Proposta de novo modelo de osteossíntese em fêmur: pinos intramedulares múltiplos bloqueados / Proposal of a new type of osteosynthesis in femur: multiple intramedullary pinning blocked

ABSTRACT

Background: Currently many methods of internal fixation for the treatment of fractures in dogs are used. Attempting bone fixation with intramedullary nails is a traditional concept, making it a simple and versatile technique. However, biomechanical faults are frequent, and rotational instability, migration of the pin and the collapse of comminuted fractures are the most common problems observed afterwards. To avoid these complications, multiple intramedullary pins were first used and finally the intramedullary pin was locked into place (interlocking nail). In this study, a new method of intramedullary fixation using multiple locking intramedullary pins was developed for the treatment of femoral shaft fractures in dogs. Materials, Methods & Results: Seventeen mixed breed dogs, weighing between 10 and 20 kg, irrespective of the gender and age, that suffered different traumatic fractures, including complete, closed, transverse or short oblique of the middle third of the femur, were selected as subjects to the study. The fractures were stabilized with 3 Steinmann pins of different diameters that partially occluded the intramedullary canal. The pins were locked distally and proximally to the fracture by transverse insertion of Schanz pins. The diameters of the Steinmann and Schanz pins, used to stabilize the fractures, were selected by the measurement of the diameter of the proximal and distal intramedullary canal in radiographs of the contralateral limb. After a minimal invasive lateral approach to the femur, the bone fragments were exposed. A Shanz pin was inserted in the medial-lateral direction. The pin was inserted in such a way to divide the intramedullary canal in the proximal and caudal thirds of the femur. Upon insertion, the pin was cut short against the outer cortex. Next, the three Steinmann pins were inserted into the spinal canal by the retrograde method. The first to be introduced in the cranial part was the third largest pin in diameter. The distal fragment was exposed and a second Schanz screw was inserted. The fracture was reduced and Steinmann pins were inserted into the distal fragment until resistence was achieved. The three Steinmann pins were cut as close as possible to the greater trochanter. The knee and hip were tested for freedom of movement and lack of interference by the intramedullary pins. The patients were clinically and radiographically evaluated for bone healing. The procedure was performed without difficulty and bone healing progressed satisfactorily with consolidation being achieved between 45 and 90 days. Discussion: Femoral fractures occur frequently in dogs and result in a high number of studies describing different methods for bone fixation. Such studies usually conclude that internal fixation is the best option in most of the fracture types, which is the reason femoral fractures were chosen for our study. The advantages of the technique used in this study are gentle handling of soft tissues with little damage to the vasculature, prevention of the migration of Steinmann pins by locking the Schanz screws, allowing an override in the placement of external fixators to avoid complications, also allowing preoperative planning. The technique was proven an effective method for reducing femoral fractures in dogs weighing between 10 and 20 kg, being easy to perform and complying with the principles of biologic osteosynthesis. Currently, there is not an ideal fixation method for all types of fractures in small animals; all have their advantages and disadvantages, depending on the type of fracture and patient, requiring further and ongoing studies regarding the methods and techniques for fixation of fractures.