THA had historically been reserved for the low-demand, elderly patient. Younger patients with longer life expectancies and higher activity levels are most commonly at risk of aseptic loosening and osteolysis requiring early revision compared with their older counterparts.^1,2,3 Improvements in implant technology, surgical technique, and expanding indications have increased the use of THA in young, active patients. Importantly, contemporary studies have shown that young, active patients can undergo THA with expectations of good outcomes and survivorship. This patient population has high expectations after THA, desiring to return to sports (RTS) and work (RTW). Military service members and other patients with high-demand active occupations (eg, firefighters, law enforcement, farmers, and laborers) pose an even greater challenge to the survivorship of THA due to the increased physical demands they will place on their arthroplasties.

There is a paucity of literature on military patients returning to active duty after total joint arthroplasty, even though osteoarthritis is the most common cause of disability among service members who are medically separated.⁴ The rate of osteoarthritis in military service members older than 35 years is double that of the general population.⁵ Causes of osteoarthritis include posttraumatic osteoarthritis from sports or combat-
related injuries and wear and tear degeneration over a long career of military service. Data from a cohort of combat-injured service members showed that only 21% of those wounded warriors developed posttraumatic hip osteoarthritis.⁶ The literature is even more limited on war traumatic hip wounds eventually converted to arthroplasty.⁷ Therefore, most of the hip osteoarthritis cases in military service members that have been reported are presumed to be degenerative in nature.

The overall incidence of primary hip osteoarthritis in the military has been reported to be 35 cases per 100,000 person-years, and differences emerge based on branch of service, ethnicity, age, and rank.⁵ The reported incidence of hip osteoarthritis in cases per 100,000 person-years is 43.3 for the Army, 37.0 for the Navy, 26.8 for the Air Force, and 26.3 for the Marines Corps, all of which exceed the rates of the general population.^7,8 Degenerative osteoarthritis develops over time from physically demanding tasks such as those required of military service members, including lifting, carrying, lowering, pushing, pulling, climbing, digging, walking, marching, jumping (in and out of tall vehicles including aircraft), and/or running while nondeployed and deployed, often performing these tasks while under load.³ Additionally, military service members are required to perform physical fitness tests annually or semiannually in order to remain on active duty. Because of the demands of their jobs, many military service members delay joint arthroplasty until after leaving the service. However, there are a growing number who elect to proceed with total joint arthroplasty while still on active duty, return to active duty, and even deploy to combat zones after total joint arthroplasty. Medical evaluation boards, changes in occupation, and/or possible discharge can occur if a service member is not able to maintain a certain level of physical fitness and/or perform their military occupation.

In addition to different occupational demands in service members, there are anatomic differences to consider based on ethnicity and age. Studies show the incidence of hip osteoarthritis is higher among African American than white service members.^5,8 Greater muscle mass and higher bone mineral density in African Americans may contribute to the increased incidence of hip osteoarthritis.^9,10 There are also anatomic differences in young patients based on bone morphology. The canal flare index is the ratio of the femoral canal diameter at the isthmus on anteroposterior radiographs to the medullary diameter 20 mm above the lesser trochanter. The canal flare index is typically higher in younger patients than in older patients due to widening of the canal with age.^11,12 A high canal flare index coupled with higher-density cortices (Figure 21.1) may cause the femoral stem to be hung up distally, which can lead to thigh pain and a lack of osseointegration.¹³ In patients with this bone morphology, THA surgery may require a different type of stem design or removal of distal bone with a flexible reamer to prevent these complications (Figures 21.2 and 21.3). Although these may be subtle differences anatomically, they may pose significant challenges intraoperatively and are important considerations when performing DAA THA. For patients with tight, dense proximal femoral bone, battery powered automated broaching may also be beneficial to help open the tight canal and broach more effectively (Figures 21.4 and 21.5).

Another consideration worth noting in the care of the military service member is the potential for prior hip surgeries due to femoroacetabular impingement (FAI). FAI is an abnormal bone condition of the femoral neck and acetabulum, which can put undue stress on the hip joint, leading to labral tears and further hip degeneration. Between 39% and 80% of service members who undergo hip arthroscopy for FAI are able to return to duty.^13,14,15 Within 2 years after hip arthroscopy, 21.9% will receive a clinical diagnosis of osteoarthritis.¹⁶ The time between symptom onset of FAI and surgical intervention with hip arthroscopy is 10 to 12 months longer for military service members versus civilians, and this delay in treatment may contribute to the increased disability.¹⁷ Patients with osteoarthritis from FAI can present several challenges intraoperatively during DAA THA. Scar tissue, suture anchors, and infection risk are valid concerns during DAA THA after hip arthroscopy. However, multiple studies have shown that previous hip arthroscopy does not affect outcomes after THA,^18,19,20,21 with very few studies showing worse outcomes.^22,23

Kuklo et al²⁴ published the first study of total joint arthroplasty in military service members. This study was in the era of hybrid THAs and included a small cohort of 27 patients with 67% remaining on active duty and 10% revised due to aseptic loosening at a mean follow-up of 7.2 years. The largest study of THA in a military population evaluated 177 primary THAs performed in Army soldiers with 2 years of follow-up with 31% of patients able to return to active duty, 14% able to complete a combat deployment, and 69% either retired or medically separated after THA.²⁵ A smaller cohort by a single surgeon showed even higher return to duty at 86% with 70% of post-THA patients deploying to a combat zone.²⁶ However, this cohort consisted of 45 patients having undergone “major joint arthroplasty” and did not categorize patients based on the joint replaced. The surgeon from this study performed all THAs via a posterior approach. Of the service members who were able to deploy post-THA in this study, 58% reported difficulty sitting in vehicles or aircraft due to posterior thigh and buttock pain over the site of their incision. Alternative approaches to the hip, rather than posterior, were suggested at that time. To date, no studies comparing THA approaches or DAA THA in military service members have been published; this will be an important area of future research.