**6. Patellar luxations in cats**

**4. Radiography**

**5. Treatment**

[6, 8] and allow the prognosis of limb function.

164 Canine Medicine - Recent Topics and Advanced Research

The diagnosis of patellar luxation is clinical, but radiography may help to confirm the diagnosis, showing the luxated patella in more severe cases, and can demonstrate any bony deformities that are present [6]. Mediolateral and craniocaudal radiographs enable assessment of femoral and tibial deformities (**Figure 3A, B**). Tangential views of the flexed stifle enable assessment of the femoral trochlea and its depth (**Figure 3C**). Radiographs can also delineate the morphological changes of the patella and trochlea, demonstrate secondary osteoarthritis

**Figure 3.** Anteroposterior radiograph of the limbs of a dog, showing: (A) medial luxation grade IV in a 16-month-old Pekinese (left); (B) bilateral medial luxation grade III; (C) tangential view of flexed stifle showing an absent trochlea; (D) tangential view showing shallow trochlea (blue arrow), and ectopic patella in a new trochlea (red arrow).

Surgical management of patellar luxation in asymptomatic small-breed dogs is controversial and is not considered necessary. However, surgery is recommended early in young puppies A slight increase in the occurrence of patellar luxation has been observed in cats; however, it is far less common than in dogs [21]; it has been reported in breeds such as the Abyssinian, Devon Rex, Siamese, domestic shorthair cats [22–24], and non-pedigree cats [21, 25]. Some authors report a relationship with hip dysplasia [8], but this remains controversial. As in the dog, medial patellar luxation is the most common and may be either unilateral or bilateral. Most affected cats are usually relatively young at the time of presentation [25]. Some anatomical considerations are necessary to prevent misdiagnosis. The patella in the cat is relatively wider and has more physiological laxity than in dogs. It can be manually moved onto the trochlear ridge of the femoral condyles in many normal cats. Therefore, the grading system developed for dogs should be used with caution [26].

Considering these peculiarities, Voss et al. [27] suggested the following grading system for patellar luxation in cats:

Grade A. Patella can be completely luxated with digital pressure, but immediately returns into position after pressure is released.

Grade B. Patella can be completely luxated with digital pressure and remains temporarily luxated after the pressure is released.

Grade C. Patella luxates when the tibia is internally rotated without exerting direct digital pressure.

Grade D. Patella is temporarily or permanently luxated without any manipulation.

Anatomical changes are similar to those in the dog, including a shallow trochlear groove and medial displacement of the tibial tuberosity. Severe conformational changes are rarely observed, and secondary osteoarthritis is generally absent or mild [28]. It may be associated with the age at diagnosis of patellar luxation because older cats may have severe degenerative changes in their stifle joints [28]. Erosions in the patella and on the condylar ridge may be seen as in dogs. Although surgical treatment is suggested when the luxation results in lameness [21], it should be considered early, aiming to align the quadriceps and prevent degenerative changes.

Congenital bilateral patellar aplasia has been described in two Siamese cat littermates [29].
