Molly’s Trick Knee: A Common Problem in Small Dogs

Dr. Ernie Ward

I’ve got a beef with evolutionary anatomy: knees and shoulders. To my biomechanical eye, those joints joint seem awkwardly oriented, hastily designed, and assembled from spare parts. Whatever the reason, I diagnose a lot of pets with knee and shoulder conditions. Which brings me to Molly’s Trick Knee.

Molly was a tiny teacup Yorkie pup. Barely a pound-and-a-half at 10-months, she was a dainty dog with eyes as big as her persona. If you met Molly, your first instinct would be to clutch her to your chest and coo softly. Or maybe that’s just me. I love me some Yorkies!

This morning, however, Molly’s mom was distraught. She feared she had “broken Molly’s leg.” Not an unreasonable concern, given the breed’s notoriously fragile limbs. Earlier that day, she had carried Molly outside to potty and gently placed her on the ground. Molly took off, as usual, and suddenly pulled up her left rear leg and wouldn’t put it down again. Molly didn’t cry or resist when mom touched the leg. When we put Molly on the floor in my exam room, she proudly pranced on all fours as if to say, “Why all the fuss?” I had a pretty good idea what was going on.

Medial Patellar Luxation

Molly had a medial patellar luxation (MLP) [also confusingly referred to as medial luxating patella (MPL)] or “trick knee.” This developmental disease is the result of improper orientation of the many bones, muscles, and ligaments that make up the knee. About 95% of cases deviate medially (toward the body) and are very common in toy and small breeds. In simplest terms, the knee cap (patella) “pops out,” locking the knee in the extended position. When the patella returns to its normal location, the dog miraculously returns to normal. Some trick. 

Diagnosis is made primarily on physical exam and clinical signs, but radiographs and CT may be helpful in many cases. Patellar luxations are graded 1 (rare or no clinical signs) to 4 (severe or constant limping). Grade 1 cases generally do not require surgery, while grade 4 require surgical repositioning of the patella in the groove. Grade 2 and 3 treatments will be determined by severity of limping, pain, and other symptoms. Surgical treatment includes some sophisticated techniques: trochleoplasty, en block recession trochleoplasty, wedge recession trochleoplasty, abrasion trochleoplasty, trochlear chondroplasty, tibial tuberosity transposition (TTT), antirotational sutures, and joint capsule imbrication or release. Try saying that three times fast.

Most dogs will fully recover after surgery. Grade 1 MLP patients need to be kept at a lean weight, consider joint supplements, and regular low-impact exercise to maintain strong joint support structures. Molly was diagnosed with a grade 1 MLP and placed on joint supplements and easy hill walks to strengthen quadriceps and maintain a healthy weight.

If your small dog has the occasional “hiccup limp,” I encourage you to have it carefully examined by your veterinarian. Knee, hip, “ankle,” and paw problems can be a challenge to diagnose at home, and often require a skilled and attentive veterinarian. X-rays, ultrasound, and CT/MRI may be required to fully understand the issue in some dogs or cats. The great news is modern veterinary medicine allows us to treat most conditions and eliminate pain and discomfort. Molly’s Trick Knee ended up being a trick I knew how to solve. Chances are your veterinarian can solve your pet’s problem, too.