Documentation:FIB book/Hip Fractures and Compliant Flooring

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Introduction

CT of a Pertrochanteric Fracture

In older communities, falls and fall-related injuries make up the one of the leading causes of injury deaths worldwide, and can often be a huge financial burden on an individual and their family.[1] The number of people that suffer a hip fracture due to a fall or a fall-related injury in the US is as high as 100 per 100,000 individuals, most of which are within older demographics.[2] More specifically, over 50% of fractures in individuals over the age of 65 are due to falls at home.[2] Although there are many factors affecting the incidence of fall-related hip fractures, one important factor is the peak force experienced by a falling individual. When looking at older populations, the higher incidence of osteoporosis is a major contributing factor causing fracture under loading conditions that would be non-injurious in other demographics.[1] Since 1 in 3 women and 1 in 5 men over the age of 50 experience an osteoporotic fracture, the necessity to evaluate different measures to reduce the incidence of fall-related fractures becomes evident.[1]

One method of reducing the peak forces experienced during a fall is to utilize compliant flooring in hospitals and long term care facilities.[1] Compliant flooring is flooring that has relatively low stiffness and high energy absorbance properties. Compliant flooring is a particularly attractive hip injury prevention method because it does not require patient compliance unlike interventions such as hip protectors. Despite the potential injury prevention benefits of compliant flooring, one factor to consider is the effect of compliant flooring on balance. Balance can be hindered through the application of flooring that is too compliant which can increase the incidence of falls.[3]

In this literature review, the biomechanics of hip fracture, types of compliant floorings in use, and issues regarding balance will be discussed. Additionally, the economic feasibility of compliant flooring as well as potential areas of future research will be addressed.

Biomechanics

Labelled Human Femur

Hip fracture is a fracture that occurs at the neck of the proximal femur. The peak impact force delivered to the greater trochanter during a fall determines whether a person will suffer a hip fracture.[3][4] Fall impact forces can be reduced by dissipating some of the fall energy through soft tissue or artificially through hip protectors and compliant flooring.[3][4][5][6] The impact force in similar scenarios is different for individuals as it is dependent on weight and height.[4] Individuals with higher body mass index tend to have higher amounts of soft tissue over the greater trochanter which can be a protective factor against hip fractures.[5] As previously mentioned, hip fractures are more likely to occur in older individuals due to an increased prevalence of osteoporosis, which reduces the strength of bones and lowers the force required to cause a fracture.[1][3][4][6]

Compliant flooring can potentially reduce the peak impact forces on the hip during a fall.  The decrease in impact force is given as a percentage of the impact force of a standard stiff floor, called force attenuation.[3][4][5] However, the floor must have some amount of stiffness, as floors with little to no stiffness can cause balance issues and increase the rates of falls.[3][4]

Studies to date have used human volunteer tests and biomechanical modelling to determine the force attenuation of different flooring types and peak impact forces on the hip. Human volunteer tests typically involve supporting the volunteer by a sling and dropping them from a low height ( < 5 cm) onto different types of flooring. Surface forces on the hip are measured using force plates placed under the flooring.[5][7] Though these tests provide in vivo force measurements, human volunteer tests are limited by the fact that the drop height is restricted to below injurious levels.[5] The drop heights used in volunteer tests limit the speed of impact to 1 m/s which is well below the impact speed of the average fall (approximately 3 m/s).[5] Furthermore, because human volunteers are typically of a younger demographic, the results are not as generalizable to an older population.[5]

Biomechanical modelling is another method that is commonly used to determine force attenuation of floor types. These tests usually model the proximal femur using anatomical representations for the greater trochanter and femoral neck.[1][3][4] These models are typically either dropped vertically or through a pendulum onto a load cell/displacement potentiometer to measure the impact forces.[1][3][4] Biomechanical modelling is advantageous as higher impact forces can be tested.[3] Additionally, the models can be fitted with sensors in the proximal femur to obtain direct femoral loads which cannot be done in volunteers.[3] However, biomechanical models are also limited as they typically model the femur as an isolated system which doesn’t mimic the behavior of the complex connections to the rest of the body.[4][6]

Types of Flooring

There are many different flooring types currently used within elderly communities, ranging from types more commonly seen in residential settings, such as carpet and wood, to types more commonly seen in hospitals and long term care facilities, such as vinyls and foams. When considering the effectiveness of compliant flooring, two important measures are evaluated: force attenuation and changes in balance. The latter will be covered in a later section. In this context, force attenuation refers to the flooring’s ability to absorb a fraction of the energy of a fall compared to the energy of that same fall on solid concrete, lessening the force experienced by the falling individual and, in turn, decreasing the probability of hip fracture. Moreover, force attenuation is also a measure of the flooring’s ability to deform and deflect, termed compliance, which also affects balance.

Of the most basic types of compliant flooring are wood, carpet, and wood sub-floor with carpet.[8] Traditionally, these floorings have been the most commonly used and offer decent force attenuation, attenuating impact forces by up to 25% when compared to impacts on solid concrete.[8][9] More specifically, a wood sub-floor with carpet flooring offers the highest force attenuation of these conventional flooring types, although carpeted floorings in general result in a higher number of falls due to issues with balance.[8] In more clinical and long-term care settings, the use of medical grade vinyl, sometimes combined with a rubber underlay has also been a long standing convention.[2] This type of flooring offers similar force attenuation to a wooden sub-floor carpeted floor, but with significantly better balance properties translating to a lower incidence of falls.[2] Soft and hard foams are other types of conventional flooring used more often in athletic conditions, such as gymnasiums, but tend to exhibit lower force attenuation with increasing impact velocities.[3]

To add to the degree of force attenuation, floorings are often combined with an underlay, such as polyvinyl chloride (PVC) foam or rubber.[2] Of these underlay materials, PVC foam tends to produce the best results with regards to force attenuation.[2][10]

More recently, a newer class of compliant floorings, called novel compliant floorings (NCFs) have emerged and gained recognition for their force attenuation properties. Some commercial types of NCFs include SmartCell, SofTile, Tarkett Omnisport EXCEL, Kradal, and Penn State Flooring, all of which are made up of synthetic rubbers with differing thicknesses and internal geometries.[3][10] Compared to concrete flooring, these NCFs are generally able to attenuate the forces applied on a falling individual by up to 51%, making them a great alternative to the standard flooring types discussed above.[10] Of these NCFs, SmartCell and SofTile exhibit the highest energy absorption and, in turn, force attenuation.[5] Although these NCFs offer a significantly improved force attenuation measure compared to conventional wooden and carpeted flooring, a drawback to consider is their material cost. Considering that they utilize more sophisticated internal geometries and more expensive materials, these NCFs tend to cost more than conventional floorings.[10] The economic feasibility of NCFs is discussed in a later section.

Generally, in terms of force attenuation, utilizing NFCs such as SmartCell or SofTile in combination with an underlay, such as PVC foam, offers the greatest results if this were the only aspect of flooring to be evaluated.[1][3] However, using these composite floors presents a risk of having a floor that is too compliant, which can affect balance and the incidence of falls.[1][3]

Balance Considerations

Despite the potential hip injury prevention benefits of compliant floors, there remains concerns regarding increased risk of poor balance effects which can lead to falls.[10] This is especially important for older populations that already have loss of plantar foot surface proprioceptors and pressure receptors, reduction of toe clearance, decrease in total effective stiffness of ankles, and decreased reaction time, all of which contribute to a loss of coordination.[3][4] Additionally, walking requires a higher amount of energy expenditure, which, coupled with a decrease in strength and endurance, makes this population extremely vulnerable to falls.[3][4] Flooring compression rate and maximum deflection can both adversely affect balance and create physical barriers for the traveling foot.[7] Such effects have been studied in detail, but results are highly inconclusive.

Laing et al. (2009) conducted extensive testing to determine the effects of flooring stiffness and compression on balance and falling rates of elderly women. It is widely accepted that significant compression does lead to loss of balance, especially in older populations with decreased response times, but the minimum stiffness for this effect to be noticed is unclear.[11] To determine the effects of stiffness on balance Laing et al. (2009) conducted three different experiments based on different criteria and methodologies.[3] The need for three different tests stems from the high variability of results and various ways of characterizing balance. The tests consisted of a Timed Get Up and Go (GUG) metric which measured standing up, walking and sitting down abilities with various flooring types.[12] Another test was a Sway During Quiet Stance test which measured the variability in the center of pressure (COP) of an individual standing still on various floor types. The final test consisted of a Backwards Floor Translation, designed to test effects of startling responses, where the individual stands on a plate that suddenly moves.[3]

The results from the GUG test, based on speed and correct foot placement, confirmed a 19% longer GUG time on softer, more compliant flooring types compared to a rigid floor.[3][12] This confirms that ambulating in compliant flooring environments can lead to a loss in stability and security.[3] Root mean square distance of sway and mean velocity of COP results were inconclusive and sometimes contradicted the hypothesis that softer floors would be harder to stand on. However, since the test was conducted with both eyes open and eyes closed, a confounding variable was present.[3] With closed eyes, swaying was significantly higher and greatly affected stability and balance.[3] The Backwards Floor Translation test results showed that compliant flooring does not impact the startle response.[3] These findings do not fully agree and the various flooring types can affect the final results greatly. However, the overall findings confirm that significantly softer flooring materials can lead to loss of balance control and can lead to falls, but the extent is yet unknown.[3] It was also shown that current technologies used in the field such as SmartCell and SofTile are adequate and do not lead to significant increases in loss of balance or stability.[13] Preventing a fracture requires a small reduction in the peak force (8-12% decrease); therefore floors such as SmartCell and firm foam achieve this without drastically compromising stiffness and loss of stability.[3] In a later study, Laing et al. (2014) further examined COP movement under the foot and determined that rigid foam NCF used in industry were deemed safe with regards to balance considerations.[5]

A similar study that analyzed stability on compliant flooring concluded that the compliant surface did not have any consequences on balance.[14] Sittichoke et al. (2019) conducted a Time Up and Go test, identical to the test conducted by Laing et al. (2006), but incorporated patient walking performance to generate a modified Dynamic Gait Index (mDGI).[7][14] The mDGI metric considers gait speed, cadence, step width, step length, stance time, step time and swing time to report a score out of 21, where 21 represents optimal performance. Similar to Laing et al. (2006), Sittichoke et al. (2019) concluded that compliant flooring does not adversely affect balance and stability when ambulating.[7][14]

Despite inconclusive results about the extent to which soft compliant flooring impacts balance, the above studies certainly demonstrate that no severe adverse consequences arise. Though the studies to date have provided important foundational knowledge, there are several limitations that should be addressed in future studies. Most studies to date used simple movements to test balance which may not resemble everyday life tasks. Analyzing more complex movements can provide further insight into the extent of balance loss.[15] Furthermore, testing the transition between hard and compliant flooring, as opposed to solely testing walking on compliant flooring, is essential as it may be the major cause of loss of balance.[3] Lastly, since elderly individuals often use ambulation aids and mechanical equipment such as wheelchairs, future studies should investigate how compliant flooring affects their mobility using these aids.

Economic Feasibility

Economic feasibility is a key factor in the widespread implementation of compliant flooring in senior care homes and other high-risk environments. Several studies have quantified both the cost-effectiveness and cost-utility of compliant flooring as compared to traditional flooring.[3][16][17][18] Cost effectiveness analyses consider direct costs of flooring and installation, as well as indirect savings from reduced morbidity of falls. Cost-utility assessments, on the other hand, also factor in differential impacts in length and quality of life due to different fall severities.[16] A typical cost-utility metric is a quality adjusted life-years (QALYs) factor where an effective medical intervention would provide a gain in QALYs.

A direct cost comparison between typical hospital-grade vinyl flooring and a commercial synthetic rubber compliant flooring system revealed that the compliant flooring was approximately $100 USD more expensive per square meter.[3] However, when considering the differences in hip fracture rate between the two floor types, the compliant floor had a payoff period of only 1.5 years. It is important to note that this analysis did not consider the indirect cost savings associated with injury morbidity and mortality which would have made complaint flooring more economically attractive.

In a prospective randomized controlled trial, Latimer et al. (2013) assessed the cost effectiveness and utility of a type of compliant flooring installed in 8 hospitals with 226 participants in comparison to a standard type of flooring.[16] Through their analysis, they determined that compliant flooring is associated with a cost reduction of approximately $1200 USD per patient. When an equal risk of falling was assumed for the two groups (but with a lower proportion of severe falls in the complaint flooring group), the compliant flooring provided both cost savings and QALY gains.

Other analyses similarly found that compliant flooring was a dominant strategy both in costs and QALYs when considering the expected reduction in hip fractures.[17][18]

When modelling cost-effectiveness, many variables and assumptions can be made. In the handful of studies conducted on this topic, the analyses had differences in their assumptions of the injury prevention capability of the flooring, the differential incidence of falls, and direct/indirect costs of injury.[10] Though the cost-effectiveness of compliant flooring can be highly sensitive to these assumptions, it is promising that several different types of analyses have all determined the economic benefits of compliant flooring.[10] However, despite the studies conducted to date, several considerations remain for future economic feasibility assessments of compliant flooring.

In the cost-utility assessments, it is debated whether the cost of added life years should be included. Ryen et al. (2015) interestingly found that compliant flooring became more economically attractive when excluding costs of added life years.[18] Most investigators agree that future costs related to compliant flooring should be included in analyses but disagree on whether future unrelated or non-related health care costs should be included as well. These extraneous costs can include, for example, future healthcare costs related to the management of dementia developed due to the reduction in morbidity of falls, or future social services costs due to added life years.[18] Future studies on this topic should clearly justify their assumptions about these extraneous costs.

Additional considerations for future cost-effectiveness and cost-utility assessments can include factoring in the reduction of not only hip fractures but also other fall-related injuries (e.g., wrist fractures) due to the energy absorption capabilities of complaint flooring.[10][18] These considerations can further improve the economic benefit of compliant flooring.

Finally, when considering the economic feasibility of compliant flooring for a particular residential care setting, the context and location of the care setting should be considered. Regional differences in the residential care organization, hip fracture incidence and costs, among other factors, can affect the transferability of results of the different cost-effectiveness analyses conducted to date.[18]

Future Work

The literature in this review examined the strategy of using compliant flooring to reduce the severity of hip fractures caused by falls. Effective strategies for hip fracture prevention have the potential to save lives and improve the quality of life for many. Despite the demonstrated benefits of compliant flooring, there are several barriers to full scale implementation of this hip injury prevention method.

The most severe barriers are methodological limitations in assessing the benefits of compliant flooring need to be further examined. For example, in Mackey et al. (2019), fall and injury prevention interventions were already in place during their study.[19] This prevented the independent examination of compliant flooring as the interventions present already limited the occurrence of these falls to a degree.

Current NCFs are limited to a handful of commercial types. Further research should be conducted on the design of compliant floors including investigating different material types, thicknesses, and internal geometries of flooring materials. Studies to date typically involve comparing one or two types of compliant floors with varying methodologies which prevents objective comparison of the effectiveness of each type.[7][19] A more systematic investigation of the different compliant floor properties can be beneficial.

Lachance et al. (2017) provides an interesting review surrounding the biomechanical efficacy, clinical effectiveness, cost-effectiveness, and workplace safety of compliant flooring, however, additional blinded, randomized controlled clinical trials are needed to determine the clinical effectiveness of NCFs.[10] Additional studies are also needed to determine the most beneficial locations to prioritize the installation of NCFs.

Many people belonging to the elderly population rely on wheeled medical devices, such as wheelchairs, for mobility. Keenan et al. (2020) examined the comparison of floor surfaces for injury prevention in care settings using the impact forces and horizontal pulling force required to move wheeled equipment.[1] However, their test rig limitations prevented them from testing a range of possible wheel orientations. The wheels on these devices are not always simply oriented facing forward prior to movement, so an examination of a wider range of wheel orientations would provide more realistic results on the pulling forces required on compliant flooring.

Studies to date have evaluated the effects of compliant flooring on dynamic balance and more complex mobility tasks using subjects of a young demographic.[5][7] The reaction time for elderly people might differ from the demographic typically tested in these balance studies. Though using elderly subjects could provide more representative results, such studies are largely unethical due to the increased injury risk and can be otherwise difficult to conduct. These methodological limitations should be addressed before drawing conclusions about the effects of compliant flooring on balance and fall risk.

Other factors related to flooring conditions, such as whether or not the floor is wet, have yet to be extensively studied. It is also important to note that the biofidelity of any study setup must be considered and improved in future studies.

To conclude, effective compliant flooring has a promising potential for hip injury prevention, however, the discussed limitations of the studies conducted to date need to be addressed before compliant flooring can be widely and feasibly implemented.

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 B. E. Keenan et al, "A comparison of floor surfaces for injury prevention in care settings: impact forces and horizontal pulling force required to move wheeled equipment," Osteoporosis International, vol. 31, (12), pp. 2383-2394, 2020.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 J. M. B, F. Nabhani and J. S. Bamford, "Can flooring and underlay materials reduce hip fractures in older people?: Julian Minns and colleagues suggest that many care homes and hospitals have flooring and floor covering that is inappropriate and does nothing to help reduce the incidence of hip fracture among older people," Nursing Older People, vol. 16, (5), pp. 16-20, 2004.
  3. ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.20 3.21 3.22 3.23 3.24 3.25 3.26 3.27 A. C. Laing and S. N. Robinovitch, "Low stiffness floors can attenuate fall-related femoral impact forces by up to 50% without substantially impairing balance in older women," Accident Analysis and Prevention, vol. 41, (3), pp. 642-650, 2009.
  4. ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 T. N. Gardner et al, "Measurement of impact force, simulation of fall and hip fracture," Medical Engineering & Physics, vol. 20, (1), pp. 57-65, 1998.
  5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 S. Bhan, I. C. Levine and A. C. Laing, "Energy absorption during impact on the proximal femur is affected by body mass index and flooring surface," Journal of Biomechanics, vol. 47, (10), pp. 2391-2397, 2014.
  6. ↑ 6.0 6.1 6.2 N. Li, E. Tsushima and H. Tsushima, "Comparison of impact force attenuation by various combinations of hip protector and flooring material using a simplified fall-impact simulation device," Journal of Biomechanics, vol. 46, (6), pp. 1140-1146, 2013.
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 A. C. Laing et al, "Effect of compliant flooring on impact force during falls on the hip," Journal of Orthopaedic Research, vol. 24, (7), pp. 1405-1411, 2006.
  8. ↑ 8.0 8.1 8.2 Simpson, A H R W et al, "Does the type of flooring affect the risk of hip fracture?" Age and Ageing, vol. 33, (3), pp. 242-246, 2004.
  9. ↑ B. E. Maki and G. R. Fernie, "Impact attenuation of floor coverings in simulated falling accidents," Applied Ergonomics, vol. 21, (2), pp. 107-114, 1990.
  10. ↑ 10.0 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 C. C. Lachance et al, "Compliant flooring to prevent fall-related injuries in older adults: A scoping review of biomechanical efficacy, clinical effectiveness, cost-effectiveness, and workplace safety," PloS One, vol. 12, (2), pp. e0171652-e0171652, 2017.
  11. ↑ A. D. Wright and A. C. Laing, "The influence of novel compliant floors on balance control in elderly women—A biomechanical study," Accident Analysis and Prevention, vol. 43, (4), pp. 1480-1487, 2011.
  12. ↑ 12.0 12.1 K. Bennell, F. Dobson and R. Hinman, "Measures of physical performance assessments: Self-Paced Walk Test (SPWT), Stair Climb Test (SCT), Six-Minute Walk Test (6MWT), Chair Stand Test (CST), Timed Up & Go (TUG), Sock Test, Lift and Carry Test (LCT), and Car Task," Arthritis Care & Research (2010), vol. 63, (S11), pp. S350-S370, 2011.
  13. ↑ A. D. Wright et al, "Novel safety floors do not influence early compensatory balance reactions in older adults," Gait & Posture, vol. 40, (1), pp. 160-165, 2014.
  14. ↑ 14.0 14.1 14.2 C. Sittichoke et al, "Effects of Compliant Flooring on Dynamic Balance and Gait Characteristics of Community-dwelling Older Persons," The Journal of Nutrition, Health & Aging, vol. 23, (7), pp. 665-668, 2019.
  15. ↑ C. C. Lachance et al, "Study protocol for the Flooring for Injury Prevention (FLIP) Study: a randomised controlled trial in long-term care," Injury Prevention, vol. 22, (6), pp. 453-460, 2016.
  16. ↑ 16.0 16.1 16.2 N. Latimer et al, "Cost--utility analysis of a shock-absorbing floor intervention to prevent injuries from falls in hospital wards for older people," Age and Ageing, vol. 42, (5), pp. 641-645, 2013.
  17. ↑ 17.0 17.1 C. Zacker and D. Shea, "An economic evaluation of energy-absorbing flooring to prevent hip fractures," International Journal of Technology Assessment in Health Care, vol. 14, (3), pp. 446, 1998.
  18. ↑ 18.0 18.1 18.2 18.3 18.4 18.5 L. Ryen et al, "Modelling the cost-effectiveness of impact-absorbing flooring in Swedish residential care facilities," European Journal of Public Health, vol. 26, (3), pp. 407-411, 2016.
  19. ↑ 19.0 19.1 D. C. Mackey et al, "The Flooring for Injury Prevention (FLIP) Study of compliant flooring for the prevention of fall-related injuries in long-term care: A randomized trial," PLoS Medicine, vol. 16, (6), pp. e1002843-e1002843, 2019.
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