Mechanical study in vitro of the resistance of axial forces of 3.5 mm cannulated and conventional screws in head and femoral neck fractures / Estudo mecânico in vitro da resistência a forças axiais dos parafusos canulado e convencional de 3, 5 mm de diâmetro em fraturas de cabeça e colo femoral

ABSTRACT

Background: Proximal femoral fractures account for 25% of all femoral fractures in dogs and are more common in younganimals. Osteosynthesis of femoral head and neck fractures is a complex procedure that can be performed using conventionalscrews or wires. However, proper fracture reduction and fi xation are diffi cult to achieve and, despite many advancements,such fractures remain challenging to solve. Cannulated screws have good compressive capacity and can be employed tosimplify the surgical procedure while optimizing outcomes. This study was designed to compare the resistance of conventional and cannulated screws to axial loading following experimental femoral neck fracture in dogs.Materials, Methods & Results: Fourteen cadaveric canine femurs were used in this study. Femurs were collected from dogsover 20 pounds in body weight with no gross or radiographic signs of orthopedic disease. Cadaveric femurs were submitted to experimental femoral neck fracture using a Gigli saw and allocated to osteosynthesis using either conventional orcannulated screws (seven bones each). All screws were inserted below the greater trochanter of the femur from the lateralaspect of the bone and screw topography confi rmed radiographically. Test specimens were then potted in polymethylmethacrylate, coupled to a hinged device and submitted to axial loading. Data on maximum load, maximum displacement, loadwithin the proportional limit, offset within the proportional limit and load required to produce a 3 mm displacement werecollected. Mean values were calculated and compared using the Student’s t test (P < 0.05). Mean values varied greatlywithin groups. Maximum load and displacement correspond to the critical point from which biomechanical testing becomesdestructive. Data were missing from one test specimen (conventional screw group) due to abrupt diaphyseal fracture atthe start of the axial loading trial...