Impact Experiments of an External Hip Protector in Young Volunteers

Abstract

This study represents the first measures and experiences of using an external hip protector in humans under forces that could, without the protector, fracture the proximal femur of some of the elderly persons. In other words, we wanted to know if it is possible, using the hip protector, to hit the proximal femur of young volunteers with forces that have the power to fracture some individuals' proximal femur, and if so, how intense is the pain reaction under the impacted area? Four of the researchers (JP, AH, HS, and PK) volunteered to be the study subjects. In the impact experiments, we wore the protector on both sides of the pelvis (greater trochanter), and the pendulum, with an effective mass of 40 kg, was impacted on the protector. The descent height was gradually increased and the highest impact energy used was 115 J. With a load cell mounted on the head of the pendulum we ensured that the external forces used were high enough to fracture the proximal femur of some of the elderly people. Using the external hip protector we tolerated the impacts well although after the high energy impacts every subject reported mild tenderness on the skin area under the contact surface of the protector. Repeated examinations of the impacted area of the study subjects did not reveal hematoma or swelling. In conclusion, our test results suggested that, when wearing an anatomically designed energy-shunting and energy-absorbing hip protector, the fall-induced peak impact forces do not cause undue pain to the impacted hip region, and, in all probability, the forces entering into the proximal femur remain below the range of force capable of fracturing the proximal femur of the elderly. The protector was found to be comfortable to wear and it did not move (slip away) during the experiment. We feel that our protector is now ready for a feasibility study and then for a randomized clinical trial.

Hip protectors: recommendations for biomechanical testing—an international consensus statement (part I)

“…Previous experiments indicate that, during impact to the hip, the body vibrates with a single natural frequency reflecting vertical movement of a single effective mass resting on a parallel spring–damper support [40–43]. In general, the force developed by a spring is proportional to its deflection, while the force developed by a damper is proportional to its velocity or rate of deflection.…”

Subject-specific planning of femoroplasty: An experimental verification study

“…The risk of fracture also depends on a variety of factors including patient anatomy, height of fall, floor covering etc. (Parkkari et al, 1997; Kannus et al, 1999; Bhan et al, 2014). A patient-specific model of the fall such as the ones developed by Robinovitch et al (1991; 1997) could help the surgeon estimate the impact load and set the goal of augmentation accordingly.…”

Subject-specific planning of femoroplasty: A combined evolutionary optimization and particle diffusion model approach

“…The impact load on the femur depends on several other factors including height of the fall, floor covering, body weight etc. (Parkkari et al, 1997; Kannus et al, 1999). To improve the optimization, one can benefit from a patient-specific fall model, e.g.…”