**8. Results**

A total of 280 luxated joints from 202 dogs were assessed; 244 were in medial luxation, whereas 36 were in lateral luxation. Sixteen (5.7%) were classified as grade I, 118 (42.1%) as grade II, 57 (20.4%) as grade III and 89 (31.8%) as grade IV.

The patellar lesions identified included cartilage erosion of one-fourth (15.0%), one-half (11.8%) or all (1.8%) of the patella, exposure of subchondral bone (4.3%), a flattened or concave patellar surface (15.0%) (**Figure 4**), the presence of enthesophytes (12.1%), cartilage flap at the edge of femoral condyle, joint mice and lesions caused by the patella rubbing on the long digital extensor tendon (**Figure 5**). **Tables 1** and **2** show the lesions according to degree of dislocation, weight and age.

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

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

This was a retrospective study that assessed the clinical surgical records of dogs treated for patellar luxation from January 2005 to January 2016 at the Veterinary Hospital, Federal University of Minas Gerais (FUMG) in Brazil. Data describing age, body weight and the degree of patellar luxation at admission were collected for each animal. The animals were then categorized based on body weight (≤5, 5–15 and ≥15 kg), age (<12, 12–24 and >24 months) and degree of luxation according to Putnam's [10] classification as adapted by Singleton [19]. In addition, data relative to the intraoperative period were recorded; these included the presence of stifle joint damage, classified as patellar or extrapatellar lesions and the frequency of postoperative re-luxation. The associations between patellar or extra-patellar lesions and the animal's age, body weight and degree of luxation were investigated. Patellar lesions included the presence of cartilage erosion, the extent of the erosion (one-fourth, one-half or the full patellar articular surface), the morphology of the patella (concave or flat), the exposure of subchondral bone and the presence of enthesophytes. Extra-patellar lesions included the presence of erosion and subchondral bone exposure in the medial or lateral femoral condyles, the presence of osteophytes, synovitis, capsular thickening or shallowing of the trochlea, an absent or convex trochlear groove, cruciate ligament rupture and injury of the long digital

The frequency of lesions in the stifle joint was subjected to descriptive analysis, and the rate of patellar re-luxation was assessed using the chi-square test. The significance level was set at *P*

This retrospective study also included the clinical records of eight cats (13 joints) treated for patellar luxation. Data describing age, body weight and the degree of patellar luxation at

A total of 280 luxated joints from 202 dogs were assessed; 244 were in medial luxation, whereas 36 were in lateral luxation. Sixteen (5.7%) were classified as grade I, 118 (42.1%) as grade II, 57

The patellar lesions identified included cartilage erosion of one-fourth (15.0%), one-half (11.8%) or all (1.8%) of the patella, exposure of subchondral bone (4.3%), a flattened or concave

changes.

**7. Materials and methods**

166 Canine Medicine - Recent Topics and Advanced Research

extensor tendon and the menisci.

admission were collected for each animal.

(20.4%) as grade III and 89 (31.8%) as grade IV.

< 0.05.

**8. Results**

**Figure 4.** Photograph of the stifle joint of a dog subjected to surgery for patellar luxation. Notice the erosion of the patellar articular surface (black arrow). (A) Superficial erosion; (B) moderate erosion, (C and D) severe erosion; (E) severe erosion in the whole extension of the patella; (F) erosion of the edge of the medial condyle and erosion of the patella with subchondral bone exposure (blue and black arrows); (G) notice the flattened patellar surface (black arrow) and shallow trochlear groove (blue arrow); (H) convex femoral trochlea (black arrow); (I) patella concave.

**Figure 5.** Photograph of the stifle joint of a dog subjected to surgery for patellar luxation. Notice the lesion by rubbing of the patella on the long digital extensor tendon (black arrow).

One rare instance of resorption of the patella was diagnosed in a dog with a grade III luxation. Some remnants of the bone were found adhered to the patellar tendon, while the central area was soft and exhibited loss of bone and cartilage. A 1-year history of severe lameness with frequent non-weight-bearing and grade II medial luxation in the contralateral limb existed. Resorption of the patella was treated with implantation of polyhydroxybutyrate patellar prosthesis. The outcome was favourable.


\* The weight was not reported in 12 animals that were excluded from this assessment.

\*\* The age was not reported in six animals that were excluded from this assessment.

**Table 1.** Estimated patellar lesions in dogs with patellar luxation treated at the Veterinary Hospital, FUMG, 2005–2016 according to the degree of luxation, body weight and age.

The frequency of cartilage erosion affecting one-fourth or one-half of the patella accompanied by subchondral bone exposure was higher among those with grade II or III luxation. Erosion of the full patellar surface occurred only in grade III or IV luxation. Patellar lesions were frequently observed on the lateral surface in medial luxation, but were seen on the medial surface in lateral luxation. Anatomical changes of the patella, such as a flattened or concave surface, occurred primarily in grade III or IV luxation, whereas enthesophytes were

most frequently found in grade III luxation. In animals older than 24 months, the lesions most frequently found were cartilage erosion affecting one-fourth or one-half of the patella, subchondral bone exposure and the presence of enthesophytes. The frequency of anatomical changes of the patella (flattened or concave surface) was highest among those older than 24 months of age and lowest in those aged 12–24 months. The frequency of patellar lesions was proportionally higher among those animals weighing more than 15 kg (**Table 1**). Joint mice and flap formation (**Figure 6**) were observed in two dogs with patellar luxation grade III. One dog was 6 months of age and weighed 22 kg and the other was 10 years old and weighed 5.8 kg.

One rare instance of resorption of the patella was diagnosed in a dog with a grade III luxation. Some remnants of the bone were found adhered to the patellar tendon, while the central area was soft and exhibited loss of bone and cartilage. A 1-year history of severe lameness with frequent non-weight-bearing and grade II medial luxation in the contralateral limb existed. Resorption of the patella was treated with implantation of polyhydroxybutyrate patellar

**Subchondral bone**

**Severity n° % n° % n° % n° % n° % n° % n°** Grade I 1 6.3 0 0 0 0 0 0 0 0 0 0 16 Grade II 22 18.6 17 14.4 0 0 6 5.1 12 10.1 11 9.3 118 Grade III 13 22.8 10 17.5 2 4.1 5 8.8 11 19.3 15 26.3 57 Grade IV 6 6.7 6 6.7 3 3.4 1 1.1 19 21.3 8 9.0 89 Total 42 33 5 12 42 34 280

Weight Assessed dogs

**Table 1.** Estimated patellar lesions in dogs with patellar luxation treated at the Veterinary Hospital, FUMG, 2005–2016

The frequency of cartilage erosion affecting one-fourth or one-half of the patella accompanied by subchondral bone exposure was higher among those with grade II or III luxation. Erosion of the full patellar surface occurred only in grade III or IV luxation. Patellar lesions were frequently observed on the lateral surface in medial luxation, but were seen on the medial surface in lateral luxation. Anatomical changes of the patella, such as a flattened or concave surface, occurred primarily in grade III or IV luxation, whereas enthesophytes were

<5 kg 22 21.4 5 6.0 3 2.8 0 0 14 13.0 13 12.0 108 5–15 kg 11 21.2 12 23.1 1 1.9 5 9.6 9 17.3 10 19.3 52 >15 kg 6 20.0 10 33.3 2 6.7 5 16.7 7 23.3 6 20.0 30 Total 39 27 6 10 30 29 190\* Age (n°) <12 months 6 7.0 5 5.8 3 3.5 5 5.8 13 15.1 5 5.8 86 12–24 months 3 15.0 1 5.0 0 0 0 0 1 5.0 3 15 20 >24 months 27 30.0 22 24.4 4 4.4 7 7.8 16 17.8 20 22.2 90 Total 36 28 7 12 30 28 196\*\*

 The weight was not reported in 12 animals that were excluded from this assessment. \*\* The age was not reported in six animals that were excluded from this assessment.

according to the degree of luxation, body weight and age.

**Flattened/concave**

**Enthesophytes Assessed**

**joints**

(n°)

**patella**

**exposure**

prosthesis. The outcome was favourable.

168 Canine Medicine - Recent Topics and Advanced Research

**Cartilage erosion**

**½ patella** 

**Full patella** 

**¼ patella** 

\*


**Table 2.** Estimated extra-patellar articular lesions in dogs with patellar luxation treated at the Veterinary Hospital, UFMG, 2005–2016 according to degree of luxation, body weight and age.

**Figure 6.** Photography of the stifle joint of a dog to surgery for patellar luxation. Notice the erosion of the patellar articular surface (black arrow), joint mice (blue arrow) and flap formation on the edge of the medial condyle (black S arrow).

Several extra-patellar lesions involving soft or hard tissue were observed. On intraoperative assessment, 29.3% of the joints exhibited synovitis, 26.1% had periarticular osteophytes, 43.9% had shallow trochlear grooves, 12.9% had absent trochlea, 35.7% exhibited cartilage erosion in condylar margins, 7.9% exhibited subchondral bone exposure in condylar margins, 23.6% had thickened capsules (**Table 2**), 3.6% had long digital extensor tendon injuries associated with lateral luxation, 0.7% exhibited joint mice and flap formation, 9.3% had ruptured cranial cruciate ligaments and 3.1% exhibited prolapse of the menisci. Synovitis occurred in 37.5% of the animals with grade I luxation. Periarticular osteophytes and shallow trochlear grooves were most frequently found among the animals with grade II luxation. Erosion of the femoral condylar margins and thickened capsules occurred most frequently among those with grade III luxation, while absent trochlear grooves were most frequently among those with grade IV luxation. Exposure of subchondral bone on the condylar margins predominated among those with grade III or IV luxation. Lesions in medial condyles were observed in joints in medial luxation, whereas lesions in lateral condyles were frequent in joints in lateral luxation. Extra-patellar lesions were proportionally higher among those weighing more than 15 kg.

The frequency of extra-patellar articular lesions according to age, body weight and degree of luxation is presented in **Table 2**.

Patellar re-luxation after surgical repair occurred in 12.9% of the joints distributed across all grades, ranging between 6% and 15%. Statistical analysis using the chi-square test suggests that no statistically significant differences exist between the variable "re-luxation patellar" and "degree of luxation," and "type of luxation (medial or lateral)" (*P* > 0.05).

The frequency of re-luxation according to type and degree of luxation is shown in **Table 3**.


**Table 3.** Estimated patellar re-luxation in dogs treated at the Veterinary Hospital, FUMG, 2005–2016 according to the type (medial or lateral) of luxation and degree of luxation. The rate of patellar re-luxation was assessed using the chisquare test.

**Figure 6.** Photography of the stifle joint of a dog to surgery for patellar luxation. Notice the erosion of the patellar articular surface (black arrow), joint mice (blue arrow) and flap formation on the edge of the medial condyle (black S ar-

Several extra-patellar lesions involving soft or hard tissue were observed. On intraoperative assessment, 29.3% of the joints exhibited synovitis, 26.1% had periarticular osteophytes, 43.9% had shallow trochlear grooves, 12.9% had absent trochlea, 35.7% exhibited cartilage erosion in condylar margins, 7.9% exhibited subchondral bone exposure in condylar margins, 23.6% had thickened capsules (**Table 2**), 3.6% had long digital extensor tendon injuries associated with lateral luxation, 0.7% exhibited joint mice and flap formation, 9.3% had ruptured cranial cruciate ligaments and 3.1% exhibited prolapse of the menisci. Synovitis occurred in 37.5% of the animals with grade I luxation. Periarticular osteophytes and shallow trochlear grooves were most frequently found among the animals with grade II luxation. Erosion of the femoral condylar margins and thickened capsules occurred most frequently among those with grade III luxation, while absent trochlear grooves were most frequently among those with grade IV luxation. Exposure of subchondral bone on the condylar margins predominated among those with grade III or IV luxation. Lesions in medial condyles were observed in joints in medial luxation, whereas lesions in lateral condyles were frequent in joints in lateral luxation. Extra-patellar lesions were proportionally higher among those

The frequency of extra-patellar articular lesions according to age, body weight and degree of

Patellar re-luxation after surgical repair occurred in 12.9% of the joints distributed across all grades, ranging between 6% and 15%. Statistical analysis using the chi-square test suggests that no statistically significant differences exist between the variable "re-luxation patellar" and

The frequency of re-luxation according to type and degree of luxation is shown in **Table 3**.

"degree of luxation," and "type of luxation (medial or lateral)" (*P* > 0.05).

row).

weighing more than 15 kg.

luxation is presented in **Table 2**.

170 Canine Medicine - Recent Topics and Advanced Research

A total of 13 luxated joints from eight cats were assessed, and all were medial luxations. Four (30.7%) were classified as grade IV, seven (53.4%) as grade III and two (15.4%) as grade II. Six cats were younger than 12 months and two were 12–24 months of age. Hip dysplasia was present in two cats (25%). Two cats from the same litter had patellar luxation grade IV associated with bone and tail deformity (**Figure 7**). One of them had unilateral patellar aplasia. These cats showed gait abnormalities, but were able to move around the house. Six were mixedbreed cats, one was Siamese, and one was an exotic cat. The surgical treatment was successful, and there was no recurrence of luxation.

**Figure 7.** Anteroposterior radiograph of the limbs of a cat, showing: (A) bone deformity, and tail, dysplasia and medial patellar luxation grade III on the left side in a 7-month-old cat; (B) abnormal stance associated with bone deformities and medial patellar luxation grade III.

Lesions such as flattened patellar surface and shallow trochlear groove were also observed in cats with patellar luxation grades III and IV (**Figure 8**).

**Figure 8.** Photography of the stifle joint of a cat to surgery for patellar luxation. Notice the erosion of the edge of the medial condyle (A, blue arrow), flattened patellar surface (B, blue arrow) and shallow trochlear groove (C, blue arrow).
