**2. Risk factors**

Several modifiable and nonmodifiable risk factors should be considered prior to undertaking hip arthroplasty. Modifiable risk factors include tobacco, alcohol use, and obesity [15, 16]. Modern hip arthroplasty utilizing press fit implants relies on

#### **Figure 2.**

*Large diameter femoral heads have larger jump distances than smaller diameter heads [14]. Of note, due to the fixed radius of the acetabular component, a larger femoral head will decrease the space available for polyethylene. This can be seen in Figure 2A versus Figure 2B.*

immediate stability at the bone/implant interface through a variety of tapers and coatings. Although the exact mechanism is not understood, this stability is weakened from tobacco use. Several researchers have demonstrated the adverse effects of delayed bone healing with tobacco use and this theory has been extended to include delayed bone-implant ingrowth [17, 18]. Elective arthroplasty offers a unique opportunity for patients to cease smoking, and some literature demonstrates continued abstinence [19]. A careful history with a targeted effort at reducing modifiable risk factors should be considered prior to hip arthroplasty.

Tobacco and alcohol use are correlated with wound complications and potential instability [16, 17]. Also, patients who abuse alcohol are less likely adhere to precautions and suffer more frequent falls, leading to interprosthetic instability. The immunosuppression from alcohol misuse has shown an increased risk of prosthetic joint infections thereby impairing bony ingrowth [17].

Currently, more than two-thirds of Americans are classified as obese (body mass index (BMI) ≥ 30 kg/m2) [20]. Groups with the highest BMI are increasing in size at the fastest rate, as evidenced by the greater than 50% annual increase in prevalence of patients with a BMI ≥ 40 kg/m2 [21, 22]. Elevated BMI will increase the soft tissue envelope around the hip, thereby increasing the risk of implant malpositioning. This malpositioning along with soft tissue impingement are known risk factors for instability [23]. Patients with elevated BMI tend to be younger. Younger aged patients statistically place more stress on their implants and with the increased weight these patients may have elevated wear rates and higher risk of aseptic loosening [24].

Non modifiable risk factors include advanced age, cognitive impairment, and in some earlier studies, female sex [16]. Several comorbid conditions also predisposing patients to dislocation following THA include developmental dysplasia of the hip,

neuromuscular disorders, and other connective tissue disorders. Abductor muscle deficiency, prior surgical revision, a history of instability, and prior spinal disease or surgery [25–28]. Previous instances of instability are also risk factors for future instability events.
