Although THA has been widely utilized in elderly patients with advanced hip disease, its application in younger patients remains controversial. Torchia[11]discovered that the failure rates in young patients increased significantly over time, reaching as high as 45%. Halvorsen[12] reported 747 patients (881 hips) under the age of 21 who received THA and discovered an 86% 10-year survival rate. These high reported failure rates may be attributed to the design of early prosthesis and the cemented technique[13]. In light of these high failure rates, few young patients receive THA, and relevant data and study findings are still lacking. However, compared with the "hip preservation" treatment with uncertain efficacy and eventual surgery, THA can help young patients in regaining hip function, rebuilding normal social attributes, and reducing the impact of the disease on their studies, work and life. In this study, we focused on patients ≤ 25 years who received uncemented THA. During an average of 8.3 years follow-up, the mHHS and WOMAC index significantly improved at the last follow-up, indicating that the uncemented THA is suitable for young patients and can achieve optimal performance. The quality of life, both physical and mental components, as measured by the SF-36, showed significant improvement in 49 hips. Furthermore, the latest X-ray revealed that the position of the implants did not change substantially since the postoperative image, and that there was no obvious loosening, wear, osteolysis, or heterotopic ossification. All components were stable and integrated. The total survival rate was 98%, which was comparable to the survival rate recorded in literature[4; 9; 14–16].
Traditionally, the most common THA fixation methods are cemented and uncemented fixation. Cemented THA can achieve good initial stability, but the bone cement is particularly prone to fatigue fracture under long-term stress, and the bone cement particles generated can cause osteolysis around the prosthesis and lead to prosthesis loosening, which is more common in patients with high activity or young age; within contrast to cemented THA, the early stability of uncemented THA depends on the tight compression of bone tissue and prosthesis, while the later stability depends on the bone tissue growing into the prosthesis[17; 18]. It is generally accepted that uncemented THA has a better prognosis and is more conducive to at least one revision surgery in the future for patients with younger age, longer life expectancy, greater mobility, and good bone growth function[18–20]. Although modern cement technology has increased the efficacy of prosthesis fixation, the risk of failure remains higher than with uncemented fixation. Buddhdev[21] reported 51 patients accepting uncemented THA at the age of 16.7 years, with an average survival rate of 97% after 9.3 years of follow-up. Smith[22] conducted a long-term follow-up of 50 hips undergoing cemented THA and found the revision rate to be 38%. Boyle[23] observed that the revision rates of cemented THA was significantly higher than uncemented THA. In this study, all 49 hips were treated with uncemented THA, thereby avoiding complications such as osteolysis and prosthesis loosening caused by bone cement.
Although uncemented prostheses reduce several issues associated with cemented prostheses, intraoperative and postoperative complications still exist. For instance, intraoperative cleavage fractures frequently occur in the proximal femur in order to ensure a close fit between implants and bone bed; in addition, a large amount of evidence proves that uncemented prostheses within two years of THA frequently exhibit varying degrees of micro thigh pain related to the distal femoral prosthesis [24]. In this study, no postoperative thigh pain was identified in 49 hips until the follow-up, which may be attributable to the close fit of the prosthesis to the bone bed during surgery and the patients' healthy bone mass.
As uncemented implants have generally replaced the traditional cemented implants, the prosthesis bearing surfaces have undergone several iterations to reduce excessive wear and osteolysis[5; 25]. The CoP bearing has superior wetness, hardness and inertness, whereas the CoC bearing improves wear, wetness, biological inertia and osteolysis, and has become the most prevalent bearing surface in young patients over the past decade[21; 26–31]. In this study, 49 THA were treated with CoP (23 cases, 46.9%) and CoC bearings (26 cases, 53.1%) respectively. The survival rate and clinical results of these two bearings at the latest follow-up were similar to those of Pallante[26], who retrospectively analyzed the clinical outcomes of CoP, CoC and metal-on- highly cross-linked polyethylene (MoP), finding CoC and CoP with excellent outcomes. Kim[32] found that highly cross-linked polyethylene had superior wear resistance compared to traditional polyethylene, and that neither osteolysis nor aseptic loosening of the prosthesis occurred. Buddhdev[21] evaluated 51 patients (60 hips) receiving THA at a mean age of 16.7 years, 60 hips adopted CoC bearing, and the overall survival rate was 97% after an average follow-up of 9.3 years. Therefore, it is wise to utilize CoP and CoC as the bearing of choice for youth[26; 28].
In this study, AVN (30 hips) was the most common diagnosis among 49 hips, and the pathogenic factors were trauma (8 hips), idiopathic (9 hips), hormone (8 hips) and alcohol (2 hips). This is comparable to the findings of Konopitski[5], who revealed that THA indications had evolved over time. From 1971 to 1992, the most prevalent surgical indication was JIA, followed by DDH and post-traumatic arthritis. From 2000 to 2015, the most common indication for THA was AVN. This may be related to the early diagnosis and treatment of JIA and DDH, resulting in a lower frequency of late complications associated with these diseases[33].
In young patients, acetabular and femoral prosthesis loosening and polyethylene wear are the major causes of revision, with aseptic loosening accounting for up to 60% of THA failure[8; 34; 35]. The history of one or more previous procedures, hip trauma, disorders affecting lower limb function, and a high preoperative BMI will all raise the failure rate[4]. Besides, Ravi[36] believed that the risk of revision is also closely related to the annual operation volume of the surgeon. When the surgeon does fewer than 35 THA per year, the probability of early revision of THA increases. Therefore, competent surgeons and a thorough preoperative examination can effectively lower the chance of THA failure in young patients. In our study, all patients got a thorough preoperative evaluation, and the operations were performed by experienced chief physicians, resulting in good clinical and imaging outcomes.