Preoperative Functional Mobility as a Predictor of Exceeding the Planned Length of Hospital Stay after Lumbar Fusion Surgery for Spinal Stenosis

ABSTRACT

Objectives:

This study aimed to determine the association between preoperative functional mobility and exceeding the planned length of hospital stay (LOS) after lumbar fusion surgery for lumbar spinal stenosis (LSS) and to identify factors associated with preoperative functional mobility.

Methods:

A total of 122 patients who underwent lumbar fusion for LSS were included. Preoperative functional mobility was assessed using the Timed Up-and-Go (TUG) test. LOS was categorized as standard (≤14 days) or exceeded (>14 days). Risk ratios (RRs) with 95% confidence intervals (CIs) were estimated using modified Poisson regression to analyze the association between preoperative TUG performance and LOS. Additionally, linear regression was used to identify factors associated with preoperative TUG performance.

Results:

In the univariate modified Poisson regression model, exceeding the planned LOS was associated with preoperative TUG performance (RR, 1.10; 95% CI, 1.06 to 1.14; P <0.001). In the adjusted model, this association remained significant (RR, 1.10; 95% CI, 1.06 to 1.14; P <0.001). Poorer preoperative TUG performance was also associated with female sex (mean difference, −2.02 s; 95% CI, −3.60 to −0.43; P = 0.014) and psychiatric comorbidities (mean difference, 7.91 s; 95% CI, 1.95 to 13.87; P = 0.010).

Conclusions:

Poorer preoperative functional mobility is an independent predictor of exceeding the planned LOS after lumbar fusion surgery for LSS. Routine preoperative assessment with the TUG test may help identify high-risk patients, and targeted strategies such as enhanced preoperative and postoperative rehabilitation could reduce the likelihood of prolonged hospitalization.

INTRODUCTION

Lumbar spinal stenosis (LSS) affects an estimated 103 million people worldwide¹⁾ and significantly impairs activities of daily living (ADL)²⁾ and quality of life. When symptoms such as leg pain, numbness, and neurogenic claudication become severe and refractory to conservative treatment, surgical interventions such as decompression or fusion surgery are performed to alleviate symptoms and improve functional ability.²⁾ In Japan, the number of these surgeries has increased over recent decades,^3,4) reflecting the growing burden of degenerative spinal conditions on healthcare systems.

A prolonged length of hospital stay (LOS) after surgery is a major concern, not only because of increased healthcare costs but also because of the potential for a higher risk of nosocomial infections, deep vein thrombosis, and other postoperative complications.^5,6,7) Previous studies have reported that between 2.4% and 21% of patients experience prolonged LOS,^8,9,10) underscoring the critical need to identify and address contributing factors. Predictors of prolonged LOS after lumbar spine surgery include older age,¹⁰⁾ longer operative time,⁸⁾ certain comorbidities such as diabetes and heart disease,^11,12) and poor preoperative physical status, as indicated by a higher American Society of Anesthesiologists Physical Status (ASA-PS) classification.¹⁰⁾ Additionally, preoperative functional mobility has been reported to be associated with prolonged LOS in thoracolumbar spine surgery,¹³⁾ highlighting the importance of assessing preoperative physical function. However, the study’s heterogeneous cohort, which included various pathologies and procedures, limits the applicability of the findings to specific procedures such as lumbar fusion for LSS. Furthermore, because the analysis did not differentiate the reasons for prolonged hospitalization, it could not specifically assess whether delays were attributable to medical or physical factors.

Predictors identified in previous studies may also have limited relevance, because they were reported in cohorts from countries with much shorter LOS. These findings may not be directly applicable to countries such as Japan (22.3 days),¹⁴⁾ Korea (20.9 days),¹⁵⁾ and China (18.5 days),¹⁶⁾ where LOS are relatively long. Clarifying the association between these predictors and prolonged LOS in countries with similarly lengthy hospital stays would therefore provide valuable information for healthcare systems in these regions. Most predictors reported to date, such as age and comorbidities, are nonmodifiable. In contrast, functional mobility is a modifiable factor, and clarifying its association with prolonged LOS is critical for developing strategies to prevent such outcomes.

Therefore, this study aimed to determine the association between preoperative functional mobility and prolonged LOS (defined as exceeding the planned LOS) after lumbar fusion surgery for LSS. In addition, we sought to identify factors strongly associated with preoperative functional mobility. We hypothesized that poorer preoperative functional mobility was associated with an increased risk of exceeding the planned LOS after lumbar fusion surgery for LSS, and that preoperative mobility would be associated with patient attributes.

MATERIALS AND METHODS

Study Design

This retrospective cohort study used data from electronic medical records and institutional databases at a single orthopedic hospital. This study was approved by the Institutional Review Board of Juntendo University (approval number: 00227).

Participants

The study included patients who underwent lumbar fusion surgery (one to four levels) for LSS between 1 October 2023 and 30 September 2024. The following exclusion criteria were used: (1) postoperative deterioration in general condition (e.g., requiring intensive care) or new neurological symptoms; (2) preexisting musculoskeletal, neurological, degenerative, cardiovascular, or respiratory conditions affecting gait; (3) severe psychiatric comorbidities that interfered with social life; and (4) cognitive impairment. Informed consent was obtained from all participants through the opt-out method.

Surgical Procedures and Perioperative Care

On the day before surgery, all patients underwent assessments of functional mobility and functional disability. They also received preoperative education, including instructions on daily activity precautions and postoperative rehabilitation. For the surgical intervention, patients underwent either posterior lumbar interbody fusion (PLIF) or extreme lateral interbody fusion (XLIF). After lumbar fusion surgery, patients were prescribed a rigid lumbar brace or a flexible lumbar brace. Physical therapy began on the first postoperative day, starting with bed mobility and transfer training, followed by gait training. Regarding the discharge target, in Japan, shortening hospital stays is encouraged, and the average LOS for general hospital beds is approximately 14–15 days.¹⁷⁾ To achieve this target even in the postoperative course after spine surgery, our institution also set the clinical pathway to 14 days.

Outcome

The primary outcome was whether the patient exceeded the planned LOS. The LOS, defined as the number of days from surgery to discharge, was obtained from electronic medical records. The LOS was categorized into two groups: patients discharged within 14 days after surgery (standard group) and those not discharged home within this period (exceeded group). Discharge decisions were made collaboratively by the attending physician and the physical therapist, based on the patient’s overall medical condition and physical functional status. The medical condition for discharge required sufficient wound healing and no sign of infection. For physical functional status, discharge eligibility was determined according to standardized clinical criteria: patients were required to walk independently (with or without a walking aid) for at least 100 m indoors and 100 m outdoors to ensure safe mobility upon discharge. Additionally, the reasons for exceeding the planned LOS were extracted from the electronic medical records and classified into four groups. Personal reasons referred to cases in which the patient’s own wishes delayed discharge. Social reasons included factors such as family transportation availability, family preferences, and home environment issues. Medical reasons referred to nonfunctional conditions such as postoperative hematoma, delayed wound healing, or abnormal blood test results (e.g., elevated inflammatory markers). Physical functional reasons were defined as the inability to achieve the necessary ADLs for discharge, such as getting up or walking. Group assignment was determined by two independent researchers. They independently classified the reasons and subsequently compared their classifications. Any disagreements were resolved through discussion and consensus. Inter-rater reliability for the classification was assessed using Cohen’s κ coefficient, which demonstrated substantial agreement [κ = 0.90; 95% confidence interval (CI), 0.80 to 0.99]. Because preoperative functional mobility was unlikely to be associated with delays caused by personal or social reasons, only patients whose LOS exceeded the planned duration for medical or physical functional reasons were included in the statistical analysis to evaluate the association with preoperative functional mobility.

Exposure

Functional mobility was assessed preoperatively using the Timed Up-and-Go (TUG) test, one of the most commonly used objective measures of function in patients with lumbar degenerative disease.¹⁸⁾ The reliability and validity of the TUG test have been well established.¹⁹⁾ The test involved measuring the time required for a patient to stand up from a chair (seat height: 44 cm, with armrests), walk 3 m, turn around a marker, walk back, and sit down again. Patients were instructed to perform the test with maximal effort, following standardized instructions to walk as fast as possible.¹³⁾ Measurements were obtained using a digital stopwatch, and the faster of two trials was recorded as the representative value for each patient.

Covariates

Confounding factors, including age, sex, body mass index (BMI), ASA-PS classification, number of fused vertebral levels, and operative time, were selected based on previous literature and their clinical relevance. The ASA-PS is a system defined by the American Society of Anesthesiologists to describe a patient’s preoperative physical status and is commonly used as an indicator of perioperative risk. This assessment considers factors such as smoking, alcohol use, obesity, and underlying medical, neurological, and cardiac conditions. Higher ASA-PS scores have been associated with an increased risk of perioperative complications and mortality.^20,21)

Baseline Data

In addition to the covariates, demographic data such as family status (i.e., cohabitation with others) and clinical characteristics, including intraoperative blood loss and preoperative functional disability assessed with the Oswestry Disability Index (ODI),²²⁾ were collected.

Statistical Analysis

A complete-case analysis was conducted. Although missing data accounted for 2.2% of the dataset, these cases were excluded from the analytical models and were considered unlikely to introduce significant bias. Patient characteristics, including demographic and clinical variables, were summarized descriptively. Continuous variables, such as age, BMI, operative time, intraoperative blood loss, preoperative TUG performance, and ODI scores, were expressed as medians with interquartile ranges (IQRs). Categorical variables, including sex, ASA-PS classification, and family status, were presented as frequencies and percentages.

To examine the association between preoperative TUG performance and exceeding the planned LOS, risk ratios (RRs) with 95% CIs were estimated using a modified Poisson regression model. In the univariate modified Poisson regression model, the dependent variable was the LOS group (standard vs. exceeded), and the independent variables included preoperative TUG performance, age, sex, BMI, ASA-PS classification, number of fused vertebral levels, and operative time. In the adjusted model, the dependent variable remained the LOS group (standard vs. exceeded), with preoperative TUG performance as the primary independent variable. Covariates, including age, sex, BMI, ASA-PS classification, number of fused vertebral levels, and operative time, were included to control for potential confounding factors. As a sensitivity analysis, the above procedure was repeated in two subgroups according to the reasons for exceeding the planned LOS (medical or physical functional). In addition, when preoperative TUG performance was significantly associated with exceeding the planned LOS, linear regression analysis was performed to examine preoperative characteristics associated with poorer TUG performance. To assess multicollinearity among covariates in the multivariable modified Poisson regression models and the multiple linear regression analysis, we calculated variance inflation factors (VIFs). A VIF larger than 10 was considered indicative of strong multicollinearity. Statistical significance was set at P <0.05. All analyses were performed using SPSS Statistics, version 29.0 (IBM, Armonk, NY, USA).

RESULTS

A total of 136 patients were initially included in this study. Of these, 14 patients were excluded: 4 because of conditions affecting gait, 1 because of postoperative general deterioration, 7 because of new-onset neurological symptoms, and 2 because of cognitive decline. The final study population comprised 122 patients.

Among these patients, 55 (45.1%) exceeded the planned LOS: 4 for personal reasons, 14 for social reasons, 14 for medical reasons, and 23 for physical functional reasons. Consequently, 104 patients were included in the analyses (Fig. 1). The surgical procedures included PLIF in 78 patients (75.0%) and XLIF in 26 patients (25.0%). The median LOS was 11.0 days (IQR, 10.0 to 13.0) in the standard group and 25.0 days (IQR, 20.0 to 29.0) in the exceeded group. With respect to preoperative TUG performance, the standard group had a median result of 8.2 s (IQR, 6.7 to 9.7), whereas the exceeded group had a median result of 10.5 s (IQR, 9.1 to 13.3) (Fig. 2). Table 1 shows the baseline characteristics of the included patients.

Fig. 1.

 Flowchart of study participant selection.

Fig. 2.

 Comparison of preoperative TUG performance between patients discharged within the planned LOS (standard group, LOS ≤14 days) and those exceeding the planned LOS (exceeded group, LOS >14 days). The box represents the IQR, the line within the box indicates the median, and the whiskers extend to the minimum and maximum values within 1.5 times the IQR from the box.

Table 1.  Demographic and clinical characteristics of the study cohort.

Characteristic	Total cohort (n=104)	Standard group a (n=67)	Exceeded group b (n=37)
Age, years	71.0 [64.8 to 78.0]	71.0 [63.0 to 77.5]	73.0 [69.0 to 82.0]
Female sex, n (%)	39 (37.5)	19 (28.4)	20 (54.1)
BMI, kg/m2	23.9 [21.4 to 26.6]	24.2 [22.0 to 26.7]	23.1 [20.7 to 26.0]
ASA-PS classification, n (%)
I	31 (29.8)	22 (32.8)	9 (24.3)
II	56 (53.8)	33 (49.3)	23 (62.2)
III	16 (15.4)	11 (16.4)	5 (13.5)
IV	1 (1.0)	1 (1.5)	0 (0.0)
History of lumbar surgery, n (%)	21 (20.2)	12 (17.9)	9 (24.3)
Cohabitation, n (%)	89 (85.6)	56 (83.6)	33 (89.2)
Number of fused vertebral levels, n (%)
1	34 (32.7)	28 (41.8)	6 (16.2)
2	49 (47.1)	28 (41.8)	21 (56.8)
3	13 (12.5)	7 (10.4)	6 (16.2)
4	8 (7.7)	4 (6.0)	4 (10.8)
LOS, days	13.0 [11.0 to 20.3]	11.0 [10.0 to 13.0]	25.0 [20.0 to 29.0]
Operative time, per 30 min	6.9 [5.3 to 8.5]	6.6 [5.0 to 8.2]	7.8 [5.7 to 8.7]
Blood loss, mL	200.0 [106.8 to 344.0]	200.0 [105.5 to 354.0]	200.0 [111.0 to 311.0]
ODI, %	33.3 [22.2 to 42.2]	31.1 [20.0 to 41.1]	33.3 [26.7 to 44.4]

Data are presented as median [interquartile range] or number (percentage).

^a LOS ≤14; ^b LOS >14.

In the univariate modified Poisson regression model, exceeding the planned LOS was significantly associated with age (RR, 1.04; 95% CI, 1.01 to 1.06; P = 0.010), sex (RR, 0.51; 95% CI, 0.31 to 0.85; P = 0.010), number of fused vertebral levels (RR, 1.37; 95% CI, 1.08 to 1.74; P = 0.010), and preoperative TUG performance (RR, 1.10; 95% CI, 1.06 to 1.14; P <0.001) (Table 2). In the adjusted model, exceeding the planned LOS remained significantly associated with age (RR, 1.03; 95% CI, 1.01 to 1.06; P = 0.017) and preoperative TUG performance (RR, 1.10; 95% CI, 1.06 to 1.14; P <0.001) (Table 3). In the adjusted model, VIFs ranged from 1.07 to 1.48, indicating that multicollinearity was not a concern. As shown in Table 4, sensitivity analysis restricted to medical or physical functional reasons yielded similar results. Given the significant association between preoperative TUG performance and exceeding the planned LOS, further analysis was conducted to identify factors influencing preoperative TUG performance. As shown in Table 5, preoperative TUG performance was significantly poorer in female patients (mean difference, −2.02 s; 95% CI, −3.60 to −0.43; P = 0.014) and in those with psychiatric comorbidities (mean difference, 7.91 s; 95% CI, 1.95 to 13.87; P = 0.010). In the multiple linear regression analysis, VIFs ranged from 1.08 to 2.37, indicating that multicollinearity was not a concern.

Table 2.  Results of univariate modified Poisson regression model predicting prolonged LOS.

Outcome	Risk ratio	95% CI	P value
Age (per year)	1.04	1.01 to 1.06	0.010
Male (vs. female)	0.51	0.31 to 0.85	0.010
BMI (per 1 kg/m2)	1.01	0.95 to 1.07	0.807
ASA-PS classification (per 1 class increase)	1.04	0.73 to 1.48	0.845
Number of fused vertebral levels (per 1 level increase)	1.37	1.08 to 1.74	0.010
Operative time (per 30 min)	1.08	0.99 to 1.19	0.092
Preoperative TUG performance (per 1 s)	1.10	1.06 to 1.14	<0.001

Table 3.  Results of multivariable modified Poisson regression model predicting prolonged LOS.

Outcome	Risk ratio	95% CI	P value
Age (per year)	1.03	1.01 to 1.06	0.017
Male (vs. female)	0.62	0.39 to 1.00	0.051
BMI (per 1 kg/m2)	1.02	0.98 to 1.06	0.414
ASA-PS classification (per 1 class increase)	0.83	0.60 to 1.15	0.261
Number of fused vertebral levels (per 1 level increase)	1.23	0.92 to 1.66	0.163
Operative time (per 30 min)	1.04	0.93 to 1.17	0.506
Preoperative TUG performance (per 1 s)	1.10	1.06 to 1.14	<0.001

Adjusted risk ratios were estimated using a modified Poisson regression model. The model included age, sex, BMI, ASA-PS classification, number of fused vertebral levels, and operative time as covariates, with preoperative TUG performance as the predictor.

Table 4.  Sensitivity analysis: factors associated with prolonged LOS, stratified by medical or physical functional reasons.

Outcome	Medical reason model				Physical reason model
	Risk ratio	95% CI	P value		Risk ratio	95% CI	P value
Age (per year)	1.00	0.96 to 1.05	0.900		1.07	1.02 to 1.12	0.006
Male (vs. female)	0.45	0.16 to 1.28	0.135		0.51	0.26 to 1.01	0.054
BMI (per 1 kg/m2)	1.06	0.93 to 1.20	0.364		1.02	0.96 to 1.07	0.598
ASA-PS classification (per 1 class increase)	1.22	0.74 to 2.02	0.439		0.62	0.41 to 0.94	0.026
Number of fused vertebral levels (per 1 level increase)	1.36	0.87 to 2.16	0.183		1.27	0.84 to 1.92	0.264
Operative time (per 30 min)	1.03	0.82 to 1.28	0.826		1.08	0.94 to 1.25	0.289
Preoperative TUG performance (per 1 s)	1.10	1.04 to 1.15	<0.001		1.13	1.06 to 1.21	<0.001

Adjusted risk ratios were estimated using a modified Poisson regression model. Each model included age, sex, BMI, ASA-PS classification, number of fused vertebral levels, and operative time as covariates, with preoperative TUG performance as the predictor.

Table 5.  Factors associated with preoperative TUG performance: multiple linear regression analysis.

Outcome	Mean difference	95% CI	P value
Age (per year)	0.08	−0.004 to 0.16	0.063
Male (vs. female)	−2.02	−3.60 to −0.43	0.014
BMI (per 1 kg/m2)	0.06	−0.15 to 0.26	0.575
Number of affected intervertebral levels (per 1 level increase)	−0.14	−1.19 to 0.92	0.798
Hypertension (yes vs. no)	0.94	−0.78 to 2.67	0.277
Heart disease (yes vs. no)	−0.27	−2.27 to 1.74	0.791
Diabetes (yes vs. no)	0.54	−2.08 to 3.16	0.680
Psychiatric comorbidities (yes vs. no)	7.91	1.95 to 13.87	0.010
Smoking (yes vs. no)	−0.39	−2.74 to 1.96	0.742
Low back pain (per 1 mm increase)	0.01	−0.03 to 0.04	0.646
Leg pain (per 1 mm increase)	0.01	−0.03 to 0.04	0.768
Leg numbness (per 1 mm increase)	0.02	−0.02 to 0.04	0.323

DISCUSSION

This study is the first to specifically investigate the association between preoperative functional mobility, assessed by the TUG test, and exceeding the planned LOS among patients who underwent lumbar fusion surgery for LSS. Our analysis demonstrated that poorer preoperative TUG performance was significantly associated with an increased risk of exceeding the planned LOS. Specifically, for every 1-s increase in preoperative TUG performance, the risk of exceeding the planned LOS increased by 10%. Sensitivity analyses indicated that the association between poorer preoperative functional mobility and increased risk of exceeding the planned LOS was consistent across both medical and physical functional reasons, supporting the robustness of the main findings. In the sensitivity analysis for physical functional reasons, a higher ASA-PS classification was associated with a lower risk of exceeding the planned LOS. Given that this subgroup consisted of only 23 patients, this association is likely to be unstable and should be interpreted with caution. A possible explanation is that patients with higher perioperative risk may have received more intensive perioperative management, although this remains speculative. Furthermore, female sex and psychiatric comorbidities were identified as factors associated with poorer preoperative TUG performance. The association with female sex may be explained by unmeasured physical factors, such as lower muscle mass and strength, or a higher prevalence of frailty compared to males,^23,24) which are known to affect functional mobility. Regarding psychiatric comorbidities, previous studies have reported that psychological factors, such as depression and anxiety, are associated with poorer preoperative functional status and greater disability in patients with spinal disorders.²⁵⁾ These psychological factors may influence pain perception, kinesiophobia, and overall physical activity, leading to poorer TUG performance.

The TUG test is an indicator of objective functional impairment and is known to correlate with limitations in ADL²⁶⁾ and frailty.²⁷⁾ Therefore, poorer preoperative TUG performance may indicate reduced physical capacity, which may affect recovery efficiency and lead to exceeding the planned LOS after lumbar fusion surgery. A previous study¹³⁾ reported an association between TUG performance and prolonged LOS in patients who underwent thoracolumbar spinal surgery. However, that study included heterogeneous surgical procedures and spinal regions. Our study reduced this variability by focusing specifically on patients who underwent lumbar fusion for LSS, thereby enhancing the specificity and applicability of the findings. Furthermore, by excluding cases in which exceeding the planned LOS was attributable to personal or social reasons, we were able to isolate medical and physical functional reasons, thereby improving the accuracy and clinical relevance of our conclusions. Building on these findings, identifying patients at risk of exceeding the planned LOS may enable targeted interventions in the early postoperative period. For example, a randomized controlled trial that examined the effects of early rehabilitation showed that rehabilitation beginning on the day of surgery shortened LOS without adverse events.²⁸⁾ These findings suggest the need for enhanced postoperative rehabilitation for patients at high risk of exceeding the planned LOS.

Recently, enhanced recovery after surgery (ERAS) programs have been implemented, incorporating multifaceted strategies such as preoperative patient education, nutritional management, intraoperative management, surgical technique, and postoperative pain management.²⁹⁾ Systematic reviews of ERAS in spine surgery have demonstrated that these programs reduce complications, readmission rates, LOS, and opioid use.^30,31) Similarly, a combination of preoperative intervention and early rehabilitation initiated on the day of surgery has been shown to accelerate improvements in functional disability and shorten LOS without increasing adverse events.³²⁾ These findings suggest that patients with poorer preoperative TUG performance—particularly women and those with psychiatric comorbidities—may benefit from tailored, multifaceted preoperative interventions to reduce the risk of exceeding the planned LOS.

This study has several limitations. First, its retrospective, single-center design may limit generalizability. Second, although we adjusted for several important confounders, the potential for unmeasured confounding factors, such as nutritional status or specific psychological conditions (e.g., kinesiophobia or depression), remains. Third, the definition of planned LOS (14 days) was based on our institution’s clinical pathway and may differ elsewhere, potentially affecting the applicability of the risk estimates to settings with different standard LOS benchmarks.

CONCLUSION

The results of this study showed that poorer preoperative functional mobility, as measured by the TUG test, is an independent predictor of exceeding the planned LOS after lumbar fusion surgery for LSS. Furthermore, female sex and psychiatric comorbidities were associated with significantly poorer preoperative TUG performance. Routine preoperative TUG test assessment may help identify high-risk patients, and targeted strategies such as enhanced preoperative and postoperative rehabilitation may ultimately reduce the risk of exceeding the planned LOS.