Tibial plateau leveling osteotomy in dogs: an ex vivo comparative study of knee's surrounding structures protection methods

Background: Cranial cruciate ligament failure is one of the leading causes of pelvic limb lameness in dogs and one of the most recommended treatments is tibial plateau leveling osteotomy (TPLO) surgery. However, this procedure may lead to some complications as fractures of the fibula, laceration in varying degrees of the popliteal vasculature and its branches, neuropraxia, neurotmeses, among others. The goals of this study were to compare the effectiveness of 8 methods used during TPLO, to prevent damage to the cranial tibial artery, fibula, tibial and fibular nerve (surgical compresses, specific surgical retractors I and II and an osteotomy technique variation). Materials, Methods & Results: A total of 40 canine cadavers weighing 25.9 ± 3.7 kg were submitted to TPLO. Animals were previously prepared with 1: 4 barium red latex solution, to provide radiopacity of arteries surrounding the knee (n = 80). TPLO was performed using 8 methods to protect the cranial tibial artery, fibula, and tibial and fibular nerves. Each method was used in one of the knees of 5 animals. The contralateral knee was maintained as a control (without protection). The knees were radiographed in orthogonal projections before and after the osteotomies and then anatomically dissected. The evaluated structures were photographed, and the images sent to four blind evaluators (visual macroscopy) to classify the possible injuries. The highest incidence of injuries was identified when protection methods were used. However, this difference was not significant (P > 0.05). No significant differences regarding efficacy were found between all 8 protection methods. Discussion: In this study, the total incidence of injuries following TPLO was 20% was much higher than that presented in the literature which indicates when considering only intraoperative injuries. The dogs cadavers tissue resistance and stiffened latex may have predisposed the osteotomy injury, as soft tissues with greater flexibility are less susceptible to trauma caused by the oscillatory saw. When compared to others cadaveric studies that also evaluated the efficacy of surgical dressings to protect the cranial tibial artery, during TPLO, we also find a higher incidence of damage. Maybe the limb's position was responsible for this difference, once in the after mentioned researches the limb was positioned suspended to simulate a dorsal decubitus position and we choose the limb position with the lateral face resting on the surface of the operating table, and this may have provided extra pressure from the structures towards the osteotomy saw, increasing the occurrence of those damages. Although the present study did not reveal a significant difference for the use of protection methods, we believe that the dimensions of the compresses used herein may have contributed to a higher incidence of injuries. They probably increased the tissue trauma needed for their allocation and led to a lower positioning accuracy for the isolation of these structures. Maybe for the same reason, the specific type II surgical retractor was the only shield that, observationally, did not increase the occurrence of injuries, once less dissection was required to allocate it. The difference in geometric dimensions between the retractors may justify the superiority of the retractor II, since it allows a more careful and apparently less traumatic allocation. Performing TPLO without adopting these protection methods did not lead to a higher risk of injury to the cranial tibial artery, fibula, and tibial and fibular nerves.

AVALIAÇÃO COMPARATIVA DE DIFERENTES MÉTODOS DE PROTEÇÃO AOS TECIDOS PRÓXIMOS AO JOELHO DURANTE OSTEOTOMIA PARA NIVELAMENTO DO PLATÔ TIBIAL (TPLO). ESTUDO EX-VIVO EM CÃES

Objetivou-se comparar a eficácia de oito diferentes métodos de proteção à artéria poplítea, fíbula e nervos tibial e fibular após osteotomia da TPLO. Foram utilizados 40 cadáveres (80 joelhos) caninos com massa corpórea de 25,9±3,7Kg, distribuídos igualmente em oito grupos experimentais. No primeiro grupo (G1) utilizou-se a compressa cirúrgica, posicionada na face craniolateral da tíbia proximal. No G2 a compressa foi alocada na face caudolateral da tíbia proximal. No G3, a compressa foi aplicada na face craniolateral, porém sendo tracionada até sua visibilização na face caudal da tíbia. O afastador cirúrgico I e II foram utilizados nos grupos G4/G5 e G7\G8, respectivamente. No G4 e G7, o afastador foi utilizado na craniolateral e no G5 e G8, na face caudolateral. No grupo G6, a osteotomia foi realizada de forma parcial na cortical trans e completada, de forma manual, por aplicação de pressão digital. As avaliações foram realizadas por meio de comparação radiográfica pré e pós osteotomia, assim como por meio de dissecação anatômica de forma cega por 4 avaliadores experientes para classificação das possíveis lesões em 3 graus. Encontrou-se uma incidência total de lesões de 20%, sendo 13,8% das lesões grau 2 e 6,2% de lesões grau 3. Das lesões grau 2, 81,8% e 60% das lesões grau 3 foram identificadas quando se utilizou os métodos de proteção. Apesar da maior incidência de lesão quando se utilizou os métodos de proteção, tal diferença não foi significativa (p>5%). Os métodos de proteção que foram utilizados no sentido cranial para caudal foram os que apresentaram piores resultados e o afastador tipo II no sentido caudal para cranial o que menos prejudicou as estruturas avaliadas, porém tal comportamento também não foi significativo. Pelas condições do estudo, conclui-se que o uso dos métodos de proteção adotados não traz benefícios de proteção à artéria poplítea, fíbula e nervos tibial e fibular durante a TPLO.

The propose of the study was to compare the effectiveness of eight different methods of protection of the popliteal artery, fibula, tibial and fibular nerves after TPLO osteotomy. 40 canine corpses (80 knees) with body weight 25,9±3,7Kg were separated in eight experimental groups. In the first group, denominated G1 was used a surgical sponge in the craniolateral aspect of the proximal tibial. In G2 the surgical sponge was allocated in the caudolateral aspect of the proximal tibial. In G3, the surgical sponge was applied in the craniolateral aspect, but it was pushed through caudally to the tibia until it being visible in the operative field. The special retractors I and II developed by the team for this purpose were used in groups G4\G5 and G7\G8, respectively. In G4 and G7, the retractor was used in the craniolateral direction and in G5 and G8, in the caudolateral aspect of the proximal tibial. In G6, the trans cortex osteotomy was partially performed and completed with digital pression. The evaluations were performed through radiographic comparison before and after osteotomy and by dissection of the structures adjacent to the osteotomy line. The images were prepared and sent to 4 evaluators for damage graduation in 3 degrees. A 20% of total incidence of injuries was found with 13,8% of grade 2 injuries and 6,2% of grade 3 injuries. Of grade 2 injuries, 81,8% and 60% of grade 3 injuries were identified when protective methods were used. Despite the higher incidence of injury when protective methods were used, this difference was not significant (p>0,05). The protection methods that were used in the cranial to caudal direction were the ones that showed the worst results and the type II retractor in the caudal to cranial direction was the one which least harmed the evaluated structures, but this behavior was also not significant. Due to the conditions of the study, it is concluded that the use of these methods does not bring benefits to the popliteal artery, fibula and tibial and fibular nerve protection during TPLO.