Participants and baseline data

Baseline data of the 152 enrolled patients after hip fracture are shown in Table 1. At baseline, 65 patients (43%) were malnourished or at risk of malnutrition, and 87 patients (57%) were well-nourished. Of all patients, 85% lived independently at home before the fracture, with no significant differences by nutritional status. Mean age of patients malnourished or at risk was 78.3 years, vs. 74.9y in well-nourished patients (between-group difference: p = 0.03). Medical data indicated a high prevalence of comorbidities: in the total group, 55% had a history of cardiovascular disease, 20% had diabetes, 17% a disease of the nervous system, 11% osteoporosis, and 36% other diseases of the musculoskeletal system and/or connective tissue. Patients malnourished or at risk had a significantly higher prevalence of heart diseases, osteoporosis, COPD and asthma, gastro-intestinal disorders, and “other diseases of the musculoskeletal system and connective tissue” (ICD10: M00–99 except osteoporosis); they also tended to have a higher ASA score (p = 0.052). Fracture type, type of surgery and laboratory parameters at baseline were similar in subjects of different nutritional status categories. The average time between admission and surgery was 0.72 days (~ 20 h), and time between surgery and baseline assessment was 3.2 days, without significant difference between the nutritional categories.

Physical measures of nutritional status at baseline were highly significantly different between the nutritional status categories: patients who were malnourished or at risk of malnutrition weighed ~8.7 kg less than well-nourished patients (Table 1). This weight difference was due to both difference in fat mass (~4.9 kg) and in fat-free mass (~4.0 kg). Although weight loss in the 6 months preceding the fracture tended to be higher in patients malnourished or at risk than in well-nourished patients (− 1.8 kg vs. -0.2 kg, p = 0.058), this recent weight loss accounted for less than 20% of the total weight deficit in patients malnourished or at risk (i.e. -1.6 kg difference in weight loss out of the total weight deficit of − 8.7 kg). Patients malnourished or at risk had also significantly lower BMI, mid-upper arm circumference, mid-arm muscle area and handgrip strength (Table 1) than well-nourished patients.

Moreover, patients malnourished or at risk had significantly more physical restrictions (GARS-ADL, GARS-IADL and GARS-Total), a worse cognitive state (MMSE), a worse score on depression (HADS) as well as on most health-related quality of life indicators as measured by EuroQoL (Table 1).

Short-term clinical outcome

As shown in Table 2, patients who were malnourished or at risk of malnutrition had a shorter duration of surgery (64 vs. 71 min, adjusted difference: − 16 min, 95% CI-29 − 4 min, p = 0.010) and lost less blood during surgery (306 vs. 382 ml, adj. difference - 97 ml, 95% CI -172 − 22 ml, p = 0.012).

Table 2 Prognostic value of nutritional status for clinical outcome after hip fracture

Post-operative complications occurred in 55.4% of patients malnourished or at-risk compared to 35.6% of well-nourished patients (adj. OR 2.00, 95% CI 1.01–3.98, p = 0.047). The mean number of complications per patient was 0.85 vs. 0.45 (adj. Difference 0.34, 95% CI 0.07–0.62, p = 0.016). OR’s for specific subtypes of complications were also consistently elevated but none reached statistical significance due to low frequency of specific complications. Pressure ulcers (grade 2, 3 or 4) occurred in only one well-nourished patient vs. five patients malnourished or at risk (OR 7.21, p = 0.104). When we split up the study population into three MNA-levels (malnourished vs. at-risk vs. well-nourished), the association was statistically significant: OR per MNA-level: 5.52 (95% CI 1.24–24.4, p = 0.025), implying a (5.52)2 = 30.4-fold odds (i.e. risk) of pressure ulcers in malnourished patients relative to well-nourished patients.

Two malnourished or at-risk patients and one well-nourished patient died in hospital, and one patient each died during rehabilitation, without significant difference between the groups (p = 0.944 and 0.847, respectively).

Out of 58 patients malnourished or at risk who before the hip fracture had lived at home, 27.6% were directly discharged back to their home from hospital, as compared to 52.4% of 84 home-dwelling well-nourished patients (adj. OR 0.41, 95% CI 0.18–0.98, p = 0.044). After rehabilitation, the proportion of home-dwelling patients discharged back to their home was 85.2% vs. 91.6% (p = 0.511), indicating that after rehabilitation the vast majority of both groups in our study population returned to their homes.

Overall, three times as many patients malnourished or at risk were readmitted to hospital one or more times after discharge (29.2%) compared to well-nourished patients (9.2%; adj. OR 4.59, 95% CI 1.70–12.4, p = 0.003); the average number of readmissions was almost four times higher (0.43 vs. 0.11, adj. difference 0.34, 95% CI 0.15–0.54, p = 0.001). This analysis was repeated excluding patients (n = 10) who had been readmitted for reasons directly related to hip fracture surgery (n = 5 malnourished / at risk, n = 5 well-nourished). In the 17 patients readmitted for reasons unrelated to hip fracture surgery (e.g. Crohn’s disease, diabetic foot, myocardial infarction, respiratory insufficiency), 14 (23.3%) were malnourished or at risk vs. 3 (3.7%) well-nourished (adj. OR 10.1, 95% CI 2.55–39.6, p = 0.001).

Length of stay

Kaplan Meier plots of length of stay in hospital and rehabilitation clinics are shown in Fig. 2A - D. Length of primary hospital stay (Fig. 2A) was not significantly different by nutritional status. However, total length of hospital stay including readmissions (Fig. 2B) was longer both in malnourished patients (adj. HR of being discharged from hospital: 0.44, 95% CI 0.22–0.90, p = 0.023) and patients at risk (adj. HR: 0.68, 95% CI 0.47–0.97, p = 0.034; for patients malnourished and at risk combined: adj. HR: 0.63, 96%CI 0.44–0.89, p = 0.008). Malnourished patients also had a significantly longer length of stay in rehabilitation clinics (Fig. 2C, HR 0.41, 95% CI 0.19–0.87, p = 0.020) and overall length of stay (Fig. 2D, HR 0.34, 95% CI 0.16–0.70, p = 0.004). In patients at risk of malnutrition, length of stay in rehabilitation and overall length of stay were not significantly different from well-nourished patients.

Functional outcome, fatigue and quality of life

Functional outcomes at 6 months after hip fracture are shown in Supplementary Table 1. Comparison with Table 1 shows that at 6 months, only cognition and general quality of life (EuroQoL EQ-5D VAS) had improved relative to baseline measurements. By contrast, all other functional outcomes had not fully recovered to pre-fracture values at 6 months after hip fracture. In multivariable analyses, functional outcomes at 6 months were highly significantly associated with their respective baseline values: standardized regression coefficients (comparable with correlations) varied from 0.30–0.83, with p-values mostly < 0.001 (Suppl. Table 1). In contrast, baseline nutritional status was not independently associated with functional recovery except for the EuroQoL subscale of mobility (standardized RC: − 0.182, p = 0.036) and the CIS subscale ‘motivation’ (standardized RC: 0.197, p = 0.045; Suppl. Table 1).

Curves over time (0, 3 and 6 months) of physical disability (GARS) by nutritional status (Fig. 3) show that the three nutritional status categories followed almost parallel trajectories from baseline until 6 months after hip fracture, suggesting that malnourished patients starting at a relatively low level of function retained their relative position throughout the 6-month observation period. The curves show that from 3 to 6 months after hip fracture, physical function partly improved in well-nourished patients and in patients at risk, though not completely back to baseline levels. In contrast, in malnourished patients, curves of GARS IADL (Fig. 3B) and overall physical disability (GARS total, Fig. 3C) showed an absolute deterioration between 3 and 6 months; statistical testing (ANOVA) confirmed a significant difference between the three MNA categories in slope of the curves of GARS IADL (p = 0.006) and GARS total (p = 0.050) from 3 to 6 months.

New fractures at 1 and 5 years after hip fracture

The proportion of patients with one or more new fractures during the first year after hip fracture was 3.1% in patients malnourished or at risk vs. 1.1% in well-nourished patients (adj. OR 1.79, 95% CI 0.14–23.0, p = 0.655, Table 2). After five years, new fractures had occurred in 16.9% of patients malnourished or at risk vs. 16.1% of well-nourished patients (adj. OR 0.87, 95% CI 0.34–2.24, p = 0.769). Specific subtypes of fractures were also unrelated to nutritional status (data not shown). Almost half the total population (n = 73, 48%) had had one or more bone fractures in the past, of whom 20 patients (13%) had ≥2 fractures. In multivariable analyses, of all studied prognostic factors, the number of previous fractures was the only significant predictor of new fractures over 5 years (OR 2.22, 95% CI 1.34–3.68, p = 0.002).

All-cause mortality at 6 months, 1 and 5 years after hip fracture

At 6 months after hip fracture, 12.3% (n = 8) of patients malnourished or at risk had died, compared to 3.4% (n = 3) in well-nourished patients, but the difference did not reach statistical significance (adj OR 3.11, 95% CI 0.55–17.5, p = 0.198, Table 2). At 1 year, mortality was 15.4% in patients malnourished or at risk, compared to 3.4% of well-nourished patients (adj. OR 4.30, 95% CI 0.90–20.6, p = 0.068), and at 5 years, 47.7% in patients malnourished or at risk vs. 19.5% of well-nourished patients (adj. OR 3.94, 95% CI 1.53–10.2, p = 0.005). Survival analysis using Cox regression showed that the adjusted hazard ratio of dying over 5 years after hip fracture was 2.48 (95% CI 1.33–4.59, p = 0.004) in patients malnourished or at risk, relative to well-nourished patients.

As shown in Fig. 4, survival decreased in the order well-nourished > at risk > malnourished. Relative to well-nourished patients, the adjusted HR of dying over 5 years after hip fracture was 3.72 (95% CI 1.41–9.81, p = 0.008) in malnourished patients, and 2.28 (95% CI 1.20–4.34, p = 0.012) in patients at risk of malnutrition.

Fig. 4

Five-year survival in elderly subjects after hip fracture, by nutritional status at baseline (MNA). Overall test of equality of MNA categories: p = 0.008. Malnourished vs. well-nourished: HR 3.72, 95% CI 1.41–9.81, p = 0.008; at risk vs. well-nourished: HR 2.28, 95% CI 1.20–4.34, p = 0.012. P-values were derived from Cox regression, adjusted for age, sex, American Society of Anesthesiologists (ASA) score, and osteoarthritis (see Methods)