Characteristics of Very Young Patients Undergoing Total Hip Arthroplasty: A Contemporary Assessment

Background This study aims to compare indications, patient characteristics, hospital factors, and complication rates between total hip arthroplasty (THA) patients aged 30 years or younger and those older than 30 years using a large national database. Methods The Premier Healthcare Database was utilized to identify primary THA patients from 2015 to 2021 who were aged ≤30 or >30 years. Patient demographics, hospital factors, and primary indications were compared for each cohort. Rates of complications and readmissions were assessed for each cohort by primary indication. Differences were assessed through univariate analysis. Results Overall, 539,173 primary THA patients were identified (age ≤30: 1849; >30: 537,234). Compared to the >30 cohort, the ≤30 cohort was more likely to be male (56.5% vs 44.9%, P < .001) and non-White (34.0% vs 14.2%, P < .001). The most common indications for THA in the ≤30 cohort were osteonecrosis (49.3%), osteoarthritis (17.8%), and congenital hip deformities (16.0%), and in the >30 cohort, they were osteoarthritis (77.0%), other arthritis (11.3%), and osteonecrosis (5.4%). Patients aged ≤30 years had lower rates of respiratory failure (0.16% vs 0.57%, P < .001), acute renal failure (0.32% vs 1.72%, P < .001), and urinary tract infection (0.38% vs 1.11%, P = .003) than those aged >30 years, but higher rates of wound dehiscence (0.59% vs 0.29%, P = .015) and transfusion (3.68% vs 2.21%, P < .001). There were no differences in 90-day readmission rates (P = .811) or 90-day in-hospital death (P = .173) between cohorts. Conclusions Younger patients undergoing THA differed significantly in indication, patient characteristics, and hospital factors compared to the older population on univariate analysis. Despite differences in indications, the cohorts did not differ markedly with regard to complication rates in this study.


Introduction
Historically, surgeons have exhibited caution when considering total hip arthroplasty (THA) in young patients, primarily due to the concern for increased revision rates [1,2].However, advances in implant materials and surgical techniques have decreased revision rates over time, and surgeons have become less reticent to indicate young patients for THA in the appropriate setting [3][4][5][6].Indications for THA in young patients, often defined as aged <30 or <50 in the literature, include symptomatic, irreparable cartilage loss, extensive bone loss, erosion of the acetabulum, and femoral head collapse [1,5,[7][8][9][10][11][12].Kahlenberg et al. examined THAs performed in patients aged <21 years in the United States at a single institution and noted an increase in surgeries performed in this population from 347 in 2000 to 551 in 2016 [13].Few large-scale epidemiological data on this subset of arthroplasty patients are available, particularly with contemporary data.
Young patients with a complex hip disease are increasingly willing to undergo THA to maintain desired levels of function and reduce pain [3].While there is extensive literature regarding rates of revision in the young population [2,5,14], there is a paucity of data examining rates of specific complications among young THA patientsdquestions important in guiding patient counseling, perioperative care, and clinical research [1].Therefore, this study aims to assess for differences in the indications, patient characteristics, hospital factors, and complication rates of patients aged 30 years and >30 years who underwent primary THA.

Material and methods
The Premier Healthcare Database [15] was queried for all patients who underwent primary, elective THA from January 1, 2015, to December 31, 2021.The Premier Healthcare Database is an allpayer claims database containing patient and hospital characteristics, medications, International Classification of Diseases (ICD) diagnosis and procedural codes, Current Procedural Terminology codes, and patient-specific billing information from approximately 25% of all United States hospital admissions.ICD-10 procedural and Current Procedural Terminology codes were utilized to identify these procedures [15].Those who underwent THA for nonprimary, nonelective indications were excluded (Supplemental Table 1).This study was exempt from institutional review board approval as all information was de-identified in accordance with the Health Insurance Portability and Accountability Act.

Identification of study cohorts
Two subsets of primary, elective THA patients were identified: age 30 years ("30 cohort") and age >30 years (">30 cohort") at the time of index surgery.
Using ICD-10 diagnosis codes, patients were categorized by the primary indication for THA (ie, osteoarthritis [OA], osteonecrosis, posttraumatic arthritis, neoplasm, congenital hip deformity, inflammatory/infectious, and other arthritis; Supplemental Table 2).For patients meeting 2 indications, the indication other than OA was considered as the primary diagnosis as it would likely represent the most immediate cause for surgery.For example, if an ICD-10 diagnosis code for inflammatory arthritis and OA were present, we assumed the patient underwent THA due to the inflammatory process.This methodology has been performed by Yakkanti et al. [16].Patients meeting 2 indications other than OA (1.2%) or meeting >2 indications (2.5%) were excluded from this analysis as these scenarios precluded the ability to identify the most likely indication for surgery reliably.Patients with miscoded (eg, arthritis of the knee) or nonspecific (eg, orthopedic aftercare, presence of orthopedic joint implants, and so on) diagnosis codes (0.2%) were also excluded from the analysis.In total, 561,528 primary, elective THA patients were identified with 539,173 (96.0%) remaining after applying the exclusion criteria (Fig. 1).

Independent variables
Patient demographics (ie, age, sex, race, length of stay, year of procedure, and total cost), hospital factors (ie, size, urban/rural setting, teaching status, and region), and the prevalence of patient comorbidities were assessed and compared between the 30 and >30 cohorts.

Statistical analysis
All patient demographics, hospital factors, comorbidities, and postoperative complications were evaluated with descriptive statistics.In order to assess differences between the 30 and >30 cohorts, independent t-tests were performed for continuous variables while Fischer's exact or chi-squared tests were utilized for categorical variables where appropriate.Statistical significance was defined as P < .050.All statistical analyses were performed using STATA (version 16.1; StataCorp, College Station, TX).

Discussion
While THA is more commonly performed in older adults, an increasing number of young people undergo this procedure.This patient population will continue to grow as both patient and surgeon confidence in the durability of THA increases over time.However, contemporary data characterizing the postoperative outcomes of this unique population are lacking.In this study, patients aged 30 years were more likely to be non-White and male, had osteonecrosis as the most common indication for surgery, and had minimal differences in rates of 90-day postoperative complications when compared to patients aged >30 years.
Existing data on the indications for THA among young arthroplasty patients are limited by study heterogeneity.Prior studies have used various age cutoffs including <50 years [17][18][19][20][21][22], 35 years [23][24][25][26][27][28][29][30][31], and 25 years [32][33][34].Thirty years of age was utilized as the age cutoff presently as that is what has been used most frequently to define a very young arthroplasty population [23][24][25][26]28].However, examining age beyond a binary variable may be of interest to future investigations.Of studies that utilized a similar age cutoff as the present study, none included patients who underwent surgery beyond the first decade of the 21st century [23][24][25][26]28].As operative techniques, perioperative care, and implant design continue to improve, contemporary data on outcomes in this unique patient population are necessary to further guide these efforts and potentially expand indications to help more patients in need.The data presented here represent the most contemporary data published on indications and outcomes in patients aged <30 years who underwent a primary, elective THA in the United States.
While inflammatory arthropathies comprised the most commonly studied and most common indication for THA in young patients in the 1900s and early 2000s [23,29,30,35], more contemporary studies report higher numbers of patients aged 35  years who underwent THA for congenital dysplasia [24], osteonecrosis [25], or OA secondary to pediatric hip disease [26].In our study, most patients aged <30 years underwent THA from 2015 to 2021 for osteonecrosis (49.3%), which corroborates the data presented by Girard et al. [25].These data demonstrate that the primary etiology for which young patients are seeking out THA has changed, likely owing to advancements in the medical management of rheumatologic diseases, which may be relevant in longitudinal studies on implant survivorship in this population.
In the present study, low rates of 90-day medical and surgical complications in patients aged 30 years were observed regardless of the indication for THA.Most existing studies defined revision and radiographic loosening as the endpoints of interest [23,29,31] and less have commented on other medical and surgical complications [24][25][26]28,30].None have examined outcomes stratified by index diagnosis as reported in this study.We observed minimal differences in postoperative complication rates between patients aged 30 years and >30 years by surgical indication.Understanding the types of patients that undergo THA and the outcomes experienced by this population is important to patient counseling, resource allocation, and perioperative care optimization.
The data presented identify sociodemographic differences that warrant discussion.In this study, patients aged 30 years who underwent primary, elective THA were more likely to be non-White, male, and from the South than their >30-year-old counterparts.These observations may be explained in part by epidemiologic differences of various hip diseases, such as avascular necrosis secondary to sickle cell [36], hip fracture [37], and slipped capital femoral epiphysis [38].The greater proportion of White patients in the >30-year-old cohort may also be explained by a higher total joint arthroplasty utilization rate among Medicareeligible White patients than that among non-White patients [39].Prior studies examining the young arthroplasty population did not comment on the racial breakdown of their respective study cohorts.
A number of limitations to this study require acknowledgment.First, as a retrospective study, it is reliant on the accuracy of administrative coding.However, we believe that in the absence of systematically biased errors, the accuracy of the data reported from a comparative standpoint is unlikely to be compromised.Second, this study examines a 30 cohort although different definitions of "young" regarding THA patients have been used in the literature.We elected to use this cutoff as (1) this is what has been used most commonly by the orthopedic community [23][24][25][26]28] and (2) this cohort may have differences in baseline health and functional demands compared to even those aged <40 and <50 years, in addition to Medicare-eligible patients.Third, it must be noted that a multivariate analysis was not performed.However, as the purpose of the study was to describe contemporary data on young and old THA patients, we do not believe this is a critical limitation but rather aligns with the study design.Further elucidating whether differences between the 2 age groups exist after accounting for confounders and the clinical implications of that is a pursuit that would warrant a separate study.
There are numerous strengths to this study that warrant mention.First, to the best of our knowledge, this study comprises the largest sample of young patients undergoing primary, elective THA in the United States.Young patients are challenging to study due to the relatively low number of THAs performed in this population, and the relatively rare incidence of complications associated with elective THAs precludes robust studies in this unique but important population.This crucial limitation in the prior literature is addressed by the present study.Second, existing studies on this subset of patients utilize heterogeneous study cohorts in which many disease etiologies are aggregated for analysis.Furthermore, few studies discuss the outcomes of THA in young patients with noninflammatory hip degeneration.In the present study, we examined common hip disease etiologies independently, providing data that can be more accurately applied in clinical settings.The data in this study also demonstrate the importance of future clinical studies to focus on patients with noninflammatory diseases, as this is now the most common etiology for THA in the young arthroplasty population.

Conclusions
In this study, we identified 1849 patients aged 30 years and 537,234 patients aged >30 years who underwent primary, elective THA from 2015 to 2020.Patients aged 30 years were more likely to be non-White and male and carry a primary diagnosis of osteonecrosis as the indication for THA.Young patients had minimal differences in 90-day postoperative complications when compared to patients aged >30 years.The study comprises the largest sample of young patients undergoing primary, elective THA in the United States, an increasingly relevant patient population as implant longevity and surgical care continue to improve.

Table 1
Patient demographics and hospital characteristics.

Table 4
Overall complication rate by cohort.

Table 2
Indications for total hip arthroplasty by age group.