Effect of external hip protectors on hip fractures

11

Effect of external

hip protectors on hip fractures

Most hip fractures seem to be related to trauma near the hip, so a controlled trial was conducted to investigate the effect of external hip protectors on the prevention of such fractures in residents of a nursing home. 10 of the 28 wards in the nursing home were randomised to receive external hip protectors; thus 167 women and 80 men were given protectors and 277 and 141 men no protectors. A fall register was set up for 2 treatment wards (45 residents) and 2 control wards (76 residents). There were 8 hip and 15 non-hip fractures in the hip-protector group and 31 hip and 27 non-hip fractures in the control group. The relative risk of hip fractures among women and men in the intervention group was 0·44 (95% Cl 0·21-0·94). None of the 8 residents in the intervention group who had a hip fracture was wearing the device at the time of the fracture. 154 falls were registered and 20% of these falls produced a direct impact to the hip. In 25 falls direct impact to the hip was sustained at a time when hip protectors were not being worn, and 6 fractures were produced. The study indicates that external hip protectors can prevent hip fractures in nursing-home

concentrations of parathyroid hormone (iPTH), and one quarter had biochemical indications of osteomalacia.1O All residents with injury or fractures are treated at the Rigshospitalet, University of Copenhagen. To compare the age-specific incidence of hip fractures in the nursing home with that in the general population in the catchment area for Rigshospitalet (table I), the number of hip fractures and population size for the area were obtained from the National Hosptial Register (which includes patients treated in Danish hospitals) and the Bureau of Statistics, respectively. The National Hospital Register distinguishes between local citizens and patients from other geographical areas. 95% confidence intervals for relative risk (RR) were calculated for fractures in the nursing home (annual incidence of fractures in the nursing home divided by the incidence of fractures in the general population) by logarithmic transformation." The ageadjusted RR was constructed through the indirect method of standardisation and the confidence intervals for the standardised incidence ratio was calculated by assuming observed hip fractures to be a Poisson variable.12 p-values less than 0-05 were taken as being

statistically significant. TABLE I-HIPFRACTURES IN NURSING HOMEAND BACKGROUND POPULATION IN 1989

residents. Introduction Most hip fractures (60-90%) are related to direct trauma the hip.1-3 Energy absorption rather than bone strength has been suggested to be the main determinant of hip fractures.2,4 Experimental studies have shown that soft tissue covering the hip may influence energy absorption during a fall,2,4-6 which partly explains the reduced risk of hip fractures in overweight women.2 A simple fall on the hip from a standing position generates sufficient kinetic energy to fracture the bone even in young healthy persons.4’ The incidence of hip fractures among elderly people remains high although there are reports of a preventive effect of postmenopausal oestrogen replacement therapy.8,9 We have found that about 14% of all patients treated in hospitals for hip fractures are admitted from nursing homes (unpublished). We have devised external hip protectors6 and describe here an open randomised nursing-home study on their preventive effect against hip fractures. to

Methods and patients

Subjects and baseline incidence of fractures 497 women and 204 men aged over 69 years in the nursing home

De Gamles By in Copenhagen were followed up throughout 1989. Most of the residents had been referred to the nursing home because of "ageing" and inability to look after themselves at home. A third of the residents had mild to severe senile dementia. An earlier study in the same nursing home had shown that only 40% of the residents around freely and the rest were dependent on some walking aid. 10 The residents were very old. Many had altered vitamin D status with depressed serum concentrations of total calcium, phosphorus, and alkaline phosphatase, and increased were

able

to move

of 1000 per year n = number

hip fractures;

N = number of people, incidence= number of fractures/

Hip protectors The external hip protector was designed to divert a direct impact away from the greater trochanter during falls from standing heights

and offers nearly full protection to this region. At impact the protector transmits released energy to the soft tissue and muscles anterior and posterior to the femoral bone. The outer shield is made of polypropylene and the inner part of plastozote (figure). The protector is fixed in special underwear.

Clinical study 10 of the 28 wards in the nursing home were chosen to receive external hip protectors; a ward was selected when its number was drawn by an independent doctor. The treatment group included 247 residents (167 women, 80 men) and the control group included 418 residents (277 women, 141 men). The groups were unequal in size because of economic limitations. Every resident in the treatment group was given three sets of underpants and one pair of hip protectors. The study period was the 11 months from Feb 1, 1991. No special adjustments were made in the statistical analyses

Department of Orthopaedic Surgery U 2161, Rigshospitalet, University of Copenhagen, Blegdamsveij 9, DK-2100 Copenhagen Ø, Denmark (J B Lauritzen, MD, M. M. Petersen, MD, Prof B. Lund, MD). Correspondence to Dr J. B. Lauritzen.

ADDRESS

12

TABLE III-TYPES OF FALLS RECORDED IN FALL REGISTER

Effect of hip protectors

Hip protector. for deaths occurring

during

the

study period

since deaths

were

balanced immediately by new arrivals from a waiting-list. All new arrivals were included in the study. The study was approved by the ethics committee for Copenhagen and Frederiksberg and the study was conducted according to guidelines in the Helsinki II declaration for biomedical research involving human beings.

Fall registration study Two wards assigned hip protectors (39 women, 25 men) and two control wards (67 women, 23 men) were randomly selected for a prospective register of falls occurring during the study period. Age, sex, type of impact, and type of trauma, if any, were recorded in the register by nursing-home staff.

Results Baseline incidence of hip fracture

During 1989 41 of the 701 nursing home residents had a hip fracture, giving an incidence of 58/1000 residents per year. The relative risk of hip fractures in the nursing home compared with that of the general population in the area was 3-3 (95% CI 2.3-4.8) for women and 3-1 (16-61) for men (table I). The ratio between incidence of hip fractures in women and that in men in the nursing home was 13 (0-40-1-6). TABLE II-DISTRIBUTION OF FRACTURES DURING STUDYOFHIP PROTECTORS

During the study with external hip protectors 8 residents in the treatment group and 31 in the control group had a hip fracture (table III); the corresponding numbers for non-hip fractures were 15 and 27. The RR of hip fractures in the intervention group was 0-46 (0-20-1 -0) for women, and 0-29 (004-25) for men (table ii). The RR of hip fracture for women and men together was 0-44 (0-21-0 94), and if adjusted for skewness in age the RR was 0-41 (0.18-0.82). None of the 8 residents in the intervention group who had a hip fracture was wearing external hip protectors at the time of the fracture. The higher-than-expected number of non-hip fractures in the control group (27 in 418 subjects) could be accounted for by the age profile, which was skewed towards older age. The RR of non-hip fractures in the intervention group was 0-94 (0-51-1-7) (table II). Fall register data

Among the 116 residents (45 treatment group, 71 controls) in the fall registration study there were 154 falls (64 treatment group, 90 controls) during the 11 months’ observation giving an estimated incidence of falls in the nursing home of 1448/1000 residents per year. In the treatment group 84% of the women had at least one fall, compared with only 65% of the men. The corresponding figures for the control group were 80% and 75%. The proportion of fallers having more than one fall was 33% for and 15% for men in the treatment group and 27% for men and 27% for women in the control group. Repeat falls made up 35 % of falls in the treatment group (31 falls for women, 20 for men) and 46% for the control group (78 for women, 25 for men). Nearly a third of those who fell were unable to explain how they fell (table II). The impact was directly to the hip in 20% of all the falls registered, in 24% of falls in women, and in 13% of falls in men. The external hip protectors were being used during 11 of the 45 registered falls in the treatment group. 10 hip fractures were registered, 6 associated with impact to the hip and 4 associated with trauma of unknown nature. 1 of the 6 hip fractures occurred in a resident in the treatment group, and 5 in residents in the control group. By intention to treat analysis, 1 in 12 falls on the hip in the treatment group produced a hip fracture, compared with 5 in 19 in the control group (p 0-30, Fisher’s exact test, one-tailed). Analysis by whether a hip protector was actually being worn at the time of falls on the hip showed that no fracture occurred in the 6 instances when a protector was being worn, compared with 6 fractures in the 25 falls that occurred when no protector women

=

being worn (p = 0-32). frequent fallers in the control group had hip fractures. The risk of hip fractures among recurrent fallers, treated earlier in the acute ward of Rigshospitalet within the study period was 41 %. was

3 of the 15

*Fractures to upper limb; none to lower tAge-adjusted relative risk 0-41 (018-0

limb82).

13

Discussion

REFERENCES

The use of external hip protectors in the randomised study reduced the risk of hip fracture by 53%, and 9 hip fractures were estimated to have been avoided in the intervention group. In the fall registration study, analysis according to whether or not hip protectors were being worn at the time of fall showed that no hip fracture was sustained by any of the 6 residents who was wearing a protector at the time of direct trauma to the hip. In the main study, none of the 8 residents in the intervention group who had a hip fracture was wearing a hip protector at the time of the fracture. The study confirms the hypothesis that direct trauma to the hip contributes greatly to the development of a hip fracture, although only one quarter of impacts to the greater trochanter lead to a hip fracture. A hip fracture is unlikely to be the cause of a fall, although in rare cases hip fractures may occur without direct traumaY-15 No pelvic or femoral shaft fractures were noted in the treatment group. The diversion of the trauma from the greater trochanter did not result in an increase in non-hip fractures. During the summer one user had prickly heat under the protector. The fall register study indicated that only 24% of residents given hip protectors wore them regularly, yet the randomised study showed that the devices conferred 53% protection against hip fractures. A possible explanation for this discrepancy might be that recurrent fallers were more likely than the others to wear hip protectors. We also noted that nurses were more keen to make recurrent fallers than other residents wear hip protectors. The process of putting on the hip protectors might be difficult for subjects with musculoskeletal or cerebral disorders. Compliance with wearing of the hip protectors might be improved by, for example, building the protectors into the clothing, or by designing appliances that can be attached directly to the skin. The energy sufficient for fracture of the proximal femur in cadavers ranges from 5-51 joule.4 Soft tissue is able to attenuate peak force by about 25-40% in tests where the impact does not produce a breach in the soft tissue. When the soft tissue is breached by the impact the total energy is transmitted directly to the greater trochanter .2 Bone strength, as reflected by bone mineral content, can therefore influence riskI6 of hip fracture when a fall produces an impact on the hip. This observation may explain why women with hip fractures have a marginally lower bone mineral density in the proximal femur than do controls of similar age; there is, however, substantial overlap in bone density values between these groups.17 Three-quarters of femoral-neck fractures occur indoors and environmental hazards contribute to two-thirds of these.18 Our findings may be helpful in the management of subjects at high risk of hip fractures, when subjects have severe osteoporosis or when measures to prevent falls have all been taken or are difficult to attain. Improvement in design of the protector may increase compliance. If the hip protectors are worn, the doubling of hip fractures expected in the next few decades because of the ageing of the population might not turn out to be a reality.

Cummings SR, Nevitt MC. A hypothesis: the causes of hip fractures. J Gerontol 1989; 44: M107-11. 2. Lauritzen JB, Askegaard V. Protection against hip fractures by energy absorption. Dan Med Bull 1992; 39: 91-93. 3. Hayes WC, Myers ER, Maitland LA, Resnick NM, Lipsitz LA, Greenspan SL. Relative risk for fall severity, body habitus and bone density in hip fracture among the elderly. Trans Orthopaed Res Soc

We thank the SAHVA Foundation, TYTEX and the Health Board of the of Copenhagen (Health director Erik Juhl), and the Nursing Home Administration of De Gamles By for their support; the Danish Medical Council for statistical help; the participating residents and nursing staff for their enthusiasm; and staff nurse G. Kubel for coordinating the work.

Municipal

1.

1991;

16: 139.

4. Lotz

JC, Hayes WC. The use of quantitative computed tomography to estimate risk of fracture of the hip from falls. J Bone Joint Surg 1990; 72A: 689-700.

5.

Hipp JA, Myers ER, Greenspan SL, Maitland LA, Hecker AT, Hayes WC. Soft tissue thickness and energy absorption capacity as potential determinant of hip fracture risk. Trans Orthopaed Res Soc 1991; 16:

135. 6. Lauritzen JB, Lund B.

Impacts in patients with hip fractures and in vitro study of the padding effect: introduction of a hip protector. Acta Orthop Scand (Abstr) 1990; 61 (suppl): 239. 7. Robinovitch SN, Takeuchi T, Hayes WC, McMahon TA. Prediction of femoral impact force in standing height falls. Trans Orthopaed Res Soc 1991; 16: 434. 8. Williams AR, Weiss NS, Ure CL, Ballard J, Daling JR. Effect of weight, smoking, and estrogen use on the risk of hip and forearm fractures in postmenopausal women. Obstet Gynecol 1982; 60: 696-99. 9. Kiel DP, Felson DT, Anderson JJ, Wilson PWF, Moskowitz MA. Hip fractures and the use of estrogen in postmenopausal women. N Engl J Med 1987; 317: 1169-74. 10. Egsmose C, Lund B, McNair P, Storm T, Sørensen OH. Low serum levels of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D in institutionalized old people: influence of solar exposure and vitamin D supplementations. Age Ageing 1987; 16: 35-40. 11. Katz D, Baptista J, Azen SP, Pike MC. Obtaining confidence intervals for the risk ratio in cohort studies. Biometrics 1978; 34: 469-74. 12. Breslow NE, Day NE. Statistical methods in cancer research. Vol 2. The design and analysis of cohort studies. Oxford: Oxford University Press, 1988: 69. 13. Freeman MAR, Todd RC, Pirie CJ. The role of fatigue in the pathogenesis of senile femoral neck fractures. J Bone Joint Surg (Br) 1974; 56: 698-702. 14. Sloan J, Holloway G. Fractured neck of the femur: causes of the fall? Injury 1981; 12: 210-12. 15. Smith LD. Hip fractures: the role of muscular contraction or intrinsic forces in the causation of fractures of the femoral neck. J Bone Joint Surg (Am) 1953; 35: 367-83. 16. Melton LJ, Kan SH, Wahner HW, Riggs BL. Lifetime fracture risk: an approach to hip fracture risk assessment based on bone mineral density and age. J Clin Epidemiol 1988; 41: 985-94. 17. Cummings SR. Are patients with hip fractures more osteoporotic? Am J Med 1985; 78: 487-94. 18. Dias JJ. An analysis of the nature of injury in fractures of the neck of the femur. Age Ageing 1987; 16: 373-77.

From The Lancet The call of the new year The new year, with its promises and its threats, so clearly makes a call upon the ardent endeavour and uncompromising altruism of every individual in the community that the general position of affairs has no message to convey to medical men which it has not to convey to all. But inside the particular boundaries of medicine-and he today is bold who attempts to define those boundaries-there will obviously be room for vast developments in our organisation during the year to come.... We look forward during the coming year to a development of mutal comprehension, first between the public and the medical profession, and secondly between the various ranks and grades of that profession. No year, whatever its trials, will be anything but a successful year for medicine, which sees the growth of this spirit of union.

(Jan 5, 1918)