Smoking and hip fracture; a study of 3617 cases

Injury, Int. J. Care Injured (2006) 37, 152—156

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Smoking and hip fracture; a study of 3617 cases P. Johnston *, K.S. Gurusamy, M.J. Parker Orthopaedic Department, Peterborough District General Hospital, Thorpe Road, Peterborough PE3 6NA, UK Accepted 1 August 2005

KEYWORDS Hip fractures; Smoking

Summary We analysed the characteristics and outcome for 467 hip fracture patients, who reported that they were currently smoking at the time of admission, against 3150 non-smoking hip fracture patients. Those patients who smoked were younger (72 years versus 81 years mean age), more likely to be male (35.3% versus 19.5%), more mobile and less likely to be living in institutional care (7.5% versus 25.0%). Preoperative outcomes and complication rates were similar, despite the smokers’ relative youth. Mortality at 30 days was similar for the two groups (6.2% versus 7.6%), but lower for the smokers at one year (22.7% versus 27.6%). However, with adjustment for the younger age and sex of these patients, this difference in mortality was not statistically significant. These findings suggest that smoking results in hip fracture occurring at a younger age. Despite this, the outcome for smokers was similar to that for the average hip fracture patient. # 2005 Elsevier Ltd. All rights reserved.

Introduction The association between smoking and cardiorespiratory disease is well-documented.16 A recent review highlighted the adverse effect of smoking on tissue healing following surgery and trauma.6 In vivo studies have demonstrated the microvascular effects of nicotine in reducing tissue perfusion.10 This reversible small-vessel disease may have wider reaching effects if the exposure to nicotine is prolonged, and smoking is implicated as one of the contributory * Corresponding author at: Department of Orthopaedics, Norfolk & Norwich University Hospital, Colney Lane, Norwich NR4 7UY, UK. Tel.: +44 1603 286286; fax: +44 1603 287498. E-mail address: [email protected] (P. Johnston).

factors in osteoporosis15 and therefore fracture occurrence.18 Law and Hackshaw7 reported an increased risk of hip fracture of 17% for those aged 60 who smoked. This increased to 41% at 70 years and 71% at 80 years. One hip fracture in eight was attributed to smoking. Several researchers have looked specifically to see if there is a deleterious effect from smoking on healing after open tibial fractures and in the context of hip or knee elective arthroplasty.1,8 To date, little has been published on the association between smoking and hip fracture, in particular with respect to the surgical management. We have looked at our hip fracture patients to see how the characteristics of patients with a hip fracture who smoke differ from those of the non-smoking hip

0020–1383/$ — see front matter # 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.injury.2005.08.001

Smoking and hip fracture fracture patients. In addition, outcomes for the smoking patients were compared against those for non-smokers to determine if pre-injury cigarette consumption had an adverse effect on predilection for hip fracture or outcome following admission and treatment.

Materials and methods All patients admitted to Peterborough District Hospital with a hip fracture are entered onto the Hip Fracture Database. From July 1989 to March 2003 a total of 3887 patients were admitted for treatment. The database is operated with the appropriate ethical approval. Data collected includes demographics, smoking habits, pre morbid medical and social status, operative data and postoperative information including complications, postoperative mobility and social status and days to death if appropriate. We define smokers as patients who admit to use of at least one cigarette daily regularly at the time of admission. All surviving patients are followed up for at least one year following injury. Mobility is assessed using a scale of 0—9.13 9 represents full mobility indoors and outdoors without walking aids; 0 represents a bed-bound patient. The use of walking aids within the home is also noted. Differences in pre-injury residential status are recorded as a further measure of independence. For our study we compared firstly the proportion of each group living ‘‘independently’’ (own or rented home or warden controlled accommodation) and secondly the proportion living ‘‘dependently’’ (in residential accommodation or a nursing home). Patients excluded from this analysis had been previously resident either in hospital or rehabilitation beds and therefore were in a state of flux with regard to living status. Mental agility is scored using a standard ‘‘mini mental-state test’’ commonly employed by Care of the Elderly Physicians.14 One point is scored for each correct answer including short and long term memory questions, simple arithmetic, concentration and orientation in time and place. A range is therefore possible from 0 (unable to answer a single question) to 10 (full marks). Co-morbidity is documented, as is preoperative haemoglobin concentration. The American Society of Anaesthesiologists (ASA) grading is employed for preoperative morbidity scoring.2 A history of current cardiac or respiratory disease, hypertension requiring therapy, diabetes mellitus or malignancy is noted. All delays to theatre are recorded, as is a delay to surgery if due specifically to a respiratory cause. The fracture pattern is classified into intracapsular, trochanteric and subtrochan-

153 teric and the presence of a previous contralateral hip fracture noted. Postoperative complications are recorded, as is the length of stay for each patient, both for inpatient bed days on the acute Orthopaedic ward as well as total stay (which include bed days in a ‘‘stepdown’’ or rehabilitation facility). For the survivors at one year from fracture, presence and severity of pain is assessed using a scale from 0 (none) to 6 (constant and severe) as originally defined by Charnley.3 Mobility and residential status are again recorded, allowing any change in either to be calculated. Statistical analysis of the data was performed using GraphPad InStat software (GraphPad InStat version 3.00 for Windows 95, GraphPad Software, San Diego, California, USA). Proportional results (e.g. sex ratio, etc.) were compared using the Chi-square statistic with Yates correction for unequal variances. For continuous outcomes, mean and standard deviation were calculated and the data was analysed using the unpaired t-test with Welch correction for unequal variances. Differences were assumed to be statistically significant with p < 0.05. In addition, 95% confidence intervals (CI) were calculated for all comparisons. Mortality for the two groups was analysed using Kaplan—Meier survival curves.

Results Two hundred and seventy patients had no recorded data with respect to smoking habits and were therefore excluded from the study. The age and sex distribution of these patients was compared with the remaining 3617 to rule out the possibility that the exclusion of this group introduced significant bias into the study. The average age of the study group (n = 3617) was 79.6 years (S.D. = 10.99) and that of the ‘‘no data’’ group (n = 270) was 80.6 years (S.D. = 12.04). This difference was not statistically significant ( p = 0.17). The sex distribution of the study group was 78.4% female and of the ‘‘no data’’ group was 76.3% female. This difference was not statistically significant ( p = 0.56). For the 3617 patients about whom data was available with respect to smoking habits, there were 467 patients in the smokers group and 3150 in the non-smokers group. The patient characteristics and pre-injury co-morbidities are shown in Tables 1 and 2. Postoperative complications are shown in Table 3. Mortality and outcome for the surviving patients is shown in Table 4 and survival curves for the two groups is displayed in Fig. 1. Although univariate analysis shows that the one-year survival rate was

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Table 1 Characteristics of patients Number Mean age Female sex Using walking aids Mean mobility score Mean mental test score Living in own home Living in institutional care Previous hip fracture Intracapsular fracture Trochanteric fracture Subtrochanteric fracture

Smokers

Non-smokers

p-value

95% CI smokers

95% CI non-smokers

467 71.7 302 (64.7%) 132 (28.3%) 6.0 7.8 413 (89.2%) 35 (7.5%) 30 (6.4%) 258 (55.3%) 186 (39.8%) 23 (4.9%)

3150 80.7 2535 (80.5%) 1474 (46.8%) 5.2 6.8 2196 (69.7%) 789 (25.0%) 362 (11.5%) 1810 (57.5%) 1246 (39.5%) 94 (3.0 %)

<0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 0.013 0.394 0.951 0.038

70.5—72.9 60.1—69.1% 24.2—32.5% 5.7—6.2 7.2—8.1 85.2—91.2% 5.3—10.3% 4.4—9.0% 50.6—59.8% 35.3—44.4% 3.1—7.3%

80.4—81.1 79.1—81.8% 45.0—48.6% 5.0—5.4 6.7—6.9 68.0—71.4% 23.6—26.6% 10.4—12.7% 55.7—59.2% 37.8—41.3% 2.4—3.6%

Table 2 Medical conditions present on admission No co-morbidity Cardiac disease Respiratory disease Hypertension Diabetes mellitus Malignant disease Mean haemoglobin (g/dL) ASA Grade 1 or 2 Mean ASA grade Delay to surgery due to medical reasons Delay to surgery due to respiratory disease Delay to surgery due to anaemia

Smokers

Non-smokers

p-value

95% CI smokers

95% CI non-smokers

137 (29.3%) 92 (19.7%) 88 (18.8%) 46 (9.9%) 18 (3.9%) 18 (4.0%) 13.0 175 (37.5%) 2.6 42 (9.2%)

790 (25.1%) 938 (29.8%) 262 (8.3%) 326 (10.3%) 221 (7.0%) 125 (3.9%) 12.3 1023 (32.5%) 2.7 408 (13.2%)

0.056 <0.0001 <0.0001 0.803 0.014 0.906 <0.0001 0.037 0.26 0.020

25.3—33.7% 28.2—31.5% 15.4—22.6% 7.3—13.0% 2.3—6.0% 3.3—4.7% 12.9—13.1 33.1—42.1% 2.6—2.7 6.7—12.1%

23.6—26.6% 16.2—23.6% 7.4—9.3% 9.3—11.5% 6.1—8.0% 2.3—6.0% 12.2—12.4 30.9—34.1% 2.7—2.7 12.0—14.4%

7 (1.5%)

13 (0.4%)

0.009

0.6—3.1%

0.2—0.7%

7 (1.5%)

94 (3.0%)

0.097

0.6—3.1%

2.5—3.7%

higher in smokers ( p = 0.03), as appears to be demonstrated on the Kaplan—Meier curves, using a multivariate logistic regression analysis including the variables both of age alone and of both age and sex, this becomes statistically insignificant ( p = 0.066 and p = 0.148, respectively).

Discussion Smoking is again generating controversy in the medical press.5 There have been two recent studies looking specifically at the effect that smoking has in the context of orthopaedic surgery. The first of

Table 3 Post operative complications and hospital stay Cardiac Pneumonia Deep venous thrombosis Pulmonary embolism Confusion Pressure sores Superficial wound infection Deep wound infection Mean orthopaedic stay (days) Mean total hospital stay (days)

Smokers

Non-smokers

p-value

95% CI smokers

95% CI non-smokers

9 (1.9%) 18 (3.9%) 8 (1.7%) 0 15 (3.2%) 15 (3.2%) 7 (1.5%) 2 (0.4%) 15.6 18.0

84 (2.7%) 125 (4.0%) 48 (1.5%) 24 (0.7%) 87 (2.8%) 110 (3.5%) 59 (1.9%) 21 (0.6%) 13.0 21.8

0.432 0.906 0.914 0.113 0.690 0.862 0.705 0.770 0.002 0.008

0.9—3.6% 2.3—6.0% 0.7—3.4% 0 1.8—5.3% 1.8—5.3% 0.6—3.1% Too small 14.0—17.1 15.5—20.5

2.1—3.3% 3.3—4.7% 1.1—2.0% 0.4—1.1% 2.2—3.4% 2.9—4.2% 1.4—2.4% 0.4—1.0% 12.5—13.5 20.6—22.9

Smoking and hip fracture

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Table 4 Outcome for patients Mortality at 30 days Mortality at 6 months Mortality at 1 year Adjusted mortality at 1 year Mean pain at 1 year Using walking aids Mean mobility score Mean change in mobility Same residential status

Figure 1

Smokers

Non-smokers

29 (6.2%) 78 (16.7%) 106 (22.7%)

238 (7.6%) 640 (20.3%) 869 (27.6%)

p-value

0.346 0.078 0.030 0.148 2.16 2.02 0.024 188/348 (54.0%) 1561/2213 (70.5%) <0.0001 5.7 4.3 <0.0001 1.4 1.5 0.59 311/351 (88.6%) 1880/2211 85.0% 0.091

Kaplan—Meier survivorship figures.

these concluded that because of the risk of delayed union and wound healing problems, patients should be advised to stop smoking after sustaining an open tibial fracture1; the second that smoking is the most significant risk factor for development of complications following hip or knee arthroplasty, including an increase in length of in-patient stay and risk of admission to an intensive care bed.8 The traumabased study used demographically matched groups while the elective study did not, and found the smoking group to be from a younger population. In our study, the two patient groups again appear to be distinct entities, with the smokers generally younger with more males, more independently living and mobile, a higher mental agility score and although more likely to have respiratory disease, less likely to have cardiovascular co-morbidity. The smokers were more likely to have a greater total number of co-morbidities; however the ASA scores for each group were comparable. There was a slightly lower admission haemoglobin level in the non-smokers, but this did not appear to cause these patients a delay to theatre because of need for transfusion. The fracture pattern appeared to be unrelated to smoking habits for the two groups, except for a statistically, but probably not clinically, significantly higher rate of subtrochanteric fracture

95% CI smokers 95% CI non-smokers 4.2—8.8% 13.5—20.4% 18.9—26.7%

6.7—8.5% 19.0—21.8% 26.0—29.2%

2.0—2.3 48.7—59.4% 5.3—5.9 01.2—1.6 84.8—91.8%

2.0—2.1 68.5—72.5% 4.2—4.4 1.4—1.5 83.5—86.5%

in the smokers group. The rate of detected malignancy was comparable for each group. The smokers had a longer postoperative stay in the Orthopaedic ward but were less likely to be transferred to rehabilitation wards and ultimately therefore had a shorter total hospital stay. The most striking finding from our results is that smoking is associated with a significantly reduced age at time of hip fracture. The average age of patients in the smoking group was approximately nine years younger than the patients in the nonsmoking group. It is already known that smoking is linked with the development of osteoporosis,15 and osteoporosis is a well-established risk factor for hip fracture4 It is not therefore surprising to demonstrate this association. Given that the two patient groups are distinct with respect to age and pre morbid lifestyles, it is somewhat surprising to note that the postoperative factors are essentially similar for each group, i.e. complication rates and fracture outcome. It might be expected that a generally younger population would have significantly fewer adverse events following admission. An explanation for this might be the physiological aging effects of smoking,11 rendering the tissues of the smokers comparable to their older counterparts. The other important finding from our study was that smokers comprised 13% of the total population. In the context of hip fracture patients therefore, while patients who smoke are a minority, this is not so small a group to be clinically unimportant. In particular we found that the smokers were more likely to have a delay to surgery because of a respiratory problem, although we did not demonstrate the previously well-documented fact that smokers are more likely to have respiratory complications in the postoperative period.9,17 Smoking is also associated with a slower rate of wound healing, both in experimental12 and in vivo10 studies. We did not find a higher rate of wound infection, deep or superficial, or a higher incidence of skin pressure ulceration in the smokers, but this

156 may be due either to the relatively small numbers who developed these complications in both groups or because as the hip is a well-covered joint, the overlying tissues are not of such tenuous vascularity compared with pre-tibial tissues, implicated in the higher rate of adverse events in the series of open tibial fractures in smokers.

Conclusion In conclusion, this prospective case-control series demonstrates that smoking appears not to affect the peroperative complication rate or postoperative course of hip fracture patients. However, hip fractures are shown to occur at a younger age in the smoking population. This therefore implies that smoking appears to negate the effect of youth in these patients, raising the risk of complications and mortality to that equivalent to a much older cohort.

Conflict of interest statement None of the authors has a conflict of interest in relation to this work.

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