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American Journal of Physical Medicine & Rehabilitation:
doi: 10.1097/PHM.0000000000000054
Original Research Articles

Can the Length of Hospital Stay After Total Hip Arthroplasty be Predicted by Preoperative Physical Function Characteristics?

van Aalst, Michiel J.H. PT, MSc; Oosterhof, Jan PT, PhD; Nijhuis-van der Sanden, Maria W.G. PT, PhD; Schreurs, B. Wim MD, PhD

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Author Information

From the Department of Orthopaedic Surgery (MJHvA, JO, MWGN-vdS, BWS) and Department of IQ Healthcare (MWGN-vdS), Radboud University Nijmegen Medical Centre, Nijmegen, the Netherlands.

All correspondence and requests for reprints should be addressed to: Jan Oosterhof, PT, PhD, Department of Orthopedic Surgery 645, Radboud University Nijmegen Medical Centre, PO Box 9101, 6500 HB Nijmegen, the Netherlands.

Financial disclosure statements have been obtained, and no conflicts of interest have been reported by the authors or by any individuals in control of the content of this article.

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Abstract

Objective

The aim of the present study was to identify independent preoperative hip function characteristics sensitive for preoperative intervention that are predictive of an extended length of hospital stay (LOS) after primary total hip arthroplasty (THA).

Design

This is a longitudinal cohort study. A retrospective chart analysis was conducted on prospectively collected data of patients (158) who underwent unilateral primary elective cemented THA in a 4-yr period. The main outcome measure was LOS after primary THA.

Results

The median LOS was 6.0 days. The authors found an 18.5% increased chance of requiring an LOS of more than 6 days (odds ratio, 2.15; 95% confidence interval, 1.03–4.50) for the patients who needed to use a walking aid preoperatively and a 23.6% increased chance (odds ratio, 2.74; 95% confidence interval, 1.31–5.74) for the patients who had difficulties managing stairs. Sex, age, body mass index, comorbidity, and preoperative pain did not reach the level of significance in the multivariate analysis.

Conclusions

Patients who are at risk for a longer stay in the hospital after THA can be identified preoperatively on simple physical function characteristics. These findings enable the identification of appropriate patients for preoperative training to improve functional recovery and decrease the LOS after primary THA.

Total hip arthroplasty (THA) is a highly cost-effective procedure1–3 resulting in substantial and sustained pain relief, improvement in physical function, and enhanced health-related quality-of-life.4–10 Current local clinical rehabilitation protocols are typically aimed at a quick discharge from the hospital. Nevertheless, the discharge may be delayed for several reasons, including postoperative complications and delayed functional recovery, with a negative influence on patient satisfaction and patient flow. Furthermore, the number of hip arthroplasties will increase based on demographic data and increasing patient-driven demand for this type of surgery. To reduce the risks of delayed functional recovery after surgery, preoperative training is recommended,11,12 and it is important to identify the patients at high risk for delayed recovery.13 Patient characteristics sensitive to preoperative training interventions are especially needed.

In previous studies, a number of factors have been shown to increase the length of hospital stay (LOS) after THA: increased age,14–18 female sex,14–17 increased body mass index (BMI),19,20 presence of comorbidity,16 and smoking.19–21 Nonetheless, these factors are not or hardly sensitive to specific preoperative training interventions.

Recently, Dall et al.14 demonstrated that a lower preoperative combined Harris Hip Score (HHS) function and activity score was an independent predictor of an extended LOS after THA. However, aiming at preoperative training interventions, it is important to know which physical function characteristics are at risk for delayed functional recovery.

The aim of the present study was to identify independent preoperative hip function characteristics that are predictive of an extended LOS after primary THA and that might also be sensitive to preoperative intervention. For this purpose, a retrospective chart analysis was conducted on available prospectively collected data of patients who underwent unilateral primary elective cemented THA during a 4-yr period.

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MATERIALS AND METHODS

Patients

Patients who underwent a cemented THA between January 2005 and January 2009 were selected from the data bank of the department of orthopedic surgery. Exclusion criteria were THA for secondary osteoarthritis caused by rheumatic diseases, THA for proximal femoral fractures, and all THAs in which a reconstruction was performed with acetabular bone impaction grafting. Furthermore, patients who had a contralateral hip implant or surgery within 1 yr before surgery were also excluded. Thus, 158 patients were included with 158 hip implantations. The local Committee on Research Involving Human Subjects approved this study.

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Patients’ Characteristics

Individual patient characteristics included demographic, clinical, and comorbidity factors and were obtained from the medical dossiers. The collected demographic factors were sex, age, height, body weight, and BMI. The clinical factors were obtained from the hospital discharge summary for each patient and included indication for THA, American Society of Anesthesiologists Physical Status Classification, type of anesthesia (general or regional), date of operation, date of discharge, and discharge destination. Destinations at discharge included the categories home, nursing home, or rehabilitation hospital. Collected comorbidity factors were preexisting cardiovascular disease (coronary artery disease, myocardial infarction, congestive heart failure, valvular heart disease, arrhythmia, peripheral vascular disease, thrombophlebitis, thromboembolic disease, hypertension, transient ischemic attack, and stroke), pulmonary disease (chronic obstructive pulmonary disease and asthma), diabetes mellitus, and other preexisting medical problems that required medical treatment (e.g., hypothyroidism or hyperthyroidism). Furthermore, preoperative HHS and Oxford Hip Questionnaire (OHQ) data were collected. Visual analog scales (VASs) were obtained for pain at rest and pain during physical activity on a scale from “no pain” (0 mm) to “unbearable pain” (100 mm). All scores were administered at the outpatient department, approximately 1 mo before surgery according to the preoperative consultation protocol.

To obtain information on potentially predictive factors that might be sensitive to preoperative intervention, those items concerning hip strength and mobility were extracted from the HHS and the OHQ. Selected factors from the HHS included the items limping, the need to use a walking aid, the ability to use public transport, and range of hip motion. Range of hip motion was defined as the summation of degrees of flexion, abduction, adduction, external rotation, and internal rotation. Selected factors from the OHQ included the use of (public) transport and stairs. Subsequently, the scores of the selected items from the HHS and the OHQ were dichotomized. HHS “limping” was classified as yes (slight, moderate, or severe) or no (none); HHS “support” was classified as “no use of walking aid” (none) or “else” (cane for long walks, cane most of the time, one crutch, two canes, two crutches, or not able to walk); HHS “enter public transportation” was classified as yes or no; and OHQ “public transport” and OHQ “stairs” were classified as “difficult” (with moderate difficulty, with extreme difficulty, or not able to do) or “not” (easily or with little difficulty).

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Outcome Measure

LOS was defined as the full number of days between the date of surgery and the date of discharge from the hospital.

Discharge criteria for going home were (1) independent transfer from supine to sit and from sit to stand, (2) safe mobilization with the aid of one or two crutches, and (3) climbing stairs independently and safely. If these criteria could not be met within a reasonable period (aiming at a hospital LOS of 1 wk), the patients were referred to a nursing home or an external rehabilitation center. The decision to discharge the THA patients to the home environment, to a nursing home, or to an external rehabilitation center was eventually made by the physician in dialogue with the physical therapist, the nursing staff, the patient, and the patient’s family.

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Interventions

All hip prostheses were implanted according to a standardized surgical technique. A posterolateral approach without trochanteric osteotomy was used in all hips. In all THA patients, a conventional acetabular full polyethylene Exeter Contemporary cup was cemented, predominantly with an inner diameter of 28 mm and, in some cases, with an inner diameter of 32 mm in combination with a cemented femoral Exeter stem (Stryker Howmedica, Newbury, UK). All THA patients received antibiotic prophylaxis consisting of 2 g of cefazolin intravenously just before surgery. Postoperatively, nonsteroidal anti-inflammatory drugs were used for 7 days to prevent heterotopic ossification. The patients with a contraindication for nonsteroidal anti-inflammatory drugs were treated by one dose of radiation therapy. All patients received thrombosis prophylaxis with low–molecular-weight heparin for 6 wks.

During hospitalization, all patients had physical therapy according to a standard protocol. On the first postoperative day, the therapy was focused on isometric strengthening and increasing the range of hip motion. On the second postoperative day, the THA patients were mobilized with a walking aid under supervision of a physical therapist to train transfers and ambulation.

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Data Analysis

To identify preoperative patient characteristics that are predictive of an extended LOS after THA, the THA patients were divided into two groups according to the median LOS used as a cutoff. Univariate associations between preoperative patient characteristics and LOS were determined using two-tailed unpaired Student’s t tests or χ2 tests when appropriate. A multivariate logistic regression analysis was conducted to determine the predictors associated with an extended LOS, including potential confounding factors. The first step in the regression procedure was to determine a model containing only the potential confounding variables (age, sex, BMI, presence of comorbidity [yes or no], and VAS pain at rest and during movement). Subsequently, the selected dichotomized preoperative HHS and OHQ variables were added to the logistic regression equation one at a time using the criterion of reducing the −2 log likelihood error for the included variables. After each variable was entered separately, it was checked for a significant association with LOS, adjusted for the potential confounding factors. Nonsignificant variables were not used in the final regression model, whereas variables significantly associated with LOS were added together with the confounding factors to the regression analysis to fit a model to obtain estimates for each predictive factor in the presence of all of the other covariates. Classification accuracy of the regression model was tested with the area under the receiver operating characteristic curve. A P value of less than 0.05 was considered to indicate statistical significance.

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RESULTS

Patients’ Characteristics

One hundred sixty-seven patients fulfilled the inclusion criteria. Nine patients (three men and six women; mean [SD] age, 70.2 [7.8] yrs; median [range] LOS, 6.0 [3–12] days) were excluded from further analysis; for five patients, BMI was not known; for three patients, pain intensity scores were missing; and for one patient, the OHQ scores were not available. Therefore, the study cohort consisted of 158 THA patients. Seventy-seven THA patients (49%) had surgery using general anesthesia. Eighty-one (51%) had surgery with spinal/epidural anesthesia. Eighty-eight THA patients (56%) had at least one relevant comorbid condition, and 21 patients (13%) had multiple (two or more) comorbidities. For further subject characteristics, see Table 1.

TABLE 1
TABLE 1
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Outcome Measure

The mean (SD) LOS in the hospital surgical unit was 7.5 (4.4) days (median [range], 6.0 [3–41] days). Overall, 76 THA patients (48 %) had an LOS of more than 6 days. For the THA patients with an LOS of more than 6 days, the mean (SD) LOS was 10.3 (5.0) days (median [range], 8.0 [7–41] days); for those with an LOS of 6 days or less, the mean (SD) LOS was 4.8 (1.0) days (median [range], 5.0 [3–6] days). One hundred forty-nine THA patients (94.3%) were discharged to the home environment; seven (4.4%), to a nursing home; and two (1.3%), to an external rehabilitation center.

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Outcome Predictors

Using univariate analysis, the THA patients who required an LOS of more than 6 days were more likely to be older (P < 0.001), to have one or more comorbid conditions (P = 0.008), to have used a walking aid preoperatively (P = 0.002), and to have had trouble with climbing stairs preoperatively (P < 0.001) compared with the THA patients who required an LOS of 6 days or less. The complete results of the univariate analysis are shown in Table 2.

TABLE 2
TABLE 2
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The final multivariate model included the factors sex, age, BMI, presence of comorbidity, preoperative pain at rest, preoperative pain during movement, preoperative HHS support, and preoperative OHQ stairs (classification accuracy of 76%). There was no significant association between LOS and age, sex, BMI, and presence of comorbidity. Logistic regression analysis revealed a significant independent association between the preoperative need to use a walking aid and LOS (P = 0.04) and between the preoperative ability to climb stairs and LOS (P = 0.007). The THA patients who preoperatively had used a walking aid had an 18.5% increased chance of requiring an LOS of more than 6 days compared with those who did not need to use a walking aid preoperatively (odds ratio [OR], 2.15; 95% confidence interval, 1.03–4.50). The THA patients who preoperatively were not able to climb stairs or who had moderate to extreme difficulty in climbing stairs had a 23.6% increased chance of requiring an LOS of more than 6 days compared with those who experienced very little trouble or no trouble at all with climbing stairs preoperatively (OR, 2.74; 95% confidence interval, 1.31–5.74). The complete results of the final multivariate model are shown in Table 3.

TABLE 3
TABLE 3
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DISCUSSION

The primary aim of the present study was to identify independent specific physical function characteristics that may be sensitive for preoperative training intervention and that are predictive of an extended LOS after primary elective THA. The THA patients who preoperatively had difficulties climbing stairs and those who used a walking aid preoperatively had a considerably increased chance of requiring an extended LOS. The latter finding is consistent with previously described results of Husted et al.,16 who reported that preoperative use of a walking aid was associated with an increased LOS in individuals who were admitted for hip and knee replacement surgery.

In this study, the mean hospital LOS was 7.5 days, and 94.3% of the patients were discharged home. This LOS is slightly shorter than the LOS of the studies of Hayes et al.22 (9.5 days and 98% of the patients were discharged home) and Dall et al.14 (8.1 days and 92% of the patients were discharged home). However, in the United States, the mean hospital LOS for primary THA declined from 9.1 days in 1992 to 3.7 days in 2008, and the proportion of patients discharged home declined from 68.0% to 48.2%.23 These differences may be explained by differences in factors driving LOS; in this study, functional milestones were used aiming at discharge to home, similar to the studies of Hayes et al.,22 Dall et al.,14 and Husted et al.16 In the United States, the reduction in hospital LOS is accompanied by a significant reduction in the proportion of patients discharged directly home and a significant increase in the proportion of patients discharged to postacute care facilities.23 Therefore, the findings of this study to reduce hospital LOS may not be directly applicable in the United States; however, because the authors used functional milestones aiming at discharge to home, these predictors of hospital LOS may identify patients at risk for a delayed recovery of physical functioning after primary THA.

There was no significant independent association between LOS and age, sex, BMI, presence of comorbidity, and preoperative pain at rest or during movement. When comparing these findings with the results of two larger studies14,16 with similar discharge criteria, the results on BMI and comorbidity are in agreement with both these studies, although the results on age and sex do not seem to match with their findings. However, Husted et al.16 found ORs for age (OR, 1.02) and sex (OR, 0.6) as predictors for LOS, which are quite similar to the findings of this study (OR, 1.03 and 0.63, respectively). Therefore, the negative findings could be explained by the difference in size of the study population and thus in a lack of power of this study. However, a 10-yr increase in age would provide an independent 6.5% increase in LOS, which is of minor value. Presumably, concerning functional recovery, muscle strength largely determines the predictive value of increased age.24

Both predictors for LOS—the preoperative use of a walking aid and difficulty managing stairs—may be explained by the loss of hip muscle strength. Patients with hip osteoarthritis are frequently reported to have reduced hip muscle strength25 compared with control individuals26–28 or compared with the less severely affected side.26 Hip muscle weakness in osteoarthritis has been suggested to be caused by disuse atrophy as a result of pain-related arthrogenous inhibition of muscle function and reflex inhibition of muscles moving the affected joints.29–31 Consequently, both these disabilities may serve as an important target for preoperative training, for example, by improving muscle strength and therefore reducing LOS; however, this hypothesis needs further proof. For reasons described above in the current study, analyses were controlled for pain intensity at rest and during movement 1 mo before surgery; however, both pain qualities did not significantly contribute in predicting LOS; therefore, pain approximately 4 wks before surgery is not predictive of LOS. However, earlier long-standing pain could have induced muscle weakness.

The findings of this study may have important implications for future studies regarding the selection of patients who may benefit from preoperative physical therapy.

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Study Limitations

The retrospective design of this study may be considered a weak point, although the data of the patients who underwent unilateral primary elective cemented THA in a 4-yr period were collected prospectively. However, this design ensures independent data collection and determination of LOS because of the fact that at the time of gathering these data, the aim of this study was not yet known. The authors assume that a strong point of this study is the large group of patients who underwent the same standardized surgery for primary THA following the same protocol during hospital stay, using clear discharge criteria. However, the results of this study may be limited for THA with cemented implants because of the fact that patients with uncemented stems may have a delayed functional recovery because of restricted weight bearing during walking.

The use of one dichotomous variable for all different comorbidities, assuming similar effect on physical function, may have limitations. However, in a large study predicting LOS, Dall et al.14 found no significant effect of diabetes, ischemic heart disease, or other medical comorbidities when analyzed as separate variables. Possibly, the use of an index of comorbid diseases that impair physical function, for example, as developed by Groll et al.,32 would have been more appropriate.

For logistic reasons, some patients may not have visited the research assistants (students) for assessment of physical function (HHS and OHQ score) and pain, which, at the authors’ outpatient clinic, is the standard procedure for patients indicated for total hip and knee replacement arthroplasty. However, the authors have no information about these missing data.

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CONCLUSIONS

This study demonstrated that the THA patients who preoperatively had difficulties climbing stairs and those who were preoperatively required to use a walking aid showed a considerably increased chance to require an extended LOS, while controlling for known possible confounders. These findings may help to identify patients who are at risk for an increased LOS after primary THA and who may benefit from preoperative physical training.

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REFERENCES

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Keywords:

Hip; Replacement Arthroplasty; Prognosis; Activities of Daily Living; Comorbidity

Copyright © 2014 by Lippincott Williams & Wilkins

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