Younger Age Is a Risk Factor for Discontinuing Military Service After THA

With improved implant survival, THA is becoming more common in younger patients. Despite similar patient-reported outcomes between younger and older cohorts, it remains unclear whether age at THA may limit a patient's ability to return to their job. Evaluation of the return-to-duty rate in military personnel after THA may shed light on the potential functional status of civilian patients who are of a similar demographic in physically demanding professions.

(1) What proportion of active-duty military personnel return to duty after THA? (2) What demographic and surgical factors were associated with this return-to-duty proportion?

We performed a retrospective chart audit of all active-duty US military personnel who underwent primary THA between 2017 and 2020 at US military hospitals globally. A total of 452 patients underwent primary THA during the study period. Twenty-one percent (93 of 452) of patients with medical records lacking critical information for the primary analysis were excluded, leaving 79% (358) eligible for analysis. Most patients were men (85% [306 of 358]), and the median (range) age was 46 years (22 to 65). Approaches included direct anterior (58% [206]), posterior (40% [143]), and lateral (3% [9]). The most common indications were primary osteoarthritis (63% [226]), avascular necrosis (18% [64]), and secondary osteoarthritis attributed to dysplasia (15% [52]). Univariate analyses considered demographic and operative variables. Multivariable logistic regression analysis was utilized to assess independent factors for return to duty versus medical separation.

Ten percent (35 of 358) of patients underwent medical separation from service because of their hip after THA, with the remaining 90% returning to duty. After controlling for potentially confounding variables such as surgical approach, complications, and BMI, we found that decreasing age was associated with higher risk of medical separation, such that each year of increasing age was associated with a decreased risk of medical separation by 17% (OR 0.83 [95% CI 0.76 to 0.90]; p < 0.01). Patients serving in the US Navy were less likely to undergo separation from service than patients in the Army (OR 0.19 [95% CI 0.04 to 0.87]; p = 0.03). Complications and surgical approach were not found to be associated with increased odds of separation.

When treating active-duty military patients who qualify for THA, one must consider the occupation and age implications that surgical intervention may have on the patient. Analysis of this unique patient population may allow for improved understanding of outcomes in the growing number of young active civilian patients who undergo THA. These data can potentially be applied to that population, especially those in physically demanding jobs that may be analogous to military duty. The results of this study would also be of use when providing an evidence-based preoperative risk assessment for these patients regarding their postoperative functional outcomes.

Level III, therapeutic study.