Femoral Neck Fracture With Anterior Tilt

ABSTRACT

Objective

Posteriorly tilted femoral neck fractures have been extensively studied, whereas anteriorly tilted fractures remain largely unreported. This study aims to characterize the clinical features, radiographic patterns, and postoperative outcomes of femoral neck fractures with anterior tilt.

Methods

This retrospective cohort study included adult patients with OTA/AO type 31B femoral neck fractures who underwent internal fixation within 36 h at a single orthopedic center from 2018 to 2022 and had ≥ 24 months of follow‐up. Tilt angle was assessed using preoperative radiographs and CT. Associations between fracture characteristics and postoperative outcomes were examined using univariate and multivariable logistic regression, with covariates selected according to clinical relevance and univariate significance.

Results

Among 212 patients (median age: 55 years, 53.3% male), anterior tilt fractures were more common in females (57.6%) and those with valgus malalignment (69.7%). Anteriorly tilted femoral neck fractures required a distinct reduction technique compared to conventional femoral neck fractures. Displaced fractures were significantly associated with a higher risk of femoral head necrosis (adjusted odds ratio [aOR] = 4.16; 95% confidence interval [CI] 1.29–13.42; p = 0.017). Stratified analysis revealed that anteriorly tilted femoral neck fractures with varus malalignment—herein referred to as the “anterior‐flexion/adduction” subtype—were significantly associated with increased risk of femoral head necrosis (aOR = 7.19; 95% CI 1.12–46.18; p = 0.038).

Conclusions

Anterior tilt alone is not a general prognostic risk factor; however, fractures characterized by anterior tilt combined with varus alignment represent a high‐risk subtype requiring careful preoperative recognition and treatment planning. Further prospective studies are needed to validate these findings.

In patients with OTA/AO type 31B femoral neck fractures, anterior tilt fractures were more common among females and those with valgus malalignment. Although outcomes and complication rates did not differ significantly among fracture patterns, patients with displaced fractures had a higher risk of developing femoral neck necrosis.

1. Introduction

Femoral neck fractures remain a significant clinical challenge due to their risk of nonunion and femoral head necrosis, complications that significantly affect long‐term function and quality of life [1, 2]. Numerous factors, including patients' age, degree of fragment separation, displacement, and presence of posterior comminuted fractures, have been associated with poor outcomes after internal fixation [3, 4]. Additionally, variations in femoral anatomy, such as valgus and varus, may influence fracture fixation stability and post‐surgical outcomes [5, 6].

Although posterior tilt and posterior femoral neck cortical defects have been well documented as predictors of fixation failure [7, 8], much less attention has been given to anterior cortical defects and anterior tilt, despite their potential relevance to fracture stability and reduction mechanics. In our previous cohort study [9], approximately 10% of displaced femoral neck fractures exhibited the anterior portion of the femoral neck defects, highlighting the importance of considering the fracture pattern and its impact on treatment and recovery.

Recent literature has highlighted limitations in the current understanding and application of closed reduction techniques. Zhu et al. [10] emphasized that commonly used methods, such as those described by Leadbetter and Whitman, are largely designed for posteriorly angulated fractures and may be suboptimal for anteriorly angulated femoral neck fractures. Many existing studies provide limited discussion of morphology‐specific reduction challenges, which may contribute to inconsistent reduction quality and clinical outcomes [11].

Mechanically, anterior tilt presents a distinct stress environment: the anterior cortex undergoes compression while the posterior cortex bears tension, complicating efforts to achieve and maintain anatomic reduction [6, 12]. Despite these unique characteristics, anteriorly tilted fractures are not explicitly addressed in major classification systems (e.g., Garden, Pauwels, Arbeitsgemeinschaft für Osteosynthesefragen/Orthopedic Trauma Association [AO/OTA]) [6, 11], potentially limiting clinical recognition and appropriate surgical planning.

Building upon these prior observations, the present study focuses on a distinct and underexplored subset of femoral neck fractures characterized by anterior tilt. Although anterior tilt fractures are often under‐recognized in routine clinical practice, their unique biomechanical characteristics—particularly the reversed tension‐compression pattern—render conventional reduction techniques less effective. Given the lack of morphology‐specific guidance in the existing literature, there is a critical need to better understand the reduction challenges specific to anterior tilt fractures. This study aims to address this gap by systematically examining the radiographic and clinical features of anteriorly tilted femoral neck fractures and evaluating factors that may influence the success of closed reduction in these cases.

2. Methods

2.1. Study Design and Sample

This retrospective cohort study extracted data of patients with femoral neck fracture being treated surgically between January 1, 2018, and December 31, 2022 at the Trauma Orthopedics Department of Shanghai Sixth People's Hospital. Eligible patients diagnosed with type 31B femoral neck fractures according to the AO/OTA fracture and dislocation classification system, and who had undergone internal fixation surgery within 36 h of injury (without receiving any prior medical treatment before hospital presentation), and had a minimum follow‐up period of 24 months, were included in the cohort. Skeletally immature patients, had associated fractures involving the acetabulum, femoral head, or greater trochanter, were treated by joint replacement, or had died within the follow‐up period, were excluded. Aside from those exclusions, patients without complete X‐ray records so that the affected hip could not be compared with the contralateral side were also excluded from the study cohort. These exclusion criteria were applied to ensure a homogeneous study population and reliable assessment of radiographic parameters, minimizing confounding factors that could impact reduction evaluation or outcomes.

This study was conducted and reported in accordance with the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) guidelines, and the completed STROBE checklist is provided in the Supporting Information (Table S1).

2.2. Main Study Outcomes

Surgical outcomes for patients with femoral neck fractures characterized by anterior or posterior tilt were compared. Fracture tilt direction was determined preoperatively based on standardized radiographic and CT criteria, as described in the Tilt Assessment section. Classification was primarily based on sagittal‐plane alignment on lateral radiographs and CT images, incorporating fracture angulation, anterior–posterior compression patterns, and impaction characteristics. Patients were assigned to the anterior or posterior tilt group accordingly before outcome analysis.

Primary study outcomes were fixation failure, femoral head necrosis, and postoperative complications. The outcomes were assessed by specialized physicians using clinical evaluation and radiographic imaging. Femoral head necrosis was diagnosed during follow‐up based on serial anteroposterior and lateral hip radiographs demonstrating subchondral sclerosis, crescent sign, femoral head flattening, or collapse. When radiographic findings were equivocal, magnetic resonance imaging (MRI) was performed to confirm the diagnosis of osteonecrosis [13]. Internal fixation failure was defined as any mechanical failure occurring during the follow‐up period that required re‐intervention or revision surgery. This included loss of reduction (displacement > 5 mm or change in neck–shaft angle > 10° compared with immediate postoperative images), screw or implant cut‐out, breakage, back‐out, or nonunion at the fracture site. Any case requiring revision, internal fixation, or conversion to arthroplasty was classified as fixation failure. Postoperative complications included surgical site infection, implant‐related complications (e.g., irritation or loosening), and other documented adverse events. Early complications were recorded during hospitalization and within 30 days postoperatively, while late complications (including femoral head necrosis and fixation failure) were assessed throughout the entire follow‐up period of at least 24 months.

2.3. Closed Reduction Technique

All patients in this study were treated according to the standardized clinical protocols of the department, including uniform surgical techniques, reduction criteria, and postoperative rehabilitation regimens. All procedures were performed by a consistent surgical team, ensuring uniformity in surgical technique and minimizing inter‐operator variability.

Specifically, all patients underwent closed reduction on a standard orthopedic traction table. Flexion–internal rotation maneuvers were strictly avoided. Instead, a 2.5‐mm Kirschner wire (K‐wire) was inserted percutaneously and anchored into the anterior cortex of the femoral neck, close to the bone surface, to control the femoral head using the joystick technique. Under fluoroscopic guidance, reduction was achieved by combining joystick manipulation with proximal upward pressure on the distal fragment. Once an acceptable closed reduction was confirmed, internal fixation was performed.

Figure 1 illustrates intraoperative fluoroscopic images demonstrating the use of a percutaneously inserted Kirschner wire (K‐wire) as a joystick to assist in the closed reduction of an anteriorly tilted femoral neck fracture (Figure 1).

FIGURE 1.

Intraoperative fluoroscopic images showing joystick‐assisted closed reduction of an anteriorly tilted femoral neck fracture. A 2.5‐mm Kirschner wire was percutaneously inserted into the anterior aspect of the femoral neck, ensuring that the tip remained in close contact with the bone surface to avoid injury to the neurovascular structures anterior to the femoral neck. The wire was used as a joystick to displace the femoral head upward and posteriorly along the femoral neck axis, thereby correcting the anterior tilt and achieving near‐anatomic alignment. This technique offers angular control and temporary fixation during reduction, which is especially valuable in fractures with anterior cortical comminution or insufficient anterior cortical support.

2.4. Reduction Criteria

Reduction quality was evaluated using multiple radiographic parameters, including the Garden alignment index (assessing neck‐shaft angle and medial trabecular alignment), the Lowell S‐curve on anteroposterior radiographs, and the criteria described by Collinge et al., which emphasize restoration of cortical continuity and anatomic alignment [12, 14, 15].

2.5. Tilt Assessment

All patients received pre‐operative imaging, including anteroposterior pelvis X‐ray, lateral hip X‐ray, and CT scans of both hips with a slice thickness of 1.0 mm or less. Specific criteria were used to define and evaluate the tilt [16].

Femoral neck fractures with anterior tilt can be identified on lateral X‐rays by a distinct posterior angulation of the fracture ends, indicating anterior displacement of the femoral head. The varus or valgus alignment of the fracture is assessed comprehensively based on the positional relationship of the proximal and distal fracture ends, the neck‐shaft angle, and the Garden index [5, 6, 16].

In cases of severe displacement due to high‐impact trauma, the characteristics of the fracture ends can aid in assessment. If comminuted bone fragments are present anteriorly, while the posterior aspect exhibits only a linear fracture line without fragmentation, the anterior portion has likely sustained compressive stress while the posterior portion was subjected to tensile stress, indicating an injury with anterior tilt.

In cases of mild anterior tilt, assessment can be performed using sagittal and/or axial CT scans. Fractures with anterior tilt typically exhibit anterior compression impaction or a greater degree of compression impaction anteriorly compared to posteriorly.

2.6. Covariates

Patients' demographic and clinical characteristics, including age, sex, fracture characteristics by Garden classification, femoral head malalignment, and surgical subtype were extracted and analyzed. Femoral head fractures were classified according to the Garden classification system, as previously described [17].

2.7. Garden Fracture Typing

In this study, we adopted a refined interpretation of the Garden classification system to better characterize fracture morphology and displacement severity. This refinement, based on the original Garden classification, was developed to enhance consistency in radiographic assessment and to guide clinical decision‐making more precisely.

Specifically, Garden Type I fractures were defined as impacted valgus or varus fractures of the femoral head, with a smooth and continuous medial cortical line of the femoral neck observed on anteroposterior radiographs. Type II fractures were complete but non‐displaced, characterized by a fracture line traversing the full transverse diameter of the femoral neck without impaction of the fracture ends. Type III fractures were partially displaced, with a visible step‐off at the fracture site on anteroposterior or lateral radiographs. The femoral neck axis remained aligned with the central half of the femoral head, or the trabecular structure of the femoral head exhibited angulation exceeding 15°. Impacted fractures with an opening of > 5 mm on the contralateral side of the fracture required reduction. Type IV fractures were severely displaced, with an overlap of the proximal and distal fracture fragments exceeding 5 mm or a femoral neck axis positioned in the lateral quarter of the femoral head. Displacement was primarily characterized by angulation and lateral translation, with the fracture ends showing minimal or no impaction. Based on this classification, fractures of Garden types I and II were considered non‐displaced, whereas types III and IV were classified as displaced [17].

Femoral head malalignment was divided into varus or valgus conditions. The surgery types included screw fixation and femoral neck system.

2.8. Statistical Analysis

Descriptive statistics were used to summarize the characteristics, with continuous data presented as median with an interquartile range (IQR) and categorical variables presented as frequencies and percentages. Group differences were assessed using the Wilcoxon rank‐sum test for continuous variables and the χ ² test or Fisher's exact test for categorical variables. Univariate and multivariable regression analyses were conducted to evaluate associations between clinical variables and postoperative outcomes. Binary logistic regression was used for complications, and multinomial logistic regression was applied for fixation failure. Results are presented as adjusted odds ratios (aORs) with 95% confidence intervals (CIs). Multivariable models were adjusted for covariates with a p < 0.15 in univariate analyses, and the covariates included differed by outcome. Subgroup analyses were performed to evaluate the association between anterior versus posterior tilt and postoperative outcomes. These analyses were stratified by age, sex, Garden classification, femoral head malalignment, and surgical subtype. All p‐values were two‐sided, and p < 0.05 was established as statistical significance. All statistical analyses were performed using the statistical software package SAS software version 9.4 (SAS Institute Inc., Cary, NC, USA).

3. Results

3.1. Study Population

Figure 2 depicts the patient selection process. A total of 314 patients admitted with femoral neck fractures were included. Of these, 35 patients were excluded due to missing follow‐up data, incomplete X‐ray records, or inability to compare the fracture with the contralateral hip joint. An additional 42 patients with follow‐up periods of less than 24 months, 2 patients who died, 19 patients initially treated with joint replacement, 2 patients with immature skeletal development, 1 patient with a pathological or stress fracture, and 1 patient with hip dislocation or fractures involving the acetabulum, femoral head, or greater trochanter were also excluded. Ultimately, 212 patients were included in the final analyses (Figure 2).

FIGURE 2.

Flow chart of study population selection.

3.2. Patients' Demographic and Clinical Characteristics

Table 1 displays patients' characteristics. Among the 212 patients included in this study, 66 (31.13%) were classified as having femoral neck fractures with anterior tilt, whereas 146 (68.87%) were classified as having posterior tilt. The median age of patients with femoral neck fractures was 55 years, 53.3% were male, and the median follow‐up time was 29.0 months. Patients with femoral neck fractures characterized by anterior tilt had a higher proportion of females (57.6% vs. 41.8%) and valgus alignment (69.7% vs. 30.1%), along with a lower incidence of displaced fractures (56.1% vs. 80.1%), compared to those with posterior tilt (Table 1).

TABLE 1.

Characteristics of patients with femoral neck fractures.

Characteristics	Total (n = 212)	Anterior tilt (n = 66)	Posterior tilt (n = 146)	p
Age, years	55.0 (48.0–61.5)	56.0 (49.0–63.0)	54.0 (48.0–59.0)	0.083
Sex				0.033
Male	113 (53.3)	28 (42.4)	85 (58.2)
Female	99 (46.7)	38 (57.6)	61 (41.8)
Fracture characteristics
Garden classification				< 0.001
Non‐displaced fracture	58 (27.4)	29 (43.9)	29 (19.9)
Displaced fracture	154 (72.6)	37 (56.1)	117 (80.1)
Femoral head malalignment				< 0.001
Varus	122 (57.5)	20 (30.3)	102 (69.9)
Valgus	90 (42.5)	46 (69.7)	44 (30.1)
Surgery subtype				0.967
Screw fixation	177 (83.5)	55 (83.3)	122 (83.6)
femoral neck system	35 (16.5)	11 (16.7)	24 (16.4)
Follow‐up time (months)	29.0 (19.5–39.0)	31.5 (13.0–49.0)	27.5 (22.0–37.0)	0.270
Outcome
Fixation failure				0.831
No fixation failure	119 (56.1)	37 (56.1)	82 (56.2)
Femoral head necrosis	70 (33.0)	23 (34.8)	47 (32.2)
Failed internal fixation	23 (10.8)	6 (9.1)	17 (11.6)
Complications	12 (5.7)	5 (7.6)	7 (4.8)	0.522

Note: Continuous variables are presented as median (25th–75th percentile) and performed as Wilcoxon rank‐sum test. Categorical variables are presented as n (%) and performed by the χ ² test or Fisher's exact test, as appropriate. p < 0.05 are shown in bold.

3.3. Associations Between Femoral Neck Fracture and Postoperative Outcomes

Table S1 displays the associations between variables, including femoral neck fractures and postoperative outcomes, as assessed using univariate and multinomial logistic regression models. After adjusting for relevant confounders in multivariable analysis, the associations between femoral neck fractures and postoperative outcomes are summarized in Table 2.

TABLE 2.

Associations between study variables and postoperative outcomes using multivariable multinomial logistic regression analysis.

Study variables	Femoral head necrosis		Internal fixation failure		Complication
	aOR (95% CI)	p	aOR (95% CI)	p	aOR (95% CI)	p
Femoral neck fracture characteristics
Anterior tilt	1.42 (0.51–3.98)	0.506	0.53 (0.10–2.83)	0.457	1.30 (0.38–4.47)	0.681
Posterior tilt	Ref.		Ref.		Ref.
Age (years)					1.04 (0.97–1.12)	0.261
Garden classification
Non‐displaced fracture	Ref.		Ref.		Ref.
Displaced fracture	4.16 (1.29–13.42)	0.017	2.94 (0.33–26.52)	0.337	0.59 (0.14–2.49)	0.469
Femoral head malalignment
Varus	Ref.		Ref.
Valgus	1.66 (0.64–4.29)	0.294	0.86 (0.14–5.32)	0.870
Surgery subtype
Screw fixation	Ref.		Ref.
femoral neck system	1.78 (0.68–4.70)	0.244	0.69 (0.09–5.21)	0.723
Follow‐up time, month	0.86 (0.82–0.90)	< 0.001	0.72 (0.65–0.79)	< 0.001

Note: p < 0.05 are shown in bold.

Abbreviations: aOR, adjusted odds ratio; CI, confidence interval; ref., reference.

No significant associations were found between the tilt and fixation failure or complications. Displaced fracture was significantly associated with a higher risk of femoral head necrosis compared to non‐displaced fracture (aOR = 4.16; 95% CI 1.29–13.42; p = 0.017). Longer follow‐up time was associated with a significantly lower risk of femoral head necrosis (aOR = 0.86; 95% CI 0.82–0.90; p < 0.001) and internal fixation failure (aOR = 0.72; 95% CI 0.65–0.79; p < 0.001) (Table 2).

Table 3 summarizes the results of regression analysis stratified by age, sex, Garden classification, femoral head malalignment, and surgery subtype. After adjusting for variables that were p < 0.15 in univariate analysis (except for the stratified variables), the multivariable analysis revealed that patients with femoral neck fractures characterized by anterior tilt had significantly increased odds of femoral head necrosis when accompanied by varus malalignment—herein referred to as the “anterior‐flexion/adduction” subtype (aOR = 7.19; 95% CI 1.12–46.18; p = 0.038) (Table 3).

TABLE 3.

Associations between anterior versus posterior tilt and postoperative outcomes, stratified by age, sex, garden classification, femoral head malalignment, and surgery subtype.

Study variables	Femoral head necrosis		Internal fixation failure		Complication
	aOR a (95% CI)	p	aOR a (95% CI)	p	aOR b (95% CI)	p
Age (years)
≥ 60	2.32 (0.36–14.78)	0.375	NE	—	1.26 (0.28–5.68)	0.761
< 60	0.90 (0.24–3.38)	0.880	0.57 (0.07–4.80)	0.602	0.83 (0.08–8.84)	0.876
Sex
Male	0.60 (0.14–2.60)	0.498	2.27 (0.14–35.85)	0.562	NA	—
Female	3.44 (0.49–24.35)	0.216	0.20 (0.003–12.39)	0.443	5.50 (0.58–52.62)	0.139
Garden classification
Non‐displaced fracture	2.25 (0.29–17.32)	0.436	NE	—	2.33 (0.38–14.12)	0.359
Displaced fracture	1.21 (0.36–4.06)	0.759	0.60 (0.09–3.93)	0.591	0.59 (0.07–5.25)	0.292
Femoral head malalignment
Varus	7.19 (1.12–46.18)	0.038	1.81 (0.16–20.78)	0.635	2.96 (0.62–14.12)	0.173
Valgus	0.78 (0.19–3.17)	0.733	0.63 (0.01–41.15)	0.830	1.01 (0.12–8.28)	0.996
Surgery subtype
Screw fixation	1.52 (0.48–4.84)	0.478	0.57 (0.09–3.43)	0.537	1.01 (0.27–3.80)	0.990
Fracture neck system	1.68 (0.11–25.36)	0.708	NE	—	NA	—

Abbreviations: aOR, adjusted odds ratio; CI, confidence interval; NA, not applicable (no event occurred in one group); NE, the sample size in a subgroup is too small to perform adjustments; ref., reference.

^a Adjusted for p < 0.15 in univariate analyses (except for the stratified variables), including garden classification, femoral head malalignment, surgery subtype, and follow‐up time.

^b Adjusted for p < 0.15 in univariate analyses (except for the stratified variables), including age (continuous) and garden classification.

3.4. Representative Case Presentation

A 61‐year‐old man presented with a valgus‐impacted femoral neck fracture exhibiting marked anterior tilt (Garden index −20) on preoperative radiographs and CT imaging (Figure 3). The patient underwent closed reduction and internal fixation with cannulated screws. Although early postoperative recovery was uneventful, radiographs obtained 41 months later demonstrated segmental collapse of the femoral head consistent with avascular necrosis (Figure 4).

FIGURE 3.

Preoperative imaging demonstrates the characteristic morphology of an anteriorly tilted femoral neck fracture. (A) Anteroposterior pelvic radiograph showing a valgus‐impacted femoral neck fracture with anterior tilt (Garden index: –20). (B) Additional anteroposterior view confirming valgus impaction and external rotation deformity. (C) Axial CT image revealing anterior femoral head tilt and anteromedial butterfly fragment. (D) 3D CT reconstruction demonstrating overall fracture morphology. Anterior tilt angle was measured on lateral radiographs or sagittal CT as the angle between the femoral neck axis and a line perpendicular to the fracture line, with positive values indicating anterior tilt and negative values indicating posterior tilt.

FIGURE 4.

Forty‐one‐month follow‐up imaging showing avascular necrosis of the femoral head. (A) Anteroposterior pelvic radiograph demonstrating segmental collapse and sclerosis of the right femoral head, consistent with avascular necrosis. (B) Frog‐leg lateral view confirming femoral head deformity and loss of sphericity.

4. Discussion

4.1. Clinical and Radiographic Significance of Anterior Tilt Fractures

To our knowledge, this is the first study to systematically characterize femoral neck fractures with anterior tilt as a distinct clinical presentation. While previous research has largely focused on posterior tilt—reporting its association with fixation failure and femoral head necrosis—anterior tilt has received limited attention in terms of its radiographic features, clinical characteristics, and prognostic implications. In our study, anterior tilt was more frequently observed in patients with valgus malalignment and was less likely to be displaced at presentation. Although anterior tilt alone was not significantly associated with fixation failure or complications, stratified analysis demonstrated that anterior tilt combined with varus malalignment significantly increased the risk of femoral head necrosis, defining the high‐risk anterior‐flexion/adduction subtype. This observation highlights the importance of fracture morphology and alignment during preoperative evaluation, particularly because anterior tilt is not included in current classification systems.

Anteriorly tilted femoral neck fractures represent a distinct clinical and radiographic pattern that differs from the more extensively studied posterior tilt variants. These injuries follow the typical bimodal distribution of femoral neck fractures and can be misinterpreted as nondisplaced on anteroposterior (AP) radiographs [18]. On lateral radiographs or sagittal CT, anterior tilt manifests as posterior angulation of the femoral head relative to the neck, frequently accompanied by anterior‐medial cortical comminution and cancellous compression defects [19]. This structural deficiency complicates closed reduction, and the “joystick” technique using a percutaneous K‐wire may improve angular control and facilitate reduction in such cases.

4.2. Prognostic Relevance of Sagittal‐Plane Deformity

Previous studies have consistently demonstrated that posterior tilt is a clinically important predictor of fixation failure and femoral head osteonecrosis. Dolatowski et al. [7], Sjöholm et al. [20], Cong et al. [21], Kalsbeek et al. [22], and a recent systematic review by Papadelis et al. [23] all reported that posterior tilt angles ≥ 20° markedly increase the likelihood of treatment failure, particularly in otherwise nondisplaced Garden I‐II fractures. This body of evidence highlights the broader prognostic relevance of sagittal‐plane deformity and provides a necessary foundation for evaluating whether anterior tilt may exert similarly important biomechanical and vascular effects.

Despite the extensive literature focusing on posterior tilt, the clinical implications of anterior tilt have been far less frequently investigated. Notably, Sjöholm et al. [19] and Sjöholm et al. [24] demonstrated that both anterior and posterior tilt independently increased the risk of fixation failure in Garden I‐II fractures, especially among older adults. Our findings extend these observations by showing that anterior tilt alone was not universally associated with adverse outcomes. However, when an anterior tilt occurred in conjunction with varus malalignment, it defined a distinct high‐risk configuration with substantially elevated odds of femoral head necrosis.

4.3. Implications for Treatment Strategy and Clinical Decision‐Making

Recent evidence further underscores the importance of fracture morphology when considering treatment strategies for femoral neck fractures. A comprehensive network meta‐analysis involving more than 5000 patients demonstrated that arthroplasty provides superior functional outcomes and significantly lower reoperation rates compared with internal fixation, particularly in older adults or fractures with unstable characteristics [25]. These findings highlight that certain fracture patterns—such as those associated with adverse sagittal alignment—may be less amenable to internal fixation and may warrant early consideration of arthroplasty as a definitive treatment option. In this context, our observation that anterior tilt combined with varus malalignment markedly increases the risk of femoral head necrosis provides clinically relevant information that may help refine treatment selection and guide preoperative decision‐making.

4.4. Incidence of Femoral Head Necrosis and Potential Sources of Bias

The incidence of femoral head necrosis observed in the present study (33%) exceeds the rates reported in several prior investigations. This finding likely reflects characteristics of both the study setting and study population. As a national trauma referral center, our institution manages a higher proportion of complex, high‐energy, and displaced femoral neck fractures. Displaced fractures are well recognized to carry substantially higher risk of osteonecrosis, with recent meta‐analytic data reporting AVN rates of approximately 20% in displaced fractures compared with less than 5% in nondisplaced injuries [26]. Furthermore, our inclusion criteria restricted the cohort to patients treated with internal fixation and required a minimum of 24 months of follow‐up, which may introduce selection bias and increase the detection of late‐onset osteonecrosis. These factors likely contributed to the comparatively elevated incidence observed in our study. In addition, the inverse association between follow‐up duration and femoral head necrosis observed in our multivariable models likely reflects the natural course of osteonecrosis, which typically manifests within the first postoperative year in high‐risk fractures. Patients who remain event‐free early in the postoperative period tend to accumulate longer follow‐up without developing necrosis, resulting in an apparent protective effect in regression models [27, 28]. This pattern underscores the importance of adjusting for observation time to avoid differential detection bias.

4.5. Biomechanical Considerations Underlying High‐Risk Fracture Patterns

Various biomechanical and vascular factors may explain why anterior tilt combined with varus alignment confers an increased risk of femoral head necrosis. Anterior tilt increases anterior cortical compression and posterior cortical tension, amplifying shear forces across the fracture site [5, 6]. Varus alignment further concentrates load on the inferior and posteromedial femoral head, where perfusion is most vulnerable. Disruption or stretching of the retinacular vessels in such configurations may compromise the femoral head blood supply [4]. When anterior tilt and varus alignment coexist, these mechanical and vascular insults likely interact synergistically, predisposing the femoral head to collapse and osteonecrosis. However, these mechanistic explanations remain hypothesis‐driven, as direct biomechanical validation specific to anterior tilt is currently lacking.

While these mechanisms warrant confirmation through dedicated biomechanical and vascular studies, our results provide new clinical evidence that anterior tilt—particularly when combined with varus malalignment—represents a previously underrecognized high‐risk fracture morphology. This finding underscores the importance of carefully assessing sagittal‐plane alignment during preoperative planning and supports the consideration of anterior tilt in future refinements of femoral neck fracture classification systems. Improving recognition of this morphology may help guide reduction strategies, optimize fixation constructs, and enhance individualized risk stratification.

4.6. Strengths and Limitations

The relatively large sample size in this study is a definite strength, allowing for a comprehensive analysis of femoral neck fractures and their postoperative outcomes. The use of both clinical evaluations and radiographic imaging, including CT scans, provides a comprehensive assessment of femoral head anterior tilt preoperatively and its impact on fracture healing. Multivariable regression analysis was adjusted for various potential confounders, enhancing the reliability of the findings. Nevertheless, several limitations should be acknowledged. First, its retrospective single‐center design limits causal inference and generalizability. Second, selection bias may exist because only patients treated with internal fixation and with ≥ 24 months of follow‐up were included. Third, certain key clinical variables, including exact onset dates for femoral head necrosis/fixation failure and relevant confounders such as BMI, injury mechanism severity, polytrauma status, and metabolic comorbidities, were unavailable, preventing time‐to‐event analyses and potentially introducing residual confounding despite covariate adjustment. In addition, the number of anterior‐varus cases was relatively small, resulting in wide confidence intervals. Future multicenter prospective studies are needed to validate these findings.

4.7. Prospects of Clinical Application

The findings of this study have important implications for clinical practice. Routine assessment of sagittal‐plane alignment using lateral radiographs or CT should be emphasized, as anterior tilt—particularly when combined with varus malalignment—identifies patients at increased risk of femoral head necrosis. In such high‐risk configurations, surgeons may consider more cautious selection for internal fixation, closer postoperative surveillance, and a lower threshold for alternative strategies such as primary arthroplasty in selected cases. Intraoperatively, awareness of the unique biomechanical characteristics of anterior tilt fractures may help anticipate difficulties with conventional closed reduction and support the use of adjunctive techniques to improve angular control. However, the lack of a universally accepted quantitative definition of anterior tilt and the relatively low prevalence of the anterior–varus subtype may limit immediate standardization of management algorithms. Future prospective multicenter studies and dedicated biomechanical investigations are therefore needed to validate these findings and to facilitate the integration of sagittal‐plane deformity into fracture classification systems and treatment guidelines.

5. Conclusions

This study identifies anterior tilt combined with varus malalignment as a distinct high‐risk configuration of femoral neck fractures, significantly associated with an increased likelihood of femoral head necrosis. Recognition of this anterior‐flexion/adduction subtype, which is not represented in current classification systems, may improve preoperative assessment and guide morphology‐specific reduction strategies. These findings highlight the need to incorporate sagittal‐plane deformity into clinical decision‐making for femoral neck fractures. Further studies with larger cohorts are warranted to validate these observations and clarify underlying biomechanical mechanisms.

Author Contributions

Jiong Mei: project administration, writing – review and editing, writing – original draft, conceptualization, methodology, data curation.

Funding

This Study was supported by the National Natural Science Foundation of China (Numbers: 62376159, 12172224).

Ethics Statement

This study was approved by the Ethics Committee of Shanghai Sixth People's Hospital (Approval No: 2019‐KY‐037).

Consent

The authors have nothing to report.

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Data S1: Supporting Information.

Table S1: STROBE checklist for cohort studies.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.