THAs in young patients are demanding primarily attributed to their long life expectancy and expected high levels of sports. Concerns persisted regarding polyethylene wear, the presence of osteolysis, and aseptic loosening of THA using hard-on-soft bearings; in contrast, the use of ceramic-on-ceramic bearing THA showed promising results, as they reduced osteolysis with improved wear characteristics, leading to lower revision surgery rates.

Paediatric hip disease encompasses various disease entities. Previous studies reported that osteonecrosis and sequelae of childhood hip disease were predominant among patients who underwent THA [13, 27, 28], which was comparable to that of our study. The most common pathologies encountered in this study were osteonecrosis of the femoral head, followed by sequelae of previous infection, juvenile rheumatoid arthritis, and sequelae of Perthes disease.

Overall, our study demonstrated favourable results of THA in patients younger than 20 years. Similar to most other studies, we observed good to excellent improvements in functional outcome scores [10, 11, 28,29,30,31,32,33]. The modified Harris Hip Score was commonly used to assess clinical outcomes in these studies. Clohisy et al. have reported an increase in HHS from 42 to 83 points [33]. Finkbone et al. have documented a final HHS of 93.4 points [28]. Ozdemir et al. have recently demonstrated an increase in HHS from 51 to 81 points in young patients [12]. In our study, the mean modified HHS improved from 44.6 points (range, 33 to 57 points) preoperatively to 90.1 points (range, 71–100 points) at the final follow-up.

Due to young age of patients, complications and subsequent revision surgeries were inevitable. Although THA has become a reliable option for end-stage hip disease in recent times, it is rarely performed on adolescents mainly due to concerns about bearing wear, peri-implant osteolysis, and implant loosening. Additionally, reoperations related to infection, periprosthetic fractures, and implant failures must be taken into account. Clohisy et al. have reported a revision rate of 6.9% after an average follow-up of 4.2 years, utilizing various types of bearings [33]. Kamath et al. have reported a revision rate of 4.8% in 4.1 years of follow-up for 21 hips with various types of bearings [11]. In a study with a longer follow-up period, revision rates of 25.0% and 6.3% for acetabular component and femoral stem, respectively, were observed in 16 hips with 13.6 years of postoperative follow-up [10]. In the present study, the revision rate was higher than previously reported, with 19 (24.4%) out of 78 hips undergoing reoperation due to aseptic loosening of the implants.

The introduction of cross-linked polyethylene and advancements in sterilization methods have significantly enhanced the durability of polyethylene liners [34]. Highly cross-linked UHMWPE (HXLPE) was adopted for routine use in the early 2000s to reduce revision rates associated with wear, osteolysis, and aseptic loosening resulting from conventional UHMWPE wear. Since its inception, a substantial body of evidence consistently supports the utilization of HXLPE in THA, revealing notable reductions in wear rates and osteolysis. Paxton et al. have reported that at a 7-year follow-up, metal-on-conventional UHMWPE exhibits higher adjusted risks of all-cause revisions (hazard ratio [HR]: 1.75; 95% CI: 1.37–2.24; p < 0.001) and aseptic revisions (HR: 1.91; 95% CI: 1.46–2.50, p < 0.001) compared to metal-on-HXLPE [35]. A retrospective analysis by Hanna et al. focusing on patients aged 45–65 years with revision for polyethylene wear as the endpoint has shown an implant survivorship of 86% for conventional UHMWPE versus 100% for HXLPE at a minimum 13-year follow-up [36]. While CoC bearings exhibited superior performance compared to hard-on-soft bearings with a previous-generation polyethylene in the present study, further investigations are warranted to determine whether contemporary cross-linked polyethylene bearings would yield enhanced survivorship in this specific young patient population.

Moreover, a higher revision rate observed in this study might be attributed to excessive wear of traditional polyethylene in patients with higher activity levels. Concerns regarding elevated serum metal ion levels and wear of traditional polyethylene have prompted surgeons to explore alternative bearing options. Ceramic components have emerged as one such option, exhibiting good longevity in adult patients [37,38,39,40]. Notably, in young patients, ceramic-on-ceramic bearings have demonstrated outstanding outcomes, with Finkbone reporting only a 4.2% revision rate over 4.1 years of follow-up [28]. Trisolino et al. have reported a 2.7% revision rate [41] and Chapot et al. have reported no revision in 12 hips over an average follow-up of 6 postoperative years [13]. However, these results might be due to a relatively short follow-up period (Table 3). In our study, subgroup analysis revealed that patients operated with CoC bearings had a similar revision rate of 2.2%, with only one hip out of 46 requiring reoperation. Although ceramic component fracture remained a concern, no incidence of ceramic head or liner fracture occurred in our cohort.

Among revised hips, 18 out of 19 had initially been operated with hard-on-soft bearings. While there was no difference in the occurrence of dislocation or heterotopic ossification between the two groups, the incidence of wear-related complications was higher in the hard-on-soft bearing group. Notably, the revision rate in this cohort was comparatively higher, even when compared to other studies. This might be partly due to the longer follow-up period in our study, with an average of 7.4 years between the index surgery and the revision surgery, while most other previous studies on young patients had shorter average follow-up periods, typically less than seven years [11, 28,29,30, 41].

The survivorship of THA in patients under 20 years of age varied across studies. For instance, Tsukanaka et al. reported a ten year survival rate of 70% for 132 hips with hard-on-soft bearings, most of which were cementless [31]. Halvorsen et al. reported similar long-term survival rates of 86% at ten years and 73% at 15 years using various bearing options [42]. More recently, Trisolino et al. published results from 74 hips that underwent cementless THA with CoC bearings, demonstrating excellent overall survivor rates (97.6% at 5 years and 94.4% at 15 years) [41]. Özdemir et al. reported results from an average six year follow-up of cemented THA with metal-on-polyethylene bearings, showing survivor rates of 99% and 88% at ten years and 15 years, respectively [12]. In our study, the survivor rate of THA in young patients using CoC bearings was 97.8% (95% confidence interval [CI]: 93.5% to 100%) at postoperative 23 years, which was comparable to those of CoC THAs in other studies. However, the survivor rate of metal-on-polyethylene or ceramic-on-polyethylene bearings was 36.7% (95% CI: 14.9% to 58.5%) at 31 years. Such lower rates might be attributed to the extended follow-up and the use of traditional polyethylene.

The rate and subsequent survivorship of THA in patients with pediatric hip diseases may vary based on pre-existing hip pathology. Tan et al. recently reported that the rate of THA in patients with Perthes disease was 32% for those with a history of previous operative intervention and 40% for those without such history (p = 0.458) [43]. Similarly, in patients with a history of slipped capital femoral epiphysis, it was estimated that 45% of patients would undergo THA, with an overall revision rate of 11.9% manifesting at a mean of postoperative 6.5 years [44]. The rate of THA in patients with a previous hip infection during childhood varied. However, the revision rate was reported to be 8% in a recent study [45]. As illustrated above, the rate of THA may vary in different pediatric orthopaedic conditions. Thus, adequate patient stratification should be performed. However, the small number of subjects within a single centre impeded subsequent analysis. Future studies with registry data are warranted to minimize the bias.

This study has several limitations. First, this was a retrospective study with a relatively small sample size comprising 65 patients (78 hips), which might have a selection bias. Thus, caution is needed when interpreting findings of this study. However, the extended follow-up duration (mean: 13.2 years, range: 5.0–3.12 years) offered insights into longitudinal outcomes of THA in individuals under 20 years. Second, various confounding variables such as different implants and sizes, surgical approaches, and multiple surgeons were not meticulously assessed. Third, this study was conducted in an East Asian country where individuals frequently engaged in squatting and sitting on the floor, which might have increased the frequency of polyethylene wear. We also lacked information on activity levels of our patients, which could have a substantial impact on implant wear and longevity.