the prevalence and the severity of posture and gait disorders increase with ageing ( salthouse and somberg 1982 ; maki et al 1994 ; mourey et al 1998 ; rankin et al 2000 ) . indeed , balance controlis a complex sensori - motor function which requires the integration of vestibular , visual , and somesthetic information into the central nervous system ( pyramidal , extrapyramidal , and cerebellar systems ) in order to maintain antigravitar postures and to produce a suitable response to any balance perturbation ( horak and mcpherson 1996 ) . in addition , the quality of muscle and joints is important in the balance function ( alencar et al 2007 ) . increased age is associated with impaired performance in vestibular , visual and somesthesic systems , a decline in the speed of information transmission and changes in the mode of information processing in the brain , allof which lead to balance and postural disorders ( brocklehurst et al 1982 ; aniansson et al 1986 ; woollacott 1993 ; choy et al 2003 ; yordanova et al 2004 ) . concerning the vestibule , it has been reported that the number of vestibular hair cells falls by 20% to 40% in healthy subjects aged 70 years and older , when compared to young subjects , and the number of vestibular nerve fibers has also been found to decrease with age ( alpini et al 2004 ) . regarding vision , decreased visual acuity , restriction of visual field , poor depth perception , losses in contrast sensitivity at the intermediate and high spatial frequencies have been found in elderly subjects ( alpini et al 2004 ) . at the somesthesic level , various alterations in the morphology and functions of the peripheral nervous system are related to ageing . elderly subjects also suffer from a loss of myelinated and unmyelinated nerve fibers associated with axonal atrophy . aging also induces a decline in nerve conduction velocity and sensory discrimination ( verdu et al 2000 ) . moreover , the age - related decline in muscle and joint quality contributes to the proprioceptive abnormalities and also explains effector disorders found in elderly subjects . indeed , with advancing age , the frequency of sarcopenia increases and the decrease in muscle mass is associated with the replacement of muscle fibers by fat and connective tissue ( lexell 1995 ; alpini et al 2004 ; crepaldi and maggi 2005 ) . moreover , there is an increase in degenerative osteoarticular lesions and osteoporosis ( crepaldi and maggi 2005 ) . independently of sensorimotor system , postural controlis also enabled by spatial references such as the subjective vertical ( massion 1992 ) . the subjective vertical ( which can be haptic , postural , or visual ) corresponds to an individual s perception of the vertical and is therefore different from the true or gravitational vertical ( manckoundia et al 2007a ) . concerning gait , physiological ageing is associated with a reduction in the length and the height of step , an increase in dual foot contact time , and a resulting reduction in gait speed ( craik et al 1992 ; alexander 1996 ) . the negative effects of certain chronic afflictions on posture and gait will compound those of physiological ageing . these chronic diseases may be neurological ( parkinson s disease or syndrome , the after - effects of stroke , neuropathy , normal pressure hydrocephalus and amyotrophic lateral sclerosis , for example ) or osteoarticular ( osteoarthritis of the lower limbs  ) , muscular , visual ( cataract , age - related macular degeneration ) , vestibular and can be associated with certain geriatric syndromes such as psychomotor disadaptation syndrome ( knutsson 1972 ; fisher 1982 , pfitzenmeyer et al 1999 ; hausdorff 2000 ; lee and scudds 2003 ; corriveau et al 2004 ; manckoundia et al 2008 ) . these balance and postural disorders make elderly people vulnerable , accelerate functional decline and contribute to the loss of autonomy ( rankin et al 2000 ) . backward disequilibrium ( bd ) is a postural disorder which is characterized by a posterior position of the centre of mass with respect to the base of support in the standing and sitting position predisposing subjects to backward falls . this postural disorder is defined by a posterior body tilt ( mourey et al 2004 ) . the pathophysiological mechanisms leading to bd behavior , however , have not yet been clearly identified . nevertheless , as observed in patients with stroke , deterioration in the subjective vertical could be associated with the appearance of bd . indeed , the literature reports that the pusher behavior due to hemiplegia is associated with deterioration in the representation of the subjective verticalin the frontal plane ( lopez et al 1997 ; prennou et al 1998 ) . a similar patho - physiological hypothesis may be involved in bd . to test this hypothesis we conducted a pilot study and found a direct correlation between the subjective vertical and the bd ( manckoundia et al 2007a ) . in this pilot study , the subjective vertical was assessed by measuring the postural vertical , which corresponds to the self - perception of the body s orientation in space and in the sagittal plane ( manckoundia et al 2007a ) . moreover , bd could be related to accentuated postural tone of the extensor muscles due to a disorder in the excitability of the corresponding descending pathways ( porter and lemon 1993 ) , or to the fear of the void in front of the subject linked to the fear of falling in the context of post - fall syndrome ( murphy and isaacs 1982 ; pfitzenmeyer et al 1999 ; mourey et al 2004 ) . although the geriatrician can recognize bd , which is not uncommon in daily clinical practice , there are no tools to evaluate the severity . moreover , only a few authors have examined this postural disorder in elderly subjects ( mourey et al 2004 ) and these studies concern mainly parkinsonian syndromes in the anglo - saxon literature ( visser et al 2003 ) . finally , there are no epidemiological data on bd . thus , in this paper , we review bd , a postural disorder that has severe consequences and can compromise functional autonomy in elderly subjects . indeed , the autonomy and functional well - being of elderly subjects suffering from bd could be improved by early diagnosis and management using basic interventions ( manckoundia et al 2007b ) . cortical and subcortical lesions of the central nervous system are the main abnormalities leading to bd . there are reports of a positive correlation between cortical and subcortical cerebral lesions , identified on magnetic resonance imaging , and bd ( pfitzenmeyer et al 2002 ) . ischemic , degenerative and traumatic lesions of the cerebral trunk , the white matter , the frontal lobes , the gray matter and the cerebellum could induce bd in elderly subjects ( van wegen et al 2002 ) . ischemic and hemorrhagic strokes are the most frequent etiologies of bd as they are in nonidiopathic parkinsonian syndromes ( visser et al 2003 ) . in addition , the literature reports other subcortical abnormalities such as normal pressure hydrocephalus or amyotrophic lateral sclerosis , which could also be associated with bd ( desai and swash 1999 ; blomsterwall et al 2000 ) . backward disequilibrium could also be due to an imbalance between the ankle extensor muscles and the ankle flexor muscles , because of hypertonia of extensor muscles , which could be caused by a peripheral neurological lesion ( porter and lemon 1993 ) . the main psychosomatic disorder associated with bd is psychomotor disadaptation syndrome and its acute form , the post - fall syndrome ( pfitzenmeyer et al 2001 ) . psychomotor disadaptation syndrome , which was first described by gaudet and colleagues in 1986 , is characterized by postural impairments , including bd , neurologic signs and psychological disorders ( mourey et al 2004 ) . several chronic diseases such as parkinsonian syndromes , multiple system atrophy , progressive supranuclear palsy , lewy body disease , binswanger s disease , subcortical vascular lesions , normal pressure hydrocephalus , lymphomas of nervous system , meningoencephalitis , hiv infection , and depression may be associated with psychomotor disadaptation syndrome ( pfitzenmeyer 1999 ; mourey et al 2004 ) . finally , other situations such as confinement to bed and/ or depression could be associated with motor and postural disorders including bd ( mobily and skemp kelley 1991 ; mourey et al 2004 ; turcu et al 2004 ) . elderly subjects suffering from bd have a high risk of falling backwards ( pfitzenmeyer et al 1999 ) . falls are associated with an increase in morbi - mortality in the elderly ( wild et al 1981 ) . hip fracture is the more dreaded injury ( rose and maffulli 1999 ) , and there is a risk of posttraumatic subdural hematoma ( noltie and denham 1981 ) . fallers can also be affected by many other injuries ( tinetti et al 1995 ) . these traumatic consequences are associated with a high risk of mortality ( tinetti et al 1995 ) . among the psychological consequences of falls , there is the fear of standing , walking , and falling ( gomez and curcio 2007 ) , allof which can exacerbate bd behavior and result in a vicious circle . the social consequences of falls include the loss of autonomy , institutionalization and the risk of becoming bedridden ( tinetti and williams 1997 ) . in addition , the loss of autonomy is associated with a decrease in physical activity leading to reduced muscle mass and functional decline which predispose the elderly to falls . falls therefore have economic repercussions and represent a major public health problem ( tinetti et al 1994 ) . regarding the consequences of falls , it is necessary for all health workers , especially physicians , involved in the management of elderly subjects to know how to recognize and manage syndromes and afflictions that could cause falls . in this context , bd , which is one of main risk factors of falls , must be detected . however , elderly subjects suffering from mild form of bd show postural instability that does not necessarily result in falls . this , nevertheless , limits their daily activities , induces hypoactivity and may lead to the use of walking aids . backward disequilibrium could have severe psychological consequences in elderly subjects even in the absence of falls . indeed , bd is often associated with a loss of self - confidence during standing and walking . this could cause fear of standing , walking and falling as described in psychomotor disadaptation syndrome ( mourey et al 2004 ; manckoundia et al 2007b ) . this fear of standing , walking and falling can appear even in the absence of a history of falls ( legters 2002 ) . the progressive loss of autonomy is the logicaloutcome of both loss of self - confidence during standing / walking , and fear of standing . bd and its motor and psychological consequences lead to postural disadaptation which in turn leads to dependence . finally , bd can bring about depression mostly because of the fear of walking and falling , loss of independence and decreased of quality of life . indeed , elderly people who become aware of the deterioration in their physical capacities will lose self - confidence and self - esteem , develop a sense of insecurity and become withdrawn . as a result elderly subjects suffering from bd have a high risk of falling backwards ( pfitzenmeyer et al 1999 ) . falls are associated with an increase in morbi - mortality in the elderly ( wild et al 1981 ) . hip fracture is the more dreaded injury ( rose and maffulli 1999 ) , and there is a risk of posttraumatic subdural hematoma ( noltie and denham 1981 ) . fallers can also be affected by many other injuries ( tinetti et al 1995 ) . these traumatic consequences are associated with a high risk of mortality ( tinetti et al 1995 ) . among the psychological consequences of falls , there is the fear of standing , walking , and falling ( gomez and curcio 2007 ) , allof which can exacerbate bd behavior and result in a vicious circle . the social consequences of falls include the loss of autonomy , institutionalization and the risk of becoming bedridden ( tinetti and williams 1997 ) . in addition , the loss of autonomy is associated with a decrease in physical activity leading to reduced muscle mass and functional decline which predispose the elderly to falls . falls therefore have economic repercussions and represent a major public health problem ( tinetti et al 1994 ) . regarding the consequences of falls , it is necessary for all health workers , especially physicians , involved in the management of elderly subjects to know how to recognize and manage syndromes and afflictions that could cause falls . in this context , bd , which is one of main risk factors of falls , must be detected . however , elderly subjects suffering from mild form of bd show postural instability that does not necessarily result in falls . this , nevertheless , limits their daily activities , induces hypoactivity and may lead to the use of walking aids . backward disequilibrium could have severe psychological consequences in elderly subjects even in the absence of falls . indeed , bd is often associated with a loss of self - confidence during standing and walking . this could cause fear of standing , walking and falling as described in psychomotor disadaptation syndrome ( mourey et al 2004 ; manckoundia et al 2007b ) . this fear of standing , walking and falling can appear even in the absence of a history of falls ( legters 2002 ) . the progressive loss of autonomy is the logicaloutcome of both loss of self - confidence during standing / walking , and fear of standing . bd and its motor and psychological consequences lead to postural disadaptation which in turn leads to dependence . finally , bd can bring about depression mostly because of the fear of walking and falling , loss of independence and decreased of quality of life . indeed , elderly people who become aware of the deterioration in their physical capacities will lose self - confidence and self - esteem , develop a sense of insecurity and become withdrawn . as a result among the tests to assess balance and gait in elderly subjects , only the minimum motor test includes items for a qualitative analysis of bd ( mourey et al 2005 ) . the other usual tests , such as the tinettitest ( tinetti 1986 ) , the timed up and go test ( podsiadlo and richardson 1991 ) or the berg balance scale ( berg et al 1992 ) , are not able to diagnose bd . indeed , these tests are only suitable to evaluate the consequences of bd on certain daily tasks such as sit - to - stand , back - to - sit , maintaining a standing position or walking . given the absence of a specific tool to assess bd , diagnosis remains only qualitative , based on observations of elderly subjects in the sagittal plane , in the sitting position as well as in the static and dynamic standing position . however , a quality assessment of this kind of postural disorder requires a quantitative scale . the management of elderly subjects suffering from bd has to be multidisciplinary , associating different categories of health professionals including physicians , physiotherapists , psychologists , nurses , and nurse s aides . in addition , the management of bd must begin quickly , immediately after making the diagnosis , which is based on clinical observation . the medical management consists of the search for and the treatment of possible causes of the bd . the physician must therefore make a detailed examination , which could be completed by targeted biological analyses or radiological examinations . there are few reports concerning the rehabilitation of frail patients showing major limitations in motor performance . the association of strength training and progressive functional training improves the physical capacities in frail geriatric patients ( hauer et al 2001 ) . a recent review of the literature shows that progressive resistance training alone is not an effective therapy for balance control ( orr et al 2008 ) . improving the dynamic and static control of the centre of mass is the main objective of physiotherapy . practicing turning over in bed is introduced very early in the rehabilitation program in order to restore autonomy in bed and the capacity to achieve transfers . then , balance training is implemented in static and dynamic positions . it is advisable to start balance rehabilitation using intrinsic exercises first , followed by extrinsic exercises in the sitting position as well as in the standing position . the forward projection of the trunk and the stabilization of the head in space are developed in order to make the sit - to - stand easier . indeed , the sit - to - stand is a determinant stage of functional rehabilitation . in the standing position , the use of a removable heelpiece could help to reduce bd at the beginning of the physiotherapy . in addition , subjects suffering from bd have to be trained to rise from the floor . the physiotherapist , therefore has to control the heart rate and the breathing frequency ( brondel et al 2005 ) . the choice of exercise must be personalized according to the postural abilities of the subject . in parallel with rehabilitation by the physiotherapist , nurses and nurse s aides have to stimulate elderly patients suffering from bd through the activities of everyday life , but in doing so they must avoid pulling on the patient s upper limbs during transfers . finally , the psychologist must reassure and motivate elderly subjects suffering from bd and not overdramatize the situation to help them regain self - confidence . besides , the psychologist must help elderly subjects suffering from bd to overcome disafferentation , fear of standing and walking as well as fear of falling ( manckoundia et al 2007b ) . although it has been known by physicians for several decades , bd , which could have serious physical , psychologicalor social consequences , has rarely been studied in the literature . the causes of bd are often mixed and associate somatic and psychological pathologies among which there is post - fall syndrome . the management of bd must be interdisciplinary ( involving physicians , physiotherapists , psychologists , nurses , nurses aides ) . physiotherapy , which is a major component of the management strategy , must be started early and adjusted to allof the situations of everyday life .