Radiological measures of patellofemoral alignment in healthy small-breed dogs: reference values and sex variability

Background: The evaluation of vertical kneecap position within the trochlear groove is essential for understanding the anatomical changes that may lead to canine patellar luxation. Unlike other important diagnostic imaging measurements (e.g. measures of pelvic limb alignment), no data on patellofemoral congruence parameters of canine stifles (congruence angle, linear axial patellar displacement, lateral patellofemoral angle, patellar tilt angle) are reported. The aim of this study was to present metric values of these parameters in healthy dogs from small breeds from both sexes in order to use them for identification of animals with increased risk for medial patellar luxation. Materials, Methods & Results: The study was performed on 44 stifle joints from 22 healthy dogs of both sexes from 4 small breeds (Pinscher, Pomeranian, Chihuahua and Yorkshire terrier). Inclusion criteria were negative patellar displacement and dancing patella tests after orthopaedic examination, lack of femoral and gluteal muscles asymmetry after palpation, lack of signs of long-term proprioceptive dysfunction, normal patellar and withdrawal reflexes after neurological examination. The translation of the patella in the axial plane was evaluated by means of congruence angle and axial linear patellar displacement. The rotation of the patella in the axial plane was evaluated through measurement of lateral patellofemoral angle and patellar tilt angle. Reference ranges of parameters were analysed in agreement with the guidelines of the American College of Veterinary Pathologists for the determination of reference intervals in veterinary species for sample sizes of 40-120 with non-Gaussian distribution - robust method, 95% confidence interval (CI) with 90 % CI for upper and lower reference limits. All measured patellofemoral congruence angles were negative. Their reference range was from -8.06o to -0.58o (median value -3o ). The axial patellar displacement was negligible, with values ranging from 0.1 to 0.8 mm. Lateral patellofemoral angles in all dogs were open to the lateral side (positive); the computed reference interval was from 21.61o to 41.80o (median 31.5o ). Patellar tilt angles ranged from 2o to 8o (median 5o ). A statistically significant difference between sexes was demonstrated for angles describing the rotation of the patella in the axial plane: the lateral patellofemoral angle (P = 0.0248) and the patellar tilt angle (P = 0.0004) were greater in stifles of male dogs. Discussion: This is the first study presenting reference values of parameters describing patellofemoral alignment in healthy dogs from small breeds on tangential radiographs. The values of one of most commonly measured parameters on tangential radiographs (the lateral patellofemoral angle) in stifles of small breed dogs were higher than values in humans, supposedly due to the specific joint anatomy. The patellar tilt angle is considered as more objective and not influenced by limb rotation. For the detection of patellar misalignment, the tilt angle was reported to be almost as specific as the congruence angle but more sensitive and more accurate. It is the most specific and sensitive parameter determining the direction of patellar luxation. In male dogs, the median lateral patellofemoral angle was greater than in females (P = 0.0248). Similar tendency was shown for patellar tilt angle that was also greater in male stifles (P = 0.0004). The reported statistically significant between-sex differences in lateral patellofemoral angle and patellar tilt angle with higher values of both angles in stifles of male dogs could be attributed to the better developed femoral muscles, in particular m. vastus medialis and m. sartorius, and to differences in trochlear groove and kneecap morphology. The presented reference intervals may be useful for early detection of subjects with increased risk to medial patellar luxation.

Short-term outcomes of trochlear recession surgery combined with "Watermelon" autograft for treatment of canine medial patellar luxation: a case series / Resultados a curto prazo da cirurgia de recessão trocolear combinada com o auto-enxerto "Melancia" para tratamento da luxação patelar medial canina: uma série de casos

The aim of this study was to present a novel surgical method for correction of medial patellar luxation in small-breed dogs with trochlear dysplasia and marked hypoplasia of the medial femoral condyle. The "Watermelon" approach was applied together with trochlear wedge recession or trochlear block recession and consisted in increasing the height of the medial condyle with an osteochondral autograft resembling a watermelon slice, placed into an additional slot in the medial femoral condyle to prevent the postoperative reluxation of the patella. The study cohort included 19 dogs (25 joints) from small breeds (Pinscher, Pomeranian, and Chihuahua) with second-grade medial patellar luxation. Fourteen joints were submitted to wedge recession surgery combined with "Watermelon" grafting, and 11 joints: to block recession surgery with "Watermelon" grafting. The sulcus-deepening trochleoplasty combined with "Watermelon" grafting was clinically successful and with low percentage of minor postoperative complications. The mean duration of anesthesia was significantly longer for block recession combined with "Watermelon" (P<0.001), but the recovery period was shorter (P<0.05).

O objetivo deste estudo foi apresentar um novo método cirúrgico para correção da luxação patelar medial em cães de raça pequena com displasia troquelar e hipoplasia marcada do côndilo femoral medial. A abordagem "Melancia" foi aplicada juntamente com a recessão da cunha trocolear ou recessão do bloco trocolear e consistiu em aumentar a altura do côndilo medial com um auto-enxerto osteocondral parecido com uma fatia de melancia, colocado em uma fenda adicional no côndilo femoral medial para evitar o relaxamento pós-operatório da patela. A coorte do estudo incluiu 19 cães (25 juntas) de raças pequenas (Pinscher, Pomeranian, e Chihuahua) com luxação patelar medial de segundo grau. Catorze juntas foram submetidas à cirurgia de recessão em cunha combinada com enxerto de "melancia", e 11 juntas: para bloquear a cirurgia de recessão com enxerto de "melancia". A trocleoplastia de "melancia" combinada com o enxerto de "melancia" foi clinicamente bem sucedida e com baixo percentual de pequenas complicações pós-operatórias. A duração média da anestesia foi significativamente maior para a recessão em bloco combinada com "Melancia" (P<0,001), mas o período de recuperação foi mais curto (P<0,05).

Simultaneous osteosarcoma in two limbs of a Maltese dog

Osteosarcoma (OSA) is rarely diagnosed in small breed dogs and it is usually restricted to a single bone, despite its aggressive biological behavior. This paper aims to report a rare case of OSA in an eight-year-old female spayed Maltese dog with simultaneous presentation in thoracic and pelvic limbs, associated with lung and kidney micrometastasis. Physical exam revealed an increase volume in the distal region of the left femur and in the proximal region of the left humerus with intense pain sensibility at palpation. Pelvic limb´s radiographs revealed an extensive area of bone lysis in the distal femur, lamellated periosteal reaction and formation of the Codman triangle, while in the thoracic limb, it was evident a cortical fracture of the proximal humerus and mixed periosteal reaction, suggestive of neoplastic or infectious disease. Cytological analysis showed the presence of a large number of malignant star-shaped cells, with prominent anisocytosis and anisokaryosis, moderate to prominent cellular and nuclear pleomorphism, rare mitotic figures, besides abundant extracellular matrix compatible with osteoid, suggestive of osteosarcoma. Histopathological findings were compatible with OSA. The dog died of a cardiorespiratory arrest and necropsy revealed a grade II osteoblastic osteosarcoma in the humerus and femur, along with renal metastasis and neoplastic emboli in the kidney and lungs.

Simultaneous osteosarcoma in two limbs of a Maltese dog

Osteosarcoma (OSA) is rarely diagnosed in small breed dogs and it is usually restricted to a single bone, despite its aggressive biological behavior. This paper aims to report a rare case of OSA in an eight-year-old female spayed Maltese dog with simultaneous presentation in thoracic and pelvic limbs, associated with lung and kidney micrometastasis. Physical exam revealed an increase volume in the distal region of the left femur and in the proximal region of the left humerus with intense pain sensibility at palpation. Pelvic limb´s radiographs revealed an extensive area of bone lysis in the distal femur, lamellated periosteal reaction and formation of the Codman triangle, while in the thoracic limb, it was evident a cortical fracture of the proximal humerus and mixed periosteal reaction, suggestive of neoplastic or infectious disease. Cytological analysis showed the presence of a large number of malignant star-shaped cells, with prominent anisocytosis and anisokaryosis, moderate to prominent cellular and nuclear pleomorphism, rare mitotic figures, besides abundant extracellular matrix compatible with osteoid, suggestive of osteosarcoma. Histopathological findings were compatible with OSA. The dog died of a cardiorespiratory arrest and necropsy revealed a grade II osteoblastic osteosarcoma in the humerus and femur, along with renal metastasis and neoplastic emboli in the kidney and lungs.(AU)