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Association of surgical procedure and radiographic hip alignment with hip abductor strength ratio at discharge after proximal femoral fracture surgery
⁎Corresponding author: Satoshi Hakukawa. s.hakukawa@gmail.com
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Received: ,
Accepted: ,
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Abstract
Hip abductor weakness is common after proximal femoral fracture and may contribute to gait instability. The influence of postoperative hip alignment on early recovery of hip abductor strength during inpatient rehabilitation after surgery remains unclear.
To examine longitudinal changes in hip abductor strength and identify factors associated with the operated-to-non-operated hip abductor strength ratio at discharge, focusing on surgical procedure and radiographic alignment.
This retrospective observational cohort study enrolled 64 patients transferred to a rehabilitation hospital after proximal femoral fracture surgery (34 femoral neck fractures treated with hemiarthroplasty; 30 intertrochanteric fractures treated with cephalomedullary nailing). Hip abductor strength was measured using a handheld dynamometer at rehabilitation admission and discharge and normalized by body weight. Radiographic parameters were measured on supine anteroposterior pelvic radiographs; side-to-side differences (operated minus non-operated) were calculated for the neck–shaft angle, hip center of rotation, femoral offset, and trochanteric height. Multivariable linear regression (ANCOVA-type) was performed with the discharge strength ratio as the dependent variable and the admission strength ratio as an adjustment factor.
Hip abductor strength improved on both sides (p < 0.001). The operated side increased from 1.04 ± 0.5 to 1.8 ± 0.7 N/kg and the non-operated side from 1.6 ± 0.6 to 2.3 ± 0.8 N/kg; the operated-to-non-operated ratio improved from 62.7 % to 72.9 %. In the adjusted model (R2 = 0.325), cephalomedullary nailing (vs hemiarthroplasty) was associated with a higher discharge strength ratio (B = 0.114, p = 0.027). A greater neck–shaft angle difference was also associated with a higher discharge strength ratio (B = 0.0073 per degree, p = 0.011). The admission strength ratio remained a significant predictor (B = 0.245, p = 0.002).
Early recovery of the hip abductor strength ratio after proximal femoral fracture was associated with surgical procedure and postoperative neck–shaft angle asymmetry, independent of baseline strength ratio. Postoperative radiographic alignment may aid in stratifying recovery and tailoring rehabilitation, although causal inference is limited.
Keywords
Proximal femoral fracture
Hip abductor strength ratio
Neck–shaft angle
Hemiarthroplasty
Cephalomedullary nailing
1 Introduction
Proximal femoral fractures are among the most common fall-related orthopedic injuries in older adults and often lead to substantial declines in physical function. These declines can result in reduced activities of daily living (ADL) and quality of life (QOL), underscoring the importance of postoperative rehabilitation aimed at restoring and improving physical function. Indeed, approximately half of patients with proximal femoral fractures do not regain their pre-injury functional level and experience impaired gait stability, and about 10 % become unable to walk independently.1 Gait instability after proximal femoral fracture is largely attributable to hip muscle weakness2 and is closely associated with fall risk; therefore, hip muscle strength is one of the most important indicators in rehabilitation programs designed to facilitate return to community living. Among hip muscles, reduced hip abductor strength—primarily generated by the gluteus medius—is frequently observed after proximal femoral fracture.3 Weakness of the gluteus medius can also cause a Trendelenburg gait pattern, further contributing to gait instability.4
Several factors may influence postoperative hip muscle strength recovery, including fracture location and surgical management. The two most common types of proximal femoral fractures are femoral neck fractures (FN) and intertrochanteric fractures (IT). Hemiarthroplasty is commonly performed for FN, enabling early weight bearing after surgery; however, it carries a risk of postoperative dislocation. In contrast, IT is generally treated with internal fixation, which preserves the native hip joint and may help maintain physiological joint function. Nevertheless, depending on fracture characteristics and fixation stability, early weight bearing may be restricted, potentially limiting early mobilization. In addition to fracture type and procedure, hip alignment may substantially affect hip muscle function. Malalignment following surgery is not uncommon in patients with proximal femoral fractures.5 This may occur due to fracture type and osteoporosis-related collapse leading to postoperative varus deformity or progressive shortening6–8, technical factors such as suboptimal screw or implant positioning,9 and secondary postoperative deformity or degenerative changes in adjacent joints that alter functional alignment.10 Accordingly, even among patients with proximal femoral fractures, postoperative rehabilitation strategies may differ considerably depending on fracture type and postoperative alignment, which may in turn contribute to variability in postoperative hip muscle strength recovery.
Previous studies have suggested that recovery of hip abductor strength may be more favorable after hemiarthroplasty than after intramedullary nailing,11 that the quality of reduction may influence the ability to generate hip abductor strength,12 and that unfavorable neck–shaft alignment—particularly excessive valgus—and femoral neck shortening can reduce hip abductor strength by decreasing the abductor moment arm and/or shortening muscle length.13 In addition, maintaining or increasing femoral offset relative to the contralateral side has been reported to contribute to hip abductor strength generation.14 However, these factors have not been comprehensively examined, and no study has evaluated the early postoperative trajectory of hip abductor strength recovery through the period leading to return to community living.
The objective of this study was to longitudinally assess hip abductor strength after proximal femoral fracture surgery and to investigate its associations with surgical procedure and postoperative hip alignment. We prespecified the hypothesis that hip abductor strength recovery is influenced not only by surgical procedure but also by postoperative alignment, and that alignment indices—particularly side-to-side differences in the femoral neck–shaft angle (NSA)—are associated with the operated-to-non-operated hip abductor strength ratio at discharge. In addition, we explored whether these associations may differ by surgical procedure.
2 Methods
2.1 Study design and participants
This retrospective observational cohort study used routinely collected clinical data, with repeated measurements of hip abductor muscle strength at two postoperative time points: admission to and discharge from an inpatient rehabilitation hospital. Patients who sustained a first-time proximal femoral fracture between 2024 and 2025 and were transferred to an inpatient rehabilitation hospital after surgery were eligible. Inclusion criteria were treatment with either hemiarthroplasty or cephalomedullary nailing. Exclusion criteria were a history of neurological disease, impaired cognitive function, and inability to ambulate independently at discharge. Fracture location, surgical procedure, and the weight-bearing protocol at the start of inpatient rehabilitation (full weight bearing, partial weight bearing, or non–weight bearing) were confirmed from the medical records. Pre-injury ambulatory status (independent walking vs use of a cane) was obtained by interview. We also calculated the time from surgery to transfer to the inpatient rehabilitation hospital and the length of stay from rehabilitation admission to discharge home. Sample size adequacy was examined using a sensitivity analysis with G*Power (version 3.1.9.6; Heinrich Heine University Düsseldorf, Düsseldorf, Germany).15,16 To estimate the minimum detectable effect size, the analysis was conducted based on the observed group allocation ratio and the total sample size, using a two-sided α of 0.05 and 80 % power. This study was conducted in accordance with institutional and governmental regulations for human research and was approved by the institutional review board of the participating institution. All procedures adhered to the principles of the Declaration of Helsinki. The study protocol was approved by the institutional review board, and written informed consent was obtained from all participants before participation. No financial incentives were provided.
2.2 Radiographic measurements
Hip alignment was assessed using radiographs. A radiologic technologist obtained a standardized anteroposterior pelvic radiograph with the patient in the supine position and the hip in a neutral (mid-)position. Using these images, we measured the bilateral femoral neck–shaft angle,17 hip center of rotation,18 femoral offset,19 and the side-to-side difference in trochanteric height (Fig. 1). To assess the reliability of radiographic measurements, we randomly selected 10 patients from the study cohort. Three independent investigators (Observer 1: an experienced investigator with >15 years of experience in musculoskeletal research with specific expertise in image-based analysis; Observers 2 and 3: physical therapists with 5 years of clinical experience in orthopaedic rehabilitation) measured all radiographic parameters in these 10 patients to evaluate interobserver reliability. In addition, Observer 1 repeated all measurements in the same 10 patients twice, with an interval of at least 2 weeks between sessions and blinded to the initial results, to evaluate intraobserver reliability. Side-to-side differences in radiographic alignment parameters were calculated as the value on the operated side minus that on the non-operated side (operated − non-operated) for the femoral neck–shaft angle (NSA difference), hip center of rotation (HCR difference), and femoral offset (Offset difference). Negative values indicate smaller values on the operated side than on the non-operated side.
2.3 Lower-limb muscle strength assessment
Lower-limb muscle strength was assessed as the maximal isometric strength of the hip abductor muscles. Participants lay supine on a bed, and the pelvis was stabilized to the bed using a belt. Hip abductor strength was measured using a handheld dynamometer (MT-201, SAKAI Medical Co., Ltd., Tokyo, Japan) placed on the lateral aspect of the distal two-thirds of the thigh. After one practice trial, participants performed a 5-s maximal voluntary isometric contraction under a make-test condition.20 Measurements were performed three times, with sufficient rest between trials, and the highest value was used for analysis. Strength values were normalized to body weight.
2.4 Statistical analysis
All statistical analyses were performed using statistical software (R version 4.x.x). Normality of continuous variables was assessed using the Shapiro–Wilk test. Variables with an approximately normal distribution are presented as mean ± standard deviation, and non-normally distributed variables as median [interquartile range]. Categorical variables are presented as frequency (%). Reliability of radiographic measurements was evaluated using data from 10 randomly selected patients. Interobserver reliability was assessed using measurements obtained by three raters and quantified using the intraclass correlation coefficient based on a two-way random-effects model (ICC [2,1]). Intraobserver reliability was assessed using repeated measurements by the same rater and quantified using the intraclass correlation coefficient based on a two-way mixed-effects model (ICC [3,1]). For each ICC, 95 % confidence intervals were also reported.
To investigate factors associated with hip abductor strength recovery (operated-to-non-operated strength ratio), we performed a multivariable linear regression analysis (ANCOVA-type), with the discharge operated-to-non-operated strength ratio as the dependent variable and the admission operated-to-non-operated strength ratio entered as an adjustment factor. Candidate independent variables entered simultaneously included age, length of stay, surgical procedure, and side-to-side differences in radiographic alignment parameters. All alignment variables were expressed as side-to-side differences (operated minus contralateral side). Prior to multivariable analyses, correlations among alignment variables were examined to assess potential multicollinearity (Pearson's r or Spearman's ρ, as appropriate). To avoid collinearity, highly correlated variables were not entered simultaneously in the same model.
As a sensitivity (secondary) analysis, we added the weight-bearing protocol at rehabilitation admission (full weight bearing, partial weight bearing, or non–weight bearing) and pre-injury ambulatory status (independent walking vs cane use) to the primary model to examine whether these clinical factors influenced the main results. Multicollinearity in the regression models was assessed using the variance inflation factor (VIF). Model assumptions were evaluated by assessing the normality of residuals using the Shapiro–Wilk test and by conducting residual diagnostics. To test the homogeneity of regression slopes (i.e., whether the association of the admission ratio with the discharge ratio differed by surgical procedure), we fitted an additional model including an interaction term between surgical procedure and the admission strength ratio. If the interaction was not statistically significant, the final model excluded the interaction term. Standardized regression coefficients were obtained by re-estimating the regression model after z-standardizing the dependent and independent variables. Statistical significance was set at a two-sided p value of <0.05.
3 Results
3.1 Participant characteristics
A total of 80 patients were initially screened. Of these, 16 were excluded, and 64 were included in the final analysis. Reasons for exclusion were severe deformity of the contralateral hip, inability to complete the initial hip abductor strength assessment due to substantial pain, and missing data due to missed measurement opportunities. The baseline characteristics of the participants are summarized in Table 1. Thirty-four patients had femoral neck fractures and 30 had intertrochanteric fractures. All patients with femoral neck fractures underwent hemiarthroplasty, whereas all patients with intertrochanteric fractures underwent cephalomedullary nailing. Owing to postoperative weight-bearing restrictions, at the time of transfer to the inpatient rehabilitation hospital, three patients in the intertrochanteric fracture group were prescribed partial weight bearing and three were prescribed non–weight bearing. Regarding pre-injury outdoor ambulation, 17 patients used a cane.
| Variable | Total (N = 64) |
| Age, years | 82.0 ± 7.0 |
| Sex, n (%) | Male: 14 (21.8), Female: 50 (78.2) |
| Height, cm | 154.7 ± 8.1 |
| Body mass, kg | 49.4 ± 8.5 |
| Body mass index (BMI), kg/m2 | 25.1 ± 4.3 |
| Affected side, n (%) | Right: 26 (40.6), Left: 38 (59.4) |
| Fracture location, n (%) | Femoral neck: 34 (53.1), Intertrochanteric: 30 (46.9) |
| Weight-bearing instruction, n (%) | WBAT: 58 (90.6), Partial: 3 (4.7), Non-weight-bearing: 3 (4.7) |
| Time from surgery to rehabilitation transfer, days | 20.7 ± 10.0 |
| Length of rehabilitation stay, days | 62.2 ± 20.4 |
| Pre-injury functional status, n (%) | Independent ambulation: 47 (73.4), Cane: 17 (26.6) |
3.2 Radiographic measurement results and reliability (ICC)
Radiographic measurement results and reliability are summarized in Table 2. Side-to-side differences (affected − contralateral) were −0.1 ± 9.9° for NSA, −2.0 ± 26.5 mm for HCR, 0.8 ± 8.4 mm for femoral offset, and 9.5 ± 12.1 mm for GT height (N = 64). ICCs were calculated using radiographs from 10 randomly selected participants (n = 10). Interobserver reliability across three observers was substantial for NSA (ICC[2,1] = 0.761; 95 % CI, 0.576–0.926) and GT height (0.740; 0.442–0.920), moderate for HCR (0.524; 0.334–0.784), and almost perfect for femoral offset (0.928; 0.813–0.980). Intraobserver reliability assessed by repeated measurements by the same observer was substantial for NSA (ICC[3,1] = 0.667; 95 % CI, 0.258–0.867) and GT height (0.604; 0.168–0.851), moderate for HCR (0.440; 0.256–0.773), and almost perfect for femoral offset (0.805; 0.496–0.948).
| Parameter | Diff (N = 64) | Interobserver ICC(2,1) | SA | Intraobserver ICC(3,1) | SA |
| NSA diff (°) | −0.1 ± 9.9 | 0.761 (0.576–0.926) | Substantial | 0.667 (0.258–0.867) | Substantial |
| HCR diff (mm) | −2.0 ± 26.5 | 0.524 (0.334–0.784) | Moderate | 0.440 (0.256–0.773) | Moderate |
| Offset diff (mm) | 0.8 ± 8.4 | 0.928 (0.813–0.980) | Almost perfect | 0.805 (0.496–0.948) | Almost perfect |
| GT height diff (mm) | 9.5 ± 12.1 | 0.740 (0.442–0.920) | Substantial | 0.604 (0.168–0.851) | Substantial |
3.3 Changes in hip abductor strength during inpatient rehabilitation
Changes in hip abductor strength during inpatient rehabilitation are shown in Fig. 2. At admission to the inpatient rehabilitation hospital, maximal hip abductor strength was 1.04 ± 0.5 N/kg on the operated side and 1.6 ± 0.6 N/kg on the non-operated side, corresponding to an operated-to-non-operated strength ratio of 62.7 %. At discharge, maximal hip abductor strength increased to 1.8 ± 0.7 N/kg on the operated side and 2.3 ± 0.8 N/kg on the non-operated side, and the operated-to-non-operated ratio improved to 72.9 %. Hip abductor strength significantly improved from admission to discharge on both sides (p < 0.001).
3.4 Factors associated with hip abductor strength recovery
To examine factors associated with the operated-to-non-operated hip abductor strength ratio at discharge, we performed a multivariable linear regression analysis (ANCOVA-type) adjusted for the admission operated-to-non-operated strength ratio (Table 3). The overall model was significant (F(7,56) = 3.86, p = 0.0017), with an R2 of 0.325 (adjusted R2 = 0.241). In the multivariable model, surgical procedure (hemiarthroplasty = 0, cephalomedullary nailing = 1) was independently associated with the discharge strength ratio, with a higher ratio in the cephalomedullary nailing group (B = 0.114, p = 0.027). The neck–shaft angle side-to-side difference (operated minus non-operated) was also independently associated with the discharge strength ratio, such that a greater asymmetry was associated with a higher discharge ratio (B = 0.0073 per degree, p = 0.011). Among alignment variables (side-to-side differences), the neck–shaft angle difference showed a moderate negative correlation with the femoral offset difference (r = −0.60), and the hip center of rotation difference correlated weakly-to-moderately with the trochanteric height difference (r = 0.38); full correlation results are provided in Supplementary Table S1. In addition, the admission strength ratio was significantly associated with the discharge strength ratio (B = 0.245, p = 0.002). In contrast, age, length of stay, hip center of rotation difference, and femoral offset difference were not significantly associated with the discharge strength ratio (all p > 0.05).
| Predictor | B | SE | 95 % CI | t | p | Std β |
| Intercept | 0.4841 | 0.2355 | 0.0123 to 0.9559 | 2.055 | 0.0445 | 0 |
| Age | 0.0004 | 0.0028 | −0.0053 to 0.0060 | 0.125 | 0.9011 | 0.015 |
| Length of stay | 0.0011 | 0.001 | −0.0009 to 0.0032 | 1.092 | 0.2796 | 0.14 |
| Procedure (BHP vs IMN) | 0.1141 | 0.0504 | 0.0132 to 0.2150 | 2.265 | 0.0274 | 0.352 |
| NSA difference | 0.0073 | 0.0028 | 0.0017 to 0.0128 | 2.619 | 0.0113 | 0.445 |
| HCR difference | 0.0011 | 0.0034 | −0.0058 to 0.0079 | 0.314 | 0.7549 | 0.039 |
| Offset difference | 0.001 | 0.0029 | −0.0048 to 0.0067 | 0.339 | 0.7356 | 0.051 |
| Baseline abductor ratio | 0.2453 | 0.076 | 0.0930 to 0.3975 | 3.227 | 0.0021 | 0.374 |
To evaluate the potential impact of leg length discrepancy, we conducted a sensitivity analysis adding the trochanteric height side-to-side difference to the primary model. Trochanteric height difference was not significantly associated with the discharge strength ratio (p = 0.93), and the interpretation of the primary findings (surgical procedure, neck–shaft angle difference, and admission strength ratio) was unchanged. We further performed a sensitivity analysis additionally adjusting for weight-bearing restrictions at rehabilitation admission (full, partial, or non–weight bearing) and pre-injury ambulatory status (independent walking vs cane use) (Supplementary Table S2). Neither factor showed a significant association, and the interpretation of the main results remained broadly unchanged. Finally, to assess whether the association between admission and discharge strength ratios differed by surgical procedure, we fitted a model including an interaction term (surgical procedure × admission strength ratio); the interaction was not significant (B = −0.131, p = 0.391). Therefore, the primary analysis adopted the model without the interaction term.
4 Discussion
In this study, we investigated factors associated with the operated-to-non-operated hip abductor strength ratio at discharge in patients after proximal femoral fracture surgery using a multivariable linear regression model (ANCOVA-type) adjusted for the admission strength ratio. Surgical procedure and postoperative neck–shaft angle (NSA) asymmetry (operated minus non-operated) were independently associated with the discharge strength ratio, and the admission strength ratio was also a significant predictor of the discharge ratio. These findings support our main hypothesis that, in addition to surgical procedure, postoperative alignment—particularly NSA asymmetry—may contribute to early recovery of hip abductor strength. Although we also explored whether the strength of these associations differed by surgical procedure, the interaction term was not significant; therefore, we could not conclude that the relationships differed between procedures.
Notably, our results indicated that patients treated with cephalomedullary nailing had a higher operated-to-non-operated hip abductor strength ratio at discharge than those treated with hemiarthroplasty, which contrasts with some previous reports.11 This discrepancy suggests that the observed difference may reflect not only the procedure itself but also fracture-type–related changes in hip alignment and their influence on hip abductor function. NSA is known to decrease with aging, reflecting a tendency toward varus alignment.21 In addition, postoperative varus collapse and proximal femoral shortening due to lag screw sliding have been reported to impair the hip abductor mechanism and may contribute to worse gait and functional outcomes.22 In our cohort, however, NSA difference was moderately negatively correlated with femoral offset difference, suggesting that NSA changes occurred in tandem with offset changes. Because both excessive varus (decreased NSA) and potential overcorrection (increased NSA relative to the contralateral side) may alter the abductor lever arm, interpretation of the isolated effect of NSA should be made cautiously. Our radiographic parameters demonstrated overall acceptable measurement reliability (Table 2). However, HCR showed only moderate interobserver and intraobserver agreement, which may have introduced measurement variability and attenuated associations with the outcome, potentially contributing to the non-significant findings for HCR in the regression model. In addition, our sensitivity analysis incorporating GT height difference (as a surrogate of leg length discrepancy) did not change the interpretation of the primary findings, supporting the robustness of the main conclusions. Nonetheless, our findings collectively suggest that maintaining postoperative NSA close to the contralateral side may be clinically important after proximal femoral fracture surgery.
In this study, weight-bearing restrictions during inpatient rehabilitation and pre-injury ambulatory status were not independently associated with the discharge hip abductor strength ratio. One possible explanation is that the isometric contraction assessed by handheld dynamometry may not fully reflect the neuromuscular demands and activation patterns during weight-bearing and walking. Experimental studies that induced hip abductor weakness have reported that gait biomechanics may not necessarily change.23 Moreover, gait instability associated with a Trendelenburg pattern—often attributed to hip trauma or hip osteoarthritis—has been reported to show only a weak relationship with measured hip abductor strength.24,25 In addition, unloading-related muscle weakness tends to be more pronounced in antigravity muscles such as the knee extensors and ankle plantar flexors,26,27 and hip abductor activity during quiet standing may be relatively low.28 In routine postoperative rehabilitation, hip abductor activation can still be achieved through supine or side-lying therapeutic exercises and functional training (e.g., bed mobility and sit-to-stand practice), even under partial weight-bearing constraints. These factors may explain why prescribed weight-bearing restriction did not emerge as an independent determinant of early recovery of the hip abductor strength ratio.
Clinically, our results suggest that the operated-to-non-operated hip abductor strength ratio at discharge may be associated with surgical procedure and postoperative alignment after accounting for baseline strength status. Rather than assuming a uniform recovery trajectory based solely on postoperative time, clinicians may consider stratifying patients using both the admission strength ratio and postoperative radiographic measures to inform individualized intervention planning and discharge support. First, the association between admission and discharge strength ratios supports the value of early muscle function assessment at the start of inpatient rehabilitation for short-term prognostication. Because the outcome was a ratio, it may partially account for generalized deconditioning and reduced activity affecting both limbs, and bilateral assessment may provide a practical index for tracking relative recovery and supporting goal-setting during rehabilitation. Second, the association between NSA asymmetry and the discharge strength ratio suggests that postoperative alignment may be relevant not only for reduction assessment but also for identifying patients at risk of slower recovery. Radiographic evaluation may help guide prioritization of hip abductor strengthening, selection of gait aids, and titration of intervention intensity (e.g., graded loading practice, pain management, and progression of walking training). Third, within the scope of our analyses, the primary associations were robust to sensitivity analyses that accounted for additional clinical factors, suggesting that combining procedure, alignment, and baseline strength ratio may offer a feasible framework for early communication of recovery expectations and post-discharge planning, including fall prevention, assistive device selection, home environment modification, and the need for continued rehabilitation.
Several limitations should be acknowledged. First, this retrospective observational study is susceptible to confounding by indication: surgical procedure is closely linked to fracture type (e.g., femoral neck vs intertrochanteric), bone quality, displacement severity, pre-injury activities of daily living, cognitive status, comorbidities, postoperative pain, and postoperative protocols (including weight-bearing strategies)29–31. Therefore, even after adjustment, residual confounding cannot be excluded, and the observed associations should not be interpreted as causal effects of procedure on strength recovery. Surgical procedure may also partially proxy differences across the entire care pathway, including surgical invasiveness and feasibility of early mobilization.32,33 Second, strength recovery during inpatient rehabilitation is influenced by multiple factors, including rehabilitation dose and content (frequency/intensity of hip abductor training, progression of loading practice, amount of gait training), daily physical activity, pain, fear avoidance, complications, and nutritional status34–37. These factors were not sufficiently quantified in our dataset and may have contributed to unmeasured confounding. Additionally, adherence to prescribed weight-bearing restrictions and actual loading in daily practice likely varied between individuals, which may have led to exposure misclassification and attenuation of weight-bearing–related effects. Third, alignment parameters (NSA, hip center of rotation, femoral offset, and trochanteric height) were measured primarily from two-dimensional radiographs and may be influenced by pelvic rotation/tilt, limb positioning, and radiographic conditions. Measurement error could lead to unstable estimates and potential under- or overestimation of associations. Finally, the sample size was modest for a multivariable model with multiple covariates; in particular, the study may have been underpowered to detect interaction effects or to support procedure-specific subgroup analyses. A non-significant interaction does not necessarily indicate the absence of effect modification.
This study focused on the period from transfer to an inpatient rehabilitation hospital through discharge home. Future studies should evaluate longer-term outcomes, including gait function and falls after discharge, to clarify the clinical significance of the operated-to-non-operated hip abductor strength ratio and the radiographic indices associated with it, and to support refinement of surgical and rehabilitation strategies.
5 Conclusion
In this study of patients after proximal femoral fracture surgery, the operated-to-non-operated hip abductor strength ratio at discharge was independently associated with surgical procedure and postoperative neck–shaft angle asymmetry (operated minus non-operated) in multivariable analyses adjusted for the admission strength ratio. In addition, the admission operated-to-non-operated strength ratio was a significant predictor of the discharge ratio. These findings suggest that, alongside early postoperative strength assessment, evaluation of postoperative alignment may help stratify recovery and individualize intervention planning; however, prospective studies are required to confirm causality.
Artificial intelligence (AI) authoring tools
A generative AI tool (ChatGPT) was used only for auxiliary assistance in drafting portions of the text. All content was reviewed, edited, and finalized by the authors, who take full responsibility for the accuracy, interpretation, and conclusions of the manuscript. The AI tool was not used for data analysis, result interpretation, or generating scientific conclusions.
CRediT author statement
Satoshi Hakukawa; Conceptualization, Methodology, Formal analysis, Investigation, Writing - Original Draft, Visualization, Shunsuke Onuma; Methodology, Formal analysis, Investigation, Writing - Review & Editing, Kanata Yoshihara; Methodology, Validation, Formal analysis, Investigation, Writing - Review & Editing. All authors have read and approved the final manuscript and agree to be accountable for all aspects of the work.
Data availability statement
The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.
Permission to reproduce material from other sources
Not applicable. No previously published material was reproduced in this manuscript.
Ethical approval statement
The study protocol complied with ethical guidelines for medical and health research involving human subjects. Ethical approval for this study was obtained from the Institutional Review Board Reiwa rehabilitation hospital (APPROVAL NUMBER is 2023-014).
Patient consent statement
Written informed consent was obtained from all participants prior to enrollment in the study.
Funding statement
This research was supported by research funding from Chiba Physical Therapy Association (APPROVAL NUMBER is CPTA2024-01).
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