Patella luxation is a relatively common hereditary condition commonly reported in small breed dogs.
Medial patellar luxation is defined as medial (or less commonly lateral) displacement of the patella from the trochlear groove. In dogs, medial luxations account for 75% of all patellar luxation cases, and are frequently associated with patella alta (unusually small patella that develops above the joint).
Patellar luxation is usually the result of anatomic abnormalities involving the entire hind limb, arising in the hip with coxa vara and decreased anteversion of the femoral head and neck. There is a decreased angle of inclination between the femoral longitudinal axis and the femoral neck, combined with a lesser caudal to cranial angle of the femoral neck. This skeletal abnormality in the growing animal displaces the extensor muscles of the hind limb, chiefly the quadriceps group, medially . This muscular displacement has an effect on the distal femoral physis, resulting in impaired growth of the medial side and accelerated growth of the lateral side of the distal extremity of the femur. The net effect is medial bowing and rotation of the distal extremity of the femur and proximal extremity of the tibia. The patella is simply pulled along with all the other bony and soft tissue structures. Further compounding the problem is the fact that a chronically luxated patella does not exert pressure in the trochlear groove, which is crucial in producing a groove of sufficient width and depth in the growing animal.
Although patella luxation is more frequently observed in small breed dogs, it may also be seen in large breed dogs, particularly the Labrador Retriever due to the angle of inclination of the femoral neck and medio-lateral bowing of the femur and tibia at the stifle (coxa valga). Medial patella luxation is associated with a relatively long patellar ligament and patella alta in medium to giant breed dogs. Lateral patella luxation in larger breeds of dogs is usually associated with a relatively long proximal tibia and patella alta.
Clinically affected dogs show characteristic intermittent lameness on the affected hindleg, which hopping and non-weight bearing and reduced stifle range of motion. Severity of patella luxation is frequently graded from I (mild) to IV (severe).
Diagnosis is usually suspected on manipulation of the affected stifle, with lateral 'popping' of the patella outside the trochlea groove. Concurrent cruciate ligament injury is relatively common (up to 50%) in affected older patients due to the chronic cartilage erosion of the medial patella articular surface and trochlea groove as well as the unusual gait adopted by patients when ambulatory.
Surgery is indicated only in those dogs that are experiencing significant clinical signs or in young dogs where soft tissue techniques might be utilized in an attempt to mitigate the negative effects of the condition on growing bone. In the asymptomatic adult dog, despite the risk of degenerative joint disease and rupture of the cranial cruciate ligament, there is no evidence that surgery is beneficial prophylactically.
Common surgical treatments for medial luxation are para-patellar fascial imbrication, trochleoplasty, lateral transposition of the crest and tibial tuberosity osteotomy to drive the patella into the correct anatomical alignment.
The prognosis after surgical correction of patellar luxation is generally good, at least for those that are Grades I, II or III. In excess of 90% of cases achieve an acceptable functional outcome.
Postoperative complications for this procedure are estimated to be between 18 - 29% of cases, with up to 48% of complications involving reluxation.
In cases where surgery is unwarranted or the dog an anesthetic risk, long-term use of anti-inflammatory and analgesic medications are indicated.
- Harasen G (2006) Patellar luxation: pathogenesis and surgical correction. Can Vet J 47(10):1037-1039
- Segal U et al (2012) Latero-distal transposition of the tibial crest in cases of medial patellar luxation with patella alta. Vet Comp Orthop Traumatol 25(4):281-285
- Roush JK (1993) Canine patellar luxation. Vet Clin North Am Small Anim Pract 23:855–868
- Hulse DA (1995) The stifle joint. In: Olmstead ML ed. Small Animal Orthopedics St Louis: Mosby. pp:395–404
- Bound N et al (2009) The prevalence of canine patellar luxation in three centres. Clinical features and radiographic evidence of limb deviation. Vet Comp Orthop Traumatol 22(1):32-37
- Mostafa AA et al (2008) Proximodistal alignment of the canine patella: radiographic evaluation and association with medial and lateral patellar luxation. Vet Surg 37(3):201-211
- Campbell CA et al (2010) Severity of patellar luxation and frequency of concomitant cranial cruciate ligament rupture in dogs: 162 cases (2004-2007). J Am Vet Med Assoc 236(8):887-891
- Yeadon R et al (2011) Tibial tuberosity transposition-advancement for treatment of medial patellar luxation and concomitant cranial cruciate ligament disease in the dog. Surgical technique, radiographic and clinical outcomes. Vet Comp Orthop Traumatol 24(1):18-26
- Daems R et al (2009) Grossly apparent cartilage erosion of the patellar articular surface in dogs with congenital medial patellar luxation. Vet Comp Orthop Traumatol 22(3):222-224
- Wander KW et al (1999) Cartilage changes in dogs with surgically treated medial patellar luxations. Vet Comp Orthop Traumatol 12:183–187
- Willauer CC & Vasseur PB (1987) Clinical results of surgical correction of medial luxation of the patella in dogs. Vet Surg 16:31–36
- Piermattei DL & Flo GL (1997) Handbook of Small Animal Orthopedics and Fracture Repair. Philadelphia: WB Saunders. pp:516–534
- Edwards GA & Jackson AH (2012) Use of a TTA plate for correction of severe patella baja in a Chihuahua. J Am Anim Hosp Assoc 48(2):113-117
- Langenbach A & Marcellin-Little DJ (2010) Management of concurrent patellar luxation and cranial cruciate ligament rupture using modified tibial plateau levelling. J Small Anim Pract 51(2):97-103