PFNA-II has been the mainly method for the treatment of intertrochanteric fractures due to its advantages of short operative time and less bleeding19. AO/OTA 31-A1 and A2 accounted for 80%-94.7%20 of all intertrochanteric fractures. The fracture line distribution of A1 and A2 is different from that of the reverse intertrochanteric fractures (A3), and the implant failure mechanism is also different with each other21. Many studies have not analyzed these two types of intertrochanteric fractures separately22, which may lead to different results. For patients with A1 and A2, PFNA-II with nail length less than 240 mm is generally recommended23. Therefore, A1 and A2 intertrochanteric fractures stabilized with short PFNA-II (nail length less than 240 mm) is the most common clinical case. It is important to determine the risk factors of implant failure for guiding intertrochanteric fractures treatment.
In this study, the difference of reduction quality between the failure group and the non-failure group was statistically significant and the incidence of implant failure in failure group was higher than that in non-failure group. This may be suggested that reduction quality and implant failure were directly related. Morvan A et al.24 retrospective analyzed 228 patients aged over 75 years operated by Gamma 3 and Dynamic hip screw (DHS). Cut-out rate was 0.89% in good reduction and 12.12% in poor reduction. To minimize mechanical complications, great attention should be paid to fracture reduction and lag-screw position. The same results found in De Brujin’ s study25. In our study, reduction quality is risk factor of implant failure in intertrochanteric fracture treated with short PFNA-II. Implant failure rate was 33.3% in poor reduction and 4.5% in good and acceptable reduction. In multivariate analysis, the risk of implant failure in poor reduction was 8.75 times higher than that in good and acceptable reduction (OR = 8.75, 95%CI 1.215–62.99, p = 0.0313).
According to the postoperative X-rays, the medial femoral cortex was discontinuous in 66.7% of the patients with implant failure in this study. Posterior medial support is considered to be an important factor affecting the stability of intertrochanteric fractures, which has been confirmed in both basic and clinical studies. Do et al.26 reported that fixation strength was approximately 5 times greater in small defect of femoral medial cortex than in large defect of femoral medial cortex. Nie et al.27 confirmed by biomechanics that medial reconstruction is more important than lateral wall reconstruction. Similar findings have been found in clinical research. Mariani et al.28 analyzed 20 patients with nonunion of intertrochanteric fractures and found that all of them were unstable fractures and the reason of implant failure was related to posterior medial comminuted. In this study, 66.7% of the patients with implant failure had poor medial reconstruction suggested that medial reconstruction is a keystone of intertrochanteric fractures (A1 and A2) treated with short PFNA-II.
Even if the continuity of the femoral medial cortex is restored, the implant failure such as cut out may still occur during the weight bearing. Our previous study proposed the concepts of secondary stability and cortical or implant support29. In this study, we confirmed this phenomenon (Fig. 1 to 3). If the medial femoral shaft cortex or helical blade forms a support to the medial cortex of the head-neck fragment, the fracture is healed (Figs. 1 and 2). Otherwise, the fracture will result in loss of reduction, secondary stabilization may result in implant support (Fig. 3). According to our team’s early research in recent years30, most of the anterior cortex of intertrochanteric fracture is simple fracture, so the anterior medial cortex needs to provide stable support. In patients with intertrochanteric fractures, osteoporosis is severe, and the strength of the anterior medial cortex is limited. In Ender’s classification31, this fracture of varus deformity and retrocurvature proximal fragment impacted into trochanteric spongiosa, leaving a cavity after reduction danger of secondary varus was defined as impacted fractures. In 2013, Gotfried et al.32 also reported a similar phenomenon and defined it as negative and neutral support. Since then, there have been a lot of relevant reports, but the reasons for the failure of neutral support have not been explained33,34. We found that the compressed area of cancellous bone in the medullary cavity forms a triangular void structure after reduction of head-neck fragment. If the medial femoral cortex fails to provide stable mechanical buttress during the weight bearing, the head-neck fragment is prone to varus again. Hence, we considered this triangular void structure may have a strong association with postoperative implant failure.
There are some limitations in this study. First of all, it was a retrospective study that the data which were not collected initially could not be evaluated. We only included a few common indicators for evaluation. Nonetheless, we have specified strict inclusion and exclusion criteria to reduce confounders and minimize interference with the results. Besides, the sample size is relatively small which may cause statistical bias.