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Age and Ageing Advance Access originally published online on May 11, 2006
Age and Ageing 2006 35(4):438-441; doi:10.1093/ageing/afl018
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© The Author 2006. Published by Oxford University Press on behalf of the British Geriatrics Society. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Research Letter

Women with wrist fractures are at increased risk for future fractures because of both skeletal and non-skeletal risk factors

Sir—Osteoporosis is a major cause of morbidity, mortality and institutionalisation in older adults. The cost of osteoporosis in the United States (2002) was $17.9 billion and, by 2050, the global incidence of hip fractures will approach 6.3 million fractures per year, at a cost of $131.5 billion [1]. A prior fracture is an independent risk factor for hip fracture [2–4]. Two mechanisms proposed for this increased risk of a hip fracture include skeletal factors: (i) accelerated bone resorption and (ii) mechanical impairment caused by the fracture. Bone resorption following a fracture may be increased as much as 18% following a wrist or ankle fracture and may persist for up to 2 years [5–7]. Non-skeletal factors may also play a role, and neuromuscular and sensorimotor (NMS) changes have been proposed as explanations of how impaired balance leads to an altered gait and increased risk of falls [8].

The extent to which the increased risk of hip fractures that follows an initial fracture episode is dependent on skeletal and non-skeletal factors remains to be elucidated. Therefore, the purpose of our study was to evaluate non-skeletal factors in relation to balance and gait function in women with wrist fractures.


   Materials and methods
Top
 Materials and methods
Results
 Discussion
 Conclusion
 Key points
 References
 
Study participants
This retrospective cohort study included community-dwelling women with prior falls and low bone mass. Of these, those with falls and wrist fractures were designated the study group. The study was approved by the Institutional Review Board, and all participants provided informed consent. Inclusion criteria included: (i) women aged >50 years, (ii) independence in ambulation, (iii) low bone mass defined as calcaneal ultrasound BUA 76.2 MHz/dB (T-score≤–1.0) and (iv) having fallen at least once in the past 2 years. Study subjects had sustained a low trauma wrist fracture (women were examined a minimum of 6 months after wrist fracture). Controls had fallen without sustaining a fracture. A fall was defined as an unintentional loss of balance in which the body comes to rest upon the ground [9]. Exclusion criteria are listed in Appendix 1 (see supplementary data available at http://www.ageing.oxfordjournals.org).

Measurements
A variety of functional performance assessments included the Berg Balance Scale (BBS) [10], the Dynamic Gait Index (DGI) [11] and a timed 10-m walk.

Self-assessments
An individual’s perception of their health and fear of falling is associated with the performance of physical functions and walking speed. Participants completed the Activities-specific Balance Confidence (ABC) Scale [12].

Sensorimotor and neuromuscular performance measures
We used the Falls Risk Assessment, including tests of individual NMS systems [13]. Two vision tests (contrast sensitivity and depth perception); three somatic sensory tests (vibratory threshold, proprioception, and sway); reaction time, and quadriceps strength (see Appendix 2 available as supplementary data on the journal website http://www.ageing.oxfordjournals.org).

Calcaneal ultrasound
Quantitative ultrasound (QUS) is an approach to bone density testing that is achieved by passing a pulse of ultrasonic waves (200–1,000 kHz) through bone. The relationship between attenuation of ultrasound wave (measured in dB) and frequency (MHz) is linear and provides the broadband ultrasound attenuation (BUA). BUA is associated with future fracture risk. We used the QUS-2 Quidel® Ultrasonometer (San Diego, CA, USA) [14].

Statistical analyses
Descriptive statistics were tabulated. Parametric independent samples t-tests were utilised to compare study and control groups. 95% confidence intervals were conducted. The analysis was conducted with non-parametric statistics with similar results. Logistic regression was used to analyse the effect of speed of walking on fractures. Statistical analyses were performed using SPSS 13 (SPSS, Chicago, IL, USA).


   Results
Top
 Materials and methods
 Results
Discussion
 Conclusion
 Key points
 References
 
Twenty-six of the 50 women had fallen and sustained a wrist fracture (study group), whereas 24 fell without fracture (controls). All subjects averaged one fall in the past 12 months and had low BUA≤76.2 MHz/dB (T-score≤–1.0). The groups were comparable in age, weight and body mass index (BMI). For NMS measures, the study group women exhibited greater impairment in visual factors such as visual contrast sensitivity and depth perception (Table 1). Other NMS measures were comparable.


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  		Table 1.. Group characteristics of wrist fracture and control subjects

 

Regarding functional performance, the study group exhibited a trend towards greater deficits in stationary (BBS) and dynamic balance (DGI). ABC scores were in the normal range, but the study group exhibited a tendency (P = 0.20) towards lower ABC scores. They also had lower BUA (P = 0.02) and T-scores (P = 0.01).

All subjects with poorer standing balance (P<0.001) (BBS≤50/56) had slower walking speeds (study, n = 6; control, n = 7). Fracture participants with high balance scores (BBS>50/56) (study group, n = 20) walked faster at both usual and fast walking speeds (1.43 ± 0.1 m/s) than controls (n = 17; 1.28 ± 0.6 m/s; P = 0.04; 95% CI –0.25, –0.002). To examine whether the effect of speed of walking on fractures was influenced by visual factors, we performed logistic regression analysis with fractures as dependent variable and depth perception, visual contrast sensitivity (VCS) and the speed of walking as independent variables. The joint model explained 39% of the variance, with visual factors being responsible for the majority of the variance (35%).


   Discussion
Top
 Materials and methods
 Results
 Discussion
Conclusion
 Key points
 References
 
We identified that the study group exhibited impairment in visual contrast sensitivity, depth perception and BUA and a trend towards lower stationary and dynamic balance. Additionally, those study subjects who had ‘relatively normal balance’ had higher gait speeds.

Visual factors are crucial in the maintenance of balance [15]. Ageing impairs visual acuity, contrast sensitivity and depth perception [16]. Visual deficits negatively affect ADLs [16] and lead to social isolation and risk of institutionalisation. Older adults with impaired depth perception are at a higher risk of falls and fractures [17]. They may have difficulty perceiving and responding to unstable body movements induced by standing or walking on an uneven or compliant surface [2, 15]. Subjects unable to estimate distances appropriately may have inappropriate planning and execution of protective balance responses or strike the support surface or ground with excessive force.

Impairment of visual contrast sensitivity may impair an older woman’s ability to discriminate between objects in cluttered environments and lead to tripping over obstacles within the home and outdoors, such as steps, curbs, tree roots, pavement cracks and surface irregularities [17]. Subjects with visual impairment and higher walking speed may trip and be unable to develop suitable protective mechanisms. The combination of a fall occurring in a woman with low bone mass (BUA) may result in a fracture [18].

Impaired visual acuity augmented the risk for hip fracture in the Study of Osteoporotic Fractures (SOF), Framingham, Auckland and EPIDOS hip fracture cohorts [2, 19–21]. The SOF and Auckland studies identified impaired contrast sensitivity as a risk factor for hip fracture, and in SOF, impaired depth perception was a risk factor for first and recurrent hip fractures [22]. The population-attributable risk for impaired visual acuity and depth perception may be as high as 40% [20]. Women with wrist fractures displayed a trend towards lower levels of stationary and dynamic balance. Balance confidence scores were in the normal range; however, the study group exhibited a trend towards lower self-perceived balance confidence that was more likely due to a negative prior fracture experience.

For adults, usual gait speed that is necessary for community ambulation is ~1.3 m/s [23]. We identified that study subjects with high balance scores had higher usual and fast walking speeds than controls. We hypothesise that the effect of speed of walking, although modest independently, is enhanced by the presence of visual factors. Thus, in these women, the speed of walking may be ‘too high’ and, coupled with impaired visual factors, may contribute to the development of injurious falls. The increased walking speed may lead to trips and falls to the front, with the hand outstretched to break the fall [24, 25]. With faster walking speeds, balance disruptions may result in a significantly higher moment of inertia, sufficient to develop injurious falls or fractures [25, 26]. Lower gait speeds in subjects with impaired standing balance have been previously described [27].

Subjects with wrist fractures had lower BUA. The degree of bone loss may be greater in fracture subjects and may possibly be exacerbated by post-fracture accelerated bone resorption. The relation between low BUA and risk of future fractures has been well established [14]. It is probable that the presence of both skeletal (BUA) and non-skeletal risk factors contributes to the future occurrence of hip fractures in women with wrist fractures.

Our study suggests that skeletal and non-skeletal factors (impaired visual contrast sensitivity and depth perception) act in concert to increase the risk for fractures. The extent to which the increased risk of future fracture is dependent on skeletal and non-skeletal factors remains to be elucidated. A greater understanding of the development of injurious falls and fractures should, in the future, allow us to develop interventions that are specific to individual impairments in the non-skeletal factors in addition to providing anti-resorptive therapy for the low BUA.

Limitations of this study include the limited sample size, mostly Caucasian participants, retrospective analysis and multiple comparisons. There were trends suggesting that the fracture group had worse balance than the non-fracture group. These findings might have reached significance in a larger sample; further research in this area is necessary.


   Conclusion
Top
 Materials and methods
 Results
 Discussion
 Conclusion
Key points
 References
 
Women with wrist fractures display lower BUA and deficits in visual function. The combination of non-skeletal and skeletal risk factors may explain why these women are at a high risk for future hip fractures.


   Key points
Top
 Materials and methods
 Results
 Discussion
 Conclusion
 Key points
References
 

  • A prior wrist fracture is a risk factor for hip fracture.
  • Women with wrist fractures have, in addition to low bone mass, NMS risk factors for falls and fractures. These NMS factors include impairment in visual contrast sensitivity and depth perception.
  • The impairment of visual contrast sensitivity would lead to tripping or bumping into objects, whereas problems with depth perception may result in inappropriate protective responses on balance disruption.
  • The combination of low bone mass and NMS changes may explain a higher risk for injurious falls and fractures.
  • Further studies in this area are needed.

Beatrice J. Edwards1,*, Craig B. Langman2, Kathy Martinez3, Marjorie Johnson3, Marie Laure Mille3 and Mark W. Rogers3

1 Department of Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
2 Department of Pediatrics, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
3 Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA

* To whom correspondence should be addressed: Email: bje168{at}northwestern.edu


   References
Top
 Materials and methods
 Results
 Discussion
 Conclusion
 Key points
 References
 

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