[A biomechanical study on the senile intracapsular fracture of the femoral neck--speculation concerning the fracture lines and etiological factors (author's transl)].
In this study, intracapsular fracture of the femoral neck in the elderly was classified into three types, the typical type with the fracture line about 70 degrees from the horizontal line with the spike of the neck (60%), the crescent type with the arch-like fracture line without the spike of the neck (30%) and the mixed type with the fracture line about 70 degrees from the horizontal line without the spike of the neck (10%). After that, each etiological factor of these three types of the fracture was studied. From the investigation of the osteoporotic changes at the upper end of the femur in patients over 50 years old with the intracapsular fracture of the femoral neck, the statistical loading test on the head of the human cadaveric femur, the analyses of the upper half model of the human femur using the experimental stress analysis based on photoelasticity and the finite element method and the observations of the microscopic trabecular fractures, the following facts were found at the area of the upper capito-cervical junction near the epiphyseal scar; (1) that the cancellous bone is easily affected by the influence of osteoporotic changes, (2) that the acting stress is higher than the ultimate strength of the bone in activities of daily living, (3) and that many microscopic trabecular fractures can be observed. Therefore, this area will become "the area of reduced strength", that may sometimes remain unrecognized and heal spontaneously. Since any fracture starts from here, this area can be regarded as "the trigger" of the clinical intracapsular fracture of the femoral neck. Factors dividing the intracapsular fracture of the femoral neck into three types, except the unrecognizably remained and spontaneously healed one, may be as follows. 1) When the load approximately as heavy as body weight with the abruptly rotational force (especially external rotational force) is applied, the fracture classified into the typical type occurs (it has been examined experimentally). 2) Always when the repeated load is applied on the increase in number of the microscopic trabecular fractures, which happen because of severe osteoporotic changes and bone density loss, the fracture classified into the crescent type occurs. 3) When both the factors are present, the fracture classified into the mixed type occurs.
D001696:Biomechanical Phenomena; D005265:Femoral Neck Fractures / Q000145:classification / Q000209:etiology*; D005272:Femur Neck / Q000033:anatomy & histology; D006801:Humans; D008875:Middle Aged; D008953:Models, Anatomic