TYPE OF FALL AND RISK OF HIP AND WRIST FRACTURES: THE STUDY OF OSTEOPOROTIC FRACTURES

To the Editor: I am writing to comment on an excellent paper entitled “Type of fall and risk of hip and wrist fractures: The study of osteoporotic fractures”.1 The paper states, “Most hip fracture cases (66%) fell sideways and onto the hip, side of the leg, or buttocks. …” “… falling onto a hard surface increases the risk of hip fractures. This suggests interventions that attenuate the force or impact of the fall such as the application of padding over the hip … might help decrease the risk of hip fracture.”1 The paper did not mention another plausible mechanism for hip fractures. Severe musculoskeletal injuries in the lower extremities often occur with no direct contact with the ground at all. For instance, in the classic work on Knee Pain and Disability, Rene Cailliet comments on meniscus injuries to the knee and states, “The combination of weight bearing with rotary stress during flexion or extension as a cause of meniscus injury appears to be well accepted.”2 Turning to the hip, 100 years ago Kocher “produced fractures in cadavers either by a direct blow on the greater trochanter or a blow on the long axis of the femur with simultaneous lateral rotation of the extremity”.3 “Kocher thought that the fractures were caused by vertical loading of the femur with simultaneous external rotation of the limb. The head is firmly fixed by the anterior capsule and iliofemoral ligament while the neck rotates posteriorly. The posterior cortex of the femoral neck then impinges against the posterior rim of the acetabulum and the neck buckles.”4 Lotz and Hayes recently reported loading the hips of fresh human cadavers in a way that produced fractures similar to those observed clinically.5 “The directions of the loads were such that the axes of the diaphysis and femoral neck formed an angle of 30 degrees with the plane perpendicular to the applied loads. To facilitate testing, each bone was sectioned at the midpoint of the diaphysis, and the distal end was rigidly fixed, with the lateral aspect of the greater trochanter in contact with the horizontal platform … A vertical load was then applied to the femoral head.”5 The accompanying diagram actually shows the load was applied to the anterior aspect of the femoral head and the posterior aspect of the greater trochanter. This loading system certainly has a significant torsional component and includes a fixed distal femur. A textbook on musculoskeletal disorders by Robert D. D'Ambrosia states in the section on intertrochanteric features of the femur. I would speculate that a mechanism for hip fracture is a fall with rotation of the torso around the axis of the femur held in postion by the foot fixed to the ground. The acetabulum, ligamentous, and muscular attachments rotating with the torso shear the fixed hip before the patient hits the ground. I do not know the actual vectors involved in most hip fractures. However, an indirect torsional mechanism of some hip fractures should be considered. Protective hip pads would have to be constructed so as not to impede protective responses. I look forward to the author's comments.