Independent Risk Factors for Lag Screw Cut-Out: The Role of Open Reduction in Intertrochanteric Fracture Fixation With the Proximal Femoral Nail

Introduction

Intertrochanteric femoral fractures are among the most common hip fractures in older adults and remain clinically important due to their high morbidity and mortality, largely driven by increasing osteoporosis and low-energy trauma [1,2]. Clinically, these fractures typically present with acute hip pain, inability to bear weight, and a shortened, externally rotated limb after low-energy trauma. Diagnosis is confirmed with anteroposterior and lateral hip radiographs, with computed tomography (CT) used selectively to assess fracture morphology. Early mobilization is the primary treatment goal, and intramedullary fixation particularly the proximal femoral nail (PFN) is widely preferred for its biomechanical advantages [3,4]. The PFN is an intramedullary fixation device designed to provide stable fixation by allowing controlled impaction, reducing bending forces, and facilitating early mobilization. The implant consists of a cephalomedullary nail with a lag screw that provides angular and rotational stability. Despite its biomechanical advantages, PFN fixation is associated with specific complications such as lag screw “cut-out”, varus collapse, Z-effect phenomena, lateral wall fractures, implant breakage, and peri-implant fractures [5].

One of the most serious mechanical complications following PFN fixation is lag screw cut-out, which is characterized by progressive migration of the lag screw into the femoral head, penetration of the articular surface, and the frequent need for revision surgery [6]. Reported cut-out rates in the literature vary between 2% and 16% [6]. Several factors contribute to this complication, including unstable fracture morphology, inadequate reduction, and improper implant positioning [6,7]. A tip–apex distance (TAD) greater than 25 mm and lag screw placement in non-ideal zones of the Cleveland index have repeatedly been emphasized as risk parameters [8–11]. The precision of reduction and implant placement is therefore crucial for minimizing failure risk [12].

Reduction quality also strongly affects mechanical stability [13]. Although closed reduction is commonly attempted, comminuted or unstable fractures may require open reduction, and the long-term effects of these approaches remain debated [13,14].

Data regarding positional changes of the lag screw in patients without cut-out are limited. Some biomechanical and clinical studies have reported millimetric movements even without implant failure, although these changes are generally considered clinically insignificant. Evaluating whether the lag screw remains stable in the long term in non–cut-out cases therefore provides important insights into implant reliability [15].

In this study, we aimed to evaluate whether fracture stability and the use of open reduction are independent risk factors for cut-out and to investigate long-term lag screw stability in non–cut-out cases using radiographic parameters, such as tip–apex distance (TAD), calcar tip–apex distance (CalTAD), collodiaphyseal angle, and advancement distance.

Material and Methods

STUDY DESIGN AND ETHICS APPROVAL:

This study was conducted as a single-center, retrospective, observational clinical investigation. Approval was obtained from the Clinical Research Ethics Committee of Ankara Etlik City Hospital (approval No: AEŞH-BADEK1-2025-253). Medical records and radiographic images of patients who underwent PFN fixation for intertrochanteric femoral fractures between January 2023 and December 2024 were retrospectively reviewed. All PFN implants used in this study were supplied by the same manufacturer and consisted of the Gamma3 Trochanteric Nail System (Trauson, China). All measurements were performed on the hospital’s picture archiving and communication system (PACS).

INCLUSION AND EXCLUSION CRITERIA:

Eligible patients were aged 18 years or older, had a unilateral intertrochanteric femoral fracture treated with PFN, and had a minimum follow-up of 12 months. Exclusion criteria included pathological fractures, prior hip surgery on the same side, and incomplete clinical or radiological data.

STUDY POPULATION:

A total of 302 patients were initially screened. Of these, 60 were excluded due to loss to follow-up, 45 died within the first postoperative year, and 7 had incomplete clinical or radiological data. After applying the eligibility criteria, 190 patients were included in the final analysis (Figure 1). Patients were categorized according to fracture type (stable vs unstable) and surgical technique (open vs closed reduction).

RECORDED VARIABLES:

The collected data included demographic characteristics (age, sex, side), clinical features (surgical approach, fracture type, reduction quality), and radiographic parameters: TAD, CalTAD, collodiaphyseal angle, Cleveland index, lag screw advancement distance, and time to cortical callus formation.

RADIOGRAPHIC EVALUATION:

TAD and CalTAD were measured at 3 time points: early postoperative, 1.5 to 3 months, and final follow-up. All radiographic measurements were performed on standardized anteroposterior and true lateral hip radiographs obtained in the supine position. TAD and CalTAD were measured digitally on the PACS system using the original method described by Baumgaertner et al [16]. The collodiaphyseal angle was measured on anteroposterior radiographs by drawing the femoral shaft and neck axes and was categorized as good, acceptable, or poor, according to Baumgaertner and Chang. Reduction quality was evaluated on immediate postoperative anteroposterior and lateral radiographs using the same criteria. Lag screw position was determined using the Cleveland index on anteroposterior and lateral views. The radiographic measurement techniques used in the study are illustrated in Figure 2. In non–cut-out patients, changes in TAD (mm), CalTAD (mm), collodiaphyseal angle (°), and lag screw advancement distance (cm) were compared across the 3 radiographic time points. In contrast, variables used in the univariate and multivariate analyses of cut-out risk factors (TAD, Cleveland index, reduction quality, collodiaphyseal angle) were evaluated only from early postoperative radiographs. To ensure measurement reliability, all radiographic parameters were measured twice by the same surgeon at 2 separate time points, and the mean value was used for statistical analysis.

DEFINITIONS:

Lag screw advancement distance was defined as the longitudinal displacement of the lag screw between the early postoperative and final follow-up radiographs. Time to cortical callus formation was defined as the first follow-up (in months) at which continuity of at least 3 cortices was observed on both the anteroposterior and lateral radiographs. Intertrochanteric fractures were considered stable if the posteromedial cortex and lateral wall remained largely intact, whereas fractures with comminution of the posteromedial cortex, deficiency of the lateral wall, or multiple proximal fragments were classified as unstable [2]. Cut-out was defined as any migration of the lag screw through the femoral head resulting in loss of fixation stability on follow-up radiographs [17].

STATISTICAL ANALYSIS:

All statistical analyses were performed using IBM SPSS Statistics for Windows, Version 28.0 (IBM Corp, Armonk, NY, USA). Continuous variables are summarized as mean±standard deviation, while categorical variables are presented as frequencies and percentages. Normality of continuous variables was assessed using the Shapiro-Wilk test. Between-group comparisons were conducted using the independent samples t test for normally distributed data and the Mann-Whitney U test for non-normally distributed data. Differences in categorical variables were evaluated using the chi-square test.

For longitudinal comparisons of repeated measurements, paired t tests or repeated-measures analysis of variance were applied, as appropriate. Risk factors associated with lag screw cut-out were first analyzed using univariate logistic regression. Variables with statistical significance in the univariate model were subsequently entered into a multivariate logistic regression analysis to identify independent predictors. Statistical significance was defined as a 2-tailed P value <0.05.

Results

A total of 190 patients were included in the study: 113 men (59.5%) and 77 women (40.5%); 160 in the non–cut-out group and 30 in the cut-out group. The mean age was 72.5±9 years, with no significant difference in age between patients with and without cut-out (73.1±8.7 vs 72.4±9.1 years; P=0.64). The side distribution was also comparable (right: 51.1%, left: 48.9%; P=0.82).

When fracture type was analyzed, most patients with cut-out were noted to have presented with unstable fractures (83.3% vs 78.7%; P=0.007). Regarding surgical method, cut-out occurred significantly more frequently in patients who underwent open reduction, compared with closed reduction (33.3% vs 6.3%; P=0.008). The mean follow-up duration was similar between groups (13.1±7.4 months vs 14.5±6.5 months; P=0.38). In terms of reduction quality, most cases were classified as good, with fewer cases categorized as acceptable, and no significant difference was found between groups (P=0.88) (Table 1).

Univariate logistic regression analysis demonstrated that unstable fracture type (OR, 3.12; 95% CI, 1.31–7.45; P=0.007) and open surgery (OR, 3.45; 95% CI, 1.29–9.27; P=0.008) were significantly associated with cut-out development. Multivariate analysis confirmed both factors as independent predictors (unstable fracture: OR, 2.98; 95% CI, 1.18–7.52; P=0.021; open surgery: OR, 3.41; 95% CI, 1.22–9.56; P=0.019). No significant associations were found for age, sex, TAD, CalTAD, Cleveland index, or collodiaphyseal angle (Table 2, Figure 3).

In the radiographic follow-up of 160 patients without cut-out, no significant changes were observed in TAD, CalTAD, or collodiaphyseal angle between early postoperative and final measurements. The mean TAD was 17.4 mm, the mean CalTAD was 17.8 mm, and the mean collodiaphyseal angle was 132.5°. The mean lag screw advancement distance was 4 mm (Table 3). These results indicate that in non–cut-out patients, the lag screw remained radiographically stable throughout the follow-up period.

Discussion

LIMITATIONS:

The main strengths of this study are the direct comparison of patients with and without cut-out and the detailed radiographic follow-up of non–cut-out cases. Nevertheless, several limitations should be acknowledged. First, the retrospective and single-center design may limit the generalizability of the findings. Second, all radiographic measurements were performed by a single surgeon, which could have introduced observer bias. Third, the rate of loss to follow-up and the number of deaths within the first postoperative year were relatively high, which may have reduced the final sample size and introduced selection bias. Finally, important parameters such as bone mineral density and functional outcomes were not evaluated, and their inclusion might have provided additional insight into the results.

Conclusions

Unstable fracture morphology and open surgical approach were confirmed as independent risk factors for lag screw cut-out. This study contributes to the limited literature by highlighting open surgery as an independent predictor of failure. Furthermore, in cases in which closed reduction cannot achieve sufficient alignment and open surgery is required – particularly in older adult patients with osteoporotic bone – our clinical opinion is that arthroplasty may represent a more reliable alternative to PFN fixation, particularly in older patients with osteoporotic bone.