Biomechanical comparison of hard and soft hip protectors, and the influence of soft tissue
Introduction
More than 90% of all hip fractures are the consequence of a fall [1]. However, only 1–2% of all falls result in a hip fracture [2], [3]. For a fall to result in a hip fracture, the force applied to the proximal femur must exceed its strength [2]. Three conditions influencing this outcome are: (a) the faller must land on or near the hip; (b) protective responses must fail; and (c) local soft tissues must absorb less energy than necessary to prevent fracture [2]. Because gait speed decreases with increasing age [4], frail elderly people are more likely to land on the hip. Furthermore, reaction time slows with age and therefore, protective responses may be delayed. Absorption of energy may be decreased due to weakness or atrophy of the muscles and reduced fat around the hip and buttocks. In addition, bone strength decreases with aging.
A preventive measure to reduce the impact of a fall on the hip is the hip protector [5]. Basically, two types of hip protectors exist: (1) hard, shell-shaped protectors, which primarily shunt away energy towards the surrounding tissues, including femoral shaft, iliac crest and soft tissues; and (2) soft protectors, which primarily absorb energy. Their effectiveness in practice depends on two issues: (1) the force attenuation capacity, which is in our study defined as the “the capability of a hip protector to decrease the peak force”; and (2) compliance, which is influenced by wearing comfort [6]. In the literature, two biomechanical studies suggest that the force attenuating capacity of the hard, energy-shunting hip protectors is superior to the soft, energy-absorbing ones [7], [8]. However, compliance may be higher with soft hip protectors [9], [10].
In our study, we examined the force attenuation capacity of hip protectors that are currently commercially available. After the above two biomechanical studies were carried out, several new hip protectors have been developed and the biomechanical properties of existing hip protectors have been improved. Therefore, the aim of this study was to compare the force attenuation capacity of all hip protectors that were commercially available at the start of our study. In addition, based on an earlier study that reported a high correlation between increased soft tissue thickness and decreased peak force, the influence of soft tissue thickness on the peak force of the different hip protectors was examined [11].
Our hypotheses were: (1) The force attenuation capacity of hard hip protectors, which primarily shunt away energy, will be higher than those of soft hip protectors, which primarily absorb energy. (2) The force exerted on the hip will be lower for hip protectors combined with thicker soft tissue than for hip protectors combined with thinner soft tissue, because part of the energy will be absorbed by the soft tissue.
Section snippets
Hip protectors
All hip protectors were selected that could be identified by the literature or the Internet and were commercially available at the start of our study. Of the 11 manufacturers selected, nine different manufacturers were willing to participate. One manufacturer refused to participate, and one hip protector used in a previous patient study was no longer commercially available. Of each type, six underpants, including 12 protectors, were ordered. Of the Safehip hip protector, also the old model was
Results
In Table 2, the coefficients of variation for the different experiments are presented. In general, the coefficients of variation were very low (0.01–0.08), with two experiments having somewhat higher coefficients (0.18–0.19). In Fig. 3, two time-versus-force graphs are presented. The first graph represents the time-versus-force curves of the hard and soft hip protector with the lowest average peak force in the 1-inch soft tissue test. In the second graph, the results of the 1/2-inch soft tissue
Discussion
In this study, a biomechanical comparison of 10 different hip protectors was made. It was shown that, in combination with a thicker soft tissue layer, all hip protectors were able to reduce the peak force below the average fracture threshold of 3100 N. However, in combination with thinner soft tissue, only the hard hip protectors were able to reduce the peak force of a severe fall below the average fracture threshold. In both experiments, the hard hip protectors reduced the impact on the
Acknowledgment
We would like to thank the manufacturers for providing the hip protectors.
References (21)
- et al.
Comparison of force attenuation properties of four different hip protectors under simulated falling conditions in the elderly: an in vitro biomechanical study
Bone
(1999) - et al.
Anatomical hip model for the mechanical testing of hip protectors
Med. Eng. Phys.
(2005) - et al.
Mechanical testing of hip protectors
J. Mater. Process. Technol.
(2002) - et al.
Majority of hip fractures occur as a result of a fall and impact on the greater trochanter of the femur: a prospective controlled hip fracture study with 206 consecutive patients
Calcif Tissue Int.
(1999) - et al.
A hypothesis: the causes of hip fractures
J. Gerontol.
(1989) - et al.
Etiology and prevention of age-related hip fractures
Bone
(1996) - et al.
Studies of gait and mobility in the elderly
Age Ageing
(1981) - et al.
Hip protectors for preventing hip fractures in the elderly
Cochrane Database Syst. Rev.
(2004) - et al.
Acceptance and compliance with external hip protectors: a systematic review of the literature
Osteoporos. Int.
(2002) - et al.
Energy-shunting hip padding system attenuates femoral impact force in a simulated fall
J. Biomech. Eng.
(1995)
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