Medial patellar luxation
A congenital condition commonly seen in young, toy-breed dogs, medial patellar luxation (MPL) is characterized by medial displacement
of the patella out of the trochlear groove. Conformational changes resulting in MPL include:
- Lateral femoral bowing
- Distal femoral varus
- Lateral torsion of the distal femur
- Medial displacement of tibial tuberosity
- Medial bowing of the proximal tibia
- Lateral torsion of the distal tibia.
These conditions lead to signs that include intermittent lameness and gait change.
Dogs with MPL are often not in pain. Pomeranians, Yorkshire terriers, Boston terriers and poodles are commonly affected. In
the past, we thought MPL was most common in toy breeds, while lateral patellar luxation was most common in larger breeds,
and if we did encounter MPL in a large breed, it was more likely caused by trauma and less likely to be congenital. But we
now recognize congenital MPL in some larger breeds as well, such as Labrador retrievers, Chow Chows and Staffordshire terriers.
Photo 3: A craniocaudal view of a stifle with MPL. Note the displaced patella and the torsional deformity of the tibia.
MPL is diagnosed based on clinical signs and orthopedic examination results—less commonly on a radiographic examination. (To
give a full evaluation using radiographs, a craniocaudal radiograph should ideally contain the hip femur, stifle, tibia and
hock in a single view.) The patella may be reduced at the time of the image; however, other conformational changes contributing
to the MPL are usually still evident (Photo 3).
Surgical correction of MPL is recommended and usually involves all or a combination of the following: trochlear wedge/block
recession, tibial crest transposition, medial capsular release and lateral capsular imbrication. Severe, grade IV MPLs with
marked limb deformity typically require corrective femoral or tibial osteotomies, or both. Grade I, II and III MPLs treated
appropriately have a good prognosis for return to function and resolution or lessening the grade of luxation.
Cranial cruciate injury
Cranial cruciate injury is the single most common orthopedic injury seen in dogs. Fortunately, it's not as common in juvenile
dogs, but it should remain on the differential diagnosis list for dogs demonstrating hindlimb lameness localized to the stifle,
particularly when effusion and instability are noted.