bursa. Centesis of the intertendinous calcanean bursa confirmed sepsis and the patient underwent repeated surgical procedures to lavage the bursa and debride infected bone. A tract from the skin wound to the region of calcaneal bone lysis was confirmed. Recovery was prolonged, with the patient developing laminitis in the contralateral limb.