Case Study: Femur and Tibia Stress Fracture

Why do an MRI when we have x-rays and ultrasound?
History and Physical Examination
This is a 10 year old, warmblood, gelding that competed in upper level 3-day eventing. He came to Cave Creek Equine Surgical and Diagnostic Imaging Center with a 2 month history of not performing well. He was ‘falling-out behind’, heavy on the forehand, resents collection, has a stiff back and pelvis, doesn’t canter well behind, has a stabbing gait behind, and a pelvic waddle.

Following initial examination the lower hock joints, the sacroiliac joints and the lumbosacral joints were identified as the main areas of concern. All three areas were medicated with anti-inflammatory medication.

Two weeks later, re-evaluation reveals improved movement behind, but a right hind and left front lameness is apparent. A stifle joint block is performed (medial femorotibial joint) and the right hind lameness resolves. The stifle is medicated with anti-inflammatory medication.

This horse improved following the stifle injection, but five weeks later, was lame again in the right hind. The medial femorotibial joint was again blocked and the lameness resolved. A pastern ring block of the left front, eliminated the left front lameness.

Radiographs
Radiographs of the right stifle and left foot/pastern did not show any significant bony abnormalities.

Ultrasound Ultrasound of the right stifle showed no bone, cartilage or ligament abnormalities.

Due to a lack of x-ray and ultrasound findings to explain the lameness, an MRI scan of the right stifle and left front foot was performed.
None of these injuries could be appreciated on x-ray or ultrasound.

Stress fracture (trabecular microfractures) of the femur and tibia. Some cartilage damage associated with the stress fractures on the femur.

The white areas indicated by the arrows represent fluid within the bone that indicates the areas of the microfracture or stress fracture. The dark area in the bottom photo indicates fatty replacement of normal bone in the area of the fracture.


MRI findings on the Left Front Foot
Injury to the medial collateral ligament of the coffin joint
Mild navicular bone edema
Mild impar ligament injury
Mild to moderate pastern joint arthritis
Injury to the chondrocoronal ligament – medial and lateral
Treatment and Recommendations
• Administered 500 mg Tildren in 3 liters IV fluids intravenously to promote navicular, femur, and tibial bone healing. This single administration of Tildren continues to heal bone for 6-12 months, with most of the bone healing occurring between 2-3 months after administration of the drug.
• Stall confinement with daily handwalking for the first 4 months.
• Re-check x-rays and ultrasound in 2 and 4 months to determine future rehabilitiaton regimen
Prognosis for future athletic soundness is good, if he has no ongoing injury to the right stifle during the bone healing process.

How common are stress fractures associated with the stifle joint?

More common than you may think. These are difficult to diagnose without MRI since they can not be seen on x-rays or ultrasound.

Two cases of stress fractures within the femur. Both had minimal to no x-ray abnormalities.

MRI image of a stifle with a large stress fracture.

The x-ray of the stifle shows a cystic lesion in the femur, but the area of microfracture is difficult to appreciate on the x-rays.

MRI image of a stifle with a stress fracture in the femur.

This is the x-ray of the horse. There is little evidence of the area of microfracture on the x-rays.

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