Total hip arthroplasty (THA) is an effective intervention for patients with severe hip disease and has been shown to lead to marked improvement in health outcomes (1). Because of the significant benefits realized with THA, utilization rates for this procedure have been increasing in most Western and Asian countries, including Korea (23). Thus, many Western epidemiological studies have examined the incidence of THA and reported osteoarthritis (OA) as the most common underlying condition for THA in Western countries (2345). However, Western epidemiological data cannot be applied to Korea, and most of these studies only determined the prevalence and trends of THA or were limited to THA for patients with OA. The pathogenesis of coxarthrosis leading to THA is complex, with many risk factors (67). Many conditions that can lead to THA include primary OA, secondary OA resulting from femoroacetabular impingement (FAI), dysplasia and peripheral joint involvement of seronegative spondylitis, such as ankylosing spondylitis (AS) and diffuse idiopathic skeletal hyperostosis, avascular necrosis (AVN), and fractures. Although the ratios of primary OA have previously been considered high, morphological deformities around the hip may cause OA over several decades (89). Recently, several studies have reported that FAI results in early OA and hip OA pathology related to FAI (101112). To our knowledge, no previous study has evaluated the epidemiology of causes leading to THA in Koreans, particularly with a focus on the incidence of FAI.

The purposes of the present study were 1) to analyze the causes leading to THA, 2) to clarify the incidence of FAI among these causes, and 3) to compare the incidence in Korea with those in other countries.

In total, 1,206 hips in 818 patients underwent THA at out institute between January 2000 and December 2014. There were 477 male and 341 female patients. The numbers of cases undergoing THA has increased consistently since 2000 (Fig. 1). The changes of causes leading to THA showed that AVN has been decreased since the interval between 2003 and 2005 and fracture has been increased (Fig. 2).

There were 32 patients (3.91%; 13 males, 19 females) in the primary OA group (Fig. 3), 41 (5.01%; 12 males, 29 females) in the RA group, 84 (10.27%; 43 males, 41 females) in the posttraumatic arthritis group, 39 (4.77%; 17 males, 22 females) in the post infectious arthritis group, 365 (44.62%; 270 males, 95 females) in the AVN group, 39 (4.77%; 17 males, 22 females) in the fracture group, 21 (2.57%; 16 males, 5 females) in the AS group, 52 (6.36%; 16 males, 36 females) in the DDH group, 71 (8.68%; 52 males, 19 females) in the LCPD group, 52 (6.36%; 13 males, 39 females) in the FAI group, and 22 (2.69%; 8 males, 14 females) in the ‘others’ group. In the FAI group, there were 36 patients (69.23%; 9 males, 27 females) of the cam type (Fig. 4), 15 (28.85%; 3 males, 12 females) of the pincer type (Fig. 5), and 1 (1.92%; 1 male) of the mixed type (Table 1).

Intraobserver and interobserver correlations for causes and the combination of all measurements were found to be reproducible and reliable among observers (Tables 2 and 3).

Primary THA has increased globally, including Korea. Yoon et al. (3) reported that both the number and the rate of primary THAs increased substantially between 2007 and 2011 in Korea: 7,229 hips in 2007, 7,829 hips in 2008, 8,124 hips in 2009, 8,652 hips in 2010 and 8,926 in 2011 underwent primary THAs. Our study showed similar results between 2000 and 2014 in our institution. The most common cause will be OA because OA is a leading cause of disability (2345). The 2 main categories of hip OA are primary and secondary. Although the precise proportion of each category remains controversial, primary hip OA is commonly believed to account for the majority of all hip OA cases in Western populations (19). Western epidemiological studies showed that more than 75% of primary THAs have been performed for OA (20). In the United States, hip OA affects approximately 5% of those over the age of 60 years, and approximately 360,000 hip replacement surgeries are performed annually (21). However, Korean epidemiological studies have reported that primary OA accounted for only 18% of THA cases in Korea, and the most common indication for primary THA in Korea was AVN (5), similar to our findings. This result suggests that severe hip OA is much rarer in Korea than in Western countries. This discrepancy between the Western and Korean incidence of hip OA and primary THA may be attributed partially to lifestyle factors, such as frequent kneeling or squatting, which are common in daily living in Asia and may protect against hip OA (5).

Many studies have reported that FAI could be a cause of cartilage or acetabular labrum lesions, ultimately resulting in degenerative arthritis (911). It has also become clear that so‑called primary OA of the hip is often FAI-positive. Harris (8) reported that most cases of primary OA of the hip had mild dysplasia and/or a pistol-grip deformity, with true primary OA being extremely rare. Tanzer and Noiseux (22) reported that the etiology of OA in 125 of 200 consecutive patients undergoing THA was idiopathic arthritis, but all 125 patients also had a pistol-grip deformity. Takeyama et al. (15) reported that 6 (0.6%) and 693 (73.3%) of 946 hips that underwent primary surgery for OA or other diseases of the hip were associated with FAI and DDH in Japan, respectively, and only 11 (1.2%) hips were classified as primary OA of unknown etiology. The exact reason as to why the incidence of FAI is low in Japan remains unknown, but it was suggested that the normal Japanese acetabulum may be more dysplastic than that of Caucasians, and the antero-posterior size of the proximal femur was smaller in Japanese subjects, decreasing impingement between the acetabulum and femur (15). In this study, 52 (6.36%) of 818 patients who underwent primary THA were associated with FAI and 52 (6.36%) of the patients were associated with DDH in Korea. Only 32 (3.91%) patients were associated with primary OA. The rate of FAI in Korea was higher than that in Japan. These results may be due to lifestyle. It has been suggested, for example, that frequent squatting or a crossed-legged position, particularly on the floor, common to daily life in Korea, may increase impingement.

This study has some limitations. First, there was patient bias due to geographical or institutional predominance, potentially influencing the epidemiological results. Second, this was a single center study. Thus, the sample size was small for a cohort study. However, to our knowledge, no reported study has evaluated the epidemiology of the causes leading to THA in Koreans, particularly, with a focus on the incidence of FAI.

In conclusion, the causes leading to THA in Korea differ from those in Western countries. In particular, the incidence of primary OA as a factor leading to THA in Korea is much lower than that in Western countries, whereas the incidence of AVN in Korea is much higher than that in Western countries. Also, FAI could be cause of severe secondary OA that requires THA in Korea, therefore symptomatic FAI should not be neglected.