Case Study: Femoral Stress Fracture

This is an 8 year old quarter horse mare, cutting horse, who originally presented to us 30 months ago with a history of bilateral stifle lameness and osteoarthritis of both stifles. She was treated multiple times over the past 30 months with IRAP in both stifles, and has had several treatments of both stifles with adipose-derived stem cells. When that therapy did not resolve all of her stifle problems, arthroscopic debridement of damaged cartilage on the medial femoral condyles (see initial ultrasound image) and microfracture of the subchondral bone was performed. She was treated with IRAP and stem cells postoperatively to promote cartilage repair.

Initial X-Rays

Initial radiographs showed bone spurs associated with the joint, but no other abnormalities.


Initial Ultrasound

Initial ultrasound showed moderate to severe fraying of the articular cartilage on the weight-bearing surface of the medial femoral condyle, and a large effusion of the medial femorotibial joint.

The horse was doing well after surgery and regenerative medicine therapy, and was returning to full training 7 months after surgery. She suddenly developed acute onset 4/5 lameness (toe-touching lameness) of the left hind limb with acute, severe swelling and effusion of the left stifle. She became increasingly comfortable over the next couple of weeks with stall rest, and was 1.5/5 lame on the left hind at the time of our examination 4 weeks later. The stifle edema and most of the effusion had resolved.

She became sound with intraarticular anesthesia of the medial femorotibial joint.

X-rays, ultrasound and MRI were performed on the left stifle at the time of our examination.


Radiographs showed minimal changes when compared to the initial radiographs from 30 months earlier.



No more obvious fraying of the joint cartilage was seen; however, the articular (joint) cartilage remained thicker and more hyperechoic (more white) than normal.


Although no radiographic or ultrasound findings were identified to explain the severe acute left stifle lameness, MRI told a different different story – a large, severe stress fracture of the medial femoral condyle (inside portion of the femur in contact with the tibia) was found on MRI of the left stifle. This injury involves the adjacent articular cartilage and now has a small cystic area (hole in the bone) in the femoral condyle that communicates with the joint. This small bone cyst developed because of focal collapse of the subchondral bone plate, which occurred secondary to the new subchondral stress fracture.


The joint was treated with adipose derived stem cells, and we administered IV Tildren to encourage bone turnover and healing. Stall rest with controlled hand walking was prescribed.

When this patient presented with acute, recurrent left hindlimb lameness, it would have been easy to assume that this acute lameness was due to treatment failure and further degeneration of the original problems in the joint. However, this horse sustained a completely new injury to her left stifle, unrelated to her original stifle problems. It may be important to note that the recurrence of lameness may not be due to treatment failure or progression of disease, but may be due to a completely new injury.

As of June 2012, this case is on-going, and updates will be posted.

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