Conversion to total hip arthroplasty after failed proximal femoral nail antirotations or dynamic hip screw fixations for stable intertrochanteric femur fractures: a retrospective study with a minimum follow-up of 3 years

Most retrospective studies have investigated intertrochanteric fractures in a comprehensive manner. However, most follow-up period is commonly reduced to 2-years post-operation, and the implants are often compared in terms of their use [8, 11, 12]. Consequently, these studies had substantial differences compared with our study in terms of the inclusion criteria and the parameters investigated.

The evidence in the literature regarding the optimal method that should be used for the initial internal fixation of stable intertrochanteric fractures is inconclusive [8, 11, 12, 14]. Prior evidence has suggested that DHS may be superior to PFNA, but these findings were based on studies with small sample sizes and low event numbers [15]. Moreover, in China, 70% of surgeons prefer PFNA over DHS for treating a stable intertrochanteric fracture in active elderly patients [10]. Other studies have previously reported that DHS was the best choice for the initial treatment of stable intertrochanteric fractures [6, 7, 9, 16, 17]. Although the complication rates of DHS devices ranged from 12 to 34% [10], DHS was still regarded as a preferred device for stable intertrochanteric fractures in active elderly patients. However, another problem that must be considered is that the results of CTHA after a failed DHS fixation compared to a failed PFNA fixation are relatively controversial [7, 8, 16–18]. There is currently no consensus about which type of implant to use or what technique to perform in patients with stable intertrochanteric fractures previously treated with DHS fixation or PFNA. Some studies reported no difference in the clinical and radiological outcomes [7–12, 19, 20], while others reported higher complication rates and revision rates for one approach after CTHA [17, 21]. To address this controversy, we compared the clinical and radiological outcomes of CTHA after a failed PFNA or DHS fixation for stable intertrochanteric fractures.

There have only been a few previous reports that have focused on CTHA after a failed PFNA or DHS fixation for stable intertrochanteric fractures. Furthermore, the majority of these studies had low numbers of patients and short follow-up periods, and therefore, drawing conclusions about the relative superiority of one implant over the other is inappropriate. Unnanuntana et al. [22] retrospectively reviewed 78 patients who underwent CTHA after failed DHS fixations of stable intertrochanteric fractures and found that orthopaedic complications were more frequent. Diwanji et al. [9] performed 163 CTHAs after failed DHS fixations of a prior stable intertrochanteric fracture and noted a 14.1% (23/163) orthopaedic complication rate, including 11 dislocations (6.7%) and 12 femur fractures (7.4%). In the current study, a 37.1% orthopaedic complication rate (42.9% total complication rate) was identified in the DHS group compared with a 16.7% orthopaedic complication rate (20.8% total complication rate) in the PFNA group. The present complication rate in the DHS group was comparable to those of other series using similar osteosynthesis techniques.

In the previous study [3, 8, 19, 23], the incidence of periprosthetic fractures after CTHA ranged from 11.9% to 28%. The incidence of periprosthetic fractures in these studies was higher in comparison with the results of our study (14 out of 142, 9.9%). A recent study has reported the incidence of periprosthetic fractures after CTHA was used to treat failed PFNA or DHS fixations of intertrochanteric fractures in a large cohort [12]. Fifty-two of the 594 patients (8.8%) sustained a periprosthetic fracture during a mean follow-up of 4 years, and 71% of the fractures occurred within 1 year. The incidence of periprosthetic fractures in that study was consistent with the results of our study. In this study, prior DHS-treated patients receiving CTHA tended to have less resistance to periprosthetic fractures. One of the major reasons for this finding might be that the patients sustaining stable intertrochanteric fractures treated with a DHS tended to have poorer bone quality caused by stress shielding, which was in line with the prior consensus that a high incidence of mechanical complications (periprosthetic fractures) was recorded in patients who had received prior DHS treatment [7, 9, 16, 24]. As demonstrated by recent biomechanical testing [19], patients undergoing DHS may have poorer bone quality caused by stress-shielding than patients undergoing PFNA, which might partly explain the destruction of the bone and the disuse and atrophy of the proximal femur.

Both cemented and uncemented CTHA designs are being successfully used for the treatment of failed DHS fixations of stable intertrochanteric fractures, despite the fact that uncemented CTHAs are commonly offered to youthful patients [16]. Moreover, previous studies had evaluated the outcome of the cemented and uncemented CTHA, and reported no difference between cemented and uncemented CTHA was observed with respect to stem performance [2, 22, 24]. That was consistent with our conclusion.

A growing but still very limited body of literature has shown that conversion from prior PFNA fixation is better compared with conversion from prior DHS fixation with regard to the postoperative HHS after 0.5–1.5 years of follow-up [8, 15, 17, 25]. However, similar to a multi-centre, randomized study [26], we found no obvious differences in the postoperative HHS between the groups treated with the two types of conversions after a median of 3 years of follow-up. An obvious explanation for this may be the differences in the follow-up period compared to other studies. In addition, our results were also in line with other previous studies based on data acquired from the Healthcare Cost and Utilization Project’s Nationwide Inpatient Sample [13, 21, 23, 27].

This study should be interpreted in light of important limitations. First, this study is observational and it is possible that we failed to address every potential confounding variable in our analyses. Second, it is a retrospective study with all the problems inherent with this methodology. Third, because the conversion often occurred several years after the initial treatment with PFNA or DHS, the initial fracture pattern of stable intertrochanteric fractures may not have been recorded. It is possible that the fractures treated with DHS may have been more complex than those treated with PFNA, which might have eventually led to more malunions and fractures in the DHS group, thus making intra- and post-operative complications more common than in randomized, controlled cohorts.