Hip Protectors for Preventing Hip Fracture

Hip fractures in older individuals are a major public health concern worldwide. These fractures are expensive to treat and represent one of the most important causes of long-standing pain, functional impairment, disability, and death in this population.^{1 - 2} Experiencing a hip fracture, or even fear of the consequences of fracture, such as social withdrawal, loss of independence and confidence, and admission to a care home, can cause significant mental distress and psychological burden to older individuals.³

In osteoporosis-related research, hip fracture has been observed as a consequence of age-related bone loss or osteoporosis.^{2 ,4 - 5} However, studies on the injury mechanisms of hip fracture in elderly adults have suggested that a fall onto the hip is the strongest risk factor, with the majority of fractures occurring as a result of a fall and direct trauma to the greater trochanter of the proximal femur.^{6 - 12} Furthermore, a sideways fall onto the hip may not be just a simple trauma but a serious high-impact injury capable of fracturing the proximal femur of even young healthy men.¹³

In view of these findings, prevention of hip fractures has created a great deal of interest, including development and testing of various external hip protectors particularly since the early 1990s. The rationale behind this approach is that a device (a foam pad, a plastic shield, or combination of the 2) to protect the hips worn at the time of a fall attenuates and shunts the force and energy of the impact away from the greater trochanter, preventing fracture.¹⁴ However, most commercially available hip protectors have reached the market with a dearth of basic science and clinical research to support their use. For various reasons, including differences in the types of hip protectors, user adherence, and study designs (individually or cluster randomized trials), the results of clinical trials have been contradictory and conflicting. Despite these differences and discrepancies, some meta-analyses and systematic reviews suggest that in nursing homes and institutions with high rates of hip fracture, the use of hip protectors might help to reduce the risk of fracture by 20% to 60%.^{15 - 17} However, there is no evidence of benefit from hip protectors for lower-risk (usually home-dwelling) elderly people.¹⁵ Thus, additional biomechanical research and better controlled clinical trials are needed for development of evidence-based recommendations.

In this issue of JAMA, Kiel and colleagues¹⁸ report the results of a relatively large randomized trial of hip protectors for prevention of hip fracture. Rather than randomizing treatment units or individuals, the investigators randomized nursing homes to provide left or right hip protection to their residents, such that each person served as his or her own control. By using this approach, many problems inherent in traditional designs of cluster or individually randomized trials were avoided and thus only 1 group of study participants was needed. The key finding was that risk of hip fracture was not reduced in the protected vs unprotected hips. In all comparisons, including both the intention-to-treat and per-protocol analyses, the fracture incidence was higher in the protected hip, although the side-to-side differences were not statistically significant.

In the most robust biomechanical evaluation of the hip protector model, comparing rates of hip fracture in the protected hip vs the unprotected hip, there were 13 hip fractures in protected hips and 7 hip fractures in unprotected hips. When the nursing home residents were not wearing the protector (ie, were nonadherent), 13 fractures occurred, and these fractures were distributed almost equally in protected hips (6 fractures) and unprotected hips (7 fractures). These observations raise 2 possibilities. First, the device used was biomechanically ineffective (or even fracture-predisposing) and its position on the greater trochanter not optimal; or second, the use of a 1-sided hip protector modified the individual's standing and walking such that it increased the risk of hazardous fall onto the protected hip. Kiel et al¹⁸ provide evidence to refute the first possibility, although they later acknowledge that the hip protector they chose may not have been sufficient to prevent hip fractures. The device used in the study was relatively new and this was the first attempt to evaluate its use in actual falls of frail, elderly individuals.

Because the authors could not determine the direction of the falls of the participants, the second possibility (that the asymmetric design of the hip protector may affect the side to which a person wearing one might fall) cannot be excluded. As the authors acknowledge, having only 1 hip protected could have modified the propensity to fall to the protected side either because of the mechanical positioning of the pad or because of sensory cues from the pad that altered gait. It is also possible that the protector users actively modified their gait to avoid falling or, after fall initiation, tried to fall toward the protected side. A step forward in future studies using a unilateral protector design would be to record the sideways falls according to the fall direction (protected vs unprotected side), analyze the number of hip fractures per side (protected vs unprotected side), and calculate the risk of hip fracture in protected vs unprotected sideways falls. If gait and falling are unaffected by the presence of a unilateral hip protector, side-to-side falls (right-to-left hip) should be distributed equally.

Although Kiel et al provide useful data from an important trial, these findings and those from past studies are not sufficient to make evidence-based recommendations for or against use of hip protectors among frail, nursing home residents. Given the wide variation in the biomechanical force attenuation capacity among various hip protector models¹⁹ and potential differences in adherence among users, the anti-fracture efficacy of each protector model should first be examined in vitro (as it was for the protectors used by Kiel et al¹⁸ ) and then in actual falls, continuing with analyses of protector position at the time of fall impact, as well as user adherence. Additional randomized trials should be conducted in which the individual is randomized to hip protection or not, or the individual serves as his or her own control, as in the study by Kiel et al. To help address the need for internationally recognized standards for biomechanical and clinical testing of hip protectors, Canadian researchers are now organizing a large International Hip Protector Research Group and its work has received initial funding from the Canadian Institute of Health Research.²⁰ The importance of this health problem—falls and hip fractures among older adults—should make the work a compelling ongoing priority for health research throughout the world.