With the background of an accelerated ageing population, all types of fragility fractures are increasing [4], as well as the acetabular fracture [1, 5, 6]. It was reported that the annual mean age of acetabular fracture patients and the proportion of elderly patients in California from 1980 to 2007 presented an increasing trend, and compared with in the earlier period (1980–1993), the proportion of elderly people in the later period (1994–2007) of the study increased 1.4 times from 10 to 24% [1]. And the mean age of acetabular fracture was 66 ± 22 years in France (2006–2016) [6]. As for developing countries, it was reported that the mean age of acetabular fracture patients in India increased from 33 years in 2013 to 40 in 2019 [7]. And the mean age of patients suffering from an acetabular fracture between 2008 and 2010 was 36 years in Qatar [8]. In this study, the mean age in China was between the developed and other developing countries, which was parallel to China’s ageing degree. And the changing trends of mean age of the acetabular fracture patients and the proportion of the elderly acetabular fractures in this study is in line with the literature. Compared with the first five years (2010–2014), the mean age of the second five years (2015–2019) increased by approximately four years, and the proportion of the elderly patients almost doubled. The gender distribution of the elderly acetabular fractures patients is generally the same as that of patients in the entire age group, mostly male, and the proportion of female patients increased by years and age, which is correlates with previous studies [7]. However, there were more female patients than males among octogenarians. The reason may be that females live longer than males, and there were more elderly females than males in China.

For the elderly, a considerable proportion of acetabular fractures were osteoporotic (fragile) fractures caused by low-energy injuries [1]. When the patient with osteoporosis fell laterally, the force acted on the greater trochanter, and the forward and medial force was transmitted to the acetabulum through the femoral neck and head, which would break and displace the anterior column and quadrilateral plate of the acetabulum [1, 9]. Therefore, the anterior column-posterior hemitransverse fracture pattern was recognized as one of the classic osteoporotic acetabular fracture patterns [10]. In related studies [1, 11], both-column fracture was the most common acetabular fracture pattern in the elderly (23% ~ 26%); fractures involving the anterior column were the second most common, including anterior column-posterior hemitransverse pattern (15% ~ 19%) and anterior column fractures (11% ~ 19%), which were comparable to those in this study.

As for posterior wall fracture, it is the most common acetabular fractures pattern in adults (approximately 23%) [12, 13]. The main injury mechanism is that drivers with the hip and knee flexed are subjected to backward violence transmitted to the acetabulum from the dashboard in traffic accident [14]. In this study, the proportion of posterior wall fractures in elderly patients (27.4%) was significantly higher than the reported 8% ~ 13% in the literature [1, 11], it was also significantly higher than that of the younger group (18.4%), which may be attributed to the bias of the small sample size of the elderly patients in this study.

ORIF was the main surgical method for displaced acetabular fractures in the elderly in this study, and most patients obtained satisfactory clinical outcomes.

A systematic review [11] including 15 studies showed that the mortality rate of 203 acetabular fractures patients > 55 years old (mean age 69.5 years) after ORIF was 15.3% at a mean follow-up of four years. The mortality rate in this study was 7.6%, lower than in the literature. The difference may be due to the lower mean age in this study.

It was reported by Laflamme et al. [15] that the Harris hip score of the elderly acetabular fracture patients after ORIF was 87.9 points, with an excellent and good rate of 70.6%. And the Harris hip score after acute total hip arthroplasty (THA) was 70.4 points with an excellent and good rate of 59% [16]. The treatment of ORIF combined THA for the elderly acetabular fracture patients provided a Harris hip score of 88 points [17]. The Harris hip score in this study is better and the excellent and good rate is higher, which might be a result of that the patients in this study were relatively younger.

Only few studies using SF-12 to assess the quality of life in the elderly acetabular fracture patients after operation. The PCS score of the SF-12 for the elderly acetabular fracture patients after ORIF was 45.3 points, and the MCS score was 55.9 points in literature [15], which is roughly in line with this study.

For reoperation, Daurka et al. [11] reported that about 22.4% of the elderly acetabular fracture patients underwent secondary THA two to three years after ORIF. Many studies reported a high conversion rate of THA after ORIF for acetabular fractures in the elderly [11, 16, 18,19,20,21]. Therefore, acute THA is recommended if conditions permit. In this study, 98.4% of the patients were treated with ORIF. Although some patients had limited mobility and hip pain, no patient underwent acetabulum re-operation, significantly less than in previous studies [11, 16, 18,19,20, 22]. And this might be a result of the cultural difference and the lower functional requirements of the chinese elderly. The high satisfaction scores indicate that most patients achieve satisfactory mid-term to long-term outcomes after ORIF. In addition, the difference of clinical outcomes between the 2010–2014 group and the 2015–2019 group was not statistically significant, indicating that appropriate treatment for elderly patients with acetabular fractures can lead to relatively persistent hip function and quality of life from the mid-term to long-term.

This is the first study to reveal the epidemiological trends in acetabular fracture in China, and also report the mid-term to long-term postoperative clinical outcomes of the elderly. It will provide important evidence for the understanding and treatment of acetabular fractures in China and other developing countries. Also, this study possessed some limitations: ① It was a retrospective study, the information we collected was limited. ② The patients were only followed up by telephone, the physical and radiological examination could not be performed. ③ Hip function was assessed by the HHS (self-report). Thus, the outcome could not be compared with previous studies. ④ This was a single center study, the results of this study must be validated in larger multicenter studies with longer follow-up.

In conclusion, acetabular fractures suffered from a significant ageing trend in China, and the fracture patterns of the elderly patients differed from those in the young patients. Operative treatment for elderly acetabular fractures yielded satisfactory and persistent clinical outcomes from mid-term to long-term.