The Pullout Test For The Treatment Of Femoral Neck Fracture Using Internal Fixation With Cannulated Cancellous Screws

ObjectiveThe femoral neck fracture is one of the old-age common fractures. It accounts for 3.6% of all fractures. Because of the specialty of the vascular supply to femoral head, it would be injured easily when the fracture took place. This not only affected the fracture healing but also would produce ischemic necrosis of femoral head easily. The purpose of this experimental study was to find the important factors affecting the stability of cannulated cancellous screws in femoral head and provide experimental basis in clinical use on femoral neck fracture using internal fixation with cannulated cancellous screws.Materials and Methods1.1 Materials and standards:7.3mm cannulated cancellous screws: screw shaft diameter 4.5mm, screw thread diameter 7.3mm, screw thread length 18mm, screw length 75mm, stainless steel;Operative instrument: a 7.3mm tap, two 2.8mm guide pins, a 4.5mm cannulated aiguille , a electric drill, a cannulated screwdriver;2 vacuum flasks, a vernier caliper, a dividers, some pieces of ice.1.2 experimental apparatusWDW multifunctional mechanical experimental apparatusdual energy X-ray absorptiometry(DEXA) Lunar DXP-LC-shaped X-ray vidicon GESPSS11.5 for windowsa fixity of femoral head and a fixity of screw extremity31 femoral heads were from the patients of femoral neck fracture, cannulated cancellous screws were embedded into them by the method for the treatment of femoral neck fracture(two points for embedding, different depths). We recorded the ages of the patients, the diameters of the femoral heads measured by the vernier caliper, the BMDs of the femoral head measured by the DEXA, the distances from the tips of the screws to the articular surfaces of femoral heads. Then we fixed up femoral head and screw extremity into the WDW multifunctional mechanical experimental apparatus and carried out the tests. We got the stress-strain curves and the maximal pullout stresses of the screws. The data were analysed by multiple regression of SPSS for windows 11.5.ResultsThe difference of the femoral head's BMDs and the depths of the screws which were embedded into the femoral heads brought about the difference of the maximal pullout stresses. By multiple regression, we found that the maximal pullout stresses of the screws were correlated with the femoral head's BMDs and the distances from the tips of the screws to the articular surfaces of femoral heads, the maximal stresses positively were correlated with the fore(p=0.002) and negatively correlated with the latter(p=0.000). DiscussionThe stability of the cannulated cancellous screws which were embedded into the femoral heads mainly depended on the hold between the screw threads and the femoral heads, so we can find the mechanical characters of the femoral neck fractures after embedding screws according to this experiment.There is compact bone under the cartilage of articular surface of femoral head. To some extent, the closer tip of screw is to compact bone, the more stable it is. BMD is a important sign of bone strengther. The higher femoral head has BMD, the more stable the screw which is embedded into it is. Osteoporosis of patients brings about descent of bone strengthen and BMD, maybe internal fixation with cannulated cancellous screw do not afford stability for these patients of femoral neck fracture.ConclusionsWe should choose the higher BMD's patients of femoral neck fracture to treat them with cannulated cancellous screws and embed cannulated screws into the special depth of femoral head. We should treat severe osteoporotic patients of femoral neck fracture with arthroplasty.