Development and Internal Validation of a Nomogram for Predicting Early Muscular Calf Venous Thrombosis Following Hip Fracture

Summary

This retrospective study developed and internally validated a six-variable nomogram to estimate the risk of early muscular calf vein thrombosis within 48 h of hip fracture. The model accounts for nonlinear triglyceride effects and may support risk awareness pending external validation.

Abstract

Early muscular calf vein thrombosis (MCVT) detected within 48 h after injury may affect perioperative management in patients with hip fractures. This study aimed to develop and internally validate a nomogram for estimating early MCVT risk in this population. This study retrospectively screened hip fracture patients admitted between 2021 and 2024. Patients were categorized into MCVT and non-MCVT groups based on an admission ultrasound performed within 48 h after injury. Least Absolute Shrinkage and Selection Operator (LASSO) regression was used for feature selection, and restricted cubic splines (RCS) were used to evaluate nonlinear associations. A multivariable logistic regression model was constructed and visualized as a nomogram. Model performance was assessed by discrimination (area under the receiver operating characteristic curve, AUC), calibration (Brier score), and clinical utility (decision curve analysis, DCA), with internal validation using 1,000 bootstrap resamples, following Transparent Reporting of a Multivariable Prediction Model for Individual Prognosis or Diagnosis Plus Artificial Intelligence (TRIPOD + AI) guidance. Among 665 patients included, 44 (6.6%) had early MCVT. Six variables were retained in the final prediction model: time from injury to admission (TFIA), triglycerides (TG), total cholesterol (TC), activated partial thromboplastin time (APTT), neutrophil-to-lymphocyte ratio (NLR), and platelet-to-lymphocyte ratio (PLR). RCS analysis revealed a significant nonlinear association between TG and MCVT risk (p-value for non-linearity <0.001). The model showed good discrimination (AUC: 0.894; 95% CI: 0.829–0.941) and acceptable calibration (Brier score: 0.041). The optimism-corrected C-index was 0.884. DCA suggested potential clinical net benefit across relevant threshold probabilities. In conclusion, the developed nomogram may assist early risk stratification, but external validation in independent cohorts is required before clinical application.

Introduction

Hip fractures in older adults represent a significant global public health challenge and are frequently associated with high morbidity, mortality, and substantial healthcare expenditure¹. Current clinical guidelines strongly advocate accelerated surgical intervention, ideally within 48 h of admission, to alleviate pain, facilitate early mobilization, and mitigate life-threatening complications^2,3. However, preoperative deep vein thrombosis (DVT) remains a formidable barrier to timely surgery. Muscular calf vein thrombosis (MCVT), a specific subtype of distal DVT, involves thrombus forma....

Protocol

The study protocol was approved by the hospital's Institutional Review Board (IRB) ([2025B], IIT Ethics Approval No. 0407).

Study design and participants

This single-center retrospective cohort study was conducted at the First Affiliated Hospital, Zhejiang University School of Medicine. This study consecutively screened the clinical records of patients admitted with hip fractures between January 2021 and December 2024. As this was a retrospective study, a waiver of informed consent from study participants was requested and granted. Based on findings from routine color Doppler ultrasound perfo....

Results

Demographic data

A total of 665 patients with hip fractures met the inclusion criteria and were enrolled in this study (Figure 1). Among them, 44 patients (6.6%) were diagnosed with early MCVT detected on admission ultrasound within 48 h after injury. A detailed comparison of the demographic and clinical characteristics between the MCVT and non-MCVT groups is summarized in Table 2.

LASSO regress.......

Discussion

Following a hip fracture, restricted lower limb mobility can reduce gastrocnemius pump function and venous blood flow velocity. Due to their relatively small diameters and paucity of valves, the muscular calf veins are susceptible to blood stasis and may become an early site of thrombus detection. A previous study by Zhao et al. reported a preoperative MCVT incidence of 23.5% in hip fracture patients¹⁴. In contrast, the cohort incidence was lower at 6.6%. This discrepancy may be attributable to st.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Color Doppler ultrasound system	Philips	EPIQ-5 with eL18-4	Detection and diagnosis of MCVT
Coagulation analyzer	Stago	STAR MAX (https://www.stago-cn.com)	APTT measurement
Hematology analyzer	Cobas	8000 (https://www.cobase.com/)	Blood cell counts, NLR, PLR
Laboratory biochemical analyzer	Sysmex	BC7500 (https://www.sysmex.com.cn/)	TG and TC measurement
Microsoft Excel	Microsoft	2023 (https://www.microsoft.com)	Data organization
R software	R Foundation	https://www.r-project.org/	Statistical analysis
R package glmnet	CRAN	https://cran.r-project.org/web/packages/glmnet/index.html	LASSO regression
R package rms	CRAN	https://cran.r-project.org/web/packages/rms/index.html	RCS, nomogram, calibration
R package pROC	CRAN	https://cran.r-project.org/web/packages/pROC/index.html	ROC analysis
R package rmda / dcurves	CRAN	https://cran.r-project.org/web/packages/dcurves/index.html	Decision curve analysis