Femoral Neck Fractures in Elderly Patients: Dual Mobility Cup Arthroplasty or Hemiarthroplasty? A Narrative Review of the Literature

1. Introduction

Proximal femoral fractures (PFFs) are the most frequent bone fractures in elderly people. In Italy, from 2007 to 2017, there were 906,111 hospitalizations for hip fractures. Moreover, in 11 years, the hip fractures rates increased by 14.3% in women and 29.4% in men [1]. Several authors [2,3] describe an increasing incidence of proximal femur fractures in elderly. Oulianski et al. [4] reported a decrease of 21.64% in PFF per week during the COVID-19 pandemic compared to the pre-covid period. The median age of patients hospitalized with a diagnosis of PFF was 83 years, and the incidence of diagnosis increased with age from 145.3 events per 100,000 person-years among patients aged 65–69 years old to 3563 in subjects aged 95–99 years old [5]. These fractures are expected to reach up to 21.3 million globally by 2050 as a consequence of aging [6].

The incidence of proximal femoral fractures among people aged 65 years or older varies in different countries depends on age, sex, comorbidities, and lifestyle. It peaks at 85–89 years, it affects more women than men, and it is exacerbated by cognitive disfunction and institutionalization [7]. However, Walter at al. [8] found a general decrease in the incidence of head/neck fractures by about 26.6% between 2009 and 2019.

The costs related to this fracture represent an important burden for healthcare systems worldwide. The total combined health care and loss of productivity costs reached €456M and increased with age, following the pattern of incidence [9]. Roberts et al. [10] declared that in 2011 in the USA, hip fracture treatment was 13th out of the top 20 most expensive diagnoses for Medicare.

2. Anatomic Reference

The proximal femur is characterized by a head and neck and two large bone projections, the greater and lesser trochanthers. The head of the femur articulates with the acetabulum, creating an enarthrosis articulation. The greater and lesser trochanthers are important because they provide muscular insertion at the hip muscles. The joint capsule encloses the hip joint and is attached medially to the acetabulum margin, laterally at the intertrochanteric line on the anterior aspect, and at the base of the neck at the posterior aspect [11].

The vascular supply at proximal femur passes through the vascular ring of the femoral head. It is formed by the medial femoral circumflex artery and lateral femoral circumflex artery. Terminal branches arise from these vessels and provide vascular supply to the femoral head. These branches can be destroyed following displaced hip fractures, and the vascularization of the femoral head can be interrupted. This generate osteonecrosis of the femoral head [12,13].

3. Diagnosis

There is usually a history of fall or low energy trauma, followed by pain in the hip or groin [14], but in 2-3% of cases, there is no a history of trauma, and the fracture may be pathologic or secondary to stress fracture [15]. Patients with displaced femoral neck fractures usually present a shortened and externally rotated limb and inability to bear weight [16]. Patient examination may also reveal tenderness to palpation over the groin and anterior hip and pain with log roll maneuver (passive internal and external rotation of lower leg), but ecchymosis is typically not initially present [17].

A patient with stress, non-displaced, or impacted fractures may lack deformity and may able to bear weight; however, they could have non-specific symptoms such as groin pain and pain during axial compression [18]. It is important to underscore that physical findings do not differ significantly from extracapsular fractures, so on a clinical basis, the hip fractures groups are difficult to distinguish. Therefore, radiological diagnosis plays an important rule for the correct diagnosis of proximal femur fractures (PFFs).

Cross table lateral view and anterior-posterior (AP) X-rays are the appropriate initial diagnostic test for hip fractures (Figure 1). A frog leg view is not recommended because the positioning of the limb results in severe pain [19]. On the anteroposterior (AP) pelvis, the evaluation of the integrity of Shenton’s arch can help the diagnosis in an undisplaced fracture. A break in this line will reveal a subtle intracapsular fracture [20].

Magnetic resonance (MR) imaging has been considered more sensitive than a computed tomography (CT) scan for femoral neck fractures. However, there are no enough data comparing MR imaging with current CT technology, which affords thinner slices and high-quality reconstructions. Often, the greater availability of CT imaging leads to it being used rather than MR imaging for first-line screening [21,22].

4. Classification

Classifications are important for orthopedic surgeons because they help the surgeon in diagnosis and correct decision making [23]. Proximal femur fractures can be classified based on the relationship with the hip articular capsule in extracapsular fractures (trochanteric fractures) or intracapsular fractures (femoral neck fractures) [24]. Each one requires a different surgical treatment. In this paper, we will discuss only intracapsular fractures.

In Garden’s classification, the fracture is assessed on AP view x-ray with the following [25]:

• Type 1: incomplete and undisplaced
• Type 2: complete undisplaced (Figure 1)
• Type 3: partial displacement and misalignment of trabecular bone
• Type 4: complete displaced

Pauwels’ classification [26] is based on the obliquity of the fracture line, which is described as the angle between the tangential the plane tangential to the most superior aspect of the femoral head and the fracture (Type 1: angle <30°, Type 2: angle of 30-50°, Type 3: angle >50°.

According to the AO classification system [27], femoral neck fractures are classified as AO31B. In addition, there are many subgroups according to the features of the fracture:

AO31B1.1: valgus impacted fracture;

AO31B1.2: nondisplaced fracture;

AO31B1.3: displaced fracture;

AO31B2.1: simple fracture;

AO31B2.2 multifragmentary fracture;

AO31B2.3: shear fracture;

AO31B3: basicervical fracture;

5. Treatment

5.1. Conservative Treatment

Nowadays, the gold standard in displaced femoral neck fractures is surgical treatment. However, there are some exceptional cases where there is space for non-surgical treatment [28]:

• Life expectancy is short, and the risks of the intervention exceed the potential benefits;
• Inveterate fractures with signs of consolidation;
• The patient is constantly lying in bed;
• When the patient refuses the surgical treatment.

5.2. Hemiarthroplasty (HA)

Endoprosthesis, partial prosthesis, or hemiarthroplasty consists of partial replacement of the hip. After removing the femoral head, the femoral canal is prepared, and then the femoral stem is placed. We distinguish between unipolar prostheses, which are used less and less, and bipolar prostheses. The femoral head of a bipolar hip prosthesis (BHP) consists of a steel outer shell and polyethylene liner with an inner steel head moving inside [29]. In this type of surgery, no treatment is carried out on the acetabulum. The stem can be held on the femur by press fit or by using cement.

HA is indicated in patients whose self-sufficiency and physical activity are limited [30]. The advantages of this procedure are limited surgical time and less invasive surgery than total prosthesis. On the other hand, there are some complications related to this surgery. Common complications are dislocation periprosthetic fracture, acetabular erosion, and leg-length inequality. Less frequently seen complications include neurovascular injury and capsular interposition [31].

Kizkapan et al. [32] described that pelvic morphologic features and surgical factors affect dislocation. Graulich et al. [33] found that dementia and insufficient posterior wall angle were associated with higher risk of dislocation in HA. Olesen et al. [34] cited dementia as the only risk factor for dislocation in HA.

Falsetto et al. [35] found that dementia and low preoperative lateral center-edge angle were associated with increased risk of dislocation in HA after femur neck fracture. Lumbar spinal fusion (LSF) was found to be an independent risk factor for increased joint complications in patients undergoing either a THA or hemiarthroplasty for displaced femoral neck fractures [36]. Macheras et al. [37,38] showed that age is a significant factor in acetabular wear after HA surgery. Particularly, patients <75 years old showed more acetabular wear than patients >75 years old.

5.3. Total Hip Arthroplasty (THA)

In THA, we replace some parts of the upper femur and acetabulum with biocompatible materials [39]. Younger, more active patients have better outcomes with total hip replacement, thus making the slightly increased risk of complications with the procedure acceptable [40]. Others authors stated that THA must be recommended for patients with displaced femur neck fractures if the patients had a life expectancy >4 years and in patients younger than 80 years [41]. However, THA to treat femoral neck fractures in elderly patients is associated with a significantly higher risk of 12-month dislocation [42].

5.4. Dual Mobility Total Hip Arthroplasty (DM-THA)

The dual mobility cup (DMC) concept was proposed by Professor Gilles Bousquet in 1974 [43]. Due to a simulated large-head articulation and increased jumping distance, DMCs can contribute to a high range of motion in the hip joint and reduce the risk of instability [44]. It allows for increased range of motion prior to impingement and dislocation. However, there are some complications related to a dual mobility hip implant that every orthopedic surgeon must know. They are intraprosthetic dislocation [45,46], corrosion, and femoral notching [47,48]. Some authors [48] found higher rates of heterotopic ossification in DM-THA than THA in patients with femur neck fracture.