Yoren Gaffary

Maud Marchal

Adrien Girard

Marine Pellan

Anouk Asselin

Benoît Peigné

Mathieu Emily

Florian Gosselin

Anthony Chabrier

Anatole Lécuyer

Studying

Benoit Peigne

Studying One and Two-Finger Perception of Tactile Directional Cues

Keywords: tactile perception, fingertip stimulation, multifinger

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

The fingertips are among the most sensitive parts of the human body [START_REF] Scheibe | Tactile feedback at the finger tips for improved direct interaction in immersive environments[END_REF]. When haptically exploring the world with our hands, we usually make use of multiple fingers and multiple fingertips. In doing so, it is commonly considered that the more fingers involved the better perception, and that, among fingers the index fingertip is the most sensitive and efficient one. But there are actually rather few studies which specifically compare the perception of tactile cues using the index versus the other fingers and/or a single-finger versus multiple fingers.

Numerous haptic studies investigated the tactile perception obtained with one finger at the level of fingertip [START_REF] Vitello | An instance of tactile suppression: Active exploration impairs tactile sensitivity for the direction of lateral movement[END_REF][START_REF] Gleeson | Perception of Direction for Applied Tangential Skin Displacement: Effects of Speed, Displacement, and Repetition[END_REF]. As an example, Gleeson et al. [START_REF] Gleeson | Design of a Fingertip-Mounted Tactile Display with Tangential Skin Displacement Feedback[END_REF] studied the perception of a tactile directional cue applied on a single finger. They designed a tactile display enabling skin displacement at the level of fingertip and evaluated the perception of two different directions of stimulation along the horizontal axis (left, right) with the right index.

On the contrary, only few studies investigated the use of several fingers ( [START_REF] Guinan | A video game controller with skin stretch haptic feedback[END_REF][START_REF] Jansson | Exploring tactile maps with one or two fingers[END_REF]). For example, a game controller able to stimulate both thumbs using a tactor displacement was proposed by Guinan et al. [START_REF] Guinan | A video game controller with skin stretch haptic feedback[END_REF]. This setup involved stimulating both thumbs of the user with four possible directional stimuli. The stimuli were displayed sequentially on both thumbs. Recognition rate depended on the delay time between the two displays. Jansson and Monaci [START_REF] Jansson | Exploring tactile maps with one or two fingers[END_REF] investigated the influence of the number of fingers used on the tactile exploration of a 2D tactile map. They did not find a clear improvement when using two fingers instead of one. However, they observed a significant learning effect when using two fingers, and an improvement of performance over sessions in this case.

In this paper we specifically address the influence of the finger used (index, middle, ring), or the possibility to use two fingers simultaneously, for the perception of tactile directional cues. We present an experiment in which directional stimuli are displayed either on the index, middle or ring finger, or on any couple of these fingers. We measure both the recognition rate in four directions (horizontal, vertical, and the two diagonals), and the subjective preference of participants.

The next section describes our experimental method for studying tactile perception using one or two fingers. We successively present our experimental apparatus based on a 2 DOF tactile display, our experimental protocol, and the data we collected. The section 3 presents the results of this experiment, followed by a conclusion.

2 User study: One and two-finger perception of tactile directional cues

Objective and Hypotheses

Our study aims at determining which combinations of index, middle or ring finger allow the most accurate perception, i.e., the highest recognition rate regarding the direction of the haptic stimuli displayed to the participants (vertical, horizontal, diagonal). In this study, we specifically focused our attention on a combination between one and two fingers. Three hypotheses are evaluated:

H1 Finger efficiency. The accurate perception of a stimulus relies on the finger(s) used to perceive this stimulus. Commonly, the index is thought as the most accurate to perceive directions [START_REF] Gleeson | Perception of Direction for Applied Tangential Skin Displacement: Effects of Speed, Displacement, and Repetition[END_REF]. H2 Redundancy efficiency. The redundant display of a stimulus on two fingers provides a higher recognition rate than if presented on one finger alone, as more cutaneous receptors are stimulated. H3 Learning effect. The recognition rate increases during the experiment due to the presence of a learning effect when using two fingers as suggested in [START_REF] Jansson | Exploring tactile maps with one or two fingers[END_REF].

Experimental setup

The experimental setup is based on a tactile device called Haptip and presented in [START_REF] Girard | Hap-Tip: Displaying Haptic Shear Forces at the Fingertips for Multi-Finger Interaction in Virtual Environments[END_REF] (see Figure 1a). It stimulates fingertips through the 2D displacement of a tactor. This kind of skin stretching device is suitable to display directional information on the fingertips [START_REF] Gleeson | Design of a Fingertip-Mounted Tactile Display with Tangential Skin Displacement Feedback[END_REF].

The experiment includes either one or two devices depending on the number of fingers to be stimulated (see Figures1b and 1c). When a single finger is stimulated, only one device is required. Two identical devices are required when two fingers are stimulated. In this case, the two devices are synchronized using the API provided by the manufacturer to display the same stimulus at the same time.

Experimental plan

Apparatus. The participants were seated with their forearms placed on a table. The participants were seated in front of a 24 inch screen displaying the questions concerning the stimuli directions, with their forearms placed on a table (see Fig. 2). The haptic devices were fixed to the table in front of the dominant hand of the participant using velcro. The velcro was used to prevent the devices from moving during the experiment. The position of each tactor on the table was adjusted to the length of the participant's finger. The non-dominant hand of the participant was holding a mouse used to answer the questions displayed on the screen. Participants. Eighteen participants took part to the experiment. There were 7 males and 11 females, aged from 21 to 32 (mean= 23, SD = 2.8). 15 participants identified their right hand as the dominant one. When asked about their experience with haptics, 10 participants reported that they were familiar, 8 reported that they were not familiar.

Procedure. Participants were asked to complete a perception task that consisted in recognizing the direction of the tactile stimuli that were displayed under their fingers. The different possible directions were displayed on the screen and each participant could answer using a mouse in his or her non-dominant hand. At the beginning of the experiment, the instructor presented the different tactile stimuli and explained them how to put their fingers on the device. Each participant completed a short training session during which a random stimulus was presented to him.

Four different stimuli were presented to the participants, each corresponding to a specific direction in space. These stimuli were generated through specific displacements of the tactor scratching the fingertip. All the stimuli used the maximum range of motion of the device (i.e. 4 mm) and lasted one second. The stimuli differed by the direction of their movement from the vertical: 0 • , 45 • , 90 • and 135 • in direct order. The displacement of each tactor followed a sinusoidal law, with an amplitude of 4 mm and a frequency of 1 Hz. For each stimulus, the tactor starts from the center of the device, and then moves in three steps: 1) the tactor moves to an extremity, 2) the tactor moves to the opposite extremity, crossing the center, and 3) the tactor moves to the center. Figure 3 illustrates the four directions with the three different steps of the tactor movement.

The stimuli were presented to the participants on a combination of one or two fingers, the possible combinations being: the index, middle or ring finger alone, and index-middle, index-ring and middle-ring couples. The thumb was not considered in this study as the stimuli could not be presented in the same configuration as for the other fingers. The little finger was also removed as our haptic device was too large for this finger. All 4 directions × 6 fingers combinations were presented to each participant. A trial was considered valid after 1s stimulus and when the participant had reported a direction between the four proposed on the screen using the mouse in his or her non-dominant hand. The participant could ask for a break at any time between each trial.

Conditions and experimental design. The independent variables of the experiment were: the Finger used to perceive the stimulus (Index, Middle, Ring, Index-Middle, Index-Ring and Middle-Ring), the Direction of the stimuli displayed on the fingertips ( Vertical, Horizontal, Diagonal 1 and Diagonal 2) and Repetition (10 different trials for each finger combination and each direction). While the directions of the stimuli were randomly presented, the order of the fingers used to perceived the stimuli was counterbalanced across participants to avoid privileging a combination of fingers among another one. The duration of the experiment was approximately 30 minutes including breaks. In total, we had 18 participants × 6 finger combinations × 4 directions × 10 repetitions = 4,320 trials.

Collected data.

Main measure. We recorded the perceived direction of the stimulus presented in each case. Therefore, the participants had to select the direction of the stimulus they perceived between four possible directions using arrows (see Fig. 2). This measure aims at evaluating the influence of the finger on recognition rate, redundancy efficiency and learning effect (H1, H2 and H3).

Subjective questionnaire. At the end of the experiment, the participant fulfilled a subjective questionnaire to evaluate the coherence between their objective performances and their subjective feeling.

The two first questions were:

Ms1 "Was it is easy to recognize directions with the X finger(s)? " This question was asked six times, one for each combination of fingers. Participants answered each time using a 5-item Likert scale. Ms2 "Classify the directions by their easiness to recognize". There were three items to order: horizontal stimuli, vertical stimuli and diagonal stimuli.

Following questions were answered by participants using a 5-item Likert scale:

Ms3 "Did you feel the perception was easier with a combination of two fingers instead of one finger? " This question aims at evaluating the coherence between perceived redundancy efficiency and true redundancy efficiency. Ms4 "Did your perception changed during the experiment? " This question aims at evaluating the subjective perception of a learning effect. Ms5 "Was the task easy to perform? " This question aims at determining if the selected stimuli were not too easy or too difficult to recognize.

Results and Analysis

Recognition rate

To study the recognition rate of the direction of the stimuli in function of the combination of fingers, we used a logistic regression model on the collected data to model the probability of recognition with respect to the independent variables Finger and Direction defined in the experimental design. The probability is thus comprised between 0 and 1, 0.25 corresponding to the guess rate, a higher probability highlighting a better recognition rate while a lower probability highlighting the confusions between the potential answers. The participants are considered as a random effect in the model.

Learning effect. In order to investigate the presence of a learning effect during the experiment, we incorporated the Repetition factor in the model. We separated the i first presented stimuli for each combination of fingers from the 40 -i last stimuli, with i ∈ [START_REF] Essock | Superior sensitivity for tactile stimuli oriented proximally-distally on the finger: Implications for mixed class 1 and class 2 anisotropies[END_REF]39]. Results showed that for i ∈ [1, 13], the first stimuli provided lower recognition rate (74 % vs 77 % correct recognition rate, p-values ∈ [0.004, 0.047]). These results highlight a learning effect and support H3. The statistical analysis reported in the following section were then performed by removing the first 13 stimuli from the data of each combination of finger and for each participant.

Main analysis. We performed an analysis of deviance of the logistic regression model and we found a significant marginal effect for both Finger (p = 0.003) and Direction (p < 0.001), as well as an interaction effect between Finger and Direction (p = 0.04). Table 1 displays the recognition rates in function of the displayed directions and combination of fingers. We performed a post-hoc analysis on the Direction using a Tukey test adapted to the logistic generalized regression model. We found that the Vertical direction was significantly better recognized than the other directions (Z = -6.56, Z = -5.25, Z = -4.34 for the Diagonal 1, Horizontal and Diagonal 2 and p < 0.001 for the three directions). We did not find a significant effect between the other directions.

We performed a post-hoc analysis on the Finger using the same Tukey test. We found that the stimuli display on the Index finger were significantly better recognized than the Middle-Ring combination (Z = 3.2, p = 0.18). We also found that the stimuli displayed on the Index-Middle finger were significantly better recognized than the Middle-Ring combination (Z = 3.5, p = 0.005). We did not find any other significant effect between the other combinations of fingers.

Interaction between Direction and Finger. We performed a post-hoc analysis to analyze the interaction between the Direction and Finger variables using a pairwise comparison based on least squares means estimates. All the significant differences concerned the Vertical direction. We found that the two diagonal directions Diagonal 1 and Diagonal 2 for the Middle-Ring combination were less recognized than the Vertical direction for the following finger combinations: Index (Z = 4.59, p < 0.01 and Z = 4.41, p < 0.01 respectively), Middle (Z = 4.75, p < 0.01 and Z = 4.58, p < 0.01 respectively), Index-Middle (Z = 4.6, p < 0.01 and Z = 4.42, p < 0.01 respectively), Index-Ring (Z = 3.88, p = 0.02 and Z = 3.69, p = 0.04 respectively). We found also that the Vertical direction for the combinations Middle alone and Index-Middle had a significantly higher recognition rate than the Horizontal direction for the Index and Middle fingers (Z = 3.83, p = 0.02; Z = 3.88, p = 0.02; Z = 3.63, p = 0.04 and Z = 3.69, p = 0.04 respectively). Finally, we found that the Vertical direction for the Index was better recognized than the Horizontal direction for the Middle finger (Z = 3.68, p = 0.04), and that the Vertical direction for the Middle was better recognized than the Diagonal 1 direction for the Index-Ring combination (Z = 3.78, p = 0.02).

One vs. two fingers. To investigate the influence of the number of fingers used to perceive the stimuli on recognition rate, we grouped together the results obtained with the same number of fingers (the variable Finger has only two values: one vs. two fingers). As previously, we used a logistic regression model on the collected data to model the probability of recognition with respect to the independent variables Finger and Direction. We performed an analysis of deviance of the logistic regression model and we found a significant marginal effect for Direction (p < 0.001), as well as an interaction effect between Finger Table 1: Recognition rate (in percent) according to the direction of the stimuli and the fingers used to perceived them. The grey cells represent the cells where the perceived direction is the direction of the stimulus.

fingers (Z = -3.22, p = 0.03) and the Diagonal 2 direction for One finger (Z = -3.25, p = 0.02).

Subjective questionnaire

The results of our subjective questionnaires showed that the condition allowing to recognize the directions the most easily was Middle (Ms1, M = 3.67/5). At the opposite, the Ring alone was perceived as the most difficult condition to recognize stimuli (M = 3.11/5). Participants reported that the Vertical direction was the easiest to recognize (Ms2, for 77.8 % of the participants). At the opposite, 88.9 % of the participants reported that the Diagonal direction was the most difficult to recognize. Concerning the subjective evaluation of one vs two finger configurations (Ms3), participants reported they did not feel any difference between one and two-finger display presentation (M = 3.11/5). Participants reported they felt an evolution of their tactile performance during the experiment (Ms4, for 77 % of the participants). More specifically, the participants reported that their performance increased during the experiment (median: 4). This is in line with the objective results, especially for two-finger configurations. Finally, the participants reported the task was not too easy or too difficult (Ms5, M = 3.11/5).

Results summary

For one finger configurations, we observed a higher recognition rate with the Index and Middle than with the Ring finger, in accordance with [START_REF] King | Perceptual thresholds for single vs. multifinger haptic interaction[END_REF][START_REF] Gleeson | Perception of Direction for Applied Tangential Skin Displacement: Effects of Speed, Displacement, and Repetition[END_REF]. We also observed that the Vertical direction displays the highest recognition accuracy. This is inline with [START_REF] Essock | Superior sensitivity for tactile stimuli oriented proximally-distally on the finger: Implications for mixed class 1 and class 2 anisotropies[END_REF][START_REF] Gentaz | The visual perception of orientation, and "the oblique effect[END_REF] as this direction is generally better recognized as a proximodistal axis.

Regarding two fingers configurations, we observed a learning effect as previously mentioned in [START_REF] Jansson | Exploring tactile maps with one or two fingers[END_REF]. We also found that the two diagonal directions Diagonal 1 and Diagonal 2 for the Middle-Ring combination were less recognized than the Vertical direction for the other combinations. This explains the low results for the Middle-Ring.

Finally, our results highlight a difference between one and two-fingers configurations. Two-fingers combinations seem to be more effective for perceiving the Horizontal direction. However, diagonals seem to be more commonly mistaken with the Horizontal direction in a two-finger configuration.

The subjective appreciation of the participants (obtained with the subjective questionnaire) is consistent with their objective accuracy.

Conclusion

This study aimed at determining the influence of the number of fingers used to perceive directional stimuli on recognition accuracy. Three fingers were involved: index, middle and ring.

The results of our experiment showed that the fingers used and their number influence the accuracy in perceiving directions. Among single fingers, the index and middle gave the highest recognition rate. The influence of the number of fingers displayed contrasted results. The diagonals are better perceived using a single finger, but the horizontal direction is better perceived using two fingers.

Future works could investigate the influence of parameters such as the position of the fingers during the stimulation or distance between fingers. This would enable to further investigate the relation between the number of fingers used and the perceived directions. Different durations and shapes of stimuli could also be tested. In a long-term perspective, these results could serve as guidelines for the development of a new haptic device aiming at stimulating effectively fingertips.

Fig. 1 :

 1 Fig. 1: Tactile device used in the study: (a) top view of the device, (b) and (c) profile views with one or two actuated tactors.

Fig. 2 :

 2 Fig. 2: Experimental apparatus: example of a participant reporting the direction of the stimulus he just perceived on the fingertip of his middle finger (here 45 • ).

Fig. 3 :

 3 Fig. 3: The four different stimuli displayed to the participants. The tactor displacement follows four possible directions: vertical, horizontal or one of the two diagonals.

Acknowledgments

This work was supported by the European Commission through the HAP-PINESS project (SEP-210153552) and by French National Research Agency through the MANDARIN project (ANR-12-CORD-0011) labeled by French Cluster Cap Digital.

and Direction (p = 0.04). We did not find any significant effect this time for the Finger combination.

Concerning the Direction, we performed a post-hoc analysis using a Tukey test. We found the same significant effects: the Vertical direction was significantly better recognized than the others directions (Z = -6.44, Z = -5.1, Z = -4.4 for the Diagonal 1, Horizontal and Diagonal 2 and p < 0.001 for the three directions). We did not find a significant effect between the other directions.

Concerning the interaction, we found that the Vertical direction for One finger was better recognized than the other combinations, except for the Vertical direction for Two fingers. We also found that the Diagonal 1 direction for Two fingers was less recognized than the Horizontal direction for Two


Lorene Zerah

Judith Cohen-Bittan

Mathieu Raux

Anthony Meziere

Cendrine Tourette

Christian Neri

Marc Verny

Bruno Riou

Frederic Khiami

Jacques Boddaert
email: jacques.boddaert@aphp.fr

Pr Jacques Boddaert

Association between cognitive status before surgery and outcomes in elderly patients with hip fracture in a dedicated orthogeriatric care pathway

Keywords: Unit of Peri-Operative Geriatric care, Hip fracture, Dementia, Elderly

Background: Dementia is associated with a worse prognosis of hip fracture, but the impact of a dedicated geriatric care pathway on the prognosis of these patients has not been evaluated.

Objective: According to the cognitive status before surgery, our main objective was to compare mortality rate at 6 months; secondary outcomes were to compare in-hospital complications, the risk of new institutionalization and the ability to walk at 6 months.

Methods: Between 2009 and 2015, all patients (> 70 years) admitted after hip fracture surgery into a dedicated unit of peri-operative geriatric care were included: patients with dementia (DP), without dementia (NDP) and with cognitive status not determined (CSND).

Data are expressed as Hazard Ratio(HR) for multivariate cox analysis or Odds Ratio(OR) for multivariate logistic regression analysis and their 95% confidence interval (CI).

Results:

We included 650 patients (86 ± 6 years): 168 DP, 400 NDP and 82 CSND. After adjustment for age, sex, comorbidities, polypharmacy, pre-fracture autonomy, time-to-surgery and delirium, there were no significant differences for 6-month mortality (DP vs NDP: HR=0.7[0.4 -1.2], DP vs CSND: HR=0.6[0.3 -1.4], CSND vs NDP: HR=0.8[0.4 -1.7]); but DP and CSND were more likely to be newly institutionalized after 6 months compared to NDP .9], p=0.003, OR CSND=2.9[1.4 -6.1], p=0.004). 92% of population was walking after 6 months (63% with assistance): no difference was found between the 3 groups.

Conclusion:

In a dedicated geriatric care pathway, DP and CSND undergoing hip surgery have the same 6-month mortality and walking ability as NDP.

Introduction

As a consequence of the aging of the population, the incidence of osteoporotic fractures, especially hip fractures (HF), is increasing [START_REF] Johnell | An estimate of the worldwide prevalence and disability associated with osteoporotic fractures[END_REF][START_REF] Prestmo | Comprehensive geriatric care for patients with hip fractures: a prospective, randomised, controlled trial[END_REF]. In 2000, the worldwide incidence of HF was estimated at 1.6 million in people aged 50 years and older [START_REF] Johnell | An estimate of the worldwide prevalence and disability associated with osteoporotic fractures[END_REF]. The annual global incidence of HF is expected to rise to between 7.3 and 21.3 million by the year 2050 [START_REF] Gullberg | World-wide projections for hip fracture[END_REF]. Nearly all HF occur as a result of a fall and many fall again soon after sustaining the fracture [START_REF] Stenvall | A multidisciplinary, multifactorial intervention program reduces postoperative falls and injuries after femoral neck fracture[END_REF]. Direct medical costs incurred are staggering, estimated at between US $153.5 billion and US $446.3 billion annually by 2050 [START_REF] Johnell | The socioeconomic burden of fractures: today and in the 21st century[END_REF]. The rate of death is high, varying from 12 to 23% during the 6 months following the fracture, higher than in the general population in the following months and years [START_REF] Abrahamsen | Excess mortality following hip fracture: a systematic epidemiological review[END_REF][START_REF] Hannan | Mortality and Locomotion 6 Months After Hospitalization for Hip Fracture: Risk Factors and Risk-Adjusted Hospital Outcomes[END_REF].

Dementia affects 36 million people worldwide, with numbers expected to double every 20 years to 66 million by 2030 [START_REF] Jackson | Screening for dementia in general hospital inpatients: a systematic review and meta-analysis of available instruments[END_REF]. Among dementia, notably in the geriatric population, Alzheimer's disease (AD) is the most frequent neurodegenerative disorder [START_REF] Ferri | Alzheimer's Disease International (2005) Global prevalence of dementia: a Delphi consensus study[END_REF], but cognitive impairment remains under diagnosed [START_REF] Jackson | Screening for dementia in general hospital inpatients: a systematic review and meta-analysis of available instruments[END_REF]. In 2009, Sampson et al. showed that 42% of unselected older medical inpatients had dementia, half of these had not previously been diagnosed with dementia [START_REF] Sampson | Dementia in the acute hospital: prospective cohort study of prevalence and mortality[END_REF].

AD and HF are closely related [START_REF] Weller | Hip fractures and Alzheimer's disease in elderly institutionalized Canadians[END_REF]. Baker and al. found that patients with AD had a 3.2 hazard ratio for risk of HF (95% CI, 2.4 -4.2) compared to non-AD patients, after controlling for potential confounders [START_REF] Baker | Hip fracture risk and subsequent mortality among Alzheimer's disease patients in the United Kingdom, 1988-2007[END_REF]. In their study, the incidence of HF among patients with and without AD was 17.4 (95% CI, 15.7-19.2) and 6.6 (95% CI, 5.8-7.6) per 1,000 person years, respectively [START_REF] Baker | Hip fracture risk and subsequent mortality among Alzheimer's disease patients in the United Kingdom, 1988-2007[END_REF]. In particular, mortality and poor functional recovery after HF seem to be more frequent in patients with dementia than in patients without dementia [START_REF] Baker | Hip fracture risk and subsequent mortality among Alzheimer's disease patients in the United Kingdom, 1988-2007[END_REF][START_REF] Smith | Pre-operative indicators for mortality following hip fracture surgery: a systematic review and meta-analysis[END_REF][START_REF] Diamantopoulos | Predictors of Short-and Long-Term Mortality in Males and Females with Hip Fracture -A Prospective Observational Cohort Study[END_REF][START_REF] Hershkovitz | Factors affecting mortality of frail hip-fractured elderly patients[END_REF]. Among the patients who experienced a HF, 24 to 27% of patients with dementia and 10 to 14% of patients without dementia did not survive more than six months after the occurrence of a HF [START_REF] Hannan | Mortality and Locomotion 6 Months After Hospitalization for Hip Fracture: Risk Factors and Risk-Adjusted Hospital Outcomes[END_REF][START_REF] Baker | Hip fracture risk and subsequent mortality among Alzheimer's disease patients in the United Kingdom, 1988-2007[END_REF].

Because most of HF occur in older patients, the prevalence of comorbid conditions and frailty is high among this population [START_REF] Clerencia-Sierra | Multimorbidity Patterns in Hospitalized Older Patients: Associations among Chronic Diseases and Geriatric Syndromes[END_REF][START_REF] Fried | Frailty in older adults: evidence for a phenotype[END_REF]. They are at high risk of developing complications such as delirium, infection and drug related problems. Recently, there has been an increasing interest for the development of collaborations between orthopedic surgeons, anesthesiologists and geriatricians. Hospitals and health systems have implemented ortho-geriatric care to improve patient outcomes, with conflicting results [START_REF] Prestmo | Comprehensive geriatric care for patients with hip fractures: a prospective, randomised, controlled trial[END_REF][START_REF] Stenvall | A multidisciplinary, multifactorial intervention program reduces postoperative falls and injuries after femoral neck fracture[END_REF][START_REF] Huusko | Randomised, clinically controlled trial of intensive geriatric rehabilitation in patients with hip fracture: subgroup analysis of patients with dementia[END_REF][START_REF] Adunsky | A comparative study of rehabilitation outcomes of elderly hip fracture patients: the advantage of a comprehensive orthogeriatric approach[END_REF][START_REF] Friedman | Impact of a Comanaged Geriatric Fracture Center on Short-term Hip Fracture Outcomes[END_REF][START_REF] Kammerlander | Ortho-geriatric service--a literature review comparing different models[END_REF][START_REF] Deschodt | Effect of an Inpatient Geriatric Consultation Team on Functional Outcome, Mortality, Institutionalization, and Readmission Rate in Older Adults with Hip Fracture: a Controlled Trial[END_REF][START_REF] Stenvall | A Multidisciplinary Intervention Program Improved the Outcome After Hip Fracture for People with Dementia-Subgroup Analyses of a Randomized Controlled Trial[END_REF][START_REF] Wagner | Comparison of complications and length of hospital stay between orthopedic and orthogeriatric treatment in elderly patients with a hip fracture[END_REF][START_REF] Grigoryan | Ortho-Geriatric Care Models and Outcomes in Hip Fracture Patients: A Systematic Review and Meta-Analysis[END_REF].

In a previous study [START_REF] Boddaert | Postoperative Admission to a Dedicated Geriatric Unit Decreases Mortality in Elderly Patients with Hip Fracture[END_REF], we demonstrated that early admission to a dedicated geriatric unit improved 6-month mortality and morbidity in elderly patients with HF. Our study did not focus on patients with dementia (38% of our population). However, the question of the benefit of a dedicated geriatric unit post HF in patients with dementia is still unexplored.

Our hypothesis was that, whatever the cognitive status before surgery, all patients admitted with hip fracture in an orthogeriatric-dedicated care pathway, with staff trained to manage patients with dementia, would have the same prognosis at 6 months. Our main objective was to compare mortality rate at 6 months regarding the cognitive status before surgery. Secondary outcomes were to compare: in-hospital complications, including delirium; the risk of new institutionalization and the ability to walk at 6 months, according to the cognitive status before surgery.

Materials and Methods

This study was approved by the hospital ethics committee (CPP Ile de France VI, Paris, France), and informed consent was waived, as the study was observational. The database was declared to the French National Commission on Computing and Liberty (CNIL, Paris, France).

Study population

From July 2009 to December 2015, all patients admitted to our emergency department (ED) were evaluated for eligibility. Detailed methodology including the opening of a new geriatric unit (UPOG: Unit for Peri-Operative Geriatric care) has been previously reported [START_REF] Boddaert | Postoperative Admission to a Dedicated Geriatric Unit Decreases Mortality in Elderly Patients with Hip Fracture[END_REF], and some of these patients were included in previous studies [START_REF] Boddaert | Postoperative Admission to a Dedicated Geriatric Unit Decreases Mortality in Elderly Patients with Hip Fracture[END_REF][START_REF] Vallet | Prognostic Value of Serum Procalcitonin After Orthopedic Surgery in the Elderly Population[END_REF]. Patients were included if their primary admission was due to HF and if they were aged over 70. Patients were not included if they were admitted with multiple fractures, a metastatic fracture or a fracture complicated by a previous hip prosthesis or osteosynthesis.

Their cognitive status before surgery was obtained from the patients themselves, family members, caregivers and from their general practitioners who were systematically contacted (phone call), and determined as follows:

1-Patients with dementia (DP): with a previous diagnosis of dementia by a geriatrician or a neurologist using internationally recognized criteria and DSM-IV criteria [START_REF] Jackson | Screening for dementia in general hospital inpatients: a systematic review and meta-analysis of available instruments[END_REF][START_REF] Ferri | Alzheimer's Disease International (2005) Global prevalence of dementia: a Delphi consensus study[END_REF][START_REF] Sampson | Dementia in the acute hospital: prospective cohort study of prevalence and mortality[END_REF][START_REF]Dementia, a Public Health Priority[END_REF]. These patients had had a cognitive screening with a neuropsychologist using screening instruments and a cerebral imaging. Some of them were treated by specific treatments (anticholinesterase inhibitors or antiglutamate) that only neurologists, psychiatrists and geriatricians are authorized to prescribe in France.

2-Patients without dementia (NDP): with no known previous cognitive impairment, without memory or cognitive complaint before admission to our hospital (according to family and to general practitioner), without specific treatment and still complaint-free at 6 months. Because they were not included in DSM-IV criteria that defined dementia, it is to note that these patients did not have a complete cognitive assessment with a neuropsychologist before or after the hospitalization.

3-Patients with cognitive status not determined (CSND): with a history of previous cognitive impairment without cognitive evaluation or conclusive cognitive evaluation (unexplored or unlabeled). As detailed in the introduction, there are a significant proportion of patients under diagnosed [START_REF] Jackson | Screening for dementia in general hospital inpatients: a systematic review and meta-analysis of available instruments[END_REF][START_REF] Sampson | Dementia in the acute hospital: prospective cohort study of prevalence and mortality[END_REF]. In this group, patients possibly had dementia, mild cognitive impairment (MCI) or other conditions with cognitive consequences. Without an accurate diagnosis, we have chosen to create this third group of patients.

Design study

The data were prospectively entered in the database, including age, sex, own home or nursing home, living conditions, walking ability, medical history, type of fracture and surgical treatment, time-to-surgery (delay) and duration of surgery. Co-morbidity severity was assessed using the Cumulative Illness Rating Scale (CIRS-G) [START_REF] Linn | Cumulative illness rating scale[END_REF] in which co-occurring medical conditions are weighted from 0 to 4 in 13 main systems. Pre-hospitalization functional status was assessed using the Activities of Daily Living (ADL) scale [START_REF] Katz | Assessing self-maintenance: activities of daily living, mobility, and instrumental activities of daily living[END_REF]. We recorded preoperative hemoglobin level and its lowest value during the hospitalization, serum creatinine and estimated creatinine clearance using the Cockcroft formulae. All complications during the hospitalization were recorded, including delirium using the Confusion Assessment Method scale [START_REF] Inouye | Delirium in elderly people[END_REF] (assessment on arrival and then once a day consistently), use of physical restraints, stool impaction, urinary retention requiring drainage, morphine administration, pressure ulcer, infection, phlebitis or pulmonary embolism, blood transfusion, cardiac insufficiency (i.e. acute cardiac failure or acute pulmonary edema), and admission into an intensive care unit (ICU). To prevent and manage the occurrence of possible delirium, we used the recommendations proposed by Inouye et al. (non-pharmacological and pharmacological acute treatment strategies) [START_REF] Inouye | Delirium in elderly people[END_REF][START_REF] Fong | Delirium accelerates cognitive decline in Alzheimer disease[END_REF]. Management strategy focused on early mobilization with the aim of chair-sitting and walking (first steps) within 24 and 48 hours.

Patients were studied until death or 6 months after admission, for survival, walking ability (outdoors, with or without assistance) and new institutionalization. Surviving patients or their relatives were evaluated in the usual ambulatory clinic assessment, or contacted and interviewed by telephone; ADL scale and MMSE (Mini-Mental State Examination) were usually done [START_REF] Jackson | Screening for dementia in general hospital inpatients: a systematic review and meta-analysis of available instruments[END_REF][START_REF] Sampson | Dementia in the acute hospital: prospective cohort study of prevalence and mortality[END_REF]. Missing patients were tracked through health care providers, particularly general practitioners, or any identified acquaintances. The primary endpoint was 6-month mortality and secondary endpoints were i) 6-month functional outcome including new institutionalization and ability to walk ii) postoperative complications including delirium. Our study compared the 3 groups of patients, in pairs: patients with dementia (DP), patients without dementia (NDP) and patients with cognitive status not determined (CSND).

Statistical analysis

Data are presented as mean ± SD, median [25-75 interquartile] for non-Gaussian variables, or number (percentages). Comparisons between 3 groups were performed using a Kruskal Wallis test for quantitative variables, followed by a Dunn test when a significant difference was found; and Fisher's exact method for qualitative variables. Survival and the risk of a new institutionalization in the 3 groups of patients were estimated by a multivariate logistic regression analysis and for survival by the Kaplan-Meier method too (differences were assessed by the log-rank test) adjusted for the factors known in the published literature [START_REF] Abrahamsen | Excess mortality following hip fracture: a systematic epidemiological review[END_REF][START_REF] Baker | Hip fracture risk and subsequent mortality among Alzheimer's disease patients in the United Kingdom, 1988-2007[END_REF][START_REF] Smith | Pre-operative indicators for mortality following hip fracture surgery: a systematic review and meta-analysis[END_REF][START_REF] Diamantopoulos | Predictors of Short-and Long-Term Mortality in Males and Females with Hip Fracture -A Prospective Observational Cohort Study[END_REF][START_REF] Hershkovitz | Factors affecting mortality of frail hip-fractured elderly patients[END_REF][START_REF] Adunsky | A comparative study of rehabilitation outcomes of elderly hip fracture patients: the advantage of a comprehensive orthogeriatric approach[END_REF][START_REF] Boddaert | Postoperative Admission to a Dedicated Geriatric Unit Decreases Mortality in Elderly Patients with Hip Fracture[END_REF][START_REF] Liang | Interrelationship of Postoperative Delirium and Cognitive Impairment and Their Impact on the Functional Status in Older Patients Undergoing Orthopaedic Surgery: A Prospective Cohort Study[END_REF][START_REF] Bellelli | Duration of postoperative delirium is an independent predictor of 6-month mortality in older adults after hip fracture[END_REF] (semi-parsimonious method): age (< 80,81-85, 86-90, > 90), sex (female as reference), comorbidities (CIRS-G, ≤ or > 8) [START_REF] Linn | Cumulative illness rating scale[END_REF], number of drugs per day (< or ≥ 5), prefracture ADL6 (≤ 5 or = 6) [START_REF] Katz | Assessing self-maintenance: activities of daily living, mobility, and instrumental activities of daily living[END_REF], the ability to walk without assistance before surgery, time-tosurgery (≤ or > 48 hours) and the occurrence of delirium during hospitalization. We tested the association of survival / new institutionalization and cognitive status before surgery in UPOG by calculating the odds ratio (OR) or Hazard ratio (HR) and their 95 percent confidence interval (CI) with these prognostic variables. There was 11 missing data (lost of follow-up) for death at 6 months and new institutionalization at 6 months; we excluded these patients from the main analysis (1,7%).

To assess the weight of dementia in some intra-hospital complications (delirium), admission to rehabilitation care after hospitalization, a multivariate logistic regression analysis was performed and adjusted for the same factors. All P values were two-sided and P < 0.05 was considered significant. R software 3.3.1 was used for statistical analyses (www.cran.rproject.org last date accessed August 10, 2016).

Results

Characteristics of the population and the 3 groups of patients before HF

Among the 711 patients with HF admitted to the ED, 650 were included (mean age 86 ± 6 years; 495 (76%) female, median CIRS-G: 9 [6 -12]): 168 patients with dementia (DP: 26%), 400 patients without dementia (NDP: 61%) and 82 with cognitive status not determined (CSND: 13%) (Figure 1).

Cardiovascular comorbidities were more prevalent (Table 1), 97% of patients previously walked, with assistance in 51% of cases (cane, walking frame, human assistance). Baseline characteristics are presented in Table 1.

Among patients with a previous diagnosis of dementia, 59% (n = 99) of them had a diagnosis of Alzheimer's disease, 9% (n = 15) of them had a diagnosis of vascular dementia, 17% (n = 28) of them had a diagnosis of Alzheimer's disease and vascular dementia, 7% (n = 11) of them had a diagnosis of dementia associated with Parkinson's disease, 8% (n = 13) of them had a Lewy body disease, 1 patients suffered from corticobasal degeneration and 1 from multisystem atrophy. Among CSND patients, 20% of them (n = 19) had a cognitive assessment before HF without a diagnosis. Reported by family and / or the general practitioner and / or the patient, memory complaint was the main symptom in 68% (n = 56) of cases, behavioral disorders (aggressiveness or apathy) in 5% (n = 4) of cases, and both in 27% (n = 22) of cases.

DP and CSND patients differed from NDP patients (table 1): they were older, had more comorbidities and were less autonomous : they had a pre-fracture ADL 6 lower than NDP patients, they were more often institutionalized, and, when they lived at home, DP patients needed more assistance. In the same way, CSND patients differed from DP patients (table 1): they were older, they had a pre-fracture ADL6 higher than DP patients, they were less often institutionalized and, when they lived at home, they needed less often assistance. DP patients were more at risk of repeated falls. There was no significant difference between the 3 groups considering care (type of surgery, time to surgery, time to the UPOG, duration of surgery).

Hospitalization: complications and discharge

Other post-operative complications are described in Table 2. During hospitalization, 39% of patients suffered from delirium. Delirium appeared more often in DP (n = 99, 59%) and CSND (n = 50, 61%) patients than in NDP patients (n = 105, 26%), without difference between DP and CSND patients. DP patients had a OR that was 3.12 (95% CI[1.97 -4.96]) times higher that NDP patients; CSND patients had a OR that was 3.30 (95% CI[1.87 -5.80]) times higher that NDP patients (p < 0.001) after controlling for potential confounders (table

3).

At discharge from the hospital, they were no difference in walking (few steps) between the 3 groups, but DP patients less frequently benefited from rehabilitation stay than NDP and CSND patients (respectively: 67%, 84%, 80%). Nevertheless, after controlling for potential confounders (table 3), no difference was found between the 3 groups.

Mortality rate at 6 month

At 6 month, 15% of patients were dead (table 2). In univariate analysis, no difference was found between DP/NDP patients (16% vs 14%) and CSND/DP patients (22% vs 16%) for the 6-months mortality rate. There was a significant difference between CSND patients (22%) and NDP patients (14%) (Table 2). After controlling for potential confounders (multivariate logistic regression analysis and cox regression analysis), no difference was found (Table 3,

Functional outcomes at 6 month (walk and new institutionalization)

Considering functional outcome, 92% of the patients were walking after 6 months (63% with assistance). No difference was found between 3 groups for walking with assistance: 64% of NDP, 61% of DP and 62% of CSND patients (Table 2).

No difference was found between CSND and DP patients for new institutionalization at 6 months in univariate analysis (23% vs 19%). In contrary, DP patients were more frequently newly institutionalized than NDP patients at 6 months (19% vs 8%), as CSND patients compared to NDP patients at 6 months (23% vs 8%) (Table 2). After controlling for potential confounders (multivariate logistic regression analysis, Table 3), the difference still remains for DP patients vs NDP patients (OR=2.56 95% CI [1.36 -4.86], p=0.003) and CSND patients vs NDP patients (OR=2.91 95% CI [1.37 -6.07], p=0.004).

DP and CSND patients had lower ADL score at 6 months that NDP patients (respectively 2 [1 -4], 3[2 -5] and 5 [3 -6]), and the difference was also significant between CSND and DP patients (table 2).

At 6 month, 17% of CSND patients (14 patients) had had a neurocognitive assessment with a diagnosis of Alzheimer's diseases (n=4), vascular dementia (n=3), Alzheimer's disease and vascular dementia (n=1), Lewy body disease (n=1), supranuclear paralysis (n=2), and 2 without a diagnosis. Considering patients without cognitive assessment, 17 had a MMSE score < 11, 15 a MMSE score > 25, 5 patients did not speak french, 3 refused any assessment.

For 28 patients, we did not have cognitive data at 6 months.

Discussion

To our knowledge, this is the first study considering the association between cognitive status before surgery and mortality and functional outcomes when geriatricians, together with other specialists in an orthogeriatric dedicated care pathway, manage patients with HF. Interestingly, and despite a higher risk of new institutionalization for patients with dementia and cognitive status not determined, we report a lack of significant difference in 6-month mortality and walking ability between the 3 groups of patients (DP, NDP and CSND).

Outcomes

These results differ from the published literature in the field where mortality and functional recovery after HF in patients with dementia appear to be worse compared to patients without dementia [START_REF] Baker | Hip fracture risk and subsequent mortality among Alzheimer's disease patients in the United Kingdom, 1988-2007[END_REF][START_REF] Smith | Pre-operative indicators for mortality following hip fracture surgery: a systematic review and meta-analysis[END_REF][START_REF] Diamantopoulos | Predictors of Short-and Long-Term Mortality in Males and Females with Hip Fracture -A Prospective Observational Cohort Study[END_REF][START_REF] Hershkovitz | Factors affecting mortality of frail hip-fractured elderly patients[END_REF] and where patients with dementia benefited less often from rehabilitation services, whose role in the recovery of autonomy and mobility has been repeatedly demonstrated [START_REF] Mcgilton | Evaluation of patient-centered rehabilitation model targeting older persons with a hip fracture, including those with cognitive impairment[END_REF][START_REF] Al-Ani | Does rehabilitation matter in patients with femoral neck fracture and cognitive impairment? A prospective study of 246 patients[END_REF]. In our population, the mortality rate at 6 months in patients with dementia (16%) or patients with cognitive status not determined (22%) was lower that the rate reported in the literature (24 to 27%) [START_REF] Hannan | Mortality and Locomotion 6 Months After Hospitalization for Hip Fracture: Risk Factors and Risk-Adjusted Hospital Outcomes[END_REF][START_REF] Baker | Hip fracture risk and subsequent mortality among Alzheimer's disease patients in the United Kingdom, 1988-2007[END_REF]. These results suggest, in agreement with other published studies investigating the role of an orthogeriatric assessment [START_REF] Stenvall | A multidisciplinary, multifactorial intervention program reduces postoperative falls and injuries after femoral neck fracture[END_REF][START_REF] Huusko | Randomised, clinically controlled trial of intensive geriatric rehabilitation in patients with hip fracture: subgroup analysis of patients with dementia[END_REF][START_REF] Adunsky | A comparative study of rehabilitation outcomes of elderly hip fracture patients: the advantage of a comprehensive orthogeriatric approach[END_REF][START_REF] Friedman | Impact of a Comanaged Geriatric Fracture Center on Short-term Hip Fracture Outcomes[END_REF][START_REF] Kammerlander | Ortho-geriatric service--a literature review comparing different models[END_REF][START_REF] Deschodt | Effect of an Inpatient Geriatric Consultation Team on Functional Outcome, Mortality, Institutionalization, and Readmission Rate in Older Adults with Hip Fracture: a Controlled Trial[END_REF][START_REF] Stenvall | A Multidisciplinary Intervention Program Improved the Outcome After Hip Fracture for People with Dementia-Subgroup Analyses of a Randomized Controlled Trial[END_REF][START_REF] Wagner | Comparison of complications and length of hospital stay between orthopedic and orthogeriatric treatment in elderly patients with a hip fracture[END_REF][START_REF] Grigoryan | Ortho-Geriatric Care Models and Outcomes in Hip Fracture Patients: A Systematic Review and Meta-Analysis[END_REF], that the management of elderly people with HF should systematically consider a geriatric expertise. Indeed, (1) the management of multimorbidity and frailty in the elderly; (2) a quick surgery and an appropriate anesthesia protocol for the elderly; (3) a prevention of common post-operative complications such as delirium; (4) an assessment of the risk-benefit ratio of treatments (especially analgesics); (5) a management strategy focused on early mobilization with the aim of chair-sitting and walking (first steps) within 24 and 48 hours and (6) an access for all patients (whatever their cognitive status) to rehabilitation care, are all necessary conditions in a dedicated orthogeriatric unit for a reduction of mortality and the resumption of a rapid autonomy, especially for patients with dementia.

To prevent and manage the occurrence of possible delirium (avoidable with a 30 % risk reduction when using a specialized geriatric intervention [START_REF] Fong | Delirium accelerates cognitive decline in Alzheimer disease[END_REF][START_REF] Marcantonio | Reducing Delirium After Hip Fracture: A Randomized Trial[END_REF][START_REF] Deschodt | Preventing Delirium in Older Adults with Recent Hip Fracture Through Multidisciplinary Geriatric Consultation[END_REF]), we used the recommendations proposed by Inouye et al [START_REF] Inouye | Delirium in elderly people[END_REF][START_REF] Fong | Delirium accelerates cognitive decline in Alzheimer disease[END_REF] every day of hospitalization. Delirium is common after hip fracture surgery (occurring in 35% to 65% of patients) [START_REF] Marcantonio | Reducing Delirium After Hip Fracture: A Randomized Trial[END_REF], frequently associated with preexisting cognitive impairment and it is predictive of functional decline, institutionalization, and mortality [START_REF] Liang | Interrelationship of Postoperative Delirium and Cognitive Impairment and Their Impact on the Functional Status in Older Patients Undergoing Orthopaedic Surgery: A Prospective Cohort Study[END_REF][START_REF] Marcantonio | Reducing Delirium After Hip Fracture: A Randomized Trial[END_REF]: each day of delirium increased the risk of death within 6 months by 17% [START_REF] Bellelli | Duration of postoperative delirium is an independent predictor of 6-month mortality in older adults after hip fracture[END_REF].

We show that dementia was not associated with the time-to-surgery (delay), suggesting that all actors of the perioperative period, particularly emergency physicians, orthopedic surgeons and anesthetists, managed these patients with the same accuracy.

Despite good results for mortality rate at 6 months and a lack of difference in 6-month walking ability (after taking into account their pre-existing conditions), DP and CSND patients were significantly more prone to new institutionalization compared to NDP patients.

One of the main risk factors in our multivariate logistic regression was pre-fracture walking ability: patients who needed assistance to walk before surgery (more common in patients with dementia) had 2 times more likely to be newly institutionalized than the others. Despite an early geriatric intervention, HF remains a serious condition that precipitates time to institutionalization and this is probably ahead of the fracture time that we can act to prevent future loss of autonomy.

Although this study cannot conclude to a causal link, our results suggests that an early implementation of a geriatric expertise in the management of hip fractured patients leads to dementia becoming comorbidity among others, and no longer a particularly serious comorbidity.

Why we choose to create the group "CSND patients":

We deliberately chose to create a group of CSND patients in order to be able to make effective comparisons because according to published literature, cognitive impairment remains under diagnosed [START_REF] Sampson | Dementia in the acute hospital: prospective cohort study of prevalence and mortality[END_REF], and because the situation of undetermined cognitive status of patients in perioperative care is frequent. CSND patients, with no diagnosis of dementia, would have been ranked among the patients without dementia and so, we would have been wrong to compare these two populations (potential differences would have been reduced).

Indeed, despite missing data, this group was closer to DP patients (than NDP patients) since 17% of these patients had a diagnosis of dementia, and 20% of them were too severe to be explored according to MMSE score at 6 months. However, they were less often institutionalized before HF, probably due to a lack of medical care for a cognitive diagnosis that was not previously considered, or because they had less severe cognitive deterioration.

Finally, CSND group was a heterogeneous group with patients with too severe cognitive disorder to be assessed, patients with early stage of cognitive disorder without assessment and patients without any conclusive cognitive information.

We obtained informations about cognitive disorder from patients, proxy, family and general practitioners because the use of scales is not always appropriate to the acute phase of hospitalization [START_REF] Prestmo | Comprehensive geriatric care for patients with hip fractures: a prospective, randomised, controlled trial[END_REF]. We do think that our groups were well defined, considering the time of management of these patients in the acute and preoperative period before HF surgery, and differences between the 3 groups (especially DP/CSND vs NDP) have strengthened our inclusion criteria and group constitution:

-DP patients were less autonomous (ADL 3 [START_REF] Johnell | An estimate of the worldwide prevalence and disability associated with osteoporotic fractures[END_REF][START_REF] Prestmo | Comprehensive geriatric care for patients with hip fractures: a prospective, randomised, controlled trial[END_REF][START_REF] Gullberg | World-wide projections for hip fracture[END_REF][START_REF] Stenvall | A multidisciplinary, multifactorial intervention program reduces postoperative falls and injuries after femoral neck fracture[END_REF]); they often lived in institutions (40%) and suffered more often from postoperative delirium (56%); -NDP patients were more autonomous (ADL 6 [START_REF] Johnell | The socioeconomic burden of fractures: today and in the 21st century[END_REF][START_REF] Abrahamsen | Excess mortality following hip fracture: a systematic epidemiological review[END_REF]), they rarely lived in institutions (4%), and they suffered less often from postoperative delirium (26%).

Limits

This study had some limitations. It was an observational, single center study. Nonetheless, mono-centric studies ensure a high level of homogeneity in the way that data are collected and analyzed (we only had 11 patients lost to follow up). Although this study cannot conclude to a causal link, the impact of our orthogeriatric-dedicated unit on HF mortality in the population of patients with dementia should have been ideally studied by an interventional study (orthogeriatric-dedicated unit versus standard procedure). But, we previously published a study [START_REF] Boddaert | Postoperative Admission to a Dedicated Geriatric Unit Decreases Mortality in Elderly Patients with Hip Fracture[END_REF], showing that early admission to a dedicated geriatric unit improved 6-month mortality and morbidity in elderly patients with HF. After completion of this study [START_REF] Boddaert | Postoperative Admission to a Dedicated Geriatric Unit Decreases Mortality in Elderly Patients with Hip Fracture[END_REF], it could be considered not ethical to randomize patients between standard procedure and orthogeriatric-dedicated unit.

We did not have information about the degree of dementia and the date of diagnosis, known to be prognostic factors [START_REF] Weller | Hip fractures and Alzheimer's disease in elderly institutionalized Canadians[END_REF][START_REF] Baker | Hip fracture risk and subsequent mortality among Alzheimer's disease patients in the United Kingdom, 1988-2007[END_REF][START_REF] Hershkovitz | Factors affecting mortality of frail hip-fractured elderly patients[END_REF][START_REF] Stenvall | A Multidisciplinary Intervention Program Improved the Outcome After Hip Fracture for People with Dementia-Subgroup Analyses of a Randomized Controlled Trial[END_REF][START_REF] Marcantonio | Reducing Delirium After Hip Fracture: A Randomized Trial[END_REF]. Because it was a retrospective study, we did not have systematic data on cognitive assessment at 6 months to better define CSND patients.

There is growing evidence from multiple studies that a similar benefit may be obtained elsewhere [START_REF] Prestmo | Comprehensive geriatric care for patients with hip fractures: a prospective, randomised, controlled trial[END_REF][START_REF] Sabharwal | Orthogeriatrics in the management of frail older patients with a fragility fracture[END_REF]. On these grounds, we anticipate that the deployment of new UPOG units in France as from 2014 will hopefully confirm these results, refine them and help find new ways to improve the outcome of patients facing HF surgery with or without cognitive disorders.

In conclusion, our study provides new information on the association between cognitive status before surgery and global outcomes. When cared for in a dedicated orthogeriatric care pathway, the global prognosis (mortality and functional outcome) of patients with dementia seems to be the same as patients without dementia.  P logrank: patients with dementia vs patient without dementia: 0.18; C Index = 0.60  P logrank: patients with dementia vs cognitive status not determined: 0.29; C index = 0.70  P logrank: cognitive status not determined vs patient without dementia: 0.62; C Index = 0.58

Figure 2 ,

 2 Figure 2, Appendix 1-2-3): DP vs NDP patients (HR=0.67 95% CI [0.38 -1.20], p=0.19),

Figure 1 :

 1 Figure 1: Flow Chart

Figure 2 :

 2 Figure 2: Survival curves for mortality adjusted for age, sex, Cumulative Illness Rating Scale, number of drugs per day, pre-fracture ADL6, walking before fracture with assistance, time to surgery, delirium and cognitive status (calculated with a Cox regression analysis).

Table 2 . Post-operative complications and 6-month outcomes in the 3 groups of patients: without dementia (NDP), with cognitive status not determined (CSND) and with dementia (DP)

 2

			All patients	NDP	DP	CSND
			N = 650	N = 400	N = 168	N = 82
	Time to first sitting (days)	1 [1 -2]	1 [1 -2]	1 [1 -2]	1 [1 -3] $
	Time to first walking (days)	2 [1 -4]	2 [1 -4]	2 [1 -3]	3 [2 -4]** $
	Post-operative complications
	Delirium	254 (39)	105 (26)	99 (59)**	50 (61)**
	Pain	621 (96)	384 (96)	156 (93)	81 (99) $
	Morphine administration	586 (90)	359 (90)	153 (91)	74 (90)
	Min. in-hosp hemoglobin (g/dL -1 ) 9.2 ± 1.4	9.2 ± 1.4	9.3 ± 1.4	9.1 ± 1.6
	In-hospital transfusion	357 (53)	223 (56)	87 (52)	47 (57)
	Total packed RBC per patient	1 [0 -2]	1 [0 -2]	1 [0 -2]	1 [0 -2]
	Stool impaction	277 (43)	164 (41)	78 (46)	35 (43)
	Urinary retention	168 (26)	108 (27)	39 (23)	21 (26)
	Pressure ulcer	79 (12)	47 (12)	20 (12)	12 (15)
	Acute heart failure	83 (13)	54 (14)	13 (8)	16 (20) $
	Acute coronary syndrome	68 (10)	40 (10)	17 (10)	11 (13)
	Acute atrial fibrillation	57 (9)	34 (8)	16 (10)	7 (9)
	Infection	121 (19)	68 (17)	37 (22)	16 (20)
	Acute thromboembolism disease	29 (5)	16 (4)	7 (4)	6 (7)
	Admission into ICU	31 (5)	23 (6)	3 (2)**	5 (6)
	LOS (days)	11 [9 -15]	11 [9 -15]	11 [8 -14]	13 [10 -17]** $
	Death during hospitalization	23 (4)	16 (4)	2 (1)	5 (6) $
	Walking at discharge	568 (88)	351 (89)	149 (89)	68 (84)
	Walking with assistance at
	discharge	546 (86)	344 (88)	138 (83)	64 (84)**
	Admission to rehabilitation care	514 (79)	335 (84)	113 (67)**	66 (80) $
	Home return a	102 (16)	41 (10)	51 (30)**	10 (12) $
	After 6 months
	Walk with assistance (MD = 26)	331 (63)	209 (64)	85 (61)	37 (62)
	ADL score (MD = 323)	4 [2 -5]	5 [3 -6]	2 [1 -4]**	3 [2 -5]** $
	Newly institutionalized patients	81 (12)	30 (8)	32 (19)**	10 (23)**
	(MD = 11)
	Death (MD = 11)	97 (15)	53 (14)	26 (16)	18 (22)**
	Home return a (MD = 33)	464 (89)	296 (92)	118 (84)**	50 (85)
		Data are mean ± SD, median [25-75 interquartile], or number (percentage).
		**: Comparison with NDP; $ Comparison with DP = p <0.05: Comparison between 3 groups was performed using the Kruskal
		Wallis test followed by the Dunn test for quantitative variables, and Fisher's exact method for qualitative variables
		ADL: activity daily living; UPOG: post-operative geriatric unit. LOS: length of stay. ICU: Intensive care unit. RBC: red
		blood cell
		MD: Missing data

Table 3 . Multivariate logistic regression analysis predicting the risk of delirium, the opportunity to go to rehabilitation care at discharge, death and new institutionalization at 6 month

 3

	Variables

of drugs per day, reference value < 5

	-Number of drugs per day ≥ 5	0.98 [0.56 -1.75]	0.96
	Pre-fracture ADL6, reference value = 6
	-Pre-fracture ADL ≤ 5	0.89 [0.49 -1.65]	0.72
	Walking

before fracture without assistance, reference value = yes

  CIRS: cumulative illness rating scale; ADL: activity daily living; OR: Odds Ratio AIC : Akaike Information Criterion There was 11 missing data for death at 6 months and new institutionalization at 6 months; we excluded these patients from the analysis (1,7%).

	-Walking before fracture with assistance	2.00 [1.14 -3.60]	0.02*
	Time to surgery, reference value ≤ 48 hours
	-Delay > 48 hours	0.55 [0.22 -1.20]	0.16
	Delirium, reference value = no
	-Delirium = Yes	1.15 [0.67 -1.97]	0.60
	Cognitive status, reference value = Without dementia
	-Patients with dementia	2.56 [1.36 -4.86]	0.003*
	-Patients with cognitive status not determined	2.91 [1.37 -6.07]	0.004*
	CI: confidence interval;

Funding: This study was supported only by institutional sources.

Conflicts of interest:

The authors declare that they have no conflict of interest.

Acknowledgments:

We thank Mrs Diane Cohen for her valuable English proofreading.