Femoral neck shortening is a common phenomenon after internal fixation of femoral neck fractures. Weil et al.  reported a shortening rate of 56% (> 5 mm) and a severe shortening rate of 22% (> 10 mm) after using multiple cannulated screws to fix femoral neck fractures. Moreover, Stockton et al.  found that femoral neck shortening and severe shortening rates could go up to 54% and 32%, respectively, after using multiple cannulated screws or an SHS + anti-rotating screw, with the former being lower than the latter. Zlowodzki et al.  also found, in a multi-center joint study, that the postoperative shortening and severe shortening rates of femoral neck fractures fixed by cannulated screws were up to 66% and 30%, respectively. Furthermore, another study showed that the shortening of the femoral neck permanently affects hip function after surgery, primarily impacting gait velocity and gait symmetry , with older patients tending not to have the ability to compensate for the impact. Therefore, determining the appropriate internal fixation method to minimize the shortening of the femoral neck has become a research focus.
Since Hassan Mir  first proposed the concept of the medial buttress plate of the femoral neck, relevant anatomical and biomechanical studies have been continuously conducted, verifying the effectiveness of this method [16, 17]. Currently, the focus of debate in this type of surgeries is whether open reduction can impair the blood supply of the femoral head, thus increasing the possibility of femoral head necrosis. In this regard, the direct anterior approach has been proven safe and reliable. In 2019, Utnam et al.  further confirmed through human autopsy that the placement of the buttress plate on the medial side of the femoral neck had been safe and did not destroy the blood supply to the femoral head, with the optimal placement position being at 6 o’clock of the femoral neck.
In our study, 40 patients with complete follow-up data who received cannulated screws combined with a medial buttress plate were selected for analysis. For this cohort, we found that the postoperative femoral neck shortening rate (> 5 mm) of this internal fixation method was 27.5% and that the severe shortening rate was 20%. It can be seen that the shortening rate of this internal fixation method is lower than that of other previously reported internal fixation methods; however, the severe shortening rate is less than or equal to that in previous reports [19, 20, 25]. These findings suggest that cannulated screws combined with a medial buttress plate can provide higher stability but cannot prevent the shortening of the femoral neck after internal fixation.
Stockton et al.  conducted a study on femoral neck shortening after fixation using the SHS + anti-rotating screw and multiple screws, suggesting that the degree of fracture displacement and internal fixation method are independent risk factors for femoral neck shortening. Similarly, our study involving Garden III/IV fractures showed that the quality of cannulated screws was an independent risk factor for femoral neck shortening and that there was no significant correlation with age, sex, fracture site, Pauwels type, and reduction quality. These findings suggest that despite the use of a medial buttress plate, the quality of the cannulated screws still plays the most important role. Risk factors for femoral neck shortening after internal fixation have not been reported.
Postoperative internal fixation failure of femoral neck fracture is another issue, with a reported failure rate of 10–30% . The nonunion rate of fixation using three cannulated screws alone was 21.8% . In our study, all patients had Pauwels type II/III or Garden III/IV fractures, although all had displaced fractures and high shear force, with an internal fixation failure rate that was 20% lower than that of fixation using simple cannulated screws. The nonunion rate of fractures after fixation with cannulated screws, SHS + screw, and locking compression plate is up to 11.9% according to a previous report . However, many patients with Garden II femoral neck fractures had been included in this previous report, and thus, the results are not directly comparable with those of our study.
Numerous studies [28, 29, 31] have reported that the internal fixation method, degree of fracture displacement, and poor reduction are risk factors for postoperative internal fixation failure of femoral neck fractures. However, the risk factors for postoperative internal fixation failure of femoral neck fractures, specifically treated using cannulated screws combined with a medial buttress plate, have not yet been reported. Our study found that femoral neck shortening is an independent risk factor for internal fixation failure; however, it was not related to age, sex, reduction quality, Pauwels type, fracture site, or screw quality. Therefore, the prevention of femoral neck shortening should be the main approach for preventing internal fixation failure. Nevertheless, more stable internal fixation methods still need to be studied.
This study has some limitations. First, due to the lack of multicenter data, as well as our low number of cases and short follow-up times, femoral head necrosis could not be analyzed. Second, since all patients treated with this internal fixation method were Garden type III/IV or Pauwels type II/III, Garden type I/II and Pauwels type I have been excluded from the comparative analysis. Due to the adaption of open reduction, all reduction qualities have been categorized as anatomic and acceptable, whereas borderline acceptable and unacceptable were excluded from the comparative analysis. Finally, because image examination in some patients was not standard, there was inevitable error in this data subset.