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Abstract

The risk of falling reportedly increases almost 2.5-times in those with lower extremity osteoarthritis (OA_LE) compared with age-matched controls. However, the mechanisms underlying the increased risk are not clear. The risk factors for falls in people with OA_LE found in the literature are mostly the same as the risk factors for people without OA_LE. It is hypothesized that risk factors for falls are exacerbated by OA_LE, such that these individuals are more likely to become dynamically unstable and, once this has occurred, are less able to perform an appropriate compensatory stepping response compared with people without OA_LE. To the extent that this is true, task-specific training targeting the compensatory step, which decreases falls in middle-aged and older women, should be effective for people with OA_LE. The purpose of the present review is to provide the rationale for the above hypothesis. Furthermore, the present authors present evidence that the fall risk of people with OA_LE could be efficiently and effectively reduced using task-specific training previously shown to reduce falls in middle aged and older women.

Keywords

aging compensatory stepping dynamic stability falls osteoarthritis risk factor task specificity

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Release date: 22 November 2012; Expiration date: 22 November 2013

Learning objectives

Upon completion of this activity, participants should be able to:

Analyze the risk of falls among older adults

Assess traditional risk factors for falls

Distinguish factors associated with osteoarthritis which increase the risk of falls

Evaluate means to reduce the risk of falls among patients with osteoarthritis of the lower extremities

Financial & competing interests disclosure

CME Author

Charles P Vega, Health Sciences Clinical Professor; Residency Director, Department of Family Medicine, University of California, Irvine, CA, USA

Disclosure: Charles P Vega has disclosed no relevant financial relationships.

Financial & competing interests disclosure (cont.)

Mackenzie L Hoops, Department of Kinesiology and Nutrition, University of Illinois at Chicago, IL, USA

Disclosure: Mackenzie L Hoops has disclosed no relevant financial relationships.

Noah J Rosenblatt, Department of Kinesiology and Nutrition, University of Illinois at Chicago, IL, USA

Disclosure: Noah J Rosenblatt has disclosed no relevant financial relationships.

Christopher P Hurt, Department of Physical Therapy, University of Alabama Birmingham, Birmingham, AL, USA

Disclosure: Christopher P Hurt has disclosed no relevant financial relationships.

Jeremy Crenshaw, Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN, USA

Disclosure: Jeremy Crenshaw has disclosed no relevant financial relationships.

Mark D Grabiner, Department of Kinesiology and Nutrition, University of Illinois at Chicago, IL, USA

Disclosure: Mark D Grabiner has disclosed no relevant financial relationships.

Editor

Elisa Manzotti, Publisher, Future Science Group

Disclosure: Elisa Manzotti has disclosed no relevant financial relationships.

Conceptually, static postural stability is a condition defined by the position of a person's center of mass being within the boundaries of the base of support. The base of support is generally defined by the perimeter established by the location of the feet or the perimeter established by the location of the feet and assistive devices such as a cane. Dynamic stability, however, is a condition defined by both the position of the person's center of mass and the velocity of the center of mass relative to the base of support. Thus, a person may be dynamically unstable even when the condition of static stability is met. A fall occurs when a person becomes dynamically unstable and, subsequently, is unsuccessful at restoring dynamic stability. Consequently, a fall is the result of two sequential events: first, going from a state of dynamic or static stability to a state of dynamic instability followed by, the failure to compensate and restore a condition of static or dynamic stability [1,2]. However, the risk of becoming dynamically unstable may not be an accurate determinant of the ability to restore static or dynamic stability and avoid a fall [3,4]. Each of the two events are associated with various risk factors that increase the likelihood of becoming dynamically unstable and/or decrease the likelihood of being able to restore static or dynamic stability. Furthermore, these risk factors may be modifiable or not modifiable. For example, although a history of falling is one of the strongest risk factors for future falls [5], having had a previous fall is not modifiable. Muscle strength, on the other hand, is modifiable. In light of the increasing incidence of falls and fall-related injuries in older adults, as well as the economic burden that is placed on the healthcare system by these events, effective clinical interventions focusing on modifiable risk factors that are causally related to falls in older adults are highly warranted.

Falls in older adults

In 2006, nearly 33% of older adults (age 65 years and older) in the USA reported at least one fall [6]. The number of older adults who fall annually, which has increased from 28% since 1981 [7], suggests that efforts to reduce falls in older adults over the past 30 or more years have not been successful. The problem of falls is particularly relevant for women in light of their having higher incidence of falls than men (nearly twice as high), and because of postmenopausal loss of bone quality that increases the likelihood of fracture [7,8]. In the absence of effective fall prevention that can be delivered on a national scale, the absolute number of falls and fall-related injuries will increase with the population of older adults. The number of older adults in the USA is expected to reach 70 million by 2030 [9]. Consequently, the economic burden that falls contribute to healthcare costs will increase. In 2000, US$19 billion in direct medical costs were attributed to fall-related injuries to older adults [6]. The increases in fall-related injury, mortality and costs emphasize the need for fall-prevention methods that are time- and cost-effective, and scalable.

Falls in people with lower extremity osteoarthritis

Arthritis has been recognized as increasing the likelihood of a fall for at least 25 years [10 –28]. The risk of falling in people with arthritis is reportedly about 2.5-times that of older adults without arthritis [29]. However, many of the studies reporting a relationship between arthritis and falls have not reported which specific joints were affected, specified the type of arthritis being considered (i.e., osteoarthritis, rheumatoid arthritis, lupus and so on), and have relied on self-report rather than a diagnosis by a physician. Indeed, in one review of risk factors for falls, only one of the included studies was specific to osteoarthritis (OA) [30] and only one of the included studies was exclusive to lower extremity osteoarthritis (OA_LE) [31]. Given that OA is the most prevalent form of arthritis [32] and that upper extremity arthritis would not be expected to directly increase fall risk, OA_LE is a much more meaningful risk factor for falls when compared with general arthritis. Notably, two studies reported that more than 50% of people with knee OA reported a fall during the previous year [21,22]. This is higher than the 33% generally attributed to older adults. One additional study reported that people with knee OA had a 30% increase in the incidence of falls compared with people without knee OA [25]. People with OA_LE also have an increased risk of hip fracture compared with control subjects [17]. This is somewhat paradoxical considering individuals with OA generally have increased bone mineral density compared with controls [33 –35], and that increased bone mineral density is generally considered to confer protection from fracture. The increase in fracture risk may, in part, be due to the increased incidence of falls and/or an increase in the severity of falls [17].

The underlying mechanisms for the increased risk of falls in people with OA_LE are not clear. The present authors propose that people with OA_LE may be at an increased risk of becoming dynamically unstable and, once dynamically unstable, they are less able to perform an appropriate compensatory stepping response. Either of these possibilities would increase fall risk. However, the factors that contribute to each possibility, as well as the clinical approaches to decrease the fall risk, are not necessarily the same. The present authors also propose that risk factors for falls in people with OA_LE found in the literature are not different from the risk factors for people without OA_LE. It is hypothesized that the exacerbation of risk factors for falls in older adults with OA_LE increases the likelihood of becoming dynamically unstable and decreases the ability to successfully perform a compensatory stepping response compared with people without OA_LE. Support for this hypothesis would suggest the need for an intervention intended to address both dynamic stability and the ability to perform a successful compensatory stepping response.

Established risk factors for falls in older adults

In addition to arthritis, the most commonly agreed modifiable risk factors for falls in older adults include gait and balance impairments, and muscle weakness [29]. Fall risk scales linearly with the number of risk factors [36]. Indeed, absolute fall risk of older adults ranges from 11%, for those with no risk factors, to nearly 55%, for those who have multiple risk factors [37]. There are multiple functional outcomes associated with OA_LE, such as gait and balance impairments and muscle weakness. These functional outcomes are not independent of other consequences associated with OA_LE that have also been shown to be related to falls (discussed later in this review). Whether considered as risk factors for falls in older adults or outcomes of OA_LE, the result is an increased probability of becoming dynamically unstable and/or decreased ability to successfully perform a compensatory stepping response ( Table 1 ).

Table 1.

Risk factors for falls, how they manifest in people with lower extremity osteoarthritis and how they could impair the compensatory stepping response, postural static/dynamic instability, or both.

	How variable manifests in OA_LE	Could this further impair CSR?	Could this further impair stability?
Established risk factors for falls†
Gait impairments	Slower walking velocity, shorter stride length, wider step width, longer double support time	Unlikely‡	Maybe§
Balance impairments	Larger static and dynamic postural sway	Unlikely‡	Yes
Muscle weakness	Weaker knee extensors and hip abductors, as well as increased knee instability, associated with limb buckling	Yes	Yes
Other risk factors for falls
Pain	Primary symptom of OA	Maybe¶	Maybe¶
Proprioception	Decreased feedback on lower limb position and orientation	Maybe¶	Yes
Gait variability	Greater variation in step length, step width and double support time	Unlikely‡	Maybe§
Obesity	Most modifiable risk factor for OA	Maybe§	Yes

†

Data taken from [29].

‡

Literature does not exist and mechanism seems unlikely.

Existing literature is unclear on the relationship between risk factor and stability/CSR.

No literature exists linking risk factor to stability/CSR, but mechanism is plausible.

CSR: Compensatory stepping response; OA: Osteoarthritis; OA_LE: Lower extremity osteoarthritis.

Gait impairments

The majority of falls in older adults occur during walking [38] and numerous studies have demonstrated associations between changes in gait and fall risk in older adults. Increased fall risk has been associated with slower walking velocity (although this appears to only be true for indoor falls [25,39]), shorter stride length, a wider step width and longer double-leg support time [25,30,39 –46]. Paradoxically, these characteristics tend to improve dynamic stability. Consequently, gait impairments associated with OA_LE are correlated with fall risk [29]. For example, individuals with knee or hip OA have slower walking speeds, increased double support time and shorter stride lengths, and wider step width compared with healthy aging controls [47 –52]. The extent to which these changes in gait are associated with, or more importantly cause, falls is not clear. Furthermore, the extent to which these spatial and temporal variables are modifiable in people with OA_LE, as well as the effects of modifying them, are unclear. For example, in isolation, faster walking velocity, which can be attained through lower extremity resistance training [53] may actually increase trip-related fall risk [54]. In general, gait impairments are organism-level changes that are secondary to, and reflective of, other functional changes at the system and tissue levels.

Balance impairments: static postural control

The broad term ‘balance deficits’ was used to describe a category of risk factors that increased fall risk by threefold [29]. Effective postural control, whether static or dynamic, relies on the integration of sensory input from multiple sensory systems with motor output that accurately matches the postural requirements. These sensorimotor systems degrade as a normal consequence of aging [55,56] and, as a result, there is an associated increase in static postural sway. People with OA_LE have larger postural sway compared with age- and sex-matched control subjects [57 –59]. The increase in static postural sway may increase the likelihood of a specific postural disturbance causing a person to become dynamically unstable. In fact, the ability to regain balance in response to small perturbations (where subjects are not allowed to take a step) is impaired in people with knee OA [60]. However, as indicated previously, the likelihood of becoming posturally unstable does not necessarily causally predict the inability to perform a compensatory stepping response and thereby prevent a fall.

Muscle weakness

Lower extremity muscle weakness is frequently reported as a significant risk factor for falls [29,61]. This follows the notion that when a person becomes dynamically unstable, in addition to the coordination required to perform a compensatory stepping response, there can be substantial lower extremity joint muscle strength and power requirements to avoid a fall. The expected age-related decrease of muscle strength, as much as 3% per year beyond age 50 years [62 –66], is accompanied by a reduction in the rate of force generation [67,68]. These important functional changes arise, in part, as a result of loss of muscle mass, which can be caused by the death of spinal motor neurons that lead to the loss of motor units (particularly large motor units that generate high contraction force and power), disuse atrophy and muscle attenuation (i.e., infiltration of muscle by fat [69]). Collectively, these structural and functional changes can contribute to the diminished ability to meet the biomechanical requirements of the compensatory stepping response. For example, the initial recovery step following a trip requires a knee extension moment that is sufficient to prevent the knee joint from buckling (i.e., flexing) [70]. Indeed, a potentially more important, but not widely studied aspect of this element of the compensatory stepping response is the power requirement at the knee joint, which can be quite large and involves eccentric contraction of the involved musculature. People with radiographic evidence OA_LE, particularly knee OA, tend to have knee extensor strength that is approximately 20% lower than people without radiographic evidence of knee OA [50,59,71]. Notably, these losses are independent of pain, one of the most commonly reported symptoms of OA [72], which may further alter the ability to perform a successful compensatory step.

Knee extensor weakness is associated with functional instability that manifests as knee buckling [73]. Knee buckling, or giving way, is characterized by an involuntary loss of postural support across the knee during weight bearing [73]. More than 60 % of people with OA_LE report sensations of knee buckling during activities of daily living [74]. Furthermore, 13% of those who report knee buckling also report falling as a result [73]. Thus, the associations between knee extensor weakness, knee buckling and falls reported for people with knee OA, even in the absence of pain, supports the hypothesis that the risk factors for falls in people with OA_LE found in the literature are not different than those for people without OA_LE. However, the extent to which the risk is increased is greater given the more frequent presence of risk factors in people with OA_LE.

Weakness of the hip joint musculature is also important with regards to fall risk. Specifically, strong hip abductors and adductors may be required to avoid laterally directed falls during gait, which increase the likelihood of hip fracture [75]. During the stance phase of walking, the hip musculature controls the frontal plane motion of the center of mass [76,77]. Weak hip abductors and adductors may diminish this control and increase the likelihood of a person becoming dynamically unstable. In general, compared with younger adults, older adults generate smaller maximum hip abduction and adduction isometric forces and do so at slower rates [78]. In people with OA_LE, hip abductor and adductor strength may be 31 and 25% less than healthy controls, respectively [79].

Few studies have reported strength measures of the trunk or ankle musculature in people with OA_LE. Specifically, the ability to arrest and reverse the trunk flexion following a trip, which, to a large extent, is a function of the trunk musculature, is a determinant of a fall following a laboratory-induced trip [54,80]. The ankle musculature contributes to static postural stability through control of postural sway and thus, can be linked to the initial loss of static postural stability. During the compensatory stepping response, ankle plantar flexion is a key source of the propulsive ground reaction forces that are influential in avoiding a fall. Dorsiflexion weakness distinguished fallers from nonfallers in nursing home residents [81]. Plantar flexion and dorsiflexion strength of people with ankle OA is significantly lower than control subjects [82]. Collectively, however, given the limited data available on the ankle joint and trunk muscles of people with OA_LE, these are potentially important areas of investigation for fall risk of people with OA_LE.

Other factors related to falls in older adults with & without OA_LE

Pain

Pain, a hallmark symptom of OA, may partially explain the increased risk of falling [18,23,24,34]. In people with OA_LE, pain is the most common reason for seeking medical help [83] and is the most debilitating symptom of knee OA. Functionally, pain or even the perception of the potential for pain, may negatively influence coordination, postural sway, muscle strength and power, and the sensory components of muscle function (e.g., proprioception) [59]. These deficits provide potential mechanisms by which pain may influence fall risk by interfering with the requirements to preserve stability, as well as those needed to perform effective compensatory mechanisms. For example, women with widespread musculoskeletal pain had a 66% increase in fall risk compared with women with no pain or mild pain at one musculoskeletal site [12]. This appears to be the only published study of prospectively measured falls and lower extremity pain. Further study of the contribution of pain to the increased risk of falling in people with OA_LE is warranted. For example, prospective analysis of individuals with radiographic evidence of OA, some of whom are in pain and others who are not, could help to establish if pain, as opposed to the structural and functional changes associated with OA, best explain the increase in falls in this population.

If pain partially explains the increased fall risk of people with OA_LE, then pain relief would be expected to reduce this risk. However, while reductions in knee pain following intra-articular injections of local anesthetic increased maximal voluntary knee extension force, this was not accompanied by concurrent improvement of proprioception or static postural sway. This suggests that factors other than pain account for these functional deficits [84]. Similarly, pain relief was associated with increased walking velocity, although the walking velocity remained significantly slower than that of healthy controls [85]. It is important to note that pain relief may negatively alter gait. For example, patients taking a NSAID to reduce pain showed significantly greater peak external adduction knee joint moments and peak external knee joint extension moments while walking compared with those with increased pain. This consequently increased knee joint forces, particularly in the medial knee joint compartment (the most frequently affected portion) [86]. These alterations in gait may reflect protective compensatory mechanisms that are secondary to pain, which act to reduce medial compartment forces by reducing the external adduction moment [86]. If so, medication use to reduce pain may have detrimental consequences. Furthermore, relieving pain using medications influences gait, such as increased walking velocity, which could increase fall risk by making other risk factors for falls more pronounced.

Proprioception

Proprioception, primarily in the lower extremities, can contribute to static and dynamic postural stability by providing feedback about limb position and joint orientation. Older adults have impaired proprioceptive feedback as a natural consequence of aging and are poorer at correcting errors in movement [87,88]. Diminished proprioception has been associated with falls in older adults [30,89 –91]. In particular, lower extremity proprioceptive deficits, as measured using a joint angle matching task, prospectively discriminated older women who had multiple falls from nonfallers [26,27]. In people with knee OA, knee proprioception, measured using both knee (re)position sense and motion sensation tests, was significantly impaired compared with healthy controls [59,92 –95].

Given the contributions of proprioception to static and dynamic stability, proprioceptive impairment exceeding that of ‘normal’ aging may cause a person to become dynamically unstable more frequently. To some extent, for people whose proprioception is impaired, monitoring static and dynamic stability can still rely on other, redundant, sensory feedback systems (visual and vestibular/otolith) to signal dynamic instability [88]. However, these systems also tend to become impaired with age. Conceptually, proprioceptive impairment could contribute to signal processing delays that result in slower performance times, the result of which may be insufficient time available for compensatory stepping responses to occur. However, the effect of proprioceptive impairment associated with OA_LE on the performance of a compensatory stepping response is not clear.

Gait variability

The topic of gait variability conceptually links increased movement variability with decreased neuromuscular control. As stated earlier, spatial and temporal step kinematics, such as increased step width, reduced stride length and slower walking speed, are associated with increased fall risk. However, for some populations, such as frail older adults, these changes may increase dynamic stability and decrease fall risk. Consequently, these variables may not necessarily represent meaningful clinical intervention targets. However, variability of step kinematics, particularly step width variability, has been prospectively associated with falling as variability may reflect errors in foot placement or ongoing attempts to compensate for an impaired ability to control destabilizing motion of the body during gait [96,97]. Similarly, the variability of the height of the toe during swing (minimum toe clearance variability) has also been related to individuals with a history of trip-related falls [98]. However, the extent to which these variables are causally related to falls, the degree to which they are modifiable, and the methods through which they may be modified are not known.

Gait variability of people with OA_LE may differ compared with people who do not have OA_LE. Individuals with knee OA have greater coefficients of variation in step length, step width and double support time compared with healthy controls [99] suggesting a decreased precision of the control of gait. The minimum toe clearance of people with symptomatic knee OA is not different than that of healthy asymptomatic control subjects; however, minimum toe clearance variability in people with OA_LE has not been reported [100]. Overall, the topic of gait variability as it relates to falls in people with OA_LE represents a potentially important area of clinical research.

Obstacle crossing is a motor task that requires accurate interjoint coordination and swing foot control. Knee OA increases the tendency to trip during obstacle crossing [101]. In people with OA_LE, proprioceptive impairment may influence interlimb coordination patterns and may be associated with an increased variability in minimum toe clearance. This increase, in addition to the proprioceptive deficits, could increase the likelihood of the swing foot coming into contact with an obstacle. After receiving pain-relieving intra-articular knee injections, people with knee OA were 31% more successful in avoiding an obstacle, although the avoidance rate remained 20% smaller than that of healthy controls [102].

Obesity

Obesity is one of the most modifiable risk factors for OA [103,104] and a large majority of individuals who are overweight/obese have OA_LE. Similar to older adults and people with OA, obese adults have slower preferred walking speeds, shorter step lengths, increased double support time and larger step widths [105 –107], all of which have been associated with fall risk, yet also associated with increased dynamic stability. In addition, similar to people with knee OA, obese people adapt their gait to reduce loading at the knee [106]. Obesity is linked to impaired static stability [108,109] and dynamic stability (as measured by the range and speed of the center of pressure motion during a maximum forward and backward lean task) [110] and impaired normalized knee extensor strength [111]. Furthermore, obesity is a risk factor for falls [112], possibly linked to compromised compensatory stepping abilities [113]. Given the associations between obesity and gait/balance impairments, obese older adults with OA may be at high risk of falling compared with those with either OA or obesity alone.

Strategies for decreasing fall risk

Given the premise that a fall is the consequence of two sequential events, the loss of static or dynamic stability followed by an unsuccessful compensatory step, interventions targeting one or both of these events would likely reduce the occurrence of falls. In older adults, interventions focusing on the ability to maintain static and dynamic stability by implementing balance training, in addition to an exercise program, reduces the occurrence of falls in approximately 20% [114]. Given the imperative need for a compensatory mechanism following a loss of dynamic stability, novel concepts of training the compensatory step have been developed [115 –117]. In particular, the present authors have developed an approach for reducing the occurrence of trip-related falls in focusing on training the compensatory step following a disturbance simulating a trip, and have found reductions in trip-related falls of almost 80% [80].

Falls result from a wide variety of causes including trips, slips, stair ascent and descent, and missteps [Rosenblatt NJ, Unpublished Data] [29,118–119]. For many trips and slips, which together account for approximately 50% of falls that occur during locomotion, it is possible to avoid falling by appropriately performing a compensatory stepping response. However, the compensatory stepping response associated with a trip and a slip involve considerably different environmental (and sensorimotor) contexts. For example, when tripped, a person falls in the same direction of travel. When slipped, the person typically continues to travel (i.e., slide) in the same direction, but actually falls backwards. Because the environmental contexts differ, the requirements of the compensatory stepping response also differ. The present authors' approach to reducing fall risk has been to improve the ability of older women to successfully perform the compensatory stepping response in response to a simulated trip. This is a task that requires a high degree of motor skill. Given that a motor skill is being trained, the effectiveness of the protocol is significantly affected by the motor learning ‘principle of specificity’ [120]. Specificity is a quality underlying the proficiency with which a motor skill (e.g., muscle strength) learned under ‘practice’ conditions (resistance training) can be performed under a different set of ‘test’ conditions (sports). According to this principle, fall risk should decrease proportionally to the similarity between the practice conditions during which the motor skill of avoiding a fall after a trip are learned, and those conditions during an actual trip in the community.

Following laboratory-induced trips, trunk flexion and the length of initial recovery step distinguish fallers from nonfallers [54]. Moreover, similar mechanisms distinguished fallers from nonfallers in response to treadmill-delivered disturbances [4]. This suggests considerable between-protocol specificity. Indeed, a task-specific training protocol, employing treadmill-delivered disturbances, decreased the number of falls in middle-aged and older women after a laboratory-induced trip, during which the women who did not fall reduced trunk flexion and increased step length following the disturbance [80]. A similar task-specific training protocol decreased falls measured prospectively in the community [Rosenblatt NJ, Unpublished Data] [Rosenblatt NJ, Marone J, Grabiner M. A novel step-training paradigm to decrease prospective community-based falls (2012), Manuscript in preparation] [121].

Compensatory step training to reduce falls in people with OA_LE

In the previous sections, the major risk factors for falls in older adults were presented in the context of their overlapping with the risk factors for falls in people with OA_LE ( Table 1 ). Even pain, and particularly pain at the affected joint(s), cannot be considered to be a risk factor unique to OA because pain can arise from numerous joint-related conditions. Therefore, given that the risk factors are more similar than not, it seems reasonable to expect that the present authors' task-specific training, found to be successful in reducing trip-related falls in older women, would also be effective in people with OA_LE.

The task-specific training targets performance of a compensatory stepping response following a posturally destabilizing disturbance delivered by a computer-controlled treadmill. This type of training reduces the number of falls in both middle-age (55–65 years of age) and older (>65 years of age) community-dwelling women after laboratory-induced trips, and reduces all-cause falls in the community [Rosenblatt NJ, Marone J, Grabiner M. A novel step-training paradigm to decrease prospective community-based falls (2012), Manuscript in preparation] [80,121]. The postural disturbances administered during the task-specific training simulated a trip [4,54,122], and were large enough to cause the subject to fall (safely into a harness) if they were not able to perform the required compensatory stepping response. The required compensatory stepping responses varied depending on the magnitude of the disturbance, where some may require one step, while others required several steps to restore dynamic stability. Biomechanically, the task-specific training significantly improved the ability of the women to restore control of the trunk following the disturbance and to coordinate this control with the recovery step(s). The risk of falling after a laboratory-induced trip decreased by 83% [80] and prospectively measured trip-related fall risk decreased by approximately 60% [Rosenblatt NJ, Marone J, Grabiner M. A novel step-training paradigm to decrease prospective community-based falls (2012), Manuscript in preparation] compared with control subjects. With regards to laterally directed disturbances where subjects are required to take a step in the mediolateral direction, compensatory stepping responses of young and older adults are quickly modified with practice [123,124]. This suggests that task-specific training may also decrease falls to the side, which significantly increases the risk of fall-related hip fracture.

For people with OA_LE, foot placement of the initial recovery step may be a significant factor limiting their ability to avoid a trip-related fall. Following contact with the ground, the initial weight-bearing phase of the recovery step involves eccentric contraction of the knee extensor muscles, which contributes to both reducing the angular momentum of the body and preventing the knee from buckling. Furthermore, the external knee adduction moment will likely increase as the width of the recovery step increases. A recovery step following a trip can thus result in relatively high compressive and shear loads at the knee joint [125]. For a person with OA_LE, such loads could elicit knee pain or even the anticipation of pain, and could lead to buckling of the knee or reluctance to complete an appropriate compensatory step to avoid a fall. Thus, training the compensatory stepping response to minimize pain, or the anticipation of pain, may increase the likelihood of successfully executing the compensatory stepping response, if and when necessary, and avoiding a fall. This may be possible by training subjects with knee pain to take steps that do not elicit high loads on the joints of the lower extremity. This too, could be addressed using a task-specific training protocol focused on reducing the external moments across the lower extremity joints.

Executive summary

On average, one-third of older adults fall each year, and women fall more often than men.

Falls in older adults are a leading cause of injury and death.

People with lower extremity osteoarthritis have an unexplained higher incidence of falls than age-matched, healthy controls and women have a higher incidence of lower extremity osteoarthritis than men.

Established risk factors for falls in older adults, which include gait impairments, balance deficits, muscle weakness, pain, increased gait variability and obesity, overlap with the risk factors associated with falls in people with lower extremity osteoarthritis.

These risk factors are not necessarily easily improved/modifiable.

From a biomechanical perspective, falls occur as a result of two sequential events:

– Loss of static or dynamic stability;

– Failed compensatory stepping response.

A task-specific intervention focused only on improving the compensatory stepping response was shown to prospectively decrease falls in older women in the community.

Given that the risk factors for falls in people with lower extremity osteoarthritis are mostly the same as those for people who do not have lower extremity osteoarthritis, this task-specific intervention will likely be an effective fall prevention approach in this large and growing clinical population.

Conclusion & future perspective

Our study of falls and fall prevention in healthy older adults has led us to hypothesize that, relative to healthy older adults, the symptoms associated with OA_LE negatively affect the ability to maintain static/dynamic stability and/or the ability to successfully meet the biomechanical requirements of the compensatory stepping response following dynamic instability. Task-specific training of the compensatory stepping response induces changes in performance marked by improvement in biomechanical variables, which have been shown to be causally related to falls in women. The next logical step of this work is to test the hypothesis, perhaps by determining the extent to which falls in people with OA_LE can be decreased by a task-specific training protocol that improves the ability to perform compensatory stepping responses while minimizing the load on diseased joints.

Footnotes

Risk factors for falls in people with lower extremity osteoarthritis

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Does Lower Extremity Osteoarthritis Exacerbate Risk Factors for Falls in Older Adults?

Abstract

Keywords

Financial & competing interests disclosure

Falls in older adults

Falls in people with lower extremity osteoarthritis

Established risk factors for falls in older adults

Gait impairments

Balance impairments: static postural control

Muscle weakness

Other factors related to falls in older adults with & without OALE

Pain

Proprioception

Gait variability

Obesity

Strategies for decreasing fall risk

Compensatory step training to reduce falls in people with OALE

Conclusion & future perspective

Footnotes

Risk factors for falls in people with lower extremity osteoarthritis

References

Other factors related to falls in older adults with & without OA_LE

Compensatory step training to reduce falls in people with OA_LE